See Figure 1 for housing product of car's speed control mechanism. Maximum size of product is 148.19 mm * 102.21mm * 57.94 mm, average thickness of plastic part is 2.33 mm, material of plastic part is PC+ABS, shrinkage rate is 1.006, and weight of plastic part is 83.64 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, etc.

 

Fig. 1 Product picture of housing of car's speed control mechanism
It can be seen from Figure 1 that plastic part has a rectangular cross-section closed cylinder with a simple structure at one end. After assembly, this end is located in the middle of driver's seat. Gear shift lever passes through center and outer surface is covered with a leather sleeve. Plastic part cylinder at the other end is tilted by 14 ゜, and multiple buckles are designed along edge of cylinder to facilitate clamping during assembly. Inner hole of plastic part needs to be designed with two sliders to pull core from the two ends respectively, distance between cut and core is relatively large. On the two large triangular planes, there are concave areas and pillars. In addition to sliding core pulling to solve inner hole cylindrical shape of plastic part, the other two sides also need to design sliding core pulling.
Structure of plastic part is complex, and mold is a complex mold. For this set of molds, primary problem of mold design is to determine direction of mold opening. Mold opening direction analysis is one of the most basic tasks of mold design. After mold opening direction analysis is completed, parting surface can be designed and next step can be carried out. Choice of mold opening direction is related to mold manufacturing cost, appearance of plastic part, quality of injection part and injection cycle, etc., and may also affect life of mold.

 

For this set of molds, plastic part can be designed to stand up, that is, axis of rectangular tube of plastic part coincides with mold opening direction; another design is to design plastic part upside down. Both of these two design schemes need to design form of 4 sliding blocks surrounding plastic part. In the way of designing plastic parts upright, center of plastic parts needs to be designed with an oblique core-pulling slider, mold opening stroke will be increased, ejection force of plastic part is relatively large, and ejection of plastic part is difficult. Therefore, actual mold design adopts design method of laying down plastic part.
Car products generally have larger production batches. Mold design cavity ranking is shown in Figure 2, and 3D mold diagram is shown in attached file. Due to four-sided sliding block of plastic part, plane layout of mold is relatively large. Mold base is a non-standard mold base 6090, which is a large-scale mold. Gating system feeds glue into two hot nozzles of hot runner. Each cavity has a gate, which is located on upper surface of plastic part. Two sliding blocks are interlocked to increase rigidity and prevent sliding blocks from dislocation due to impact force during pouring. This is one of the most important details of mold design. Hot runner brand is SINO, and Chinese name is Xianrui. It is domestic brand of Yudo company YUDO, and its quality standards are roughly equivalent to YUDO.
Mold has 8 sliders, structure is complex, contact area of parting surface is small. For this reason, a balance weight is designed on parting surface to increase pressure bearing area of parting surface. Four zero-degree positioning blocks are designed on the edge of mold base to increase accuracy of mold clamping. At the same time, four corners of front and rear mold cores are respectively designed with positioning jaws to prevent parting surface from being dislocated during injection. Angle of tiger's mouth is 5 ゜, protrusion of rear mold, and recess of front mold.
Two sliders in the center hole of plastic part are driven by an oil cylinder due to their long strokes, while the other two sliders are driven by oblique guide posts. Wear-resistant plates are designed on inclined surface and bottom surface of each slider, which is convenient for adjustment during flying mold and assembly. Due to limited position, two sliders in the middle share a shovel base. When designing a common shovel base, angles and other dimensions on both sides need to be designed completely symmetrically. Shovel base of two hydraulic cylinder sliders is an inlaid structure, end face of shovel extends into movable mold to realize backhoe locking.

 

After plastic part is opened, after all sliders are disengaged, its tightening force on movable mold is relatively small, and plastic part can be ejected by using a thimble. A dust-proof plate is designed on the top of mold to cover thimble plate to prevent debris from falling into mold.
In moving and fixed molds and all sliders, cooling circuits are all designed to ensure smooth progress of injection molding process.

 

 

 

 

Figure 2 Die diagram of housing of car's speed control mechanism

 

 

Figure 3 3D drawing of mold