Introduction to the basic knowledge of injection mold design

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I. Design basis


Dimensional accuracy and accuracy of related dimensions


According to the specific requirements and functions of the whole product of plastic products to determine the external quality and specific size belong to which kind: plastic products with higher appearance quality requirements and lower dimensional accuracy requirements, such as toys; Functional plastic products, strict size requirements; Plastic products with strict appearance and size requirements, such as cameras.


Whether the demoulding Angle is reasonable.


Demoulding slope is directly related to the demoulding and quality of plastic products, that is, related to the injection process, whether the injection can be carried out smoothly: demoulding slope is enough; The slope should be adapted to the parting or parting surface of plastic products in molding; Whether it will affect the accuracy of appearance and wall thickness size;


Whether it will affect the strength of some part of plastic products.


2. Design procedures


Analysis and digestion of plastic product drawings and entities (solid samples) :


The geometry of the product;

Dimensions, tolerances and design standards;

Technical requirements;

Plastic name and brand number

Surface requirements


Cavity number and cavity arrangement:


Product weight and injection volume of injection machine;

The projected area of the product and the clamping force of the injection machine;

Mold external dimension and effective area of injection machine mounting mold (or distance within pull rod of injection machine)

Product accuracy, color;

Whether the product has side shaft core and its treatment method;

Production batch of products;

Economic benefit (production value per mold)


Cavity number was determined, and then to the arrangement of cavity, the cavity position arrangement, cavity arrangement involves the mould size, the design of gating system, the balance of gating system, the design of the core-pulling slider) institutions, insert, and the design of the core, the design of the heat exchange system, these problems and parting surface and the selection of gate location, so the specific design process, Necessary adjustments should be made to achieve a more perfect design.


3. The determination of the parting surface


No impact on appearance

To ensure the accuracy of products, mold processing, especially the cavity processing;

Conducive to gating system, exhaust system, cooling system design;

Conducive to mold opening (parting, demoulding) to ensure that when opening the mold, so that the products remain in the moving mold side;

Facilitate the arrangement of metal inserts.


4. Gating system design


The gating system design includes the selection of the main channel, the shape and size of the shunt section, the location of the gate, the form of the gate and the size of the gate section. When using the point gate, in order to ensure the shedding of the shunt, attention should also be paid to the design of the gate device, the casting device and the gate mechanism.


When designing the gating system, the first is to choose the location of the gate.


The selection of gate position is directly related to the quality of product molding and the smooth progress of injection process. The selection of gate position should follow the following principles:


The location of the gate should be selected on the parting surface as far as possible in order to facilitate the cleaning of the gate during mold processing and use;


The distance between the gate position and each part of the cavity should be consistent as far as possible, and make the process as the shortest;


The location of the gate should ensure that when the plastic flows into the cavity, the cavity is wide and thick, so as to facilitate the smooth flow of plastic;


The gate position should be opened at the thickest section of plastic parts;


Avoid plastic in the flow down the cavity directly into the cavity wall, core or insert, so that the plastic can flow into the cavity as soon as possible, and avoid the core or insert deformation;


As far as possible to avoid the product welding mark, or make the welding mark in the product is not important parts;


The location of the gate and the inflow direction of the plastic should make the plastic flow into the cavity evenly along the parallel direction of the cavity, and facilitate the discharge of gas in the cavity;


The gate should be set on the part of the product that is easiest to remove, while not affecting the appearance of the product as much as possible.


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