Product picture of hollow lamp post is shown in Figure 1. Maximum external dimensions of product are 257.35 mm * 29.77 mm * 22.50 mm, average plastic thickness of plastic parts is 2.55 mm, material of plastic parts is ABS, shrinkage rate is 1.005, and weight of plastic parts is 48.16 G. Technical requirements for plastic parts are that there must be no defects such as peaks, underfilled injection, flow lines, pores, warpage, silver lines, cold materials, spray lines, air bubbles and so on.

 

Figure 1 Hollow lamp post product picture

It can be seen from Figure 1 that plastic part is shaped as a hollow, flat, long tube, with a through hole inside and no bone on the inner wall. Mold core can be smoothly pulled out from big end. There is a buckle at small end of plastic part and two symmetrical buckles at large end. On one side there are 7 uniformly distributed oblong through holes.
No matter what kind of mold opening direction is selected, mold must be cored by slider. If plastic parts are designed to stand upright, three buckle parts need core pulling, and 7 oblong through holes on the side also need core pulling. In particular, lateral core pulling of 7 oblong through holes on the side is very difficult, and insufficient mold strength is very easy to damage, so this design is obviously unreasonable. Another disadvantage is that closing height of mold is too high, which exceeds opening stroke of injection machine, which may cause plastic parts to be unable to be ejected.
If plastic parts are put down, stroke of slider core pulling needs to be 260mm. With such a large stroke, core of slider can not be used for core of inclined guide column, and core of hydraulic cylinder needs to be used to meet stroke requirements. Therefore, choice of mold opening direction is difficulty of this set of molds, because it determines difficulty of molds, injection production efficiency and mold cost.

 

Figure 2 Schematic diagram of gating system

If plastic part is laid down, mold core pulling system can choose hydraulic cylinder core pulling, but ejection of plastic part is difficult, because there can be no ejection marks on outer surface of plastic part. In summary, for ultra-long plastic parts such as hollow lamp posts, a mold structure was designed that ejected slider and then hydraulically cored, which effectively solved problem of insufficient mold opening stroke of injection machine and ejection of plastic parts. Mold structure is shown in Figure 3.
According to size and structural shape of plastic part, mold layout of plastic part is selected 2 cavity, two-plate mold with a large nozzle is selected for mold. When designing layout of mold, considering that one side needs core pulling, two holes are turned upside down so that slider is outside mold. Mold base adopts Long Kee standard mold base LKM CI4055. In order to ensure processing accuracy and avoid deformation caused by secondary processing, fine bases, slider grooves and shovel grooves of moving and fixed molds are all processed in mold base factory. R3 rounded corners are designed around bottom of base to avoid stress concentration and increase mold strength.

 

 
Design of gating system adopts a side gate to inject, see Figure 2. For long or long tube products, gate position must be at one end of product, and cannot be designed in the middle of length of plastic parts to avoid deformation of plastic parts.
7 oblong through-holes on the side of plastic part are used to select back mold slider core, and 7 oblong through-holes are designed as slider inserts and fixed on same slider base. Because slider insert needs to collide with long-tube slider insert, it must be made into an insert to facilitate assembly of flying mold. Long-tube slider is driven by an oil cylinder and locked with a shovel.
After mold is opened, slider with 7 long round through holes first completes core pulling. Core pulling of long-hole oil cylinder also starts core pulling at the moment of mold opening. It does not have to be completely pulled out, but only with a certain distance to loosen product. Mold is European style, ejection system is directly connected to injection molding machine through ejection insert, and ejector plate does not need to design a return spring. Under action of ejector pin of injection machine, ejector pin plate is pushed out, and condensate in runner system is ejected by ejector pin. Slider base and jack at the bottom are fixed with screws. Under action of jack, slider base drives all core-pulling system components such as oil cylinder seat and oil cylinder to eject, plastic parts are detached together on the long core of slider mold. After ejection, plastic parts can be taken out manually or by manipulator.

 

 

 Figure 3 Mould drawing of hollow lamp post

 

Figure 4 3D drawing of mold