Magnetic powder box bracket is part that fixes magnetic powder box in printer. Product of magnetic powder box bracket is shown in Figure 1. Maximum external dimension of product is 273.76 mm * 58.10 mm * 111.05 mm, average thickness of plastic part is 2.00 mm, and plastic part material is PC+ABS , shrinkage rate is 1.005, and weight of plastic parts is 80.57 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 Magnetic Powder Box Holder
As can be seen from Figure 1, the two ends of plastic part have large vertical glue positions, and on this large face, there are structural elements such as stepped through holes and raised column positions, it is necessary to design slider core. There is also an inverted mold on the top side of one end, and a small slider core needs to be designed. There are two bone positions on inner side near the two ends, there are lateral opening grooves on them, and it is necessary to design inner slider core.
Structural characteristics of plastic parts are that slender shape is closed, and vertical glue bit area at both ends is large, so it is necessary to design a large slider core. Combined with structural characteristics of plastic parts, mold design cavity ranking is 2 cavities. Mold design diagram is shown in Figure 2. Mold base is DDI4565 standard mold base, and a taper positioning block is designed on two long sides of mold, which is beneficial to resist lateral force in cavity during injection molding. Long jaws are designed on long sides of two mold cores, so that mold has accurate clamping positioning.
Vertical glue area at both ends of plastic part is large, and there are structural elements such as column position, step hole and bone position, so tightening force for slider is large, and when slider moves during mold opening, plastic part will stick to slider, forcibly opening mold will cause plastic part to be stretched and deformed. Therefore, a ejector pin must be designed on slider. When mold is opened, ejector pin of slider presses against plastic part, so that slider can be demolded smoothly. Number and position of slider thimbles are determined according to shape, structure of plastic parts and size of wrapping force. Structure of slider thimble is shown in 3D diagram, and each slider is designed with 2 slider thimbles.
Large sliders at both ends of plastic parts are located on both sides of sky and earth. Sliders are driven by inclined guide columns. Wear plates are designed on the bottom surface and inclined surface of sliders, which is convenient for adjustment when flying molds and is also conducive to replacement. Wear-resistant plate is generally designed and manufactured by 2510 oil cylinder. After quenching, it has an HRC of 58 degrees, and friction force is small, which is convenient for slider to slide. Small slider on the side of plastic part is also driven by an inclined guide column. Position of slider ejector pin is shown in Figure 5.

 

Figure 2 Magnetic powder box bracket mold diagram

 

Figure 3 Slider structure

 

Figure 4 Slider thimble

 

Figure 5 Slider thimble position
Due to large size of plastic parts, a point gate and two points of glue are used, and mold is a three-plate mold. Three parting surfaces need to be opened when three-plate mold is injected, plastic parts and gating system aggregate need to be taken out from different parting surfaces. Opening timing and distance of three parting surfaces need to be controlled by a fixed-distance parting mechanism. There are many types of fixed-distance parting mechanisms, most of which use a button machine, a limit screw, a pull rod, a pull plate or a combination of them to achieve their functions, ensure mold opening and closing sequence, mold opening distance. This set of molds adopts button machine to control sequential parting. Mold opening sequence diagram is shown in Figure 6.
During injection molding process of three-plate mold, gating system condensate and product will be automatically cut off and separated, which can realize automatic production. Three-plate mold is convenient to use manipulator for injection molding, and manipulator can take out nozzle material to realize automatic injection molding. Since three-plate mold has three parting surfaces, mold opening time is too long, which will affect injection cycle by 1 to 3 seconds. Especially for large three-plate molds, due to long flow channel, if robot is fully automatic injection molding, it is necessary to pay attention to runner as elastic pin of elastic nozzle, which is driven by a spring. Now there are many standard parts to choose from. European and American countries have rarely used three-plate molds since hot runner technology has matured. At present, proportion of three-plate molds in Europe and the United States is less than 1%. Therefore, if you design export molds, you need to obtain customer confirmation when designing three-plate molds. Spot gates have been completely replaced by hot runner molds.

 

Figure 6 Mold opening sequence diagram
For two buckle positions of rear mold, method of floating mold plate B plate is used to realize buckle position demoulding, and buckle position demoulding is realized in third mold opening.
Packing force of plastic part on back mold is very large, so combination of straight top and thimble is used to realize ejection of plastic part.