I. mold opening direction and parting line
At the beginning of the design of each injection molding product, the mold opening direction and parting line must be determined to ensure that the core pulling slider mechanism is reduced as much as possible and the influence of parting line on the appearance is eliminated.
1. After the mold opening direction is determined, the structure of the product such as reinforcing ribs, buckles and bulges shall be designed to be consistent with the mold opening direction as far as possible, so as to avoid core pulling, reduce stitching lines and prolong the service life of the mold.
2. After the mold opening direction is determined, an appropriate parting line can be selected to avoid reverse buckling in the mold opening direction so as to improve the appearance and performance.
II. Demoulding Slope
1. Proper demoulding slope can prevent the product from galling (drawing). The demoulding slope of smooth surface shall be ≥0.5 degree, the surface of fine dermatoglyphics (sand surface) shall be greater than 1 degree, and the surface of coarse dermatoglyphics shall be greater than 1.5 degree.
2. Proper demoulding slope can avoid the top injury of the product, such as white top, top deformation and top breakage.
3. The slope of the outer surface should be larger than the slope of the inner surface as far as possible in the design of products with deep cavity structure, so as to ensure that the mold core is not misaligned during injection molding, to obtain uniform wall thickness of products, and to ensure the material strength at the opening of products.
Three, product wall thickness
1, all kinds of plastics have a certain range of wall thickness, generally 0.5 ~ 4mm, when the wall thickness exceeds 4 mm, will cause the cooling time is too long, produce shrinkage printing and other problems, should consider changing the product structure.
2, uneven wall thickness will cause surface shrinkage.
3. Non-uniform wall thickness will cause pores and weld lines.
IV. Reinforcement
1. Reasonable application of reinforcing bars can increase product rigidity and reduce deformation.
2, the thickness of the reinforcement must be less than or equal to (0.5 ~ 0.7) t product wall thickness, otherwise cause surface shrinkage.
3. The one-sided inclination of the reinforcing bar shall be greater than 1.5 to avoid top injury.
V rounded corners
1. Too small fillet may cause product stress concentration and lead to product cracking.
2. Too small fillet may cause stress concentration in the mold cavity, leading to cavity cracking.
3. Setting reasonable rounded corners can also improve the processing technology of the mold. For example, the cavity can be directly milled with R-knife, thus avoiding low-efficiency electrical processing.
4. Different fillets may cause the parting line to move. Different fillets or clearance angles should be selected according to the actual situation
VI. Holes
1, the shape of the hole should be as simple as possible, generally take circular.
2. The axial direction of the hole is consistent with the mold opening direction, which can avoid core pulling.
3, when the hole length diameter ratio is greater than 2, should set the demoulding slope. At this time, the diameter of the hole should be calculated according to the small diameter size (maximum solid size).
4. The length-diameter ratio of blind holes is generally not more than 4. Anti-hole needle bending
5. The distance between the hole and the edge of the product is generally larger than the hole size.
Seven, injection mold core pulling, slider mechanism and avoid
1. When the plastic parts cannot be demoulded smoothly according to the mold opening direction, the core pulling slider mechanism shall be designed. The slide block of core-pulling mechanism can form complex product structure, but it is easy to cause defects such as stitching lines, shrinkage and the like of the product, and increases the cost of the mold and shortens the service life of the mold.
2. When designing injection molding products, if there are no special requirements, try to avoid core pulling structure. For example, the axial direction of the hole and the direction of the rib are changed to the mold opening direction, and the cavity core is used for punching through.
Eight, one hinge
1. Using the toughness of PP material, the hinge can be designed to be integrated with the product.
2. The film size used as hinge should be less than 0.5mm and keep uniform.
3. When the integral hinge is injected, the gate can only be designed on one side of the hinge.
IX. Inserts
1. Inserting inserts into injection molding products can increase local strength, hardness, dimensional accuracy and set small threaded holes (shafts) to meet various special requirements. At the same time, it will increase the cost of products.
2. The insert is usually copper or other metal or plastic parts.
3. The part of the insert embedded in plastic shall be designed with anti-rotation and anti-pull-out structures. Such as knurling, hole, bending, flattening, shaft shoulder, etc.
4, insert around the plastic should be appropriately thickened, in order to prevent stress cracking of plastic parts.
5. When designing the insert, the positioning method (holes, pins, magnetism) in the mold shall be fully considered.
X. identification
The product logo is generally set on the flat inner surface of the product and adopts a convex form. The logo is set on the surface whose normal direction may be consistent with the mold opening direction ruler to avoid strain.
XI. Precision of Injection Molded Parts
Due to the non-uniformity and uncertainty of shrinkage rate during injection molding, the precision of injection molded parts is obviously 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. China also issued GB/T 14486-93 "Dimensional Tolerance of Engineering Plastics Molded Plastic Parts" in 1993. Designers can determine the dimensional tolerance of manufactured parts according to the plastic raw materials used and the use requirements of manufactured parts and the regulations in the standard. At the same time, the appropriate design tolerance precision should be determined according to the comprehensive strength of the factory and the design precision of peer products.
XII. Deformation of Injection Molded Parts
The rigidity of the injection molding product structure is improved, and the deformation is reduced. Try to avoid flat plate structure and set up flanging and concave-convex structure reasonably. Set up reasonable reinforcement.
Thirteen, buckle position
1. The fastening device is designed to be shared by a plurality of fastening positions at the same time, so that the whole device will not be unable to operate due to damage of individual fastening positions, thereby prolonging the service life of the device, and further, more tests and filters and fillets are added to increase the strength.
2. The tolerance requirements for the relevant dimensions of the buckle position are very strict, and too many upside-down positions are easy to cause damage to the buckle position; On the contrary, if there are too few back-off positions, the assembly position is difficult to control or the assembly part is too loose. The solution is to reserve a way to change the mold and add glue easily.
Fourteen, welding (hot plate welding, ultrasonic welding, vibration welding)
1. Welding can improve the connection strength.
2. Welding can simplify product design.
Fifteen, reasonable consideration of the contradiction between process and product performance
1 When designing injection molding products, the contradiction between product appearance, performance and process must be considered comprehensively. Sometimes good appearance or performance can be obtained at the expense of some manufacturability.
2 When the structural design cannot avoid injection defects, the defects should occur in hidden parts of the product as much as possible.
Sixteen, the relationship between the diameter of the screw column and the diameter of the self tapping screw
Hole diameter of self-tapping screw column
M2 1.7mm
M2.3 2.0mm
M2.6 2.2mm
M3 2.5mm
Seventeen, BOSS design principles:
1. The strut should not be used alone as far as possible. It should be connected to the outer wall or used together with reinforcing ribs to strengthen the strength of the strut and make the rubber flow more smoothly.
2, the height of the pillar is generally not more than two and a half times the diameter of the pillar. Too high a prop can cause air entrapment during plastic component molding (too long a length can cause air holes, scorching, insufficient filling, etc.).
2. 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 method to strengthen the strength of the pillar is to use reinforcing ribs.
4. The shape of BOSS is mainly round, while other shapes are not easy to process.
5. The position of BOSS should not be too close to the corner or outer wall. It should keep a certain distance from the outer wall of the product.
6), around the BOSS can remove part of the meat thickness (i.e., open crater) to prevent shrinkage subsidence
7), BOSS dial angle: usually take 0.5 outside, take 0.5 inside or 1
