一、“假废品”的由来及其公差带的确定在制订另件机械加工工艺过程时,由于工艺上的原因,往往使设计基准与工艺基准(定位基准或测量基准)不重合。在这种情况下,现在大多采用极值法进行尺寸换算,从而确定工序尺寸。这种换算往往伴随着“假废品”问题的存在。所谓假废品,就是工序尺寸超差了,而另件仍有可能是合格的产品。例如图1所示另件,镗孔前,表面 A、B、C 已经过加 First, the origin of “fake scrap” and determine the tolerance band In the development of another piece of machining process, due to process reasons, often make the design basis and the process of reference (positioning or measurement benchmark) do not coincide. In this case, the most extreme method is now used for size conversion, to determine the size of the process. This conversion is often accompanied by the existence of “false waste” issue. The so-called fake scrap, that is, the size of the process tolerance, while the other pieces may still be qualified products. For example, the other components shown in Figure 1, before boring, the surface A, B, C has been added