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Simulation of isothermal forging of compressor disc by combined numerical and physical modelling techniques
Journal of Materials Processing Technology 72 (1997) 392 – 395
Simulation of isothermal forging of compressor disc by combined numerical and physical modelling techniques Abhijit Dutta *, A. Venugopal Rao Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500058, India Received 2 August 1996
Abstract The process design, preform and die-designs for a sub-scale compressor disc for an aero engine have been investigated with the help of a finite element method numerical model and two physcial models. The physical models employed in these investigations are a layered coloured-plasticine model and an aluminium-alloy model. The law of similarity was followed for the physical models. Optimization of the size and shape of the preforms, the die-filling, the prediction of the load and the microstructure was carried out for each of the three models. © 1997 Elsevier Science S.A. Keywords: Isothermal forging; Compressor disc; Numerical model; Physical model
1. Introduction There is no denying that so far the forging industries have successfully developed many complicated forgings through ‘trial-and-error’ and empricial routes. However, for a new and complicated forging, a fullsize trial might be very expensive, particularly for isothermal forging where the cost of the die is prohibititively high. Analytical methods with closed-form solutions can be used for the simplest of geometries. For complicated geometries, finite-element methods (FEM) have been used successfully by many research workers to predict under-filling, laps, folds, etc. for a particular die-design [1 – 4]. However, this technique is not very popular in the shop-floor environment because of the necessity to obtain a powerful FEM code, a powerful computer and software personnel. On the other hand, the physical modelling method is quite expensive but does not need in-depth knowledge of plastic deformation. According to many studies, the behaviours of plasticine and lead are similar to that of real forging materials, such as steel, titanium, etc. [5]. Although the physical-modelling approach
* Corresponding author. 0924-0136/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S 0 9 2 4 - 0 1 3 6 ( 9 7 ) 0 0 2 0 0 - 8
might fall short of the ideal, plant operators can easily use this inexpensive and easy-to-use method, if the ‘similarity’ rule is maintained. A reputed steel corporation has even set-up a plasticine modelling laboratory for solving practical problems [6], the plasticine modelling being a scaled-down mock-up of the real die. Transparent acrylic dies are sometimes used to enable the following of the progress of deformation, uninterruptedly. It is however, not always possible to enforce the rule of similitude perfectly between the model material and the real material. Metallic model materials such as Al-alloys at high temperature behave the same way as a titanium alloy would at its forging temperature. Both may flow superplastically, when in the fine-grained condition. Therefore, in the present investigation, in addition to FEM and plasticine modelling, aluminium-alloy modelling has also been attempted. The best way to remove the doubt about similitude is to forge a scaled-down component with real material, as the last step in simulation. Whilst the present authors have started these experiments in the real material IMI-685, with a scaleddown die, the results are not described here. The present investigation attempts to generate complimentary information through FEM, plasticine and Al-alloy models in sub-scale version.
A. Dutta, A.V. Rao / Journal of Materials Processing Technology 72 (1997) 392–395
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Fig. 3. Microstructures at different regions of a 4047 Al alloy forging. Fig. 1. Photograph of the two die-havles for the forging of a miniature compressor disc.
2. Experimental investigations The miniature forging dies for a compressor disc with scaled-down (: 8:1) dimensions were designed and machined from superalloy APK-1; a photograph of these dies is illustrated in Fig. 1. The dies were fitted to the platens of a 100 kN servo-hydraulic, programmable, DARTEC hot-compression testing machine. Cylindrical billets were made from plasticine with different colours for different layers, so that the coloured layers can serve to demonstrate the flow pattern. After each experiment of compression of the plasticine billets, they were sectioned to observe the flow at different stages. In some billets, vertical layers were also made in addition to the horizontal layers. Finite-element simulations were also carried out in a personal computer using the FEM program developed by INCO Engineered Products, UK. The material data needed for this simulation were generated from hot compression tests of Al-alloy model material and the real compressor disc material (i.e. titanium alloy IMI685) over wide range of strain rates and temperatures (o; : 0.001–0.01 s − 1 and temperatures of 573 – 773 K
Fig. 2. Plasticine forging showing the flow pattern of various layers.
for Al-alloy and 1223–1273 K for titanium alloy). It has been observed that the flow curves under optimum forging conditions, i.e. 773 K, 0.001 s − 1 for 4047 Al alloy and 1273 K, 0.001 s − 1 for IMI-685 titanium alloy, are nearly similar. Thus, the condition of similitude is satisfied better with the modelling of Al alloy 4047. Before starting the FE simulation, it was ensured that the program correctly generates the flow stress– strain data through its assumed constitutive equations. The microstructure from different regions of the model aluminium alloy forging was observed also.
3. Results and discussion It is apparent from the sectioned plasticine forging shown in Fig. 2 that the central layers are highly
Fig. 4. The strain patterns developed at different stages during the compression of 4047 Al alloy, where the original billet dimension is f27 × 37.5 mm height: (a) After 16.35 mm compression; (b) after 25.67 mm compression; and (c) final compression of 33.5 mm.
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A. Dutta, A.V. Rao / Journal of Materials Processing Technology 72 (1997) 392–395
Fig. 5. The load – stroke diagram obtained with 4047 Al alloy billets of different dimensions.
compressed, whilst the shear deformation is much greater in the upper ribs. The central portion is quite uniformly pressed to develop a uniform radial flow. The microstructure shown in Fig. 3 also supports the same flow pattern, i.e. a heavily worked and elongated microstructure at the centre and shear flow at the top rib entrance. In both cases, the initial cast dendritic microstructures have broken. However, the microstructure is coarser near to the surface. The FE analysis at different stages of compression of the forging shows a wide variation of strain at different regions, Fig. 4. However, on completion of the total forging operation, the central and bottom portions of the forging show uniformity of strain. Only regions near to the top ridges show greater strains, due to the shear flow involved in these regions.
Die-filling was good with the present die design and the flash thickness and width could be correctly designed. The initial volume of the cylindrical preform and its aspect ratio (height:diameter) were varied to optimize to the correct dimensions of the perform: These were f27×42 mm height to ensure the presence of sufficient material to flow into the gutter after filling the flash, within the available load capacity of the machine (100 kN in the present case) as represented by curve 3 in Fig. 5. However, to economize further on the load requirements whilst ensuring die filling, the best dimensions are f27× 37.5 mm height. In this case, even a 60 kN load is adequate, as shown by curve 4 in Fig. 5. FE simulation could also predict the load–stroke diagram for a particular billet material and geometry, within reasonable tolerance limits. The real forging curve and the predicted curves are compared in Fig. 6. Thus, the suitability of a forging machine to forge a particular component can be examined before hand.
4. Conclusions (1) Physical modelling with plasticine billets shows the flow pattern and die-filling correctly. (2) Physical modelling with metals such as aluminiumalloy billets forms a good guide for the selection of the correct preform size and die design. (3) FE modelling can predict the metal flow, the strain patterns, die-filling and above all, the load requirements.
Fig. 6. Comparison of load–stroke diagrams between FEM predictions and experiment, for 4047 Al alloy forged at 773 K and 0.001 s − 1.
A. Dutta, A.V. Rao / Journal of Materials Processing Technology 72 (1997) 392–395
Acknowledgements The authors are grateful to S.L.N. Acharyulu, Director, DMRL and Dr D. Banerjee, Associate Director, for their permission to publish this research work. The authors would like to acknowledge the contribution of undergraduate students R. Ranganath and M.V.S.S.R.V. Prasad in the preparation of the plasticine billets.
References [1] J.J. Park, N. Rebelo, S. Kobayashi, Int. J. Mach. Tool Des. Res. 23 (1985) 71 – 79.
.
395
[2] N. Kim, S. Kobayashi, Int. J. Mach. Tool Manu. 30 (2) (1990) 269. [3] N. Kim, S. Kobayashi, T. Altan, Int. J. Mach. Tool Manu. 31 (4) (1991) 55. [4] V.K. Jain, L.E. Matson, H.L. Gegel, R. Srinivasan, Comparison of viscoplastic modelling and computer simulation, in: E. Erman, S.L. Semiatin (Eds.), Physical Modelling of Metalworking processes, Metallurgical Society, Warrandale, 1987, pp. 127 – 142. [5] Eun Deog Chu, Yang-Tack Im, Naksoo Kim, Jongsoo Lee, J. Mater. Process Technol. 48 (1995) 143 – 149. [6] E. Erman, N.M. Medei, A.R. Resch, D.C. Shah, Physical modelling of upsetting process in open-die press forging, in: E. Erman, S.L. Semiatin (Eds.), Physical Modelling of Metalworking processes, Metallurgical Society, Warrandale, 1987, pp. 59 – 79.
Simulation of isothermal forging of compressor disc by combined numerical and physical modelling techniques Abhijit Dutta *, A. Venugopal Rao Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500058, India Received 2 August 1996
Abstract The process design, preform and die-designs for a sub-scale compressor disc for an aero engine have been investigated with the help of a finite element method numerical model and two physcial models. The physical models employed in these investigations are a layered coloured-plasticine model and an aluminium-alloy model. The law of similarity was followed for the physical models. Optimization of the size and shape of the preforms, the die-filling, the prediction of the load and the microstructure was carried out for each of the three models. © 1997 Elsevier Science S.A. Keywords: Isothermal forging; Compressor disc; Numerical model; Physical model
1. Introduction There is no denying that so far the forging industries have successfully developed many complicated forgings through ‘trial-and-error’ and empricial routes. However, for a new and complicated forging, a fullsize trial might be very expensive, particularly for isothermal forging where the cost of the die is prohibititively high. Analytical methods with closed-form solutions can be used for the simplest of geometries. For complicated geometries, finite-element methods (FEM) have been used successfully by many research workers to predict under-filling, laps, folds, etc. for a particular die-design [1 – 4]. However, this technique is not very popular in the shop-floor environment because of the necessity to obtain a powerful FEM code, a powerful computer and software personnel. On the other hand, the physical modelling method is quite expensive but does not need in-depth knowledge of plastic deformation. According to many studies, the behaviours of plasticine and lead are similar to that of real forging materials, such as steel, titanium, etc. [5]. Although the physical-modelling approach
* Corresponding author. 0924-0136/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S 0 9 2 4 - 0 1 3 6 ( 9 7 ) 0 0 2 0 0 - 8
might fall short of the ideal, plant operators can easily use this inexpensive and easy-to-use method, if the ‘similarity’ rule is maintained. A reputed steel corporation has even set-up a plasticine modelling laboratory for solving practical problems [6], the plasticine modelling being a scaled-down mock-up of the real die. Transparent acrylic dies are sometimes used to enable the following of the progress of deformation, uninterruptedly. It is however, not always possible to enforce the rule of similitude perfectly between the model material and the real material. Metallic model materials such as Al-alloys at high temperature behave the same way as a titanium alloy would at its forging temperature. Both may flow superplastically, when in the fine-grained condition. Therefore, in the present investigation, in addition to FEM and plasticine modelling, aluminium-alloy modelling has also been attempted. The best way to remove the doubt about similitude is to forge a scaled-down component with real material, as the last step in simulation. Whilst the present authors have started these experiments in the real material IMI-685, with a scaleddown die, the results are not described here. The present investigation attempts to generate complimentary information through FEM, plasticine and Al-alloy models in sub-scale version.
A. Dutta, A.V. Rao / Journal of Materials Processing Technology 72 (1997) 392–395
393
Fig. 3. Microstructures at different regions of a 4047 Al alloy forging. Fig. 1. Photograph of the two die-havles for the forging of a miniature compressor disc.
2. Experimental investigations The miniature forging dies for a compressor disc with scaled-down (: 8:1) dimensions were designed and machined from superalloy APK-1; a photograph of these dies is illustrated in Fig. 1. The dies were fitted to the platens of a 100 kN servo-hydraulic, programmable, DARTEC hot-compression testing machine. Cylindrical billets were made from plasticine with different colours for different layers, so that the coloured layers can serve to demonstrate the flow pattern. After each experiment of compression of the plasticine billets, they were sectioned to observe the flow at different stages. In some billets, vertical layers were also made in addition to the horizontal layers. Finite-element simulations were also carried out in a personal computer using the FEM program developed by INCO Engineered Products, UK. The material data needed for this simulation were generated from hot compression tests of Al-alloy model material and the real compressor disc material (i.e. titanium alloy IMI685) over wide range of strain rates and temperatures (o; : 0.001–0.01 s − 1 and temperatures of 573 – 773 K
Fig. 2. Plasticine forging showing the flow pattern of various layers.
for Al-alloy and 1223–1273 K for titanium alloy). It has been observed that the flow curves under optimum forging conditions, i.e. 773 K, 0.001 s − 1 for 4047 Al alloy and 1273 K, 0.001 s − 1 for IMI-685 titanium alloy, are nearly similar. Thus, the condition of similitude is satisfied better with the modelling of Al alloy 4047. Before starting the FE simulation, it was ensured that the program correctly generates the flow stress– strain data through its assumed constitutive equations. The microstructure from different regions of the model aluminium alloy forging was observed also.
3. Results and discussion It is apparent from the sectioned plasticine forging shown in Fig. 2 that the central layers are highly
Fig. 4. The strain patterns developed at different stages during the compression of 4047 Al alloy, where the original billet dimension is f27 × 37.5 mm height: (a) After 16.35 mm compression; (b) after 25.67 mm compression; and (c) final compression of 33.5 mm.
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A. Dutta, A.V. Rao / Journal of Materials Processing Technology 72 (1997) 392–395
Fig. 5. The load – stroke diagram obtained with 4047 Al alloy billets of different dimensions.
compressed, whilst the shear deformation is much greater in the upper ribs. The central portion is quite uniformly pressed to develop a uniform radial flow. The microstructure shown in Fig. 3 also supports the same flow pattern, i.e. a heavily worked and elongated microstructure at the centre and shear flow at the top rib entrance. In both cases, the initial cast dendritic microstructures have broken. However, the microstructure is coarser near to the surface. The FE analysis at different stages of compression of the forging shows a wide variation of strain at different regions, Fig. 4. However, on completion of the total forging operation, the central and bottom portions of the forging show uniformity of strain. Only regions near to the top ridges show greater strains, due to the shear flow involved in these regions.
Die-filling was good with the present die design and the flash thickness and width could be correctly designed. The initial volume of the cylindrical preform and its aspect ratio (height:diameter) were varied to optimize to the correct dimensions of the perform: These were f27×42 mm height to ensure the presence of sufficient material to flow into the gutter after filling the flash, within the available load capacity of the machine (100 kN in the present case) as represented by curve 3 in Fig. 5. However, to economize further on the load requirements whilst ensuring die filling, the best dimensions are f27× 37.5 mm height. In this case, even a 60 kN load is adequate, as shown by curve 4 in Fig. 5. FE simulation could also predict the load–stroke diagram for a particular billet material and geometry, within reasonable tolerance limits. The real forging curve and the predicted curves are compared in Fig. 6. Thus, the suitability of a forging machine to forge a particular component can be examined before hand.
4. Conclusions (1) Physical modelling with plasticine billets shows the flow pattern and die-filling correctly. (2) Physical modelling with metals such as aluminiumalloy billets forms a good guide for the selection of the correct preform size and die design. (3) FE modelling can predict the metal flow, the strain patterns, die-filling and above all, the load requirements.
Fig. 6. Comparison of load–stroke diagrams between FEM predictions and experiment, for 4047 Al alloy forged at 773 K and 0.001 s − 1.
A. Dutta, A.V. Rao / Journal of Materials Processing Technology 72 (1997) 392–395
Acknowledgements The authors are grateful to S.L.N. Acharyulu, Director, DMRL and Dr D. Banerjee, Associate Director, for their permission to publish this research work. The authors would like to acknowledge the contribution of undergraduate students R. Ranganath and M.V.S.S.R.V. Prasad in the preparation of the plasticine billets.
References [1] J.J. Park, N. Rebelo, S. Kobayashi, Int. J. Mach. Tool Des. Res. 23 (1985) 71 – 79.
.
395
[2] N. Kim, S. Kobayashi, Int. J. Mach. Tool Manu. 30 (2) (1990) 269. [3] N. Kim, S. Kobayashi, T. Altan, Int. J. Mach. Tool Manu. 31 (4) (1991) 55. [4] V.K. Jain, L.E. Matson, H.L. Gegel, R. Srinivasan, Comparison of viscoplastic modelling and computer simulation, in: E. Erman, S.L. Semiatin (Eds.), Physical Modelling of Metalworking processes, Metallurgical Society, Warrandale, 1987, pp. 127 – 142. [5] Eun Deog Chu, Yang-Tack Im, Naksoo Kim, Jongsoo Lee, J. Mater. Process Technol. 48 (1995) 143 – 149. [6] E. Erman, N.M. Medei, A.R. Resch, D.C. Shah, Physical modelling of upsetting process in open-die press forging, in: E. Erman, S.L. Semiatin (Eds.), Physical Modelling of Metalworking processes, Metallurgical Society, Warrandale, 1987, pp. 59 – 79.