When starting the design of each injection molded product, the mold opening direction and parting line must first be determined to ensure that the core-pulling slider mechanism is minimized and the impact of the parting line on the appearance is eliminated.
1. After the mold opening direction is determined, the product's reinforcing ribs, buckles, bulges and other structures should be designed to be consistent with the mold opening direction as much as possible to avoid core pulling, reduce stitching lines, and extend the life of the mold;
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 appearance and performance.
Draft angle
1. Appropriate demoulding slope can avoid product nap (drawing). The draft angle of the smooth surface should be ≥0.5 degrees, the surface with fine texture (sand surface) should be greater than 1 degree, and the surface with coarse texture should be greater than 1.5 degrees.
2. Appropriate draft angle can avoid product top damage, such as top whitening, top deformation, and top breakage.
3. When designing products with deep cavity structures, the outer surface slope should be larger than the inner surface slope 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.
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 problems such as long cooling time and shrinkage. Consider changing the product structure.
2. Uneven wall thickness will cause surface shrinkage.
3. Uneven wall thickness will cause pores and weld marks.
Reinforcement ribs
1. Reasonable application of reinforcing ribs can increase product rigidity and reduce deformation.
2. The thickness of the reinforcing rib must be ≤ (0.5~0.7)t product wall thickness, otherwise it will cause surface shrinkage.
3. The single-sided slope of the reinforcing rib should be greater than 1.5° to avoid top injuries.
rounded corners
1. If the fillet is too small, it may cause stress concentration on the product, leading to product cracking.
2. If the fillet is too small, it may cause stress concentration in the mold cavity, leading to cavity cracking.
3. Setting reasonable fillets can also improve the processing technology of the mold. For example, the cavity can be directly milled with an R cutter to avoid inefficient electrical machining.
4. Different fillets may cause the parting line to move. Different fillets or clear corners should be selected based on the actual situation.
hole
1. The shape of the hole should be as simple as possible, generally round.
2. The axial direction of the hole is consistent with the mold opening direction, which can 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 based on the small diameter size (maximum physical size).
4. The aspect ratio of blind holes generally does not exceed 4. Anti-hole needle punching and bending
5. The distance between the hole and the edge of the product is generally larger than the hole diameter.
Injection mold core pulling, slider mechanism and avoidance
1. When the plastic parts cannot be demoulded smoothly according to the mold opening direction, a core-pulling slider mechanism should be designed. The slider of the core pulling mechanism can form complex product structures, but it can easily cause defects such as seam lines and shrinkage of the product, increase the cost of the mold and shorten the life of the mold.
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 direction of mold opening, and methods such as cavity core collision are used.
Integrated hinge
1. Taking advantage of 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 should be uniform.
3. When injection molding an integrated hinge, the gate can only be designed on one side of the hinge.
Insert
1. Inserting inserts into injection molded products can increase local strength, hardness, dimensional accuracy and set up small threaded holes (shafts) to meet various special needs. It will also increase product costs.
2. The insert is generally copper, but can also be other metal or plastic parts.
3. 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.
4. The plastic around the insert should be appropriately thickened to prevent stress cracking of the plastic parts.
5. When designing the insert, full consideration should be given to its positioning method in the mold (holes, pins, magnetism)
buckle
1. The buckle device is designed to be shared by multiple buckles at the same time, so that the entire device will not be unable to operate due to damage to individual buckles, thus increasing its service life. Furthermore, more filters and rounded corners can be added to increase the strength.
2. The tolerance requirements for the dimensions related to the buckle position are very strict. Too many undercut positions will easily cause damage to the buckle position. On the contrary, if there are too few undercut positions, the assembly position will be difficult to control or the assembled parts will be too loose. The solution is to reserve a way to easily add glue when modifying the mold.
Welding (hot plate welding, ultrasonic welding, vibration welding)
1. Welding can improve the connection strength.
2. Using welding can simplify product design.
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