1757-899X_17_1_012043

This content has been downloaded from IOPscience. Please scroll down to see the full text.

Download details:

IP Address: 180.245.204.111This content was downloaded on 13/05/2015 at 08:43

Please note that terms and conditions apply.

Analyzing the effect of cutting parameters on surface roughness and tool wear when

machining nickel based hastelloy 276

View the table of contents for this issue, or go to the journal homepage for more

2011 IOP Conf. Ser.: Mater. Sci. Eng. 17 012043

(http://iopscience.iop.org/1757-899X/17/1/012043)

Home Search Collections Journals About Contact us My IOPscience

1

Analyzing the effect of cutting parameters on surface roughness and tool wear when machining nickel based hastelloy 276.

Basim A. Khidhir1 and Bashir Mohamed1

Department of Mechanical Engineering, College of Engineering, University Tenaga Nasional, 43009 Kajang, Selangor, Malaysia Email: [email protected]

Abstract Machining parameters has an important factor on tool wear and surface finish, for that the manufacturers need to obtain optimal operating parameters with a minimum set of experiments as well as minimizing the simulations in order to reduce machining set up costs. The cutting speed is one of the most important cutting parameter to evaluate, it clearly most influences on one hand, tool life, tool stability, and cutting process quality, and on the other hand controls production flow. Due to more demanding manufacturing systems, the requirements for reliable technological information have increased. For a reliable analysis in cutting, the cutting zone (tip insertworkpiecechip system) as the mechanics of cutting in this area are very complicated, the chip is formed in the shear plane (entrance the shear zone) and is shape in the sliding plane. The temperature contributed in the primary shear, chamfer and sticking, sliding zones are expressed as a function of unknown shear angle on the rake face and temperature modified flow stress in each zone. The experiments were carried out on a CNC lathe and surface finish and tool tip wear are measured in process. Machining experiments are conducted. Reasonable agreement is observed under turning with high depth of cut. Results of this research help to guide the design of new cutting tool materials and the studies on evaluation of machining parameters to further advance the productivity of nickel based alloy Hastelloy - 276 machining.

1. Introduction Increasing the productivity and the quality of the machined parts are the main challenges of manufacturing industry. Modern cutting tools allow cutting at high speeds, thus increasing the volume of chips removed per unit time and this objective requires better management of the machining system corresponding to cutting tool-machine tool-workpiece combination to go towards more rapid metal removal rate. Exploring higher cutting speed depends to a greater extend on the cutting tool materials [1]. General information on operating parameters employed when turning Nickel based alloys are available in both academic [2-5] and industrial literatures [6, 7]. From the very beginning, development of an adequate predictive theory of the process was of a major concern for all researchers. In relation to machining operations with defined cutting edges, workpiece surface integrity aspects when turning Inconel 718 with coated carbide cutting tools [8, 9]. Due to their high temperature strength and high corrosion resistance, nickel based alloys are used for engines for commercial and military aircraft and space engines. Is considered by machinists one of the most challenging areas. This is due to a complex of material properties [10,11] namely: low thermal conductivity leading to increased temperatures at the tool point rake face, work-hardening tendency during machining, high thermal affinity to tool

CAMAN IOP PublishingIOP Conf. Series: Materials Science and Engineering 17 (2011) 012043 doi:10.1088/1757-899X/17/1/012043

Published under licence by IOP Publishing Ltd 1

2

materials resulting in welding-adhesion of workpiece material to the cutting edge, presence of hard abrasive particles (e.g. carbides, oxides) resulting in intense tool wear [12]. The heat generated during a cutting operation is the summation of plastic deformation involved in chip formation and the friction between tool and workpiece and between the tool and the chip [13]. Metallurgical changes that have improved superalloys making the metal stronger, tougher or more resistant to oxidation or corrosion, have also made these metals more difficult to machine. For the nickel based superalloys, high temperature characteristics translate directly to machining challenges. The combination of high cutting force and high temperature when machining these materials leads to edge breakdown of the tool through chipping or deformation. In addition, for the majority of these metals, work hardening takes place rapidly. A hardened surface created during machining can result in depth-of-cut-line notching of the tool and may also compromise the fatigue strength and geometric accuracy of the part [14]. Many nickel alloys are age hardenable, meaning that the hardness of the alloy increases dramatically upon heat treatment. As second phase particles form, the alloy becomes stronger and more abrasive, thus more difficult to machine [15]. The geometry of the tool plays a big part in controlling wear. The geometry of the cutting tool must allow for chip removal in order to take the heat out with the chip. Tool geometry should allow for smoother cutting and less vibration and better chip evacuation. In addition, higher rpm and feed rates with shallow depth-of-cut are typically required to maintain chip flow and heat [16-17]. This study intend to investigate the effect of insert geometries on cutting performance in terms of tool life and tool wear when machining of nickel-based alloys - 276. 2. Experimental procedure The machining tests were performed by single point. A CNC turning machine OKUMA CNC turning machine supported with Spindle Drive motor 11 KW and 6000 Rpm maximum speed. Z- axis Simens AC Servo motor 8 Nm and X- axis Simens motor 6 Nm as shown in Figure 1.

Figure 1. CNC machine used in experiments

The workpiece of nickel based Hastelloy 276 specimens were 300 mm long and 50 mm diameter. The chemical compositions of the workpiece materials as [Ni:57%; Co:1.62%; Cr:15.44%; Mo:15.34%; Fe:5.43%; W3.67%; V:0.41%; Mn:0.52%; C:0.004%; Others (Si

3

Table 2. Insert tools and holders used during experiments.

No Insert material Tool insert code Tool holder code

3 RNGN 120400E CRSNR 2525M 12-ID

4 SNGN 120412E SNGN 120412E

5

Ceramic

CNGN 120408 E CCLNR 2525M 12-4 Surface roughness measurement was carried out on the machined surfaces using a Hand held Roughness Tester TR200 instrument. Three measurements were made on the each surface. The worn cutting tools were also examined under a Philips XL 30 ESEM type scanning electron microscope (SEM). 2.1. Design of experiment Response surface methodology (RSM) is used to find a combination of factors which gives the optimal response. RSM is actually a collection of mathematical and statistical technique that is useful for the modeling and analysis of problems in which a response of interest is influenced by several variables and the objectives is to optimize the response [18]. There are essentially two main types of designs experiments which are based on response surface analysis as follows: 1. Central Composite Design (CCD). 2. Box-Behnken Design (BBD). Both of these methodologies require a quadratic relationship between the experimental factor and the responses. In this paper the BBD has been chosen as shown in Figure 2.

Figure 2. The 3N full factorial

The levels of independent variables and coding identifications used in this design are presented in Table 3.

Table 3. Variables coding identifications

Code -1 0 +1

Cutting speed (m/min) 150 200 250

Feed rate (mm/rev) 0.15 0.2 0.25

Depth of cut (mm) 0.5 1 1.5

Nose radius (deg.) 0.8 1.2 12


3

4

Table 5 shows the experimental conditions and results obtained using ceramic inserts. All of the turning tests were run dry. Box- Behnken Design is normally used when performing non-sequential experiments. That is, performing the experiment only once. These designs allow efficient estimation of the firstorder coefficients. Because Box-Behnken Design has fewer design points, they are less expensive to run than central composite designs with the same number of factors. Box-Behnken Design do not have axial points, thus can be sure that all design points fall within the safe operating. Box- Behnken Design also ensures that all factors are never set at their high levels simultaneously [19]. Figure 3 shows the 3N full factors Box-Behnken. Preliminary tests were carried out to find the suitable cutting speed V, feed rate f, depth of cut d and approach angle K as shown in Table 4. Every one passes (one pass is equal to 20mm), the cutting test was stopped. The same experiment has been repeated for 3 times to get more accurate result.

Table 4. Experimental conditions and results obtained using ceramic inserts

Run order

Cutting speed,

V (m/min)

Feed rate, f (mm/rev)

Depth of cut, d (mm)

Nose radius, r (mm)

Exp. Surf. Rogh. Ra (um)

1 0 -1 0 -1 0,184 2 1 1 0 0 0,25 3 0 0 -1 -1 0,382 4 0 -1 -1 0 0,555 5 1 0 0 1 1,045 6 1 0 -1 0 0,8 7 0 0 -1 1 1,04 8 0 1 0 -1 0,378 9 -1 0 1 0 2,373 10 -1 0 0 1 1,404 11 0 -1 0 1 1,162 12 0 1 -1 0 1,349 13 1 0 1 0 1,436 14 0 1 1 0 1,771 15 0 1 0 1 1,076 16 1 -1 0 0 0,844 17 1 0 0 -1 0,466 18 -1 -1 0 0 0,423 19 0 -1 1 0 5,216 20 0 0 0 0 0,78 21 0 0 1 -1 3,532 22 0 0 1 1 1,064 23 -1 0 -1 0 1,327 24 0 0 0 0 0,78 25 -1 0 0 -1 2,333

26 0 0 0 0 0,78


4

5

2.2. Regression model

The surface roughness (Linear + interaction) regression model is: SR = - 27,3 + 0,105 V + 141 f + 9,16 d - 0,069 r - 0,536 Vf- 0,0023 Vd - 0,00119 Vr - 38,2 fd + 0,52 fr + 0,177 dr ---------------(1) Where SR is Surface roughness (Ra um), V is cutting speed (m/min), f is feed rate (mm/rev), d is depth of cut (mm), r is nose radius (mm).

Table 5. Analysis of Variance

Source DF Seq SS Adj SS Adj MSFP Regression 10 23 23.4096 2.34096 3.24 0.018

Linear 4 11 10.8013 2.70033 3.74 0.025 Interaction 6 11 11.9106 1.98511 2.75 0.050 Residual Error 16 11 11.5659 0.72287

The p-value for lack of fit is 0.095 suggesting that this model adequately fits the data.

Table 6. P- value for the terms of surface roughness Ra

Term T P Constant 7.021 0.000 V -1.852 0.083 f -0.073 0.943 d 3.291 0.005 r -0.718 0.483 V * f -2.995 0.009 V* d -0.195 0.848 V* r -0.988 0.338 f *d -2.637 0.018 f * r 0.341 0.737 d * r 1.548 0.141

Table 6 gives the results of the ANOVA of surface roughness of machined specimen. It can be seen from table 7, that the most significant parameters influencing the surface roughness is the cutting speed, see the main effects plots for SN ratio in Fig. 3. It is known from the fundamental theory of machining that the feed rate and nose radius play an important role in roughness of the machined surface when the cutting edge is sharp [20]. However, when the cutting edge is not sharp or modified as in this case, the cutting edge is chamfered, then other factors come into effect and influence the surface roughness. It is observed that the surface roughness is higher (poor surface finish) at the lower cutting speed. The surface roughness is lower (good surface finish) as the cutting speed increases to its highest level. Thus, at higher MRR, the volume of the accumulated material is more, thereby suppress the effect of cutting edge radius and feed rate more effectively. Consequently, the surface finish is better [21]. Generally, the increase of cutting speed will improve of the surface finish while increasing depth of cut will increase the value of surface roughness to become larger. On the other hand, the changing in feed rate will take no effect on surface roughness as shown in Figure 3.


5

6

Figure 3. Main Effects Plot (data means) for Exp. surface roughness Ra (um) The proposed linear equation is valid only for cutting ceramic tools with a (-6) rake angle within the cutting conditions range used in the experimentation. Figure 4 shows the plot of experimental surface roughness versus predicted surface roughness from eq. (1) it is clear that the predicted values are in good agreement with the experimental readings. This indicates that the obtained linear model is useful to be the empirical modal for selecting cutting speed values.

Figure 4. Prediction of cutting force with experimental cutting force.

3. Results and discussions Generally, cutting tool materials are exposed to high mechanical stresses and thermal disturbances when machining nickel based Hastelloy C-276 resulting in low surface roughness, cutting tool wear and short tool life. Results showed That the most dependent parameter affected the surface finish is cutting speed followed by depth of cut and the interaction of cutting speed versus depth of cut, nose radius and feed rate as shown in Figures 5, 6 and 7 respectively.

(No. of Exp.)

Surface roughness (m)


6

7

Figure 5. Surface roughness in the cutting speeds - depth of cut plane.

Figure 6. Surface roughness in the cutting speeds - nose radius plane.

Figure 7. Surface roughness in the cutting speeds - feed rates plane.

Different type of tool wears appears during experiments as flank wear and chipping as shown in Figures 8 and 9. Built up edge (BUE) was the factor appears during experiments as shown in Figures 10.

Feed rate (mm/rev) Cutting speed (m/min)


Depth of cut (mm)

Cutting speed (m/min)

Nose radius (mm) Cutting speed (m/min)




7

8

Figure 8. Flank wear in the cutting speed feed rate plane for 0.5 mm depth of cut and 0.8 mm nose radius.

Figure 9. Chipping wear in the cutting speed feed rate plane for 1 mm depth of cut and 1.2 mm nose radius.

Figure 10. BUE in the cutting speed depth of cut plane for 0.15 mm feed rate and 0.8 mm nose radius. Tool wear type while cutting the Hastelloy - 276 is chipping wear at the line depth of cut due to high thermal, high work hardness, high strength of the work-piece and abrasive particles. Furthermore; flank wear, chipping and severe damages are the causes of tool wear. The inserts were tested by cutting Hastelloy - 276 under different cutting parameters as listed in Table 3. For each experiment, Reference flank wear value VBB = 0.3 mm is chosen as wear criterion according to International Standard Organization. A cutting tool was rejected and further machining was stopped based on one or a combination of the following rejection criteria in relation to ISO Standard 3685 for tool life testing:


8

9

Average flank wear P0.3 mm. Maximum flank wear P0.4 mm. Nose wear P0.5 mm. Notching at the depth of cut line P0.6 mm. Excessive chipping (flaking) or catastrophic fracture of the cutting edge.

Ceramic tool tips used to machine the nickel based Hastelloy-276 workpiece material were examined by The SEM images of the worn cutting edges. It is seen from these images that wear predominantly occurred in two regions during the tests: at the depth of cut line and the nose. However, wear at the nose radius of cutting edge directly influences the machined surface finish since the nose edge is in direct contact with the newly machined surface. However, further increasing in the depth of cut increases the extent of tool wear.

In this study, flank wear and excessive chipping wear, which are important problems reducing tool life, are mainly observed in the machining experiments ceramic tools. It is considered that the tools having negative and larger approach angle with bigger nose radius must be used in order to solve chipping wear problem. 4. Conclusion Turning tests were performed on Nickel based Hastelloy C-276 using two different inserts of ceramic cutting tools. The influences of cutting speed, tool inserts type and workpiece material were investigated on the machined surface roughness. Based on the results obtained, the following conclusions can be drawn: 1. Cutting speed was found to have a significant effect on the machined surface roughness values. 2. Influence of Depth of cut was found to affect the surface roughness when it increased from

medium to high value. 3. Interaction of cutting speed and depth of cut influence the surface roughness and tool wear and

generating BUE in the low to medium speed. 4. Nose radius wear, evidenced by the SEM examinations, were found to be responsible for the

surface roughness values. 5. Round insert found to produce better surface roughness associated with decreasing the depth of

cut and increasing the cutting speed. 6. Feed rate uneducated the surface finish for that it recommended to increase the feed rate with

cutting speed and low to medium depth of cut. References [1] E.O. Ezugwu, Key improvements in the machining of difficult-to-cut aerospace superalloys,

Int. J. Mach. Tool Manu. 45 (2005) (12/13), pp. 13531367. [2] Byrne, G., Dornfeld, D., Denkena, B., 2003, Advancing Cutting Technology, Annals of the

CIRP, 52/2:483-507. [3] Settineri, L., Levi, R., 2005, Surface properties and performance of multilayer coated tools in

turning Inconel, Annals of the CIRP, 54/1: 515-518. [4] Narutaki, N., Yamane, Y., Hayashi, K., Kitagawa, T., Uehara, K., 1993, High-speed machining

inconel 718 with ceramic tools Annals of the CIRP, 42/1: 103-106. [5] Vigneau, J., Bordel, P., Leonard, A., 1987, Influence of the microstructure of the composite

ceramic tools on their performance when machining Nickel alloys, Annals of the CIRP, v 36/1:13-16.

[6] Machining data handbook, 1980, Mectcut Research Associate Inc., Cincinnati. [7] Sandvik Coromant, Gas turbine-Application guide, C- 2920:18-EN/01. [8] Arunachalam R., Mannan, M., Spowage, A., 2004, Surface integrity when machining age

hardened Inconel 718 with coated carbide cutting tools, Int. J. of Mach. Tools and Manuf., 44/14:1481-1491.


9

10

[9] Axinte, D., Axinte M., Tannock, J.D.T., 2003, A multicriteria model for cutting fluid evaluation, Proceedings of the IMECHE Part B, Journal of Engineering Manufacture, 217/10:1341-1353.

[10] Shaw, M.C., 1984, Metal cutting principles, Clarendon Press Oxford. [11] Trent. E.M., 1984, Metal cutting, Butterworths. [12] D. A. Axinte, P. Andrews, W. Li, N. Gindy, P.J. Withers Turning of advanced Ni based alloys

obtained via powder metallurgy route Annals of the CIRP Vol. 55/1/2006 [13] Komvopoulos, K., and Erpenbeck, S. A., 1991. Finite element modeling of orthogonal metal

cutting. Journal of Engineering for Industry, 113, pp. 253267. [14] Deng Jianxin* and Ai Xing Wear behavior and mechanisms of alumina-based ceramic tools in

machining of ferrous and nonferrous alloys Tribology International Volume 30 Number 11 1997

[15] Don Graham Turning Difficult-To-Machine Alloys Feature Article, www.mmsonline.com [16] Arnold, D.B., 2000 Trends that drive cutting tool development In: Metalworking Technology

Guide. Kennametale Inc. [17] Fleischer, P., 1964 The effect of material and geometry on the wear characteristics of cutting

tools during face milling Int. J. Mach. Des. Res. 4, 4749. [18] Montgomery, D.C., 1984. Design and Analysis of Experiments. 2nd Edition. John Wiley, New

York. [19] G.E.P. Box, K.P. Wilson, 1951, On the experimental attainment of optimum condition, J. Roy.

Stat. Soc. 13. [20] M. Anderson, R. Patwa, Y.C. Shin, (2006), Laser-assisted machining of Inconel 718 with an

economic analysis, Int. J. Mach. Tools Manuf. 46 (14), 18791891. [21] R.S. Pawade, Suhas S. Joshi, P.K. Brahmankar, M. Rahman, (2007), An investigation of cutting

forces and surface damage in high-speed turning of Inconel 718 Journal of Materials Processing Technology 192193 (2007) 139146.


10

1757-899X_17_1_012043

Documents

important cutting parameter

higher cutting speed

tool stability

tool life

tool tip wear

modern cutting tools

machining experiments

tool wear whenmachining