What are the Principles and Core of Injection Mold Design?

1、 Mold opening direction and parting line

At the beginning of the design of each injection molded product, the mold opening direction and parting line should be determined to minimize the impact of the core pulling slider mechanism and eliminate the influence of parting lines on the appearance as much as possible.

1. After determining the mold opening direction, the reinforcing ribs, buckles, protrusions, and other structures of the product should be designed to be as consistent as possible with the mold opening direction to avoid core pulling, reduce seam lines, and extend the mold life.

2. After determining the direction of the mold opening, an appropriate parting line can be selected to avoid any reverse bending in the mold opening direction, in order to improve the appearance and performance.

2、 Demoulding slope

1. Appropriate demolding slope can avoid product fraying (flower pulling). The demolding slope of a smooth surface should be ≥ 0.5 degrees, with fine grain (sand surface) surfaces greater than 1 degree and coarse grain surfaces greater than 1.5 degrees.

2. Appropriate demolding slope can avoid product top damage, such as top whitening, top deformation, and top breakage.

3. When designing products with deep cavity structures, the outer surface slope should be greater than the inner surface slope as much as possible to ensure that the mold core does not deviate during injection molding, obtain uniform product wall thickness, and ensure material strength at the opening of the product.

3、 Wall thickness of Hebei injection mold products

1. All kinds of plastics have a certain degree of wall thickness range, generally 0.5-4mm. When the wall thickness exceeds 4mm, it will cause problems such as long cooling time and shrinkage, and the product structure should be considered to be changed.

2. Uneven wall thickness can cause surface shrinkage.

3. Uneven wall thickness can cause porosity and weld marks.

4、 Strengthening muscles

1. The rational application of reinforcing bars can increase product rigidity and reduce deformation.

2. The thickness of the reinforcing rib must be ≤ (0.5-0.7) T product wall thickness, otherwise it will cause surface shrinkage.

3. The single-sided slope of the reinforcing rib should be greater than 1.5 ° to avoid top damage.

5、 Rounded corners

1. Too small a fillet may cause stress concentration in the product, leading to cracking.

2. Too small a fillet may cause stress concentration in the mold cavity, leading to cavity cracking.

3. Setting reasonable rounded corners can also improve the machining process of the mold, such as directly milling the mold cavity with an R-knife to avoid inefficient electrical machining.

4. Different rounded corners may cause movement of the parting line, and different rounded corners or cleaning corners should be selected based on the actual situation.

6、 Hole

1. The shape of the hole should be as simple as possible, usually circular.

2. The axial direction of the hole is consistent with the mold opening direction, which can avoid core pulling.

3. When the aspect ratio of the hole is greater than 2, a demolding slope should be set. At this point, the diameter of the hole should be calculated based on the small diameter size (up to the large solid size).

4. The aspect ratio of blind holes generally does not exceed 4. Anti hole needle punching and bending

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

7、 Core pulling and sliding mechanism of injection molds in Hebei and its avoidance

1. When the plastic part cannot be smoothly demolded according to the mold opening direction, a core pulling slider mechanism should be designed. The sliding block of the core pulling mechanism can form complex product structures, but it is prone to defects such as seam lines and shrinkage, which increase mold costs and shorten mold life.

2. When designing injection molded products, if there are no special requirements, try to avoid core pulling structures as much as possible. If the axial direction of the hole and the direction of the rib are changed to the mold opening direction, methods such as using the cavity core to penetrate can be used.

8、 Integrated hinge

1. By utilizing the toughness of PP material, hinges can be designed to be integrated with the product.

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

3. When injecting integrated hinges, the sprue can only be designed on one side of the hinge.

9、 Embedded components

1. Inserting inserts into injection molded products can increase local strength, hardness, dimensional accuracy, and provide small threaded holes (shafts) to meet various special requirements. At the same time, it will increase product costs.

2. The embedded parts are generally made of copper, but can also be other metals or plastic parts.

3. The part embedded in plastic should be designed with anti rotation and anti pull structures. For example: embossing, punching, bending, flattening, shaft shoulder, etc.

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

5. When designing inserts, full consideration should be given to their positioning in the mold (holes, pins, magnetism)

10、 Identification

Product identification is generally set on the flat surface of the product and adopts a raised form. The identification is set on the surface that may be consistent with the normal direction and the mold opening direction ruler to avoid pulling.

11、 Hebei injection mold injection part accuracy

Due to the unevenness and uncertainty of shrinkage rate during injection molding, the accuracy of injection molded parts is significantly lower than that of metal parts, and the dimensional tolerances of mechanical parts cannot be simply applied. The appropriate tolerance requirements should be selected according to standards In 1993, China also released GB/T14486-93 "Dimensional tolerances for molded plastic parts of engineering plastics". Designers can determine the dimensional tolerances of the parts based on the plastic raw materials used and the requirements for the use of the parts, according to the provisions in the standard. At the same time, the appropriate design tolerance accuracy should be determined based on the comprehensive strength of the factory and the design accuracy of peer products.

12、 Deformation of injection molded parts

Improve the rigidity of injection molded product structure and reduce deformation. Try to avoid flat structures as much as possible, and set up flanging and concave convex structures reasonably. Set reasonable reinforcement bars.

13、 Buckling position

1. Design the buckle device to share multiple buckles simultaneously, so that the overall device will not be unable to operate due to damage to individual buckles, thereby increasing its service life. Additionally, consider adding more filters and rounded corners to increase strength.

2. The tolerance requirements for the relevant dimensions of the buckle are very strict, and too many reverse buckle positions can easily cause damage to the buckle; On the contrary, if there are too few reverse positions, it is difficult to control the assembly position or the combination parts may become too loose. The solution is to reserve a way to easily add glue for mold modification.

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

1. Welding can improve the connection strength.

2. Welding can simplify product design.

15、 Reasonably consider the contradiction between process and product performance

When designing injection molded products, it is necessary to comprehensively consider the contradictions between product appearance, performance, and process. Sometimes sacrificing some craftsmanship can result in a good appearance or performance.

When it is impossible to avoid injection molding defects in structural design, try to make the defects occur in concealed parts of the product as much as possible.

16、 The relationship between the diameter of the screw column and the diameter of the self tapping screw

Self tapping screw, screw post aperture

M2        1.7mm

M2.3      2.0mm

M2.6      2.2mm

M3        2.5mm

17、 BOSS design principles:

1. Pillars should not be used alone, but should be connected to the outer wall or used together with reinforcing ribs as much as possible, in order to enhance the strength of the pillar and make the rubber flow smoother.

2. The height of the pillar is generally not more than two and a half times the diameter of the pillar. Excessive support can cause air entrapment during the molding of plastic components (such as porosity, burning, and insufficient filling when the length is too long).

3. If the height of the pillar exceeds two and a half times the diameter of the pillar, especially for pillars far away from the outer wall, the method to strengthen the pillar is to use reinforcing ribs

4 The shape of BOSS is mainly circular, while other shapes are not easy to process

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

6. You can remove some of the flesh thickness around the boss (i.e. open a volcano) to prevent shrinkage and subsidence

7. BOSS's mold shifting angle: usually taken as 0.5 ° externally, 0.5 ° internally, or 1