Studies on Process Parameters in End Milling Operations of Aluminium Alloy

Studies on Process Parameters in End Milling Operations of Aluminium Alloy

International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 2 Issue 3, March – 2013

S. Madhava Reddy1 and A. Chennakesava Reddy2

1. Associate Professor, Dept. Of Mechanical Engineering, MGIT, Hyderabad

2. Professor, Dept. Of Mechanical Engineering, JNTUH, Hyderabad

Abstract

Aluminum is one of the most widely used metals in the construction of aero planes, truck wheels, screw machine products and turbine manufacturing industries. Accurate prediction of process parameters is important in controlling the dimensional accuracy of thin walled aeroplane components. The effects of various process parameters such as pressure and friction acting on the cutter – chip interface, cutter geometry on chip flow and specific cutting energy are studied. Pressure and friction acting on the cutter – chip interface decrease with the increase of feed rate. Chip flow angle increases with the increase of feed rate. Effect of cutting speed on the pressure and friction parameters for aluminium has a negligible effect on the process parameters. Specific cutting energy decreases with an increase in feed rate

1. Introduction

   The milling process is a highly non-linear plastic deformation process with many independent and dependent variables process parameters change as functions of the feed rate, tool rotation angle and the position angle of a point along the cutting edge. As a result of using constant process parameters, the measured force components are underestimated during the engagement and disengagement periods. The average chip thickness is a function of the feed rate and the radial immersion, to determine the average parametric relationships many tests with different combinations of feed rate, and radial and axial immersions must be performed (3). Therefore, computing the variation of the parameters as a function of the tool rotation angle for slot cutting tests at different cutting conditions would be enough to establish parametric relationships for the forces. The purpose of this work is to demonstrate the feasibility of obtaining process parameters as functions of the tool rotation angle, feed rate and cutting speed from a few milling cutting tests. A study of process parameters in machining of aluminum (2024) is presented in this paper.

2. Experimental work

   A 3 axis CNC milling machine was used in the experiments. The work piece was clamped on the measuring platform. The force-measuring platform consisted of piezoelectric transducers capable of measuring the three Cartesian force components. A

   digitizing oscilloscope was coupled with a magnetic pick up coil to precisely determine the spindle sped. A series of slot cutting experiments was conducted using single fluted titanium nitride coated HSS sharp milling cutters with radius of

   12.5 mm, helix angle of 300 and rake angle of 130 .

   Cutting action was chatter free for all of the cutting tests and the collected chips were uniformly curved into spirals with smaller sizes and appearance. No cutting fluid was used. Table 1 shows the testing conditions for the slotting tests conducted in cutting 2024 free machining aluminum. While cutting aluminum some indication of built up edge formation was observed where a very thin film of aluminum stuck to the cutting edges practically served as another layer of coating on the cutter surface. The depth of this layer was found to be negligible on comparison to chip thickness.

   Table 1. Cutting Conditions

   Workpiece material	Cutting speed (rpm)		Feed rate (mm/ min)	Values of cutting speed and feed rate
   2024	n1,	n2,	f1, f2,	n1=1600,
   aluminum	n3		f3	n2=2000,
   				n3=2500
   				f1= 0.025,
   				f2=0.127,
   				f3=-0.203

   Work material: 2024 aluminum, youngs modulus

   = 70 GPa, Poisson ratio=0.345, tensile strength

   =900 MPa, hardness=120 HB; HSS cutter: helix angle = 300, diameter = 25 mm, rake angle = 130

3. Results and Discussion

   3.1 The Effect Of Feed Rate

   The feed rates were varied from 0.025 mm/rev to

   0.203 mm/rev while keeping rake angle =130

   Pressure parameter as a function of spindle rotation angles at various feed rates is plotted in Fig 1.

   4500

   4000

   3500

   Pressure(N/mm2)

   Pressure(N/mm2)

   3000

   2500

   2000

   1500

   1000

   500

   0

   fd=0.025mm/rev

   fd=0.127mm/rev

   fd=0.203mm/rev

   fd=0.025mm/rev

   fd=0.127mm/rev

   fd=0.203mm/rev

   0 1 2 3 4

   Rotation Angle(rad)

   2

   1.5

   Friction

   Friction

   1

   0.5

   0

   fd= 0.025mm/rev

   fd=0.127mm/rev

   fd=0.203mm/rev

   fd= 0.025mm/rev

   fd=0.127mm/rev

   fd=0.203mm/rev

   0 1 2 3

   Rotation angle (Rad)

   Fig.2 Measured friction parameter at various feed rates: rpm 1600, Ra = 2.54 mm; Rd = 12.7 mm

   Fig.1 Measured pressure parameter at various feed rates: rpm 1600, Ra = 2.54 mm; Rd = 12.7 mm

   It can be seen that pressure parameter (Kn) decreases as feed rate increases. The decaying rate of pressure parameter is higher around smaller feed rate values, which is an expected behavior. Fig 2. shows the friction parameter, Kf, as a function of feed rate. It can be seen that the friction parameter Kf, also decreases with increasing feed rate.

   This behavior is analogous to the decreasing friction coefficient with increasing feed rate in oblique cutting operations.Fig.3 shows the chip orientation angle (direction of friction force) as a

   0.8

   Chip flow angle (Radians)

   Chip flow angle (Radians)

   0.6

   0.4

   0.2

   0

   fd=0.025mm

   /rev

   fd=0.127mm

   /rev

   0 1 2 3

   Rotation angle (Rad)

   function of the tool rotation angle and feed rate. The direction of the friction force is closely related to the direction of the chip flow angle. Although for some materials, the direction of the chip flow may be the same direction of friction force due to the lateral effects perpendicular to the chip motion in general, there may be some differences between those two directions. It has been found that chip flow angle generally increases with the increase of feed rate. A close relationship between the friction parameter and the chip flow angle was observed. Chip flow angle was also found to decrease with increasing friction. The friction parameter rose to a maximum value during the tool entry into the work piece. This maximum value was found to increase with the decrease of feed rate.

   3.2The effect of cutting speed

   The cutting speeds were varied from 400 rpm to 1000 rpm while keeping feed rate fd = 0.203 mm/ rev. Fig 4. shows the effect of cutting speed on the pressure parameter for 2024 aluminum work piece.

   Fig.3: Measured chip rotation angle at various feed rates: rpm = 1600, Ra = 2.54 mm; Rd = 12.7 mm

   It can be seen that the cutting speed has a negligible effect on the process parameters in the tested range.

   Fig.4: Pressure parameter at different cutting speeds. fd = 0.203 mm/rev; Ra = 2.54 mm; Rd =

   12.7 mm

   p>Fig.5 shows the effect of the cutting speed on the friction parameter in the tested range of cutting speed. A negligible effect of the cutting sped on the friction parameter in the range of cutting speed used during the tests. Therefore, the effect of the cutting speed in the testing range can be neglected.

   • Specific cutting energy decreases with an increase in feed rate.

     2

     1.5

     n=1600rpm n=2000rpm n=2500rpm

     6000

     fic cutting energy(N/mm2)

     fic cutting energy(N/mm2)

     4000

     fd=0.025mm/rev fd=0.127mm/rev fd=0.203mm/rev

     Friction

     Friction

     1

     2000

     0.5

     0

     0 1 2 3

     Rotation angle (rad)

     Fig.5 Friction parameter at different cutting speeds; fd =

     0.203 mm/rev; Ra = 2.54 mm; Rd = 12.7 mm

     3.3. Effect Of Feed Rate As A Function Of Specific Cutting Energy

     The feed rates were varied from 0.025mm/rev to

     0.203 mm/rev while keeping cutting speed = 2500 rpm. Effect of feed rate on specific cutting energy for the 2024 aluminum is plotted in fig.6. Specific cutting energy follows a similar trend with the pressure and friction parameters and it decreases with an increase in feed rate, which is in close qualitative with the reported specific cutting energy results obtained through oblique cutting by Boothroyd .

4. Conclusions

   In the present work, the important conclusions made, which are as follows:

   • Pressure parameter (Kn) decreases marginally with an increase in feed rate

   • Friction parameter (Kf) decreases with an increasing feed rate with the cutting speed of 700 rpm.

   • The chip rotation angle generally increases with the increase in feed rate

   • Negligible effect of the cutting speed on the friction parameter as well as pressure parameter.

   Fig.6 Specific cutting energy Vs rotation angle; rpm = 2500; Ra = 2.54 mm; Rd = 12.7 mm

5. References

   1. Michael P.Vogler, Richard E.Devor and Shiv G.Kapoor, Microstructure level force prediction model for micro-milling of multi phase materials, Journal of Manufacturing Science and Engineering, vol.125, pp.202-209, 2003.

   2. Myon-woong Park, Hyung-Min Rho, Generation of Modified cutting condition using Neural Network for an operation planning system Annals of the CIRP, Vol. 45, pp. 475-478, 1996.

   3. Guven Yu Cesan, Qufei xie and Abdel E.Bayoumi, Determination of parameters through a mechanistic force model of milling operations, Int.J.Mach.Tools Manufact, Vol.33, No.4, pp.627- 641, 1993.

   4. Erhan Budak and Yusuf Altintas, Peripheral Milling conditions for improved dimensional accuracy, Int. J.Mach.Tools Manufact, Vol.34, No.7, PP.907-918, 1994.

   5. Daniel C.H.Yang and Alex D.Golub, Precession Trajectory Generation for CNC Milling of arbitrary contours and surfaces, Int. J.Mach. Tools Manufact, Vol.34, No.7,pp.1005-1018, 1994.

   6. Altintas.Y. and Lee.P, Mechanics and Dynamics of ball end milling, Journal of Manufacturing Science and Engineering, Vol.120, pp.684-692, 1998.

   7. Berruti.T. and Ubertalli.G, Influence of cutting parameters on residual strane induced by Milling in pressure. Die-cast Alluminium alloy components, Transactions of the ASME, Vol.123, pp.547-551, 2001.

   8. Mahdava Reddy. S and Chennakesava Reddy.A, Studies on Machining characteristics of silicon Nitride ceramics, proceeding of National conference on Advance Materials and Manufacturing techniques, JNTU, Hyderabad, 2004.

   9. Kalpakjian, Manufacturing Engineering and Technology, Third edition, Addision Wesley publishing company, Delhi 2002.

   10. Bhattacharyya.A, Metal cutting theory and practice, New Central Book Agency (P) Ltd., Kolkatta. 1994.

   11. R.K.Jain, Production Technology, Khanna Publishers, Delhi 2001

   12. Amitabha Ghosh and Ashok Kumar Mallik, Manufacturing science, East West Press Private Limited, New Delhi, 2000.

   13. N.N.Zorev,. Metal cutting Machines, translated by H.S.M Massey edited by C.M.Shaw, pergamon press, oxford, 1996.

1. [14] G.Boothroyd. Fundamentals of metal machining and machine tools, Script Book company, New York, 1975