Fourteen key points in the design of injection molded parts

The fourteen key points of the injection molded part design are as follows:

First, the mold opening direction and parting line

At the beginning of each design, each injection molding product must first determine its mold opening direction and parting line to ensure that the core 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 reinforcing ribs, snaps, protrusions and other structures of the product are designed to be consistent with the mold opening direction as much as possible to avoid the core pulling to reduce the seam line and prolong the life of the mold.

2. After the mold opening direction is determined, the appropriate parting line can be selected to avoid the reverse buckle in the mold opening direction to improve the appearance and performance.

Second, the draft angle

1. Appropriate drafting angle can avoid product pulling (drawing). The smooth surface of the draft should be ≥ 0.5 degrees, the fine grain (sand surface) surface is greater than 1 degree, and the rough grain surface is greater than 1.5 degrees.

2, the appropriate draft angle can avoid product top injuries, such as white, top deformation, burst.

3, deep cavity structure product design when the outer surface slope should be greater than the inner surface slope as much as possible to ensure that the mold core is not biased during injection, to obtain a uniform product wall thickness, and to ensure the material strength of the product opening.

Third, the product wall thickness

1, all kinds of plastics have a certain wall thickness range, generally 0.5 ~ 4mm, when the wall thickness exceeds 4mm, it will cause the cooling time is too long, resulting in shrinkage and other issues, should consider changing the product structure.

2. Uneven wall thickness will cause the surface to shrink.

3. Uneven wall thickness can cause pores and weld lines.

Fourth, the reinforcement

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

2. The thickness of the reinforcing ribs must be ≤ (0.5 ~ 0.7) T product wall thickness, otherwise the surface will shrink.

3. The slope of the rib should be greater than 1.5° to avoid top injury.

Five, rounded corners

1. If the fillet is too small, it may cause stress concentration of the product, resulting in cracking of the product.

2. Too small a fillet may cause stress concentration in the mold cavity, resulting in cracking of the cavity.

3, set reasonable rounded corners, can also improve the processing technology of the mold, such as the cavity can be directly processed with R knife milling, and avoid low-efficiency electrical processing.

4. Different rounded corners may cause the movement of the parting line. Different rounding or clearing angle should be selected according to the actual situation.

Six, the hole

1, the shape of the hole should be as simple as possible, generally take a round shape.

2. The axial direction of the hole is the same as the direction of the mold opening, and the core can be avoided.

3. When the aspect ratio of the hole is greater than 2, the draft angle should be set. The diameter of the hole at this time should be calculated according to the size of the small diameter (the largest physical size).

4. The aspect ratio of blind holes is generally not more than 4. Anti-hole punching 5, the distance between the hole and the edge of the product is generally larger than the aperture size.

7. The core of the injection mold, the slider mechanism and avoidance

1. When the plastic parts cannot be demoulded smoothly according to the mold opening direction, the core pulling slider mechanism should be designed. The slider of the core pulling mechanism can form a complicated product structure, but it is easy to cause defects such as seam stitching and shrinkage of the product, and increase the cost of the mold to shorten the life of the mold.

2. When designing injection molding products, if there is no special requirement, try to avoid the core structure. For example, the direction of the hole axis and the direction of the rib is changed to the mold opening direction, and the cavity core is used to penetrate.

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 as a hinge should be less than 0.5mm and kept even.

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

Nine, inserts

1. Inserting inserts into the injection molding product 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 product costs.

2, the insert is generally copper, but also other metal or plastic parts.

3. The part of the insert embedded in the plastic shall be designed to prevent rotation and pull out. Such as: knurling, holes, bending, flattening, shoulders and so on.

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

5. When designing the insert, the positioning method (hole, pin, magnetism) in the mold should be fully considered.

X. Logo

The product identification is generally set on the flat surface of the product, and the convex form is adopted. The selection of the normal direction and the surface of the mold opening direction may be set to mark, which can avoid the strain.

XI, precision of injection molded parts

Due to the non-uniformity and uncertainty of shrinkage during injection molding, the precision of injection molded parts is significantly lower than that of metal parts. The dimensional tolerances of mechanical parts cannot be simply applied. The appropriate tolerance requirements should be selected according to the standard. China also released GB/ in 1993. T14486-93 "Dimensional Tolerance of Molded Plastic Parts for Engineering Plastics", the designer can determine the dimensional tolerance of the part according to the requirements of the standard according to the plastic raw materials and parts used.

Twelve, deformation of injection molded parts

Improve the rigidity of the injection molded product structure and reduce deformation. Try to avoid the flat structure and set the flange and the concave and convex structure reasonably. Set reasonable reinforcement bars.

Thirteen, the buckle

1. The buckle device is designed to be shared by a plurality of buckles at the same time, so that the whole device can not be operated due to the damage of the individual buckles, thereby increasing the service life thereof, and then multi-test filtering and rounding to increase the strength.

2. The tolerance of the relevant dimensions of the buckle is very strict. If the position of the buckle is too much, the buckle will be damaged. On the contrary, if the position of the buckle is too small, the assembly position is difficult to control or the combination part is too loose.

The solution is to reserve a way to change the mold and easily add glue.

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

1, using welding, can improve the joint strength.

2, using welding, can simplify product design.