六、怎样预防和矫正镦粗的缺陷?镦粗的主要缺陷是弯曲和歪斜。为防止发生弯曲,镦粗前可以先将坯料回转倒棱,即采用“铆镦法”镦粗。这样能增加坯料两端与锤砧的接触面,使变形困难锥体积加大,把镦粗变形尽可能推向坯料中间部位(见图6)。这种方法操作难度大,锤击次数多,变形时间长,并不十分理想。最常用的是“预弯曲镦粗法”(砧边矫正法),即先将竖立在锤砧上的坯料轻击一锤,观察出坯料可能发生弯曲的趋势后, Sixth, how to prevent and correct upsetting defects? The main drawback of upsetting is bending and skewing. In order to prevent the occurrence of bending, the billet can be chamfered before the upsetting, that is, upsetting by “riveting upsetting method”. This will increase both ends of the billet and anvil anvil contact surface, so difficult to deformation cone volume increases, the upset deformation as possible to the middle of the billet (see Figure 6). This method is difficult to operate, hammering times, deformation time is long, not very good. The most commonly used is the “pre-bending upsetting method” (anvil-edge correction method), that is, first erected on the anvil on the billet tap a hammer to observe the billet may be bent after the trend,