THE COMPUTER SIMULATION AND THE EXPERIMENTAL RESEARCH ON THE STRESS FORCES OF THE COMBINED EXTRUSION OF DIFFERENT SIZED ALUMINUM STAMPINGS

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1 THE COMPUTER SIMULATION AND THE EXPERIMENTAL RESEARCH ON THE STRESS FORCES OF THE COMBINED EXTRUSION OF DIFFERENT SIZED ALUMINUM STAMPINGS Piotr THOMAS Kielce University of Technology, Al. 0-lecia P.P. 7, Kielce, Poland, EU, Abstract Combined extrusion can be described as simultaneous forward extrusion of the cylindrical part and backward extrusion of the sleeved part of the stamping. The paper presents results of the computer simulation of the combined extrusion for different values of the relative deformations in the ranges of stress forces and unitary stresses. Obtained results were verified experimentally. The paper presents the also simulation and experimental research results of backward and forward extrusion for the same relative deformations. It has been proved that in the case of combined extrusion stress forces are smaller than in the case of shaping of stampings of this type by two operations, when the first operation is the extrusion of the cylindrical part of the stamping and the second one is the backward extrusion of the sleeved part. Application of combined extrusion decreases labour consumption of the production of stampings of this type, tool costs and due to decreased stress forces increases their durability. Keywords: aluminum, combined extrusion, forward extrusion, backward extrusion. 1. INTRODUCTION In industry, several shaping operations are used to make complex-shaped products. The technological process designed in this way can be used in one poly seating press or in several stamping dies on various presses Although dividing the technology into several operations (among others backward extrusion and forward extrusion with heat treatment) is not economical, it often results from a complex shape of an element as well as from maximum forces of unitary stresses acting on the tools [4,5,6,7,8,9,10,11]. Applying combined extrusion eliminates some shaping operations thus causing the decrease in both the labour consumption and its instrumentation costs as well as resulting in the reduction of unitary stresses values. The unitary stresses are considerably lower under combined extrusion than under forward and backward extrusion [1,2,3]. Since the material used in combined extrusion is technologically limited, it is appropriate to conduct research on combined extrusion, both in computer simulation and experimental research. The results of the research will be the basis for utilitarian applications of the process. 2. THE RESULTS OF THE RESEARCH Aluminium discs A1 99,5% (ENAW-1050A) in soft state, with outer diameter d 0 =24,95 mm and height h 0 =16mm were used to the combined extrusion process. The work piece element s mechanical properties, calculated on the basis of statistical tension test that was carried out according to PN-EN 02-1+AC1[12], were presented in Table 1 (columns 2-6).

2 Tab. 1 Aluminum A1 99,5% (ENAW-1050A) properties Material R 0,2 R m A A 11,3 Z C n [MPa] [MPa] [%] [%] [%] [MPa] A1 99,5% ,25 Material constant - C and flow curve exponent - n were presented in Table 1 (columns 7 and 8). Both coefficients values were determined by the method of upsetting of Rastigaiev samples with undercuts. In order to compare the values of stress forces that appear in backward and combined extrusion, experimental research were carried out by performing backward extrusion on a research stand used for combined extrusion. The tests were conducted with the ejector raised, which unabled simultaneous forward flow of the material. The diagram of backward extrusion is shown in Fig.1. Fig.1 The diagram of backward extrusion of aluminum stampings for values of relative deformation in backward part 2=0,64 (d s = mm) with the use of die insert and flat conical punch: 1 die insert, 2 flat conical punch (15 o ), 3 ejector, 4 workpiece element, 5- stamping. Fig.2 Dependence of punch pressure forces on displacement - for backward extrusion. The values obtained in the experiment (continuous line) and during simulation (dashed line) for relative deformations values: 2=0,41 (d S =16 mm), 2=0,52 (d S =18 mm), 2 =0,64 (d S = mm). Backward extrusion was carried out for three values of relative deformations in backward direction: 2 =0,41 (d s =16 mm), 2 =0,52 (d s =18 mm), 2 =0,64 (d s = mm) with the use of die insert and flat conical punch 15 o. Computer simulation of backward extrusion was conducted for the achieved tools measurements and shapes. Fig. 2 presents the dependence of punch pressure forces on displacement,for the above mentioned strain values 2. The continuous line refers to values of pressure forces obtained during experimental research, the dashed line - tovaluesobtained during computer simulation. Studying the values of pressure forces presented in Fig. 2 it can be seen that maximum values of stress forces obtained during simulation are higher by 29% (for 2=0,41), by 32% (for 2=0,52) and by 57% (for 2=0,64) than those obtained in the experimental research. The next step is to comparereal values of forces for combined extrusion and forward extrusion, which were obtained in experimental research and computer simulation. Therefore, experimental research of forward

3 extrusion for three various parameters of relative deformations in forward direction: 1 =0,77 (d 1 =12 mm), 1=0,69 (d 1 =14 mm) and 1 =0,59 (d 1 =16 mm) were made with the use of flat die inserts. Flat punch with the mean diameter equal to inner diameter of die insert in backward part was used during forward extruding. The diagram of forward extrusion was shown in Fig. 3. Fig. 4 shows the dependence of punch pressure forces on displacement for forward extruding for various values of relative deformations 1. The continuous lines refer to the results of experimental research, while the dashed lines the results of computer simulation. The maximum values of stress forces obtained during simulation are similar to the results of the experiment, particularly for higher values of relative deformations =0,77 1=0,77 1=0,69 1=0,69 1=0,59 1=0, Fig.3 The diagram of forward extrusion of aluminum stampings for the values of relative deformations in the forward part 1 =0,77 (d 1 =12 mm) with the use of flat die insert with flat punch: 1 - flat die insert, 2 - flat punch, 3 workpiece, 4 stamping. Fig.4 The dependence of punch pressure forces on displacement for forward extrusion. The values obtained in the test (continuous line) and during simulation (dashed line) for relative deformations: 1 =0,77 (d 1 =12 mm), 1 =0,69 (d 1 =14 mm), 1 =0,59 (d 1 =16 mm). In order to compare the dependence of punch pressure forces on displacement for backward, forward and combined extrusion, the values of the forces were juxtaposed; backward with combined extrusion, and separately, forward with combined extrusion. Such a juxtaposition is necessary because of high values of stress forces that appear during forward extruding. Presenting the results of forward, backward and combined extrusion on one graph results in the lapping of the forces values for backward and combined extrusion. Fig. 5 and 6 juxtapose the results of experimental research of combined extrusion (continuous black lines) with backward extrusion (continuous red lines). The results were obtained for the same values of strain deformations 1=0,84=const (d 1 =10 mm) in the forward direction (combined extrusion); and two various 2 values in the backward direction (for combined and backward extrusion). Besides, computer modeling of both combined extrusion (dashed black line) and backward extrusion (dashed red line) was carried out for the same values 1 and 2 of relative deformations. The diagrams of forces as a function of punch displacement was approximated by fourth-degree polynomial function using the least square method. The above mentioned function maps the results of the computer modeling best. For displacements smaller than 14 mm, the earlier completion of the process in a computer simulation is associated with a greater intensity of material flow in the forward direction. It can be assumed

4 that both in combined and backward extrusions (experimental investigation) there is a slow increase of pressure forces in the first stage, when the cone shaped face of the punch is forced into the material. Only after the cone shaped part of the punch is pushed inside, does the intensive growth of pressure force appear. Further stages of extrusion can even show a decrease of the force, while the values of relative deformation 2 are lower.(fig. 5,6). In case of computer simulation, there is an intensive growth of stress forces from the very beginning of the extrusion process, both for combined and backward extrusion. Comparing the maximum values of pressure forces, for the same values of relative deformations 2, both for combined and backward extrusion, it can be observed that they are higher in backward than combined extrusion (by 7,6 15% - during the experiment, and 12,3-54,2 % - during simulation, for 1 =0,84 (d 1 =10 mm, Fig. 5 i 6). In combined extrusion, the decrease of pressure forces values, may result in the increase of tool parts life due to their limited ultimate load Fig.5 The dependence of punch pressure forces on and backward extrusion (red lines) obtained in the experiment (continuous lines) and simulation (dashed lines) for the values of relative deformations: 1=0,84 (d 1 =10 mm) and 2=0,41 (d S =16 mm). Fig.6 The dependence of punch pressure forces on and backward extrusion (red lines) obtained in the experiment (continuous lines) and simulation (dashed lines) for the values of relative deformations: 1=0,84 (d 1 =10 mm) and 2 =0,64 (d S = mm). Fig. 7 and 8 show the results of experimental research of forward extrusion (blue line) and combined extrusion (black line). Pressure forces were calculated for three relative deformations values 2 for combined extrusion and a constant value of relative deformation 1 for forward and combined extrusion. In Fig.7 1 =0,77=const (d 1 =12 mm) and in Fig. 8, 1=0,59=const (d 1 =16 mm). For relative deformation s values 1=0,77=const, the maximum force value is higher under forward extrusion than under a combined extrusion by o 161% for 2=0,64 (d S = mm), 277% for 2=0,52 (d S =18 mm), 397% for 2=0,41 (d S =16 mm), which was shown in Fig. 7. In the case of 1 =0,59=const, these differences are : 61% for 2 =0,64 (d S = mm), 130% for 2 =0,52

5 (d S =18 mm), 190% for 2 =0,41 (d S =16 mm, Fig. 8), respectively. Therefore, shaping the workpiece elements using combined extrusion eliminates the need of stamping extrusion in the course of two technological operations (forward and backward extrusion), which reduces the labour consumption and tool production costs. On the other hand, however, it reduces the maximum value of shaping force almost fourfold in comparison to forward extrusion (Fig.7) for maximum values of relative deformations 1 ; and for low values of deformations 2, it reduces the maximum value of pressure force by 50% in comparison with backward extrusion (Fig.5.). The latter results in the prolongation of tools durability e 1 =0,59 e 2 =0,64 e 2 =0,52 e 2 =0, e 1 =0,59 e 2 =0,64 e 2 =0,52 e 2 =0, Fig.7 The dependence of punch pressure forces on and forward extrusion (blue line) obtained in the experiment for the values of relative deformations: 1=0,77=const (d 1 =12 mm) and 2=0,41; 0,52; 0,64 (d S =16, 18, mm). Fig.8 The dependence of punch pressure forces on and forward extrusion (blue line) obtained in the experiment for the values of relative deformations: 1=0,59=const (d 1 =16 mm) and 2=0,41; 0,52; 0,64 (d S =16, 18, mm). 3. CONCLUSSIONS On the grounds of experimental researching and calculations with the use of MES, it can be concluded that: Proper defining of flow stress work-hardening curves, geometric data and technological parameters made it possible to carry out computer simulation of combined extrusion and to compare the obtained results with the results of experimental research. The increase of relative deformations values and material) brings about the increase of punch pressure forces both during computer simulation and during experimental research. When comparing maximum press forces values in combined and backward extrusion it can be observed that the stress forces are higher during backward than combined extrusion: from 8% to 54% (during experiments) and form 13% to 94% (during simulation) - depending on the values of relative deformations 1 and 2. During experimental research the maximum values of pressure forces are higher in forward than combined extrusion from 61% to 397% depending on the values of relative deformations 1 and 2.

6 The results of the research on combined extrusion of the stampings, presented in the paper, may provide guidance on the designing of technological processes in industry. It should be stressed that the results of computer simulations and experiments that were presented in the paper, not only indicated the advantages of combined extrusion process over the forward and backward extrusion but also developed knowledge on combined extrusion. Shaping elements with the use of combined extrusion eliminates the need of producing cylindrical and sleeved stampings in two technological operations; where the former produces the cylindrical part by forward extrusion, while the latter the sleeved part of the stamping- by backward extrusion. This reduces labour consumption and tool production costs and decreases shaping forces thus influencing the durability of instrumentation. REFERENCES [1] CHAŁUPCZAK J., THOMAS P. Experimental investigation on the combined of the extrusion of aluminium stampings aluminium. Rudy i Metale Nieżelazne, Nr 10-11, Kraków 04, s [2] CHAŁUPCZAK J., THOMAS P. Computer simulation and experimental investigation on stress forces in combined extrusion. Materiały XIII Konferencji KomPlasTech, Szczawnica 06, s [3] CHAŁUPCZAK J., THOMAS P. Simulation vom komplexen Fliesspressen der Aluminiumfliesspressteile, Transcom 05, 6-th European Conference of Young Research and Science Workers in Transport and Telecommunications, Źilina 05, s [4] KRAKOWIAK, M. The analysis of pressure in backward extrusion of semi-liquid AlSi7Mg aluminium alloy. Rudy i Metale Nieżelazne, 10, R. 55, nr 8, s [5] LEŚNIAK D., RĘKAS A., LIBURA W., ZASADZIŃSKI J. Extrusion welding of tubes from 24 alloy. Metal Forming 12 proceedings of the 14th international conference on Metal Forming, September 16 19, 12, Krakow, Poland s [6] LEŚNIAK D., RĘKAS A., LIBURA W., ZASADZIŃSKI J. Numerical investigations of welding conditions during extrusion of 24 alloy through porthole dies. Key Engineering Materials, 12 vol. 491 s [7] LIBURA W., LEŚNIAK D., RĘKAS A., ZASADZIŃSKI J. Numerical analysis of multi-hole extrusion of profiles from {Al-Mg} alloy. Rudy i Metale Nieżelazne 10 R. 55 nr 1 s [8] MATERNIAK J. Obróbka plastyczna materiały pomocnicze cześć I: Wyciskanie metali na zimno, Wydawnictwo Politechniki Poznańskiej, Poznań [9] RĘKAS A., LIBURA W., GALANTY M., ZASADZIŃSKI J., BORYCZKO B. Analysis of the state of stresses and strains in the extrusion of tubes of square section of aluminium alloy. Rudy i Metale Nieżelazne 10 R. 55 nr 11 s [10] ZASADZIŃSKI J., RĘKAS A., LIBURA W., RICHERTJ., LEŚNIAK D. Numerical analysis of aluminum alloys extrusion through porthole dies. Key Engineering Materials 10 vol. 424 s [11] ZASADZIŃSKI J., RICHERT J., LIBURA W., GALANTY M., LEŚNIAK D., RĘKAS A. Selection of welding conditions for hard aluminium alloys assigned for extrusion of profiles through porthole dies. Rudy i Metale Nieżelazne 09 R. 54 nr 3 s [12] PN-EN 02-1+AC1 Tension Test.