Mold industry is a basic industry in manufacturing industry and a basis for transformation of technological achievements. At the same time, it is an important field of high-tech industries. It is called “magnetic industry” in industrialized countries such as Europe and United States.
American industry believes that “mold industry is cornerstone of American industry"; Germany considers it to be a "key industry" in all industries; Japan Die Association also believes that "mold is driving force for prosperity of society", and is it also "secret of entire industrial development" and "motivation to enter affluent society."

Each injection molding products must first determine its mold opening direction and parting line at the beginning of design to ensure that core slider mechanism is minimized and influence of parting line on appearance is eliminated.
1. After mold opening direction is determined, reinforcement ribs, snaps, protrusions and other structures of product are designed to be consistent with mold opening direction as much as possible to avoid core pulling to reduce seam line and prolong life of mold.
2. After mold opening direction is determined, appropriate parting line can be selected to avoid reverse buckle in mold opening direction to improve appearance and performance.

1. Appropriate drafting can avoid product pulling (drawing). Smooth surface of draft should be ≥ 0.5 degrees, fine grain (sand surface) surface is greater than 1 degree, and rough grain surface is greater than 1.5 degrees.
2. Appropriate draft angle can avoid product top injuries, such as white, top deformation, burst.
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 biased during injection, to obtain a uniform product wall thickness, and to ensure material strength of opening part of product.

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

2. Uneven wall thickness will cause surface to shrink.
3. Uneven wall thickness will cause pores and weld lines.

 

1. Reasonable application of reinforcing ribs can increase product rigidity and reduce deformation.
2. Thickness of reinforcing ribs must be ≤ (0.5 ~ 0.7) T product wall thickness, otherwise surface will shrink.
3. Slope of rib should be greater than 1.5° to avoid top injury.

1. Too small a fillet may cause stress concentration of product, resulting in cracking of product.
2. Too small a fillet may cause stress concentration in mold cavity, resulting in cracking of cavity.
3. Set a reasonable rounded corners, can also improve processing technology of mold, such as cavity can be directly processed with R knife milling, and avoid low-efficiency electrical processing.
4. Different rounded corners may cause movement of parting line. Different rounding or clearing angle should be selected according to actual situation.

1,. Shape of hole should be as simple as possible, generally take a round shape.
2. Axial direction of hole is same as direction of mold opening to avoid core pulling.
3. When aspect ratio of hole is greater than 2, draft angle should be set. Diameter of hole at this time should be calculated according to size of small diameter (the largest physical size).
4. Aspect ratio of blind holes is generally not more than 4 to prevent hole from being bent.
5. Distance between hole and edge of product is generally greater than aperture size.

1. When plastic parts cannot be demoulded smoothly according to mold opening direction, 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 seam line and shrinkage of product, and increase cost of mold to shorten life of mold.
2. When designing injection molding products, if there is no special requirement, try to avoid core structure. For example, direction of hole axis and rib is changed to mold opening direction, and cavity core is used to penetrate.

1. Using toughness of PP material, hinge can be designed to be integrated with product.
2. Film size as a hinge should be less than 0.5 mm and kept uniform.
3. When molding an integral hinge, gate can only be designed on one side of hinge.

1. Inserting inserts into injection molding products can increase local strength, hardness, dimensional accuracy and setting small threaded holes (shafts) to meet various special needs. At the same time, it will increase product costs.
2. Insert is generally copper, but also other metal or plastic parts.
3. Part of insert embedded in plastic shall be designed to prevent rotation and pull out. Such as: knurling, holes, bending, flattening, shoulders and so on.
4. Plastic around insert should be properly thickened to prevent stress cracking of plastic parts.
5. When designing insert, positioning method (hole, pin, magnetic) in mold should be fully considered.

Product identification is generally set on flat surface of product, and convex form is used. Selection direction is set at same surface as opening direction ruler, which can avoid strain.

Due to non-uniformity and uncertainty of shrinkage during injection molding, precision 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. In 1993, China also issued GB/T14486-93 "Dimensional Tolerance of Molded Plastic Parts for Engineering Plastics", which can be used by designers according to plastic materials used. Requirements for use of parts shall be determined according to specifications in the standard. At the same time, according to comprehensive strength of factory, design accuracy of products from peers to determine appropriate design tolerance accuracy.

Improve rigidity of injection molding products structure and reduce deformation. Try to avoid flat structure, set flanging and concave-convex structure reasonably. Set reasonable reinforcement bars.

1. Buckle device is designed to be shared by multiple buckles at the same time, so that whole device will not be unable to operate due to damage of individual buckles, thereby increasing service life, then multi-test filtering and rounding to increase strength.
2. Tolerance of relevant dimensions of buckle is very strict. If position of buckle is too much, buckle will be damaged. On the contrary, if position of buckle is too small, assembly position is difficult to control or combined part is too loose. Solution is to reserve a way to change mold and easily add material.

1. Welding can improve joint strength.
2. Welding can simplify product design.

1 When designing injection molding products, contradiction between product appearance, performance and process must be considered comprehensively. Sometimes some of craftsmanship is sacrificed to get a good appearance or performance.
2 Structural design can not avoid injection defects, as far as possible let defects occur in hidden parts of product.

Self-tapping screw column aperture
M21.7mm
M2.32.0mm
M2.62.2mm
M32.5mm

1. Pillars should not be used alone. They should be connected to outer wall as much as possible or used together with reinforcing ribs. Purpose is to strengthen strength of pillars and make rubber flow more smoothly.
2. Height of pillars is generally not more than two and a half times diameter of pillars. Excessive pillars can cause plastic parts to become trapped when they are formed (pores will cause pores, burnt, insufficient filling, etc.).
3. If height of pillar exceeds two and a half times diameter of pillar, especially pillar away from outer wall, method of strengthening strength of pillar is to use a reinforcing rib.
4, BOSS shape is mainly circular, other shapes are not easy to process.
5. Position of BOSS should not be too close to corner or outer side wall, and should be kept at a distance from outer wall of product.
6). Some of material can be removed around BOSS(ie crater) to prevent shrinkage and subsidence.
7). BOSS dialing angle: usually take 0.5 ° outside, take 0.5 ° or 1 inside.
Purpose of parting is to let product get out of mold smoothly. Let's take a picture to illustrate.

 

In above picture, except that mold cavity is separated from A-A line, any part of split mold cannot smoothly take out product because there is a buckle to buckle (shaded part in figure).
In above figure, if we divide mold from B-B line, we can see that shaded part in figure is part where product is blocked, that is, material surface between A and B is reverse buckle.
Therefore, we can draw a conclusion that in order to ensure smooth release of product, selection of product parting line should be at maximum projection edge of mold opening direction.

 

Projection, as shown in figure, parallel light is irradiated from product opening direction, forming a shadow (yellow line) on vertical plane, and the largest side of shadow is the largest projection edge of product.
There are many principles for selection of parting lines, which is the most basic one. With this one, simple flat mold, split mold is completely sufficient.
There is also an important point of knowledge here, that is, mold opening direction of product. Everything is based on this expansion.
Mold opening direction of most products is relatively easy to choose, that is, vertical direction of the largest projection surface of product is mold opening direction of product.
According to three-view principle, we can find out its three projection surfaces for any product. Projected area is different in size and find the largest projection surface.
Several principles of parting surface selection:
1: Ensure that product can be taken out of mold, and position of parting surface should be selected to be position of projected shadow in direction of product.
2: For appearance parts, mold parting can not affect appearance, appearance quality and precision should be guaranteed.
3: Ensure that product can remain in back mold after mold opening, which is conducive to demoulding and lateral core pulling.
4: Guarantee quality of product, strength and rigidity of parts during molding.
5: Considering clamping force of mold, direction in which product projection area is large is placed in mold clamping direction of front and rear molds.