Each injection product must first determine its mold opening direction and parting line at the beginning of design to ensure that core-pulling slider mechanism is minimized and effect of parting line on appearance is eliminated.
1. After mold opening direction is determined, product's ribs, buckles, protrusions and other structures should be designed to be consistent with mold opening direction as much as possible, so as to avoid core pulling and reduce seam lines and extend life of mold.
2. After mold opening direction is determined, an appropriate parting line can be selected to avoid undercutting in mold opening direction to improve appearance and performance.

 

1. Appropriate demoulding angle can avoid product fuzzing (scratching). Demolding slope of smooth surface should be ≥0.5 degrees, fine dermatome (sand surface) surface is greater than 1 degree, and coarse dermatome surface is greater than 1.5 degrees.
2. Proper demolding slope can avoid top damage, such as top white, top deformation, and top break.
3. When designing deep cavity structure products, outer surface slope should be greater than inner surface slope as much as possible to ensure that mold core is not deviated during injection molding, obtain uniform product wall thickness, and ensure material strength of product opening.

1. All kinds of plastics have a certain range of wall thickness, generally 0.5～4mm. When wall thickness exceeds 4mm, it will cause too long cooling time and produce shrinkage problems, so we should consider changing product structure.
2. Uneven wall thickness will cause surface shrinkage.
3. Uneven wall thickness will cause pores and weld marks.

1. Reasonable application of reinforcing ribs can increase product rigidity and reduce deformation.
2. Thickness of stiffener must be ≤ (0.5～0.7) T product wall thickness, otherwise it will cause surface shrinkage.
3. Single-sided slope of stiffener should be greater than 1.5° to avoid top damage.

1. Too small rounded corners may cause stress concentration in the product, leading to product cracking.
2. Too small rounded corners may cause stress concentration in mold cavity and cause cavity cracking.
3. Setting a reasonable fillet can also improve processing technology of mold. For example, cavity can be directly milled with an R cutter to avoid inefficient electrical processing.
4. Different rounded corners may cause parting line to move, so you should choose different rounded corners or clear corners based on actual situation.

1. Shape of hole should be as simple as possible, generally round.
2. Axial direction of hole is consistent with opening direction, which can avoid core pulling.
3. When length to diameter ratio of hole is greater than 2, demolding slope should be set. At this time, diameter of hole should be calculated according to minor diameter (the largest physical size).
4. Aspect ratio of blind holes is generally not more than 4 to prevent hole needle from bending.
5. Distance between hole and edge of product is generally greater than hole size.

1. When plastic part cannot be demolded smoothly in mold opening direction, a core-pulling slider mechanism should be designed. Slider of core-pulling mechanism can form a complex product structure, but it is easy to cause defects such as product stitching and shrinkage, increase cost of mold and shorten mold life.
2. When designing injection products, if there is no special requirement, try to avoid core pulling structure. For example, direction of hole axis and ribs is changed to mold opening direction, using methods such as cavity core collision.

1. Utilizing toughness of PP material, hinge can be designed to be integrated with product.
2. Size of film used as a hinge should be less than 0.5mm and kept uniform.
3. When injecting an integral hinge, gate can only be designed on one side of hinge.

1. Inserting inserts in injection molded products 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. Inserts are generally copper, but also other metal or plastic parts.
3. Part of insert embedded in plastic should be designed with anti-rotation and anti-pulling structure. Such as: knurling, hole, bending, flattening, shaft shoulder, etc.
4. Plastic around insert should be appropriately thickened to prevent stress cracking of plastic.
5. When designing inserts, fully consider its positioning method in mold (holes, pins, magnetism)

 

Product identification is generally set on inner surface of product on a relatively flat surface, and adopts a convex form. Identification is set on the surface where direction is as consistent as possible with mold opening direction to avoid strain.

Due to inhomogeneity and uncertainty of shrinkage rate during injection molding, accuracy of injection molded parts is significantly lower than that of metal parts. Dimensional tolerances of mechanical parts cannot be simply applied. Appropriate tolerance requirements should be selected according to standard. Our country also issued GB/ in 1993 T14486-93  "Dimensional Tolerance of Engineering Plastics Moulded Plastic Parts", designer can determine dimensional tolerance of parts according to plastic raw materials used and requirements of the parts, and according to regulations in the standard. At the same time, it is necessary to determine appropriate design tolerance accuracy according to comprehensive strength of factory and design accuracy of peer products.

Improve rigidity of injection product structure and reduce deformation. Try to avoid flat structure, set flanging, uneven structure reasonably, and set reasonable reinforcing ribs.

1. Design buckle device to share multiple buckles at the same time, so that overall device will not be inoperable due to damage of individual buckles, thereby increasing its service life, also adding more filter and rounded corners to increase strength.
2. Tolerance requirements for relevant dimensions of buckle are very strict. Too many undercut positions can easily cause damage to buckle; on the contrary, if undercut position is too small, assembly position is difficult to control or assembly part is too loose. Solution is to reserve a way to change mold and add material easily.

1. Use of welding can improve connection strength.
2. Use of welding can simplify product design.

1 Contradiction between product appearance, performance and process must be considered comprehensively when designing injection products. Sometimes a part of manufacturability is sacrificed to get a good appearance or performance.
2 When structural design cannot avoid injection defects, try to make defects occur in hidden parts of product as much as possible.

 

1. Pillar should not be used alone as much as possible. It should be connected to outer wall or used with reinforcing ribs as far as possible. Purpose is to strengthen strength of pillar and make rubber flow more smoothly.
2. Height of pillar is generally not more than two and a half times diameter of pillar. Excessively high pillars will cause air trapping during molding of plastic parts (too long length will cause pores, scorching, insufficient filling, etc.).
3. If height of pillar is more than two and a half times diameter of pillar, especially pillar far from outer wall, method to strengthen strength of pillar is to use stiffeners.
4. Shape of BOSS is mainly round, other shapes are not easy to process
5. Position of BOSS should not be too close to corner or outer wall, and should keep a distance from outer wall of product
6. Around BOSS can remove part of thick flesh (that is, open crater) to prevent shrinkage and subsidence
7. Boss's draft angle: usually 0.5° outside, 0.5° or 1 inside.