What are the key principles of sheet metal stamping die design? How to avoid cracking, wrinkling and excessive thinning of materials?

Key principles of sheet metal stamping die design

Material fluidity control

Reasonable parting surface design: Ensure smooth material flow path and reduce sudden change resistance.

Optimization of drawing ribs: In stainless steel sheet metal processing, drawing ribs (circular/rectangular cross-section) are arranged on the blanking surface to precisely control the material inflow and balance local stretching and compression.
Objective: To achieve uniform plastic deformation and avoid excessive thinning or accumulation in certain areas.

The structural strength and precision of molds

Rigidity and wear resistance: Made of high-hardness steel such as Cr12MoV, the hardness of key parts is HRC58-62. Increase the guide columns (≥4 groups) and interference fit to suppress the offset caused by lateral forces.

Surface finish: The working surface is polished to below Ra0.4μm to reduce frictional resistance.

Coordination of process parameters

Dynamic adjustment of blank holder force: The sheet metal processing of chassis and cabinets achieves zoned control of blank holder force through nitrogen gas springs or hydraulic systems (such as applying pressure in the edge area to prevent wrinkles and reducing pressure in the center area to prevent cracking).

Stamping speed classification: The deep drawing process adopts a "slow-fast-slow" speed curve to reduce the risk of impact cracking.

Defect prevention and control measures

Avoid cracking (material fracture)

Increase the fillet radius: The fillet of the punch/die should be ≥5 times the material thickness (t) to reduce stress concentration.

Optimize the shape of the punch: Use stepped or spherical punches to disperse tensile stress.

Lubrication enhancement: Use high-viscosity lubricants containing extreme pressure additives (such as sulfurized olefins) to reduce the coefficient of friction by more than 30%.

Inhibit wrinkling (material instability)

Precise control of blank holder force: The unit blank holder force is set at 1.5 to 2 times the yield strength of the material (for example, 2 to 3MPa for SPCC steel).

Increase the density of the stretch bars: In areas prone to wrinkling (such as where the surface changes abruptly), increase the density of the stretch bars, with a bar height of 6-8 tons and a bar width of 12-15 tons.

Material pre-stretching: Release local pressure through the process cut (Carry Hole).

Prevent excessive thinning (uneven thickness)

CAE simulation in advance: Utilize AutoForm/Dynaform to simulate material flow and identify high-risk areas with a thinning rate greater than 20%.

Thinning rate control: During the design stage, the thinning rate can be controlled to ≤15% (for aluminum materials) or ≤20% (for low-carbon steel).

Multi-process allocation: Deep drawing parts are drawn 2 to 3 times, with an additional annealing process in between (for example, stainless steel is annealed when the deformation is 40%).

Application of Typical Cases

Automobile fuel tank shell stamping

The cracking rate at the corners is 15%.

Countermeasure: Increase the fillet of the die from 3t to 6t. Add a 20° guide bevel to the punch; The blank holder force has been reduced from 250t to 180t.

Result: The cracking rate was reduced to 0.5%, and the thinning rate was optimized from 25% to 18%.

Core logic: Balance material flow through mold geometry optimization (fillet/guide Angle), and achieve dynamic balance between tension and pressure through CAE simulation and parameter regulation (blank holder force/drawing rib), fundamentally suppressing the generation of defects.