There are many problems in injection molded parts, among which drag and strain often occur in the mold trial process, so we need to master the drag, how the strain is generated, how to identify, how to solve, etc., to be a real structural design, but also to solve the problem of the engineer;
1.Problems with plastic parts: drag and strain; The details are shown in the figure below; 
2.What is strain and drag of plastic parts?
The phenomenon that the plastic parts rub the mold during the demoulding process and leave traces on the appearance of the plastic parts along the direction of the mold;
What is the effect of strain and drag on plastic parts?
Appearance defects: the strain and drag of plastic parts will lead to obvious strip whitening or wire drawing on the surface of the product, which will destroy the surface finish and aesthetics of the plastic products, and make the product have obvious appearance defects;
Dimensional accuracy decreases: the strain and drag of plastic parts may lead to the decline of dimensional accuracy of the product, which makes the size of the product deviate from the design requirements, and affects the performance and interchangeability of the product;
Decline in mechanical properties: strain and drag of plastic parts may lead to a decrease in the mechanical properties of the product, resulting in a decrease in the strength, toughness and wear resistance of the product;
4.Decreased customer satisfaction: Strain and drag of plastic parts may lead to a decrease in customer satisfaction, because these defects affect the quality and appearance of the product, and the customer's evaluation and purchase intention of the product may be affected; 
4.Why do plastic parts strain and drag occur?
Product structure design: the draft angle in the structural design of product parts is not enough;
Mold structure problems: Unreasonable mold structure, such as lack of lubrication holes, improper gate position, etc., will lead to the unsmooth flow of plastic melt in the mold, resulting in strain or drag.
Improper injection process parameters: Improper control of injection process parameters such as injection pressure and injection speed will lead to unstable flow of plastic melt in the mold, resulting in strain or drag.
Material problems: poor quality of plastic materials, excessive shrinkage, and too wide molecular weight distribution will also lead to strain and drag of plastic parts;
Improper mold maintenance: The lack of regular maintenance and maintenance of the mold, such as cleaning, lubrication, etc., will lead to the surface of the mold is not smooth, resulting in strain or drag.
5.How to solve the problem?
1.Adopt anti-strain design: In the design stage of plastic parts, anti-strain design can be considered, such as increasing the draft slope and reducing the undercut, so as to reduce the friction and strain of the plastic parts during demoulding;
2.Adjust the mold structure: modify the mold structure appropriately, such as adding lubrication holes in the mold, optimizing the gate position, etc. 3Optimize the injection process parameters: readjust the injection process parameters, such as injection pressure, injection speed, etc., and learn how to solve the problem of plastic parts today, and how to avoid it in the design process, so the design is also in continuous optimization, and continuous upgrading will get better and better;
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