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An investigation of material flow analysis in fineblanking process
Journal of Materials Processing Technology 192–193 (2007) 237–242
An investigation of material flow analysis in fineblanking process Sutasn Thipprakmas a,∗ , Masahiko Jin b , Masao Murakawa b a
Department of Tool and Materials Engineering, King Mongkut’s University of Technology Thonburi, Thailand b Department of Mechanical Engineering, Nippon Institute of Technology, Saitama, Japan
Abstract As is well known, fineblanking is an effective and economical metal cutting process which offers the ability to produce clean-cut parts with close tolerances by eliminating rough cracks in the shearing zone. These advantages over the conventional blanking are possible due to the following three special tool designs: a small clearance, a high pressure on the blank holder and a high pressure on the counterpunch. These special tool designs affect the material flow characteristics. Therefore, in this study, the material flow was investigated with respect to the various blank holder forces and counterpunch forces by the finite element method (FEM). Moreover, the simulation results agreed well with the experimental results. The results indicated that applying high blank holder force and high counterpunch force significantly suppresses the formation of rotating flow in the blanked material during fineblanking. On the basis of the results, we clarified the reason why the clean-cut surface increases with increasing blank holder force and counterpunch force. Furthermore, this study also verified that the FEM simulation results could be useful for predicting the cut surface features for fineblanking products. © 2007 Elsevier B.V. All rights reserved. Keywords: Fineblanking; Blanking; Material flow; Finite element method (FEM)
1. Introduction As is well known, fineblanking is an effective and economical metal cutting process which offers the ability to produce clean-cut parts with close tolerances by eliminating rough cracks in the shearing zone. Therefore, fineblanking is generally used in many industrial fields to produce parts which require highly reliable precision, such as parts for precision machines, automobiles, electronics and aircraft. The advantages of the fineblanking process over the conventional blanking are possible due to the following three special tool designs [1,2]: a small clearance, a high pressure on the blank holder and a high pressure on the counterpunch. Many studies have been performed on the fineblanking process. To reduce the fracture zone, Lange [3] investigated the effect of a vee-ring indenter on the hydraulic stress. Kim et al. [4] studied the relationship between the vee-ring position and the flatness of sheet metal parts. Kwak et al. [5] studied the effect of die clearance on shear planes in fineblanking by the finite element method (FEM). Aoki and Takahashi [6] proposed the Fourier phase correla-
∗
Corresponding author. Tel.: +66 2 4709218; fax: +66 2 8729080. E-mail address: [email protected] (S. Thipprakmas).
0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.04.065
tion method for analyzing the material flow during a shearing process. Although the results of most of the previous studies were in good correspondence with the theoretical prediction that the clean-cut surface increases with increasing blank holder force and counterpunch force, they are insufficient for analytical study because past studies were focused on the experimental approach. Therefore, the analytical fundamental data for fineblanking tool designs, such as the blank holder force and the counterpunch force, is insufficient. In this study, therefore, the material flow analysis was investigated with respect to various blank holder forces and counterpunch forces by FEM. The FEM results were compared with the experimental results in order to verify the accuracy of the analysis. The results of this study indicated that applying high blank holder force and high counterpunch force significantly suppressed the formation of rotating flow in the blanked material during fineblanking. Increases of the clean-cut surface as the blank holder force and counterpunch force were increased were shown, which agree substantially well with the results of experiment. On the basis of this study, therefore, we clarified the reason why the clean-cut surface increases with increasing blank holder force and counterpunch force. Furthermore, this study also verified that the FEM simulation results could be useful for predicting the cut surface features of fineblanking products.
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S. Thipprakmas et al. / Journal of Materials Processing Technology 192–193 (2007) 237–242 Table 1 Experimental and FEM simulation conditions
Fig. 1. FEM simulation model.
2. Finite element analysis
Simulation model
Axisymmetric model
Object type
Workpiece: elasto-plastic, punch/die: rigid, blank holder: rigid, counter punch: rigid
Blanked materials
S45C (φ 80 mm, thickness 5 mm) (σ B = 590 MPa, λ = 32%)
Flow curve equation
σ¯ = 2045¯ε0.73 + 385
Blanked shape
φ 60 mm
Blanking clearance (Cl)
Conventional (ClB ): 3%t Fineblanking (Clf ): 1%t
Tool cutting edges
Conventional: Rp , Rd = 0.01 mm Fineblanking: Rp = 0.01 mm, Rd = 0.5 mm
Blank holder (FB )
Conventional: 100 kN Fineblanking: 300 kN, 1000 kN
Counterpunch force (FC )
Conventional: 50 kN Fineblanking: 100 kN, 150 kN
Fracture criterion equation
Rice and Tracy (constant α: 1)
Critical fracture value (C)
0.25
Friction coefficient (μ)
0.1
2.1. Simulation models Fig. 1 shows the FEM simulation model. In this study, conventional blanking and fineblanking with clearances of 3%t (0.15 mm) and 1%t (0.05 mm), respectively, were investigated. In a case of fineblanking, a simple model with no vee-ring in either the blank holder or die was used in order to reduce calculation time. Cold-rolled steel, S45C (JIS standard), with a thickness of 5.0 mm was used as the blanked material. A two-dimensional axisymmetric analysis with the die diameter of 60 mm was performed using a commercial analytical code, DEFORM2D (Version.8.1). The blanked material is assumed to be the elasto-plastic. The punch, die, blank holder and counterpunch are assumed to be the rigid bodies. Approximately, 3000 rectangular elements were designed for the blanked material. It is also noted that very fine elements were generated in the predicted deformation zone, as shown in Fig. 2. Moreover, the calculations were performed by remeshing, so that the divergence of the calculations due to excessive deformation of the elements was prevented. 2.2. Simulation conditions Table 1 shows the FEM simulation conditions. In this study, in the case of conventional blanking, the blank holder force and counterpunch force of 100 kN and 50 kN, respectively, were applied. On the other hand, in the case of fineblanking, two levels of the blank holder and counterpunch forces were investigated. Namely, first, as the low level, the blank holder force of 300 kN and the counterpunch force of 100 kN were applied. Next, the blank holder force of 1000 kN and the counterpunch
force of 150 kN were applied as the high level. Tool cutting edge radii were 0.01 mm in the case of conventional blanking. In fineblanking, the punch cutting edge was 0.01 mm and the die cutting edge was 0.5 mm. The friction coefficient was 0.1 for both conventional blanking and fineblanking. The constitutive equation was determined from the SS-curve obtained in the tensile testing experiment and is shown in Table 1. 2.3. Fracture criterion The fracture criterion equation and critical fracture value were considered in this study to investigate crack failure and the form of the cut surface by the finite element method. The equation presented by Rice and Tracy [7] was used, where the constant α was 1 and the critical fracture value C was 0.25, as shown in Eq. (1). The validity of the simulation results obtained using the Rice and Tracy equation was verified for the analysis of crack failure in the fineblanking process in our previous study [8]. The element kill method was used in this FEM code in order to display the generation of crack failure when the calculated result of Eq. (1) reached the critical fracture value [9]. ε¯ f ασ m C= exp d¯ε (1) σ¯ ¯ effective stress, ε¯ : C: critical fracture value, σ m : mean stress, σ: effective strain, α: constant. 3. Experiment
Fig. 2. Illustration of initial meshes for FEM analysis.
The experiments were carried out in order to validate the accuracy of FEM simulation results. The circular cold-rolled steel S45C (JIS standard) specimens
S. Thipprakmas et al. / Journal of Materials Processing Technology 192–193 (2007) 237–242 of 60 mm diameter and 5 mm thickness were used as the blanked products. The mechanical properties were a tensile strength of 590 MPa and elongation of 32%, as shown in Table 1. A 4000 kN fineblanking press machine (Kawasakiyukou Co. Ltd.), in which the blank holder force and counterpunch force can be set, was used.
4. Results and discussion 4.1. Comparison of material flow analysis between conventional blanking and fineblanking Fig. 3 shows material flow for conventional blanking and fineblanking. The range of velocity was adjusted in order to clearly understand the material flow features near the shearing
Fig. 3. Comparison of material flow analysis between the conventional blanking and fineblanking.
239
zone on the scrap. Therefore, there were no material flow analysis illustrations on the blanked parts. As shown in Fig. 3(a), the material flow was investigated for conventional blanking, which had the larger clearance and smaller blank holder and counterpunch force. The FEM simulation results show that there is no significant effect on the material flow direction in conventional blanking with respect to the punch penetration. Namely, with small punch penetration, as shown in Fig. 3(a-1), near the shearing zone on the scrap, the material flow was directed into the shearing zone from the cutting edge of the punch to the cutting edge of the die. Next, as shown in Fig. 3(a-2), the material was forced to flow into the shearing zone with increasing punch penetration because of crack formation at the punch and die cutting edge, resulting in the decreasing of the hydrostatic pressure. Finally, in the final stage, as shown in Fig. 3(a-3), similar phenomena as mentioned above, namely, the material flow was directed into the shearing zone, were observed. In contrast, Fig. 3(b) shows the result of material flow analysis in the case of fineblanking. In the beginning stage, as shown in Fig. 3(b-1), the high blank holder and counterpunch forces resulted in rotating flow of the material on the scrap. This material movement increased the hydrostatic pressure near the shearing zone; hence, crack formation was prevented. At the punch penetration of 3.4 mm, as shown in Fig. 3(b-2), the initial cracks occurred, unlike conventional blanking, and the material flowed into the scrap because of the high hydrostatic pressure. As shown in Fig. 3(b-3), in the final stage, the hydrostatic pressure decreased because the number of cracks increased with increasing punch penetration, resulting in material flow into the shearing zone. In this stage, although the flow tendency was the same as that for conventional blanking, the flow velocity in the case of fineblanking was lower than those with conventional blanking. The results of comparing the cut surfaces on the blanked parts are shown in Fig. 4. In the case of conventional blanking, the amount of roll-over, the clean-cut surface and the cracks were 0.58 mm, 0.56 mm and 3.86 mm, respectively. On the other hand, with fineblanking, the amount of roll-over, the clean-cut surface and the cracks were 0.55 mm, 4.05 mm and 0.40 mm, respectively. The results that fineblanking results in larger clean-
Fig. 4. Comparison of FEM simulation results of cut surfaces between the conventional blanking and fineblanking.
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cut surface on the blanked parts compared with conventional blanking corresponds well with the theory and results of past studies [1,2,10] 4.2. Influence of blank holder force and counterpunch force on material flow features and cut surface in fineblanking Fig. 5 shows the FEM simulation results of material flow analysis for fineblanking with respect to the blank holder force and counterpunch force. The case shown in Fig. 5(a) is that of small blank holder and counterpunch forces. Fig. 5(b) shows the case when large blank holder and counterpunch forces were applied. First, with punch penetration of 0.60 mm, as shown in Fig. 5(a-
1) and (b-1), the material flow features in both cases of small and large blank holder and counterpunch forces were similar. However, Fig. 5(a-1) showed a higher flow velocity compared with Fig. 5(b-1) because of the small blank holder and counterpunch forces. Next, Fig. 5(a-2) and (b-2) show that the FEM simulation predicted increasing rotation of flow as the punch penetration increased. It is noted that the greater the blank holder and counterpunch forces applied, the greater the rotation of flow. This rotating movement of material resulted in the increase of the hydrostatic pressure near the shearing zone. This hydrostatic pressure affected the material flow as well as the cut surfaces as the punch penetration increased, as shown in Fig. 5(a-3) and (b3). Namely, the material flow was directed into the shearing zone
Fig. 5. Material flow analysis in fineblanking with respect to the blank holder force and counterpunch force.
S. Thipprakmas et al. / Journal of Materials Processing Technology 192–193 (2007) 237–242
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Fig. 6. Comparison of FEM simulation results of cut surfaces in fineblanking with respect to the blank holder force and counterpunch force (Clf 1%t, Rp = 0.01 mm, Rd = 0.5 mm).
with higher velocity in the case of the low hydrostatic pressure, as shown in Fig. 5(a-3) and with lower velocity in the case of high hydrostatic pressure, as shown in Fig. 5(b-3). In the case of low hydrostatic pressure, the maximum velocity was approximately 0.10 mm/s, whereas it was 0.07 mm/s in the case of high hydrostatic pressure. Next, similarly in both cases of low and high hydrostatic pressures, the material flow was directed into the scrap when the initial cracks occurred, as show in Fig. 5(a-4) and (b-4). On both of these cases, the flow velocity was near zero. In the final stage, as shown in Fig. 5(a-5) and (b-5), the hydrostatic pressure decreased with crack propagation when the punch penetration increased. Therefore, the material flow was forced into the shearing zone again. However, the material flow velocity in the case of low blank holder and counterpunch forces was higher than in the case of high blank holder and counterpunch forces. Therefore, the clean-cut surface ratio, as shown in Fig. 6, was larger with high blank holder and counterpunch forces than with low blank holder and counterpunch forces. Namely, the amount of roll-over, the clean-cut surface and the cracks were 0.63 mm, 3.45 mm and 0.92 mm, respectively, in the case of low blank holder and counterpunch forces, whereas, they were 0.55 mm, 4.05 mm and 0.40 mm, respectively, in the case of high blank holder and counterpunch forces. These results indicated that applying blank holder and counterpunch forces results in the rotating flow of material near the shearing zone, and this movement increases the hydrostatic pressure; therefore, crack formation is prevented.
Fig. 7. Comparison of cut surface features in fineblanking between FEM simulation results and experimental results. (a) Clf 1%t, Rp = 0.01 mm, Rd = 0.5 mm, FB = 300 kN, FC = 100 kN (b) Clf 1%t, Rp = 0.01 mm, Rd = 0.5 mm,FB = 1000 kN, FC = 150 kN.
tal results are the amount of roll-over of 0.50 mm, the clean-cut surface of 4.07 mm and the cracks of 0.43 mm. From the FEM simulation results as the above-mentioned, the errors for the amount of roll-over, the clean-cut surface and the cracks were approximately 8.5%, 1% and 3.5%, respectively, compared with the experiments. As a result, it was shown that the FEM simulation could be useful as a tool for predicting the cut surface features of fineblanking products. 5. Conclusions The finite element analysis was performed to investigate the effect of the blank holder and counterpunch forces on the material flow features and the cut surfaces in conventional blanking and fineblanking. As a result of this study, the following conclusions can be drawn:
4.3. Comparison of FEM simulation results and experiments Fig. 7 shows the cut surfaces on blanked parts for the FEM simulation and experiments. The blank holder and counterpunch forces were set as the varied parameters. The FEM simulation results show that when the blank holder and counterpunch forces increase, the amount of roll-over and crack decrease while the clean-cut surface increases. These results well agreed with those of experiments, as shown in Fig. 7. Namely, in the case of low blank holder and counterpunch forces, the experimental results show the amount of roll-over to be 0.58 mm, the clean-cut surface to be 3.47 mm and the cracks to be 0.95 mm. In the case of high blank holder and counterpunch forces, the experimen-
(1) Applying high blank holder force and high counterpunch force significantly suppresses the formation of rotating flow in the blanked material during fineblanking. (2) The reason why the clean-cut surface increases with increasing blank holder force and counterpunch force was clarified. Namely, the rotating movement of material increases the hydrostatic pressure; therefore, crack formation is prevented. (3) The FEM simulation results generally agree well with the experiments. Therefore, the FEM simulation may be useful for predicting the cut surface features of fineblanking products.
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Acknowledgements We would like to express our gratitude to the Ministry of Education, Culture, Sports, Science and Technology of Japan for their financial assistance extended to a part of this study. We thank Mr. Kanaizuka Tomokazu for his help in the experiments and also the Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Thailand. References [1] K. Lange, F. Birzer, P. Hofel, A. Mukhoty, H. Singer, Cold Forming and Fineblanking, Edelstahlwerke Buderus AG, Feintool AG Lyss, Switzerland, 1997, pp. 141–154. [2] T. Nakagawa, Fine Blanking, The Nikkan Kogyo Shinbun Ltd., Tokyo, 1998 (in Japanese). [3] K. Lange, The Potential of the Fine Blanking Technique, Feintool AG Lyss, Switzerland, 1978, pp. 1–6.
[4] J.H. Kim, J.G. Ryu, C.S. Choi, W.J. Chung, Development of fine blanking die with fluid chamber and its application to production of circular blanks in a hydraulic press, Korean Soc. Precis. Eng. 13 (5) (1996) 157–163. [5] T.S. Kwak, Y.J. Kim, W.B. Bae, Finite element analysis on the effect of die clearance on shear planes in fineblanking, J. Mater. Process. Technol. 130–131 (2002) 462–468. [6] I. Aoki, T. Takahashi, Material flow analysis on shearing process by applying Fourier phase correlation method—analysis of piercing and fineblanking, J. Mater. Process. Technol. 134 (2003) 45–52. [7] J.R. Rice, D.M. Tracy, On the ductile enlargement of voids in triaxial stress fields, J. Mech. Phys. Solids. (1969) 201–217. [8] S. Thipprakmas, M. Jin, M. Murakawa, Finite element simulation of blanked surface features in fine blanking process, in: Proceedings of the 8th ICTP, Advanced Technology of Plasticity, 1, 2005, pp. 85–86. [9] E. Taupin, J. Breitling, W. Wu, T. Altan, Material fracture and burr formation in blanking results of FEM simulations and comparison with experiments, J. Mater. Process. Technol. 59 (1996) 68–78. [10] M. Murakawa, M. Jin, S. Thipprakmas, Three-dimensional finite-element simulation of fine blanking, in: Proceedings of the 7th NUMIFORM, 2001, pp. 977–981.
An investigation of material flow analysis in fineblanking process Sutasn Thipprakmas a,∗ , Masahiko Jin b , Masao Murakawa b a
Department of Tool and Materials Engineering, King Mongkut’s University of Technology Thonburi, Thailand b Department of Mechanical Engineering, Nippon Institute of Technology, Saitama, Japan
Abstract As is well known, fineblanking is an effective and economical metal cutting process which offers the ability to produce clean-cut parts with close tolerances by eliminating rough cracks in the shearing zone. These advantages over the conventional blanking are possible due to the following three special tool designs: a small clearance, a high pressure on the blank holder and a high pressure on the counterpunch. These special tool designs affect the material flow characteristics. Therefore, in this study, the material flow was investigated with respect to the various blank holder forces and counterpunch forces by the finite element method (FEM). Moreover, the simulation results agreed well with the experimental results. The results indicated that applying high blank holder force and high counterpunch force significantly suppresses the formation of rotating flow in the blanked material during fineblanking. On the basis of the results, we clarified the reason why the clean-cut surface increases with increasing blank holder force and counterpunch force. Furthermore, this study also verified that the FEM simulation results could be useful for predicting the cut surface features for fineblanking products. © 2007 Elsevier B.V. All rights reserved. Keywords: Fineblanking; Blanking; Material flow; Finite element method (FEM)
1. Introduction As is well known, fineblanking is an effective and economical metal cutting process which offers the ability to produce clean-cut parts with close tolerances by eliminating rough cracks in the shearing zone. Therefore, fineblanking is generally used in many industrial fields to produce parts which require highly reliable precision, such as parts for precision machines, automobiles, electronics and aircraft. The advantages of the fineblanking process over the conventional blanking are possible due to the following three special tool designs [1,2]: a small clearance, a high pressure on the blank holder and a high pressure on the counterpunch. Many studies have been performed on the fineblanking process. To reduce the fracture zone, Lange [3] investigated the effect of a vee-ring indenter on the hydraulic stress. Kim et al. [4] studied the relationship between the vee-ring position and the flatness of sheet metal parts. Kwak et al. [5] studied the effect of die clearance on shear planes in fineblanking by the finite element method (FEM). Aoki and Takahashi [6] proposed the Fourier phase correla-
∗
Corresponding author. Tel.: +66 2 4709218; fax: +66 2 8729080. E-mail address: [email protected] (S. Thipprakmas).
0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.04.065
tion method for analyzing the material flow during a shearing process. Although the results of most of the previous studies were in good correspondence with the theoretical prediction that the clean-cut surface increases with increasing blank holder force and counterpunch force, they are insufficient for analytical study because past studies were focused on the experimental approach. Therefore, the analytical fundamental data for fineblanking tool designs, such as the blank holder force and the counterpunch force, is insufficient. In this study, therefore, the material flow analysis was investigated with respect to various blank holder forces and counterpunch forces by FEM. The FEM results were compared with the experimental results in order to verify the accuracy of the analysis. The results of this study indicated that applying high blank holder force and high counterpunch force significantly suppressed the formation of rotating flow in the blanked material during fineblanking. Increases of the clean-cut surface as the blank holder force and counterpunch force were increased were shown, which agree substantially well with the results of experiment. On the basis of this study, therefore, we clarified the reason why the clean-cut surface increases with increasing blank holder force and counterpunch force. Furthermore, this study also verified that the FEM simulation results could be useful for predicting the cut surface features of fineblanking products.
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S. Thipprakmas et al. / Journal of Materials Processing Technology 192–193 (2007) 237–242 Table 1 Experimental and FEM simulation conditions
Fig. 1. FEM simulation model.
2. Finite element analysis
Simulation model
Axisymmetric model
Object type
Workpiece: elasto-plastic, punch/die: rigid, blank holder: rigid, counter punch: rigid
Blanked materials
S45C (φ 80 mm, thickness 5 mm) (σ B = 590 MPa, λ = 32%)
Flow curve equation
σ¯ = 2045¯ε0.73 + 385
Blanked shape
φ 60 mm
Blanking clearance (Cl)
Conventional (ClB ): 3%t Fineblanking (Clf ): 1%t
Tool cutting edges
Conventional: Rp , Rd = 0.01 mm Fineblanking: Rp = 0.01 mm, Rd = 0.5 mm
Blank holder (FB )
Conventional: 100 kN Fineblanking: 300 kN, 1000 kN
Counterpunch force (FC )
Conventional: 50 kN Fineblanking: 100 kN, 150 kN
Fracture criterion equation
Rice and Tracy (constant α: 1)
Critical fracture value (C)
0.25
Friction coefficient (μ)
0.1
2.1. Simulation models Fig. 1 shows the FEM simulation model. In this study, conventional blanking and fineblanking with clearances of 3%t (0.15 mm) and 1%t (0.05 mm), respectively, were investigated. In a case of fineblanking, a simple model with no vee-ring in either the blank holder or die was used in order to reduce calculation time. Cold-rolled steel, S45C (JIS standard), with a thickness of 5.0 mm was used as the blanked material. A two-dimensional axisymmetric analysis with the die diameter of 60 mm was performed using a commercial analytical code, DEFORM2D (Version.8.1). The blanked material is assumed to be the elasto-plastic. The punch, die, blank holder and counterpunch are assumed to be the rigid bodies. Approximately, 3000 rectangular elements were designed for the blanked material. It is also noted that very fine elements were generated in the predicted deformation zone, as shown in Fig. 2. Moreover, the calculations were performed by remeshing, so that the divergence of the calculations due to excessive deformation of the elements was prevented. 2.2. Simulation conditions Table 1 shows the FEM simulation conditions. In this study, in the case of conventional blanking, the blank holder force and counterpunch force of 100 kN and 50 kN, respectively, were applied. On the other hand, in the case of fineblanking, two levels of the blank holder and counterpunch forces were investigated. Namely, first, as the low level, the blank holder force of 300 kN and the counterpunch force of 100 kN were applied. Next, the blank holder force of 1000 kN and the counterpunch
force of 150 kN were applied as the high level. Tool cutting edge radii were 0.01 mm in the case of conventional blanking. In fineblanking, the punch cutting edge was 0.01 mm and the die cutting edge was 0.5 mm. The friction coefficient was 0.1 for both conventional blanking and fineblanking. The constitutive equation was determined from the SS-curve obtained in the tensile testing experiment and is shown in Table 1. 2.3. Fracture criterion The fracture criterion equation and critical fracture value were considered in this study to investigate crack failure and the form of the cut surface by the finite element method. The equation presented by Rice and Tracy [7] was used, where the constant α was 1 and the critical fracture value C was 0.25, as shown in Eq. (1). The validity of the simulation results obtained using the Rice and Tracy equation was verified for the analysis of crack failure in the fineblanking process in our previous study [8]. The element kill method was used in this FEM code in order to display the generation of crack failure when the calculated result of Eq. (1) reached the critical fracture value [9]. ε¯ f ασ m C= exp d¯ε (1) σ¯ ¯ effective stress, ε¯ : C: critical fracture value, σ m : mean stress, σ: effective strain, α: constant. 3. Experiment
Fig. 2. Illustration of initial meshes for FEM analysis.
The experiments were carried out in order to validate the accuracy of FEM simulation results. The circular cold-rolled steel S45C (JIS standard) specimens
S. Thipprakmas et al. / Journal of Materials Processing Technology 192–193 (2007) 237–242 of 60 mm diameter and 5 mm thickness were used as the blanked products. The mechanical properties were a tensile strength of 590 MPa and elongation of 32%, as shown in Table 1. A 4000 kN fineblanking press machine (Kawasakiyukou Co. Ltd.), in which the blank holder force and counterpunch force can be set, was used.
4. Results and discussion 4.1. Comparison of material flow analysis between conventional blanking and fineblanking Fig. 3 shows material flow for conventional blanking and fineblanking. The range of velocity was adjusted in order to clearly understand the material flow features near the shearing
Fig. 3. Comparison of material flow analysis between the conventional blanking and fineblanking.
239
zone on the scrap. Therefore, there were no material flow analysis illustrations on the blanked parts. As shown in Fig. 3(a), the material flow was investigated for conventional blanking, which had the larger clearance and smaller blank holder and counterpunch force. The FEM simulation results show that there is no significant effect on the material flow direction in conventional blanking with respect to the punch penetration. Namely, with small punch penetration, as shown in Fig. 3(a-1), near the shearing zone on the scrap, the material flow was directed into the shearing zone from the cutting edge of the punch to the cutting edge of the die. Next, as shown in Fig. 3(a-2), the material was forced to flow into the shearing zone with increasing punch penetration because of crack formation at the punch and die cutting edge, resulting in the decreasing of the hydrostatic pressure. Finally, in the final stage, as shown in Fig. 3(a-3), similar phenomena as mentioned above, namely, the material flow was directed into the shearing zone, were observed. In contrast, Fig. 3(b) shows the result of material flow analysis in the case of fineblanking. In the beginning stage, as shown in Fig. 3(b-1), the high blank holder and counterpunch forces resulted in rotating flow of the material on the scrap. This material movement increased the hydrostatic pressure near the shearing zone; hence, crack formation was prevented. At the punch penetration of 3.4 mm, as shown in Fig. 3(b-2), the initial cracks occurred, unlike conventional blanking, and the material flowed into the scrap because of the high hydrostatic pressure. As shown in Fig. 3(b-3), in the final stage, the hydrostatic pressure decreased because the number of cracks increased with increasing punch penetration, resulting in material flow into the shearing zone. In this stage, although the flow tendency was the same as that for conventional blanking, the flow velocity in the case of fineblanking was lower than those with conventional blanking. The results of comparing the cut surfaces on the blanked parts are shown in Fig. 4. In the case of conventional blanking, the amount of roll-over, the clean-cut surface and the cracks were 0.58 mm, 0.56 mm and 3.86 mm, respectively. On the other hand, with fineblanking, the amount of roll-over, the clean-cut surface and the cracks were 0.55 mm, 4.05 mm and 0.40 mm, respectively. The results that fineblanking results in larger clean-
Fig. 4. Comparison of FEM simulation results of cut surfaces between the conventional blanking and fineblanking.
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cut surface on the blanked parts compared with conventional blanking corresponds well with the theory and results of past studies [1,2,10] 4.2. Influence of blank holder force and counterpunch force on material flow features and cut surface in fineblanking Fig. 5 shows the FEM simulation results of material flow analysis for fineblanking with respect to the blank holder force and counterpunch force. The case shown in Fig. 5(a) is that of small blank holder and counterpunch forces. Fig. 5(b) shows the case when large blank holder and counterpunch forces were applied. First, with punch penetration of 0.60 mm, as shown in Fig. 5(a-
1) and (b-1), the material flow features in both cases of small and large blank holder and counterpunch forces were similar. However, Fig. 5(a-1) showed a higher flow velocity compared with Fig. 5(b-1) because of the small blank holder and counterpunch forces. Next, Fig. 5(a-2) and (b-2) show that the FEM simulation predicted increasing rotation of flow as the punch penetration increased. It is noted that the greater the blank holder and counterpunch forces applied, the greater the rotation of flow. This rotating movement of material resulted in the increase of the hydrostatic pressure near the shearing zone. This hydrostatic pressure affected the material flow as well as the cut surfaces as the punch penetration increased, as shown in Fig. 5(a-3) and (b3). Namely, the material flow was directed into the shearing zone
Fig. 5. Material flow analysis in fineblanking with respect to the blank holder force and counterpunch force.
S. Thipprakmas et al. / Journal of Materials Processing Technology 192–193 (2007) 237–242
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Fig. 6. Comparison of FEM simulation results of cut surfaces in fineblanking with respect to the blank holder force and counterpunch force (Clf 1%t, Rp = 0.01 mm, Rd = 0.5 mm).
with higher velocity in the case of the low hydrostatic pressure, as shown in Fig. 5(a-3) and with lower velocity in the case of high hydrostatic pressure, as shown in Fig. 5(b-3). In the case of low hydrostatic pressure, the maximum velocity was approximately 0.10 mm/s, whereas it was 0.07 mm/s in the case of high hydrostatic pressure. Next, similarly in both cases of low and high hydrostatic pressures, the material flow was directed into the scrap when the initial cracks occurred, as show in Fig. 5(a-4) and (b-4). On both of these cases, the flow velocity was near zero. In the final stage, as shown in Fig. 5(a-5) and (b-5), the hydrostatic pressure decreased with crack propagation when the punch penetration increased. Therefore, the material flow was forced into the shearing zone again. However, the material flow velocity in the case of low blank holder and counterpunch forces was higher than in the case of high blank holder and counterpunch forces. Therefore, the clean-cut surface ratio, as shown in Fig. 6, was larger with high blank holder and counterpunch forces than with low blank holder and counterpunch forces. Namely, the amount of roll-over, the clean-cut surface and the cracks were 0.63 mm, 3.45 mm and 0.92 mm, respectively, in the case of low blank holder and counterpunch forces, whereas, they were 0.55 mm, 4.05 mm and 0.40 mm, respectively, in the case of high blank holder and counterpunch forces. These results indicated that applying blank holder and counterpunch forces results in the rotating flow of material near the shearing zone, and this movement increases the hydrostatic pressure; therefore, crack formation is prevented.
Fig. 7. Comparison of cut surface features in fineblanking between FEM simulation results and experimental results. (a) Clf 1%t, Rp = 0.01 mm, Rd = 0.5 mm, FB = 300 kN, FC = 100 kN (b) Clf 1%t, Rp = 0.01 mm, Rd = 0.5 mm,FB = 1000 kN, FC = 150 kN.
tal results are the amount of roll-over of 0.50 mm, the clean-cut surface of 4.07 mm and the cracks of 0.43 mm. From the FEM simulation results as the above-mentioned, the errors for the amount of roll-over, the clean-cut surface and the cracks were approximately 8.5%, 1% and 3.5%, respectively, compared with the experiments. As a result, it was shown that the FEM simulation could be useful as a tool for predicting the cut surface features of fineblanking products. 5. Conclusions The finite element analysis was performed to investigate the effect of the blank holder and counterpunch forces on the material flow features and the cut surfaces in conventional blanking and fineblanking. As a result of this study, the following conclusions can be drawn:
4.3. Comparison of FEM simulation results and experiments Fig. 7 shows the cut surfaces on blanked parts for the FEM simulation and experiments. The blank holder and counterpunch forces were set as the varied parameters. The FEM simulation results show that when the blank holder and counterpunch forces increase, the amount of roll-over and crack decrease while the clean-cut surface increases. These results well agreed with those of experiments, as shown in Fig. 7. Namely, in the case of low blank holder and counterpunch forces, the experimental results show the amount of roll-over to be 0.58 mm, the clean-cut surface to be 3.47 mm and the cracks to be 0.95 mm. In the case of high blank holder and counterpunch forces, the experimen-
(1) Applying high blank holder force and high counterpunch force significantly suppresses the formation of rotating flow in the blanked material during fineblanking. (2) The reason why the clean-cut surface increases with increasing blank holder force and counterpunch force was clarified. Namely, the rotating movement of material increases the hydrostatic pressure; therefore, crack formation is prevented. (3) The FEM simulation results generally agree well with the experiments. Therefore, the FEM simulation may be useful for predicting the cut surface features of fineblanking products.
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Acknowledgements We would like to express our gratitude to the Ministry of Education, Culture, Sports, Science and Technology of Japan for their financial assistance extended to a part of this study. We thank Mr. Kanaizuka Tomokazu for his help in the experiments and also the Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Thailand. References [1] K. Lange, F. Birzer, P. Hofel, A. Mukhoty, H. Singer, Cold Forming and Fineblanking, Edelstahlwerke Buderus AG, Feintool AG Lyss, Switzerland, 1997, pp. 141–154. [2] T. Nakagawa, Fine Blanking, The Nikkan Kogyo Shinbun Ltd., Tokyo, 1998 (in Japanese). [3] K. Lange, The Potential of the Fine Blanking Technique, Feintool AG Lyss, Switzerland, 1978, pp. 1–6.
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