Main points of mold design in SMC molding process

SMC molding is an advanced composite material molding method, and the mold is the basis of the SMC process. Good product quality is guaranteed by a reliable mold. Therefore, in the design work of the SMC molding process, the design of the mold is particularly important.

In the SMC molding design process, the cavity of the mold should be designed according to the specific dimensions of the product. In addition, the appropriate material should be selected according to the surface quality requirements of the product and the size of the demand. In order to ensure product quality and process feasibility, the cutting edge and ejection system of the mold should be designed reasonably.


1. Parting surface design

In order to facilitate the demolding of the product and ensure the accuracy and strength of the product to facilitate mold processing and other factors, the selection of the parting surface should consider the following principles: 1. To facilitate the product launch and simplify the ejection mechanism, the position of the parting surface should keep the product open After the mold, leave it in the lower mold as much as possible; 2. Minimize the damage of the flash to the appearance of the product, and at the same time it should be easy to remove the residual flash; 3. It is convenient for mold manufacturing and mold part processing; , The effect of flash thickness on the accuracy of the product should be considered, and the vertical parting surface can be taken to ensure the radial accuracy of the product; 5. to ensure the strength of the product and avoid sharp corners and thin walls.


2. Processing accuracy requirements


The machining accuracy of the new mold mainly has three aspects: dimensional tolerance, geometric tolerance and surface roughness. The processing precision requirements we usually put forward for mold manufacturers are mainly dimensional tolerance and surface roughness. Dimensional tolerance is roughly divided into: outline size and cavity size. The two types have relatively loose requirements on the external dimensions of the mold. The actual processing size and the theoretical size error of the mold drawing do not exceed + -1.5mm, and the cavity size accuracy requirements must be strictly controlled according to the drawing, generally not exceeding 0-0.1mm. The mold surface accuracy we mentioned generally refers to the surface roughness. After processing, the mold cavity roughness is generally required to be 0.4, and the rest is 12.5. We can propose the corresponding mold surface processing accuracy according to the actual product surface requirements.


3. Mold design


3.1 Design of draft angle

Since the SMC product shrinks after cooling, the product will tightly wrap the mold core and the convex part in the cavity. In order to facilitate the smooth removal of the product and prevent the product from being scratched or scratched during demolding, when designing the SMC product, its Both the inner and outer surfaces should have a sufficient draft angle along the demolding direction.

When designing, you should pay attention to the following two aspects: 1. When molding larger SMC products, the stripping slope of the inner surface is required to be greater than the stripping slope of the outer surface; 2. Common stripping values ​​are 1- 1.5 °, can also be as small as 0.5 °.


3.2 Design of shearing edges


The cutting edge of the mold is the part where the upper and lower molds bite each other, and generally requires flame quenching. During the SMC molding process, the cut edge is sandwiched by the product’s burr. The burr is a useless part of the product. From this point, the gap of the mold’s cutting edge can be larger, but too large a cutting edge is likely to cause Planing material and pressure relief, this can be solved by adjusting the height of the cutting edge, that is, there are two factors that need to be adjusted when designing the cutting, the gap of the cutting edge and the height of the cutting edge. The cutting edge is one of the most important factors of the mold. Whether the size of the cutting edge is appropriate directly affects whether the product can be molded and whether there are defects during the molding of the product, so it should be strictly required and controlled.

3.3 Rounded corner design

Except for the use of sharp corners in the above requirements, all other corners can have arc transitions. The product is prone to stress concentration at the sharp corners, and it will rupture when subjected to force or impact vibration. It may even be broken due to the suppression of internal stress during the demoulding process, which affects the strength of the product. In general, the radius of the corner is 0.5mm The strength of the product can be greatly increased. The advantages of using rounded corners are mainly in two aspects: 1. Avoiding stress concentration, improving the strength and beauty of the product; 2. The mold is not cracked due to stress concentration during quenching and use.

3.4 Determination of heating method

The temperature of the mold directly affects the molding quality and production efficiency of the product, so a heating system needs to be added to the mold to achieve the ideal temperature requirement.

The heating system is divided into electric heating, steam heating and oil heating. Electric heating is the most commonly used heating method. Its advantages are simple and compact equipment, low investment, easy installation, maintenance and use, easy temperature adjustment and easy automatic control; steam heating, fast heating, relatively uniform temperature, but difficult to control, cost The relative electric heating is relatively high; oil heating, the temperature is uniform and stable, and the heating is fast, but it pollutes the working environment.

3.5 Selection of surface treatment

In order to improve the wear resistance and corrosion resistance of the mold surface, it is often subjected to appropriate surface treatment.

Die chrome plating is one of the most used surface treatment methods. The chromium plating layer has strong passivation ability in the atmosphere, can maintain the metallic luster for a long time, and no chemical reaction occurs in a variety of acidic media. The hardness of the plating layer reaches 1000HV equivalent to HRC65, so it has excellent wear resistance. The chromium plating layer also has high heat resistance, and its appearance and hardness have not changed significantly when heated to 500 degrees in air.


Post time: Jun-11-2020

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