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塑料模具尺寸和制造公差 

Dimensions and manufacturing tolerances of plastic moulds

模具型腔和型芯的加工尺寸除了通过D=M(1+S)公式计算基本尺寸之外，还有一个加工公差的问题。按照惯例，模具的加工公差为塑件公差的1/3。但由於塑料收缩率范围和稳定性各有差异，首先必须合理化确定不同塑料所成形塑件的尺寸公差。即由收缩率范围较大或收缩率稳定较差塑料成形塑件的尺寸公差应取得大一些。否则就可能出现大量尺寸超差的废品。 

Besides calculating the basic dimension by D = M (1 + S) formula, there is also a problem of machining tolerance. According to convention, the machining tolerance of mould is 1/3 of plastic parts tolerance. However, due to the difference of shrinkage range and stability of plastics, the dimensional tolerances of plastic parts formed by different plastics must be determined rationally. That is to say, the dimensional tolerance of plastic parts formed by plastic parts with large shrinkage range or poor stability of shrinkage should be larger. Otherwise, there may be a large number of defective products.  

为此，各国对塑料件的尺寸公差专门制订了国家标准或行业标准。中国也曾制订了部级专业标准。但大都无相应的模具型腔的尺寸公差。德国国家标准中专门制订了塑件尺寸公差的DIN16901标准及相应的模具型腔尺寸公差的DIN16749标准。此标准在世界上具有较大的影响，因而可供塑料模具行业参考。

To this end, countries have formulated national or industrial standards for dimensional tolerances of plastic parts. China has also formulated ministerial level professional standards. However, there is no corresponding dimensional tolerance of mold cavity. In German national standard, the DIN16901 standard for dimensional tolerance of plastic parts and the corresponding DIN16749 standard for dimensional tolerance of die cavity are specially formulated. This standard has great influence in the world, so it can be used for reference in the plastic mould industry.