Automotive glass window guide rail is shown in Figure 1. The overall size is about 532mm * 108mm * 42mm, it is curved, wall thickness is 3.5mm, and material is ABS+PC. Main function of car glass window guide rail is to guide lifting of car glass. Formed plastic part cannot be deformed, otherwise car glass cannot be lifted normally. If mold structure design is unreasonable, injection molded plastic parts are easily deformed or outer surface is prone to defects such as gate marks, weld marks, flashes, and air bubbles. After injection is completed, outer surface of plastic part needs to be sprayed with oil. If there are subtle defects in plastic part, although it is difficult to see before oil injection, these defects will become obvious after oil injection. In addition, there are two buckles on plastic part, there are ribs inside buckle, forming a double clamping position. How to make double clamping position demould smoothly is difficulty of mold design.

 

There are 2 strip-shaped buckles on inner surface of plastic part, which are located on the side of plastic part. One buckle is turned to inside of plastic part, and the other is turned to outside of plastic part. Another rib is set inside buckle of outward flanging to form a double clamping position. 5 square piercing holes and 3 circular piercing holes are set on buckle of outward flanging, and several ribs are set on outer surface of buckle; there is 1 buckle on inner surface of one end of plastic part, there is a circular piercing hole at the bottom of buckle, and there are 3 side holes on its side, as shown in Figure 2.

 

Surface of buckle facing inner flanging of plastic part is smooth, without holes, and demoulding is realized by an oblique push structure; buckle facing outer flanging of plastic part adopts a slider mechanism to realize demoulding, but there is a rib inside, a small slider can be installed on the slider to realize demoulding, so buckle uses a nested slider structure to realize demoulding. For perforation hole on buckle, it can be realized by collision between slider and moving mold core; for buckle at the other end of plastic part, slider mechanism can be used to realize demoulding. For perforation hole on the bottom and side of buckle, it can be realized by colliding with sliding block and moving mold core.

Automobile glass window guide rails have high requirements on the outer surface, and no defects are allowed. In order to prevent gate marks on the outer surface of plastic part, gate is set on inner surface of plastic part to be formed; In order to prevent shrinkage marks near gate, try to pour on ribs of plastic part to be formed. If there are no ribs near gate, use a fan gate to pour; in order to reduce injection pressure and reduce influence of ordinary runners on melt flow performance, hot runner feeding system is selected, melt enters common runner from hot nozzle, an insert is designed on parting surface of mold, common runner is introduced into inner surface of plastic part to be formed, a gate is opened on inner surface of plastic part to be formed, and gate is fan-shaped. After mold flow analysis of plastic part by Moldflow analysis software, it is found that injection with two gates meets molding requirements, and positions of the two gates are shown in Figure 3.
For 2-point pouring scheme shown in Figure 3, according to performance of ABS+PC, filling time of melt is set to 11s, injection temperature is set to 250~265℃, mold temperature is set to 80℃, and maximum injection pressure is set to 125MPa, holding time is set to 9s, and results of mold flow analysis are shown in Figure 4.

 

 

From formability of mold flow analysis results, outer surface of molded plastic part is uniform in color and good in formability, as shown in Figure 4(a); there is a weld line in the middle of plastic part, as shown in Figure 4(b), weld line affects appearance. Weld line on molded plastic part can be lightened by increasing mold temperature and setting a push rod near weld line. Setting push rod can also help to discharge gas in cavity and reduce obstruction of gas to flow of melt; pressure distribution at the end of filling is shown in Figure 4(c). Injection pressure at gate position is the highest at 29.25MPa, and injection pressure at middle position is the lowest at about 2.9MPa. Pressure required for molding is not high, and medium-sized injection molding machine can meet requirements; melt flow rate is shown in Figure 4 (d). In high-speed filling stage of 0~2s, melt flow rate increases rapidly; 2-10s is low-speed filling stage, and melt flow rate is stable; 10-11s is pressure-holding stage, which is used to compact melt, and melt flow rate gradually decreases. Results of mold flow analysis are in line with actual mold trial conditions, indicating that 2-point gating system scheme shown in Figure 3 is reasonable for injection molding of this plastic part.

There is a rib on inner surface of outward buckle of plastic part, which cannot be forcibly removed from mold, and requires a slider structure to remove mold. Nesting structure of sliders is used in mold. Upper surface of big slider is a slope. A small slider is installed on big slider, and a groove is set on core of small slider. This groove corresponds to inner rib of plastic part to be formed. When large slider is demolded, spring pushes small slider away, and small slider slides along upper surface of large slider, so that ribs of formed plastic part are demoulded. Nested structure of slider is shown in Figure 5.

 

1. T-shaped oblique pressure plate 2, slider seat 3, screw 4, T-shaped guide rail 5, connecting bar 6, large slider 7, spring 8, limit screw 9, positioning guide plate 10, small slider
Figure 5 Slider Nested Structure
Movement process of nested slider: After injection is completed, when fixed and movable molds are separated, plastic part remains in movable mold, and T-shaped inclined pressure plate drives large slider to perform lateral demoulding movement in chute of movable mold. A spring is installed between big slider and small slider. When big slider moves away from molded part in lateral direction, small slider is separated from big slider under action of spring, so that a relative displacement occurs between small slider and large slider. Since upper surface of large slider is an inclined plane, small slider is separated from ribs on plastic part. When small slider is completely separated from rib, under action of limit screw, large slider drives small slider away from plastic part along side until it is completely separated from plastic part. When fixed and movable molds are closed, movement direction of large slider and small slider is opposite.

There is an inward-bent button on inner surface of plastic part, which cannot be demoulded normally, and requires an inclined push structure to remove mold. According to size of molded plastic part, designed inclined push structure size is 346mm*50mm*60mm. In order to smoothly push inclined push structure out of core, two inclined push rods are required. In order to protect inclined push rod from breaking, a T-shaped rod is added beside inclined push rod. When mold is pushed out, T-shaped rod guides inclined push assembly to slide horizontally in chute and bear twisting force. Structure of inclined push is shown in Figure 6. Inclined push structure is mainly divided into three parts: inclined push block, inclined push rod and guide chute plate. Inclined push block is processed according to local shape of plastic part; inclined push rod is a standard part, purchased according to different specifications, and directly installed on inclined push block; guide chute plate is customized according to actual situation of mold base, fixed on push plate with screws, and positioned by push rod fixing plate. Advantages of inclined push structure: ①Inclined push block and inclined push rod are interchangeable, and the two are fixed with screws, which is convenient for assembly. When inclined push block or inclined push rod is damaged, only corresponding parts need to be replaced instead of the entire inclined push assembly; ②A T-shaped bar is installed next to tilting pusher, which can bear most of twisting force of tilting pusher and protect tilting pusher, and tilting pusher is not easy to break; ③When disassembling and installing inclined pusher assembly, loosen screws on guide chute plate from bottom of movable mold base plate, take out guide chute plate from push rod fixing plate, then take inclined pusher assembly out of core, without disassembling the entire mold; ④ This inclined pusher assembly can be connected to cooling water. Inclined pusher is a hollow tube. Each of the two inclined pushers is connected to a water pipe joint, one is connected to water inlet pipe and water outlet pipe to form a separate cooling water circuit, which can control temperature of inclined pusher block.

 

1. Inclined push block 2, sleeve 3, slide guide plate 4, T-shaped plate 5, water inlet pipe 6, water outlet pipe 7, inclined push rod
Figure 6 Inclined thrust structure

Because there is a car glass window guide rail on the left and right sides of car, shape is just opposite, mold is designed as a structure of 2 cavities, and 2 plastic parts to be formed are placed opposite to each other. Slider is on the outside of mold, as shown in Figure 7. Advantage of this cavity arrangement is that force on both sides of mold is even, and mold parts are not easy to twist.

 

There are 2 large sliders and 2 large inclined push components on mold, and weight is relatively large. In order to reduce influence of quality of these components on mold opening and closing movement, mold is placed sideways during injection production, and chute bears burden. Quality of slider minimizes influence of quality of components on movement of opening and closing mold. Mold has 2 small sliders. In order to prevent 2 small sliders from falling out of chute when mold is opened, one end of 2 small sliders will face up during injection production, and quality of 2 sliders will be used reasonably. Under action of gravity after mold, small slider can be prevented from falling out of chute. Therefore, during injection production, mold is placed vertically, and the two small sliders are above mold, as shown in Figure 8, so that side of inclined pusher assembly and large slider can bear weight of inclined pusher and large slider. Small sliders will not fall from chute.

 

Mold adopts "I"-shaped mold base. In order to protect various parts on mold, mold feet are installed on fixed and movable mold plates of mold base. When mold base is placed on the ground, quality of mold is borne by mold feet; , in order to prevent heat loss from fixed mold base plate, install a heat insulation board on upper surface of fixed mold base plate (material of heat insulation board is resin material), and mold structure is shown in Figure 9. After injection is completed, movable mold and fixed mold are opened at parting surface, nested slider and slider on the end face of molded plastic part (conventional demoulding action) start demoulding at the same time. When movable mold moves to limit position, slider of injection molding machine pushes all push rods and inclined push components together to make a pushing movement to push out molded plastic parts. Then slider of injection molding machine drives inclined pusher assembly and push rod to reset. When push rod and inclined pusher assembly are completely reset, movable mold moves to fixed mold direction. Column and wedge position drive end slider to reset. Next injection cycle begins when nested slide is fully molded to end slide.

 

1. Heat insulation plate 2, fixed mold seat plate 3, hot runner plate 4, fixed template 5, small slider 6, large slider 7, slider seat 8, movable template 9, support column 10, push rod fixing plate 11 , push plate 12, cushion block 13, movable mold seat plate 14, fixed mold insert 15, movable mold insert 16, T-shaped inclined pressure plate 17, push rod 18, inclined push rod 19, inclined push T-shaped rod 20, water pipe connector
Figure 9 Die structure