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
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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
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
--------------------------------------------------------- 3) (External Examiner 3) Name and Signature
------------------------------------------------------- Name and Signature of Supervisor with Seal
--------------------------------------------------------- 1) (External Examiner 1) Name and Signature
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
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)
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].
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,
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
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
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
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
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
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.
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
(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)