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Preform design in axisymmetric forging by a new FEM–UBET method
Journal of Materials Processing Technology 74 (1998) 218 – 222
Preform design in axisymmetric forging by a new FEM–UBET method Qingbin Liu a, Wu Shichun a,*, Sun Sheng b a
Department of Materials Science and Engineering, Northwestern Polytechnical Uni6ersity, Xi’an 710072 People’s Republic of China b Shandong Uni6ersity of Technology, Jinan 250065 People’s Republic of China Received 22 November 1996
Abstract This paper presents a preform design method which combines the FEM-based forward simulation and the UBET-based reverse simulation techniques. The procedure is introduced briefly. The billet designed using the new technique may achieve a final forging with minimum flash. A gear blank forging is used as an example to demonstrate the preform design. The successful application of the method is shown. © 1998 Elsevier Science S.A. Keywords: Preform design; Axisymmetric forging; FEM–UBET method
1. Introduction In conventional forging process design, the tool designer must determine the required number of intermediate stages, the preform or intermediate die shape design, the billet dimensions and the process conditions, according to the given final product shape and material. These operations are performed primarily according to rule of thumb and using equations and data from forging-design handbooks or designers’ experience. This prevailing procedure is effective, but it is difficult to control quantitatively the metal flow in a die cavity. For example, it is not known what is the simplest preform figure for a complicated forging, nor what is the optimum flash geometry to obtain full filling of a cavity with minimum material waste. The formation of flash restricts the lateral flow of material and thus facilitates the filling of the die filling, the excess material of the flash being trimmed upon completion of the forging process. The cost of excess material amounts to 15% of the total forging cost and the trimming process incurs additional machining costs [1]. The forging load, which affects the die wear rate, could be reduced dramatically if flash lands can be eliminated.
* Corresponding author. 0924-0136/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S 0 9 2 4 - 0 1 3 6 ( 9 7 ) 0 0 2 7 1 - 9
To simulate the metal plastic forming process using a computer becomes a very effective way to improve the scientific basis of forming design. It may provide a means of substituting traditional preform design methods, effectively improving the level of forging-die design and controlling the quality of products through optimization of the process parameters. In this way, it could provide quantitatively much valuable information in relation to forming design and answer some questions that are not covered by rule of thumb. The results of simulation design do not have to be produced in actuality, so that some design objectives, such as excellent quality, minimum raw material and optimum metal flow could be achieved by comparing different simulation results, using various design data. Therefore, numerical simulation technology is essential to preform design. Nowadays, keen competition in the machine industry is strongly promoting reduction of cost in metal forming. Great attention is being paid to forming techniques that yield a final net shape or near net shape. Therefore, it becomes very important to perform a reasonable preform design. Park et al. [2] developed the backward-tracing method for preform design on the basis of a rigid– visco-plastic finite-element method. The process begins with the workpiece in the final product shape, with the deformation simulation conducted in reverse. Hwang
Q. Liu et al. / Journal of Materials Processing Technology 74 (1998) 218–222
and Kobayashi studied preform designs in disk forging [3], plane-strain rolling [4] and in the shell-nosing process at elevated temperature [5] by the back-tracing technique, based on the finite-element method. They also applied the FEM backward-tracing scheme in the design of preform shapes for an H-shaped cross-section axisymmetric forging problem [1]. Kang et al. [6,7] established systematic approaches for the preform design in a plane-strain forging problem using the FEMbased back-tracing scheme. Zhao et al. [8] presented a preform design method which employs an alternative boundary node release criterion in the finite-element simulation of backward deformation of forging processes. Using a reverse simulation technique based on UBET, Sun et al. [9 – 11] presented a design method for controlling metal flow and optimizing the yield of raw material. In this paper, a new preform design method, the so called FEM–UBET method, is presented, which combines FEM-based forward simulation with UBETbased reverse simulation technology. Using a complex axisymmetric gear-blank forging as an example, a preform shape developed by the present method is compared with one designed using empirical guidelines.
2. FEM–UBET preform design method Computer-aided simulation based on rigid – plastic or rigid –visco-plastic FEM has become essential in mod-
Fig. 1. Schematic flow chart of the design procedure.
219
Fig. 2. Dimensions and configuration of the gear-blank forging.
ern metal forming die and process design. There is no doubt that conventional FEM-based forward simulation of metal forming has played an important role in predicting the metal flow patterns and the formation of defects and for studying the effects of various technology parameters on product quality [12,13]. However, because the forward-simulation procedure is analogous to the practical production process, its primary contribution has been to verify the die designs obtained by using empirical design guidelines or a designer’s intuition. Unlike forward simulation, preform design carried out through reverse simulation follows a similar process as used by tool designers, where the die shapes and process conditions are determined according to the given product shape and material property requirements. Thus, it can be said that reverse simulation and the related preform design have a more direct and active function in forging die design. However, there are still reservations in applying FEM-based reverse simulation in production because of its cost and complexity, such as the treatment of boundary conditions, etc. UBET-based reverse simulation technology substitutes a curved boundary with a straight-line boundary. It is relatively simple, but the precision of the simulation results is lower than that for the FEM-based reverse simulation method. However, the method could provide relatively satisfactory results for some complex forgings, such as gear-blank forging [9,10]. Thus, a new FEM–UBET preform design method is presented, the method combining FEM-based forward simulation with UBET-based reverse simulation technology. The details of the FEM-based forward simulation and UBET-based reverse simulation technique are described elsewhere [12,14,15]. The procedure (shown in Fig. 1) consists of the following steps. 1. Obtain information on the material flow from the FEM-based forward simulation of test preforms. 2. Design a preform by the UBET-based reverse simulation method according to the information obtained from (1) above.
220
Q. Liu et al. / Journal of Materials Processing Technology 74 (1998) 218–222
3. Check the preform by FEM-based forward simulation to determine whether or not it satisfies the final design conditions. If the preform satisfies the final design conditions, stop here. Otherwise, obtain the sequence of the boundary changes of the die – workpiece interface to be used during the UBET-based reverse simulation in the next step.
Fig. 3. Metal flow patterns during the FEM forward simulation using empirical preform design: (a) initial mesh; (b) DH/H=63.4%; (c) DH/H= 72.9%; and (d) DH/H= 78.6%.
Fig. 4. Metal flow patterns during the FEM forward simulation using the FEM – UBET preform design method: (a) initial mesh; (b) DH/ H =59.5%; (c) DH/H=83.6%; and (d) DH/H=87.2%.
Q. Liu et al. / Journal of Materials Processing Technology 74 (1998) 218–222
221
Fig. 5. Photographic comparison of the results using rule of thumb methods (left) with those using the new preform-design method (right).
4. Use the UBET-based reverse simulation to improve the preform in order to satisfy the final design conditions. After obtaining a possible preform shape, return to step (3). The new method can control metal flow and optimize the yield of raw material. The billets designed using this technique not only have a simple configuration, but can also achieve a final forging with minimum flash.
An experimental billet prepared according to the preform design was forged directly, using the normal process conditions. It was seen that the die cavity was completely filled and that the flash, generally, flowed out uniformly around the die parting line. Thus the new FEM–UBET preform design method and its outcome have proven to be successful. Fig. 5 presents a photographic comparison of the final forging with its flash from a billet chosen by rule of thumb and a billet designed using the new preform design technique.
3. Application example
4. Conclusions
The design of an optimal preform shape requires the simultaneous determination of the optimal process conditions. However, what is of concern here is the determination of the best preform shape under a given set of process conditions. A gear-blank forging with an axisymmetric cross-section was selected to demonstrate preform design using the new FEM – UBET method described above. Fig. 2 presents a drawing of the final forging without flash. The computational results depend on forging parameters such as interface friction, forging speed and material properties. The following computational conditions are used: friction factor at the die–workpiece interface m=0.3; the friction stress being expressed using an arctangent function; forging speed=1.0; material properties of industrial pure lead expressed by s¯ =2.5(1 +o¯; 0.093/1.105) MPa. Since the forging is symmetrical about the vertical axis, only one half of the cross-section is considered for analysis. Fig. 3 shows the material flow during the FEM-based forward simulation of the gear-blank forging with empirical preform design. The dimensions of the initial billet are F65 × 28 mm. Material flow during the FEM forward-deformation simulation using the FEM– UBET preform design (F50 × 47 mm) is shown in Fig. 4. From Fig. 3 and Fig. 4, it can be concluded that the billet designed using the new technique can achieve a final forging with minimum flash.
In this paper, a new FEM–UBET preform design method is presented. The method combines FEM-based forward simulation with UBET-based reverse simulation technology. A gear-blank forging is used to demonstrate preform design. The billets designed using the technique may achieve a final forging with minimum flash. The method has been proven by experiment and the results are very successful.
Acknowledgements The authors are grateful to the Aeronautic Science Foundation of the Aviation Industrial of China for enabling the carrying out of this investigation. They also wish to thank Liu Hong for typing the manuscript.
References [1] K. Naksoo, S. Kobayashi, Preform design in H-shaped cross sectional axisymmetric forging by the finite element method, Int. J. Mach. Tools Manuf. 30 (1990) 243 – 268. [2] J.J. Park, N. Rebele, S. Kobayashi, A new approach to preform design in metal forming with finite element method, Int. J. Mach. Tool Des. Res. 23 (1983) 71 – 99. [3] S.M. Hwang, S. Kobayashi, Preform design in disk forging, Int. J. Mach. Tool Des. Res. 26 (1986) 231 – 243.
Q. Liu et al. / Journal of Materials Processing Technology 74 (1998) 218–222
222
[4] S.M. Hwang, S. Kobayashi, Preform design in plane-strain rolling by the finite element method, Int. J. Mach. Tool Des. Res. 24 (1984) 253 – 266. [5] S.M. Hwang, S. Kobayashi, Preform design in shell nosing at elevated temperatures, Int. J. Mach. Tools Manuf. 27 (1987) 1 – 14. [6] B.S. Kang, N. Kim, S. Kobayashi, Computer-aided preform design in forging of an airfoil section blade, Int. J. Mach. Tools Manuf. 30 (1990) 43 – 52. [7] B.S. Kang, J.H. Lee, B.M. Kim, J.C. Choi, Process design in flashless forging of rib-web-shaped plane-strain components by the finite element method, J. Mater. Process. Technol. 47 (1995) 291 – 309. [8] Z. Guoqun, E.D. Wright, R.V. Grandhi, Forging preform design with shape complexity control in simulating backward deformation, Int. J. Mach. Tools Manuf. 35 (1995) 1225–1239. [9] Sun Sheng, Luan Yiguo, A die forging design approach controlling flash formation based on reverse simulation technique and its application, in: Advanced Technology of Plasticity, Proceedings
.
.
[10]
[11]
[12] [13] [14] [15]
of the Fourth International Conference on Technology of Plasticity, Beijing, People’s Republic of China, 1993, pp. 1193 – 1198. S. Sheng, L. Yiguo, A die forging design approach for controlling metal flow way and its application in practice, Int. J. Mach. Tools Manuf. 34 (1994) 161 – 167. Sun Sheng, Luan Yiguo, Liu Qingbin, A new approach for plastic forming process simulation and its application, Advances in Engineering Plasticity and its Applications, Elsevier Applied Science,Barking, UK, 1993, pp. 887 – 892. S. Kobayashi, S.I. Oh, T. Altan, Metal Forming and the Finite Element Method, Oxford University Press, London, 1989. T. Altan, S.I. Oh, Application of FEM to 2-D metal flow simulation: Practical example, Adv. Technol. Plasticity 4 (1990) 1779–1788. A.N. Bramley, Computer aided forging design, Ann. CIRP 36 (1987) 135 – 138. S. Sheng, G. Tingdong, The reverse simulation technique of die forging based on UBET and its application, Chin. J. Mech. Eng. 4 (1991) 177 – 181.
Preform design in axisymmetric forging by a new FEM–UBET method Qingbin Liu a, Wu Shichun a,*, Sun Sheng b a
Department of Materials Science and Engineering, Northwestern Polytechnical Uni6ersity, Xi’an 710072 People’s Republic of China b Shandong Uni6ersity of Technology, Jinan 250065 People’s Republic of China Received 22 November 1996
Abstract This paper presents a preform design method which combines the FEM-based forward simulation and the UBET-based reverse simulation techniques. The procedure is introduced briefly. The billet designed using the new technique may achieve a final forging with minimum flash. A gear blank forging is used as an example to demonstrate the preform design. The successful application of the method is shown. © 1998 Elsevier Science S.A. Keywords: Preform design; Axisymmetric forging; FEM–UBET method
1. Introduction In conventional forging process design, the tool designer must determine the required number of intermediate stages, the preform or intermediate die shape design, the billet dimensions and the process conditions, according to the given final product shape and material. These operations are performed primarily according to rule of thumb and using equations and data from forging-design handbooks or designers’ experience. This prevailing procedure is effective, but it is difficult to control quantitatively the metal flow in a die cavity. For example, it is not known what is the simplest preform figure for a complicated forging, nor what is the optimum flash geometry to obtain full filling of a cavity with minimum material waste. The formation of flash restricts the lateral flow of material and thus facilitates the filling of the die filling, the excess material of the flash being trimmed upon completion of the forging process. The cost of excess material amounts to 15% of the total forging cost and the trimming process incurs additional machining costs [1]. The forging load, which affects the die wear rate, could be reduced dramatically if flash lands can be eliminated.
* Corresponding author. 0924-0136/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S 0 9 2 4 - 0 1 3 6 ( 9 7 ) 0 0 2 7 1 - 9
To simulate the metal plastic forming process using a computer becomes a very effective way to improve the scientific basis of forming design. It may provide a means of substituting traditional preform design methods, effectively improving the level of forging-die design and controlling the quality of products through optimization of the process parameters. In this way, it could provide quantitatively much valuable information in relation to forming design and answer some questions that are not covered by rule of thumb. The results of simulation design do not have to be produced in actuality, so that some design objectives, such as excellent quality, minimum raw material and optimum metal flow could be achieved by comparing different simulation results, using various design data. Therefore, numerical simulation technology is essential to preform design. Nowadays, keen competition in the machine industry is strongly promoting reduction of cost in metal forming. Great attention is being paid to forming techniques that yield a final net shape or near net shape. Therefore, it becomes very important to perform a reasonable preform design. Park et al. [2] developed the backward-tracing method for preform design on the basis of a rigid– visco-plastic finite-element method. The process begins with the workpiece in the final product shape, with the deformation simulation conducted in reverse. Hwang
Q. Liu et al. / Journal of Materials Processing Technology 74 (1998) 218–222
and Kobayashi studied preform designs in disk forging [3], plane-strain rolling [4] and in the shell-nosing process at elevated temperature [5] by the back-tracing technique, based on the finite-element method. They also applied the FEM backward-tracing scheme in the design of preform shapes for an H-shaped cross-section axisymmetric forging problem [1]. Kang et al. [6,7] established systematic approaches for the preform design in a plane-strain forging problem using the FEMbased back-tracing scheme. Zhao et al. [8] presented a preform design method which employs an alternative boundary node release criterion in the finite-element simulation of backward deformation of forging processes. Using a reverse simulation technique based on UBET, Sun et al. [9 – 11] presented a design method for controlling metal flow and optimizing the yield of raw material. In this paper, a new preform design method, the so called FEM–UBET method, is presented, which combines FEM-based forward simulation with UBETbased reverse simulation technology. Using a complex axisymmetric gear-blank forging as an example, a preform shape developed by the present method is compared with one designed using empirical guidelines.
2. FEM–UBET preform design method Computer-aided simulation based on rigid – plastic or rigid –visco-plastic FEM has become essential in mod-
Fig. 1. Schematic flow chart of the design procedure.
219
Fig. 2. Dimensions and configuration of the gear-blank forging.
ern metal forming die and process design. There is no doubt that conventional FEM-based forward simulation of metal forming has played an important role in predicting the metal flow patterns and the formation of defects and for studying the effects of various technology parameters on product quality [12,13]. However, because the forward-simulation procedure is analogous to the practical production process, its primary contribution has been to verify the die designs obtained by using empirical design guidelines or a designer’s intuition. Unlike forward simulation, preform design carried out through reverse simulation follows a similar process as used by tool designers, where the die shapes and process conditions are determined according to the given product shape and material property requirements. Thus, it can be said that reverse simulation and the related preform design have a more direct and active function in forging die design. However, there are still reservations in applying FEM-based reverse simulation in production because of its cost and complexity, such as the treatment of boundary conditions, etc. UBET-based reverse simulation technology substitutes a curved boundary with a straight-line boundary. It is relatively simple, but the precision of the simulation results is lower than that for the FEM-based reverse simulation method. However, the method could provide relatively satisfactory results for some complex forgings, such as gear-blank forging [9,10]. Thus, a new FEM–UBET preform design method is presented, the method combining FEM-based forward simulation with UBET-based reverse simulation technology. The details of the FEM-based forward simulation and UBET-based reverse simulation technique are described elsewhere [12,14,15]. The procedure (shown in Fig. 1) consists of the following steps. 1. Obtain information on the material flow from the FEM-based forward simulation of test preforms. 2. Design a preform by the UBET-based reverse simulation method according to the information obtained from (1) above.
220
Q. Liu et al. / Journal of Materials Processing Technology 74 (1998) 218–222
3. Check the preform by FEM-based forward simulation to determine whether or not it satisfies the final design conditions. If the preform satisfies the final design conditions, stop here. Otherwise, obtain the sequence of the boundary changes of the die – workpiece interface to be used during the UBET-based reverse simulation in the next step.
Fig. 3. Metal flow patterns during the FEM forward simulation using empirical preform design: (a) initial mesh; (b) DH/H=63.4%; (c) DH/H= 72.9%; and (d) DH/H= 78.6%.
Fig. 4. Metal flow patterns during the FEM forward simulation using the FEM – UBET preform design method: (a) initial mesh; (b) DH/ H =59.5%; (c) DH/H=83.6%; and (d) DH/H=87.2%.
Q. Liu et al. / Journal of Materials Processing Technology 74 (1998) 218–222
221
Fig. 5. Photographic comparison of the results using rule of thumb methods (left) with those using the new preform-design method (right).
4. Use the UBET-based reverse simulation to improve the preform in order to satisfy the final design conditions. After obtaining a possible preform shape, return to step (3). The new method can control metal flow and optimize the yield of raw material. The billets designed using this technique not only have a simple configuration, but can also achieve a final forging with minimum flash.
An experimental billet prepared according to the preform design was forged directly, using the normal process conditions. It was seen that the die cavity was completely filled and that the flash, generally, flowed out uniformly around the die parting line. Thus the new FEM–UBET preform design method and its outcome have proven to be successful. Fig. 5 presents a photographic comparison of the final forging with its flash from a billet chosen by rule of thumb and a billet designed using the new preform design technique.
3. Application example
4. Conclusions
The design of an optimal preform shape requires the simultaneous determination of the optimal process conditions. However, what is of concern here is the determination of the best preform shape under a given set of process conditions. A gear-blank forging with an axisymmetric cross-section was selected to demonstrate preform design using the new FEM – UBET method described above. Fig. 2 presents a drawing of the final forging without flash. The computational results depend on forging parameters such as interface friction, forging speed and material properties. The following computational conditions are used: friction factor at the die–workpiece interface m=0.3; the friction stress being expressed using an arctangent function; forging speed=1.0; material properties of industrial pure lead expressed by s¯ =2.5(1 +o¯; 0.093/1.105) MPa. Since the forging is symmetrical about the vertical axis, only one half of the cross-section is considered for analysis. Fig. 3 shows the material flow during the FEM-based forward simulation of the gear-blank forging with empirical preform design. The dimensions of the initial billet are F65 × 28 mm. Material flow during the FEM forward-deformation simulation using the FEM– UBET preform design (F50 × 47 mm) is shown in Fig. 4. From Fig. 3 and Fig. 4, it can be concluded that the billet designed using the new technique can achieve a final forging with minimum flash.
In this paper, a new FEM–UBET preform design method is presented. The method combines FEM-based forward simulation with UBET-based reverse simulation technology. A gear-blank forging is used to demonstrate preform design. The billets designed using the technique may achieve a final forging with minimum flash. The method has been proven by experiment and the results are very successful.
Acknowledgements The authors are grateful to the Aeronautic Science Foundation of the Aviation Industrial of China for enabling the carrying out of this investigation. They also wish to thank Liu Hong for typing the manuscript.
References [1] K. Naksoo, S. Kobayashi, Preform design in H-shaped cross sectional axisymmetric forging by the finite element method, Int. J. Mach. Tools Manuf. 30 (1990) 243 – 268. [2] J.J. Park, N. Rebele, S. Kobayashi, A new approach to preform design in metal forming with finite element method, Int. J. Mach. Tool Des. Res. 23 (1983) 71 – 99. [3] S.M. Hwang, S. Kobayashi, Preform design in disk forging, Int. J. Mach. Tool Des. Res. 26 (1986) 231 – 243.
Q. Liu et al. / Journal of Materials Processing Technology 74 (1998) 218–222
222
[4] S.M. Hwang, S. Kobayashi, Preform design in plane-strain rolling by the finite element method, Int. J. Mach. Tool Des. Res. 24 (1984) 253 – 266. [5] S.M. Hwang, S. Kobayashi, Preform design in shell nosing at elevated temperatures, Int. J. Mach. Tools Manuf. 27 (1987) 1 – 14. [6] B.S. Kang, N. Kim, S. Kobayashi, Computer-aided preform design in forging of an airfoil section blade, Int. J. Mach. Tools Manuf. 30 (1990) 43 – 52. [7] B.S. Kang, J.H. Lee, B.M. Kim, J.C. Choi, Process design in flashless forging of rib-web-shaped plane-strain components by the finite element method, J. Mater. Process. Technol. 47 (1995) 291 – 309. [8] Z. Guoqun, E.D. Wright, R.V. Grandhi, Forging preform design with shape complexity control in simulating backward deformation, Int. J. Mach. Tools Manuf. 35 (1995) 1225–1239. [9] Sun Sheng, Luan Yiguo, A die forging design approach controlling flash formation based on reverse simulation technique and its application, in: Advanced Technology of Plasticity, Proceedings
.
.
[10]
[11]
[12] [13] [14] [15]
of the Fourth International Conference on Technology of Plasticity, Beijing, People’s Republic of China, 1993, pp. 1193 – 1198. S. Sheng, L. Yiguo, A die forging design approach for controlling metal flow way and its application in practice, Int. J. Mach. Tools Manuf. 34 (1994) 161 – 167. Sun Sheng, Luan Yiguo, Liu Qingbin, A new approach for plastic forming process simulation and its application, Advances in Engineering Plasticity and its Applications, Elsevier Applied Science,Barking, UK, 1993, pp. 887 – 892. S. Kobayashi, S.I. Oh, T. Altan, Metal Forming and the Finite Element Method, Oxford University Press, London, 1989. T. Altan, S.I. Oh, Application of FEM to 2-D metal flow simulation: Practical example, Adv. Technol. Plasticity 4 (1990) 1779–1788. A.N. Bramley, Computer aided forging design, Ann. CIRP 36 (1987) 135 – 138. S. Sheng, G. Tingdong, The reverse simulation technique of die forging based on UBET and its application, Chin. J. Mech. Eng. 4 (1991) 177 – 181.