17 Rules Of Mold Design

The mold industry is a basic industry in the manufacturing industry and an important area of high-tech industries. In the process of manufacturing molds, mold design plays a key role. In summary, it can be summarized into the following 17 rules:

1. Mold opening direction and parting line

2. Appropriate demoulding slope can avoid product nap (drawing) and top damage, such as top whitening, top deformation, and top breakage. When designing products with deep cavity structures, 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 deflected during injection molding, obtain uniform product wall thickness, and ensure the material strength of the product opening.

3. Product wall thickness. Various plastics have a certain range of wall thickness. Uneven wall thickness will cause surface shrinkage, pores and weld marks.

4. Reinforcement ribs

Reasonable application of reinforcing ribs can increase product rigidity and reduce deformation. The thickness must be ≤(0.5~0.7)T product wall thickness, otherwise it will cause surface shrinkage. The slope of one side should be greater than 1.5° to avoid top injuries.

5. Rounded corners

A rounded corner that is too small may cause stress concentration on the product, leading to product cracking. It may also cause stress concentration in the mold cavity, leading to cavity cracking. Different fillets may cause the parting line to move. Different fillets or clear corners should be selected based on the actual situation.

6. Hole

The shape of the hole should be as simple as possible, generally round. The axial direction of the hole is consistent with the direction of mold opening, which can avoid core pulling. When the aspect ratio of the hole is greater than 2, the demoulding slope should be set. At this time, the diameter of the hole should be calculated based on the small diameter size (maximum physical size). The aspect ratio of blind holes generally does not exceed 4. Anti-hole needle punching and bending. The distance between the hole and the edge of the product is generally greater than the hole diameter.

7. When the plastic parts cannot be demoulded smoothly according to the mold opening direction, a core-pulling slider mechanism should be designed. When designing injection molded products, if there are no special requirements, try to avoid core-pulling structures. For example, the direction of the hole axis and ribs is changed to the mold opening direction, and methods such as cavity core collision are used.

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

9. Inserts. Inserts are generally copper, but can also be other metal or plastic parts. The part of the insert embedded in the plastic should be designed with anti-rotation and anti-pull-out structures. Such as: knurling, holes, bending, flattening, shoulders, etc. The plastic around the insert should be appropriately thickened to prevent stress cracking of the plastic part.

10. Product logos are generally set on the flat inner surface of the product and adopt a raised form. Select a surface where the normal direction may be consistent with the mold opening direction to avoid strain.

11. Due to the non-uniformity and uncertainty of shrinkage during injection molding, the designer can determine the dimensional tolerance of the part according to the plastic raw materials used and the requirements of the part, and according to the provisions of the standard.

12. Deformation of injection molded parts, improve the rigidity of the injection molded product structure and reduce deformation. Try to avoid flat structures and rationally set up flanges and concave-convex structures. Set up reasonable reinforcement ribs.

13. The buckle device is designed to be shared by multiple buckles at the same time, so that the entire device will not be inoperable due to damage to individual buckles, thereby increasing its service life. Furthermore, more filters and rounded corners can be added to increase the strength.

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

15. Reasonably consider the contradiction between process and product performance

16. Relationship between screw column hole diameter and self-tapping screw diameter

17. BOSS design principles:

The shape of BOSS is mainly round, and other shapes are difficult to process.

The location of the BOSS cannot be too close to the corner or the outer wall, and should be kept at a distance from the outer wall of the product.

You can remove part of the flesh around the BOSS (i.e. open a crater) to prevent shrinkage and subsidence. The mold dialing angle of BOSS: usually 0.5° for the outside and 0.5° or 1 for the inside.