Paying attention to the reasonable tolerance and size requirements of mold steel materials can bring convenience to mold making, improve economic efficiency, and reduce waste during manufacturing. No matter what kind of material plastic parts have higher precision dimensions, there are requirements for mold steel size and What are the manufacturing tolerances?
The shrinkage characteristics of various plastics are divided into 4 groups according to the ΔVS value of the plastics. The group with the smallest △VS value is the high-precision group, and so on, the group with the largest △VS value is the low-precision group.
Precision technology, 110, 120, 130, 140, 150 and 160 tolerance groups are prepared according to the basic dimensions. It is stipulated that the dimensional tolerances of plastic parts with the most stable shrinkage characteristics can be selected from groups 110, 120 and 130. Use 120, 130 and 140 for dimensional tolerances of plastic molded parts with moderately stable shrinkage characteristics. If the dimensional tolerance of this type of plastic forming plastic parts is selected as 110 groups, a large number of plastic parts with out-of-tolerance may be produced. The dimensional tolerances of plastic parts with poor shrinkage characteristics are selected from groups 130, 140 and 150.
In addition to the basic dimensions calculated by the D=M(1+S) formula, the machining dimensions of the die steel cavity and core also have a machining tolerance problem. By convention, the machining tolerance of the mold is 1/3 of the plastic part tolerance.
However, due to the differences in the range and stability of plastic shrinkage, the dimensional tolerance of plastic parts formed by different plastics must be rationalized first. That is to say, the dimensional tolerance of plastic molded parts should be larger due to the larger shrinkage rate range or the poorer shrinkage rate stability. Otherwise, there may be a large number of out-of-tolerance scraps. To this end, countries have specially formulated national standards or industry standards for the dimensional tolerances of plastic parts. China has also formulated ministerial-level professional standards. But most of them do not have the corresponding dimensional tolerance of the mold cavity. In the German national standard, the DIN16901 standard for the dimensional tolerance of plastic parts and the DIN16749 standard for the corresponding mold cavity dimensional tolerance are specially formulated. This standard has a great influence in the world, so it can be used as a reference for the plastic mold industry.
The German national standard has formulated the standard DIN16749 of the corresponding mold manufacturing tolerance for the tolerance of plastic parts. There are 4 tolerances in total. Regardless of the material of the plastic parts, the mold manufacturing tolerances that do not indicate dimensional tolerances use the tolerance of serial number 1. The specific tolerance value is determined by the basic size range.
No matter what kind of material, the mold manufacturing tolerance of the medium-precision size of the plastic part is the tolerance of serial number 2. No matter what kind of material, the mold manufacturing tolerance of the higher precision dimension of the plastic part is the tolerance of serial number 3. The corresponding mold manufacturing tolerance of precision technology is the tolerance of serial number 4.
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