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The study on numerical simulation of the laser tailor welded blanks stamping
Journal of Materials Processing Technology 187–188 (2007) 128–131
The study on numerical simulation of the laser tailor welded blanks stamping X.G. Qiu ∗ , W.L Chen Iron & Steel Research Institute of Pangang Group, TaoTaoyuan Road, Panzhihua 617000, China
Abstract The stamping process of the tailor welded blank (TWB) was simulated by the software of DYNAFORM. The finite element model of a boxy part was founded, and the forming of different thickness and properties of the material was studied. Meanwhile, the influence of weld seam on forming result was analyzed. The results show that the weld seam model which founded by real properties can describe the plastic deformation and strain distribution more exactly in the forming process. © 2006 Elsevier B.V. All rights reserved. Keywords: Tailor welded blanks; Weld seam; Numerical simulation; Strain distribution
1. Introduction The laser tailor welded blank is, to make use of the laser processing technology, joining sheet metal of different thickness, strength and surfaces status in a one piece before stamping process. The laser tailor welded blank has gotten the extensive application in the automobile industry. According to the introduction [1], the body and chassis of automobile is made up of more than 300 parts, the TWB can reduce 66% of the number of parts, therefore, it reduces the stamping mould of parts, increases the utilization of material. Adopting the TWB stamping technology, the whole quantity of product gets the exaltation, it plays an important role of cutting the automobile weight, reducing process, cutting cost, raising the efficiency of producing and reducing the consumption of material. Therefore, researching the TWB has very important meaning. The result of fundamental experiments indicates [2] that, the hardening function of the weld seam and its hot influence area make the property of the TWB change greatly. The different property of the weld seam and the base material and the difference of blank’s thickness make the plastic deformation capacity of the whole welded blank descend, and bring great difficulty to stamping process and the control of blank deformation. For the sake of the further research on the influence of weld seam in TWB’s stamping, this paper is about the stamping process
∗
Corresponding author. Tel.: +86 812 3380572; fax: +86 812 3380766. E-mail address: [email protected] (X.G. Qiu).
0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.11.128
of the TWB which was simulated by the software of DYNAFORM. 2. The finite element simulation research 2.1. The finite element modeling method The simulation process of TWB’s stamping, the difficulty mainly lies in the treatment of blank’s weld seam and the establishments of mould models. Since there are some differences in both sides and beyond control the thinner part, blank holders force too light makes the thinner wrinkle, blank holders force too heavy makes it breaking. Therefore, in practical stamping, in order to make blank acquire the consistent pressure, we usually adopt to take the stairs, variable form or sectional clamping ring, or increase the pad between the clamping ring and the thinner part and utilize terracing mode or assemble punch/die. In numerical simulation, also adopt the definition assembly mould method. In this paper, clamping ring adopts segmental blank holders, which makes different parts of TWB put up with different pressure and controls wrinkling and the movement of weld seam. Document [3–5] introduces two treatments of weld seam, one is the establishment of weld seam model accurately, considering its dimension and shape of the weld seam and its hot influence area, sew a mesh of the area demarcation to the weld seam. The second is to neglect the type of the weld seam, consider the position of the weld seam only, the weld seam is replaced with a line. Software of DYNAFORM can also set up the model with a series of rigid
X.G. Qiu, W.L Chen / Journal of Materials Processing Technology 187–188 (2007) 128–131
129
Fig. 3. Diagram of strain distribution.
refer to the Fig. 2. The different positions of two weld seams are called the No.1 position and No.2 position. The weld seam adopts two kinds of methods, one is to build up a weld seam model, the width is 2 mm, divide the weld seam area into finite element grids, choosing the material property from Table 1. The other is using a line to replace the weld seam. Design two clamping ring for different blanks, control two blanks of different thickness separately. The base material model choose to use three-parameter anisotropic material, in which the young’s modulus E = 2.07 × 105 MPa, Poisson’s ratio = 0.3, the property parameter refers to the Table 1. The weld seam material model chooses to use elastic–plastic exponential hardening material. The property parameter of weld seam is tested by stretching experiment (Table 1).
Fig. 1. The FEM model of the tools and blank.
3. Result and analysis 3.1. The calculation result of non-real weld seam Fig. 2. Position of the weld seam: (a) No. 1 position of the weld seam and (b) No. 2 position of the weld seam.
conjunctions (the weld spot) between the adjoin node of two blanks. This paper builds up a model of a square boxes, the mould element is defined as a rigid shell element, adopting selfadapting grid division method, divides the element into the square grids. The mould interstice = 1.1t0 , punch and blank static friction factor μ1 = 0.2, the coefficient of dynamic friction μ2 = 0.04. The punch moving speed = 2000 mm/s, blank holders force = 200 kN, refer to the Fig. 1.
Compare to the different calculation result of the same thickness blank and not which in different location, it shows that the simulative result cannot indicate the influence of weld seam, but observe the vary circumstances of the base material only, the Strain distribution of parts hasn’t difference with non-TWB, shown in the Fig. 3. Since the property of two kinds of base material are different, while stamping to deformation the fluxion of the material is different, the weld seam moves to the thicker blank obviously. 3.2. The calculation result of real weld seam Simulate the TWB of the same thickness and not and two weld seam location separately.
2.2. Simulation program and material property Designing two weld seams’ positions, one is among the parts’ central section; the other passes the opposite angles of parts,
(1) Simulative result of the same thickness TWB.
Table 1 Properties of material Materials
Thickness (mm)
RP0.2 (MPa)
Rm (MPa)
n¯
r0
r45
r90
Effective plastic stress/strain
Base materials No. 1 Base materials No. 2 Weld seam
0.8 1.2 1.0
185 130 393
336 280 490
0.22 0.28 0.13
1.73 2.14 –
1.48 1.91 –
1.86 2.75 –
σ = 600(0.0046 + εp )0.22 σ = 555(0.0058 + εp )0.28 σ = 735(0.0081 + εp )0.13
130
X.G. Qiu, W.L Chen / Journal of Materials Processing Technology 187–188 (2007) 128–131
Fig. 5. Thickness distribution of the weld seam on No. 1 position.
Fig. 4. Strain distribution of the weld seam: (a) No. 1 position of the weld seam and (b) No. 2 position of the weld seam.
Fig. 4 is the strain distribution diagram of weld seam, can see when the same thickness TWB stamping, the forming property of TWB is related to property of the base material, it depends on the correlation of weld seam and pressure direction (major strain direction). No. 1 weld seam bends to deform, while the deformation is not too large, weld seam and base material will not appear to danger. No. 2 weld seam position deforms by deep drawing, the weld seam deforms along the major strain direction by pulling, so the part appears broken, then the crack expand toward base material of both sides. (2) The simulation result of unequal thickness TWB. When unequal thickness TWB stamping, the forming property of the TWB has something to do with two kinds of property differences of material property and thickness ratio. When two kinds of property is basically same, the TWB stamping has something to do with thickness ratio, because the plane strain spot of forming limit (FLD0 ) is directly related to blank thickness, FLD0 = (67.304t + 110.95)n [6], the thicker blank has bet-
ter forming property than thinner obviously. The simulation result indicates that, in most circumstances cracking appears in the thinner material side of blank, the more the thickness ratio is big, the more the deformation of the thinner is big. Fig. 5 is the diagram of thickness distribution, strain distribution of No.1 weld seam position is similar to the equal thickness blank, both weld seam and base material will not appear danger. Fig. 6 is the strain distribution diagram of No. 2 weld seam position, it is seen that, deformation of No. 2 weld seam position attains the limiting strain value, the weld seam has began to crack and expand toward the thinner. Because of the difference of the blank thickness and base material strength, the both sides of weld seam appears uneven deformation, the weld seam moves to the thicker blank obviously, and TWB forming property becomes lower with the increasing difference of the blank thickness and strength. Because of the influence of weld seam, the limiting major strain value and minor strain value of TWB close to the weld seam district decreases, and closes to the plate strain state gradually. The simulation result indicates that, when the weld seam parallels with pressure direction (major strain direction), the weld seam position appears broken, which makes forming property lower. When the weld seam is vertical to the pressure direction, the weld seam strength is too high to deforming easily, so it is not easy to happen broken, usually in weaker material (or the thickness is thinner). Therefore, while arranging the weld seam should avoid the weld seam from paralleling with major strain direction.
Fig. 6. Strain distribution of the weld seam on No. 2 position.
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deformation and its influence to base material, while using the method that precisely establishes the finite element model of weld seam and using the real material parameter of weld seam, can get more approximate with fact calculation result accurately. 3.4. The influence of the blank holders force The calculation result indicates that, unequal thickness TWB adopting one clamping ring cannot control wrinkling and weld seam moving, such as the Fig. 7 shows. Adopting segmental blank holders makes different parts of TWB have different pressures, which can preferably control the wrinkling and weld seam moving. In stamping process of unequal thickness TWB, controlling mould and clamping ring makes the blank fixed, the movement of weld seam is mainly relation to the base material property of TWB and thicknesses ratio. 4. Conclusions
Fig. 7. The influence of the pressure on tailor welded blank: (a) wrinkling and movement of the weld seam and (b) normal.
3.3. The influence of material property and blank thickness The simulation result indicates that, when use different material and thicknesses blank for welding, the deformation of TWB depends on strength ratio and thickness ratio of two kinds of materials. In most circumstances cracking appears in the thinner blank, the more the thickness ratio is big, the more the deformation of the thinner is big. Generally speaking, broken appears at part 3–5 mm away from weld seam. Thickness difference changes the section remarkably, which results in stress centralizes, deformation augment sharply here, which causes broken. The more the material strength of the thicker blank is high, the more its deformation is small, or almost no deformation, the plastic deformation concentrates in the thinner totally. In order to making two pieces of different thickness material deform completely, the strength of the thinner material has to be higher than the thicker. Knowing from the above, the calculation result of weld seam replaced by a supposed line cannot reflect really the weld seam
1. Using the method that precisely establishes the finite element model of weld seam, the real material parameter of weld seam, can gets more approximate with fact calculation result. Adopting segmental blank holders can preferably control the wrinkling and moving of weld seam on unequal thickness TWB. 2. The weld seam’s pressure direction (major strain direction) is relation to deformation directly, when the weld seam parallels with pressure direction, the forming property of TWB is worst. 3. The weld seam movement of unequal thickness TWB depends on base material property and thickness ratio, generally speaking, weld seam moves to the thicker blank obviously. Therefore, choosing the welding material reasonably, keeping part’s deformation of TWB even and minimizing weld seam moving, which would be the emphasis of TWB in applied technology from now on. References [1] Y. Kang, Quality Control and Forming Property for Current Plate of Motor Vehicle, Metallurgical Industry Press, Bejing, 2002, pp. 18–25. [2] X.G. Qiu, The influence of the weld seam on formabilily of tailor-welded blank, Phys. Test. Chem. Anal. A: Phys. Test. 4 (2005) 166–170. [3] S.H. Zhang, Y. Xu, Z.T. Wang, State of the art stamping technology of tailir welded blanks (), Metal Form. Technol. 4 (2001) 1–4. [4] S.H. Zhang, Y. Xu, Z.T. Wang, State of the art stamping technology of tailir welded blanks (), Metal Form. Technol. 6 (2001) 1–4. [5] S.H. Li, Current development and trends of the tailored blanks application in auto-body stamping, Chin. J. Mech. Eng. 2 (2002) 1–7. [6] CamSys, Co. ASAME 4.0 Automated Analysis and Measurement Environment.
The study on numerical simulation of the laser tailor welded blanks stamping X.G. Qiu ∗ , W.L Chen Iron & Steel Research Institute of Pangang Group, TaoTaoyuan Road, Panzhihua 617000, China
Abstract The stamping process of the tailor welded blank (TWB) was simulated by the software of DYNAFORM. The finite element model of a boxy part was founded, and the forming of different thickness and properties of the material was studied. Meanwhile, the influence of weld seam on forming result was analyzed. The results show that the weld seam model which founded by real properties can describe the plastic deformation and strain distribution more exactly in the forming process. © 2006 Elsevier B.V. All rights reserved. Keywords: Tailor welded blanks; Weld seam; Numerical simulation; Strain distribution
1. Introduction The laser tailor welded blank is, to make use of the laser processing technology, joining sheet metal of different thickness, strength and surfaces status in a one piece before stamping process. The laser tailor welded blank has gotten the extensive application in the automobile industry. According to the introduction [1], the body and chassis of automobile is made up of more than 300 parts, the TWB can reduce 66% of the number of parts, therefore, it reduces the stamping mould of parts, increases the utilization of material. Adopting the TWB stamping technology, the whole quantity of product gets the exaltation, it plays an important role of cutting the automobile weight, reducing process, cutting cost, raising the efficiency of producing and reducing the consumption of material. Therefore, researching the TWB has very important meaning. The result of fundamental experiments indicates [2] that, the hardening function of the weld seam and its hot influence area make the property of the TWB change greatly. The different property of the weld seam and the base material and the difference of blank’s thickness make the plastic deformation capacity of the whole welded blank descend, and bring great difficulty to stamping process and the control of blank deformation. For the sake of the further research on the influence of weld seam in TWB’s stamping, this paper is about the stamping process
∗
Corresponding author. Tel.: +86 812 3380572; fax: +86 812 3380766. E-mail address: [email protected] (X.G. Qiu).
0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.11.128
of the TWB which was simulated by the software of DYNAFORM. 2. The finite element simulation research 2.1. The finite element modeling method The simulation process of TWB’s stamping, the difficulty mainly lies in the treatment of blank’s weld seam and the establishments of mould models. Since there are some differences in both sides and beyond control the thinner part, blank holders force too light makes the thinner wrinkle, blank holders force too heavy makes it breaking. Therefore, in practical stamping, in order to make blank acquire the consistent pressure, we usually adopt to take the stairs, variable form or sectional clamping ring, or increase the pad between the clamping ring and the thinner part and utilize terracing mode or assemble punch/die. In numerical simulation, also adopt the definition assembly mould method. In this paper, clamping ring adopts segmental blank holders, which makes different parts of TWB put up with different pressure and controls wrinkling and the movement of weld seam. Document [3–5] introduces two treatments of weld seam, one is the establishment of weld seam model accurately, considering its dimension and shape of the weld seam and its hot influence area, sew a mesh of the area demarcation to the weld seam. The second is to neglect the type of the weld seam, consider the position of the weld seam only, the weld seam is replaced with a line. Software of DYNAFORM can also set up the model with a series of rigid
X.G. Qiu, W.L Chen / Journal of Materials Processing Technology 187–188 (2007) 128–131
129
Fig. 3. Diagram of strain distribution.
refer to the Fig. 2. The different positions of two weld seams are called the No.1 position and No.2 position. The weld seam adopts two kinds of methods, one is to build up a weld seam model, the width is 2 mm, divide the weld seam area into finite element grids, choosing the material property from Table 1. The other is using a line to replace the weld seam. Design two clamping ring for different blanks, control two blanks of different thickness separately. The base material model choose to use three-parameter anisotropic material, in which the young’s modulus E = 2.07 × 105 MPa, Poisson’s ratio = 0.3, the property parameter refers to the Table 1. The weld seam material model chooses to use elastic–plastic exponential hardening material. The property parameter of weld seam is tested by stretching experiment (Table 1).
Fig. 1. The FEM model of the tools and blank.
3. Result and analysis 3.1. The calculation result of non-real weld seam Fig. 2. Position of the weld seam: (a) No. 1 position of the weld seam and (b) No. 2 position of the weld seam.
conjunctions (the weld spot) between the adjoin node of two blanks. This paper builds up a model of a square boxes, the mould element is defined as a rigid shell element, adopting selfadapting grid division method, divides the element into the square grids. The mould interstice = 1.1t0 , punch and blank static friction factor μ1 = 0.2, the coefficient of dynamic friction μ2 = 0.04. The punch moving speed = 2000 mm/s, blank holders force = 200 kN, refer to the Fig. 1.
Compare to the different calculation result of the same thickness blank and not which in different location, it shows that the simulative result cannot indicate the influence of weld seam, but observe the vary circumstances of the base material only, the Strain distribution of parts hasn’t difference with non-TWB, shown in the Fig. 3. Since the property of two kinds of base material are different, while stamping to deformation the fluxion of the material is different, the weld seam moves to the thicker blank obviously. 3.2. The calculation result of real weld seam Simulate the TWB of the same thickness and not and two weld seam location separately.
2.2. Simulation program and material property Designing two weld seams’ positions, one is among the parts’ central section; the other passes the opposite angles of parts,
(1) Simulative result of the same thickness TWB.
Table 1 Properties of material Materials
Thickness (mm)
RP0.2 (MPa)
Rm (MPa)
n¯
r0
r45
r90
Effective plastic stress/strain
Base materials No. 1 Base materials No. 2 Weld seam
0.8 1.2 1.0
185 130 393
336 280 490
0.22 0.28 0.13
1.73 2.14 –
1.48 1.91 –
1.86 2.75 –
σ = 600(0.0046 + εp )0.22 σ = 555(0.0058 + εp )0.28 σ = 735(0.0081 + εp )0.13
130
X.G. Qiu, W.L Chen / Journal of Materials Processing Technology 187–188 (2007) 128–131
Fig. 5. Thickness distribution of the weld seam on No. 1 position.
Fig. 4. Strain distribution of the weld seam: (a) No. 1 position of the weld seam and (b) No. 2 position of the weld seam.
Fig. 4 is the strain distribution diagram of weld seam, can see when the same thickness TWB stamping, the forming property of TWB is related to property of the base material, it depends on the correlation of weld seam and pressure direction (major strain direction). No. 1 weld seam bends to deform, while the deformation is not too large, weld seam and base material will not appear to danger. No. 2 weld seam position deforms by deep drawing, the weld seam deforms along the major strain direction by pulling, so the part appears broken, then the crack expand toward base material of both sides. (2) The simulation result of unequal thickness TWB. When unequal thickness TWB stamping, the forming property of the TWB has something to do with two kinds of property differences of material property and thickness ratio. When two kinds of property is basically same, the TWB stamping has something to do with thickness ratio, because the plane strain spot of forming limit (FLD0 ) is directly related to blank thickness, FLD0 = (67.304t + 110.95)n [6], the thicker blank has bet-
ter forming property than thinner obviously. The simulation result indicates that, in most circumstances cracking appears in the thinner material side of blank, the more the thickness ratio is big, the more the deformation of the thinner is big. Fig. 5 is the diagram of thickness distribution, strain distribution of No.1 weld seam position is similar to the equal thickness blank, both weld seam and base material will not appear danger. Fig. 6 is the strain distribution diagram of No. 2 weld seam position, it is seen that, deformation of No. 2 weld seam position attains the limiting strain value, the weld seam has began to crack and expand toward the thinner. Because of the difference of the blank thickness and base material strength, the both sides of weld seam appears uneven deformation, the weld seam moves to the thicker blank obviously, and TWB forming property becomes lower with the increasing difference of the blank thickness and strength. Because of the influence of weld seam, the limiting major strain value and minor strain value of TWB close to the weld seam district decreases, and closes to the plate strain state gradually. The simulation result indicates that, when the weld seam parallels with pressure direction (major strain direction), the weld seam position appears broken, which makes forming property lower. When the weld seam is vertical to the pressure direction, the weld seam strength is too high to deforming easily, so it is not easy to happen broken, usually in weaker material (or the thickness is thinner). Therefore, while arranging the weld seam should avoid the weld seam from paralleling with major strain direction.
Fig. 6. Strain distribution of the weld seam on No. 2 position.
X.G. Qiu, W.L Chen / Journal of Materials Processing Technology 187–188 (2007) 128–131
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deformation and its influence to base material, while using the method that precisely establishes the finite element model of weld seam and using the real material parameter of weld seam, can get more approximate with fact calculation result accurately. 3.4. The influence of the blank holders force The calculation result indicates that, unequal thickness TWB adopting one clamping ring cannot control wrinkling and weld seam moving, such as the Fig. 7 shows. Adopting segmental blank holders makes different parts of TWB have different pressures, which can preferably control the wrinkling and weld seam moving. In stamping process of unequal thickness TWB, controlling mould and clamping ring makes the blank fixed, the movement of weld seam is mainly relation to the base material property of TWB and thicknesses ratio. 4. Conclusions
Fig. 7. The influence of the pressure on tailor welded blank: (a) wrinkling and movement of the weld seam and (b) normal.
3.3. The influence of material property and blank thickness The simulation result indicates that, when use different material and thicknesses blank for welding, the deformation of TWB depends on strength ratio and thickness ratio of two kinds of materials. In most circumstances cracking appears in the thinner blank, the more the thickness ratio is big, the more the deformation of the thinner is big. Generally speaking, broken appears at part 3–5 mm away from weld seam. Thickness difference changes the section remarkably, which results in stress centralizes, deformation augment sharply here, which causes broken. The more the material strength of the thicker blank is high, the more its deformation is small, or almost no deformation, the plastic deformation concentrates in the thinner totally. In order to making two pieces of different thickness material deform completely, the strength of the thinner material has to be higher than the thicker. Knowing from the above, the calculation result of weld seam replaced by a supposed line cannot reflect really the weld seam
1. Using the method that precisely establishes the finite element model of weld seam, the real material parameter of weld seam, can gets more approximate with fact calculation result. Adopting segmental blank holders can preferably control the wrinkling and moving of weld seam on unequal thickness TWB. 2. The weld seam’s pressure direction (major strain direction) is relation to deformation directly, when the weld seam parallels with pressure direction, the forming property of TWB is worst. 3. The weld seam movement of unequal thickness TWB depends on base material property and thickness ratio, generally speaking, weld seam moves to the thicker blank obviously. Therefore, choosing the welding material reasonably, keeping part’s deformation of TWB even and minimizing weld seam moving, which would be the emphasis of TWB in applied technology from now on. References [1] Y. Kang, Quality Control and Forming Property for Current Plate of Motor Vehicle, Metallurgical Industry Press, Bejing, 2002, pp. 18–25. [2] X.G. Qiu, The influence of the weld seam on formabilily of tailor-welded blank, Phys. Test. Chem. Anal. A: Phys. Test. 4 (2005) 166–170. [3] S.H. Zhang, Y. Xu, Z.T. Wang, State of the art stamping technology of tailir welded blanks (), Metal Form. Technol. 4 (2001) 1–4. [4] S.H. Zhang, Y. Xu, Z.T. Wang, State of the art stamping technology of tailir welded blanks (), Metal Form. Technol. 6 (2001) 1–4. [5] S.H. Li, Current development and trends of the tailored blanks application in auto-body stamping, Chin. J. Mech. Eng. 2 (2002) 1–7. [6] CamSys, Co. ASAME 4.0 Automated Analysis and Measurement Environment.