Each injection molding product must first determine its mold opening direction and parting line at the beginning of the design to ensure that the core slider mechanism is minimized and the influence of the parting line on the appearance is eliminated.

1. After the mold opening direction is determined, the reinforcement ribs, snaps, protrusions and other structures of the product are designed to be in the same direction as the mold opening direction, so as to avoid the core pulling to reduce the seam line and prolong the life of the mold;

2. After the mold opening direction is determined, the appropriate parting line can be selected to avoid the reverse buckle in the mold opening direction to improve the appearance and performance.

Demoulding slope

1. Appropriate drafting angle can avoid product pulling (drawing). The smooth surface of the draft should be ≥ 0.5 degrees, the fine grain (sand surface) surface is greater than 1 degree, and the rough grain surface is greater than 1.5 degrees.

2, the appropriate draft angle can avoid product top injuries, such as top white, top deformation, burst.

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

Product wall thickness

1. All kinds of plastics have a certain wall thickness range, generally 0.5~4mm. When the wall thickness exceeds 4mm, it will cause the cooling time to be too long, resulting in shrinkage and other issues, and should consider changing the product structure.

2, uneven wall thickness will cause the surface to shrink.

3, uneven wall thickness will cause pores and weld lines.


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

2. The thickness of the ribs must be ≤ (0.5~0.7)t wall thickness, otherwise the surface will shrink.

3. The slope of the rib should be greater than 1.5° to avoid head injury.


1. If the fillet is too small, it may cause stress concentration of the product, resulting in cracking of the product.

2. Too small a fillet may cause stress concentration in the mold cavity, resulting in cracking of the cavity.

3, set reasonable rounded corners, can also improve the processing technology of the mold, such as the cavity can be directly processed with r-knife, while avoiding inefficient electrical machining.

4, different rounded corners may cause the movement of the parting line, should choose different rounding or clearing angle according to the actual situation.

Autumn rain, phoenix leaves fall

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

2, the axial direction of the hole and the direction of the mold opening are the same, which can avoid core pulling.

3. When the aspect ratio of the hole is greater than 2, the draft angle should be set. The diameter of the hole at this time should be calculated according to the size of the small diameter (the largest physical size).

4, the length-to-diameter ratio of blind holes generally does not exceed 4. Anti-hole punching

5, the distance between the hole and the edge of the product is generally larger than the aperture size.

Core-drawing, slider mechanism and avoidance of injection mold

1. When the plastic parts cannot be demoulded smoothly according to the mold opening direction, the core pulling slider mechanism should be designed. The slider of the core pulling mechanism can form a complex product structure, but it is easy to cause defects such as seam line and shrinkage of the product, and increase the cost of the mold to shorten the life of the mold.

2. When designing injection molding products, if there is no special requirement, try to avoid the core structure. For example, the direction of the hole axis and the direction of the rib is changed to the mold opening direction, and the cavity core is used to penetrate.

One-piece hinge

1. Using the toughness of pp material, the hinge can be designed to be integrated with the product.

2, the film size as a hinge should be less than 0.5mm, and remain even,

3. When molding an integral hinge, the gate can only be designed on one side of the hinge.


1. Inserting inserts into the injection molding product can increase local strength, hardness, dimensional accuracy and set small threaded holes (shafts) to meet various special needs. At the same time, it will increase product costs.

2, the insert is generally copper, but also other metal or plastic parts.

3, the part of the insert embedded in the plastic should be designed to prevent rotation and pull out structure. Such as: knurling, holes, bending, flattening, shoulders and so on.

4, the plastic around the insert should be properly thickened to prevent stress cracking of the plastic parts.

5, when designing the insert, should fully consider its positioning in the mold (hole, pin, magnetic)


1. The buckle device is designed to be shared by multiple buckles at the same time, so that the whole device will not be unable to operate due to the damage of the individual buckles, thereby increasing the service life, and then multi-test filtering and rounding to increase the strength.

2. The tolerance of the relevant dimensions of the buckle is very strict. If the position of the buckle is too much, the buckle will be damaged. On the contrary, if the position of the buckle is too small, the assembly position is difficult to control or the combined part is too loose. The solution is to reserve a way to change the mold and easily add glue.

Welding (hot plate welding, ultrasonic welding, vibration welding)

1. Welding can improve the joint strength.

2, using welding, can simplify product design.

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