EFFECT OF EXTRUSION PARAMETERS AND DIE GEOMETRY ON THE PRODUCED BILLET QUALITY USING FINITE ELEMENT METHOD

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1 EFFECT OF EXTRUSION PARAMETERS AND DIE GEOMETRY ON THE PRODUCED BILLET QUALITY USING FINITE ELEMENT METHOD A.Ε. Lontos 1, 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 (Equivalent stress and strain) using F.E.M. technique. For this purpose the general F.E.A. software Deform-2D has been used to set up the finite element model of the warm aluminium extrusion in two dimensions (2D) 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 400 o C to 500 o C and the extrusion die radius was varied from 1 to 4 mm. The friction 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. Optimized algorithms for extrusion parameters were proposed regarding 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 products 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 quality using Finite Element Method /1-6/. 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 (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 performance operating on extrusion dies. Proceedings of the 3 rd 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

2 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 simulation 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 ( o C): 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 assumption 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 generated, 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 Ultimate tensile Yield tensile Modulus of (gr/cm 3 ) strength (MPa) strength (MPa) elasticity (GPa) Poisson s ratio Machinability (%) Shear modulus (GPa) Shear strength (MPa) Thermal conductivity (W/m-K) Al (%) Cr (%) Cu (%) Fe (%) Mg (%) <= Mn (%) Si (%) Ti (%) Zn (%) <= <=0.15 <= rd ICMEN 2008

3 rigid-vistoplastic material) /7/. The mechanical properties and chemical composition of billet material 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 analysis 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 (400 o C) Forming 217

4 radius. The simulations were obtained with constant temperature 400 o C 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 extruded 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 estimated 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 (400 o C) rd ICMEN 2008

5 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 parameters (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 Figure 4: Pressuring load for various extrusion speeds at 400 o C Forming 219

6 Figure 5: Pressuring load for various extrusion speeds at 450 o C rd ICMEN 2008

7 Figure 6: Pressuring load for various extrusion speeds at 500 o C 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 temperature 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. Forming 221

8 Figure 7: Von-Misses strains for various extrusion speeds at 400 o C rd ICMEN 2008

9 Figure 8: Von-Misses strain for various extrusion speeds at 450 o C Forming 223

10 Figure 9: Von-Misses strains for various extrusion speeds at 500 o C As a result, for the extrusion speed values 1 and 3 mm/s and temperature 400 o C and 500 o C, 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 rd ICMEN 2008

11 Figure 10: Von-Misses stress for various extrusion speeds at 400 o C Forming 225

12 Figure 11: Von-Misses stress for various extrusion speeds at 450 o C rd ICMEN 2008

13 Figure 12: Von-Misses stress for various extrusion speeds at 500 o C As the extrusion speed was ranged from 1 to 3 mm/sec, the von-misses stress of the billet material was increased, not depending on the extrusion temperature. On the other hand, as the temperature was increased from 400 to 500 o C, 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 simulation 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 400 o C). As a result, when the extrusion radius of the die was increased Forming 227

14 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 o C to 500 o C 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 extrusion 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 temperature 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 aluminum 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 isothermal extrusion of 6061 Al alloy using 3D FEM simulation, J. of Material Processing Technology, 114 (2001), T. Chanda, J. Zhou, J. Duszczyk, FEM analysis of aluminium extrusion through square and round dies, J. of Material and Design, 21 (2000), T. Chanda, J. Zhou, L. Kowalski, J. Duszczyk, 3D FEM simulation of the thermal events during AA6061 aluminium extrusion, Scripta Materialia, vol 41, No 2, pp , 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), E.M. Herba, H.J. McQueen, Influence of particulate reinforcements on 6061 materials in extrusion modelling, J. of Materials Science and Engineering A, 372 (2004), Tze-Chi Hsu, Chien-Chin Huang, The friction modelling of different tribological interface in extrusion process, J. of materials processing technology, 140 (2003), 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: 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: rd ICMEN 2008