Several Basic Points To Be Mastered in The Design of Injection Molds

When designing each injection molded product, its mold opening direction and parting line must be determined first 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 and extend the mold life;

2. After the mold opening direction is determined, an appropriate parting line can be selected 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 the fine leather grain (sand surface) should be greater than 1 degree, and the surface of the 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. Various plastics have a certain wall thickness range, 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.

Fillet

1. Too small fillet may cause product stress concentration and lead to product cracking.

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

3. Setting a reasonable fillet can also improve the processing technology of the mold, such as 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 based on actual conditions.

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, 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).

4. The aspect ratio of the blind hole is generally not more than 4. Anti-hole pin bending

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

Injection mold core pulling, slider mechanism and avoidance

1. When the plastic part cannot be demolded smoothly in the mold opening direction, a core pulling slider mechanism should be designed. The core-pulling mechanism slider 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.

2. 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.