Why your products always have problems?


A product that is often defective in the production process, delayed delivery, mold repair, constant mold change, etc., it must be in the mold design time ignored a lot of details, or this mold design engineers are not professional enough. A good set of mold design can produce a set of precision mold, so as to produce stable quality products. So in the process of producing molds, it is not the cheaper the better the mold, if the products produced have problems, then you lose more. Below we organize the mold design issues that need attention:

Direction of mold opening and parting line

Each injection molded product in the beginning of the design should first determine its mold opening direction and parting line to ensure that as far as possible to reduce the core slider mechanism and eliminate the impact of the parting line on the appearance.

1.after the molding direction is determined, the product’s reinforcement, clips, bumps and other structures as far as possible designed to be consistent with the molding direction, in order to avoid the core to reduce the stitching line, to extend the life of the mold.

2.after the molding direction is determined, you can choose the appropriate parting line to avoid the existence of inverted buckle in the direction of molding, in order to improve the appearance and performance.

Demolding tilt

1.the appropriate demolding tilt can avoid the product pull hair (pull flowers). Smooth surface demolding slope should be ≥ 0.5 degrees, fine grain (sand surface) surface more than 1 degree, coarse grain surface more than 1.5 degrees.

2.the appropriate demolding slope can avoid the product top injury, such as top white, top deformation, top broken.

3.deep cavity structure product design, the outer surface slope as far as possible require greater than the inner surface slope to ensure that the injection mold core is not off-set, to get a uniform wall thickness of the product, and to ensure that the product opening part of the material strength.

Product wall thickness

1.a variety of plastics have a certain range of wall thickness, generally 0.5 ~ 4mm, when the wall thickness of more than 4mm, will cause excessive cooling time, resulting in shrinkage and other issues, should consider changing the product structure.

2.uneven wall thickness will cause surface shrinkage.

3.uneven wall thickness will cause air holes and fusion marks.


1.reasonable application of reinforcement, can increase product rigidity, reduce deformation.

2.thickness of the reinforcement must be ≤ (0.5 ~ 0.7) T product wall thickness, or cause surface shrinkage.

3.reinforcing rib should be more than 1.5 ° one-sided slope, in order to avoid top injuries.

Rounded corners

1.rounded corners too small may cause product stress concentration, resulting in product cracking.

2.rounded corner is too small may cause mold cavity stress concentration, resulting in cavity cracking.

3.set a reasonable rounded corners, but also to improve the mold processing, such as the cavity can be directly milling with R cutter, and to avoid inefficient electrical processing.

4.different rounded corners may cause the movement of the parting line, should be combined with the actual situation to choose a different rounded or clear angle.


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

2.the hole of the axial direction and the same direction of the mold, you can avoid core pulling.

3.when the hole length to diameter ratio is greater than 2, should be set to demold the slope. At this time, the diameter of the hole should be calculated according to the small diameter size (the largest solid size).

4.blind hole length to diameter ratio is generally not more than 4. anti-hole needle bending

5.the distance between the hole and the edge of the product is generally greater than the hole size.

Injection mold core, slider mechanism and to avoid

1.when the molded part according to the direction of the mold can not be smoothly demolded, should be designed to extract the core slider mechanism. Core slider mechanism can mold complex product structure, but easy to cause product stitching lines, shrinkage and other defects, and increase the cost of molds to shorten the life of the mold.

2.the design of injection molded products, such as no special requirements, try to avoid the core structure. Such as hole axial and tendon direction to the direction of the mold, the use of cavity core touch through and other methods.


1.the use of PP material toughness, the hinge can be designed and products as a whole.

2.as the hinge of the film size should be less than 0.5mm, and keep uniform.

3.injection molding a hinge, the gate can only be designed on one side of the hinge.


1.in the injection molded products into the insert can increase the local strength, hardness, dimensional accuracy and set up small threaded holes (shaft), to meet a variety of special needs. At the same time will increase product costs.

2.inserts are generally copper, can also be other metals or plastic parts.

3.inserts embedded in the plastic part should be designed to stop the rotation and anti-pull-out structure. Such as: knurling, holes, bending, flattening, shoulders and so on.

4.embedded parts around the plastic should be appropriately thickened to prevent stress cracking of plastic parts.

5.the design of inserts, should give full consideration to its positioning in the mold (holes, pins, magnetic)


Product marking is generally set on the inner surface of the product is relatively flat, and the use of raised form, select the normal direction and molding direction ruler may be consistent with the face of the set marking, you can avoid strains.

Injection molding precision

Due to the non-uniformity and uncertainty of the shrinkage rate of injection molding, injection molded parts accuracy is significantly lower than metal parts, can not simply apply the dimensional tolerances of mechanical parts should be selected according to the standard appropriate tolerance requirements. China also released in 1993 GB/T14486-93 “engineering plastics molded plastic parts size tolerance”, the designer can be based on the plastic raw materials used and the use of parts requirements, according to the provisions of the standard to determine the size of the parts tolerance. At the same time, according to the comprehensive strength of the factory, the design accuracy of peer products to determine the appropriate design tolerance accuracy.

Deformation of injection molded parts

Improve the rigidity of the injection molded product structure to reduce deformation. Try to avoid flat structure, reasonable setup flap, concave-convex structure. Set up reasonable reinforcement.


1.buckle device is designed to share a number of buckles at the same time, so that the overall device will not be damaged because of individual buckles and can not operate, thereby increasing its service life, and then more filtration plus rounded corners to increase the strength.

2.buckle related dimensions of the tolerance requirements are very strict, too much buckle position is easy to form buckle damage; on the contrary, too little buckle position is difficult to control the assembly position or the combination of parts of the phenomenon of excessive looseness. The solution is to set aside to change the mold is easy to add glue way to achieve.

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

1.the use of welding, can improve the strength of the joint.

2.the use of welding, can simplify product design.

Reasonable consideration of the contradiction between the process and product performance

1.design of injection molded products must be considered comprehensively when the product appearance, performance and process of the contradiction between. Sometimes sacrifice part of the process, you can get a very good appearance or performance.

2.structural design is unable to avoid injection molding defects, as far as possible, so that defects occur in the hidden parts of the product.

Relationship between the hole diameter of the screw post and the diameter of the self-tapping screws

Self-tapping screws

M2 1.7mm

M2.3 2.0mm

M2.6 2.2mm

M3 2.5mm

Design principles of BOSS:

1.the strut should not be used alone as far as possible, should try to connect to the outer wall or with the reinforcement used together, the purpose is to strengthen the strut strength 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. Because too high strut will lead to plastic parts molding trapped air (length is too long will cause air holes, burnt, underfilled, etc.).

3.If the height of the strut is more than two and a half times the diameter of the strut, especially the strut that is far away from the outer wall, the way to strengthen the strut is to use the reinforcing bar.

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

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

6.BOSS can be used to remove part of the meat around the thick (i.e. open crater) to prevent shrinkage and subsidence.

7. BOSS toggle mold angle: usually take 0.5 ° outside, take 0.5 ° or 1 inside.


If you are looking for a professional designer to help you design a new product or design a mold, Grandshine has a team of engineers with 20 years of rich experience who can provide you with professional design solutions. In addition, we can also provide a complete set of product production services, welcome to consult us for a quotation.

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