Cleaning head cable shield is an important accessory for cleaning cleaning head of robot host. Cleaning head cable cover product is shown in Figure 1. Maximum external dimension of product is 135.54 mm * 122.41 mm * 36.00 mm, average thickness of plastic part is 4.50 mm, plastic part material is ABS, shrinkage rate is 1.0045, and plastic part weight is 23.17 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 map of cleaning head cable shield
As can be seen from Figure 1, plastic parts are irregular shaped plastic parts. For this kind of plastic part, structure is not complicated at first glance, but due to irregular shape, it brings certain difficulties to selection of opening direction of mold, design of parting surface and determination of mold structure. Due to extremely irregular shape of plastic parts, mold design cavity layout is 2 cavities. If injection molding machine is large and production batch of plastic parts is large, cavity layout of 4 cavities can also be selected. If size of plastic part is particularly large, you can also choose cavity layout as 1 cavity.
There is a horizontal cylinder at the bottom of plastic part with a through hole in it, and another raised side wall also has a horizontal side groove. These two places need to design slider core. Difficulty of this set of mold design is analysis of mold opening direction. Mold opening direction analysis is closely related to ejection of plastic parts, gate design and parting surface design. Before mold design, product must first be analyzed to determine a reasonable mold opening direction. This set of molds is a step parting surface, and parting surface is not complicated. Difficulty lies in selection of mold opening direction, that is, which side of plastic part is placed on movable mold and which side is placed on fixed mold. 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 other side. In most cases, mold opening direction can be determined by using factors such as wrapping force, and plastic parts can be left in movable mold. This set of molds is designed with side with horizontal cylindrical holes on movable mold, which is beneficial to shorten core pulling distance of slider.
Actual mold design adopts 1 cavity, mold base is CT4555 non-standard mold base, and 3D drawing of mold design is shown in Figure 2. When designing mold layout, it should be noted that for multi-cavity molds with multi-step parting surfaces or large drop, front and rear mold cores of each cavity should be separated and not connected together. If they are connected together, there will be larger and more steps, and CNC cannot directly clear corners. What's more, uneven connection of mold cores affects arrangement of runners in gating system, making runners too high and low, which is not conducive to rapid and effective filling of molten plastic. Back mold is shown in Figure 3.

 

Figure 2 3D mold design

 

Figure 3 Back mold
When parting surface has multiple steps, front and rear mold cores have insertion positions, force on parting surface is not uniform when mold is closed. Therefore, a zero-degree positioning block is designed on four sides of mold base to ensure mold clamping accuracy. In addition, on parting surface, 4 sides of mold base are respectively designed with balance blocks, a total of 6 places. Balance block needs to be designed at the edge of mold base and mold cores are designed to correspond to each other, and material is same as that of wear-resistant block.
Projected area of this plastic part is mainly on parting surface, and rigidity of mold is very critical to the entire mold system. Fixed die is designed with 4 guide posts, which connect panel and A board, and play role of positioning pins to increase rigidity of fixed die. For movable mold part, a special-shaped thimble plate is designed to increase rigidity of mold base. See Mold Design Figure 4.
Plastic part adopts a single hot nozzle, which feeds glue to parting surface, and then injects it into cavity through side gate. In order to prevent heat exchange between mold and injection molding machine, a heat shield is added to panel. Cooling system of front and rear molds adopts a straight-through cooling system. Ejection of plastic parts is ejected by ejector pins.

 

 

 

Figure 4 2D mold structure diagram