The design of plastic moulds is based on the correct design of plastic products. The design and manufacture of plastic moulds are closely related to plastic processing. The success or failure of plastic processing largely depends on the effect of mould design and the quality of mould manufacturing. The structural elements that need to be considered in the design of plastic mould are as follows:

1. Parting surface, that is, the contact surface between the die and the punch when the die is closed. The selection of its position and form is influenced by the shape and appearance of the product, wall thickness, forming method, post-processing technology, die type and structure, demoulding method and the structure of the forming machine.

2. Structural parts, i.e. slider, inclined top, straight top block of complex die, etc. The design of structural parts is very critical, which relates to the life of the die, processing cycle, cost, product quality and so on. Therefore, the design of complex die core structure requires a higher comprehensive ability of the designer, and pursues a simpler, more durable and more economical design scheme as far as possible.

Die structure design

Plastic parts are small in size, low in precision grade, and require good performance, crack-free, bending resistance, and mass production. The die is designed into one mold and eight cavity structure, and the following problems are solved.

1. Balance of gating system. When designing multi-cavity mould, all the cavities should be fed at the same time as possible. As the number of cavities increases, the length of diversion channel must be increased. Before the molten material reaches the cavity, the injection pressure and heat of molten material will be greatly lost. If the design of diversion channel is slightly unreasonable, plastic parts may be produced. Defects, such as unsatisfactory injection in one or several chambers, or immediate filling, have defects such as poor welding or loose internal structure. If the injection pressure is raised, it is easy to produce flash. The design shunt in the paper adopts unbalanced layout. By setting the size of the gate and shunt, the injection process is adjusted to the value to ensure that the shrinkage rate of each cavity is the same and the most precise plastic parts are required to ensure their interchangeability. The location of the gate is marked as Y-end at the rough end of the plastic parts, which is conducive to flow and feeding. It can also avoid the occurrence of weld lines, and the molecule has the directivity to meet the requirements of bending and cracking.

2. Design of cooling system The design principle of this cooling device is to design cooling device on the basis of not increasing the structure of the die itself. On the premise of meeting the transfer area required for cooling and the allowable structure of the die, the number of cooling circuits should be designed as much as possible, and the aperture of the cooling passage should be as large as possible, in the upper and lower types. The cooling water holes are machined on the cavity plate and the movable and fixed formwork. When installed, the cooling water holes of the upper cavity plate are butted with the water holes of the fixed formwork, and then sealed with sealing rings. The cooling water holes of the lower cavity plate are butted with the water holes of the movable formwork. The water holes are also sealed with sealing rings. The water holes are arranged on the upper and lower cavity plates and the movable and fixed formwork.