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1, Opening direction and parting line
At the beginning of the design of each injection product, the opening direction and parting line should be determined first to ensure that the core pulling slider mechanism can be minimized and the influence of parting line on the appearance can be eliminated.
1. After the opening direction is determined, the stiffener, buckle, bulge and other structures of the product shall be designed to be consistent with the opening direction as far as possible, so as to avoid core pulling and reduce the seam line and extend the service life of the mold.
2. After the mold opening direction is determined, the proper parting line can be selected to avoid reverse buckle in the mold opening direction, so as to improve the appearance and performance.
2, Draft angle
1. Proper draft angle can avoid product galling (scuffing). The demoulding slope of smooth surface shall be ≥ 0.5 degree, that of fine grain (sand surface) surface shall be greater than 1 degree, and that of coarse grain surface shall be greater than 1.5 degree.
2. Proper demoulding slope can avoid top damage of the product, such as white top, deformation of the top and breaking of the top.
3. In the design of deep cavity structure products, the inclination of outer surface should be greater than that of inner surface as far as possible, so as to ensure that the mold core does not deviate during injection molding, obtain uniform product wall thickness, and ensure the material strength of product opening.
3, Product wall thickness
1. All kinds of plastics have a certain range of wall thickness, generally 0.5-4mm. When the wall thickness is more than 4mm, it will cause the cooling time to be too long, resulting in problems such as shrink printing, etc. it should be considered to change the product structure.
2. Uneven wall thickness will cause surface shrinkage.
3. Uneven wall thickness can cause porosity and weld marks.
4, Stiffener
1. The reasonable application of stiffeners can increase the rigidity of products and reduce the deformation.
2. The thickness of stiffener must be ≤ (0.5-0.7) t product wall thickness, otherwise the surface will shrink.
3. The single side slope of stiffener shall be greater than 1.5 ° to avoid top injury.
Five, fillet
1. Too small fillet may cause product stress concentration and product cracking.
2. Too small fillet may lead to 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 by r-knife, and low-efficiency electrical machining can be avoided.
4. Different fillets may cause the movement of parting line. Different fillets or cleaning angles should be selected according to the actual situation.
Six, hole
1. The shape of the hole should be as simple as possible, generally round.
2. The axial direction of the hole is the same as the opening direction, so core pulling can be avoided.
3. When the length diameter ratio of the hole is greater than 2, the demoulding slope shall be set. In this case, the diameter of the hole shall be calculated according to the minor diameter (maximum solid size).
4. The length diameter ratio of blind hole is generally no more than 4. Punching and bending of anti hole needle
5. The distance between the hole and the edge of the product is generally larger than the hole size.
7, Core pulling and slide block mechanism of injection mold and its avoidance
1. When the plastic parts cannot be demoulded smoothly according to the 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 seam line, shrinkage and so on, and increase mold cost and shorten mold life.
2. When designing injection products, if there is no special requirement, core pulling structure shall be avoided as far as possible. For example, the direction of hole axis and rib is changed to the opening direction, and the method of cavity core penetration is used.
8, Integrated hinge
1. With the toughness of PP material, the hinge can be designed to be integrated with the product.
2. The film size used as a hinge shall be less than 0.5mm and shall be uniform.
3. When the integrated hinge is injected, the gate can only be designed on one side of the hinge.
Nine. Insert
1. Inserting inserts into injection products can increase local strength, hardness, dimensional accuracy and set small threaded holes (shafts) to meet various special needs. At the same time, it will increase the product cost.
2. The insert is usually copper, or other metal or plastic parts.
3. The part of the insert embedded in the plastic shall be designed with stop rotation and pull-out structure. Such as: knurling, hole, bending, flattening, shoulder, etc.
4. The plastic around the insert shall be properly thickened to prevent stress cracking of the plastic.
5. When designing the insert, the positioning mode (hole, pin, magnetic) in the die shall be fully considered
Ten, logo
Generally, the product identification is set at the flat part of the internal surface of the product, and in the form of bulge, the identification is set at the surface where the normal direction and the opening direction ruler may be the same, so as to avoid strain.
11, Precision of injection parts
Due to the non-uniformity and uncertainty of shrinkage during injection molding, the accuracy of injection molded parts is obviously lower than that of metal parts, so the dimensional tolerance of mechanical parts that can not be simply applied should be selected according to the standard. China also issued GB / t14486-93 "dimensional tolerance of engineering plastic molded parts" in 1993. The designer can use the standard according to the requirements of plastic raw materials and parts Determine the dimensional tolerance of the part as specified in. At the same time, according to the comprehensive strength of the factory and the design accuracy of the products of the same industry, the appropriate design tolerance accuracy should be determined.
12, Deformation of injection parts
Improve the rigidity of injection product structure and reduce the deformation. Avoid flat structure as much as possible, reasonably set flanging and concave convex structure. Set up reasonable stiffeners.
13, Buckle position
1. The buckle device is designed to share multiple buckle positions at the same time, so that the whole device will not be unable to operate due to the damage of individual buckle positions, so as to increase its service life, and then more filtering and filleting to increase the strength.
2. The tolerance requirements of the relevant dimensions of the buckle position are very strict, and too many buckles are easy to cause damage to the buckle position; on the contrary, too few buckles are difficult to control the assembly position or the assembly part is too loose. The solution is to reserve a way to change the mold and easily add glue.
