PARAMETRIC INVESTIGATION ON SINGLE POINT INCREMENTAL
FORMING FOR DIFFICULT TO FORM MATERIAL
A Thesis submitted to Gujarat Technological University
for the Award of
Doctor of Philosophy
in
Mechanical Engineering
by Snehal Viranchibhai Trivedi
Enrollment No: 139997119015
under supervision of
Dr. Anishkumar Hasmukhlal Gandhi
GUJARAT TECHNOLOGICAL UNIVERSITY
AHMEDABAD
September – 2019
PARAMETRIC INVESTIGATION ON SINGLE POINT INCREMENTAL
FORMING FOR DIFFICULT TO FORM MATERIAL
A Thesis submitted to Gujarat Technological University
for the Award of
Doctor of Philosophy
in
Mechanical Engineering
by Snehal Viranchibhai Trivedi
Enrollment No: 139997119015
under supervision of
Dr. Anishkumar Hasmukhlal Gandhi
GUJARAT TECHNOLOGICAL UNIVERSITY
AHMEDABAD
September – 2019
ii
© Snehal Viranchibhai Trivedi
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x
Thesis Approval Form The viva-voce of the PhD Thesis submitted by Shri Snehal Viranchibhai Trivedi
(Enrollment No. 139997119015) entitled “Parametric investigation on single point
incremental forming for difficult to form material” was conducted on
…………………….………… (day and date) at Gujarat Technological University.
(Please tick any one of the following option)
The performance of the candidate was satisfactory. We recommend that he/she be
awarded the PhD degree.
Any further modifications in research work recommended by the panel after 3 months
from the date of first viva-voce upon request of the Supervisor or request of
Independent Research Scholar after which viva-voce can be re-conducted by the same
panel again.
(briefly specify the modifications suggested by the panel)
The performance of the candidate was unsatisfactory. We recommend that he/she
should not be awarded the PhD degree.
(The panel must give justifications for rejecting the research work)
--------------------------------------------------------- 2) (External Examiner 2) Name and Signature
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xi
ABSTRACT
Global demand of higher strength-to-weight ratio of structures leads progress in
development of variety of lightweight metals and its alloys. Metal forming processes are
preferable over range of manufacturing processes to get the lightweight products due to its
significant characteristics of obtaining homogeneous distribution of material for finished
product. Generally, high strength metals offer non uniform material distribution due to lower
nominal strain at fracture which limits the formability of material.
Hence for the proposed work Single Point Incremental Forming (SPIF) is identified
potential dieless forming process due to its characteristics to offer effective local deformation
resulting in greater formability. SPIF is flexible enough to produce customized formed
products of sheet metal. Present work focuses on investigation of formability of AMS4902
sheet using SPIF, which is having typical applications in industrial and aerospace
components, bellows, honeycomb, gaskets, aircraft skin, heat exchanger parts, medical and
dental devices, tubing, pickling baskets etc.
Methodology of the proposed work includes experimental investigation for SPIF of
square pyramid geometry ranging from 50o to 70o wall angle from AMS4902 sheet. Present
experimental investigation is an attempt to analyze the individual effect of various parameters
such as tool diameter, tool speed, tool feed rate, incremental depth of tool and their
interactions on thickness distribution, maximum formable angle, fracture depth and surface
roughness of part formed by SPIF. Based on results obtained from the experimental
investigation, tool diameter is found most significant parameter influencing percentage
thinning of pyramid wall. Tool diameter of 12 mm is offering reasonably uniform thickness
distribution compared to other diameters of tools used for forming of 50o wall angle pyramid
of AMS4902. Failure of pyramid wall is observed before designed depth due to pinning
effect of 8 mm diameter hemispherical tip tool. Incremental step depth is influencing most to
surface roughness of pyramid wall of AMS4902 formed by SPIF.
As the failure of 60o and 70o wall angle pyramid is observed during single-pass SPIF,
experimental investigation is extended to multiple pass SPIF to form60o and 70o wall angle
square pyramids out of already formed pyramids of 50o wall angle. Thinning of 87 percent of
pyramid wall is obtained in case of 60o wall angle pyramid and 13 mm failure depth is
observed in case of 70o wall angle pyramid during multi-pass SPIF.
xii
ACKNOWLEDGEMENT
With the radiant sentiment to express deep sense of gratitude from the bottom of my heart to
my respected supervisor, Dr. Anishkumar Hasmukhlal Gandhi, for his continuous
guidance, motivation, encouragement and support throughout this research work. His
guidance helped me a lot all the time during tenure of research and writing of this thesis. It
would not have been possible for me to constantly strive for better performance without his
extraordinary advises and vision.
Besides my advisor, I have been highly obliged by my Doctoral Progress Committee
Members Dr. H. K. Raval, Professor, SVNIT, Surat and Dr. K. P. Desai, Professor, SVNIT,
Surat for their rigorous reviews and precious comments during the journey of research. Their
ever valuable suggestions and constructive criticisms directed me towards progress of this
research work successfully.
I am thankful to Dr. Akshai Aggarwal, Ex. Vice Chancellor, Dr. Navin Sheth, Vice
Chancellor, Dr. K. N. Kher, Registrar and all staff members of Ph.D. Section, Gujarat
Technological University, Ahmedabad.
I acknowledge technical support provided by staff members of Central Institute of Plastics
Engineering and Technology (Centre for Skilling and Technical Support), Valsad to conduct
all experimental work as well as Indo German Tool Room, Ahmedabad to allow me to carry
out measurement using Coordinate Measuring Machine (CMM).
I must not forget to pay my sincere thanks to Dr. Devanshu Patel, President, Parul
University for believing in my potential. I extend my thanks to all teaching and non teaching
staff members of Department of Mechanical Engineering as well as Mr. Riteshbhai Patel,
Librarian of Parul Institute of Technology, Mr. Harsh Desai and who helped me directly or
indirectly for accomplishment of this research work.
It was next to impossible to progress for this research work without the moral support of my
family members. I dedicate this research work to my mother, Mrs. Geetaben Trivedi for her
blessings; to my father Dr. Viranchibhai Trivedi, my continuous source of inspiration; my
beloved wife, Mrs. Rinku Trivedi, for her caring nature as well as dedication towards social
responsibilities and my beloved son Dwij Trivedi, for his unconditional love forever. Finally,
I bow down to the Lord Almighty for providing me opportunities and favorable
circumstances in the life.
xiii
Table of Content
Chapter No. Title of Chapter Page
No. 1 Introduction 1
1.1 Metal forming processes 1 1.2 Properties influencing formability of metal 4 1.3 Properties of non-ferrous lightweight metals 6 1.4 Need of lightweight products 8 1.5 Organization of Thesis 9
References 11
2 Literature Review 13
2.1 Sheet and component attributes 14 2.1.1 Findings based on literature review on sheet and component attributes 18
2.2 Tool attributes and tool path strategies 18
2.2.1 Findings based on literature review on tool attributes and tool path strategies 25
2.3 Process attributes 25 2.3.1 Findings based on literature review on process attributes 31
2.4 Scope of Research 32 2.5 Objectives 33 2.6 Research Methodology 33
References 35 3 Experimental Investigations 40
3.1 Design of Experiments 40 3.2 Experimental set-up 43 3.3 Uni-axial tensile testing to determine properties of AMS4902 44 3.4 Circle-grid marking 45 3.5 Pilot experiments 47 3.6 Experimental set: 1 (Single-pass SPIF of 50o wall angle pyramids) 48 3.7 Experimental set: 2 (Single-pass SPIF of 50o wall angle pyramids) 50 3.8 Wall thickness measurement 51 3.9 Surface roughness measurement 52
3.10 Experimental Set: 3 (Single-pass SPIF of 60o and 70o wall angle pyramids) 54
3.11 Experimental Set: 4 (Multi-pass SPIF to form 60o and 70o wall angle pyramids from 50o wall angle pyramids) 54
3.12 Uncertainty in measurement 54
3.12.1 Wall thickness measurement 55
3.12.2 Surface Roughness measurement 56
References 57
xviii
Chapter No. Title of Chapter Page
No.
4 Results and Discussions 58
4.1 Effect of tool diameter, speed and feed (Experimental Set: 1) 58 4.2 Influence of tool diameter and incremental depth on average percentage thinning 59
4.2.1 Effect of tool diameter and incremental step depth interaction on average percentage thinning 59
4.2.2 Results of ANOVA for average percentage thinning 64 4.3 Influence of tool diameter and incremental depth on average surface roughness 66
4.3.1 Effect of tool diameter and incremental step depth interaction on average surface roughness (Ra) 66
4.3.2 Results of ANOVA for average surface roughness 68 4.4 Geometrical accuracy 71
4.5 Results and discussions to form 60o and 70o wall angle square pyramids by single-pass SPIF 75
4.6 Results and discussions on percentage thinning of 60o and 70o wall angle square pyramids formed out of 50o wall angle pyramids by multi-pass SPIF 75
4.6.1 Percentage thinning of 60o wall angle pyramid formed by multi-pass SPIF 76 4.6.2 Percentage thinning of 70o wall angle pyramid formed by multi-pass SPIF 77
5 Conclusions and Future Scope 79
5.1 Conclusions 79
5.1.1 Effect of tool diameter, speed, feed and incremental step depth on maximum formable depth of AMS4902 sheet during single-pass SPIF 79
5.1.2 Effect of parametric interactions between tool diameter and incremental step depth on average percentage thinning of pyramid walls formed out of AMS4902 sheet using single-pass SPIF
80
5.1.3 Effect of parametric interactions between tool diameter and incremental step depth on average surface roughness of pyramid walls formed out of AMS4902 sheet using single-pass SPIF
80
5.1.4 Effect of tool diameter on geometrical accuracy of pyramid wall angles formed out of AMS4902 sheet using single-pass SPIF 81
5.1.5 Effect of optimum process parameters to form 60o and 70o wall angle pyramids using single-pass SPIF 81
5.1.6 Effect of optimum process parameters to form 60o and 70o wall angle pyramids out of already formed pyramids of 50o wall angle using multi-pass SPIF
82
5.2 Future Scope 82
List of Publications 83
xv
List of Abbreviations
SHF Sheet Hydroforming SPF Superplastic Forming
HMGF Hot Metal Gas Forming EMF Electromagnetic Forming
IF Incremental Forming ISF Incremental Sheet Forming
SPIF Single Point Incremental Forming TPIF Two Point Incremental Forming CNC Computerized Numerically Control BCC Body Centered Cubic FCC Face Centered Cubic HCP Hexagonal Close Packed CP Ti Commercially Pure Titanium UV Ultraviolet
ASTM American Society for Testing and Materials ASME American Society of Mechanical Engineers AMS Aerospace Material Specifications SAE Society of Automotive Engineers AISF Asymmetric Incremental Sheet Forming DDQ Deep Drawing Quality HSS High Speed Steel AA Aluminum Alloy Al Aluminum
FLD Forming Limit Diagram FLC Forming Limit Curve
VWACF Variable Wall Angle Conical Frustum POM Polyoxymethylene PE Polyethylene PA Polyamide
PVC Polyvinylchloride PC Polycarbonate
EDD Extra Deep Drawing CMM Coordinate Measuring Machine GUM Guide to the Expression of Uncertainty in Measurement VIM International Vocabulary of Basic and General Terms in Metrology
ANOVA Analysis of Variance
xvi
List of Symbols
D Tool Diameter Z Incremental Step Depth S Tool Rotational Speed F Feed Rate σ0 Flow Stress K Strength Coefficient Ԑ Plastic Strain N Strain Hardening Exponent R Anisotropy Ratio ra Average value of anisotropy r0 Anisotropy in rolling direction r45 Anisotropy at 45o to the rolling direction r90 Anisotropy in transverse direction Δr Difference in planer anisotropy to Original thickness of sheet tf Final thickness of sheet
Mm Millimeters MPa Mega Pascal GPa Giga Pascal Ra Arithmetic Mean Roughness
Μm Micrometers
xvii
List of Figures
Figure No.
Title of Figure Chapter No.
Page No.
1.1 Types of Incremental Sheet Forming Processes (a) SPIF (b) TPIF 1 2 1.2 Various domains of applications of SPIF and TPIF 1 2 1.3 Application of incremental sheet forming processes in plastic
industries 1 3
1.4 Comparison of formability for various sheet metal forming processes 1 3 1.5 SPIF terminology with deformed part 1 4 1.6 Difference in Planer Anisotropy 1 6 2.1 Schematic diagram of Single Point Incremental Forming Process
with equipments 2 13
2.2 Various shapes used to demonstrate SPIF 2 15 2.3 Various generatrices of parts formed (a) Circular (b) Elliptical (c)
Parabolic (d) Exponential 2 16
2.4 Geometrical Errors in SPIF 2 18 2.5 Types of tool paths (a) Contour tool path (b) Spiral tool path 2 19 2.6 Various tool Profiles (a) Angular, (b) Flat, (c) Hemispherical,
(d) Parabolic 2 20
2.7 Fractography at the fracture initiation zone (left) and at its opposite section (right) for tools of Φ20 (above) and Φ 10 mm (below)
2 21
2.8 Various toolpath strategies (a) helical (b) alternating (c) inside-out 2 22 2.9 Flow chart of applied research methodology 2 34 3.1 Square pyramid as a part geometry 3 41 3.2 Experimental Set-up (a) SPIF Fixture (b) SPIF Set-up on CNC
Milling machine 3 43
3.3 (a) Tensile test set-up (b) Tested specimens of AMS4902 at 0o, 45o& 90o
3 44
3.4 Various patterns of Grid Marking 3 45 3.5 (a) 2D drawing of circle grid pattern
(b) Circle-grid printing set-up (c) Circle-grid marking on AMS4902 sheet
3 46
3.6 Failure of AMS4902 sheets marked using laser grid marking technique (a) Failure depth of 7 mm for 1 mm thick sheet (b) Failure depth of 8 mm for 1.5 mm thick sheet
3 47
3.7 Single point incremental forming of 1.5mm thick sheet of AMS4902 with good quality of deformed circle grid pattern printed using UV printing
3 48
3.8 Components formed using SPIF with parametric combinations of experimental set: 1
3 49
3.9 Components formed using SPIF with parametric combinations of experimental set: 2
3 50
3.10 Wall Thickness measurement of square pyramid using CMM 3 51
xviii
Figure No.
Title of Figure Chapter No.
Page No.
3.11 Deformed pyramid with locations for measurement of wall thickness using CMM
3 52
3.12 Fixture developed to hold the pyramid during surface roughness measurement.
3 53
3.13 Surface Roughness Measurement for Pyramid Wall (a) Calibration of Surface Roughness Tester (b) Roughness Measurement Set-up
3 53
3.14 Maximum range of permissible uncertainty of indication for CMM 3 56 4.1 Effect of tool diameter on Average Percentage Thinning for same
incremental step depth (a) Effect of tool diameters on average percentage thinning of pyramid wall at 0.25 mm step depth (b) Effect of tool diameters on average percentage thinning of pyramid wall at 0.50 mm step depth (c) Effect of tool diameters on average percentage thinning of pyramid wall at 0.75 mm step depth
4 62
4.2 Effect of incremental depths on Average Percentage Thinning for same diameter of tool (a) Effect of incremental depths on average percentage thinning of pyramid wall for 12 mm diameter tool (b) Effect of incremental depths on average percentage thinning of pyramid wall for 16 mm diameter tool
4 63
4.3 Main effects plots for means, SN ratios and standard deviations of average percentage thinning (a) Main effects plot for means of average percentage thinning (b) Main effects plot for signal to noise ratio of average percentage thinning (c) Main effects plot for standard deviations of average percentage thinning
4 64, 65
4.4 Effect of interaction of incremental depths and tool diameters on Average Surface Roughness
4 68
4.5 Main effects plots for means, SN ratios and standard deviations of average surface roughness (a) Main effects plot for means of average surface roughness (b) Main effects plot for signal to noise ratio of average surface roughness (c) Main effects plot for standard deviations of average surface roughness
4 69, 70
4.6 (a) Wall angle measurements for a pyramid formed using 12 mm diameter of tool and 0.25 mm incremental depth (b) Wall angle measurements for a pyramid formed using 16 mm diameter of tool and 0.25 mm incremental depth
4 72, 73
4.7 Average wall angles of pyramid walls formed using 12 mm and 16 mm diameter tools
4 74
4.8 Single-pass SPIF for 60o and 70o wall angle square pyramids (a) Failure of 60o wall angle square pyramid (b) Failure of 70o wall angle square pyramid
4 75
xix
Figure
No. Title of Figure Chapter No.
Page No.
4.9
Pyramid of 60o wall angle formed using multi-pass SPIF and average percentage thinning (a) 60o wall angle pyramid formed out of 50o wall angle pyramid using multi-pass SPIF (b) Measurement of wall thickness of 60o wall angle pyramid using point micrometer for the wall angle formed by multi-pass SPIF (c) Average percentage thinning Vs Component depth
4 77, 78
4.10
Pyramid of 70o wall angle formed using multi-pass SPIF and average percentage thinning (a) 70o wall angle pyramid formed out of 50o wall angle pyramid using multi-pass SPIF (b) Average percentage thinning Vs Component Depth
4 79
xx
List of Tables
Table No. Title of Table Chapter
No. Page No.
1.1 Comparison of properties of various sheet materials 1 7
2.1 Summary of findings reported for various grades of sheet blanks with component geometries 2 17
2.2 Various tool profiles and related dimensional specifications 2 20
2.3 Combination of tool materials, tool diameters, tool end geometries and tool paths in combination to form various sheet blank materials 2 24,
25 2.4 Design of experiments for some process parameters 2 26 2.5 Level of parameters to conduct experimentations using SPIF 2 29
2.6 Summary of parametric combinations reviewed for tool rotational speeds and feed rates to form specific sheet blank material using SPIF 2 30
2.7 Summary of parametric combinations reviewed for feed rates and incremental depth to form specific sheet blank material using SPIF 2 30
2.8 Summary of parametric combinations reviewed for tool rotational speeds and incremental depth to form specific sheet blank material using SPIF
2 31
2.9 Comparison of material properties of AMS4902 with other materials 2 32
3.1 DoE for Experimental Set: 1 to perform singlepass SPIF to form square pyramid of 50o wall angle 3 41
3.2 DoE for Experimental Set: 2 to perform singlepass SPIF to form square pyramid of 50o wall angle 3 42
3.3 Results of tensile testing of AMS4902 3 44 3.4 Other average property parameters of AMS4902 3 45
3.5 DoE for Experimental Set: 3 to perform singlepass SPIF to form square pyramid of 60o and 70o wall angle 3 54
3.6 Measurement uncertainty of CMM model PRISMO 5 HTG VAST prescribed by manufacturer 3 55
4.1 Results of average thickness measured using CMM 4 60
4.2 Average percentage thinning for corresponding average wall thickness after forming 4 61
4.3 Results of ANOVA for average percentage thinning of pyramid walls formed by SPIF 4 64
4.4 Results of average surface roughness for individual walls of pyramids 4 67
4.5 Results of average surface roughness for various pyramids formed using SPIF 4 68
4.6 Response table of signal to noise ratios for surface roughness 4 69
4.7 Results of wall angles measured for pyramids formed using SPIF during various experiments 4 74
4.8 Results of average wall angles measured for various pyramids formed using SPIF 4 74
Metal forming processes
1
CHAPTER: 1
Introduction
This chapter describes broad classification of metal forming processes and characteristics of
various modern metal forming processes. This chapter also discusses desired properties
influencing formability of metals and properties of non ferrous lightweight metals. This
chapter is concluded with the challenges to form non ferrous lightweight metals and aim to
takeover present research problem with respect to global need of lightweight products.
1.1 Metal forming processes
Metal forming is the process in which permanent change in shape and size can be
obtained with the application of force without causing failure of material. Metal forming
processes possess capability to control and improve the properties of material. Forming
processes can be broadly categorized in two groups; (i) Bulk Metal Forming and (ii) Sheet
Metal Forming. Bulk Metal Forming is a severe deformation process resulting in massive
shape change in which the surface area-to-volume of the work is relatively small and mostly
preferred to be done in hot working conditions. Sheet metal forming involves forming and
cutting operations performed on metal sheets, strips, plates and coils. The surface area-to-
volume ratio of the starting metal is relatively high in case of sheet metal forming.
Customized and functional demands of products forces technological advancement in basic
sheet metal forming operations performed either under tensile, compressive, bending or shear
conditions. Since past few years, considerable growth in shot peen forming, hydroforming,
electromagnetic forming, superplastic forming, laser assisted forming and incremental sheet
forming is noticed.
Shot peen forming is especially suitable for large-surface parts with a large curvature and
without sharp contour changes to endure a longer fatigue life in service without failure. Sheet
hydroforming (SHF) is a technology that uses hydraulic fluid taken to very high pressure as
an essential tool to form into complex parts with special curves even with unusual shapes out
of sheet metals and tubes fitted to a specially designed die. Superplasticity is the ability of
materials to undergo extreme elongation, and it occurs within a narrow range of temperatures
Introduction
2
and deformation rates. Integral structural parts can be produced by combining superplastic
forming (SPF) with diffusion bonding (SPF/DB). However, the SPF method is not
economically competitive because of its long cycle time. Therefore, in recent years, various
means of shortening the cycle time have been investigated with encouraging results. The
electromagnetic forming process (EMF) is a highly dynamic process using pulsed magnetic
fields to form metals with high electrical conductivity such as aluminum. In this process,
deformation of the workpiece is driven by the interaction of a current generated in the
workpiece with a magnetic field generated by a coil adjacent to it [1-3].
(a) (b)
FIGURE 1.1 Types of Incremental Sheet Forming Processes (a) SPIF (b) TPIF [4]
Incremental forming (IF), popularly known as dieless forming process, has great
potential to form sheet metal into complex three dimensional components with the use of
relatively simple and low cost tools. Sheet metal can be deformed progressively and locally
using spherical forming tool controlled by CNC machine during incremental forming process.
Negative dieless incremental forming is known as single point incremental forming (SPIF)
while positive die-less incremental forming is known as two point incremental sheet forming
(TPIF) as shown in Fig. 1.1(a) and (b).
FIGURE 1.2 Various domains of applications of SPIF and TPIF
Metal forming processes
3
The main advantages of incremental forming are high process flexibility, relatively
low hardware costs and enhanced formability compare to various other sheet metal forming
processes. In order to satisfy the global need of mass customization of recent era, potential
application domains of SPIF and TPIF include producing architectural and decorative items,
industrial items like miniatures in aerospace industry, automotive industry and biomedical
products and prototypes as shown in Fig. 1.2. As mentioned in Fig. 1.3, applications of
incremental sheet forming processes also extend to prepare moulds using blow moulding
operation useful for thermoforming process in plastic industries.
FIGURE 1.3 Application of incremental sheet forming processes in plastic industries
As depicted in Fig. 1.4, greater deformation of a sheet metal can be obtained in the
incremental forming compared to conventional forming even at room temperature due to its
ability to deform locally. The tool rotation and feed rate are two important parameters
contributing to the ability to form at higher rates of production. [2-9].
FIGURE 1.4 Comparison of formability for various sheet metal forming processes [9]
Introduction
4
Various process parameters influencing incremental forming process includes sheet blank
thickness, tool diameter, spindle rotational speed, feed rate, incremental step depth (Δz), tool
path strategy, tool end geometry, lubrication at tool-sheet interface as shown in Fig. 1.5.
FIGURE 1.5 SPIF terminology with deformed part [7]
Formability assessment of any sheet material is an interest to carry out in terms of sheet
thickness distribution after forming, maximum formable wall angle and maximum formable
depth of the component formed using SPIF. Effect of process parameters and material
property parameters on dimensional and geometrical accuracy of the component formed by
SPIF is also key interest of research.
1.2 Properties influencing formability of metal
Formability is the ability of material to withstand the stretch or draw stresses of forming
before failure in terms of necking or tearing. Formability of any material majorly depends on
its properties like yield strength, strain hardening, modulus of elasticity, anisotropy and
ductility. Yield strength is one of the important properties as it determines the force required
to start plastic deformation. Hard metals possess high yield strength and having reduced
stretch distribution characteristics, making them less stretchable and drawable means less
formable. Generally, forming of hard metals is preferable at elevated temperature but it is
challenging to control material properties while forming at room temperature. Hence, low
value of yield strength is preferred as less force and energy is needed for plastic deformation
of a sheet at room temperature. The motivation for present experimental work is to take over
Single Point Incremental Forming of hard sheet metal having higher yield strength at room
temperature.
Properties influencing formability of metal
5
Modulus of elasticity of a material plays vital role as it determines elastic springback
or recovery. It means that as modulus of elasticity of Aluminum is one-third than that of the
Steel, springback of Aluminum will be three times than that of the Steel. Hence it is desirable
to carry out the deformation beyond the desired point based on amount of springback.
Strain or work hardening is the phenomenon in which the moving dislocations interact
with each other and with the grain boundaries; therefore continuous yielding becomes more
difficult. This mechanism is called strain or work hardening. In cold forming the relation
between flow stress (σ0) and plastic strain (Ԑ) is given by;
σ0 = K Ԑn (1.1)
Where; K is strength coefficient and n is strain or work hardening rate
Higher the work hardening means need of higher load and energy, high tool wear and
higher cost. At the same time work hardening prevents local yielding and increases
elongation. Local necking takes place during the stretching of materials in the absence of
work hardening which results into non-uniform plastic deformation. Hence reasonable
amount of strain or work hardening is desired only in order to get parametric balance of
required force and stretching of sheet metal.
Anisotropy means difference in flow strength in thickness direction than that in the
plane of sheet which may result in excess wrinkling, local thinning or actual rupture. The
anisotropy ratio (r) is defined as;
r = εw / εt (1.2)
Where; εw is principal strain in width direction and εt is principal strain in the thickness
direction.
For evaluation of r, test specimens need to be cut in three directions, i.e. 0o, 45o and
90o with respect to the rolling direction. Three values of r, i.e. r0, r45 and r90 are to be
determined.
The average value of anisotropy ratio (ra) can be calculated as;
rୟ = ୰బାଶ୰రఱା୰వబସ
(1.3)
The difference (Δr) in r values is indicator of planer anisotropy as shown in Fig. 1.6 which is
responsible parameter for change in mechanical properties of metal with direction and can be
defined as;
Δr = rmax – rmin (1.4)
Introduction
6
FIGURE 1.6 Difference in Planer Anisotropy [10]
The value of ra more than unity is an indicator that the sheet is stronger in the thickness
direction. This reduces thinning and neck formation in the sheet at the highly stressed
locations during deep drawing and hence enhances drawability.
Ductility is an essential property of material for its formability but it is not an absolute
constant for any metal or alloy under all conditions. In fact, it may get modified by
optimizing the process parameters. Hence, the same material may show different formability
in different forming processes as it depends on various external factors including hydrostatic
pressure, plastic deformation already suffered, strain rate, temperature etc. Ductility of a
material also affected by some intrinsic factors like composition, grain size and crystal
structure of a material. Metals with BCC and FCC structure shows higher ductility compared
to those with HCP crystal structure [7, 10, 11, 12].
1.3 Properties of non-ferrous lightweight metals
Generally, ferrous metals have good formability as it possesses good ductility. But the
density of ferrous metal is high compared to non-ferrous lightweight metals like Aluminum,
Beryllium, Titanium and Magnesium alloys. The global industrial needs of lightweight
structures and construction lead to investigate about replacement of Steel with Aluminum,
Magnesium, Titanium, metal foams, composites and also some non-metallic materials like
polymers, elastomers and polymer matrix composites. Table 1.1 depicts about comparison of
important properties influencing formability of various materials.
Properties of non-ferrous lightweight metals
7
TABLE 1.1 Comparison of properties of various sheet materials
Properties
Various sheet materials
Steel
Alloys
Aluminum
Alloys
Magnesium
Alloys
Beryllium
Alloy
Commercially
Pure (CP)
Titanium
Density
(gm/cc) 7.75-8.05 2.7 1.77 1.84 4.51
Modulus of
Elasticity
(GPa)
195 - 215 68 – 73 45 110 – 330 105 - 120
Yield
Strength
(MPa)
150 35 – 75
(Annealed) 160 - 230 240 275 - 345
Ultimate
Tensile
Strength
(MPa)
310 90 – 185
(Annealed) 240 - 310 370 350 - 485
Percentage
Elongation in
50 mm
10 - 55 12 – 25 15 3 45
The expected properties of lightweight metals and alloys include low density, high
strength to weight ratio and low toxicity. Aluminum is good conductor of heat and electricity
and also useful as an alloying element in Steel, Titanium and Magnesium. Aluminum is
lighter than Titanium but not as strong. Aluminum alloys do not have ductile to brittle
transition. Beryllium possesses 30 percent less density than Aluminum and 50 percent greater
rigidity than Steel. Beryllium has high thermal conductivity, high specific heat dissipation
and corrosion resistant in normal ambient conditions and at elevated temperature too. The
specific rigidity of Beryllium is about four times greater than composites and six times
greater than other alloys or metals. Titanium and its alloys have higher strength to weight
ratio, good fatigue properties, excellent corrosion, heat and wear resistance. Titanium and its
alloys cover applications in marine and chemical sectors for condensers, evaporators, reaction
vessels for chemical processing, tubing and tube headers in desalinization plants, sea water
piping and cryogenic vessels due to its excellent corrosion resistance property. Titanium is
Introduction
8
also useful in biomedical applications for hip joint, knee joint and heart valve replacement
surgeries. Magnesium and its alloys are characterized by moderate strength, good ductility,
low density and excellent corrosion resistance. Magnesium based materials possess low
elastic modulus and high unit resilience [2, 5, 13, 14, 15].
1.4 Need of lightweight products Application of lightweight products plays crucial role in transport sector where
masses are subjected to motion. Reduced unsprung masses in a vehicle chassis improve
driving comfort and safety at even higher speeds. Selection of materials having maximum
strength and stiffness with lesser weight is a key criterion when selecting them for
automobile, train, ship, aircraft or defense manufacturing industries to meet requirement of
reduction in fuel consumption and greenhouse gases for improving fuel efficiency.
Improvement in fuel economy of 7 percent is estimated by every 10 percent of weight
reduction out of the total weight of a vehicle which also means that for every kilogram of
weight reduced in a vehicle, there is about 20 kg of carbon dioxide reduction. In order to
meet the recycling and recovery targets of 85 percent at the end-of-life of vehicles are driving
the automobile industry to adopt lightweight materials technology. Appropriate
manufacturing (rolling, extrusion), forming and joining technologies require development,
simulation and validation for the innovative materials and applications. Lightweight
construction deals with the use of light weight materials and with different design strategies
too. To design a body structure of trains, aircraft, ships or vehicles include design of frame
structure and shell structures both [13-15].
Metal forming processes are characterized to produce lightweight products of
improved properties by obtaining uniform distribution of material over entire volume of
product without compromising the rigidity of product. Higher strength to weight ratio of
quality sheet metal product is an integrative effort involving field of material science, design
and manufacturing too. The challenge with forming of higher strength metals like magnesium
and titanium includes non uniform distribution of material due to lower nominal strain at
fracture which ultimately limits the formability of metal. The present experimental work is an
attempt to assess formability of AMS4902 using Single Point Incremental Forming at room
temperature. AMS4902 is an unalloyed grade of titanium designated by SAE International
under Aerospace Material Specifications which contains 99-99.5 percent titanium with
balance being made up of iron and interstitial impurity elements hydrogen, nitrogen, carbon
Need of lightweight products
9
and oxygen. AMS4902 is available in the form of strip, sheet and plate. AMS4902 is of high
demand lightweight material grade for aerospace applications under the category of
commercially pure titanium grade 2 which is equivalent to ASME SB265 and ASTM B265
(Grade 2). Aerospace applications of AMS4902 include airframe skins in warm areas,
ductwork, brackets and galley equipments. Over and above exceptional strength-to-weight
ratio, AMS4902 possesses excellent corrosion resistance, good fatigue properties and low
toxicity which widens its application range in marine and chemical sectors for condensers,
evaporators, reaction vessels for chemical processing, tubing and tube headers in
desalinization plants, sea water piping and cryogenic vessels. The aim of presented
experimental work is to analyze the individual effect of various parameters such as tool
diameter, tool rotation, tool feed rate, incremental depth of tool and their interaction during
single-pass and multi-pass of hemispherical tool on thickness distribution, maximum
formable angle, maximum formable depth and surface roughness of end product.
1.5 Organization of Thesis Thesis contains five chapters to address objectives of research work. Outline of various
chapters is as follows;
CHAPTER 1 discusses about modern metal forming processes, properties influencing
formability of metals, properties of non ferrous lightweight metals and challenges to form it,
global need of lightweight products and concludes with the aim to address present research
problem.
CHAPTER 2 focuses on survey of specific literatures related to materials for sheet metals,
geometrical parameters including part geometries, process parameters influencing single
point incremental forming, tool material and tool geometries. Selection of sheet metal,
thickness of sheet, part geometry, tool diameter, tool material, tool geometry, range of
process parameters including tool speed, feed, incremental depth and lubrication is reported.
The chapter summarizes scope of research and objectives for selected range of attributes.
CHAPTER 3 addresses on design of experiments and experimentations conducted. It explains
about design of experiments, SPIF fixture and experimental set-up, pilot experiments
conducted on stainless steel and aluminum sheets, effect of grid marking on AMS4902 sheet,
experimental set: 1 and 2 of single pass SPIF for 50o, 60o and 70owall angle pyramids, multi
pass SPIF to form 50o wall angle pyramid to 60o and 70o wall angle pyramids.
Introduction
10
CHAPTER 4 reports about results and discussion on individual effects of tool diameter, tool
speed, tool feed and incremental depth on formability of AMS4902 sheet. It plots effect of
interaction of tool diameter and incremental depth on thickness distribution and surface
roughness during single pass SPIF of AMS4902 sheet. It includes results of maximum
formable depth during single pass SPIF into 50o, 60o, and 70o wall angle pyramids. It also
discusses about results of thickness distribution and maximum formable angle during multi
pass SPIF of AMS4902 sheet.
CHAPTER 5 summarizes important conclusions regarding individual effects of parameters
and parametric interactions on thickness distribution, maximum formable wall angle,
maximum formable depth and surface roughness during single pass and multi pass SPIF of
AMS4902 sheet derived from results of presented experimental work. The chapter extends
the scope of future work.
References
11
References
1. Markovina R, Blagojević B, Ban D (2008) Peen-Forming-The Possibility of Technology
Transfer from Aircraft Industry to the Production of High-Speed Ships, Brodogradnja
([email protected]); 59, 35-43.
2. Lihui L, Kangning L, Cai G, Yang X, Guo C, Bu G (2014) A critical review on special
forming processes and associated research for lightweight components based on sheet and
tube materials, Manufacturing Rev. 2014,1-9. 3. Trzepieciński T (2012) Advances in sheet metal forming technologies, Mechanika z. 84
(4/12) Rzeszow University of Technology, DOI: 10.7862/rm.2012.12, 59-70. 4. Jackson K, Allwood J (2009) The mechanics of incremental sheet forming, Journal of
Materials Processing Technology, 209, 1158–1174. 5. Jeswiet J, Geiger M, Engel U, Kleiner M, Schikorra M, Duflou J, Neugebauer R, Bariani
P, Bruschi S (2008) Metal forming progress since 2000, CIRP Journal of Manufacturing
Science and Technology, 1,2–17. 6. Park JJ, Yung HK (2003) Fundamental studies on the incremental sheet metal forming
technique, Journal of Materials Processing Technology, 140, 447–453. 7. Ham M, Jeswiet J (2006) Single Point Incremental Forming and the Forming Criteria for
AA3003, Annals of CIRP, 55/2, 241-245. 8. Nimbalkar DH, Nandedkar VM (2013) Review of Incremental Forming of Sheet Metal
Components, Intenation Journal of Engineering Research and Applications, 3/ 5,39-51. 9. Behera AK, Desousa RA, Ingarao G, Oleksik V (2017) Single point incremental forming:
An assessment of the progress and technology trends from 2005 to 2015, Journal of
Manufacturing Processes, 27,37–62. 10. Plastic deformation of metals and related properties,
ecampus.sriramanujar.ac.in/files/files_2015/Plasticity-related_properties_069bc.pdf
[Online] [Accessed 5 October 2015] 11. Fratini L, Ambrogio G, Lorenzo RD, Filice L, Micari F (2004) Influence of mechanical
properties of the sheet material on formability in single point incremental forming,
Annals of CIRP, 53/1, 207-210. 12. Billur E, Altan T (2006) Challenges in Forming Advanced High Strength Steels,
Engineering Research Center for Net Shape Manufacturing (ERC/NSM), 285-304.
Introduction
12
13. Kleiner M, Geiger M, Klaus A (2003) Manufacturing of Lightweight Components by
Metal Forming, CIRP Ann-Manuf. Technol., 52(2), 521–542. 14. Ghassemie E (2011) Materials in Automotive Application, State of the Art and Prospects,
New Trends and Developments in Automotive Industry, University of Sheffield UK,
ISBN 978-953-307-999-8, Publisher In Tech, 365-394. 15. Sivanandini M, Dhami SS, Pabla BS (2012) Formability of Magnesium Alloys,
International Journal of Modern Engineering Research (IJMER),2, Issue.4, 2464-2471,
ISSN: 2249-6645.
Literature Review
13
CHAPTER: 2
Literature Review
The present chapter emphasizes on review of literature specific to assessment of formability
of various sheet materials using SPIF within the range of parametric combinations prescribed
by researchers. The state of work is segregated mainly in three sub sections namely; (1)
literature review related to sheet and component attributes; (2) tool attributes and tool path
strategies; and (3) process attributes including tool rotational speed, feed rate and incremental
depth with lubrication at tool-blank interface.
Single Point Incremental Forming (SPIF) is a type of Asymmetric Incremental Sheet Forming
(AISF) described by Jeswiet et al. [1] as “dieless forming” of sheet metal using single point
tool patented by Edward Leszak in 1967. Emmens et al. [2] discussed about history of
development of incremental sheet forming in which distinct difference is mentioned about
patent claimed by team of Walter Berghahn of General Electric Company and Edward
Leszak. The modern AISF was first described and developed by Mason in 1978 as small
batch size sheet metal forming process. Asymmetric Single Point Incremental Forming
(AISF) can be performed by holding sheet blank rigidly against movement of tool
establishing contact with sheet blank as shown in Fig. 2.1.
FIGURE 2.1 Schematic diagram of Single Point Incremental Forming Process with equipments [3]
Single Point Incremental Forming became a key interest of research as an advance material
processing technique for researchers since more than a decade due to its characteristics of
enhanced formability compared to conventional sheet forming processes reported by Kim and
Yang, Kim and Park, Filice et al. [4-6].
Literature Review
14
2.1 Sheet and component attributes
Many researchers reported effect of sheet thickness, step down, speed, tool size on maximum
draw angle in relation with properties of various grades of sheet metals like AA1050-O,
AA6114-T4, AA3003-O, AA8008-O, Al3003-O, Al5754-O, Al5182-O, AA6111-T4P,
DC04, HSS, DDQ steel, Copper, Brass formed by SPIF. They obtained forming limit curve
of negative slop with much higher strains by forming sheets into variety of geometrical
shapes including dome, cone, hyperbola, pyramid using SPIF as shown in Fig. 2.2. They also
concluded that strain hardening exponent of the material as most influencing parameter
affecting formability followed by strength coefficient and percentage elongation. Ham and
Jeswiet [7, 8] conducted experiments using design of experiments for deforming a cone out
of AA3003-O of thickness ranging from 0.8 mm to 2.1 mm. Authors presented a
methodology to develop FLDs for forming AA6451, AA5182 and AA5754 using SPIF and
summarized that material with lower ultimate tensile strength offers more formability.
Ambrogio et al. [9] presented mathematical relation between various parameters influencing
accuracy using statistical analysis of experimental data determined for truncated pyramid of
50o and 60o wall angle formed out of 0.5 mm and 1.5 mm thick sheet of AA1050-O. Hussain
et al. [10] carried out experiments on CNC milling machine for CP Ti sheet of 0.99 mm at
room temperature by forming a variable wall angle conical frustum (VWACF). Franzen et al.
[11] evaluated the formability limit and characterization of 2 mm and 3 mm thick PVC sheets
at room temperature. Martins et al. [12] employed SPIF to form five different polymer sheets
including Polyoxymethylene (POM), Polyethylene (PE), Polyamide (PA), Polyvinylchloride
(PVC) and Polycarbonate (PC) incrementally into cones with an increasing wall angle on a
conventional CNC milling machine and confirmed potential of process to form deep complex
shape. Silva et al. [13] summarized that crack propagation at the junction of inclined wall and
the corner radius of cone with varying wall angle formed from PVC was due to tensile
meridional stresses acting under stretching modes of deformation rather than localized
necking. Hamilton and Jeswiet [14] examined a model to predict the orange peel effect in
SPIF using measured roughness values and forming parameters for 0.8128 mm thick sheets
of Al3003-H14. Bouffioux et al. [15] conducted experiments by forming AlMgSc sheet of 0.5
mm thickness into a straight wall cone angle ranging from 10o to 46o and also validated using
numerical simulation. The purpose was to study effect of wall angle on forming forces.
Sheet and component attributes
15
FIGURE 2.2 Various shapes used to demonstrate SPIF [1]
Hussain et al. [16] demonstrated forming of 2.6 mm thick sheet of AA1060 into conical,
square and hexagonal pyramidal geometry using SPIF. They optimized process parameters
for reducing defects of squeezed out wall formation, corner fold and bulge height. Based on
experimental and FEA results Malhotra et al. [17] confirmed the claim that both through
thickness shear and local bending of sheet around the tool play a role in fracture during SPIF
process of Al5052 into cone and funnel shape geometry. Ambrogio et al. [18] compared
workability of hot incremental sheet forming of 1 mm thick sheet of AA2024-T3, AZ31B-O
and Ti6Al4V (Grade5) into conical frustum with forming at room temperature. Palumbo and
Brandizzi [19] conducted a study to investigate combined effect of electric static heating with
high tool rotations during forming of 1 mm thick sheet of Ti6Al4V (Grade5) into scaled car
door shell using SPIF. Arfa et al. [20] performed Single Point Incremental Forming on 1.2
mm thick sheet of Al3003-O into truncated cones and pyramids experimentally and validated
results of equivalent plastic strain and final wall thickness obtained using numerical
simulation. Ambrogio et al. [21] conducted experiments for forming 1 mm thick sheet of
Titanium ASTM Grade2 and ASTM Grade5 (Ti6Al4V) into a cone of wall angle 30o and 25o
respectively on CNC Lathe using SPIF. Gomez-Lopez et al. [22] presented a case study of
Literature Review
16
forming DC-05 steel sheet into pyramidal shape using SPIF in Solidworks environment. Xu
et al. [23] investigated forming behavior of 1.27 mm thick sheet of AA5052-H32 into
truncated funnel shape. Kurra and Regalla [24] conducted experiments in order to assess
formability and thickness distribution. They deformed EDD steel sheet of 1 mm thickness
into Varying Wall Angle Conical Frustum (VWACF) with different generatrices of circular,
elliptical, parabolic and exponential as depicted in Fig. 2.3 using SPIF.
FIGURE 2.3 Various generatrices of parts formed (a) Circular (b) Elliptical (c) Parabolic (d) Exponential
[24] Desai et al. [25] conducted parametric investigations for Die-Less Rapid Prototyping (DLRP)
process on 0.91 mm thick Al1200-H14 sheet by forming it into 80o wall angle cone. Malwad
and Nandedkar [26] presented experiments on SPIF of AA8011 sheet into constant wall
truncated cone of 50 mm depth. Adams and Jeswiet [27] presented design guidelines for
single-pass SPIF and method of developing intermediate models for multi-pass SPIF with
case studies. Naranjo et al. [28] carried out numerical simulation of SPIF for commercially
pure titanium grade2 (ASTM B-265) of 0.8 mm sheet thickness using ANSYS workbench.
Behera et al. [29] compared accuracy of ellipsoidal shapes of medical implant formed out of
titanium grade 1 using SPIF with characterization models generated by Multivariate Adaptive
Regression Splines (MARS). They used predicated deviations to generate optimized tool
paths in order to minimize shape and dimensional inaccuracies. Uheida et al. [30] conducted
experimental study on 0.8 mm thick sheet of CP Ti Grade2 into varying wall angle conical
frustum (VWACF) of 25 mm height. Afonso et al. [31] formed tunnel and semi tunnel type
Sheet and component attributes
17
parts from 1050-H111 aluminum sheet of 2 mm thickness. Gupta and Jeswiet [32] presented
experiments to form 2.54 mm thick sheet of AA3003-O into scale version of C-channel
geometry of an airplane fuselage. Overall findings from the literature reviewed on various
sheet blank materials and component geometry is tabulated in Table 2.1. TABLE 2.1 Summary of findings reported for various grades of sheet blanks with component geometries
Part
Geometry
Grades of
Steel Alloy
Grades of Al
Alloy
Grades of Mg
Alloy
Grades of Ti
Alloy
Other
Special
Materials
Cup Shape DP600, DP800, DP1000, DP1200, DP1400.
-
AZ 31, ZK10, ZK41
- -
Truncated Cone with constant wall angle
(10o to 80o
Wall Angle)
DC04, DC05, DC06, HSS,
DDQ steel
Al1050, Al1200-H14, Al 3003-O,
Al3003-H14, Al5052,
Al5182-O, Al5754-O,
AA1050-H111, AA1050-O, AA 1100,
AA 3003-O , AA-2024-O, AA2024-T3,
AA5052, AA 5083,
AA6111-T4P, AA8008-O,
AA8011
AZ 31, AZ-31 B, AZ-
31 O, LZ61,
Yttrium- ZK10, ZK41,
CP TI Grade-2 (ASTM B265)
CP Titanium
ASTM Grade 5 (Ti6Al4V)
Polymers like
POM, PE, PA,
PVC, PC
C101
Brass
AlMgSc
Truncated Pyramid
with constant
wall angle
AISI 304 HSS,
DDQ steel,
AA1050-O, AA6114-T4, - - Copper,
Brass
Truncated Cone with
varying wall angle
EDD Steel - - CP TI Grade-2 (ASTM B265) -
Literature Review
18
2.1.1 Findings based on literature review on sheet and component
attributes Based on summary tabulated regarding sheet blank materials and component
geometries in table 2.1, it can be observed that the major work had been carried out for Steel
sheets, Aluminum sheets and its alloys. Similarly, major work on the component geometry of
constant wall or variable wall angle frustum of cone was found. Very less work had been
found on the hard sheet metal like Ti, Mg and its alloys to form it into pyramidal geometry.
From the literature survey, major research efforts were found in the direction to determine the
formability of various grades of Steel sheets, Aluminum sheets and their alloys in terms of
maximum formable wall angle or maximum forming depth during SPIF at room temperature,
hot incremental forming and multi pass forming. Potential research gap is identified to assess
formability in terms of wall thickness distribution after SPIF.
2.2 Tool attributes and tool path strategies
Ham and Jeswiet [7] performed experiments using 4.76 mm and 12.7 mm diameter of tool on
three different thicknesses of AA3003-O sheet. They concluded that the interaction of
material thickness and tool size have significant effect on formability. Ham and Jeswiet [8]
performed SPIF for forming various grades of aluminum sheets of different thicknesses using
4.76 mm, 6.35 mm and 9.52 mm tool diameters. Micari et al. [3] addressed factors
influencing various geometrical errors including pillow effect, sheet bending and springback
during SPIF as explained in Fig. 2.4. Authors suggested optimization of tool trajectories as a
promising strategy amongst suitable strategies discussed to improve geometrical accuracy of
formed component.
FIGURE 2.4 Geometrical Errors in SPIF [3]
Hussain et al. [10] carried out experiments using hemispherical tool of 8 mm, 12 mm and 16
mm diameter made of HSS in order to determine formability of CP Ti sheets. Authors
concluded that maximum formable angle decreases significantly with the increment in tool
Tool attributes and tool path strategies
19
diameter from 8 mm to 12 mm compared to 12 mm to 16 mm. Duflou et al. [31] explored
multi-step tool path strategy experimentally to compare it with simulation output in order to
contribute for better understanding of material relocation. Franzen et al. [11] evaluated
formability limit of PVC sheets by deforming at room temperature using 10 mm and 15 mm
tool diameters. Dejardin et al. [32] demonstrated SPIF through experiments and FEA for
forming a cone out of 1 mm thick sheet of AA1050 using 10 mm diameter of tool. They
reported that springback can be accurately predicted from numerical simulations based on
shell elements associated with a suitable forming tool path. Malhotra et al. [33] proposed tool
path generation strategy to obtain a smoother component base by applying in-to-out and out-
to-in tool paths for each intermediate shapes during multi pass single point incremental
forming of 1 mm thick sheet of AA5052. Authors validated the proposed strategy using 5 mm
and 10 mm diameter hemispherical tools to form a cone as initial shape out of flat sheet and
cap of sphere as final shape out of cone. Ambrogio et al. [17] conducted hot incremental
forming of AA2024-T3, AZ31B-O and Ti6Al4V using 12 mm diameter of HSS tool and
compared results of workability with results obtained at room temperature. Palumbo and
Brandizzi [19] performed experiments to form 1 mm thick sheet of Ti6Al4V using cemented
carbide tool of 16 mm diameter. Gomez-Lopez et al. [22] simulated SPIF for DC-05 sheet
using 12 mm hemispherical tool diameter of AISI420 steel. Ambrogio et al. [21] used 15 mm
diameter tool of hemispherical shape for single point incremental forming of Titanium Grade
2 and Grade 5 on CNC lathe. Kurra et al. [34] implemented tool path trajectories generated
using CAM packages into MatLab and Ls-Dyna for various geometries and found good
agreement for geometric and dimensional accuracy. Nimbalkar and Nandedkar [35] reviewed
procedure to generate the contour and spiral tool paths for incremental sheet forming as
shown in Fig. 2.5.
FIGURE 2.5 Types of tool paths (a) Contour tool path (b) Spiral tool path [20]
Hussain et al. [36] suggested guidelines for tool size selection for single point incremental forming of
AA2024-O and concluded that tool radius twice the sheet thickness offers good spifability. Cawley et
Literature Review
20
al. [37] tested results of formability and surface quality of components formed using angle,
flat and parabolic tool profiles shown in Fig. 2.6 and compared with results of hemispherical
tool profile. All the tools were machined from ASTM A681 tool steel.
(a) (b) (c) (d)
FIGURE 2.6 Various tool Profiles (a) Angular, (b) Flat, (c) Hemispherical, (d) Parabolic [37]
They compared the results for minor shape variation of proposed tool profiles tabulated in
Table 2.2 by forming components out of 1.59 mm thick sheet of Al3003-O. They concluded
that formability is highest with reduced contact area of parabolic tool head as it results in
higher localized stress which allows the sample to resist fracture more readily. TABLE 2.2 Various tool profiles and related dimensional specifications [37]
Tool Type Parameter/ Value
Angle (r=2.54mm) Φ=60o, Φ=70o, Φ=80o
Flat (D=12.7mm) r=5.08mm, r=2.54mm
Hemispherical D=5.08mm, D=10.16mm
Parabolic (D=12.7mm) y=x2, y=5x2, y=10x2
Gupta and Jeswiet [38] performed experiments to form 2.54 mm thick sheet of AA3003-O
into scaled version of C-channel geometry of an airplane fuselage using 9 mm diameter flat
tool having 3 mm corner radius. Kurra and Regalla [24] used 10 mm diameter hemispherical
head tool of EN36 to form of 1 mm thick EDD steel sheet into various component geometries
incrementally. Desai et al. [25] applied 6 mm diameter hemispherical end tool of EN08 with
out-to-in contour tool path to perform Die-Less Rapid Prototyping process. Malwad and
Nandedkar [26] used 6 mm and 12 mm diameter hemispherical head tool and concluded that
tool diameter affects both formability and surface finish. They also mentioned that 12 mm
tool diameter generates more force but it supports sheet better during forming while
formability decreases for tool diameter less than 6 mm as tool tends to penetrate inside the
sheet instead of offering uniform deformation. Centeno et al. [39] conducted experimental
analysis to compare influence of bending in SPIF and stretch-bending on 0.8 mm thick sheet
of AISI304. They used 6 mm, 10 mm and 20 mm diameters of tools with hemispherical head
Tool attributes and tool path strategies
21
to form conical frustum of circular generatrix. They reported enhancement of formability in
SPIF with decrease in tool diameter limiting up to 6 mm tool diameter as indentation mark of
forming tool was observed on the inner surface of metal sheet using 6 mm diameter tool. As
shown in Fig. 2.7, minor strain was observed closer to plane strain conditions due to small
zone of sheet placed under 10 mm diameter forming tool while in the case of 20 mm diameter
forming tool, the strain distribution slightly deviates towards biaxial conditions due to strain
distribution over more extended area. Authors concluded that although the punch radius is an
important factor for the bending effect induced in SPIF, it is not the only factor responsible to
obtain stable deformations well above the FLC. J. Jeswiet et al. [40] discussed design guide
integrating surface roughness of deformed component, tool end geometry, multi-pass
technique and SPIF at an elevated temperature. Authors recommended galvanized steel and
stainless steel flat-ended tool of 12.7 mm or larger diameter for aluminum sheet blank as it
offers best combination of good formability and very low surface roughness.
FIGURE 2.7 Fractography at the fracture initiation zone (left) and at its opposite section (right) for tools
of Φ20 (above) and Φ 10 mm (below) [39]
Bagudanch et al. [41] performed forming on 2 mm thick sheet of polycaprolactone (PLC) to
form into customized cranial geometry using 6 mm diameter hemispherical end tool of
Literature Review
22
Vanadis 23 steel by SPIF. They suggested that modification of tool path is one of the
important strategies in negative incremental sheet forming in order to improve the
geometrical accuracy of formed components. Gatea et al. [42] recommended scope for
application of new tool designs, tool materials and development of different algorithms to
generate appropriate tool paths capable to form product with good surface finish and
dimensional accuracy. McAnulty et al. [43] presented a review on interactions between
various parameters influencing SPIF and reported scope to work on the interaction between
tool material, blank material and lubrication as it has considerable influence on friction
conditions at tool-sheet interface. Salem et al. [44] investigated influence of tool path on
cumulative strain along the constant wall of cone. They performed SPIF to form the cone
from AA7075-O sheet of 1.6 mm thickness using 12.7 mm diameter tool of hemispherical tip
followed by spiral tool path. Uheida et al. [30] demonstrated SPIF to form CP Ti Grade 2
sheets using 10 mm diameter hemispherical forming tool of steel 2312 operated through out-
to-in spiral toolpath. Abbas [45] compared effect of elliptical profile tool on final product
profile, final thickness, strain and stress distribution of formed component over results by
hemispherical and flat profile tools using numerical simulation. Behera et al. [46]
summarized the maximum formable wall angle obtained by various researchers employing
various tool diameters to form constant or varying wall angle conical frustum out of variety
of sheet materials of various thicknesses. Authors suggested scope of research in the area of
simultaneous control of thickness variation with dimensional accuracy by incorporating real
time tool path correction strategies. Afonso et al. [47] used three different tool path strategies,
(i) helical toolpath, (ii) alternating strategy with stepdown at wall center and (iii) inside-out
strategy with air movements and stepdown at wall center as shown in Fig. 2.8 to form tunnel
shape component of 1050-H111 sheet.
FIGURE 2.8 Various toolpath strategies (a) helical (b) alternating (c) inside-out [47]
They found that the alternating toolpath with the side changing position from one tunnel wall
to other outside the part edge is most reliable strategy. Kumar et al. [48] conducted SPIF of
Tool attributes and tool path strategies
23
AA2024-O sheet into truncated cone using 7.52 mm, 11.60 mm and 15.66 mm diameters of
hemispherical tip tool and flat-end tool having smaller and bigger corner radii operated with
helical tool path. They found increment in formability with increase in tool diameter. They
concluded that flat-end tool with larger corner radius improved formability while flat-end
tools with lower corner radius and lower tool diameter experienced an earlier fracture of sheet
material. Yoganjaneyulu et al. [49] performed SPIF of 1 mm thick CP Ti Grade 2 sheet using
forming tool diameter of 8 mm, 10 mm and 12 mm of F6 tool steel with spiral tool path. They
observed maximum deformation fracture strain on the component deformed using 12 mm
diameter tool. Gupta and Jeswiet [38] demonstrated four different strategies of multi-stage
toolpath namely; (i) Conventional Downward strategy, (ii) Downward-Downward-
Downward-Up (DDDU) strategy, (iii) Inside Outside-Outside Inside (IO-OI) strategy, (iv)
Tunnel strategy to form vertical wall angles with complexities of C-channel geometry of
airplane fuselage. Flat profile forming tool of 9 mm diameter with 3 mm corner radius was
used in order to meet demand of tight tolerances of corner radius on formed component and
to eliminate pillow effect. They found the Conventional Downward strategy as the most
suitable strategy to form identified geometry of C-channel. Findings based on literature
review conducted regarding tool materials, tool diameters, tool end geometries and tool paths
in combination of sheet blank material is tabulated in Table 2.3;
Literature Review
24
TABLE 2.3 Combination of tool materials, tool diameters, tool end geometries and tool paths in combination to form various sheet blank materials
Tool
Materials
Sheet Blank Materials Grades of
Steel and its Alloy
Grades of Al and its Alloy
Grades of Mg and its
Alloy
Grades of Ti and its Alloy
Other Special
Materials
Cemented Carbide
Tool - - -
16 mm diameter
Hemispherical tip tool
-
HSS -
12 mm diameter Hemispherical
tip tool
12 mm diameter
Hemispherical tip tool
8 mm, 12 mm, 16 mm
diameter Hemispherical
tip tool (Spiral path)
-
EN08 -
6 mm diameter Hemispherical
tip tool (Out-to-in
Contour path)
- - -
EN36
10 mm diameter
Hemispherical tip tool
(Contour path)
- - - -
AISI 420 12 mm
diameter Hemispherical
tip tool - - - -
ASTM A681 tool
steel -
5.08 mm Angle, 12.7 mm Flat & Parabolic, 10.16 mm & 20.32 mm
diameter Hemispherical
tip tool
- - -
Vanadis 23 steel - - -
10 mm diameter
Hemispherical tip tool
6 mm diameter
Hemispherical tip tool
Steel 2312 - - -
10 mm diameter
Hemispherical tip tool
(Out-to-in Spiral path)
-
Process attributes
25
Tool
Materials
Sheet Blank Materials Grades of
Steel and its Alloy
Grades of Al and its Alloy
Grades of Mg and its
Alloy
Grades of Ti and its Alloy
Other Special
Materials
F6 tool steel - - -
8 mm, 10 mm, 12 mm
diameter Hemispherical
tip tool (Spiral path)
-
Not Specified any Tool Material
6 mm, 10 mm, 12 mm
Hemispherical tip tool
5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 15
mm, 16 mm, 20mm diameter Hemispherical
tip tool
- -
15 mm diameter
Hemispherical tip tool
2.2.1 Findings based on literature review on tool attributes and tool path
strategies
Combination of tool materials and sheet blank materials has been tabulated in table 2.3 for
which research had already been carried out including tool diameters, tool end geometries
and tool path strategies. Generally, contour and spiral strategies of tool paths were found
most common strategies of choice to apply for SPIF of various grades of sheet metals. Effect
of tool end geometries and tool diameters on formability as well as dimensional accuracy of
components formed out of variety of sheet materials was also addressed.
2.3 Process attributes
In order to develop process mechanics of Single Point Incremental Forming (SPIF) for
different sheet materials, combination of various process parameters including tool rotational
speed, feed, incremental depth and lubrication at tool-sheet interface plays vital role. Kim and
Park [5] performed straight groove test by operating tool at 0.1 mm, 0.3 mm and 0.5 mm feed
rates to investigate effect of process parameters on formability of Aluminum 1050 sheet in
rolling and transverse direction. Authors reported improvement in formability with ball tool
of 10 mm diameter operated at lower feed rate in the presence of little friction. Jeswiet et al.
Literature Review
26
[1] summarized effect of spindle speed and lubrication on surface roughness of various
shapes formed by SPIF using different sheet blank materials. They also presented challenges
to develop strategies to obtain dimensional accuracy of variety of product shapes to be
formed out of various sheet blank materials for the interest of applications of automotive,
aerospace, architectural and biomedical. Ham and Jeswiet [7] performed SPIF at the
parametric combination of 100 rpm and 600 rpm spindle speeds, 1270 mm/min and 2540
mm/min feeds with 0.0508 mm, 0.127 mm and 0.254 mm step size to determine effect on
formability of AA3003-O in terms of maximum formable angle and depth of component
formed. They concluded that the faster spindle speed improved the formability at lower feed
and also observed significant effect of material thickness, tool diameter and its interaction on
maximum formable wall angle. Hussain et al. [50] demonstrated SPIF at 2500 mm/min
horizontal feed and 0.15 mm/ revolution vertical feed to determine maximum formable angle
by forming 0.91 mm thick aluminum sheet into varying wall angle conical frustum
(VWACF). Hussain et al. [10] performed experiments to investigate effect of pitch, tool
diameter, feed rate and friction at tool-sheet interface on maximum formable wall angle of
VWACF formed using SPIF from CP Ti sheet of 0.99 mm thickness. 98.5 percent pure MoS2
(Molybdenum Disulphide) of small grain size was mixed with grease to apply as a lubricant
at tool sheet contact. Design of experiments for combination of process parameters used by
Hussain et al. is tabulated in Table 2.4 as;
TABLE 2.4 Design of experiments for some process parameters [10]
Experiment Feed Rate
(f) (in mm/min)
Tool Diameter
(d) (in mm)
Pitch
(p) (in mm )
1 2600 12 0.2
2 2600 12 0.75
3 2600 12 1.3
4 1200 12 0.75
5 4000 12 0.75
6 2600 8 0.75
7 2600 16 0.75
They concluded that drop in formability of CP Ti was higher when feed rate exceeded 2500
mm/min and friction at tool-blank interface did not play any significant role to increase
formability of CP Ti, rather higher friction offered poorer surface quality. Duflou et al. [31]
Process attributes
27
performed SPIF of 1.5 mm thick sheet of AA3103 at 2 m/min feed rate, 100 rotations/min
spindle speed and 1 mm stepdown with contour tool path to explore multi-step toolpath
strategy. Dejardin et al. [32] performed SPIF at 400 rpm rotational speed, 500 mm/min feed
rate and 0.2 mm step depth. Ambrogio et al. [51] demonstrated SPIF to form customized
ankle support out of Deep Drawing Quality (DDQ) Steel of 1 mm thick sheet.
Theyperformed SPIF using 11 mm diameter tool of hemispherical tip operated at 500 rpm
speed, 1000 mm/ min feed and 0.5 mm step depth.
Hussain et al. [16] performed SPIF at 2600 mm/min feed rate and 0.3 mm pitch to present
empirical model for optimization of process parameters. Palumbo and Brandizzi [19]
performed experiments to investigate contribution of tool rotational speed during SPIF of 1
mm thick Ti6Al4V combining with static heating. SPIF tests were performed by employing
16 mm diameter cemented carbide tool at 800-1600 rpm speed range, 1800 mm/min feed and
step depth ranging from 0.5-1 mm in the presence of OKS 280 solid lubricant to form into
scaled geometry of car door shell. They noticed that high rotational speed helped to stabilize
the necking, increase accuracy and surface quality of formed geometry. Ambrogio et al. [21]
concluded that increase in feed did not supply enough power to affect the significant change
in material microstructure for the selected feed values of 6 m/min, 60 m/min and 600 m/min
for Ti ASTM Grade2 and 5 m/min, 50 m/min and 500 m/min for Ti ASTM Grade5. They
performed experiments on 0.25 mm and 1 mm pitch for ASTM Grade2 while 0.1 mm, 0.3
mm and 0.5 mm were the pitch values selected for ASTM Grade5. Xu et al. [23] investigated
influence of low tool rotation range from 0-1000 rpm and high tool rotation range from 2000-
7000 rpm on formability mechanism by forming 1.27 mm thick sheet of AA5052-H32 into
truncated funnel shape at constant feed of 150 mm/min and step depth of 0.5 mm. They
reported that increase in through thickness shear was a key factor for increase in formability
which was observed in the range of 0-500 rpm while thermal effect became dominant reason
for enhanced formability between 2000-3000 rpm and active dynamic recrystallization due to
refinement of microstructure favored for improving formability beyond 3000 rpm. They also
observed that formability of material decreases with laser surface textured forming tool due
to reduction in friction and heat generation at tool-blank interface compared to regular SPIF
forming tool. Desai et al. [25] presented experiments on Die-Less Rapid Prototyping (DLRP)
process operated at 1250 rpm and with feed rate values of 25 mm/min, 50 mm/min and 75
mm/min with incremental depth of 0.5 mm and 0.8 mm in order to determine effect of feed
rate on formability. They also investigated effect of tool rotational speed ranging from 500-
2000 rpm at equal interval of 250 rpm on formability of Al1200-H14 for constant feed rate of
Literature Review
28
50 mm/min and 0.5 mm incremental depth. They noticed less forming time at higher feed rate
but concluded that forming of higher cone angle is possible at lower incremental depth and
optimum value of feed rate specific to blank material operated with contour tool path. They
observed no effect of tool rotation on forming time but recommended higher tool rotation for
good surface quality and lesser geometrical error. Malwad and Nandedkar [26] demonstrated
SPIF at 1000 rpm spindle speed, 1500 mm/min feed rate and 0.2 mm and 0.5 mm incremental
depth for formability assessment of AA8011. Bagudanch et al. [52] performed SPIF of 0.8
mm thick sheet of AISI 304 using 6 mm, 10 mm and 20 mm diameter tools operated at 1000
rpm speed, 3000 mm/ min feed and 0.2 mm and 0.5 mm values of step depths. They have
used Houghton TD-52 lubricant at tool-sheet interface. They observed increase in forming
force with increment in tool diameter and step depth while decrease in forming force with
increase in spindle speed due to increase in temperature caused by friction at tool-sheet
interface.
Gatea et al. [42] presented technological capabilities and limitations of Incremental Sheet
Forming (ISF) processes in detail with knowledge gap for integrated effect of process
parameters on formability, deformation and failure mechanics, geometrical and dimensional
accuracy and surface roughness for various hard to form materials including new techniques
of hot ISF and multi-pass ISF. Authors recommended that there is a need for research to
establish relations between step depth, tool rotation and feed rate with type of material, effect
of ratio of initial sheet thickness and tool radius on FLCF, development of algorithm for
prediction and improvement of springback, dimensional accuracy and surface finish with
respect to material properties, forming parameters, tool designs, tool paths and lubrication.
McAnulty et al. [43] conducted quantitative analysis on review of 35 research papers and
found lack of focus in parameter interactions for SPIF as they are highly interdependent and
material specific. Authors presented a theoretical framework for experimental parameters in
order to establish comparability of results of research in future. Uheida et al. [30] investigated
the influence of sliding velocity of hemispherical tip forming tool on thermomechanical loads
during SPIF test of CP Ti Grade2 sheets for the speed range of 450 rpm to 15000 rpm and
step size of 0.3 mm. The major conclusion drawn was about initiation of failure of sheet
above 4000 rpm due to escalation of material and reduction in forming angle was also
observed. They also found tool rotation conducive up to 2500 rpm to obtain deformation of
sheet with ease at reduced forming forces. They reported that increase in feed rate contributed
for slightly increment in in-plane forces than heat generation at tool-sheet interface. Echrif
and Hrairi [53] summarized research trend in forming methods, formed sheets, forming path
Process attributes
29
strategies, forming limits, forming tools and simulation for Incremental Sheet Forming (ISF).
Behera et al. [46] presented a progressive assessment for SPIF from 2005 to 2015 with its
current state of art in order to derive roadmap for investigation interest in future. Kumar et al.
[48] performed SPIF in order to determine impact of forming tool shape, tool diameter, wall
angle, step size, sheet thickness and tool rotation on formability of AA2024-O sheet. They
conducted experiments using hemispherical tip tool and flat tools operated at free spindle
speed, 1000 rpm and 2000 rpm with the step depth values of 0.2 mm, 0.5 mm and 0.8 mm.
They concluded that increase in wall angle and step size led to decrease in formability and
combination of higher tool diameter with higher step size was also responsible for loss of
formability due to fracture of component at lower depth. Yoganjaneyulu et al. [49] examined
variation of fracture behavior of 1 mm CP Ti Grade2 by performing SPIF for the speed
values of 300 rpm, 450 rpm and 600 rpm at constant feed of 300 mm/min and varying step
depth of 0.2 mm, 0.4 mm and 0.6 mm. They reported that limiting fracture strain values were
diminished for 12 mm diameter tool operated at speed of 600 rpm. Dwivedy and Kalluri [54]
determined effect of tool diameter, sheet thickness, feed, spindle speed, depth of indentation
(z-depth) on forming force and concluded that sheet thickness followed by z-depth had
significant effect on average axial and pick axial forces. They presented experiments for SPIF
of EDD steel using hemispherical tool of EN-36 with SAE 40 as a lubricant. Table 2.5 shows
various parameters used by Dwivedy and Kalluri [54] for performing experiments. TABLE 2.5 Level of parameters to conduct experimentations using SPIF [54]
Factor (unit) Level-1 Level-2 Level-3
Tool Diameter (mm) 10 12 14
Sheet Thickness (mm) 0.6 1.0 1.2
Feed (mm/min) 1300 1400 1500
Spindle Speed (rpm) 700 800 900
Depth of indentation (z-Depth) (mm) 0.2 0.3 0.4
Parametric combination of tool rotational speeds, feed rates and incremental depths used for
SPIF of specific sheet blank material is summarized in Table 2.6, 2.7 and 2.8.
Literature Review
30
TABLE 2.6 Summary of parametric combinations reviewed for tool rotational speeds and feed rates to form specific sheet blank material using SPIF
Range of Tool
Rotational Speed (rpm)
Range of Feed Rate (mm/min)
0-999 1000-1999 2000-2999 3000-
3999
4000-
4999
5000-
and
more
0-999
AA 1050, AA5052-H32, Al1200-H14, CP Ti Grade 2
AA3003-O, EDD Steel, Ti6Al4V,
CP Ti Grade 2
AA3003-O, AA3103,
CP Ti Grade 2 - CP Ti
Grade 2 CP Ti
Grade 2
1000-1999 AA5052-H32, Al1200-H14
AA8011 Ti6Al4V - - - -
2000-2999 AA5052-H32, Al1200-H14 - - - - -
3000-3999 AA5052-H32 - - - - - 4000-4999 AA5052-H32 - - - - -
5000-5999 AA5052-H32 - - - - -
6000-6999 AA5052-H32 - - - - - 7000 and
more AA5052-H32 - - - - -
TABLE 2.7 Summary of parametric combinations reviewed for feed rates and incremental depth to form
specific sheet blank material using SPIF Range of Feed
Rate (mm/min)
Range of Incremental Depth (mm)
0.01 - 0.49 0.5 – 0.89 0.9 – 1.29 1.3 and more
0-999 AA1050 CP Ti Grade 2
AA5052-H32, Al1200-H14,
CP Ti Grade 2 - -
1000-1999 AA3003-O,
AA8011, CP Ti Grade 2,
EDD Steel
C-101 AA8011,
CP Ti Grade 2, Ti6Al4V
Ti6Al4V -
2000-2999 AA3003-O,
AA1060, AlMgSc CP Ti Grade 2
CP Ti Grade 2 AA3103 CP Ti Grade 2
3000-3999 - - - - 4000-4999 CP Ti Grade 2 CP Ti Grade 2 - - 5000-5999 Ti ASTM Grade2 - Ti ASTM Grade2 - 6000-6999 Ti ASTM Grade5 Ti ASTM Grade5 - -
7000 and more Ti ASTM Grade2 Ti ASTM Grade5
CP Ti Grade 2 Ti ASTM Grade5 TI ASTM Grade2 -
Process attributes
31
TABLE 2.8 Summary of parametric combinations reviewed for tool rotational speeds and incremental depth to form specific sheet blank material using SPIF
Range of Tool Rotational
Speed (rpm)
Range of Incremental Depth (mm)
0.01 - 0.49 0.5 – 0.89 0.9 – 1.29
0-999 AA1050,
AA3003-O, CP Ti Grade 2
AA5052-H32, Al1200-H14, Ti6Al4V
CP Ti Grade 2
AA1050-O, AA6114-T4,
AA3103 HSS, DDQ steel, Copper, Brass,
Ti6Al4V
1000-1999 AA8011,
AA2024-O CP Ti Grade 2
AA5052-H32, Al1200-H14,
AA8011, Ti6Al4V -
2000-2999 CP Ti Grade 2 AA5052-H32, Al1200-H14, AA2024-O -
3000-3999 CP Ti Grade 2 AA5052-H32 -
4000-4999 CP Ti Grade 2 AA5052-H32 -
5000-5999 CP Ti Grade 2 AA5052-H32 - 6000-6999 CP Ti Grade 2 AA5052-H32 -
7000 and more CP Ti Grade 2 AA5052-H32 AA2024-O -
2.3.1 Findings based on literature review on process attributes
Based on tabulated combinations SPIF process parameters in Table 2.6, 2.7 and 2.8; it can be
observed that optimization of process parameters including spindle speed, feed rate,
incremental depth and lubrication at tool-sheet interface has been carried out with respect to
formability of specific sheet metals in terms of maximum formable angle and depth,
geometrical accuracy and surface roughness of components formed. Impact of interactions
between various process parameters to obtain quality of customized products formed using
SPIF is of interest of research which may also helpful database to develop dedicated
machines for Incremental Sheet Forming (ISF). In the recent era the research interest is also
to operate SPIF at higher tool rotational speed and feed rate in the benefit of industry as both
are contributing parameters in order to satisfy demand of higher production rate.
Literature Review
32
2.4 Scope of Research
The potential scope of present research work is identified to determine formability of
AMS4902 in terms of thickness distribution, maximum formable angle, fracture Depth
during single pass and multi pass SPIF at room temperature.
The scope of present work also includes determining effect of various parameters and
their interactions influencing formability, geometrical accuracy and surface quality of
components formed out of AMS4902 using SPIF.
AMS4902 possesses HCP structure having three slip systems namely prismatic plane slip,
pyramidal plane slip and basal plane slip. Although the HCP and FCC structures possess
highest atomic packing factor of 0.74 which signifies 74% of volume of unit cell
occupied by atoms, the HCP structured metals are difficult to deform due to limited
number of available active slip systems compare to BCC or FCC structured metals.
Comparing the average properties of AMS4902 with other metals; TABLE 2.9 Comparison of material properties of AMS4902 with other materials
Properties
Material
Steel
(DC-05)
Aluminum
(AA2024-O)
Magnesium
(AZ31) AMS4902
Density (gm/cc) 7.83 2.78 1.77 4.51
Modulus of Elasticity (GPa) 210 73.1 45 105
Yield Strength (MPa) 149.67 80.428 150 345
Ultimate Tensile Strength (MPa) 308.54 166.56 255 485
% Elongation in 50 mm 40 18.73 15 42.53
AMS4902 is having higher yield strength and ultimate strength; hence it is less
stretchable and difficult to form than Magnesium. At the same time, AMS4902 is 56
percent lighter than Steel and most useful in transport sectors like aerospace industries
and automobile industries. As Modulus of Elasticity of AMS4902 is 2.45 times higher
than Magnesium, the Springback for AMS4902 is expected 0.4 times lesser than
Magnesium which may offer more dimensional accuracy of formed component.
Hence, AMS4902 is having potential to develop material characteristics and process
mechanics for conducting parametric investigation using Single Point Incremental
Forming.
Objectives
33
2.5 Objectives
The following objectives are set in order to analyze formability of AMS4902 using Single
Point Incremental Forming.
(1) To decide range of speed, feed, incremental depth and tool diameter for single pass and
multi pass SPIF of AMS4902.
(2) To assess formability of AMS4902 in terms of thickness distribution, maximum formable
wall angle and failure depth (by deforming 1.5 mm thick sheet into 50°, 60° & 70° wall
angle square pyramid in a singlepass and 60° & 70° wall angle square pyramid in
multipass SPIF).
(3) To determine effect of parametric interaction between tool diameter with incremental step depth on formability of AMS4902.
(4) To determine effect of parametric interaction between tool diameter and incremental step depth for single pass SPIF on surface roughness of component formed out of AMS4902.
2.6 Research Methodology
On the basis of scope of presented research, systematic approach has been adapted to
determine formability of 1.5 mm thick sheet of AMS4902 in terms of wall thickness
distribution, maximum formable wall angle and maximum formable depth of pyramids
during single pass and multi pass SPIF. In order to perform SPIF of AMS4902, values of
tool diameter, tool rotational speed, feed rate and incremental depth have been decided
based on literature review. Design of experiments has been formulated to investigate
individual effect of process parameters on formability of AMS4902 sheet as discussed in
chapter: 3. Experimental work is extended to address the research gap identified to
investigate effect of interaction between tool diameter and incremental step depth on
percentage thinning and surface roughness of pyramid walls formed using SPIF. The
critical and interesting findings about geometrical accuracy of pyramid walls formed using
SPIF are discussed in chapter: 4 which are also highlighted in conclusions. Fig. 2.9 depicts
about the flow chart for methodology applied to address the presented research problem.
Literature Review
34
FIGURE 2.9 Flow chart of applied research methodology
Start
Selection of Process Parameters and Design of Experiments
Development of fixture for Single Point Incremental Forming
Experimental Set: 1 Single pass SPIF to form
50owall angle square
Possibility of forming
pyramid up to design
depth
No Do not consider the
parameters for Experimental Set: 2
for which the failure of sheet occurs before
forming up to design depth
Experimental Set: 2 Single pass SPIF to form
50owall angle square
Yes
Measurement of thickness of pyramid walls formed during
Experimental Set: 2
Measurement of surface roughness of pyramid walls formed during Experimental Set: 2
using fixture fabricated to hold the pyramid
Selection of combination of optimum process parameters based on calculated values of minimum average percentage thinning and minimum average surface roughness of pyramid walls
Experimental Set: 3 Single pass SPIF to form
60oand 70owall angle square pyramids
Experimental Set: 4 Multi pass SPIF to form 60oand 70owall angle square pyramids out of already formed pyramids of 50owall angle using optimum process parameters determined
Conclusion
Stop
References
35
References:
1. Jeswiet J, Micari F, Hirt G, Bramley A, Duflou J, Allwood J (2005) Asymmetric
Single Point Incremental Forming of Sheet Metal, Metal Annals of CIRP, 54(1), 623–
650.
2. Emmens WC, Sebastiani G, Vanden Boogaard AH, (2010) The technology of
Incremental Sheet Forming—A brief review of the history, Journal of Materials
Processing Technology, 210, 981–997.
3. Micari F, Ambrogio G, Filice L (2007) Shape and dimensional accuracy in Single
Point Incremental Forming: State of the art and future trends, Journal of Materials
Processing Technology, 191, 390–395.
4. Kim TJ, Yang DY (2000) Improvement of formability for the incremental sheet metal
forming process, International Journal of Mechanical Sciences, 42, 1271-1286.
5. Kim YH, Park JJ (2002) Effect of process parameters on formability in incremental
forming of sheet metal, Journal of Materials Processing Technology, 130–131, 42–46.
6. Filice L, Fratin L, Micari F (2002) Analysis of Material Formability in Incremental
Forming, Annals of the CIRP, 51/1, 199-202.
7. Ham M, Jeswiet J (2006) Single Point Incremental Forming and the Forming Criteria
for AA3003, Annals of CIRP, 55/2, 241-245.
8. Ham M, Jeswiet J (2007) Forming Limit Curves in Single Point Incremental Forming,
Annals of the CIRP, 56/1, 277-280.
9. Ambrogio G, Cozza V, Filice L, Micari F (2007) An analytical model for improving
precision in single point incremental forming, Journal of Materials Processing
Technology, 191, 92–95.
10. Hussain G, Gao L, Zhang ZY (2008) Formability evaluation of a pure titanium sheet
in the cold incremental forming process, International Journal of Advance
Manufacturing Technology, 37, 920–926.
11. Franzen V, Kwiatkowski L, Martins PFA, Tekkaya AE (2009) Single point
incremental forming of PVC, Journal of Materials Processing Technology, 209, 462–
469.
12. Martins PAF, Kwiatkowski L, Franzen V, Tekkaya AE, Kleiner M (2009) Single
point incremental forming of polymers, CIRP Annals-Manufacturing Technology, 58,
229–232.
Literature Review
36
13. Silva MB, Alves LM, Martins PFA (2010) Single point incremental forming of PVC:
Experimental findings and theoretical interpretation, European Journal of Mechanics
A/Solids, 29, 557-566.
14. Hamilton K, Jeswiet J (2010) Single point incremental forming at high feed rates and
rotational speeds: Surface and structural consequences, CIRP Annals-Manufacturing
Technology, 59, 311–314.
15. Bouffioux C, Lequesne C, Vanhove H, Duflou JR, Pouteau P, Duchêne L, Habraken
AM (2011) Experimental and numerical study of an AlMgSc sheet formed by an
incremental process, Journal of Materials Processing Technology, 211, 1684– 1693.
16. Hussain G, Gao L, Hayat N (2011) Forming Parameters and Forming Defects in
Incremental Forming of an Aluminum Sheet: Correlation, Empirical Modeling, and
Optimization: Part A, Materials and Manufacturing Processes, 26, 1546–1553.
17. Ambrogio G, Filice L, Gagliardi F (2012) Formability of lightweight alloys by hot
incremental sheet forming, Materials and Design, 34, 501–508.
18. Malhotra R, Xue L, Belytschko T, Cao J (2012) Mechanics of fracture in single point
incremental forming, Journal of Materials Processing Technology, 212, 1573– 1590.
19. Palumbo G, Brandizzi M (2012) Experimental investigations on the single point
incremental forming of a titanium alloy component combining static heating with
high tool rotation speed, Materials and Design, 40, 43–51.
20. Arfa H, Bahloul R, BelHadjSalah H (2013) Finite element modelling and
experimental investigation of single point incremental forming process of aluminum
sheets: influence of process parameters on punch force monitoring and on mechanical
and geometrical quality of parts, International Journal of Material Forming, 6, 483–
510.
21. Ambrogio G, Gagliardi F, Bruschi S, Filice L (2013) On the high-speed Single Point
Incremental Forming of titanium alloys, CIRP Annals-Manufacturing Technology,
62, 243–246.
22. Gómez-Lópeza LM, Miguela V, Martínez A, Coelloa J, Calatayud A (2013)
Simulationand Modeling of Single Point Incremental Forming Processes within a
Solidworks Environment, The Manufacturing Engineering Society International
Conference, MESIC 2013, Procedia Engineering, 63, 632 – 641.
23. Xu D, Wu W, Malhotra R, Chen J, Lu B, Cao J (2013) Mechanism investigation for
the influence of tool rotation and laser surface texturing (LST) on formability in
References
37
single point incremental forming, International Journal of Machine Tools &
Manufacture, 73, 37–46.
24. Kurra S, Regalla SP (2014) Experimental and numerical studies on formability of
extra-deep drawing steel in incremental sheet metal forming, Journal of Material
Research and Technology, 3(2), 158–171.
25. Desai BV, Desai KP, Raval HK (2014) Die-Less Rapid Prototyping Process:
Parametric Investigations, Procedia Materials Science, 6, 666 – 673.
26. Malwad DS, Nandedkar VM (2014) Deformation Mechanism Analysis of Single
Point Incremental Sheet Metal Forming, Procedia Materials Science 6, 1505 – 1510.
27. Adams D, Jeswiet J (2014) Design rules and applications of single point incremental
forming, Proceedings of the Institution of Mechanical Engineers, Part B: Journal of
Engineering Manufacture, 1-8.
28. Naranjo J, Miguel V, Martinez A, Gomez-Lopez LM, Manjabacas MC, Coello J
(2015) Analysis and Simulation of Single Point Incremental Forming by ANSYS,
Procedia Engineering, 132, 1104-1111.
29. Behera AK, Lu B, Ou H (2016) Characterization of shape and dimensional accuracy
of incrementally formed titanium sheet parts with intermediate curvatures between
two feature types, International Journal of Advance Manufacturing Technology, 83,
1099–1111.
30. Uheida EH, Oosthuizen GA, Dimitrov D (2017) Investigating the impact of tool
velocity on the process conditions in Incremental Forming of Titanium Sheets,
Procedia Manufacturing, 7, 345 – 350.
31. Duflou JR, Verbert J, Belkassem B, Gu J, Sol H, Henrard C, Habraken AM (2008)
Process window enhancement for single point incremental forming through multi-step
toolpaths, CIRP Annals-Manufacturing Technology, 57, 253–256.
32. Dejardin S, Thibaud S, Gelin JC, Michel G (2010) Experimental investigations and
numerical analysis for improving knowledge of incremental sheet forming process for
sheet metal parts, Journal of Materials Processing Technology, 210, 363–369.
33. Malhotra R, Bhattacharya A, Kumar A, Reddy NV, Cao J (2011)A new methodology
for multi-pass single point incremental forming with mixed tool paths, CIRP Annals-
Manufacturing Technology, 60, 323–326.
34. Kurra S, Khan A, Regalla SP (2013) Tool path definition for numerical simulation of
single point incremental forming, International Conference on Design and
Manufacturing, IConDM 2013, Procedia Engineering, 64, 536 – 545.
Literature Review
38
35. Nimbalkar DH, Nandedkar VM (2013) Review of Incremental Forming of Sheet
Metal Components, International Journal of Engineering Research and Applications,
3/5, 39-51.
36. Hussain G, Khan HR, Gao L, Hayat N (2013) Guidelines for Tool-Size Selection for
Single-Point Incremental Forming of an Aerospace Alloy, Materials and
Manufacturing Processes, 28, 324-329.
37. Cawley B, Adams D, Jeswiet J (2013) Examining Tool Shapes in Single Point
Incremental Forming, Proceedings of NAMRI/SME, 41, 1-8.
38. Gupta P, Jeswiet J (2019) Manufacture of aerospace component by single point
incremental forming, Procedia Manufacturing, 29, 112-119.
39. Centeno G, Bagudanch I, Martínez-Donaire AJ, García-Romeu ML, Vallellano C
(2014) Critical analysis of necking and fracture limit strains and forming forces in
single-point incremental forming, Materials and Design, 63, 20–29.
40. Jeswiet J, Adams D, Doolan M, McAnulty T, Gupta P (2015) Single point and
asymmetric incremental forming, Advance Manufacturing, 3, 253–262.
41. Bagudanch I, Lozano-Snchez L, Puigpinos L, Sabater M, Elizalde L, Zuniga E,
Garcia-Rueu M (2015) Manufacturing of polymeric biocompatible cranial geometry
by Single Point Incremental Forming, Procedia Engineering, 132, 267-273.
42. Gatea S, Ou H, McCartney G (2016) Review on the influence of process parameters
in incremental sheet forming, International Journal of Advance Manufacturing
Technology, 87, 479–499.
43. McAnulty T, Jeswiet J, Doolan M (2016) Formability in single point incremental
forming: A comparative analysis of the state of the art, CIRP Journal of
Manufacturing Science and Technology, 38, 1-12.
44. Salem E, Shin J, Nath M, Banu M, Taub AI (2016) Investigation of Thickness
Variation in Single Point Incremental Forming, Procedia Manufacturing, 5, 828-837.
45. Abass KI (2016) A study to comparing spherical, ellipse and Flat forming tool profile
effect in single point incremental forming by finite element analysis, U.P.B. Sci.
Bull., Series D, 78/ 1, 172-184, ISSN 1454-2358.
46. Behera AK, DesousaRA, Ingarao G, Oleksik V (2017) Single point incremental
forming: An assessment of the progress and technology trends from 2005 to
2015,Journal of Manufacturing Processes, 27, 37–62.
47. Afonso D, Desousa RA, Torcato R (2017) Incremental forming of tunnel type parts”,
Procedia Engineering, 183, 137–142.
References
39
48. Kumar A, Gulati V, Kumar P, Singh V, Kumar B, Singh H (2018) Parametric effects
on formability of AA2024-O aluminum alloy sheets in single point incremental
forming, Journal of Material Research and Technology, 1-9.
49. Yoganjaneyulu G, Narayanan CS, Narayanasamy R (2018) Investigation on the
fracture behavior of titanium grade 2 sheets by using the single point incremental
forming process, Journal of Manufacturing Processes, 35, 197–204.
50. Hussain G, Gao L, Dar NU (2007) An experimental study on some formability
evaluation methods in negative incremental forming, Journal of Materials Processing
Technology, 186, 45–53.
51. Ambrogio G, De Napoli L, Filice L, Gagliardi F, Muzzupappa M (2005) Application
of Incremental Forming process for high customized medical product manufacturing,
Journal of Materials Processing Technology, 162–163, 156–162.
52. Bagudanch I, Centeno G, Vallellano C, Garcia-Romeu ML (2013) Forming force in
Single Point Incremental Forming under different bending conditions, The
Manufacturing Engineering Society International Conference, MESIC 2013,Procedia
Engineering, 63, 354 – 360.
53. Echrif SBM, Hrairi M (2011) Research and Progress in Incremental Sheet Forming
Processes, Materials and Manufacturing Processes, 26, 1404–1414.
54. Dwivedy M, Kalluri V (2019) The effect of process parameters on forming forces in
single point incremental forming, Procedia Manufacturing, 29, 120-128.
Experimental Investigations
40
CHAPTER: 3
Experimental Investigations
This chapter discusses about design of experiments, experimental set-up, testing of material
property parameters, circle-grid marking and pilot experiments to demonstrate effect of circle
grid marking on AMS4902 sheet during SPIF. Discussion also includes methodology to
conduct experiments during experimental set: 1, 2 and 3 for single pass SPIF to form 50o, 60o
and 70o wall angle square pyramids of AMS4902 sheet and experimental set: 4 for multi pass
SPIF to form 60o and 70o wall angle pyramids out of already formed AMS4902 square
pyramids of 50o wall angle. Additionally, methodology used to measure thickness and
roughness of pyramid wall has also been explained.
3.1 Design of Experiments
Design of experiments is of prime importance to decide constant and variable input
parameters as well as range and level of variable parameters (factors) before performing
experiments. Based on extensive literature survey, it is decided to investigate the effect of
tool diameter, tool rotational speed, feed rate and incremental depth on formability of 1.5 mm
thick sheet of AMS4902. Other parameters such as sheet thickness, tool end geometry, tool
path, tool material and friction (lubrication) at tool-sheet interface are kept constant.
VALONA 7035 IN high performance neat oil is used as lubricant at tool-sheet interface for
all experiments including pilot experiments. The forming tool is made off AISI304 with
hemispherical end geometry. Contour tool path is selected for all SPIF experiments of
presented research work. Values of input variables such as tool diameters, tool rotational
speeds, feed rates and incremental depths are decided based on findings summarized from
literature review. In order to predict existence of any nonlinear relationship amongst input
variables and responses, three levels of each input variables are selected. This combination of
all four factors at three levels of Taguchi L9 array takes care of reliability of results
reasonably same as results by full factorial experimental set with the economy of material
expenditure and time to perform experiments as well. Table 3.1 shows the experimental
design for total 9 experiments tabulated based on L9 array of Taguchi Design of Experiments
Design of Experiments
41
as an experimental set: 1. As limited literature is found on pyramidal geometry; 50o, 60o and
70o wall angle square pyramids of 30 mm depth are decided as targeted part geometry as
shown in Fig. 3.1.
FIGURE 3.1 Square pyramid as a part geometry
TABLE 3.1
DoE for Experimental Set: 1 to perform singlepass SPIF to form square pyramid of 50o wall angle
Experiment
Tool
Diameter
(mm)
Speed
(rpm)
Feed
(mm/ min)
Incremental
Step Depth
(mm)
1 D1 = 8 S1 = 1250 F1 = 1200 z1 = 0.25
2 D1 = 8 S2 = 2250 F2 = 2600 z2 = 0.5
3 D1 = 8 S3 = 3250 F3 = 4000 z3 = 0.75
4 D2 = 12 S1 = 1250 F2 = 2600 z3 = 0.75
5 D2 = 12 S2 = 2250 F3 = 4000 z1 = 0.25
6 D2 = 12 S3 = 3250 F1 = 1200 z2 = 0.5
7 D3 = 16 S1 = 1250 F3 = 4000 z2 = 0.5
8 D3 = 16 S2 = 2250 F1 = 1200 z3 = 0.75
9 D3 = 16 S3 = 3250 F2 = 2600 z1 = 0.25
Experimental Investigations
42
Based on observations and results obtained for square pyramids formed by SPIF using
parametric combination of experimental set: 1, the parametric study is narrowed down for
experimental set: 2 to derive optimum combination of parameters as mentioned in Table 3.2.
Following parameters are decided as response parameters for fulfillment of objectives of
presented research work with reference to findings concluded from literature survey;
(1) Formability in terms of thickness distribution of pyramid wall formed out of 1.5 mm
thick sheet of AMS4902 during single pass and multi pass SPIF.
(2) Formability in terms of maximum formable wall angle of pyramid formed out of 1.5 mm
thick sheet of AMS4902 during single pass and multi pass SPIF.
(3) Formability in terms of maximum formable depth of pyramid with reference to higher
degree of wall angles formed out of 1.5 mm thick sheet of AMS4902 during single pass
and multi pass SPIF.
(4) Surface roughness of pyramid walls formed out of 1.5 mm thick sheet of AMS4902
during single pass SPIF.
TABLE 3.2 DoE for Experimental Set: 2 to perform singlepass SPIF to form square pyramid of 50o wall angle
Experiment
Tool
Diameter
(mm)
Speed
(rpm)
Feed
(mm/min)
Incremental
Step Depth
(mm)
10 D1=12 S=1250 F=4000 z1=0.25
11 D1=12 S=1250 F=4000 z2=0.5
12 D1=12 S=1250 F=4000 z3=0.75
13 D2=16 S=1250 F=4000 z1=0.25
14 D2=16 S=1250 F=4000 z2=0.5
15 D2=16 S=1250 F=4000 z3=0.75
Next sub section describes about the experimental set-up and a fixture fabricated to hold the
sheet rigidly against movement of hemispherical tip tool during SPIF as there is no need of
dedicated die and punch.
Experimental Set-up
43
3.2 Experimental set-up The presented experiments are performed using fixture capable to hold 250 mm x 250 mm of
maximum size of sheet. The fixture is facilitated with dowel pin holes in order to locate even
small size sheets. The fixture consist of three major parts namely base plate, back plate and
top plate as shown in Fig. 3.2 (a). Back plate is equipped with through square pocket of size
105 mm x 105 mm. AMS4902 sheet of 1.5 mm is hold between top plate and back plate to
form a pyramid of largest square size of 100 mm x 100 mm and depth of 30 mm as depicted
in Fig. 3.1. All experiments are conducted at Central Institute of Plastics Engineering and
Technology (Centre for Skilling and Technical Support), Valsad.
(a) (b)
FIGURE 3.2 Experimental Set-up (a) SPIF Fixture (b) SPIF Set-up on CNC Milling machine
The fabricated SPIF fixture is clamped on CNC Milling machine for present experimental
work as depicted in Fig. 3.2 (b). Specification of CNC Milling machine is given as under.
Make: Ace Manufacturing Systems, Bangalore, India Model: mcv-350
Power: 5.5 kW
Controller: FANUC
Tool travel: X-axis – 1000 mm, Y-axis – 650 mm, Z-axis – 500 mm
Table length: 510 mm, Table width:1150 mm
Groove width:10 mm, Groove spacing: 300 mm
Experimental Investigations
44
3.3 Uni-axial tensile testing to determine properties of AMS4902
(a) (b)
FIGURE 3.3 (a) Tensile test set-up (b) Tested specimens of AMS4902 at 0o, 45o& 90o
TABLE 3.3 Results of tensile testing of AMS4902
Sample No.
Yield Strength (MPa)
(0.2% Proof Stress)
Average Yield Strength (MPa)
(0.2% Proof Stress)
Ultimate Tensile
Strength (MPa)
Average Ultimate Tensile
Strength (MPa)
Test Results for Specimens at 0o of Rolling Direction 95-VN-2016 321.8
323.6
408.6
408.0 96-VN-2016 320.9 406.9
97-VN-2016 328.0 408.5
Test Results for Specimens at 45o of Rolling Direction 100-VN-2016 307.1
305.1
396.1
397.1 101-VN-2016 305.7 399.0
102-VN-2016 302.6 396.3
Test Results for Specimens at 90o of Rolling Direction 108-VN-2016 276.5
279.6
412.8
413.7 109-VN-2016 278.8 414.6
110-VN-2016 283.5 413.8
Material properties of AMS4902 are obtained by conducting uni-axial tensile test
according to ASTM E8-09 on three test specimens oriented in rolling direction (0o), three
specimens oriented at 45o of rolling direction and three specimens of transverse direction (90o
to the rolling direction). The tensile tests are performed with cross head speed of 5 mm/min
Circle-grid marking
45
and stress-strain graphs are obtained from computer controlled universal testing machine
equipped with extensometer. Fig. 3.3 (a) and (b) shows tensile test set-up with extensometer
and specimens tested respectively. The obtained value of average yield strength and ultimate
strength in each direction is tabulated in Table 3.3 while average values of other important
property parameters like strength co-efficient, strain hardening exponent, elastic modulus and
density are tabulated in Table 3.4 [1]. TABLE 3.4 Other average property parameters of AMS4902 [2, 3]
Sr. No. Property Parameter Calculated value of property parameter
1. Strain Hardening (n) 0.23
2. Strength Coefficient (K) 852.44 MPa
3. Modulus of Elasticity (E) 105x103 MPa
4. Density (ρ) 4.51gm/ cm3
3.4 Circle-grid marking
(a) 2.5mm circles (b) 2.5mm circles with center (c) 5mm circles in 12.5mm Square
(d) 5mm circles in 12.5mm Square (e) 5mm circles with 2.5mm square (f) 5mm square
FIGURE 3.4 Various patterns of Grid Marking [5] Circle-grid marking is one of the popularly used techniques for measurement of
deformation of sheet in terms of major and minor strains. The grid is an array of precisely
spaced gage points marked on a sheet metal before forming into final shape. Appropriate
combination of circle and square grid pattern is preferable in order to obtain minute
measurement of straining. Larger pattern of 6 mm to 125 mm are suggested to use for
measurement of low level strains on formed components but are not preferable to determine
Experimental Investigations
46
Forming Limit Curve (FLC). According to ASTM 2218-02, 2.5 mm square sides or circle
diameters are suggested as a gage length within the range of ±0.025 mm. It is important to
ensure that the grid pattern marked must not be damaged during operating conditions like
friction or lubrication of selected forming process. Varieties of grid patterns are shown in Fig.
3.4 (a) to (f) [4, 5].
According to ASTM E2218-02, the pattern of 5 mm circle diameter with 2.5 mm
square as shown in Fig. 3.4 (e) is selected to apply on AMS4902 sheet. Fig. 3.5 (a) depicts
2D drawing of circle grid pattern prepared using CAD tool to be printed on the central area of
150 mm x 150 mm out of overall blank size of 200 mm x 200 mm x 1 mm and 200 mm x 200
mm x 1.5 mm AMS4902 sheet.
(a)
(b) (c)
FIGURE 3.5 (a) 2D drawing of circle grid pattern (b) Circle-grid printing set-up (c) Circle-grid marking
on AMS4902 sheet
Pilot experiments
47
Several methods of printing of circle-grid pattern on undeformed sheet include Screen
printing (silk-screen printing/ serigraphy), Electrochemical etching, Photochemical etching
(UV Printing) and Laser marking. Laser marking is applied initially for trial to conduct pilot
experiments during presented course of work looking to its accuracy, durability, quality and
resolution. Due to failure of laser marked AMS4902 sheet of 1 mm and 1.5 mm thickness
from circle-grid lines before forming depth during the process of SPIF, it is decided to carry
out circle-grid printing by photochemical etching (UV printing) method as depicted in Fig.
3.5. Fig. 3.5 (b) shows the UV printing set-up for circle-grid marking and 3.5 (c) shows the
circle-grid pattern printed on AMS4902 sheet using photochemical etching (UV printing) [6].
3.5 Pilot experiments
Pilot experiments are conducted to verify feasibility of performing SPIF process by
deforming AMS4902 sheets of 1 mm and 1.5 mm thickness into designed geometry of
truncated pyramid using developed fixture and generated tool path. The purpose of pilot
experiments is also to determine the effect of circle-grid applied by laser marking and
photochemical etching (UV printing) on AMS4902 sheets during SPIF in order to select
appropriate method of circle-grid marking for further experimentations. Initially circle grid
pattern shown in Fig. 3.5 (a) is applied using laser marking technique on 1 mm and 1.5 mm
thick sheet of AMS4902. Then both sheets are deformed into designed geometry of 50o wall
angle square pyramid of 30 mm depth using 8 mm diameter hemispherical tip tool by single-
pass SPIF. The said experiment is performed at the parametric combination of 1250 rpm
speed, 1200 mm/min feed and 0.5 mm incremental depth. The failure depth of 7 mm and 8
mm is observed respectively for 1 mm and 1.5 mm thick sheet of AMS4902, marked with
circle grid pattern using laser marking technique as shown in Fig. 3.6 (a) and (b).
(a) Failure depth of 7 mm for 1 mm thick sheet (b) Failure depth of 8 mm for 1.5 mm thick sheet
FIGURE 3.6 Failure of AMS4902 sheets marked using laser grid marking technique
Experimental Investigations
48
One of the key reasons for failure of AMS4902 sheet at grid lines is high stress concentration
on the grid pattern during SPIF. The failure of sheet during SPIF can be avoided by
controlling higher penetration of laser applied during marking of circle-grid pattern. After the
failure of sheets observed from the laser grid pattern, the circle-grid printing is applied using
photochemical etching (UV printing) on 1.5 mm thick sheet and it is deformed by single-pass
SPIF as shown in Fig. 3.7.
FIGURE 3.7 Single point incremental forming of 1.5mm thick sheet of AMS4902 with good quality of
deformed circle grid pattern printed using UV printing
As depicted in Fig. 3.7, the single point incremental forming of 1.5 mm thick sheet of
AMS4902 is obtained up to 39 mm depth on which the circle grid pattern is printed using
photochemical etching (UV printing) technique. A good quality of deformed circle grid
pattern is observed with measurable gage points for strain measurement. Hence, it is decided
to apply circle grid marking using photochemical etching (UV printing) for further
experimentations as it does not affect the intrinsic properties of material during forming
process.
3.6 Experimental set: 1 (Single-pass SPIF of 50o wall angle pyramids)
Truncated square pyramid of 50o wall angle, 30 mm design depth and largest square of size
100 mm x 100 mm is formed out of 1.5 mm thick sheet of AMS4902 by operating
hemispherical tip tool at parametric combinations as given in Table 3.1 using single-pass
SPIF. Taguchi L9 array is used to get the optimum combination of tool diameter, tool
rotation, tool feed and incremental depth with each at three levels. Range of tool diameters
Experimental set: 1(Single-pass SPIF of 50o wall angle pyramids)
49
are varied from 8 mm to 16 mm with the increment of 4 mm at each level. Values of speed
are varied from 1250 rpm to 3250 rpm with the increment of 1000 rpm at each level.
Variation of feed rate is by 1400 mm/min at each level starting from 1200 mm/min. Variation
of incremental depth is by 0.25 mm at each level starting with 0.25 mm. In order to generate
contour tool path for present experimental work, the square pyramid of desired size (i.e. 100
mm x 100 mm largest size of square and 30 mm depth) and wall angle is modeled first in
MasterCAM software. The planner tool path is generated for defined combinations of speed
and feed starting from largest square of pyramid. After each planner movement of tool, an
incremental movement of tool is given by desired amount in the direction of depth till total
depth of pyramid. Identical setting of SPIF fixture for X-Y movement of table with reference
to Z movement of tool has been taken care using dial gauge before performing each
experiment.
FIGURE 3.8 Components formed using SPIF with parametric combinations of experimental set: 1
Experimental Investigations
50
The forming depth of 30 mm of square pyramid is obtained for experiment no. 1, 4, 5 and 7
out of all nine experiments of experimental set: 1 as shown in Fig. 3.8. SPIF performed at
intermediate or higher tool rotational speed of selected range in combination with lower or
intermediate feeds leads to excessive heat generation and friction at tool-sheet interface
which ultimately results into damage of sheet and tool instead of forming the sheet during
experiment no. 6, 8 and 9. The pinning effect is observed during forming of sheet with 8 mm
hemispherical headed tool during experiment no. 2 and 3. Based on detail discussion on
results of experimental set: 1 reported in next section, the study is narrowed down to
optimum values of tool diameter, tool rotational speed and feed in order to determine
interaction of parameters on thickness distribution, maximum formable wall angle, maximum
formable depth and surface roughness of pyramid with 50o wall angle by single-pass SPIF for
the experimental set: 2 reported as Table 3.2.
3.7 Experimental set: 2 (Single-pass SPIF of 50o wall angle pyramids)
FIGURE 3.9 Components formed using SPIF with parametric combinations of experimental set: 2
Wall thickness measurement
51
As depicted in Fig. 3.9, pyramids of design depth are successfully formed by all presented
combinations of parameters during all six single-pass SPIF experiments of experimental set:
2. The pyramid wall formed at 0.25 mm incremental depth offers less roughness compared to
pyramid walls formed at 0.5 mm and 0.75 mm incremental depth. Hence, Experimental Set: 3
is decided to conduct experiment to deform truncated square pyramids of 60o and 70o wall
angles by employing single-pass SPIF for parametric combination of 12 mm tool diameter,
1250 rpm tool speed, 4000 mm/min feed and 0.25 mm incremental step depth which has
offered minimum thinning and minimum surface roughness during previous set of
experiments.
3.8 Wall thickness measurement
Measurement of wall thickness distribution is carried out using Coordinate Measuring
Machine at Indo German Tool Room, Ahmedabad as shown in Fig. 3.10. Specifications of
CMM used for wall thickness measurement are as under;
Make: Carl Zeiss, Germany Model: PRISMO 5 HTG VAST
Measuring Range: X - 700 mm, Y - 900 mm, Z - 500 mm
Permissible Work piece weight: 1200 Kg
FIGURE 3.10 Wall Thickness measurement of square pyramid using CMM
Wall thickness measurement for all pyramids is carried out by defining plane of sheet with
reference to hole of dowel pin using CMM scanning of fourteen points initially. Similarly,
Experimental Investigations
52
planes of inner surface of walls of each pyramid are also defined by CMM scanning of nine
points with reference to hole provided for dowel pin.
FIGURE 3.11 Deformed pyramid with locations for measurement of wall thickness using CMM
Pyramid wall thickness is measured by CMM probe at four different depths predefined on the
outer surface of wall as shown in Fig. 3.11 with reference to predefined plane of inner surface
of pyramid wall. Average wall thickness for any pyramid is determined by averaging the wall
thickness measured at various depths on all four walls of that pyramid. The readings of
average wall thickness of a pyramid are plotted against depth of measurement.
3.9 Surface roughness measurement
In order to carry out surface roughness measurement of pyramid walls deformed out of
AMS4902 sheet, a dedicated fixture is developed which is capable to hold the pyramid
against the stylus movement of roughness tester as shown in Fig. 3.12. A fixture is also
capable to accommodate variation in pyramid wall angle to ensure contact between stylus and
surface of pyramid wall.
Surface roughness measurement
53
FIGURE 3.12 Fixture developed to hold the pyramid during surface roughness measurement
(a) Calibration of Surface Roughness Tester (b) Roughness Measurement Set-up
FIGURE 3.13 Surface Roughness Measurement for Pyramid Wall A drive unit of surface roughness tester can be used by inserting into display unit and also
can be used by detaching it from display unit. This detachable drive unit is capable to offer
flexible measurement of intricate surface too. Surface roughness measurement of pyramid
walls is followed by calibration of surface roughness tester using developed fixture as shown
in Fig. 3.13 (a) and (b). Average surface roughness for a pyramid wall is calculated from four
readings of Ra value measured for an individual wall of a pyramid. Similarly, average surface
roughness for a pyramid is determined by average of average roughness for all four walls of
that pyramid.
Experimental Investigations
54
3.10 Experimental Set: 3 (Single-pass SPIF of 60o and 70o wall angle
pyramids)
The optimum parameters derived from experimental set 1 and 2 are tabulated in Table 3.5 in
order to deform 1.5 mm thick AMS4902 sheet into 60o and 70o wall angle pyramids by
single-pass SPIF. The detail discussion on failure of higher wall angle pyramids is reported in
next section. TABLE 3.5
DoE for Experimental Set: 3 to perform singlepass SPIF to form square pyramid of 60o and 70o wall angle
Experiment
Wall
Angle
(Degree)
Tool
Diameter
(mm)
Speed
(rpm)
Feed
(mm/min)
Incremental
Step Depth
(mm)
16 60 T=12 S=1250 F=4000 z=0.25
17 70 T=12 S=1250 F=4000 z=0.25
3.11 Experimental Set: 4 (Multi-pass SPIF to form 60o and 70o wall angle
pyramids from 50o wall angle pyramids)
Further the Experimental Set: 4 is conducted for multi-pass SPIF to form 60o and 70o wall
angle square pyramids out of already formed pyramids of 50o wall angle with the parametric
combination same as experimental set: 3.
3.12 Uncertainty in measurement
Any measurement results are incomplete if they are presented without consideration of
uncertainty in the measurement as every measurement is subjected to some uncertainty.
Consideration of uncertainty in measurement confirms the confidence for validity of
measurement results. According to ‘Guide to the Expression of Uncertainty in Measurement’
(GUM), an uncertainty is defined as “a parameter associated with the result of a measurement
that characterizes the dispersion of the value that could reasonably be attributed to the
measurand”. International Vocabulary of Basic and General Terms in Metrology (VIM) have
Uncertainty in measurement
55
defined the measurement uncertainty as “non-negative parameter characterizing the
dispersion of quantity values being attributed to measurand, based on the information used”.
Various sources of measurement uncertainties include measuring instruments, type of
measurand for which measurement need to be carried out, measurement process, sampling,
environmental conditions, skill of operator etc. It is difficult to obtain repeatability and
reproducibility of measurand due to inherent instability of measuring equipment. As per
recommended good practices to reduce measurement uncertainty, four readings of wall
thickness and surface roughness for each wall of pyramids are taken to obtain average value
of measurand for presented course of work. Calibration corrections of measuring instruments/
equipments are also taken care before employing it for measurement. Range of uncertainty
for Coordinate Measuring Machine (PRISMO 5 HTG VAST) used for wall thickness
measurement and Surface Roughness Tester (SURFTEST SJ-210) used for roughness
measurement is discussed in next sub sections [7, 8, 9].
3.12.1 Wall thickness measurement
The pyramid wall thickness measurement for presented course of work is carried out using
CMM model PRISMO 5 HTG VAST (Make: Carl Zeiss, Germany) at Indo German Tool
Room, Ahmedabad. It is important before performing measurement using CMM to establish
probing strategy which includes magnitude and direction of probe force, type of probe stylus
used and the measuring speed of probe. Measurement uncertainty prescribed by the
manufacturer for the said model of CMM is as mentioned in Table 3.6. TABLE 3.6 Measurement uncertainty of CMM model PRISMO 5 HTG VAST prescribed by
manufacturer
Sr. No. Description Measurement uncertainty
1. Uncertainty in linear measurement U1 = (1.5+L/350) µm
2. Uncertainty in volumetric measurement U3 = (2.0+L/300) µm
According to terminology defined in ISO 10360; L is the measured size in millimetres and A
is positive constant in micrometers supplied by manufacturer. The value of A is 1.5 µm in the
Experimental Investigations
56
case of linear measurement and 2.0 µm in the case of volumetric measurement carried out
using CMM PRISMO 5 HTG VAST.
FIGURE 3.14 Maximum range of permissible uncertainty of indication for CMM [10]
The value of dimensionless positive constant (K) supplied by manufacturer is 350 in the case
of linear measurement and 300 in the case of volumetric measurement for CMM PRISMO 5
HTG VAST. Fig. 3.14 signifies the permissible range of uncertainty for the measurement of
pyramid wall thickness using CMM PRISMO 5 HTG VAST in presented work [10].
3.12.2 Surface roughness measurement
Measurement uncertainty of surface roughness tester, SURFTEST SJ-210 (Make: Mitutotyo),
is prescribed as (5.08+10L) µm by manufacturer wherein L is the nominal length in
micrometer. This uncertainty represents expanded uncertainty expressed at 95 percent
confidence level.
Results and discussion based on experiments conducted during all four experimental
sets are presented in Chapter: 4. Effect of parametric interactions observed on formability of
AMS4902 during experimentations are also discussed in detail in the section of results and
discussion.
.
References
57
References: 1. ASTM Designation: E8/ E8M – 09 (2009) Standard Test Methods for Tension Testing of
Metallic Materials, 1-27.
2. ASTM Designation: E646 – 00 (2000) Standard Test Method for Tensile Strain-
Hardening Exponents (n-Values) of Metallic Materials, 1-8.
3. NPL Report DEPC MPE 016 (2005) TESTAND - WP3 Final Report: Modulus
Measurement Methods, 1-41.
4. ASTM Designation: E2218 – 02 (2002) Standard Test Method for Determining Forming
Limit Curves, 1-15.
5. Strain Grid Whitepaper (2013) Universal Marking Systems Ltd. www.ums.co.uk 1-15.
6. Ozturk F, Dilmec M, Turkoz M, Ece R. E. and Halkaci H. S. (2009) Grid Marking and
Measurement Methods for Sheet Metal Formability. 5th International conference and
exhibition on design and production of machines and dies/molds, Kusadasi, Aydin,
Turkey, 1-10.
7. BIPM JCGM 100 (Joint Committee for Guides in Metrology - GUM 1995 with minor
corrections) (2008) Evaluation of measurement data — Guide to the expression of
uncertainty in measurement, 1-134.
8. Stephanie Bell (2001) Measurement Good Practice Guide No. 11 (Issue 2), A Beginner’s
Guide to Uncertainty of Measurement, ISSN 1368-6550, 1-41.
9. NABL 141 (2016) Guidelines for Estimation and Expression of Uncertainty in
Measurement (Issue 3), 1-50.
10. David Flack (2011) NPL: Measurement Good Practice Guide No. 42 – CMM
Verification, ISSN 1368-6550, 1-113.
Results and Discussions
58
CHAPTER: 4
Results and Discussions
This chapter discusses about individual effects of tool diameter, tool speed, tool feed and
incremental depth on formability of AMS4902 sheet. The results obtained for the effect of
interaction of tool diameter and incremental depth on thickness distribution and surface
roughness during single-pass SPIF of AMS4902 sheet is presented graphically. This chapter
also discusses about results of geometrical accuracy of wall angle formed by single-pass
SPIF, thickness distribution and maximum formable angle during multi-pass SPIF of
AMS4902 sheet.
4.1 Effect of tool diameter, speed and feed (Experimental Set: 1)
Out of nine experiments of Experimental Set: 1, four pyramids with full design depth
of 30 mm are obtained for experiment 1, 4, 5 and 7 as shown in Fig. 3.8. Single pyramid of
full design depth is formed during experiment 1, out of three pyramids formed using 8mm
tool diameter at various parametric combinations of speed, feed and incremental step depth of
selected ranges. The failures of pyramids before design depth are observed at 15 mm and 12
mm depth during experiment 2 and 3 respectively using 8mm diameter tool. Smaller diameter
of tool of 8 mm operated at the combination of higher and intermediate speeds with higher
and intermediate feeds of selected range respectively results into pinning effect on AMS4902
sheet which leads the failure of sheet.
Square pyramids up to design depth are formed successfully during experiment 4 and
5 out of all three experiments conducted with 12 mm diameter tool. Additionally, wavy wall
surface is observed for the pyramid obtained by parametric combination during experiment 5.
Higher speed at lower feed during experiment 6 generates excess local friction and heat
generation due to rubbing at a point of tool sheet interface ultimately results into welding of
tool with sheet blank which does not allow the tool further to carry forward the process of
SPIF even with the tool of 12 mm diameter.
A very good quality square pyramid with good quality of circle grid marking on the
formed pyramid of design depth is obtained for experiment 7 conducted using 16 mm
Influence of tool diameter and incremental depth on average percentage thinning
59
diameter tool. Experiment 8 and 9 performed using larger diameter tool operated at
intermediate and low tool speed in combination with comparatively low feed than experiment
7 results into excess local friction and heat generation due to rubbing. This excess local
friction and rubbing at a point of tool-sheet interface ultimately leads to welding of the tool
with sheet and doesn’t allow tool to further carry forward the process of SPIF.
Based on results of Experimental Set: 1 discussed, the parametric study is narrowed
down to operate SPIF with 12 mm and 16 mm tool diameter at the combination of 1250 rpm
with 4000 mm/min feed to get the uniform wall thickness distribution and minimum surface
roughness.
4.2 Influence of tool diameter and incremental depth on average percentage
thinning
4.2.1 Effect of tool diameter and incremental step depth interaction on
average percentage thinning
Pyramid wall thickness measurement is carried out using CMM for all six pyramids
formed during Experimental Set: 2 as shown in Fig. 3.9. Wall thicknesses of any pyramid are
measured at various depths of pyramid wall. In order to analyze percentage thinning by
stretching, thicknesses measured near top and bottom faces of square pyramids are not
considered as those readings of thickness measurement falls under bending zone. So, four
readings of measured thicknesses on straight zone of each wall are considered to calculate
average sheet thickness for a particular pyramid at specified depths of 7 mm, 12 mm, 17 mm
and 22 mm as shown in Fig. 3.11. Average percentage thinning at specified depth of pyramid
wall is calculated using equation given below based on average thickness results reported in
Table 4.1. The different pattern of metal flow is observed at 7 mm depth on wall A than wall
B, C and D because incremental depth after each planner movement of tool was applied at the
middle of the wall A instead of corner to avoid failure at corner of pyramid.
Average percentage thinning = ቂ୲ି୲୲ቃX 100 (4.1)
Where; (1) to = Original thickness of sheet = 1.5 mm
(2) tf= Average final wall thickness after forming (mm)
Results and Discussions
60
TABLE 4.1 Results of average thickness measured using CMM
Exp. No.
Readings of thickness measurement using CMM at specified depth Thickness at 7 mm
depth of wall-A (mm) Thickness at 12 mm
depth of wall-B (mm) Thickness at 17 mm
depth of wall-C (mm) Thickness at 22 mm
depth of wall-D (mm) Specific Reading
Avg. Thickness
Specific Reading
Avg. Thickness
Specific Reading
Avg. Thickness
Specific Reading
Avg. Thickness
10
1.2154
1.26
0.6234
1.06
0.5626
1.02
0.5931
1.03 1.3287 1.3019 1.2707 1.2835 1.2986 1.2967 1.2316 1.2122 1.1998 1.032 1.023 1.0323
11
1.0844
1.23
0.5148
1.00
0.8601
0.95
0.9131
0.97 1.3833 1.2909 1.0211 1.012 1.3668 1.238 0.9324 0.9424 1.0887 0.9901 1.003 1.021
12
1.3952
1.19
0.9185
0.91
0.849
0.87
0.649
0.89 1.2006 1.0384 1.0529 1.0852 1.0708 0.9294 0.848 0.9038 1.0939 0.7731 0.7153 0.9043
13
1.1562
1.14
0.9411
0.85
0.7543
0.73
1.0112
1.03 1.0997 0.8234 0.6644 0.9753 1.174 0.8184 0.7431 1.0224 1.1309 0.8315 0.7623 1.121
14
1.4533
1.21
0.9274
0.80
0.6958
0.74
0.6905
1.04 1.0738 0.7206 0.63 0.9418 1.2489 0.8225 0.8037 1.2199 1.0641 0.7079 0.8102 1.3004
15
1.0676
1.08
0.8268
0.73
0.4394
0.58
0.501
0.94 1.0701 0.6832 0.5749 0.9148 1.0259 0.7361 0.5641 1.2913 1.142 0.665 0.7382 1.0693
Average percentage thinning for corresponding depth and measured thickness of
pyramid wall is reported in table 4.2 and also plotted graphically as shown in Fig. 4.1 (a), (b),
(c) and Fig. 4.2 (a), (b) to determine effect of tool diameter and incremental depth interaction
on average percentage thinning of pyramid wall formed out of AMS4902 sheet. Fig. 4.1 (a),
(b) and (c) presents the effect of 12 mm and 16 mm diameters of tools on average percentage
thinning obtained at specified depths of pyramids formed when operated at incremental step
depths of 0.25 mm, 0.50 mm and 0.75 mm respectively. Looking to the graphs, it is observed
that 12 mm diameter tool offers less thinning and also reasonably
Influence of tool diameter and incremental depth on average percentage thinning
61
uniform thickness distribution compared to 16 mm diameter tool irrespective of values of the
incremental depths out of selected range due to surface contact of tools with sheet blank.
Looking to the values of average percentage thinning reported in Table 4.2,
significant increment in average percentage thinning is observed at 7 mm and 12 mm depth
of measurement compared to 17 mm depth of measurement for the pyramid walls formed
using 12 mm diameter tool of hemispherical tip for experiment 10, 11 and 12 respectively.
The increment of incremental step depth by an amount of 0.25 mm for subsequent
experiments of 10, 11 and 12 is the influencing parameter for increment in average
percentage thinning of pyramid walls formed using 12 mm diameter tool. The reduction rate
in increment of average percentage thinning at 17 mm depth of measurement for experiment
10, 11 and 12 is caused due to strain hardening. Further reduction in percentage thinning of
pyramid wall at 22 mm depth of measurement leads to increment in average thickness of
pyramid wall by small amount compared to average thickness reported at 17 mm depth of
measurement. TABLE 4.2 Average percentage thinning for corresponding average wall thickness after forming
Exp. No.
Average percentage thinning of pyramid wall at specified depth At 7 mm depth of pyramid wall-A
(mm)
At 12 mm depth of pyramid wall-B
(mm)
At 17 mm depth of pyramid wall-C
(mm)
At 22 mm depth of pyramid wall-D
(mm) Avg.
Thickness %
Thinning Avg.
Thickness %
Thinning Avg.
Thickness %
Thinning Avg.
Thickness %
Thinning 10 1.26 16.00 1.06 29.33 1.02 32.00 1.03 31.33
11 1.23 18.00 1.00 33.60 0.95 36.40 0.97 35.27
12 1.19 20.66 0.91 39.01 0.87 42.25 0.89 40.96
13 1.14 23.73 0.85 43.33 0.73 51.67 1.03 31.19
14 1.21 19.33 0.80 46.67 0.74 50.67 1.04 30.67
15 1.08 28.24 0.73 51.48 0.58 61.39 0.94 37.06
Effect of tool diameter can be observed by comparing the reduction in average wall
thickness of pyramids formed during experiments 13, 14 and 15 with average wall thickness
of pyramids formed during experiment 10, 11 and 12. It is observed that the reduction in
average wall thickness measured at 7 mm, 12 mm and 17 mm depths for pyramids formed
using 16 mm diameter tool is higher than the pyramids formed using 12 mm diameter tool
which ultimately results into more percentage thinning of pyramid walls formed using larger
diameter tool. The little increment in average thickness of pyramid wall at 22 mm dept
Results and Discussions
62
measurement is also observed for experiments 13, 14 and 15 same as experiments 10, 11 and
12. It is preferable to use 12 mm diameter tool over 16 mm diameter tool in order to obtain
less thinning of pyramid walls and comparatively uniform thickness distribution based on
overall observations reported in Table 4.2.
(a) Effect of tool diameters on average percentage thinning of pyramid wall at 0.25 mm step depth
(b) Effect of tool diameters on average percentage thinning of pyramid wall at 0.50 mm step depth
(c) Effect of tool diameters on average percentage thinning of pyramid wall at 0.75 mm step depth FIGURE 4.1Effect of tool diameter on Average Percentage Thinning for same incremental step depth
Influence of tool diameter and incremental depth on average percentage thinning
63
Fig. 4.2 (a) and (b) explains effect of incremental step depth on average percentage thinning
obtained at various depths of pyramids formed when operated with 12 mm and 16 mm
diameters of tools. The average percentage thinning is observed maximum for the SPIF
performed using 0.75 mm incremental step depth irrespective of tool diameters. In the case of
experiment 10 performed using 12 mm diameter tool in combination with 0.25 mm
incremental step depth offers minimum thinning compared to 0.50 mm and 0.75 mm
incremental step depths used for experiment 11 and 12 with 12 mm diameter tool. Looking to
Fig. 4.2 (b), it can be observed that SPIF performed using 16 mm diameter tool in
combination with 0.25 mm and 0.50 mm incremental depth during experiment 13 and 14
offers almost equal thinning.
(a) Effect of incremental depths on average percentage thinning of pyramid wall for 12 mm diameter tool
(b) Effect of incremental depths on average percentage thinning of pyramid wall for 16 mm diameter tool
FIGURE 4.2 Effect of incremental depths on Average Percentage Thinning for same diameter of tool
Results and Discussions
64
4.2.2 Results of ANOVA for average percentage thinning
Results of Analysis of Variance (ANOVA) for average percentage thinning of pyramid walls
are reported in Table 4.3. TABLE 4.3 Results of ANOVA for average percentage thinning of pyramid walls formed by SPIF
Factors DF Seq SS Adj SS Adj MS F-Value P-Value Percentage Contribution
Tool Diameter 1 105.462 105.462 105.462 44.31 0.022 58.96
Incremental Step Depth 2 68.661 68.661 34.33 14.42 0.065 38.38
Error 2 4.761 4.761 2.38 - - 2.66
Total 5 178.884 - - - - -
(a) Main effects plot for means of average percentage thinning
1612
40
38
36
34
32
300.750.500.25
Tool Diameter (mm)
Mea
n of
Mea
ns
Incremental Step Depth (mm)
Main Effects Plot for MeansData Means
Influence of tool diameter and incremental depth on average percentage thinning
65
(b) Main effects plot for signal to noise ratio of average percentage thinning
(c) Main effects plot for standard deviations of average percentage thinning
FIGURE 4.3 Main effects plots for means, SN ratios and standard deviations of average percentage
thinning
1612
-30.0
-30.5
-31.0
-31.5
-32.0
-32.50.750.500.25
Tool Diameter (mm)
Mea
n of
SN
rati
os
Incremental Step Depth (mm)
Main Effects Plot for SN ratiosData Means
Signal-to-noise: Smaller is better
1612
14
13
12
11
10
9
0.750.500.25
Tool Diameter (mm)
Mea
n of
StD
evs
Incremental Step Depth (mm)
Main Effects Plot for StDevsData Means
Results and Discussions
66
Percentage contribution of each factor influencing average percentage thinning is determined
based on factor sum and total sum of squares. Based on values of percentage contribution
obtained, tool diameter is found most significant parameter influencing average percentage
sheet thinning. As the P-value obtained for the incremental step depth is more than 0.05, it is
statistically less significant than tool diameter. The main effects plot for means, signal to
noise ratios and standard deviations shown in Fig. 4.3 (a), (b) and (c) also signify the effect of
tool diameter on average percentage thinning over incremental step depth. Based on the main
effects plot, the optimum value obtained for the tool diameter is 12 mm in order to obtain
uniform and minimum thinning of sheet. The larger surface contact of 16 mm diameter tool
with sheet blank generates higher amount of local heating which ultimately results into more
plastic flow of metal and more thinning compare to 12 mm diameter tool. Effect of
incremental depth is less compare to tool diameter on average percentage thinning because
incremental depth is applied at an instance of every cycle of tool movement while tool
diameter remains in touch with sheet material to form a wall throughout the cycle of tool
movement.
4.3 Influence of tool diameter and incremental depth on average surface
roughness
4.3.1 Effect of tool diameter and incremental step depth interaction on
average surface roughness (Ra)
Four readings of surface roughness for each pyramid wall are obtained using
Mitutoyo surface roughness tester, SURFTEST SJ-210 as shown in Fig. 3.13 (b). Average
surface roughness of each pyramid wall is calculated from four readings of surface roughness
obtained as reported in Table 4.4. Overall average roughness for a pyramid is determined by
averaging the average roughness calculated for all four walls of that pyramid as reported in
Table 4.5 and are also presented graphically in Fig. 4.4 (a) and (b). Graphs describe an
interactive effect of tool diameter and incremental step depth on surface roughness of three
pyramids formed using 12 mm diameter tool and three pyramids formed using 16 mm
diameter tool. From Fig. 4.4 (a) and (b), it is observed that irrespective of any of the tool
diameter operated at 0.25 mm incremental step depth offers less surface roughness compared
Influence of tool diameter and incremental depth on average surface roughness
67
to 0.50 mm and 0.75 mm incremental step depth. Surface roughness of the pyramid walls is
found highest while forming is performed using 12 mm diameter tool in combination with
incremental depth of 0.50 mm compared to 0.25 mm and 0.75 mm incremental depths as
depicted in Fig. 4.4 (a). While in the case of SPIF performed using 16 mm diameter tool,
surface roughness is observed highest for the forming condition at 0.75 mm incremental
depth compared to 0.25 mm and 0.50 mm incremental depths as shown in Fig. 4.4 (b). TABLE 4.4 Results of average surface roughness for individual walls of pyramids
Exp. No.
Readings of surface roughness measured using surface roughness tester Roughness readings on WallA (Ra-µm)
Roughness readings on WallB (Ra-µm)
Roughness readings on Wall C (Ra-µm)
Roughness readings on WallD (Ra-µm)
Specific Reading
Avg. Roughness
Specific Reading
Avg. Roughness
Specific Reading
Avg. Roughness
Specific Reading
Avg. Roughness
10
6.418
5.773
6.263
5.888
5.973
5.818
6.371
5.875 4.821 6.333 5.904 5.702 5.895 4.983 4.861 5.84 5.957 5.973 6.532 5.586
11
10.091
9.378
10.731
12.220
9.272
10.325
11.957
10.278 8.09 11.837 11.695 9.117 9.173 11.538 9.609 9.591
10.157 14.772 10.725 10.446
12
12.168
9.779
9.914
10.239
9.414
9.793
8.209
9.890 9.287 11.506 9.78 9.751 8.621 9.641 9.801 11.319 9.038 9.896 10.176 10.279
13
4.016
3.791
3.884
3.882
3.632
3.455
2.847
3.195 3.011 3.005 3.755 2.974 3.717 3.742 3.093 3.227 4.419 4.897 3.339 3.733
14
6.370
5.792
5.486
5.802
6.615
5.779
6.051
5.958 4.603 4.924 5.373 4.867 6.659 6.029 5.891 5.450 5.536 6.769 5.237 7.465
15
7.341
7.652
6.816
7.498
5.853
7.162
7.453
6.781 6.645 7.529 8.167 6.178 8.167 7.002 7.176 6.165 8.453 8.646 7.45 7.328
Looking to the values of average surface roughness reported in table 4.5 and plotted
in Fig. 4.4 (a) and (b); it is observed that irrespective of any of the values of incremental step
Results and Discussions
68
depths, average surface roughness of pyramid wall is less for the pyramids formed using 16
mm diameter tool compared to pyramids formed using 12 mm diameter tool. Less deflection
of larger diameter tool during operation due to its rigidity and larger contact area at tool-sheet
interface are the key reasons for the less surface roughness of pyramid walls formed using 16
mm diameter tool. TABLE 4.5 Results of average surface roughness for various pyramids formed using SPIF
Exp. No.
Average roughness of Wall-A (Ra-µm)
Average roughness of
Wall-B (Ra-µm)
Average roughness of
Wall-C (Ra-µm)
Average roughness of
Wall-D (Ra-µm)
Average roughness of
pyramid (Ra-µm)
10 5.773 5.888 5.818 5.875 5.838
11 9.378 12.220 10.325 10.278 10.550
12 9.779 10.239 9.793 9.890 9.925
13 3.791 3.882 3.455 3.195 3.581
14 5.792 5.802 5.779 5.958 5.833
15 7.652 7.498 7.162 6.781 7.273
FIGURE 4.4 Effect of interaction of incremental depths and tool diameters on Average Surface
Roughness
4.3.2 Results of ANOVA for average surface roughness
Results of Analysis of Variance (ANOVA) for average surface roughness of pyramid walls
are reported in Table 4.6.
Influence of tool diameter and incremental depth on average surface roughness
69
TABLE 4.6 Response table of signal to noise ratios for surface roughness
Source DF Seq SS Adj SS Adj MS F-Value P-Value Percentage Contribution
Tool Diameter 1 15.447 15.447 15.447 17.7 0.052 43.55
Incremental Step Depth 2 18.279 18.279 9.14 10.47 0.087 51.53
Error 2 1.745 1.745 0.873 - - 4.92
Total 5 35.472 - - - - -
(a) Main effects plot for means of average surface roughness
1612
9
8
7
6
5
0.750.500.25
Tool Diameter (mm)
Mea
n of
Mea
ns
Incremental Step Depth (mm)
Main Effects Plot for MeansData Means
Results and Discussions
70
(b) Main effects plot for signal to noise ratio of average surface roughness
(c) Main effects plot for standard deviations of average surface roughness
FIGURE 4.5 Main effects plots for means, SN ratios and standard deviations of average surface
roughness
1612
-13
-14
-15
-16
-17
-18
-190.750.500.25
Tool Diameter (mm)M
ean
of S
N ra
tios
Incremental Step Depth (mm)
Main Effects Plot for SN ratiosData Means
Signal-to-noise: Smaller is better
1612
0.7
0.6
0.5
0.4
0.3
0.2
0.750.500.25
Tool Diameter (mm)
Mea
n of
StD
evs
Incremental Step Depth (mm)
Main Effects Plot for StDevsData Means
Geometrical accuracy
71
Percentage contribution of each factor influencing average surface roughness is determined
based on factor sum and total sum of squares. Based on values of percentage contribution
obtained, incremental step depth is found most significant parameter influencing average
surface roughness of pyramid walls. The main effects plot for means, signal to noise ratios
and standard deviations shown in Fig. 4.5 (a), (b) and (c) also signify the effect of
incremental step depth on average surface roughness over tool diameter. Based on the main
effects plot, the optimum value obtained for the incremental step depth is 0.25 mm in order to
obtain minimum surface roughness of pyramid walls. Lesser stair casing effect for small
amount of incremental depth results into less surface roughness of pyramid wall. 16 mm
diameter tool exhibits less surface roughness compare to 12 mm diameter tool for same
amount of incremental depth due to larger contact area at tool-sheet interface and rigidity of
tool.
4.4 Geometrical accuracy
Measurement of pyramid wall angle is carried out using data scanned for pyramid wall by
CMM. The IGES file of data scanned for pyramid walls is used to convert it into part file of
modeling software named as Creo 2.0. The measurement of all four walls (A, B, C and D) of
square pyramids formed using 12 mm and 16 mm diameter tools with 0.25 mm incremental
depth is as shown in Fig. 4.6 (a) and (b). A representative case for the measured values of
wall angles for pyramids formed using 12 mm and 16 mm diameters of tools in combination
with 0.25 mm incremental depth is only presented in Fig. 4.6 (a) and (b) respectively as the
measured values of wall angles reported in Table 4.7 are same for the combinations even with
0.50 mm and 0.75 mm incremental step depth. Wall A, B, C and D are defined with color
code of Blue, Green, Red and Yellow respectively and angle of each wall with horizontal is
measured. Results of angles measured for all four walls of each pyramid formed during
experimental set: 2 are reported in Table 4.7. Table 4.8 shows average value of wall angles
calculated for wall A, B, C and D of square pyramids formed using 12 mm and 16 mm
diameter tools and same has been plotted graphically in Fig. 4.7. Geometrical accuracy in
terms of pyramid wall angle is observed much closer to the targeted geometry of 50o wall
angle of pyramids formed using 16 mm diameter hemispherical tip tool compared to the
pyramid walls formed using 12 mm diameter tool. More springback is observed in pyramid
walls formed using smaller diameter tool compared to larger diameter tool of selected range.
Results and Discussions
72
Based on the measured and reported values of pyramid wall angles, it can be said that larger
diameter tool is capable to form geometrically accurate component compared to smaller
diameter tool.
FIGURE 4.6 (a) Wall angle measurements for a pyramid formed using 12 mm diameter of tool and 0.25
mm incremental depth
Geometrical accuracy
73
FIGURE 4.6 (b) Wall angle measurements for a pyramid formed using 16 mm diameter of tool and 0.25
mm incremental depth
Additionally, strain hardening and tool deflection can also be considerable factor for
geometrical deviation between target and actual wall angle of pyramid. Continuous yielding
of sheet becomes difficult at higher rate of strain hardening for hard material which requires
higher load and energy to deform the sheet. Deflection of smaller diameter tool during
operation of SPIF against hard sheet metal also leads to deviation of geometrical accuracy.
Results and Discussions
74
TABLE 4.7 Results of wall angles measured for pyramids formed using SPIF during various experiments
Exp. No.
Tool Diameter
(mm)
Incremental Step Depth
(mm)
Wall Angle of Wall-A (Degree)
Wall Angle of Wall-B (Degree)
Wall Angle of Wall-C (Degree)
Wall Angle of Wall-D (Degree)
10 12 0.25 37.99 37.70 37.29 38.00
11 12 0.5 37.99 37.70 37.29 38.00
12 12 0.75 37.99 37.70 37.29 38.00
13 16 0.25 49.10 49.40 49.50 49.00
14 16 0.5 49.10 49.40 49.96 49.00
15 16 0.75 49.10 49.40 49.96 49.00
TABLE 4.8 Results of average wall angles measured for various pyramids formed using SPIF
Exp. No.
Tool Diameter
(mm)
Incremental Step Depth
(mm)
Avg. wall angle of Wall-A
(Degree)
Avg. wall angle of Wall-B
(Degree)
Avg. wall angle of Wall-C
(Degree)
Avg. wall angle of Wall-D
(Degree) 10, 11, 12 12 0.25, 0.5, 0.75 37.99 37.70 37.29 38.00
13, 14, 15 16 0.25, 0.5, 0.75 49.10 49.40 49.81 49.00
FIGURE 4.7 Average wall angles of pyramid walls formed using 12 mm and 16 mm diameter tools
Results and discussions on forming of 60o and 70o wall angle square pyramids by single-pass SPIF
75
4.5 Results and discussions on forming of 60o and 70o wall angle square
pyramids by single-pass SPIF
Square pyramids of 60o and 70o wall angles are attempted to form using 12 mm diameter
hemispherical headed tool with 0.25 mm incremental step depth at 1250 rpm and 4000
mm/min by single-pass SPIF.
(a) Failure of 60o wall angle square pyramid (b) Failure of 70o wall angle square pyramid
FIGURE 4.8 Single-pass SPIF for 60o and 70o wall angle square pyramids
Failure of 60o wall angle pyramid is observed at 8 mm depth while failure of 70o wall angle
pyramid is observed at 7 mm depth as shown in Fig. 4.8 (a) and (b) respectively. Looking to
the results, it can be derived that wall angle is also an important limiting parameter for single
point incremental forming of difficult to form material like AMS4902.
4.6 Results and discussions on percentage thinning of 60o and 70o wall angle
square pyramids formed out of 50o wall angle pyramids by multi-pass SPIF
Square pyramids of 50o wall angle formed with 12 mm diameter hemispherical
headed tool operated at 1250 rpm, 4000 mm/min and 0.25 mm incremental step depth are
employed for multi-pass SPIF to get further forming of 60o and 70o wall angle pyramids
using the same parametric combination.
Results and Discussions
76
4.6.1 Percentage thinning of 60o wall angle pyramid formed by multi-pass
SPIF
Multi-pass SPIF with 12 mm diameter tool, 0.25 mm incremental depth, 1250 rpm speed and
4000 mm/min feed is employed to form 60o wall angle pyramid out of already formed
pyramid with 50owall angle. Pyramid with 60o wall angle is successfully formed up to initial
13 mm depth of 50o wall angle square pyramid as shown in Fig. 4.9 (a).
(a) 60o wall angle pyramid formed out of 50o wall angle pyramid using multi-pass SPIF
(b) Measurement of wall thickness of 60o wall angle pyramid using point micrometer for the wall
angle formed by multi-pass SPIF
Results and discussions on percentage thinning of 60o and 70o wall angle square pyramids formed out of 50o wall angle pyramids by multi-pass SPIF
77
(c) Average percentage thinning Vs Component depth
FIGURE 4.9 Pyramid of 60o wall angle formed using multi-pass SPIF and average percentage
thinning
Thickness measurement for the pyramid of 60o wall angle obtained by multi-pass SPIF is
carried out using point micrometer as shown in Fig. 4.9 (b). The maximum amount of
average percentage thinning is 86.67 percent at 12 mm depth of measurement as shown in
Fig. 4.9 (c). No failure is observed during multi-pass SPIF to convert 50o wall angle pyramid
into 60o wall angle pyramid. The obtained results lead to conclusion that it is preferable to
apply multi-pass SPIF to form higher angle of pyramid out of difficult to form materials such
as AMS4902 in cold forming condition.
4.6.2 Percentage thinning of 70o wall angle pyramid formed by multi-pass
SPIF
Fig. 4.10 (a) shows the pyramid with wall angle of 70o deformed by multi-pass SPIF out of
50o wall angle pyramid with the same combination of operating parameters. The maximum
amount of average percentage thinning for the pyramid with 70o wall angle reaches up to
98.67 percent at 12 mm depth of measurement as shown in Fig. 4.10 (b). This higher amount
of average percentage thinning for higher angle pyramid walls lead to crack propagation due
to necking of sheet which ultimately results into failure of pyramid walls. The failure depth of
13 mm is observed for 70o wall angle pyramid which is double than 70o wall angle pyramid
formed by single-pass SPIF.
Results and Discussions
78
(a) 70o wall angle pyramid formed out of 50o wall angle pyramid using multi-pass SPIF
(b) Average percentage thinning Vs Component Depth
FIGURE 4.10 Pyramid of 70o wall angle formed using multi-pass SPIF and average percentage thinning
Based on results and discussion, the conclusion and future scope of presented work are
summarized in next chapter.
Conclusions
79
CHAPTER: 5
Conclusions and Future Scope
5.1 Conclusions
The outcome of this research encompasses effects of speed, feed, tool diameter and
incremental step depth on formability of AMS4902 sheet in terms of maximum formable
depth during single-pass Single Point Incremental Forming (SPIF). The effect of parametric
interactions between tool diameter and incremental step depth on average percentage thinning
and average surface roughness of pyramid walls formed out of AMS4902 sheet using single-
pass SPIF is an integral contribution of this presented research. The results of experimental
work also comprise of effect of tool diameter on geometrical accuracy of square pyramids,
formed using single-pass SPIF, in terms of wall angle. The research efforts have been
extended to determine maximum formable wall angle of pyramid walls during single-pass
and multi-pass SPIF performed using optimum values of process parameters derived from
previous set of experiments. Following conclusions are drawn based on results of
experimental work reported in previous chapter.
5.1.1 Effect of tool diameter, speed, feed and incremental step depth on
maximum formable depth of AMS4902 sheet during single-pass SPIF
At the combination of higher speed (3250 rpm) with higher feed (4000 mm/min) and
intermediate speed (2250 rpm) with intermediate feed (2600 mm/min) of selected range,
8 mm diameter tool tend to offer pinning effect on AMS4902 sheet which ultimately
resulted into failure of pyramid wall before targeted depth of forming.
Failure of pyramid was observed due to rapid removal of material from AMS4902 sheet
when smaller diameter hemispherical headed tool is operated at the combination of higher
speed and higher feed of selected range.
Single point incremental forming of AMS4902 sheet at much higher speed with lower
feed is not conducive as excess local friction and heat generation due to rubbing at a point
Conclusions and Future Scope
80
of tool-sheet interface leads to weld the tool with the sheet which does not allow tool to
carry forward the process of forming.
Wavy wall surface is observed for the pyramid of full depth formed with the combination
of intermediate speed (2250 rpm) and higher feed (4000 mm/min) out of selected range
even with medium size tool diameter (12 mm) and lower incremental depth (0.25 mm).
Interaction of tool rotational speed and feed plays vital role to satisfy the
thermomechanical demand to form AMS4902 sheet at reduced operating forming force
which ultimately leads to improved tool life, maintain dimensional accuracy and surface
quality of pyramid of AMS4902 formed by SPIF.
5.1.2 Effect of parametric interactions between tool diameter and
incremental step depth on average percentage thinning of pyramid walls
formed out of AMS4902 sheet using single-pass SPIF
Tool diameter is found as significant parameter influencing average percentage thinningof
pyramid walls formed out of AMS4902 sheet as its percentage contribution is higher
(58.96%) than percentage contribution of incremental step depth (38.38%).
Irrespective of any of the values of the incremental step depths of selected range, 12 mm
diameter tool offers comparatively uniform thinning than 16 mm diameter tool.
Interaction of 12 mm diameter tool with 0.25 mm incremental depth offers minimum
thinning compared to combination with 0.50 mm and 0.75 mm incremental step depths.
Irrespective of any of the values of tool diameters of selected range, combination with
0.75 mm incremental step depth offers maximum thinning.
5.1.3 Effect of parametric interactions between tool diameter and
incremental step depth on average surface roughness of pyramid walls
formed out of AMS4902 sheet using single-pass SPIF
Incremental step depth is found as significant parameter influencing average surface
roughness of pyramid walls formed out of AMS4902 sheet as its percentage contribution
is higher (51.53%) than percentage contribution of tool diameter (43.55%).
Conclusions
81
Irrespective of any of the values of the incremental step depths of selected range, average
surface roughness of pyramid wall is less for the pyramids formed using 16 mm diameter
tool compared to pyramids formed using 12 mm diameter tool.
Interaction of 16 mm diameter tool with 0.25 mm incremental depth offers minimum
roughness compared to combination with 0.50 mm and 0.75 mm incremental step depths.
Combination of 12 mm diameter tool with 0.50 mm incremental step depth and
combination of 16 mm diameter tool with 0.75 mm incremental step depth offers
maximum surface roughness.
5.1.4 Effect of tool diameter on geometrical accuracy of pyramid wall
angles formed out of AMS4902 sheet using single-pass SPIF
Geometrical accuracy in terms of pyramid wall angle is observed much closer to the
targeted geometry of 50o wall angle of pyramids formed using 16 mm diameter
hemispherical tip tool compared to the pyramid walls formed using 12 mm diameter tool.
More spring back is observed in pyramid walls formed using smaller diameter (12 mm)
tool compared to larger diameter (16 mm) tool of selected range.
5.1.5 Effect of optimum process parameters to form 60o and 70o wall angle
pyramids using single-pass SPIF
Failure depth of 8 mm is observed for 60o wall angle pyramid during single-pass SPIF of
AMS4902 sheet performed using optimum process parameters derived from previous set
of experiments (12 mm diameter tool, 1250 rpm speed, 4000 mm/min feed and 0.25 mm
incremental step depth).
Failure depth of 7 mm is observed for 70o wall angle pyramid during single-pass SPIF of
AMS4902 sheet performed using optimum process parameters derived from previous set
of experiments (12 mm diameter tool, 1250 rpm speed, 4000 mm/min feed and 0.25 mm
incremental step depth).
Conclusions and Future Scope
82
5.1.6 Effect of optimum process parameters to form 60o and 70o wall angle
pyramids out of already formed pyramids of 50o wall angle using multi-
pass SPIF
Pyramid with 60o wall angle is successfully formed up to initial 13 mm depth of 50o wall
angle square pyramid without failure during multi-pass SPIF using optimum process
parameters derived from previous set of experiments.
The maximum average percentage thinning does not exceed 87 percent for 60o wall angle
pyramid formed out of 50o wall angle pyramid using multi-pass SPIF which leads to
conclusion that it is preferable to apply multi-pass SPIF to form higher angle of pyramid
out of difficult to form materials such as AMS4902 in cold forming condition.
The failure depth of 13 mm is observed for 70o wall angle pyramid formed using multi-
pass SPIF of already formed pyramid of 50o wall angle which is almost double than 70o
wall angle pyramid formed by single-pass SPIF of AMS4902 sheet.
5.2 Future Scope
Effect of tool end geometry on average percentage thinning, geometrical accuracy and
surface roughness of component formed using SPIF at room temperature is the extended
scope of research in future.
Potential scope in future is also to include the study on effect of spiral and planer tool
path in order to obtain geometrical accuracy along with uniform thickness distribution of
component formed using SPIF at room temperature in comparison with hot incremental
forming.
Validation of results of average percentage thinning and average surface roughness of
present experimental work with the results of numerical simulation using the same
property parameters determined by UTM testing.
List of Publications
83
List of Publications
(a) Publications in International Journals
1. Shah HN, Trivedi SV, Gandhi AH (2018) Significance of parameters influencing
surface roughness during Incremental Sheet Forming of AISI202, International
Journal of Engineering, Technology, Science and Research (IJETSR), Vol. 5, Issue 4,
ISSN 2394-3386, pp. 700-708.
2. Trivedi SV, Gandhi AH (2019) Investigation of Grid Marking Techniques to assess
formability of AMS4902 Sheet formed using Single Point Incremental Forming,
Journal of Emerging Technologies and Innovative Research (JETIR), Vol. 6, Issue 3,
ISSN 2349-5162, pp. 105-110.
(b) Publications in National Conferences
1. Bhatt PR, Trivedi SV, Gandhi AH (2016) An Incremental Sheet Forming Process: Its
Need, Application and Characteristics, 7th National Conference on Emerging Vistas
of Technology (NCEVT) - Smart Innovations in Mechanical and Allied Engineering,
ISBN: 978-93-85777-49-3, pp. 180-184.
2. Gandhi PA, Trivedi SV, Gandhi AH (2017) Numerical investigation of effect of wall
geometry on formability of parts in single point incremental forming process, National
conference on Progress, Research and Innovation in Mechanical Engineering
(PRIME) SCET - Multidisciplinary Conference on Engineering and Technology,
ISBN: 978-81-933591-5-0, pp. 1-6.