Industry Insights

The essence of stamping springback is residual stress release. When the sheet metal is deformed under force in the mold, uneven residual stresses are generated in the thickness direction and in-plane direction. After the punch lifts and the constraint is removed, these stresses cause the part to undergo elastic recovery in order to rebalance, deviating from the mold surface. The magnitude and direction of springback depend on the combination of material strength, sheet thickness, mold geometry, and forming process parameters.

What Causes Springback

Material yield strength is the primary factor. High-strength steels (such as the DP series and 1.2 GPa ultra-high-strength steels) have high yield strength, and the proportion of elastic recovery after forming is greater, so the springback amount is significantly higher than that of ordinary low-carbon steel. Under the same forming force, more regions in high-strength steel remain in the elastic deformation zone and have not yielded, so springback after unloading is naturally more pronounced.

Matching of sheet thickness and mold clearance. The thinner the sheet, the greater the influence of neutral layer shift during bending, and the harder springback is to control. If the mold clearance is greater than the sheet thickness, the material in the bending zone cannot receive sufficient compression, and springback also increases.

Blank holder force and draw bead setup. The blank holder force is not better the larger it is. In the high blank holder force range, the springback angle first rises with increasing blank holder force and only then decreases. A reasonable draw bead layout can increase material flow resistance, allowing the sheet to obtain more sufficient tensile plastic deformation, thereby reducing springback.

Part geometric features. The larger the bending angle and the smaller the fillet radius, the larger the absolute springback angle usually is. For parts with bending sections, the longitudinal wall is prone to warping or wavy springback due to uneven residual stress.

How to Compensate

Step 1: Use simulation to predict springback trends, not experience-based guessing. Use AutoForm or Dynaform to perform full-process springback analysis and output springback contour maps. For irregular thin-walled parts, springback amounts in different regions may vary greatly, so zoned compensation must be used rather than overall offset.

Step 2: Geometric reverse compensation—make the mold surface "in reverse." If simulation shows that a certain region will spring 0.5 mm in the positive direction, the mold surface in that region is offset 0.5 mm in the reverse direction. In actual compensation, mold mesh nodes are adjusted in the reverse direction along the line connecting the nodes before and after springback, and then a smooth surface is reconstructed to achieve independent non-uniform compensation at different positions. In one case, for a B-pillar-type high-strength steel part, the strategy of "springback compensation in the final stage compression process, with conforming amount in each stage controlled within 2 mm" was adopted, ultimately controlling springback within ±0.5 mm.

Step 3: Coordinate process parameters to "lighten the load" for compensation. Appropriately increasing blank holder force or optimizing draw beads allows the sheet to obtain more sufficient plastic stretching, reducing the amount of springback that needs to be compensated from the source. The combined strategy of "process parameter control—draw bead setup—geometric reverse compensation" is more effective than a single measure.

Step 4: Trial mold verification and iteration. After the first round of compensation, trial stamp parts are produced, and the actual springback amount is scanned with 3D optical measurement and compared with the simulation prediction. If deviation remains, the measured deviation is used as input for a new round of compensation. High-strength steel parts usually require 2–3 rounds of iteration to converge within the tolerance band.

In short, springback compensation is not as simple as "making the mold a little bigger." It is a closed loop of "simulation prediction → reverse surface correction → process coordination → measured iteration." If Haina's mold development involves stamped parts, we will factor the springback compensation iteration cycle into the quotation and DFM stage to avoid repeated mold repair during trial molding delaying delivery.

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