There are many precautions in injection mold design, so what are they? Next, I will share with you seventeen points for attention in injection mold design. Come and have a look!

Mold opening direction and parting line

At the beginning of the design of each injection product, the mold opening direction and parting line should be determined first 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 structural design of the product, such as ribs, buckles and protrusions, should be consistent with the mold opening direction as far as possible, so as to avoid core pulling, reduce suture lines and prolong the life of the mold.

2. After the mold opening direction is determined, the proper parting line can be selected to avoid the back buckle of the mold opening direction, thus improving the appearance and performance.

Chimney taper

1. Proper demoulding slope can avoid product napping. The demoulding slope of smooth surface should be? 0.5 degree, fine dermatoglyphic (sand surface) surface is greater than 1 degree, and coarse dermatoglyphic surface is greater than 1.5 degree.

2. Proper demoulding inclination can avoid top injury of products, such as white top, deformed top and burst top.

3. When designing products with deep cavity structure, the inclination of the outer surface should be greater than that of the inner surface as much 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 the product opening.

Product wall thickness

1. All kinds of plastics have a certain range of wall thickness, generally 0.5 ~ 4 mm.. When the wall thickness exceeds 4 mm, it will cause problems such as too long cooling time and shrinkage printing, so we should consider changing the product structure.

2. Uneven wall thickness will lead to surface shrinkage.

3. Uneven wall thickness will cause blowholes and welding marks.

reinforcing steel bar

1. Reasonable application of reinforcing ribs can increase the rigidity of products and reduce deformation.

2. The thickness of the stiffener must be? (0.5 ~ 0.7) t product wall thickness, otherwise it will cause surface shrinkage.

3. The unilateral slope of stiffening rib should be greater than 1.5? , in order to avoid top injury.

fillet

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

2. Too small fillet may lead to stress concentration in the mold cavity, which may lead to cavity cracking.

3. Setting a reasonable fillet can also improve the processing technology of the die. For example, the cavity can be directly milled with an R cutter to avoid inefficient electrical machining.

4. Different fillet may cause the parting line to move, so choose different fillet or fillet cleaning according to the actual situation.

hole

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, which can avoid core pulling.

3. When the length-diameter 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 small diameter size (the largest physical size).

4. The aspect 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 usually greater than the size of the opening.

Core-pulling in injection mold. Sliding block mechanism and its evasion

1. When the plastic parts cannot be demoulded smoothly along the mold opening direction, the core-pulling slider mechanism should be designed. The slider of core-pulling mechanism can form a complex product structure, but it is easy to cause defects such as sewing and shrinkage of the product, which increases the cost of the mold and shortens the 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 opening direction, and the cavity core is knocked through.

Integral hinge

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

2. As a hinge, the film size should be less than 0.5mm and kept uniform.

3. When the integral hinge is injected, the gate can only be designed on one side of the hinge.

insert

1. Inserts in injection molding products can increase local strength, hardness and dimensional accuracy, and set small threaded holes (shafts) to meet various special requirements. At the same time, it will increase the product cost.

2. The insert is usually copper, but it can also be other metal or plastic parts.

3. The part of the insert embedded in plastic should be designed with anti-rotation and anti-pulling structure. Such as: knurling, punching, bending, flattening, shaft shoulder, etc.

4. The plastic around the insert should be properly thickened to prevent stress cracking of plastic parts.

5. When designing the insert, we should fully consider its positioning mode (hole, pin, magnetic) in the mold.

symbol

The product logo is generally set on the plane inner surface of the product and is convex. The mark can be set on the surface where the normal direction may be consistent with the mold opening direction to avoid strain.

Accuracy of injection molding parts

Due to the non-uniformity and uncertainty of shrinkage in injection molding, the precision of injection molded parts is obviously lower than that of metal parts, and the dimensional tolerance of mechanical parts cannot be simply applied. China has also issued GB/T 14486-93 "Dimensional Tolerance of Plastic Parts for Engineering Plastics Molding" in 1993, and designers can determine the parts according to the plastic raw materials used and the use requirements of the parts. At the same time, it is necessary to determine the appropriate design tolerance accuracy according to the comprehensive strength of the factory and the design accuracy of peer products.

Deformation of injection molded parts

Improve the rigidity of injection molding product structure and reduce deformation. Try to avoid flat structure and set up flanging and concave-convex structure reasonably. Set reasonable reinforcing ribs.

Buckle position

1. The locking device is designed to be used at multiple locking positions at the same time, so that the whole device will not be unable to operate because of the damage of individual locking positions, thus prolonging its service life, and adding more filters and rounded corners to increase its strength.

2. The tolerance requirements of the relevant dimensions of the buckle are very strict, and it is easy to damage the buckle if it is reversed too much; On the other hand, if there is too little inversion, the assembly position is difficult to control or the joint is too loose. The solution is to reserve a method to modify the mold, which is convenient for adding glue.

Welding (hot plate welding, ultrasonic welding and vibration welding)

1. Welding can improve the connection strength.

2. Using welding can simplify product design.

Reasonably consider the contradiction between process and product performance.

1 The contradiction between product appearance, performance and technology must be comprehensively considered when designing injection molding products. Sometimes good appearance or performance can be obtained at the expense of manufacturability.

When the structural design can't avoid the injection defects, try to make the defects occur in the hidden parts of the product.

Relationship between screw diameter and self-tapping screw diameter

Diameter of self-tapping screw column

M 2 1.7 mm

2.32 mm

2.62 mm

M32.5mm mm

BOSS design principles:

1. The column should not be used alone as far as possible, but should be connected with the external wall or used together with reinforcing ribs as far as possible to strengthen the strength of the column and make the rubber flow more smoothly.

2. The height of the column is generally not more than two and a half times the diameter of the column. Too high a pillar will lead to air retention in the molding process of plastic parts (too long a length will lead to air holes, burning, insufficient filling, etc.). ).

3. If the height of the column is more than 2. 5 times the diameter of the column, especially the column far away from the outer wall, the way to strengthen the strength of the column is to use reinforcing ribs.

The shape of 4.4. BOSS is mainly round, and other shapes are not easy to process.

The position of 5.5. BOSS should not be too close to the corner or external wall, and should keep a certain distance from the external wall of the product.

6).6) or so. BOSS, you can remove part of the meat thickness (that is, open the pit) to prevent shrinkage and subsidence.

7).BOSS mode setting angle: generally 0.5? Take 0.5? Or 1.

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