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How to Choose the Best Compression Mold? | 2022 Ultimate Guide

Join Date: 2022-08-06

The process characteristics of different plastics when compression molding are influenced by the density, specific volume, shrinkage, fluidity, and required unit pressure of the raw material. Therefore, the influence of the material on the structure of the compression mold needs to be considered when producing products using the compression molding process (#1 - #4). In addition, the structure of the part also affects the selection of the parting surface, the direction of pressure application, and the machinability of the molded part (#5 - #10). This article describes ten factors that influence compression mold, and it is important to understand them to help you choose the best compression mold for your business.

#1 Determine the structure and volume of the filling chamber based on the relationship between the density of the raw material, the specific volume and the volume of the molded part. Materials with large specific volumes are not suitable for open compression molds.

#2 The size of the molded part (convex and concave mold and core) is determined by the relationship between the shrinkage rate and the size of the molded part. At the same time, the shrinkage degree and shrinkage characteristics are used to consider the form of the release structure.

#3 According to the liquidity of the raw material, the form of closing the cavity of the compression mold can be determined, generally the material with good liquidity can reduce the unit pressure, so the semi-closed cavity can be selected. For materials with poor fluidity, closed cavities can be selected. MDC's mold polishing process can meet all the requirements of the A-class finish.

#4 According to the unit pressure, we can calculate the molding pressure, select the hydraulic press, calculate the strength of the compression mold, analyze the force of the plastic parts or molded parts, select the pressure direction, and determine the structure and volume of the compression mold, etc. MDC has 500T-4000T molding presses, which can meet the pressure requirements of different composite materials production.

#5 The inner and outer surfaces of the product should be inclined along the release direction, i.e. the release slope. This is because after the molded part is cooled, it will tightly wrap around the mold core or the protruding part of the cavity, which will cause difficulties in demolding. The value of the release slope must be within the manufacturing tolerance, generally the minimum slope of 15', usually 1 ° - 1.5 °

#6 The wall thickness of the molded part has a great impact on its quality, the wall thickness is too small, the molding flow resistance, molding large and complex products when the material is difficult to fill the mold cavity. The minimum size of the wall thickness of the molded part should meet the following requirements: have sufficient stiffness and strength for use. It can withstand the impact and vibration of the release mechanism. It can withstand the fastening force when assembling. The thickness of thermoset molded products is generally controlled from 1 to 6 mm, with the maximum not exceeding 13 mm. Thermoplastic molded products should be controlled from 2 to 4 mm as far as possible.

#7 The role of the reinforcement is to enhance the stiffness and strength of the product without increasing the thickness of the entire product, and can avoid the deformation of the molded material due to curing shrinkage warpage. When designing the reinforcement, the arrangement of the reinforcement should be considered to reduce the internal stress caused by the uneven wall thickness or the product defects such as shrinkage and bubbles due to the local concentration of the molded material. The width of the bottom of the reinforcement should be smaller than the wall thickness to which it is attached.

#8 Rounded corners and edges. All corners of the molded part (including the edge) should be rounded as far as possible, which can greatly improve the mold filling of the molded material. At the same time, it can reduce the stress concentration at the sharp corners of the part and avoid rupture due to internal stress during force and shock vibration and demolding. If the molded part is designed with rounded corners, the corresponding part of the mold cavity must also be rounded, which can exclude the possible stress concentration in the mold during heat treatment or use, thus increasing the sturdiness of the mold.

#9 The molded parts usually have through holes, blind holes and threaded holes, etc. These holes should be set in places that do not easily weaken the strength of the product. There should be enough distance between the holes and between the holes and the edge walls. The minimum distance between the hole and the edge should not be less than the diameter of the hole.

#10 The metal parts in the molded parts are called metal inserts. Its purpose is: to improve the strength, hardness, abrasion resistance, electrical conductivity, etc. of the product to meet the requirements of use. To make up for the defects caused by the lack of structure and process of molded parts. In addition, it can improve the stability of product size and manufacturing accuracy, and reduce material consumption. However, the use of metal inserts will make the mold structure complex, and reduce the production efficiency of products, so should be avoided as far as possible. In order to ensure that the insert is firmly connected with the molded part, MDC will design compression molds to round or chamfer the edges of the metal insert to prevent the insert from damaging the surrounding plastic. Also, to prevent the metal insert from being pulled out or rotated in the molded part, the surface of the metal insert will be made into a circular groove or knurled pattern. To prevent the metal insert from affecting the final product, we keep the plastic layer on the outside of the metal insert thick enough to prevent cracking of the part.

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In order to get the best compression molded parts, you need to have the best possible knowledge of the final part you want. As for compression mold, just leave it to the most professional MDC Mould, who has been providing compression molding solutions to a wide range of industries since 1997.

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