Product diagram of memory bottom case is shown in Figure 1. Maximum size of product is 170.75 mm * 121.20 mm * 38.6 mm, average thickness of plastic part is 3.2 mm, material of plastic part is ABS, shrinkage rate is 1.005, and weight of plastic part is 57.64 grams. Technical requirements for plastic parts are that there must be no defects such as peaks, underfilling of injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, bubbles, etc.

 

Figure 1 Product Picture of Memory Bottom Case

 

Figure 2 Die diagram of memory bottom shell
It can be seen from Figure 1 that plastic part structure is a flat shell, and a large slider core needs to be designed on one side. There are 3 small buckles on the inner side of this surface, which need to be designed for lifter demoulding. There are 3 places on the other side of bottom shell that need to be designed to form small sliders. There is a large area sink in the middle of top surface of plastic part, and there are many perforations at the edge of sink position. There are multiple heat sinks on the top surface of plastic part.
Before mold design, first analyze plastic parts. Size of plastic part of storage bottom shell is relatively large. For this kind of product, side gate is not suitable. Because trim of design side gate will affect appearance of plastic part, it cannot be covered after assembly. Therefore, it is necessary to design a point gate, and mold base is a three-plate mold with a fine nozzle. Large size of plastic part, coupled with multiple heat dissipation grooves and rubbing positions affect flow of molten plastic. Therefore, a two-point injection is designed, and gate position is shown in Figure 3.
In view of multiple rubbing positions of front and rear mold cores, in order to facilitate mold flying and adjustment, inserts are cut in the middle of front mold core, as shown in Figure 3, to simplify mold processing and facilitate mold flying.

 

Figure 3 Front mold core diagram

 

Figure 4 Rear mold core diagram
Ejection of plastic parts adopts lifter and ejector pin. Due to rub-through relationship between lifter and large slider, lifter must be returned in time for slider to close mold. For this reason, the first reset device is designed. The first reset device has a variety of structures, but the simplest and most practical, and the lowest cost is overall structure shown in Figure 2. Design of the first reset device needs to consider whether plastic part is grasped by a robot. Try to avoid first resetting device to affect operation of manipulator.
Cooling of mold has a great relationship with injection cycle. Both front and rear mold cores and large slider are designed with cooling circuits (not shown in 3D figure). Different plastic materials have different requirements for mold temperature due to their melting point, viscosity, crystallinity and other properties. For plastics with low viscosity and good fluidity, product is easy to run off, so mold temperature should not be too high; for plastics with high viscosity and poor fluidity, considering that relatively large stress during mold filling may cause product to crack, a higher mold temperature should be used. In addition, in order to prevent mold itself from warping and deformation due to thermal expansion and contraction, mold temperature should not be too different from ambient temperature, must be compatible with shape of product and keep mold temperature within a certain range.
Design of cooling system is mainly design of cooling circuit. A reasonable cooling circuit can greatly improve cooling efficiency of mold. There are also many types of cooling circuits, such as baffle type, jet type, spiral type and so on. When arranging cooling circuit, we must consider heat dissipation requirements of each part of mold, set a reasonable cooling channel diameter and circuit position to ensure that cavity and core surface are cooled quickly and evenly. Cooling efficiency of through water is the highest. Therefore, for storage bottom shell mold, all cooling circuits are through water.
Production practice after mold is put into production shows that mold design fully meets requirements of mold design specification. Provide reference for similar mold design.