| The working dimensions for the injection molding parts affect directly the dimension precision of plastic parts and using life of molds. Therefore how to calculate them accurately is the key point of injection mold designing. The people have been studying the calculating methods for the working dimensions and shrinkage characteristic of plastic parts to direct injection mold designing and shorten mold manufacturing cycle.Presently there are many calculating methods for the working dimensions. Each mold company has a different method in designing and manufacturing. Some mold companies don't design molds according to the methods in handbooks and documents. The disagreement between experience and theory is obviously found. Through the research on all kinds of these methods, it shows that the calculation results by method of intermediate range can ensure both the accuracy of the dimensions and convenience of calculating. Actual calculation example is given.At the same time, this paper develops calculation module of working dimensions for the injection molding parts and realizes computer aided calculation. The calculation module includes ten kinds of methods. Each method can both calculate the working dimensions and analyse the calculation results. Calculation module has significative and practical values of directing the injection mold designing and the production of plastic parts.Finally, this paper research on shrinkage characteristics of plastic parts with some familiar and typical shape(square, convex form, cave form, sector) theoretically and experimentally. Results of experiment indicate that plastic parts shrink along it's geometry center and angle of sector part enlarge after injection molding. Moreover, the effect of injection process on dimensions change trend of typical plastic parts is deeply studied. The research has the directive significance to calculate the working dimensions for the injection molding parts of these typical shape.
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