Guidelines for injection molding mold design

Table of Contents

Mold industry is a basic industry in the manufacturing industry, is the basis for the transformation of technological achievements, and at the same time itself is an important area of high-tech industry, in Europe and the United States and other industrial countries are known as “iron into gold” “magnetic industry”.

The United States industry that “mold industry is the cornerstone of the United States industry”; Germany is that it is the “key industry” in all industries; Japan Mold Association also believes that “mold is to promote social prosperity and wealth of the power “, but also “the secret of the entire industrial development”, is “into the rich society of the driving force”.

Mold opening direction and parting line

Each injection molded product should be designed to determine the mold opening direction and parting line to ensure that the core pulling slider mechanism is reduced as much as possible and to eliminate the impact of parting line on the appearance.

1. After the mold opening direction is determined, the structure of the product such as reinforcement, clips and bumps should be designed to be consistent with the mold opening direction as much as possible to avoid core extraction and reduce the parting line to prolong the injection mold life.

2. After the mold opening direction is determined, appropriate parting lines can be selected to avoid the existence of backward buckling in the mold opening direction to improve the appearance and performance.

The slope of the mold release

1. The appropriate release slope can avoid the product pulling hair (pulling flowers). Smooth surface of the mold slope should be ≥ 0.5 degrees, fine grain (sand surface) surface is greater than 1 degree, coarse grain surface is greater than 1.5 degrees.

2. The appropriate slope of the mold release can avoid product top injuries, such as top white, top deformation, or top broken.

3. Deep cavity structure product design, the outer surface slope as far as possible to require greater than the inner surface slope, in order to ensure that the mold core does not deviate when injection molding, to get a uniform product wall thickness, and to ensure the material strength of the product opening parts.

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, will cause excessive cooling time, resulting in shrinkage and other problems, 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.

The reinforcement

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

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

3. The one-sided slope of the reinforcement should be greater than 1.5 °, in order to avoid top injury.

Rounded corners

1. Rounded corners are too small may cause the product stress concentration, resulting in product cracking.

2. The rounded angle is too small may cause the mold cavity stress concentration, leading to cavity cracking.

3. Setting reasonable rounded corners can also improve the processing of the injection mold, such as the cavity can be directly milled with R cutter, and avoid inefficient electric processing.

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


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

2. The axial direction of the hole and mold opening direction, can avoid core extraction.

3. When the hole length-diameter ratio is greater than 2, should be set to release the injection mold slope. At this time, the diameter of the hole should be calculated according to the small diameter size (maximum entity size).

4. Blind hole length-diameter ratio generally does not exceed 4. Anti-hole pin punching bend.

5. The distance between the hole and the edge of the product is generally larger than the size of the aperture.

The injection mold core, slider mechanism and avoid

1. When the plastic part cannot be released smoothly according to the direction of mold opening, the core extraction slider mechanism should be designed.

Core pulling mechanism slider can shape complex product structure, but it is easy to cause defects such as product stitching line and shrinkage, and increase mold cost and shorten mold life.

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

One hinge

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

2. The size of the film used as hinge should be less than 0.5mm, and it should be kept even.

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


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

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

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

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

5. When designing the insert, its positioning in the injection mold should be fully considered (hole, pin, magnetic).


Product identification is generally set at the flatter inner surface of the product and in the form of a projection, and the identification is set at the face where the normal direction and the mold opening direction ruler may be consistent, which can avoid strains.

The precision of injection molding parts

Due to the unevenness and uncertainty of shrinkage during injection molding, the accuracy of injection molded parts is significantly lower than metal parts, can not simply apply the dimensional tolerances of mechanical parts should be selected according to the standard Huai 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 requirements of the use of the parts, according to the provisions of the standard to determine the size tolerance of the parts.

At the same time, according to the comprehensive strength of the factory, the design accuracy of the peer products to determine the accuracy of suitable design tolerances.

The deformation of injection molded parts

Improve the rigidity of the structure of injection molding products to reduce deformation. Try to avoid flat structure, set reasonable flanges, concave and convex structure. Set up reasonable reinforcement bars.

Buckle position

1. The buckle bit device is designed to share multiple buckle bits at the same time, so that the overall device will not be unable to operate because of damage to individual buckle bits, thereby increasing its service life, and then more ko filter plus rounded corners to increase the strength.

2. It is the tolerance requirements of the relevant size of the buckle is very strict, too many buckle position is easy to form a buckle damage;

On the contrary, too few buckle position is difficult to control the assembly position or the combination of part of the phenomenon of too loose. The solution is to set aside to change the injection mold easy to add glue to achieve the way.

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. The design of injection molding products must take into account the contradiction between product appearance, performance and technology. Sometimes sacrifice part of the process, can get a good appearance or performance.

2. When the structural design really can not avoid injection molding defects, as far as possible to let the defects occur in the hidden parts of the product.

The relationship between the diameter of the screw column aperture and self-tapping screws

Self-tapping screws screw column hole diameter

M2 1.7mm

M2.3 2.0mm

M2.6 2.2mm

M3 2.5mm

Design principles of BOSS

1. Pillar should not be used alone as far as possible, it should be connected to the outer wall or used together with the reinforcement as far as possible, the purpose is to strengthen the pillar and make the rubber flow more smoothly.

2. Pillar height is generally not more than two and a half times the diameter of the pillar. Because too high pillar will lead to air trapping when molding plastic parts (too long length will cause air holes, scorching, underfilling, etc.).

3. If the height of the pillar exceeds two and a half times the diameter of the pillar, especially the pillar away from the outer wall, the way to strengthen the pillar is to use reinforcing bars.

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, but should be kept at a distance from the outer wall of the product.

6. Around the BOSS can be used to remove part of the flesh thickness (i.e. open crater) to prevent shrinkage sagging.

7. BOSS dialing angle: usually 0.5 ° outside, 0.5 °, or 1 inside.

Latest Posts
Share on facebook
Share on twitter
Share on linkedin
Share on pinterest
Tell us your request right now and contact us today about getting started on your next project together!


Or Fill Out The Contact Form Below:

Ask For A Quick Quote

We will contact you within one working day, please pay attention to the email with the suffix “”.

Ask For A Quick Quote

We will contact you within one working day, please pay attention to the email with the suffix “”.

Ask For A Quick Quote

We will contact you within one working day, please pay attention to the email with the suffix “”.