When the mold is in production, various factors will affect the final quality of the mold. For example, the temperature during processing will affect the toughness and hardness of the mold, and the size and shrinkage of plastic parts will affect the size of the mold, etc. So in the mold design, what are the factors affecting the shrinkage? Let's briefly introduce the main factors affecting the shrinkage of precision molds!

Precision die

Because the size of the die can be determined by the size and shrinkage of the plastic part, the main factors affecting the shrinkage must be considered in the die design. The main factors affecting the shrinkage are: ① injection pressure; ② Resin temperature; ③ Mold temperature; ④ Gate sectional area; ⑤ Injection time; ⑥ Cooling time; ⑦ Wall thickness of plastic parts; ⑧ Reinforcement content; ⑨ Directionality; ⑩ Injection speed. However, shrinkage still exists after plastic parts are formed. The main factors affecting shrinkage after forming are internal stress, crystallinity, temperature, humidity and so on.

(1) Effect of injection pressure. The injection pressure has a great influence on the shrinkage. The injection pressure is large, the shrinkage is small, and the actual size of plastic parts is large. In a single cavity, the injection pressure varies depending on the shape of the plastic part. In the multimode cavity, the injection pressure of each cavity is different, and the shrinkage of each cavity is also different.

(2) Mold temperature. Whether it is amorphous resin or crystalline resin, the mold temperature is high and the shrinkage is large. Precision molding should maintain the mold temperature at a specific temperature, so attention should be paid to the design of cooling circuit in mold design.

(3) Gate cross-sectional area. Changing the gate cross-sectional area will change the shrinkage rate, which decreases with the gate size, which is related to the fluidity of the resin.

(4) Wall thickness of plastic parts. For non crystalline resin, the wall thickness is large and the shrinkage is large. For crystalline resin, large changes in wall thickness must be avoided. In multi-mode cavity, if the cavity wall thickness is different, the shrinkage will also be different.

(5) Reinforcement content. When using glass fiber reinforced resin, the more the glass fiber content, the smaller the shrinkage, and the shrinkage in the flow direction is smaller than that in the transverse direction. In order to prevent distortion and warpage, the influence of gate shape, position and quantity must also be considered.

(6) Orientation. All resins have directionality, and the directionality of crystalline resin is particularly large, which is different due to different wall thickness and molding conditions.

The above are the main factors affecting the shrinkage of precision molds. I hope it will be helpful to you!