Abstract

Objective
To address problems such as tearing, wrinkling, and non-uniform deformation that may occur during the cold stamping forming process of the automotive hood outer panel, AutoForm software was used to optimize the process parameters.

Methods
An aluminum alloy sheet with a thickness of 0.95 mm was used as the raw material. A three-dimensional model of the hood outer panel was established using CATIA. AutoForm software was applied to conduct numerical simulation analysis of the deep-drawing process of the hood outer panel. Single-factor experiments and orthogonal experiments were carried out to optimize the deep-drawing process parameters and improve the forming quality of the panel.

Results
The single-factor experimental results show that when the friction coefficient is 0.10 and the stamping speed is 200 mm/s, increasing the blank-holding force from 1,200 kN to 2,200 kN increases the maximum thinning rate of the product from 14.74% to 17.37%, and the proportion of the safe zone increases from 81.50% to 84.66%.

When the blank-holding force is 1,600 kN and the stamping speed is 200 mm/s, increasing the friction coefficient from 0.10 to 0.18 raises the maximum thinning rate from 15.79% to 19.47%, while the proportion of the safe zone first increases from 83.64% to 84.69% and then decreases to 84.13%. In addition, changes in stamping speed have no significant effect on the maximum thinning rate or the proportion of the safe zone.

The orthogonal experimental results indicate that when the blank-holding force is 1,400 kN, the friction coefficient is 0.10, and the stamping speed is 300 mm/s, the maximum thinning rate of the hood outer panel is optimal. When the blank-holding force is 1,700 kN, the friction coefficient is 0.16, and the stamping speed is 400 mm/s, the proportion of the safe zone and the forming quality of the hood outer panel are optimal.

Conclusion
The optimal process parameters are: blank-holding force of 1,700 kN, friction coefficient of 0.16, and stamping speed of 400 mm/s.

Figure 1 Schematic diagram of the 3D model of the automotive hood outer panel
Figure 2 Configuration of virtual drawbeads (a) and schematic of main drawbead dimensions (b)

Figure 3 Major strain maps of the product under different blank-holding forces

Figure 4 Formability results of the product under different blank-holding forces

Figure 5  Cold stamping deformation process of the product over time at a blank-holding force of 2,200 kN

Figure 6 Major strain maps of the product under different friction coefficients

Figure 7 Formability results of the product under different friction coefficients
Figure 8 Simulation results of the orthogonal experiments

Figure 9  Schematic diagram of the trial-produced product

Summary

1. When the friction coefficient is 0.10 and the stamping speed is 200 mm/s, increasing the blank-holding force from 1,200 kN to 2,200 kN increases the maximum thinning rate from 14.74% to 17.37%, and the proportion of the safe zone from 81.50% to 84.66%.

2. When the blank-holding force is 1,600 kN and the stamping speed is 200 mm/s, increasing the friction coefficient from 0.10 to 0.18 increases the maximum thinning rate from 15.79% to 19.47%. The proportion of the safe zone first increases from 83.64% to 84.69%, and then decreases to 84.13%. Meanwhile, the change in stamping speed has no significant effect on the maximum thinning rate or the proportion of the safe zone.

3. The orthogonal experimental results show that the optimal parameter combination for maximum thinning rate is A1B1C3, corresponding to: blank-holding force of 1,400 kN, friction coefficient of 0.10, and stamping speed of 300 mm/s.
   The optimal parameter combination for the proportion of the safe zone is A4B4C4, corresponding to: blank-holding force of 1,700 kN, friction coefficient of 0.16, and stamping speed of 400 mm/s.
   Based on comparative analysis, the optimal overall process parameter combination is determined to be A4B4C4.