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When designing each injection molding product, we must first determine its mold opening direction and parting line to ensure that the core pulling 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 product’s reinforcement 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 the stitching line, extending the mold life;

2. After the mold opening direction is determined, you can choose an appropriate parting line to avoid undercuts in the mold opening direction to improve the appearance and performance.

Demolding slope

1. Appropriate demolding slope can avoid product hair pulling (drawing). The demolding slope of the smooth surface should be ≥0.5 degrees, the surface of fine leather grain (sand surface) should be greater than 1 degree, and the surface of rough leather grain should be greater than 1.5 degrees.
2. Appropriate demolding slope can avoid product top damage, such as top whitening, top deformation, and top breakage.
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 offset 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 too long cooling time and shrinkage. The product structure should be changed.
2. Uneven wall thickness will cause surface shrinkage. 3. Uneven wall thickness will cause pores and weld marks.

Reinforcement ribs

1. Reasonable application of reinforcement ribs can increase product rigidity and reduce deformation.
2. The thickness of the reinforcement rib must be ≤ (0.5~0.7)t product wall thickness, otherwise it will cause surface shrinkage.
3. The single-sided slope of the reinforcement rib should be greater than 1.5° to avoid top injury.

Rounded corners

1. Too small rounded corners may cause product stress concentration and lead to product cracking.
2. Too small rounded corners may cause mold cavity stress concentration and lead to cavity cracking.
3. Setting reasonable rounded corners can also improve the processing technology of the mold. For example, the cavity can be directly processed by r-cut milling to avoid inefficient electrical processing.
4. Different fillets may cause the movement of the parting line. Different fillets or corner clearances should be selected according to the actual situation.

Hole

1. The shape of the hole should be as simple as possible, generally a circle.
2. The axial direction of the hole is consistent with the mold opening direction to avoid core pulling.
3. When the aspect ratio of the hole is greater than 2, a demolding slope should be set. At this time, the diameter of the hole should be calculated according to the minor diameter (maximum solid size).
4. The aspect ratio of the blind hole is generally not more than 4, and the hole needle is prevented from bending
5. The distance between the hole and the edge of the product is generally greater than the hole diameter.

Core pulling, slider mechanism and avoidance of injection mold

1. When the plastic part cannot be demolded smoothly in the mold opening direction, a 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 product stitching lines and shrinkage, and increase mold costs and shorten mold life.
2. When designing injection molded products, try to avoid core pulling structures unless there are special requirements. For example, the axial direction of the hole and the direction of the ribs are changed to the direction of the mold opening, and the cavity core is penetrated.

Integrated hinge

1. The hinge can be designed to be integrated with the product by using the toughness of PP material.
2. The size of the film used as the hinge should be less than 0.5mm and kept uniform.
3. When injection molding an integrated hinge, the gate can only be designed on one side of the hinge.

Insert

1. Inserting inserts in injection molded products can increase local strength, hardness, dimensional accuracy and set small threaded holes (axles) to meet various special needs. At the same time, it will increase product costs.
2. Inserts are generally copper, but can also be other metals or plastic parts.
3. The part of the insert embedded in the plastic should be designed with a rotation-stop and anti-pullout structure. Such as: knurling, holes, bends, flattening, shoulders, etc.
4. The plastic around the insert should be appropriately thickened to prevent stress cracking of the plastic part.
5. When designing inserts, the positioning method (hole, pin, magnetism) in the mold should be fully considered.

Buckle

1. Design the buckle device to share multiple buckles at the same time, so that the overall device will not fail to operate due to damage to individual buckles, thereby increasing its service life. Then consider adding fillets to increase strength.
2. The tolerance requirements for buckle-related dimensions are very strict. Too many undercut positions are prone to buckle damage; on the contrary, too few undercut positions make it difficult to control the assembly position or the combined part is too loose. The solution is to reserve a way to easily add glue for mold modification.

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

1. Welding can improve the connection strength.
2. Welding can simplify product design.