Key points of injection molding product design

1. When HDPE plastic injection molding manufacturers use injection molding technology to produce products, due to the uneven cooling and uneven shrinkage of the plastic in the mold cavity and the unreasonable product structure design, it is easy to cause various defects of the product: shrinkage, weld marks, pores, deformation, burrs, top injuries, and flash.
2. In order to obtain high-quality injection molded products, we must fully consider its structural processability when designing products. The following is an analysis of methods to avoid injection molding defects in combination with the main structural characteristics of injection molded products. 3. Mold opening direction and parting line When each injection molded product is designed, its mold opening direction and parting line must be determined first to ensure that the core pulling mechanism is minimized and the influence of the parting line on the appearance is eliminated. After the mold opening direction is determined, the product’s reinforcement ribs, buckles, protrusions and other structures are designed to be consistent with the mold opening direction as much as possible to avoid core pulling to reduce the seam line and extend the mold life. For example: The mold opening direction of the bumper is generally the x direction of the body coordinate. If the mold opening direction is designed to be inconsistent with the x axis, its angle must be indicated in the product drawing. After the mold opening direction is determined, the appropriate parting line can be selected to improve the appearance and performance. Demolding slope Appropriate demolding slope can avoid product burrs. The demolding slope of the smooth surface should be greater than 0.5 degrees, the surface of the fine leather grain should be greater than 1 degree, and the surface of the rough leather grain should be greater than 1.5 degrees.
3 Appropriate demolding slope can avoid product top damage.
4 When designing deep cavity structure products, the outer surface slope is required to be smaller than the inner surface slope to ensure that the mold core is not offset during injection molding, obtain uniform product wall thickness, and ensure the material density strength of the product opening.
5 Product wall thickness Various plastics have a certain wall thickness range, generally 0.5 to 4mm. When the wall thickness exceeds 4mm, it will cause too long cooling time and shrinkage problems. The product structure should be considered to be changed. Uneven wall thickness will cause surface shrinkage. Uneven wall thickness will cause pores and weld marks.
6 Reinforcement ribs The reasonable application of reinforcement ribs can increase product rigidity and reduce deformation. The thickness of the reinforcement ribs must be less than 1/3 of the product wall thickness, otherwise it will cause surface shrinkage. The single-sided slope of the reinforcing rib should be greater than 1.5° to avoid top injury.
7 Too small a fillet may cause stress concentration in the product and lead to product cracking. Too small a fillet may cause stress concentration in the mold cavity and lead to cavity cracking. Setting a reasonable fillet can also improve the processing technology of the mold. For example, the cavity can be directly processed by R cutter milling to avoid inefficient electrical processing. Different fillets may cause the movement of the parting line. Different fillets or corner clearances should be selected according to actual conditions. The shape of the hole should be as simple as possible, generally circular. The axial direction of the hole is consistent with the mold opening direction to avoid core pulling. When the aspect ratio of the hole is greater than 2, the demolding slope should be set. At this time, the diameter of the hole should be calculated according to the minor diameter size (maximum physical size). The aspect ratio of the blind hole is generally not more than 4 mm. The distance between the hole and the edge of the product is generally greater than the hole diameter size.

8 The core pulling mechanism of the injection mold and the core pulling mechanism should be designed to avoid the plastic part from being demolded smoothly in the mold opening direction. The core pulling mechanism can form complex product structures, but it is easy to cause defects such as product stitching lines and shrinkage, and increase mold costs and shorten mold life.
9 When designing injection molded products, if there are no special requirements, try to avoid core pulling structures. For example, change the direction of the hole axis and ribs to the mold opening direction, and use methods such as cavity core penetration.