What are the key points to pay attention to when designing injection molds?

Injection mold is an indispensable tool in the industrial production of plastic products. It is generally composed of 7 systems including gating system, guiding system, forming system, core pulling system, ejection system, cooling system and exhaust system. The design of injection molds is a very important link in the production of molds. In the design process, various factors must be comprehensively considered before the final product can meet the production requirements. Then what are the key points in the design of injection molds Need to pay attention?

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 excessive cooling time and shrink printing, so you should consider changing the product structure.

2. Uneven wall thickness will cause surface shrinkage.

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


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

2. The thickness of the stiffener must be ≤ (0.5~0.7)T product wall thickness, otherwise it will cause surface shrinkage.

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


1. Too small rounded corners may cause stress concentration in the product, leading to product cracking.

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

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

4. Different rounded corners may cause the parting line to move. Different rounded corners or clear corners should be selected according to the actual situation. What are the basic points of injection mold design?

Mold opening direction and parting line

At the beginning of the design of each injection product (Shanghai Mold Design Training School), the mold opening direction and parting line must be determined first to ensure that the core-pulling slider mechanism is minimized and the effect of the parting line on the appearance is eliminated.

1. After the mold opening direction is determined, the product’s ribs, buckles, protrusions and other structures should be designed to be consistent with the mold opening direction as much as possible to avoid core pulling and reduce seam lines and extend the life of the mold.

2. After the mold opening direction is determined, an appropriate parting line can be selected to avoid undercutting in the mold opening direction to improve the appearance and performance.Shanghai mold design training

Demoulding angle

1. Appropriate demoulding angle can avoid product fuzzing (drawing).The demolding slope of the smooth surface should be ≥0.5 degrees, the fine dermatome (sand surface) surface is greater than 1 degree, and the coarse dermatome surface is greater than 1.5 degrees.

2. Appropriate demolding angle can avoid product damage, such as top white, top deformation, and bursting. The basic requirements of injection mold design.

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


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 direction of mold opening, which can avoid core pulling.

3. When the length to diameter 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 (the largest physical size).

4. The aspect ratio of blind holes generally does not exceed 4.Anti-hole pin punching

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

Precision of injection molded parts

Due to the inhomogeneity and uncertainty of the shrinkage rate during injection molding, the accuracy of injection molded parts is significantly lower than that of metal parts. The dimensional tolerances of mechanical parts cannot be simply applied. The appropriate tolerance requirements should be selected according to the standard. my country also issued GB/ in 1993 T14486-93 “Engineering Plastic Molded Plastic Parts Dimension Tolerance”, the designer can determine the dimensional tolerance of the parts according to the plastic raw materials used and the requirements of the parts, and according to the regulations in the standard.

At the same time, it is necessary to determine the appropriate design tolerance accuracy according to the comprehensive strength of the factory and the design accuracy of the products of the same industry.

Deformation of injection molded parts

Improve the rigidity of the injection product structure and reduce the deformation. The basic points of the design of the injection mold are which mold design should avoid the flat structure as much as possible, and set the flanging and concave-convex structure reasonably.Set reasonable stiffeners.


1. The buckle device is designed to share multiple buckles at the same time, so that the overall device will not be inoperable due to the damage of individual buckles, thereby increasing its service life, and more filtering and rounding corners to increase strength.

2. The tolerance requirements for the relevant dimensions of the buckle are very strict. Too many undercut positions are likely to cause damage to the buckle; on the contrary, if the undercut position is too small, the assembly position is difficult to control or the assembly part is too loose.The solution is to reserve a way to change the mold and add glue easily.

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