Controlando o enrugamento na estamparia de metais: melhores práticas reveladas

Controlling Wrinkling in Metal Stamping: Best Practices Revealed

Factors influencing wrinkling in stamped parts and solutions

1. Impact of stretch depth

The resistance to material flow through the die cavity is directly related to the depth of stretching. Excessive depth of stretching in concave and convex curves can cause uneven distribution of deformation resistance, leading to wrinkling. It is best to avoid excessive depths whenever possible.

Best practices for wrinkling control in metal stamping revealed

2. Adjusting the strength of the blank holder

Uniform wrinkles around the part indicate insufficient strength in supporting the blank. Gradually increasing the strength of the blank holder can eliminate wrinkles. When drawing conical and hemispherical shapes, most of the material is initially suspended, making sidewall wrinkling likely.

In addition to increasing the supporting force of the blank, it is also effective to introduce stretching cords to increase the radial tensile stress within the sheet, thus eliminating wrinkles.

3. Influence of die corner radius

A large die corner radius reduces the bending resistance encountered by the blank as it flows into the die, increasing the likelihood of wrinkling. A smaller radius increases flexural strength and reduces the risk of wrinkling, but can cause cracking and tearing in the part.

Extensive production experience has shown that wrinkling in stamped parts mainly results from material accumulation and excessive speed of local material movement during stretching. Practical solutions must consider adjusting the corresponding mechanisms in the mold to obtain good results.

Measures to avoid wrinkling in printed parts

Wrinkle prevention involves ensuring the die holds the material in place and controls the flow speed of the sheet during stretching. If the material flows too quickly, wrinkling may occur; conversely, if it flows too slowly, the piece may crack.

1. Use of suitable blank media

Blank holders press and hold the deformed section of the blank in place, applying force to prevent the flange from bulging and wrinkling. The force must be appropriate. Blank holders are categorized into elastic and rigid types, where elastic holders are suitable for shallow drawing and rigid holders for deep drawing.

2. Appropriate use of drawing accounts

Drawing beads on the blank holder is an effective method to adjust and control the resistance to deformation. By regulating the flow of material, the stretch cords ensure uniform resistance during stretching, adapting the volume of material flowing into the mold cavity to the needs of the part, thus avoiding excess amounts that cause wrinkling or insufficient amounts that lead to cracking.

For complex shaped drawn parts, especially those with small flanges, the drawing cords should be placed where the radial tensile stress is lowest, i.e. where the sheet flows easily.

For parts with small flanges, additional material (process allowance) can be added to accommodate the draw beads and later removed during cutting. For drawn parts with varying depths, draw beads should be placed in areas with less material flow to prevent excess material from entering the die cavity and causing wrinkling.

Analysis of the causes of wrinkling in drawn parts Wrinkling during the drawing process can arise from several factors:

  • Excessive drawing depth in printed parts, causing the material to flow too quickly and form wrinkles.
  • A large radius at the corner of the die during stretching can prevent the punch from holding the sheet in place, causing rapid material flow and wrinkling.
  • Drawstrings incorrectly sized or positioned, failing to effectively slow the flow of the sheet, resulting in wrinkling.
  • Insufficient punch pressure, resulting in incomplete part formation and wrinkling.
  • Improper die design and alignment, causing the die to be unable to hold the material or creating a small supporting edge of the blank, which allows rapid material flow and wrinkling during drawing.
  • Excessive clearance between the punch and die, leading to inadequate control over the material and wrinkling. These are common causes of wrinkling in the drawing process of stamped parts. Specific problems require detailed analysis to identify precise reasons.

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