The mold industry is a basic industry in the manufacturing industry, the basis for the transformation of technological achievements, and an important field of high-tech industry. It is called the "magnetic industry" that "turns iron into gold" in industrially developed countries such as Europe and the United States.

The American industrial community believes that "the mold industry is the cornerstone of American industry"; Germany believes that it is the "key industry" in all industries; the Japanese Mold Association also believes that "molds are the driving force for promoting social prosperity and wealth", and are also "the secret of the entire industrial development" and "the driving force for entering a wealthy society."

1. Mold opening direction and parting line

When each injection molding product is designed, 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 are designed to be consistent with the mold opening direction as much as possible to avoid core pulling to 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.

2. 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.

3. Product wall thickness

1. Various plastics have a certain wall thickness range, generally 0.5 to 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.

4. 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.

5. Fillet

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

2. Too small fillet may cause mold cavity stress concentration and lead to cavity cracking.

3. Setting reasonable fillet can also improve the processing technology of the mold, such as the cavity can be directly processed by R cutter milling to avoid inefficient electrical processing.

4. Different fillets may cause the movement of the parting line, and different fillets or corners should be selected according to actual conditions.

6. Holes

1. The shape of the hole should be as simple as possible, generally circular.

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 demoulding slope should be set. At this time, the diameter of the hole should be calculated according to the minor diameter (maximum physical size).

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

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

VII. 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 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, 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 the cavity core is penetrated.

VIII. Integrated hinge

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

2. The size of the film used as a hinge should be less than 0.5mm and remain uniform.

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

IX. Inserts

1. 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 anti-rotation and anti-pullout structures. 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 an insert, its positioning method in the mold (hole, pin, magnetism) should be fully considered.

X. Logo

The product logo is generally set on a relatively flat inner surface of the product, and is in the form of a convex. Selecting the surface where the normal direction may be consistent with the mold opening direction to set the logo can avoid strain.

11. Injection molded parts precision

Due to the unevenness and uncertainty of shrinkage during injection molding, the precision of injection molded parts is significantly lower than that of metal parts. The dimensional tolerance of mechanical parts cannot be simply applied. Appropriate tolerance requirements should be selected according to the standard. my country also issued GB/T14486-93 "Dimensional Tolerance of Engineering Plastic Molding Plastic Parts" in 1993. Designers can determine the dimensional tolerance of parts according to the plastic raw materials used and the use requirements of parts according to the provisions in the standard. At the same time, the appropriate design tolerance accuracy should be determined based on the comprehensive strength of the factory and the design accuracy of the products of the same industry.

12. Deformation of injection molded parts

Improve the rigidity of the structure of injection molded products and reduce deformation. Try to avoid flat structures, and reasonably set flanges and concave and convex structures. Set reasonable reinforcement ribs.

13. Buckle position

1. Design the buckle position 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, and then consider adding fillets to increase strength.

2. The tolerance requirements for buckle-related dimensions are very strict. Too many undercuts can easily damage the buckles; on the contrary, too few undercuts make it difficult to control the assembly position or the combined parts are too loose. The solution is to reserve a way to easily add glue when modifying the mold.

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

1. Welding can improve the strength of the connection.

2. Welding can simplify product design.

15. Reasonable consideration of the contradiction between process and product performance

1. When designing injection molded products, the contradiction between product appearance, performance and process must be comprehensively considered. Sometimes sacrificing some processability can get a good appearance or performance.

2. When the structural design cannot avoid injection molding defects, try to make the defects occur in the hidden parts of the product.

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

Self-tapping screw Screw column hole diameter

M2 1.7mm

M2.3 2.0mm

M2.6 2.2mm

M3 2.5mm

17. Design principles of BOSS:

1. The pillar should not be used alone as much as possible. It should be connected to the outer wall or used with reinforcing ribs as much as possible. The purpose is to strengthen the strength of the pillar and make the rubber flow smoother.

2. The height of the pillar is generally not more than two and a half times the diameter of the pillar. Because the pillar is too high, it will cause air to be trapped during the molding of plastic parts (when the length is too long, it will cause pores, burning, insufficient filling, etc.).

3. If the height of the pillar exceeds two and a half times the diameter of the pillar, especially the pillar far away from the outer wall, the way to strengthen the strength of the pillar is to use reinforcing ribs.

4. The shape of BOSS is mainly round, and other shapes are not easy to process.

5. The position of BOSS should not be too close to the corner or the outer wall, and should be kept a distance from the outer wall of the product.

6) The thickness of the BOSS can be removed (i.e., a crater can be opened) to prevent shrinkage and sinking.

7) The draft angle of the BOSS: usually 0.5° for the outside and 0.5° or 1 for the inside.