How to Calculate Mold Shrinkage for Plastic Molds?

The shrinkage rate of plastic molds refers to the difference in size between the molded plastic product and the designed dimension after it is taken out of the mold during the cooling process. Due to the shrinkage of plastic during cooling, it is necessary to consider this shrinkage phenomenon in plastic injection mold making and design.

One commonly used method to calculate the mold shrinkage rate is linear shrinkage. Linear shrinkage refers to the proportion of shrinkage along various dimensions of the plastic during the cooling process. In general, the shrinkage rate of plastic molds is determined through experimentation and practical experience.

Here is a simple method to calculate the mold shrinkage rate:

1. Determine the linear shrinkage rate value of the plastic material. This value can usually be obtained from technical data or specifications provided by the plastic supplier. Different types of plastics have different shrinkage rate values.

2. Determine the design dimension of the part. This refers to the final dimension required for the part inside the mold, taking into account the shrinkage. The design dimension can be calculated based on the desired final part size and the shrinkage rate of the plastic.

Design dimension = Final dimension / (1 - Shrinkage rate)

Where the final dimension is the desired part size and the shrinkage rate is the linear shrinkage rate of the plastic material.

For example, if the linear shrinkage rate of the plastic material is 0.5% and the final part size is 100 millimeters, the design dimension for calculating the mold shrinkage rate would be:

Design dimension = 100 millimeters / (1 - 0.005) = 100.5 millimeters

It is important to note that this simple calculation method is an approximate estimate, and the actual mold shrinkage rate can be influenced by various factors including the type of plastic material, mold structure, cooling system, etc. Therefore, in practical applications, it is necessary to adjust and optimize based on actual tests and experience to ensure the accuracy of the final part dimensions.

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