Prediction of Springback in Long Channels

doi:10.1007/s40195-015-0355-0

Abstract

Abstract:

Sheet metal forming is one of the most preferred manufacturing processes in automotive and aerospace industries. However, due to increase in fuel prices and more stringent environmental regulation, these industries are facing many challenges to meet the criteria. Due to this, many efforts in design and manufacturing were considered and presented. Those efforts were implementing lighter-weight materials like aluminum and magnesium (but they have higher elasticity as compared to steel) and implementing higher-strength steel with lower thickness. The main challenge found in both cases is springback after deformation. Springback is the elastic recovery after the part is unloaded. In this paper, the 3D channels with large length were deformed numerically and springback at different section was predicted. For this purpose, tailor-welded blank was considered. The geometric change along the long axis was also discussed. In addition, the effect of flange springback on wall springback was also analyzed. It was found that different section produced different springback and greater influence of flange springback. To validate the numerical simulation approach, the experiments on one case were performed and compared.

Key words: Channel forming, Springback, Numerical simulation, Tailor-welded blanks

Chetan P. Nikhare. Prediction of Springback in Long Channels[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(12): 1525-1531.

Figures/Tables 21

Fig.1 True stress-strain curve of the soft and hard materials

Table 1 Power law parameters for both material curves

Material	Yield strength (MPa)	Strength coefficient K (MPa)	Strain hardening exponent n
Soft material	251	600	0.2
Hard material	503	1200	0.2

Fig.2 Channel forming model for channel and springback simulation

Fig.3 Springback measurement at channel wall and at flange

Fig.4 Channel forming force displacement curve for all four cases

Fig.5 2D profiles of desired shape and shape after load release of both edges and weld line for SMSTS

Table 2 Springback angle at wall and flange for front edge, weld line and back edge for the case SMSTS

Springback angle	Front edge	Weld line	Back edge
Wall angle θ₁	4.37	4.85	4.31
Flange angle θ₂	7.15	7.15	7.15

Fig.6 2D profiles of desired shape and shape after load release of both edges and weld line for SMDT

Table 3 Springback angle at wall and flange for front edge, weld line and back edge for the case SMDT

Springback angle	Front edge	Weld line	Back edge
Wall angle θ₁	3.67	4.74	2.53
Flange angle θ₂	6.04	5.83	4.54

Fig.7 2D profiles of desired shape and shape after load release of both edges and weld line for DMST

Table 4 Springback angle at wall and flange for front edge, weld line and back edge for case DMST

Springback angle	Front edge	Weld line	Back edge
Wall angle θ₁	8.60	8.29	7.05
Flange angle θ₂	12.74	11.96	11.22

Fig.8 2D profiles of desired shape and shape after load release of both edges and weld line for DMDT

Table 5 Springback angle at wall and flange for front edge, weld line and back edge for case DMDT

Springback angle	Front edge	Weld line	Back edge
Wall angle θ₁	4.24	6.52	4.46
Flange angle θ₂	7.43	7.25	5.55

Table 6 Springback level at channel wall for all case

Case	Springback level at channel wall
Case	Front edge	Weld line	Back edge
SMSTS	Same	Same	Same
SMDT	Middle	High	Low
DMST	High	Middle	Low
DMDT	Low	High	Middle

Table 7 Springback level at channel flange for all case

Case	Springback level at channel flange
Case	Front edge	Weld line	Back edge
SMSTS	Same	Same	Same
SMDT	High	Middle	Low
DMST	High	Middle	Low
DMDT	High	Middle	Low

Fig.9 Experimental deformed channels for SMDT case (painted white for scan)

Fig.10 Force-displacement curve during channel forming for SMDT case

Fig.11 Superimposed 3D reference and deformed channel for SMDT case

Fig.12 Superimposed 2D section of reference and deformed channel for SMDT case for wall and flange angle measurement

Table 8 Springback angle at channel wall and flange for SMDT case

Experiment	Springback angle	Thick front edge	Weld line	Thin back edge
No. 1	Wall angle θ₁	4.60	6.38	4.12
No. 2	Wall angle θ₁	1.13	4.78	4.41
No. 3	Wall angle θ₁	3.75	4.12	3.01
Average		4.18	5.25	3.56
No. 1	Flange angle θ₂	14.03	14.03	9.92
No. 2	Flange angle θ₂	11.86	12.63	9.46
No. 3	Flange angle θ₂	11.31	11.76	9.46
Average		12.67	12.89	9.69

Table 9 Comparison of springback level at channel wall and flange for SMDT case

Section	Springback level at channel wall		Springback level at channel flange
Section	Experiment	Simulation	Experiment	Simulation
Front edge	4.18 (medium)	3.67 (medium)	12.67 (medium)	6.04 (high)
Weld line	5.25 (high)	4.74 (high)	12.89 (high)	5.83 (medium)
Back edge	3.56 (low)	2.53 (low)	9.69 (low)	4.54 (low)

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