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Study of blank-holder technology on multi-point forming of thin sheet metal
Journal of Materials Processing Technology 187–188 (2007) 517–520
Study of blank-holder technology on multi-point forming of thin sheet metal G. Sun a,∗ , M.Z. Li a , X.P. Yan a , P.P. Zhong b a
Dieless Forming Technology Center, Jilin University, Changchun 130025, PR China b College of Foreign Languages, Jilin University, Changchun 130025, PR China
Abstract Multi-point forming (MPF) is an advanced flexible manufacture technology, and the technology results from the idea that the whole die is separated into small punches that can be adjusted height. This idea is applied to the traditional rigid blank-holder (RBH), so flexible blank-holder (FBH) idea can be obtain. Different technologies about RBH forming and FBH forming are simulated in this paper, and the impact on wrinkle, crack and forming limit from the two different technologies is also analyzed. Furthermore this process is simulated by explicit software (LS DYNA) for the saddle workpiece with two kinds of thickness and the experiment is completed, Results indicated that the sheet with large deformation will wrinkle in the RBH forming, until blank-holder force (BHF) increasing the sheet cracked. But under the same condition the sheet is good in the FBH forming. When 1/2 area of blank-holder surface is cut out, and BHF is increased, the sheet also can be well gained. So the technology of FBH can sharply increase material utilization ratio, improve forming limit and decrease most disfigurements. © 2006 Elsevier B.V. All rights reserved. Keywords: Multi-point forming; Flexible blank-holder; Rigid blank-holder; Numerical simulation; Sheet metal; Forming force
1. Introduction
2. Principle of flexible and rigid blank-holders forming
MPF technology can achieve all kinds of curve surfaces by computers controlling elements of height adjusted, and this method is a flexible manufacture technology which substitutes the whole-die to realize three-dimension figure [1,2]. To traditional die MPF technology can realize a lot of functions, also every function that traditional die have can be achieved by a given equipment, so this method both can save mass time of designing and manufacturing, even can sharply reduce expenses of making product, eventually accelerates the rate of old product substituted by new one [3]. Now, MPF technology is applied to 3D sheet metal in shipboard, ornaments in architectures, streamline sheet metal in train and medicine fields. With blank-holders forming and without blank-holders forming are often used in current MPF technology mode. The technology modes of flexible and rigid blank-holders influences on the sheet metal forming are studied in this paper.
Fig. 1 is a photo that shows the punch, die and blank-holder parts of MPF equipment with the function of blank-holder, and elements are adjusted to the shape of saddle in the midst of the photo [4,5]. Furthermore, the distinct difference about RBH and FBH is blank-holder. The blank-holder device of MPF equipment (see Fig. 1) is that a circle hydraulic cylinders (HC) (total 40) dispose around with upper and lower elements, also there are two blank-holders, one is placed on the top of workpiece, and other is placed on the below of workpiece, these blank-holders can bring into press on workpiece by HC, so this method can realize blank-holder function of MPF. When the thickness of blank-holder is thick, the upper and lower HC are set the same or different press, therefore blank-holder surface can move up and down, and can realize flexible control in the height direction of blank-holder surface. When the thickness of blank-holder is thin, the blank-holder device cannot only realize flexible control in the height direction of blank-holder surface, but can also realize flexible blank-holder surface corresponding with the height of workpiece curve surface by blank-holder bending, consequently the latter can acquire better forming. The former, we name RBH of MPF, the latter, we name FBH of MPF [6,7].
∗ Corresponding author at: Dieless Forming Technology Center, Roll Forging Research Institute, Jilin University, Changchun 130025, PR China. Tel.: +86 431 509 4340; fax: +86 431 509 4340. E-mail address: sungang [email protected] (G. Sun).
0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.11.133
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G. Sun et al. / Journal of Materials Processing Technology 187–188 (2007) 517–520
In the same condition, L2Y2 sheet formed with the two kinds of blank-holders, and the result sharply different. Results show that wrinkles appear in the workpiece formed by RBH, and none any of wrinkle in the workpiece formed by FBH. 3.2. Strain contrast after forming
Fig. 1. Workbench of MPF press.
3. Influence on forming by two kinds of blank-holders 3.1. Influence on wrinkle defects The influence on forming results with the two kinds of materials L2Y2 and 08Al is discussed by FBH and RBH forming. The thickness of 08Al materials is 0.5 mm, and the target curvature radius is 400 mm in the direction of horizontal and vertical, also the press is 5 MPa on blank-holder, FBH and RBH forming are studied in numerical simulation. From Fig. 2(a), there are distinct wrinkles in the workpiece formed by RBH, and the district wrinkles distribute in the middle of the workpiece, but none any of wrinkle in the workpiece formed by FBH, also the surface of the workpiece is lubricous (see Fig. 2(b)).
Fig. 2. Contrast of the two kinds of blank-holders. (a) Forming of rigid blankholder and (b) forming of flexible blank-holder.
By simulation we can understand the two kinds of blankholders influence to workpiece strain clearly. The workpiece of saddle formed by two kinds of blank-holders, and the target curvature radius is 400 mm in the direction of horizontal and vertical, material is 08Al. Workpiece strain named strain in the direction of thickness in this paper, and strain of workpiece formed by RBH is disorder, at the same time the strain is small in the middle of workpiece, also the strain value is 0.2. Sheet will became thinner in the course of forming, and transition section in long axis is thinner than that in short axis, so sheet will crack in long axis direction, hence big deformation will be difficultly come true. But strain of workpiece formed by FBH is only 0.08, just because the workpiece by this mode forming has no transition section, the strain of all of whole sheet is average, so the workpiece formed by FBH hardly cracks. 3.3. Influence on material utilization ratio In addition, from the two technology modes, we know that FBH can save material. Because the material inside of blankholder will become small with sheet deformation, this method sharply reduces the area of transition section, namely saves material. Blank-holder device has an important function that it can transport sheet in a certain speed in the course of forming to prevent wrinkle, so it can achieve successfully complex curve surface in sheet metal forming, but the sheet inside of blankholder will be cut in the last, namely this sheet is waste, however, FBH forming mode reduces the material inside of blank-holder, and it is good to save sheet material. The technology of FBH can settle well the contradiction for both wrinkling and saving material of sheet. For example, the workpiece of saddle is formed with the two kinds of blank-holder modes, and the target curvature radius is 400 mm in the direction of horizontal and vertical, also BHF is 7 Mpa, using these conditions the influence on FBH saving material is distinct. When the sheet size is 480 mm in horizontal direction and 400 mm in vertical direction, and blank-holder width is 20 mm, we can compute that only using 82.52% material in FBH forming can acquire the same workpiece formed by RBH. Fig. 3 shows workpiece outline line, and the target curvature radius of workpiece is 450 mm in the direction of horizontal and vertical, also the workpiece is saddle shape. In the figure of Fig. 3, the outside dashed is the original sheet borderline, and inside dashed is the target workpiece borderline, so between the outside dashed and inside dashed are blank-holder region. The solid line is the borderline include blank-holder region after formed, and the material flow trend can be acquired clearly. Fig. 3(a) is the workpiece outline in RBH forming, and the sheet in the blank-holder surface near the symmetry center easily flows
G. Sun et al. / Journal of Materials Processing Technology 187–188 (2007) 517–520
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into the transition section than the sheet away from the symmetry center. Ultimately it is little sheet metal in blank-holder surface. But in the mode of FBH forming, blank-holder surface moved up and down with the sheet deformation, so the transition section disappears and the borderline of sheet before forming and after forming is not change (see Fig. 3(b)). 3.4. Influence on deformation quantity In some case, the technology of FBH not only saves material, but also extends forming limit of sheet, and some workpieces cannot be formed under the mode of RBH will be formed under the mode of FBH, so FBH extends application scope of MPF. For example, experiments are accomplished, and L2Y2 is selected material, also sheet is formed by MPF equipment with blank-holder function, at the same time the target curvature radius is 350 mm in the direction of horizontal and vertical, when BHF is 8 Mpa, the workpiece formed by RBH cracked (see Fig. 4(a)), but at the same condition the workpiece formed by FBH achieved well result (see Fig. 4(b)). From Fig. 4(b), the photo shows that the surface is smooth and not any crack, but in Fig. 4(a) shows a crack in the middle of long axis. 3.5. Influence on forming force
Fig. 3. Contrast of sheet outline. (a) Rigid blank-holder and (b) flexible blankholder.
Target surface can be achieved by MPF press, when press working, the forming force of HC can act on elements by moving beam, finally act on sheet. So we studies forming force in the course of forming is very important to exactly select MPF equipment for us, by studying forming force we can control well sheet forming and reduce forming defect. Also the forming force is important for us to manufacture MPF equipment, if the forming force of MPF equipment is less than that of material forming needed, target shape will not be achieved, but if the forming force is big, also can result in crack in sheet. So fit forming force is needed by engineers selecting. For some hard material, if the material cannot be processed before can be processed by technology improved now, this method can
Fig. 4. Contrast of experiment photos. (a) Rigid blank-holder and (b) flexible blank-holder.
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G. Sun et al. / Journal of Materials Processing Technology 187–188 (2007) 517–520
two kinds of blank-holder technologies (RBH and FBH) in this paper. We can summarize several conclusions: 1. By FBH technology the height difference between blankholder surface and workpiece, and the height sharply less than that of RBH, so the workpiece cannot be processed by RBH forming before can be formed by FBH forming now, ultimately the forming limit will increase. 2. The workpiece formed by FBH used few material than that formed by RBH, but the quality is the same to that, so this method increases material utilization rate. Acknowledgements Fig. 5. Contrast of forming force.
settle the insufficiency forming force in MPF. FBH is just this method. Fig. 5 is a forming force curve by the two kinds of blank-holder modes, and the target curvature radius is 400 mm in the direction of horizontal and vertical, also the target workpiece is saddle, from Fig. 5 we can see that when punch reached the most far away distance in RBH forming, the distance needed the most great forming force, namely 30.06 kN, but in the FBH forming, the forming force is 14.98 kN. So when the same workpiece formed, the forming force by FBH forming is 1/2 of that by RBH forming, also this method can come true big deformation and thickness material forming by small forming force equipment. At the same time we can see the forming force by FBH forming increases slowly with the punch distance increasing, simultaneity this trend is slowly increase, also the forming force of sheet by RBH forming changes slowly at the initial stage. When the punch reach to 35 mm, the forming force sharply increase, it shows resistance of material forming increase too, so some defects appear. 4. Conclusions The influence on different thicknesses, different materials, wrinkle and forming limit are studied by forming sheet with
The work reported here is supported by National Natural Science Foundation of China (No. 50275063) and Project 985, Automotive Engineering of Jilin University. The authors appreciate their encouragement and support. References [1] M.Z. Li, K. Nakamura, S. Watanabe, First report: research on multi-point forming for sheet metal (study of the basic principles), in: Proceedings of the Japanese Spring Conference for Technology of Plasticity, 1992, pp. 519–522 (in Japanese). [2] Li Mingzhe, Liu Yuhong, et al., Multi-point forming: a flexible manufacturing method for a 3D surface sheet, J. Mater. Process. Technol. 87 (1999) 277–280. [3] M.Z. Li, Z.Y. Cai, Z. Sui, et al., Multi-point forming technology for sheet metal[J], J. Mater. Process. Technol. 129 (2002) 333–338. [4] Zhong-Yi Cai, Ming-Zhe Li, Multi-point forming of three-dimensional sheet metal and the control of the forming process[J], Int. J. Pres. Ves. Pip. 79 (2002) 289–296. [5] L. Mingzhe, L. Shuhui, L. Ze, Numerical simulation on wrinkling during multi-point forming process of sheet metal, Chin. Mech. Eng. 9 (10) (1998) 34–38 (in Chinese). [6] Z.Y. Cai, M.Z. Li, Optimum path forming technique for sheet metal and its realization in multi-point forming, J. Mater. Process. Technol. 110 (2001) 136–141. [7] Z.Y. Cai, M.Z. Li, Q.G. Yan, Flexible forming for sheet metal, J. Appl. Sci. 20 (2002) 202–206 (in Chinese).
Study of blank-holder technology on multi-point forming of thin sheet metal G. Sun a,∗ , M.Z. Li a , X.P. Yan a , P.P. Zhong b a
Dieless Forming Technology Center, Jilin University, Changchun 130025, PR China b College of Foreign Languages, Jilin University, Changchun 130025, PR China
Abstract Multi-point forming (MPF) is an advanced flexible manufacture technology, and the technology results from the idea that the whole die is separated into small punches that can be adjusted height. This idea is applied to the traditional rigid blank-holder (RBH), so flexible blank-holder (FBH) idea can be obtain. Different technologies about RBH forming and FBH forming are simulated in this paper, and the impact on wrinkle, crack and forming limit from the two different technologies is also analyzed. Furthermore this process is simulated by explicit software (LS DYNA) for the saddle workpiece with two kinds of thickness and the experiment is completed, Results indicated that the sheet with large deformation will wrinkle in the RBH forming, until blank-holder force (BHF) increasing the sheet cracked. But under the same condition the sheet is good in the FBH forming. When 1/2 area of blank-holder surface is cut out, and BHF is increased, the sheet also can be well gained. So the technology of FBH can sharply increase material utilization ratio, improve forming limit and decrease most disfigurements. © 2006 Elsevier B.V. All rights reserved. Keywords: Multi-point forming; Flexible blank-holder; Rigid blank-holder; Numerical simulation; Sheet metal; Forming force
1. Introduction
2. Principle of flexible and rigid blank-holders forming
MPF technology can achieve all kinds of curve surfaces by computers controlling elements of height adjusted, and this method is a flexible manufacture technology which substitutes the whole-die to realize three-dimension figure [1,2]. To traditional die MPF technology can realize a lot of functions, also every function that traditional die have can be achieved by a given equipment, so this method both can save mass time of designing and manufacturing, even can sharply reduce expenses of making product, eventually accelerates the rate of old product substituted by new one [3]. Now, MPF technology is applied to 3D sheet metal in shipboard, ornaments in architectures, streamline sheet metal in train and medicine fields. With blank-holders forming and without blank-holders forming are often used in current MPF technology mode. The technology modes of flexible and rigid blank-holders influences on the sheet metal forming are studied in this paper.
Fig. 1 is a photo that shows the punch, die and blank-holder parts of MPF equipment with the function of blank-holder, and elements are adjusted to the shape of saddle in the midst of the photo [4,5]. Furthermore, the distinct difference about RBH and FBH is blank-holder. The blank-holder device of MPF equipment (see Fig. 1) is that a circle hydraulic cylinders (HC) (total 40) dispose around with upper and lower elements, also there are two blank-holders, one is placed on the top of workpiece, and other is placed on the below of workpiece, these blank-holders can bring into press on workpiece by HC, so this method can realize blank-holder function of MPF. When the thickness of blank-holder is thick, the upper and lower HC are set the same or different press, therefore blank-holder surface can move up and down, and can realize flexible control in the height direction of blank-holder surface. When the thickness of blank-holder is thin, the blank-holder device cannot only realize flexible control in the height direction of blank-holder surface, but can also realize flexible blank-holder surface corresponding with the height of workpiece curve surface by blank-holder bending, consequently the latter can acquire better forming. The former, we name RBH of MPF, the latter, we name FBH of MPF [6,7].
∗ Corresponding author at: Dieless Forming Technology Center, Roll Forging Research Institute, Jilin University, Changchun 130025, PR China. Tel.: +86 431 509 4340; fax: +86 431 509 4340. E-mail address: sungang [email protected] (G. Sun).
0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.11.133
518
G. Sun et al. / Journal of Materials Processing Technology 187–188 (2007) 517–520
In the same condition, L2Y2 sheet formed with the two kinds of blank-holders, and the result sharply different. Results show that wrinkles appear in the workpiece formed by RBH, and none any of wrinkle in the workpiece formed by FBH. 3.2. Strain contrast after forming
Fig. 1. Workbench of MPF press.
3. Influence on forming by two kinds of blank-holders 3.1. Influence on wrinkle defects The influence on forming results with the two kinds of materials L2Y2 and 08Al is discussed by FBH and RBH forming. The thickness of 08Al materials is 0.5 mm, and the target curvature radius is 400 mm in the direction of horizontal and vertical, also the press is 5 MPa on blank-holder, FBH and RBH forming are studied in numerical simulation. From Fig. 2(a), there are distinct wrinkles in the workpiece formed by RBH, and the district wrinkles distribute in the middle of the workpiece, but none any of wrinkle in the workpiece formed by FBH, also the surface of the workpiece is lubricous (see Fig. 2(b)).
Fig. 2. Contrast of the two kinds of blank-holders. (a) Forming of rigid blankholder and (b) forming of flexible blank-holder.
By simulation we can understand the two kinds of blankholders influence to workpiece strain clearly. The workpiece of saddle formed by two kinds of blank-holders, and the target curvature radius is 400 mm in the direction of horizontal and vertical, material is 08Al. Workpiece strain named strain in the direction of thickness in this paper, and strain of workpiece formed by RBH is disorder, at the same time the strain is small in the middle of workpiece, also the strain value is 0.2. Sheet will became thinner in the course of forming, and transition section in long axis is thinner than that in short axis, so sheet will crack in long axis direction, hence big deformation will be difficultly come true. But strain of workpiece formed by FBH is only 0.08, just because the workpiece by this mode forming has no transition section, the strain of all of whole sheet is average, so the workpiece formed by FBH hardly cracks. 3.3. Influence on material utilization ratio In addition, from the two technology modes, we know that FBH can save material. Because the material inside of blankholder will become small with sheet deformation, this method sharply reduces the area of transition section, namely saves material. Blank-holder device has an important function that it can transport sheet in a certain speed in the course of forming to prevent wrinkle, so it can achieve successfully complex curve surface in sheet metal forming, but the sheet inside of blankholder will be cut in the last, namely this sheet is waste, however, FBH forming mode reduces the material inside of blank-holder, and it is good to save sheet material. The technology of FBH can settle well the contradiction for both wrinkling and saving material of sheet. For example, the workpiece of saddle is formed with the two kinds of blank-holder modes, and the target curvature radius is 400 mm in the direction of horizontal and vertical, also BHF is 7 Mpa, using these conditions the influence on FBH saving material is distinct. When the sheet size is 480 mm in horizontal direction and 400 mm in vertical direction, and blank-holder width is 20 mm, we can compute that only using 82.52% material in FBH forming can acquire the same workpiece formed by RBH. Fig. 3 shows workpiece outline line, and the target curvature radius of workpiece is 450 mm in the direction of horizontal and vertical, also the workpiece is saddle shape. In the figure of Fig. 3, the outside dashed is the original sheet borderline, and inside dashed is the target workpiece borderline, so between the outside dashed and inside dashed are blank-holder region. The solid line is the borderline include blank-holder region after formed, and the material flow trend can be acquired clearly. Fig. 3(a) is the workpiece outline in RBH forming, and the sheet in the blank-holder surface near the symmetry center easily flows
G. Sun et al. / Journal of Materials Processing Technology 187–188 (2007) 517–520
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into the transition section than the sheet away from the symmetry center. Ultimately it is little sheet metal in blank-holder surface. But in the mode of FBH forming, blank-holder surface moved up and down with the sheet deformation, so the transition section disappears and the borderline of sheet before forming and after forming is not change (see Fig. 3(b)). 3.4. Influence on deformation quantity In some case, the technology of FBH not only saves material, but also extends forming limit of sheet, and some workpieces cannot be formed under the mode of RBH will be formed under the mode of FBH, so FBH extends application scope of MPF. For example, experiments are accomplished, and L2Y2 is selected material, also sheet is formed by MPF equipment with blank-holder function, at the same time the target curvature radius is 350 mm in the direction of horizontal and vertical, when BHF is 8 Mpa, the workpiece formed by RBH cracked (see Fig. 4(a)), but at the same condition the workpiece formed by FBH achieved well result (see Fig. 4(b)). From Fig. 4(b), the photo shows that the surface is smooth and not any crack, but in Fig. 4(a) shows a crack in the middle of long axis. 3.5. Influence on forming force
Fig. 3. Contrast of sheet outline. (a) Rigid blank-holder and (b) flexible blankholder.
Target surface can be achieved by MPF press, when press working, the forming force of HC can act on elements by moving beam, finally act on sheet. So we studies forming force in the course of forming is very important to exactly select MPF equipment for us, by studying forming force we can control well sheet forming and reduce forming defect. Also the forming force is important for us to manufacture MPF equipment, if the forming force of MPF equipment is less than that of material forming needed, target shape will not be achieved, but if the forming force is big, also can result in crack in sheet. So fit forming force is needed by engineers selecting. For some hard material, if the material cannot be processed before can be processed by technology improved now, this method can
Fig. 4. Contrast of experiment photos. (a) Rigid blank-holder and (b) flexible blank-holder.
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G. Sun et al. / Journal of Materials Processing Technology 187–188 (2007) 517–520
two kinds of blank-holder technologies (RBH and FBH) in this paper. We can summarize several conclusions: 1. By FBH technology the height difference between blankholder surface and workpiece, and the height sharply less than that of RBH, so the workpiece cannot be processed by RBH forming before can be formed by FBH forming now, ultimately the forming limit will increase. 2. The workpiece formed by FBH used few material than that formed by RBH, but the quality is the same to that, so this method increases material utilization rate. Acknowledgements Fig. 5. Contrast of forming force.
settle the insufficiency forming force in MPF. FBH is just this method. Fig. 5 is a forming force curve by the two kinds of blank-holder modes, and the target curvature radius is 400 mm in the direction of horizontal and vertical, also the target workpiece is saddle, from Fig. 5 we can see that when punch reached the most far away distance in RBH forming, the distance needed the most great forming force, namely 30.06 kN, but in the FBH forming, the forming force is 14.98 kN. So when the same workpiece formed, the forming force by FBH forming is 1/2 of that by RBH forming, also this method can come true big deformation and thickness material forming by small forming force equipment. At the same time we can see the forming force by FBH forming increases slowly with the punch distance increasing, simultaneity this trend is slowly increase, also the forming force of sheet by RBH forming changes slowly at the initial stage. When the punch reach to 35 mm, the forming force sharply increase, it shows resistance of material forming increase too, so some defects appear. 4. Conclusions The influence on different thicknesses, different materials, wrinkle and forming limit are studied by forming sheet with
The work reported here is supported by National Natural Science Foundation of China (No. 50275063) and Project 985, Automotive Engineering of Jilin University. The authors appreciate their encouragement and support. References [1] M.Z. Li, K. Nakamura, S. Watanabe, First report: research on multi-point forming for sheet metal (study of the basic principles), in: Proceedings of the Japanese Spring Conference for Technology of Plasticity, 1992, pp. 519–522 (in Japanese). [2] Li Mingzhe, Liu Yuhong, et al., Multi-point forming: a flexible manufacturing method for a 3D surface sheet, J. Mater. Process. Technol. 87 (1999) 277–280. [3] M.Z. Li, Z.Y. Cai, Z. Sui, et al., Multi-point forming technology for sheet metal[J], J. Mater. Process. Technol. 129 (2002) 333–338. [4] Zhong-Yi Cai, Ming-Zhe Li, Multi-point forming of three-dimensional sheet metal and the control of the forming process[J], Int. J. Pres. Ves. Pip. 79 (2002) 289–296. [5] L. Mingzhe, L. Shuhui, L. Ze, Numerical simulation on wrinkling during multi-point forming process of sheet metal, Chin. Mech. Eng. 9 (10) (1998) 34–38 (in Chinese). [6] Z.Y. Cai, M.Z. Li, Optimum path forming technique for sheet metal and its realization in multi-point forming, J. Mater. Process. Technol. 110 (2001) 136–141. [7] Z.Y. Cai, M.Z. Li, Q.G. Yan, Flexible forming for sheet metal, J. Appl. Sci. 20 (2002) 202–206 (in Chinese).