Proceedings of the 3rd International Conference on Manufacturing Engineering (ICMEN), 1-3 October 2008, Chalkidiki, Greece

Edited by Prof. K.-D. Bouzakis, Director of the Laboratory for Machine Tools and Manufacturing Engineering (ΕΕΔΜ),

Aristoteles University of Thessaloniki and of the Fraunhofer Project Center Coatings in Manufacturing (PCCM),

a joint initiative by Fraunhofer-Gesellschaft and Centre for Research and Technology Hellas, Published by: ΕΕΔΜ and PCCM

215

EFFECT OF EXTRUSION PARAMETERS AND DIE GEOMETRY ON

THE PRODUCED BILLET QUALITY USING FINITE ELEMENT METHOD

A.Ε. Lontos1, F.A. Soukatzidis

2, D.A. Demosthenous

1, A.K. Baldoukas

2

1. Mechanical Engineering Department, Frederick University Cyprus, Nicosia-Cyprus

2. Aircraft Technology Department, Technological Educational Institution (T.E.I.) of Chalkida, Psachna Evia-Greece

ABSTRACT The aim of this paper is to study the effect of extrusion parameters (extrusion speed and temperature) and die geometry, i.e. extrusion radius, on the extruded billet quality (Equiva-lent stress and strain) using F.E.M. technique. For this purpose the general F.E.A. soft-ware Deform-2D has been used to set up the finite element model of the warm aluminium extrusion in two dimensions (2D). 6061 Aluminium was used as billet material, with 40mm diameter and 50mm length. The extrusion process was modelled as isothermal, which means that the billet material was preheated at a specific temperature and then it was pressured into the circular die, with extrusion ratio 3.3. The extrusion speed was varied from 1 to 3 mm/s, the extrusion temperature varied from 400o C to 500o C and the extru-sion die radius was varied from 1 to 4 mm. The friction between i) workpiece and die, con-cerns Coulomb model with 0.3 friction factor, ii) workpiece and stem, concerns Shear model with 0.9 friction factor and iii) workpiece and container, concerns Shear model with 0.96 friction factor. Optimized algorithms for extrusion parameters were proposed regard-ing to the concluded simulating results. KEYWORDS: Extrusion procedure, 2D FEM simulation, Aluminium Hot extrusion

1. INTRODUCTION

Extrusion has numerous applications in the manufacture of continuous as well as discrete prod-ucts from a wide variety of metals and alloys. In the extrusion process, a cylindrical billet is forced through a die in a manner similar to squeezing toothpaste from a tube or extruding Play-Doh in various cross-section in a toy press. Typical products made by extrusion are railing for sliding doors, windows frames, tubing having various cross-sections, aluminium ladders and numerous structural and architectural shapes.

A characteristic of extrusion is that large deformation can take place without fracture, because the material is under high triaxial compression during extrusion. As a result the extruded billet quality depended directly by the mechanical properties of billet and die, the extrusion speed, the die geometry and the extrusion shape. In the bibliography there are few papers that describe the extrusion process and the effect of extruding parameters on the developed workpiece qual-ity using Finite Element Method /1-6/.

The aim of this paper is to study the effect of extrusion parameters (extrusion speed and tem-perature) and die geometry, i.e. extrusion radius, on the extruded billet quality (Equivalent stress and strain) using F.E.M. technique. These simulating results will be useful during the execution of the experimental procedure and they will guide the experimental tests, which are going to take place in a real press with coated and non-coated extrusion dies. More specifically, during these experimental tests different coatings types will be evaluated according to their per-formance operating on extrusion dies.

216 3rd

ICMEN – 2008

2. FINITE ELEMENT MODEL OF WORM ALUMINIUM EXTRUSION PROCESS

The general-purpose F.E.A. software Deform-2D /7/ has been used to set up the finite element model of the warm aluminium extrusion process in two dimensions (2D). While primarily used to model a metal forging process, the above software has been successfully applied to the simula-tion of rolling and forming process in recent years /8,9/. The applied F.E.M. program is based on an implicit Lagrangian incremental formulation, i.e. the finite element mesh is generated to the workpiece and follows its deformation. The Sparce solver with Newton-Raphson iteration method was used in order to estimate the deformation of billet material. In Figure 1 the FEM model and extrusion parameters are illustrated.

Extrusion FEM model Extrusion parameters

Extrusion speed (mm/sec): 1,2,3 Extrusion temperature (oC): 400, 450, 500 Billet diameter (mm): 40 Extrusion diameter (mm): 12 Extrusion radius value (mm): 1, 2, 3, 4

Figure 1: Extrusion FEM model and simulation parameters The pressing stem, die and container liner are considered perfectly rigid. Based on this assump-tion there is no need to assign their mechanical properties. Moreover, the extrusion equipment elastic deformation can be neglected without loss of accuracy due to its very small magnitude compared with the large plastic deformation of the billet material. Since no mesh has to be gen-erated, the extrusion equipment is represented by their reference profile. Aluminium 6061 was used as billet material and discredited at the FEM program by bilinear 4-node quadrilateral elements. The billet material was modeled as plastic object (compressible

Table 1: Mechanical properties and chemical composition of billet material

Aluminium 6061

Density (gr/cm3)

Ultimate tensile strength (MPa)

Yield tensile strength (MPa)

Modulus of elasticity (GPa)

Poisson’s ratio

2.7 124 55.2 68.9 0.33

Machinability (%)

Shear modulus (GPa)

Shear strength (MPa)

Thermal conductivity (W/m-K)

30 26 82.7 180

Al (%) Cr (%) Cu (%) Fe (%) Mg (%)

95.8-98.6 0.04 0.15-0.4 <=0.7 0.8-1.2

Mn (%) Si (%) Ti (%) Zn (%)

<=0.15 0.4-0.8 <=0.15 <=0.25

Forming 217

rigid-vistoplastic material) /7/. The mechanical properties and chemical composition of billet ma-terial are given in Table 1. The boundary conditions in the billet and the extrusion equipment are quite complex, influenced by a number of factors such as temperature, lubricant type, material properties of billet and equipment, ram speed. Various friction models i.e. shear and Coulomb and experimental analy-sis techniques i.e ring rolling test, are available in order to calculate the friction phenomena and the friction coefficient between workpiece and extrusion equipment. In the present paper, the friction between workpiece and the extrusion equipment between i) workpiece and die, concerns Coulomb model with 0.3 friction factor, ii) workpiece and stem concerns Shear model with 0.9 friction factor and iii) workpiece and container concerns Shear model with 0.96 friction factor. 3. SIMULATIONS RESULTS

3.1. Effect of extrusion die radius on the developed billet quality

Figure 2 shows the simulations results of pressuring load against four deferent extrusions die

Extrusion die radius Ra=1mm Extrusion die radius Ra=2mm

Extrusion die radius Ra=3mm Extrusion die radius Ra=4mm

Figure 2: Pressuring load for various extrusion die radius with constant temperature (400oC)

218 3rd

ICMEN – 2008

radius. The simulations were obtained with constant temperature 400oC and extrusion speed 1 mm/s for the four deferent extrusions die radius. It is obvious that the average pressuring load was remanded almost unchanged (with increasing trend) for the variation of extrusion radius form Ra=1 mm to Ra=4 mm. On the other hand, the flow stress point was moved righter at the pressuring load-time curve, for the same extrusion radius variations. Figure 3 shows the von-Misses strains of the billet material during the extrusion process. By increasing the extrusion die radius from Ra=1 mm to Ra=4 mm, the von-Misses strain in the billet material, was decreased and as a result a better surface quality was produced on the ex-truded billet. Finally, if the simulations results of pressuring load and von-Misses strains were considered together, it could be concluded that the optimum extrusion die radius could be esti-mated at Ra=1mm.

Extrusion die radius Ra=1mm Extrusion die radius Ra=2mm

Extrusion die radius Ra=3mm Extrusion die radius Ra=4mm

Figure 3: Von-Misses strains for various extrusions die radius with constant temperature

(400oC)

Forming 219

3.2. Effect of extrusion parameters on the developed billet quality According to the optimum extrusion die radius Ra=1 mm, the effect of other extrusion parame-ters (extrusion speed and temperature) was investigated on the produced billet quality. Figures 4, 5 and 6 illustrate the effect of extrusion speed and temperature on the pressuring load.

Extrusion speed 1mm/s Extrusion speed 2 mm/s

Extrusion speed 3 mm/s

Figure 4: Pressuring load for various extrusion speeds at 400oC

220 3rd

ICMEN – 2008

Extrusion speed 1mm/s Extrusion speed 2 mm/s

Extrusion speed 3 mm/s

Figure 5: Pressuring load for various extrusion speeds at 450oC

Forming 221

Extrusion speed 1mm/s Extrusion speed 2 mm/s

Extrusion speed 3 mm/s

Figure 6: Pressuring load for various extrusion speeds at 500oC By increasing the extrusion speed from 1 to 3 mm/s the average pressuring load was increased. The reason is that during the faster billet sliding through the die, the dispatch and the dead zone was increased. On the other hand the pressuring load was decreased as the extrusion tempera-ture increases, whilst seems to be independent of the extrusion speed. Figures 7, 8 and 9 illustrate the effect of extrusion speed and temperature on the von-Misses strains in billet material.

222 3rd

ICMEN – 2008

Extrusion speed 1mm/s Extrusion speed 2 mm/s

Extrusion speed 3 mm/s

Figure 7: Von-Misses strains for various extrusion speeds at 400oC

Forming 223

Extrusion speed 1mm/s Extrusion speed 2 mm/s

Extrusion speed 3 mm/s

Figure 8: Von-Misses strain for various extrusion speeds at 450oC

224 3rd

ICMEN – 2008

Extrusion speed 1mm/s Extrusion speed 2 mm/s

Extrusion speed 3 mm/s

Figure 9: Von-Misses strains for various extrusion speeds at 500oC As a result, for the extrusion speed values 1 and 3 mm/s and temperature 400 oC and 500oC, it could be concluded that the von-Misses strain of the billet material was kept almost unchanged. On the other hand for the extrusion speed value 2 mm/s and the same temperature range, the von-Misses strains of the billet material were increased. Figures 10,11 and 12 illustrate the effect of extrusion speed and temperature on the von-Misses stress.

Forming 225

Extrusion speed 1mm/s Extrusion speed 2 mm/s

Extrusion speed 3 mm/s

Figure 10: Von-Misses stress for various extrusion speeds at 400oC

226 3rd

ICMEN – 2008

Extrusion speed 1mm/s Extrusion speed 2 mm/s

Extrusion speed 3 mm/s

Figure 11: Von-Misses stress for various extrusion speeds at 450oC

Forming 227

Extrusion speed 1mm/s Extrusion speed 2 mm/s

Extrusion speed 3 mm/s

Figure 12: Von-Misses stress for various extrusion speeds at 500oC As the extrusion speed was ranged from 1 to 3 mm/sec, the von-Misses stress of the billet ma-terial was increased, not depending on the extrusion temperature. On the other hand, as the temperature was increased from 400 to 500oC, the von-Misses strain of the billet material was decreased. The reason is that the billet can plunge into the die more easily. 4. CONCLUSIONS Based on this study, the most remarkable results can be drawn from the evaluation of simula-tion data:

o In order to investigate the effect of extrusion die radius on the developed billet quality, the extrusion parameters are kept unchanged for all the simulations process (Extrusion speed: 1mm/s, temperature 400oC). As a result, when the extrusion radius of the die was increased

228 3rd

ICMEN – 2008

from 1 to 4 mm, the average extrusion force was kept almost unchanged. In contrast the von-Misses strains in the billet were increased for the same extrusion radius ranges.

o If the average pressuring load and von-Misses strains were considered together, it could be concluded that the optimum extrusion radius of the die could be estimated at Ra=1 mm.

o It was observed that when the extrusion temperature was increased form 400 oC to 500oC the average extrusion force and the von-Misses stress of the billet was decreased. On the other hand the von-Misses strain of the billet was kept almost unchanged, for the same ex-trusion temperature changes.

o If the extrusion speed was increased form 1 to 3 mm/s, the average extrusion force and the von-Misses stress of the billet was increased. On the other hand the von-Misses strain of the billet was kept almost unchanged, for the same extrusion velocity changes.

o The most remarkable result concluded from the simulating process is that extrusion tem-perature and speed were independent variables.

5. ACKNOWLEDGEMENT

The work presented in this paper was financially supported by the Cyprus Research Promotion Foundation in the frame of the research project entitled “Improvement of the working life of alu-minum extrusion dies by means of advance and innovative procedures”.

6. REFERENCES

1. T. Chanda, J. Zhou, J. Duszczyk, A comparaitive study on iso-speed extrusion and isother-mal extrusion of 6061 Al alloy using 3D FEM simulation, J. of Material Processing Technol-ogy, 114 (2001), 145-153.

2. T. Chanda, J. Zhou, J. Duszczyk, FEM analysis of aluminium extrusion through square and round dies, J. of Material and Design, 21 (2000), 323-335.

3. T. Chanda, J. Zhou, L. Kowalski, J. Duszczyk, 3D FEM simulation of the thermal events dur-ing AA6061 aluminium extrusion, Scripta Materialia, vol 41, No 2, pp 195-202, 1999.

4. C. Sommitsch, R. Sievert, T. Wlanis, B. Gu¨nther, V. Wieser, Modelling of creep-fatigue in ontainers during aluminium and copper extrusion, J. of Computer Materials Science, 39 (2007), 55-64.

5. E.M. Herba, H.J. McQueen, Influence of particulate reinforcements on 6061 materials in ex-trusion modelling, J. of Materials Science and Engineering A, 372 (2004), 1-14.

6. Tze-Chi Hsu, Chien-Chin Huang, The friction modelling of different tribological interface in extrusion process, J. of materials processing technology, 140 (2003), 49-53.

7. DEFORM-2D manual, Scientific Forming Technologies Corporation.

8. Dyi-Cheng Chen, Cheng-Fu Chen, Use of Taguchi method to develop a robust design for the shape rolling of porous sectioned sheet, J. of Materials Processing Technology 2006; 177:104–108.

9. Dyi-Cheng Chen, Rigid-plastic finite element analysis of plastic deformation of porous metal sheets containing internal void defects, J. of Materials Processing Technology 2006; 180: 193–200.