Product of data acquisition instrument mounting base is shown in Figure 1. Maximum external dimension of product is 106.60 mm * 101.90 mm * 33.50 mm, average thickness of plastic part is 2.00 mm, plastic part material is PS, shrinkage rate is 1.005, and plastic part weight is 49 grams . Technical requirements for plastic parts are that there shall be no defects such as peaks, underfilling, flow lines, pores, warpage deformation, silver lines, cold materials, and spray lines.

 

Figure 1 Product diagram of data acquisition instrument mounting base
As can be seen from Figure 1, shape of plastic part is a flat cylinder, and bottom is connected to a rectangular flange with a rectangular opening. Plastic parts look simple in structure, but there are actually difficulties in mold design. If mold structure is selected poorly, it will damage life of mold and make it difficult to meet production needs. Difficulty of mold design is choice of mold opening direction.
Now product development cycle is accelerated, and product replacement cycle is greatly accelerated. In order to seize market, mold design time is very short, so a reasonable mold structure must be selected. Before mold design, product must first be analyzed to determine a reasonable mold opening direction.
Three elements of mold design scheme are pouring system, ejection system and parting surface design. Analysis and selection of mold opening direction is the most important link in determining mold design scheme. Analysis of mold opening direction is closely related to ejection and gate design of plastic parts. Selection of mold opening direction is basis and premise of parting surface design. Parting surface can only be correctly selected after correct mold opening direction is selected. For parts with same shape and different sizes, size value will affect selection of parting surface. Selection of parting surface is related to mold structure. Qualitative analysis can only summarize general laws, and quantitative analysis needs to be combined with size of plastic parts. For many structural parts with many bone positions, complex shape and characteristics, choice of mold opening direction is relatively simple, and mold opening direction can be determined by using factors such as wrapping force.
Determining mold opening direction of a plastic part is generally divided into two cases. For some plastic parts, selection of parting surface is not complicated, and even parting surface is a plane in the middle of product. Difficulty lies in selection of opening direction, that is, which side of plastic part is placed on movable mold and which side is placed on fixed mold. This problem is sometimes difficult to judge, and even experienced engineers may make mistakes in judgment. Correct judgment will leave side with high sticking force in movable mold to facilitate ejection and demoulding of plastic parts, and design gating system on the other side. We call this problem choice of mold opening direction. Sometimes the simpler shape of plastic part, the more difficult it is to judge mold opening direction. Round products, products with simple shapes, the more complicated choice of mold opening direction.
In analysis of mold opening direction, in addition to selection of movable and fixed mold side of plastic part mentioned above, there is also a problem of vertical mold opening or horizontal mold opening of plastic part. If mold opening direction is unreasonable, it will seriously affect mold accuracy, plastic part quality, injection molding cycle, mold life and mold manufacturing cost. This is case with this set of molds. Mold opening direction shown in Figure 2 is to stand plastic part upright, design rectangular flange and rectangular window in direction of slider. Because of rectangular small square hole on the other side, slider core needs to be designed. It will increase ejection stroke of plastic part, increase closed height of mold, and make ejection of plastic part difficult.

 

Figure 2 Analysis of mold opening direction

 

Figure 3 3D mold design
Actual mold design scheme is shown in Figure 3. Turn plastic part down to reduce closed height of mold. Slider in long direction has a large stroke, and oil cylinder is used for core pulling. Narrow groove on outside of plastic part uses another slider to pull core and drive it with an inclined guide column. Cylinder slider adopts partial core-pulling, non-core-pulling inserts, and internal guide grooves are designed. This design can avoid plastic parts sticking to slider, and at the same time increase guiding stability of slider.
Ejection of plastic part uses a flat thimble to eject edge bone of rectangular flange of plastic part.

 

Figure 4 Product mold diagram of data acquisition instrument mounting seat