当边缘材料受到的阻力超过极限值后边缘就会起皱失稳。为了避免出现起皱，必须时材料可以在凸模和压边圈之间顺利流动。造成拉深破裂的两个主意原因是拉深件直径与坯料直径比值超过极限值和拉深半径太小。

从平整的坯料拉深成壳体和将壳体拉深为直径更小的壳体时材料向内流动距离都有一个极限值，通常称之为拉深系数。极限拉深系数受到材料流动性、材料抗压能力和由受压而引起的流动阻力等因素的影响。过大的流动阻力使壳体边缘破坏起皱，该区域是材料抵抗力最弱的区域。

厚度不同材料的拉深系数也不一样。举例来讲，将一坯料进行大深度拉深，第一次拉深直径比值厚度0。015英寸的材料是32％，而0。125英寸厚的材料是48％。

对拉深凹模有一最小和最大拉深圆角半径值，拉深圆角半径直接影响材料的流动性。对深拉深件，0。015英寸厚的材料合适的圆角半径是从5/32英寸到1/4英寸这个范围。而对于0。0125英寸厚的材料，最小圆角半径不小与11/32英寸，最大圆角半径不大于15/32英寸。

如果圆角半径太小，金属流动阻力增加，会造成制件严重变薄或在壳帽边缘破裂，不能很好地拉深成形。而如果半径太大，金属一离开凹模与压边圈的接触点还没形成直壁就开始起皱。

人们经常是将半径做得小一些,因为在试模期间将圆角半径从小改为较大值比较容易，而把较大得圆角半径改小困难得多。结果造成在杯形边缘应力集中过大，制件变薄严重或破裂。很多时候采用不适当得拉深百分比或不合适得圆角半径在第一次拉深时看不出来，但在后续工位中要花很多时间去调整。

Progressive die stamping is a cost-effective and safe method of producing components。 Careful design and construction of dies will ensure optimum performance。

A progressive die performs a series of fundamental sheet metal operations at two or more stations in the die during each press stroke。 These simultaneous operations produce a part from a strip of material that moves through the die。 Each working station performs one or more die operations, but the strip must move from the first station through each succeeding station to produce a complete part。 Carriers, consisting of one or more strips of material left between the parts, provide movement of the parts from one die station to the next。 These carrier strips are separated from the parts in the last die station。

There are six elements that should be addressed when designing and building a progressive die to maximize its performance: 

• Interpreting the part print, 

• Starting material into the die, 

• Part lifters and part feeding, 

• Flexible part carriers, 

• Upper pressure pads, and 

• Drawn shells。

Interpreting the Part Print

The first step in the proper design of a progressive die is to correctly analyze the part print。 The tool designer must interpret the print to determine the function of the part by looking for such things as the type of material, critical surfaces, hole size and location, burr location, grain direction requirements, surface finish and other factors。

The die designer must understand the part well, particularly if it has irregular shapes and contours。 However, modern computer-drawn prints make this more difficult because computer-drawn part data can be downloaded directly to the die-design computer。 As a result, the designer may not become thoroughly familiar with important part features。