What are the principles and core of injection mold design?

Mold opening direction and parting line

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

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

2. After the mold opening direction is determined, the appropriate parting line can be chosen to avoid the existence of backlash in the injection mold opening direction to improve the appearance and performance.

The slope of the mold release

1. The appropriate release slope can avoid the product from pulling hair (pulling flowers). The smooth surface of the mold slope should be ≥ 0.5 degrees, the 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 injection mold release can avoid product top injuries, such as top white, top deformation, and top broken.

3. In deep cavity structure product design, the slope of the outer surface as far as possible requires greater than the slope of the inner surface, 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 °, to avoid top injury.

Rounded corners

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

2. Rounded corners that are too small may cause the mold cavity stress concentration, leading to cavity cracking.

3. Set a reasonably rounded corner, but also can improve the processing of the injection mold, such as the cavity can be directly milled with an R cutter, to avoid inefficient electrical processing.

4. Different rounding angles may cause the movement of the parting line, which should be combined with the actual situation to choose a different rounding or clear angle.

The hole

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

2. The axial direction of the hole and injection mold opening direction in line with the core can be avoided.

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

4. The distance between the hole and the edge of the product is generally larger than the size of the hole diameter.

The injection mold core, slider mechanism, and avoid

1. When the plastic parts according to the mold opening direction can not be smoothly off the mold, should be designed to draw the core slider mechanism.

The core pulling mechanism slider can shape complex product structure, but it is easy to cause defects such as product stitching lines and shrinkage, increase mold cost and shorten injection 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 open the direction of the mold, the use of cavity core touch through, and other methods.

One-piece hinge

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

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

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

Inserts

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

2. The insert is generally copper, can also be other metals or plastic parts.

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

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

5. The design of the insert, should be fully considered in the mold positioning mode (hole, pin, magnetic).

Marking

Product identification is generally set at the flatter inner surface of the product, and the use of raised form, choosing the normal direction and the mold opening direction ruler may be consistent with the face of the logo, can avoid strains

The precision of injection molded 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 appropriate tolerance requirements.

China also released in 1993 GB/T14486-93 “engineering plastics injection 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 determines 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 structures, set reasonable flanges, and concave and convex structures. Set up reasonable reinforcement bars.

Buckling

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. The tolerance requirements of the relevant dimensions of the buckle are very strict, too many buckle position is easy to form buckle damage; on the contrary, too few buckle position is difficult to control the assembly position or the combination of parts appears to lose phenomenon. The solution is to set aside to change the mold easily 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 contradictions between the process and product performance

1. Design of injection molding products must take into account the contradictions between product appearance, performance, and technology. Sometimes sacrificing part of the process, can get a very good appearance or performance.

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

The relationship between the screw column aperture and the diameter of 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. The pillar should not be used alone, should be connected to the outer wall or used with the reinforcement as far as possible, the purpose is to strengthen the pillar’s 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 a pillar will lead to trapped air when molding plastic parts (too long will cause air holes, scorching, underfilling, etc.).

3. If the height of the pillar is more than 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 reinforcement 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 of the outer wall but should be kept at a distance from the outer wall of the product.

6. Some of the flesh around the BOSS can be removed (i.e., open crater) to prevent shrinkage and sagging.

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