How to Calculate the Manufacturing Accuracy of Injection Molds

How to Calculate the Manufacturing Accuracy of Injection Molds

The manufacturing accuracy of injection molding mold parts is determined by the allowable tolerance of the size of the molded product. Although each company has its own internal standards, one of the standards adopted by the major developed countries is the recommended standard of the VDI (Institute of German Engineers) adopted by the Federal Republic of Germany.

VDI's molded products allow tolerance content as shown below.

The allowable tolerance of the size of the molded product = 100, then

Manufacturing tolerance of injection mold = 1/3 = 33%

Wear allowance of injection mold =1/6=17%

Error in injection molding shrinkage = 1/2 = 50%

Let us calculate the manufacturing accuracy of the mold based on this criterion.

【Case 1】

When the allowable dimensional tolerance of the molded product is ±0.3mm, what is the manufacturing accuracy of the injection mold?

【Examination example】

The allowable dimensional tolerance of the molded product is +0.3+|-0.3|=0.6mm

(｜ ｜ indicates absolute value)

Therefore, the allowable manufacturing tolerance of the mold is 0.6×1/3=0.2mm

∴Injection mold manufacturing accuracy=±0.1mm is appropriate.

【Case 2】

When the allowable dimensional tolerance of the molded product is ±0.05mm, what is the manufacturing accuracy of the mold?

【Examination example】

The allowable dimensional tolerance of injection molded products is +0.05+|-0.05|=0.1mm

Therefore, the allowable manufacturing tolerance of the mold is 0.1×1/3=0.03mm

∴ The manufacturing precision of injection mold = ±0.015mm is appropriate.