What Are The Design Principles And Core Of Injection Molds?


   Mold opening direction and parting line     At […]

   Mold opening direction and parting line


  At the beginning of the design of each injection product, the mold opening direction and parting line should be determined to minimize the core-pulling slider mechanism and eliminate the influence of the parting line on the appearance.


  1. After the mold opening direction is determined, the design of the ribs, buckles, and bumps of the product should be as consistent with the mold opening direction as possible to avoid pulling the core, reduce the stitching line, and extend the die cutting line. The life of the mold.


  2. After the mold opening direction is determined, a suitable parting line can be selected to avoid the mold opening direction from being reversed, thereby improving the appearance and performance.


  Demoulding angle


  1. Proper demolding angle can avoid product drawing. The release slope of the smooth surface is greater than or equal to 0.5 degrees, the fine-grained (sand surface) surface is greater than 1 degree, and the coarse-grained surface is greater than 1.5 degrees.

  2. A proper unmixing angle can avoid top surface damage such as top surface whitening, top surface deformation, and top surface fracture.

  3. When designing deep cavity structure products, the slope of the outer surface should be greater than the slope of the inner surface as much as possible to ensure that the mold core is not eccentric during injection molding, obtain uniform product wall thickness, and ensure the material strength of the product opening.

   Product wall thickness

  1. All kinds of plastics have a certain range of wall thickness, generally 0.5~4mm. When the wall thickness exceeds 4mm, it will cause problems such as excessive cooling time and shrinkage, so you should consider changing the product structure.

  2. Uneven wall thickness will cause surface shrinkage.

  3. Uneven wall thickness will produce pores and weld marks.

   Strengthen tendons

  1. Reasonable application of reinforcing ribs can increase product rigidity and reduce deformation.

  2. The thickness of the steel bar must be less than or equal to (0.5 ~ 0.7) T product wall thickness, otherwise it will cause surface shrinkage.

  3. The single side slope of the stiffener should be greater than 1.5° to avoid top damage.


  1. Too small rounded corners may cause product stress concentration and cause product cracking.

  2. Too small rounded corners will cause stress concentration in the mold cavity, resulting in cavity cracking.

  3. Setting reasonable corners can also improve the mold processing technology. For example, the cavity can be directly milled with an R milling cutter to avoid low electrical processing efficiency.

  4. Different rounded corners may cause the parting line to move, so you should choose different rounded corners or bright corners according to the actual situation.


  1. The shape of the hole should be as simple as possible, generally round.

  2. The axial direction of the hole is consistent with the opening direction, which can avoid core pulling.

  3. When the hole length-to-diameter ratio is greater than 2, the demolding slope should be set. The diameter of the hole should be calculated according to the small diameter size (the largest solid size).

  4. Blind hole length-diameter ratio is generally not greater than 4. Anti-hole acupuncture bending

  5. The distance between the hole and the edge of the product is generally greater than the hole size.

  Injection mold core pulling, slider mechanism and avoidance

  1. When the plastic part cannot be demolded successfully in the mold opening direction, the core-pulling slider mechanism should be designed. The slider of the core-pulling mechanism can mold a complex product structure, but it is easy to cause defects such as stitching and shrinkage, which increases the cost of the mold and shortens the life of the mold.

  2. When designing injection products, if there are no special requirements, try to avoid core-pulling structures. For example, change the hole axis and rib direction to the mold opening direction, and use the cavity core to punch through.

  Integrated hinge

  1. The toughness of PP material can integrate the hinge with the product.

  2. The size of the film used as the hinge should be less than 0.5mm and kept uniform.

  3. Injection integrated hinge, the gate can only be designed on one side of the hinge.

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