Battery pack cover product is shown in Figure 1. Maximum dimensions of product are 365.0 mm * 230.0 mm * 55.0 mm; average thickness of plastic part is 2.50 mm, material of plastic part is ABS, shrinkage rate is 1.005, and weight of plastic part is 307.94 grams. Technical requirements for plastic parts are that there should be no defects such as peaking, underfilled injection molding, flow lines, pores, warping deformation, silver streaks, cold material, jetting lines, and meet ROSH environmental protection requirements.

 

Figure 1 Product picture of the battery pack cover
It can be seen from Figure 1 that plastic part is a rectangular closed shell, and cross section is a plane plus an arc surface. There are two round holes on the front side, and latent gates can be designed in holes. There are 1 to 2 small holes on the two end faces of plastic part, and it is necessary to design core-pulling of tunnel slider of front mold. Size of plastic part is large, mold cavity is designed to be 1 cavity, and mold base is CI4560 A140 B120 C120. In order to improve mold clamping precision, prevent front and rear mold cores from being dislocated by lateral force during injection molding, 4 slope positioning blocks are designed on the edge of mold base. Positioning pins are also designed between panel and plate A, and between plate B, square iron and bottom plate to ensure rigidity of mold. Threaded holes are designed at both ends of ø16 positioning pin to facilitate removal of positioning pin. Mold is produced by injection molding on European NB400 injection molding machine. Therefore, code mold plate is relatively large. Code mold groove is designed at the bottom of code mold plate to provide support for mold. This code pattern is a common code pattern in European and American molds.
Since the entire edge and top surface of plastic part are appearance surfaces, gate can only be selected in a round hole on the top surface. Mold gating system adopts latent gate of large nozzle mold. Since round hole is eccentric, an inclined gate sleeve is used. Molten plastic flows obliquely from sprue sleeve to parting surface in round hole and then enters circumference at three points, structure of submerged gate submerged front mold is adopted. Submerged gates are divided into two types: pre-submerged mold and post-submerged mold. When front mold is submerged, a large pulling force is required in cold material well to break gate, so as to prevent cold material from being pulled out from rear mold and remaining in sprue sleeve.
There are two types of latent gates: push-cut type and pull-cut type according to ejection form. The two gate forms of latent movable mold (surface of plastic part) and latent push rod belong to push-cut ejection method, submerged fixed mold (surface of plastic part) belongs to pull-cut ejection method. Regardless of ejection method, it is necessary to carefully analyze parameters of runner and position of gate during design to ensure that condensate of gating system can be ejected effectively. This set of mold adopts pull-cut latent product side wall gate, its parameters are shown in Figure 4, and has following characteristics:
(1) There is no need for post-processing of side wall gate of appearance of pull-cut latent product, but there are traces on gate part, which can be used when customer allows it.
(2) Because this type of gate needs pulling force to break sprue, cold slug well cannot be used with a draft angle to prevent cold slug well from being pulled out and stuck in sprue bushing.
There are many mold structures for front mold slider, and most of them need to use opening and closing of mold plates to realize core pulling action. This set of molds is a Dashuikou mold, and front mold mold plates are all fixed, so it is difficult to design front mold slider core-pulling mechanism. There are also hot runner molds in which front mold mold plate cannot be separated. Panel of hot runner mold, fixed plate of manifold and A plate are generally inseparable. Therefore, this type of front mold slider core pulling needs to use an oil cylinder to pull core.

 

Figure 2 3D mold structure diagram

 

Figure 3 Die parting surface diagram

 

Figure 4 Pull-cut latent product sidewall gate

 

Figure 5 Front mold core-pulling structure diagram

 

Figure 6 Mold Design Specification Book
As for lateral core-pulling and parting mechanism, it is driven by inclined guide columns as much as possible. This set of mold adopts oil cylinder core pulling, its advantages and disadvantages are analyzed as follows: If core pulling area is small, wrapping force is small, and slider locking force is small, you can directly use oil cylinder to pull core without locking it. For example, needle puller of this set of molds, slider is just a needle insert. In this case, bold design does not need to lock cylinder, and problem will not occur. Recommended cylinder piston diameter is 50mm, and stroke is 100~150mm.
If core-pulling area on plastic part is large and locking force of slider is large, then slider needs to be locked at this time. Action of slider is often after mold is closed. At this time, it is very difficult to lock slider. Yes, because mold has not moved, so slider is required to lock slider. There are many structures, which will be analyzed in detail later.