Product diagram of shield is shown in Figure 1. Maximum size of product is ø85.7 mm * 55.20 mm, average thickness of plastic part is 1.50 mm, material of plastic part is HIPS, shrinkage rate is 1.005, and weight of plastic part is 10.5 grams. Technical requirements of 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, and bubbles.

 

It can be seen from Figure 1 that structure of plastic part is hemispherical. There is a long hollow column in the center of plastic part. Side of column is open, divided into two pieces, and each has a buckle on the head for clamping during assembly. Difficulty of mold design is design of demoulding method of central column buckle. Buckle here needs to be designed with a tunnel-type slider to solve it. Another difficulty is need to design a forced demoulding mechanism after buckling slider is disengaged.
After careful analysis of plastic parts, there are two core-pulling directions of tunnel slider, as shown in Figure 3. A and B two core-pulling design schemes, moving direction of slider is perpendicular to each other. Both of these two design schemes can make products, but details are different. Details determine success or failure, and mold design must be able to observe details, analyze and compare different results. Mold design adopts Scheme A. Scheme A makes two buckles on same slider, buckle part has a vertical clamping line, but it has advantage that two buckles are on same slider, which can prevent buckles from sticking to slider and deforming. Scheme B designs each buckle separately on same slider, which may cause buckle to stick to slider and deform.
Cavity layout of mold design is 1 out 2. Mold base is DI3045, gate is a horn gate, and glue is injected from bottom of edge of plastic part. Advantage of horn gate is that it can be automatically disconnected after mold is opened, position of gate at the bottom of edge of plastic part will not affect appearance. In order to ensure accuracy of mold clamping, a zero-degree positioning block is designed on the edge of mold base.
Principle of forced demolding is that plastic part has deformation space. Second factor is plastic material. Most thermoplastics can be forced out of mold, provided that plastic part has room for deformation. In extreme case where there is no space for deformation, only a few plastics such as PP and PE can be forced to demold, but amount of strong release must be less than 0.3. In order not to damage product during strong release, back mold core is designed with a slope of 40 ゜ to facilitate release of buckle position during strong release, as shown in Figure 4.
Column buckle must be forced off back mold after slider core is pulled. In order to form a deformation space for buckle to be forced off, it is necessary to pull out insert in the inner hole of column first, so that buckle can be deformed inward. After mold is opened, mold is first opened between push plate and backing plate, push plate bounces 40, and insert 27 is first withdrawn from inner hole of column. Mold is opened again, parting surface is opened, latent slider completes buckle and core pulling.
Ejector of plastic part is ejected by a thimble. In order to make thimble plate system return in time and accurately, a yellow rubber 14 is designed at the bottom of needle. Ejection system adopts method of strong tension and strong ejection. No return spring is installed on ejector plate, and threaded holes are drilled at KO hole of ejector plate.  

   

Figure 1 Product Picture of Shielding Cover
Mold cooling system is designed with two rounds of straight-through water transport on front mold, divided into two layers with different heights, so that cavity can be fully cooled. Cooling of movable mold is a combination of straight-through water transportation and a pond.
Sliding block is driven by an oblique guide column, and positioning of sliding block adopts tiger buckle of DME, model is PSM-0001. This kind of sliding block positioning method is powerful and reliable, and it is very popular in American molds.

 

 

 

 

 

 

 

Figure 2 Shield mold diagram

 

Figure 3 Analysis of core-pulling direction of tunnel slider

 

Figure 4 Design of forced demoulding bevel