Precision Injection Molding Related Knowledge

Precision plastic injection molding, strictly speaking, refers to the dimensional accuracy of plastic products produced by injection molding equipment, which can achieve a precision of less than 0.01mm, usually between 0.01 to 0.001mm. The custom plastic injection molding is mainly used in industrial and civil products such as aerospace, automobile parts, precision instruments, sports equipment, and testing tools.

Definition of precision injection molding

Generally, precision injection molding that is a kind of precision plastic molding has two indicators: one is the equipment accuracy, and the other is the mold error. The former is difficult to compare due to the different sizes and thicknesses of the products, which represents the comprehensive level of the injection molding machine. The weight repeatability error of the general injection molding machine is about 1%, and the better machine can reach 0.8%. Less than 0.5% is precision machine, and less than 0.3% is ultra-precision machine. According to relevant information, the international highest level is less than 0.15%. The other is the accuracy of the mold, which not only requires the experience of engineering and technical personnel, but also relies on high-precision mold processing equipment to complete. Therefore, first-class mold processing equipment is a necessary condition for precision injection molding.

Factors affecting precision injection molding

• Consider the plastic shrinkage rate.

• The shape and size of the product.

• Mold accuracy.

• Accuracy of mold processing.

• The Injection molding machine has strict requirements for product accuracy.

Specific requirements of precision injection molding

• Firstly, the injection pressure should be greater than 25 MPa; the injection speed is greater than or equal to 300mm/s；

• The dimensional accuracy of the product is 0.001mm; the standard deviation coefficient of product quality (variation rate) is less than 0.1%;

• The precision of mold opening and closing position: opening ≤0.03mm, closing ≤0.01;

• Injection position accuracy (end point of holding pressure) is less than 0.03mm;

• The force balance degree of the tie rod is less than 1%; the pre-molded position accuracy is less than 0.03mm;
  

• Balance degree of fixed and moving templates A: less than 0.03mm when the clamping force is zero B: less than 0.005 mm when the clamping force is maximum;
  

• The temperature control accuracy of barrel and screw is less than ±0.5°C.
  

Key points of precision injection molding technology

• Clamping force: In the process of precision injection molding, a high injection pressure is generally required, otherwise it is difficult to form.

• Measurement accuracy: In order to maintain high stability of plastic products, the hot melt plastic injected into the cavity must be equal each time.
  

• Injection speed: Injection speed is an important indicator of precision injection molding machine.
  

• Injection pressure: Precision injection molding requires higher injection pressure to improve the compactness of plastic parts, reduce shrinkage deformation, and ensure the accuracy of parts.
  

• Holding pressure: Holding pressure has a great influence on precision plastic parts.
  

• Mold temperature: The temperature change on the surface of the mold cavity should be controlled within ±1°C.