|
|
发表于 2009-6-13 10:36:30
|
显示全部楼层
Wrinkling is one of the major defects that occur in the sheet metal forming process. For both functional and visual reasons, wrinkles are usually not acceptable in a finished part. There are three types of wrinkle which frequently occur in the sheet metal forming process: flange wrinkling, wall wrinkling, and elastic buckling of the undeformed area owing to residual elastic compressive stresses. In the forming operation of stamping a complex shape, draw-wall wrinkling means the occurrence of wrinkles in the die cavity. Since the sheet metal in the wall area is relatively unsupported by the tool, the elimination of wall wrinkles is more difficult than the suppression of flange wrinkles. It is well known that additional stretching of the material in the unsupported wall area may prevent wrinkling, and this can be achieved in practice by increasing the blank-holder force; but the application of excessive tensile stresses leads to failure by tearing. Hence, the blank-holder force must lie within a narrow range, above that necessary to suppress wrinkles on the one hand, and below that which produces fracture on the other. This narrow range of blank-holder force is difficult to determine. For wrinkles occurring in the central area of a stamped part with a complex shape, a workable range of blank-holder force does not even exist.
起皱是金属板料成型中常见的失效形式之一。 由于功能的和视觉效果的原因, 起皱通常不能为零件制品所接受。在金属板料成型加工中通常存在三种类型的起皱现象：法兰起皱，侧壁起皱，和由于残余压应力在未变形区产生的弹性变形。在冲压复杂形状之间时，拉伸壁起皱就是在模具型腔中形成的起皱。由于金属板料在拉伸壁区域内相对无支撑，因此消除拉伸壁起皱比抑制法兰边起皱要难得多。我们知道在不被支撑的拉伸壁区域中材料的外力拉伸可以防止起皱，这可以在实践中通过增加压边力而实现，但是运用过大的拉伸力会引起破裂失效。因此，压边力必须控制在一定的范围内，一方面增抑制起皱，另一方面防止破裂。合适的压边力范围是很难决定的。因为起皱在冲压零件的中心位置以一个复杂的形状形成，甚至不存在一个合适的压边力范围。 |
|
[复制链接]
|小黑屋|手机版|模具论坛
( 浙ICP备15037217号 )
/5 
