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How important is the mould design in plastic mould making?

10.18

To Take Measures to Prevent the Problems from Occurring in the First Place

The molding accuracy is not only completely dependent on the injection mold, but even its intrinsic quality and molding efficiency. Once any problem appears on design, it will easily cause an increase in cost and delay in the construction period. Therefore, how to complete the design of injection mold products with high quality, speed and standardization will be the main issues discussed here.

The basic requirements for plastic part design and development is to have sufficient strength and rigidity. Can obtain the products that meet the requirements; Less or fewer post-processing and secondary processing needed; Plastic parts can be directly used for assembly; The molding is reliable and efficient; The manufacturing cost is low and it is easy to maintain.

According to the injection volume of the injection machine to determine the number of injection mold cavity; according to the rated clamping force to calculate the number of cavities; The number of cavities consider factors: products accuracy, economy, molding process, maintenance. 

The parting line is determined according to the shape of the part. The parting line is the dividing line that divides the product into two parts, one part is fixed-molded and the other part is formed by dynamic molding. The parting line of the mold can be obtained by moving the parting line to the moving and fixed molds along the extension or scanning.

The size of the inner mold insert is determined by the size and quantity of the shaped article, and by reasonable alignment. The principle of product ranking should be followed: to ensure the pressure balance and temperature balance of the injection mold: to achieve pressure balance and temperature balance, the product should be symmetrical or diagonally ranked as far as possible.

The principle of uniform gate position: in the case of a multi-cavity, the gate position should be arranged uniformly. The same product should be glued from the same position, in order to ensure that the shrinkage of each product is consistent, making it interchangeable. When the gate affects the position of the plastic product, first determine the gate position and then lay out. Shorter sub-channel principle: The shorter the runner channel of the gating system, the less the flocculation of the flow runner, the lighter the exhaust load of the mold, the less the pressure and temperature of the melt in the runner, and the shorter the molding cycle.

Runner venting: The air in the mold injecting system should be discharged as much as possible in the splitter to reduce the exhausting load of the mold cavity. The venting groove of the branching channel is opened in the parting surface, the effect is good, it is not easy to block, and the depth can be 0.05mm larger than the depth of the venting groove of the cavity.

Parting surface venting: The parting surface is where the air is mainly discharged. If the parting surface is flat, it is processed by grinding, the parting surface after grinding is very good, the air in the cavity is not easy to discharge, and the exhaust groove should be exhausted on the side of the cavity; If the surface is curved or beveled, CNC, electrode machining or wire cutting need be used. The processed parting surface can be directly vented without having to reprocess the venting groove on the parting surface.

In the process of designing and manufacturing the injection mold, any deviation in the link will seriously affect the quality of the plastic parts. It is necessary to continuously accumulate more design and manufacturing experience, and systematically and standardize mold design to create more production and economic benefits.