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#113 Accuracy of Mold Preparation

Category : Mold Preparation Accuracy
February24, 2012

The accuracy of preparation of parts of a mold for plastic injection molding is determined by the dimensional tolerance of the molded product. While each company may have its own internal standards about the policies for this accuracy, one of the standards used in major advanced countries is the standard recommended by VDI (Association of German Engineers).

The details of the molded product tolerances according to the VDI standard are as follows.

Taking the dimensional tolerance of the molded product as 100,
Mold preparation tolerance = 1/3 = 33%
Wear margin of mold = 1/6 = 17%
Fluctuation of molding shrinkage = 1/2 = 50%

Let us obtain the accuracy of mold preparation based on the above standards.

[Case 1]

What is the accuracy of mold preparation when the dimensional tolerance of the molded product is ±0.3 mm?

[Example of investigations]

The dimensional tolerance of the molded product is +0.3 + | -0.3 | = 0.6 mm
(| | indicates the absolute value.)

Therefore, the tolerance of mold preparation is 1/6 × 1/3 = 0.2 mm.
∴ A mold preparation accuracy of ±0.1 mm is appropriate.

[Case 2]

What is the accuracy of mold preparation when the dimensional tolerance of the molded product is ±0.05 mm?

[Example of investigations]

The dimensional tolerance of the molded product is +0.05 + | -0.05 | = 0.1 mm

Therefore, the tolerance of mold preparation is 0.1 × 1/3 = 0.03 mm.
∴ A mold preparation accuracy of ±0.015 mm is appropriate.

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