Mixer base structure is shown in Figure 1. The overall dimensions are 250 mm*130 mm*184 mm, wall thickness is 2 mm, and plastic part consists of two parts, one high and one low. Center distance between the two is 120 mm, height of higher part is 178 mm, and height of lower part is 16 mm. There is a structure for installing panel on positive side of higher part, which contains multiple holes and a ring groove similar to a runway. There is a countersunk hole ① on the side of higher part facing lower part. There is an inner hole of φ82 mm in the middle of higher part, and a countersunk hole ② on its inner surface is connected to countersunk hole ①; there is a through hole and an annular groove in the middle of lower part, outer diameter of annular groove is φ81 mm, inner diameter is φ36 mm, and there are two evenly distributed buckles on outer diameter side wall of annular groove; in order to match with other parts, there is a circle of steps at mouth of plastic part, there are two square holes on both sides of steps, and there are several cylindrical holes on inner surface of plastic part.

 

Figure 1 Mixer base

In addition to main parting surface, circular holes in the middle of high and low parts of plastic part should be designed with parting surfaces. Parting surfaces of these two circular holes are located at minimum contour of inner diameter of circular hole. According to structure of plastic part, a total of three parting surfaces are designed for mold, as shown in Figure 2. Two circular holes are formed by contact between fixed mold and movable mold. Main parting surface is located at maximum contour of mouth of plastic part. Step of mouth of plastic part is located below main parting surface and is formed by movable mold.

 

Figure 2 Parting surface design

Due to high requirements on outer surface of plastic part, no trace of slider is allowed. Panel assembly position and countersunk hole ① must be demolded using fixed mold slider structure. Countersunk hole ② and two evenly distributed buckle positions on outer diameter side wall of annular groove are demolded by fixed mold inner slider structure. A total of 2 fixed mold sliders and 3 inner sliders need to be designed, as shown in Figure 3 (a); 4 square holes on the step of mouth of plastic part are demolded by movable mold oblique push rod mechanism, with a total of 4 movable mold oblique push rod mechanisms, as shown in Figure 3 (b). Cylindrical hole on inner surface of plastic part is pushed out by a push tube.

 

Figure 3 Demolding mechanism

Panel assembly position and countersunk hole ① are demolded by fixed mold slider mechanism, but structures of two sliders are slightly different. Since slider of panel assembly position is close to the edge of mold frame, there is not enough space to design clamping wedge and inclined guide column. Demoulding is carried out by "T-shaped inclined wedge + slider mechanism", and slider pressure strip is installed at the bottom of slider to ensure smooth movement of slider, as shown in Figure 4 (a). Demoulding of countersunk hole ① is carried out by "inclined guide column + slider mechanism". In order to simplify mold structure, slider pressure strip is installed on the bottom surface of fixed mold plate, as shown in Figure 4 (b). In order to enhance strength and rigidity of slider, slider and slider seat are an integral structure. There is a notch on pressure strip of slider of countersunk hole ①, which is used to avoid inclined wedge of inner slider 2 and inner slider 3 in Figure 3 (a).

 

Figure 4 Demolding mechanism of fixed mold slider

Countersunk hole ② on inner surface of plastic part is suitable for demoulding by inner slider mechanism driven by inclined guide column, as shown in Figure 5. Countersink diameter of countersunk hole is φ15 mm, diameter of hole is φ10 mm, and depth is 2 mm. Probability of core of molded countersunk hole breaking is small. In order to ensure strength and rigidity of slider, core of countersunk hole is connected to slider seat as a whole.

 

Figure 5 Demolding mechanism of countersunk hole ②

The two buckles on inner ring side wall of outer surface of lower part of plastic part need to be designed with a demolding mechanism. The two buckles are located in fixed mold. Demolding of inner slider mechanism driven by inclined wedge can simplify mold structure. As shown in Figure 6, a T-shaped bar is set on slider, and a T-shaped groove is designed on inclined wedge. Slider is in an inverted "convex" shape. Shoulders on both sides of slider cooperate with corresponding slide grooves of fixed mold plate to guide slider to move in horizontal direction. Inclined wedge is connected to slider through an inclined T-shaped groove. When inclined wedge is lifted upward, slider is driven to start demolding in horizontal direction in slide groove.

 

Figure 6 Demolding mechanism of buckle position

There are 4 buckle positions below main parting surface at mouth of plastic part. Mold is demolded by an inclined push rod mechanism, as shown in Figure 7. Due to small size of buckle positions, core of buckle positions is connected to inclined push rod. Inclined push rod is connected to inclined push seat through a T-slot. During push-out movement, inclined push rod moves horizontally in T-slot of inclined push seat. Inclined push seat is fixed to push plate by screws at the bottom. When inclined push rod needs to be removed, screws can be loosened from direction of movable mold seat plate to remove inclined push rod, disassembly and assembly workload is small.

 

Figure 7 Demolding mechanism of inclined push rod

Based on design experience of plastic part structure and similar molds, mold adopts a two-plate mold structure, a casting system of ordinary runners and two latent gates. Gate is set on the side wall of inner hole at a higher position of plastic part to be molded, gate sleeve is set on the side of inner hole center that deviates from higher part and close to lower part, as shown in Figure 8 (a). Since inner slider shown in Figure 3 (a) is set directly below gate sleeve, in order to avoid core of inner slider 1 directly below gate sleeve, branch channel is surrounded on outer cylindrical surface of core of inner slider 1 in an arched shape, then branch channel is divided into left and right branches for casting with a latent gate, as shown in Figure 8 (b). A cold material hole is set on each of two branch channels on moving mold plate to eliminate undesirable phenomena such as flow marks on the surface of plastic part.

 

Figure 8 Casting system design

According to structure of plastic part, a push rod is used for demoulding. A flat push rod is set at mouth of higher part of plastic part, and a round push rod is set on inner surface of lower part. Several cylindrical holes on inner surface of plastic part are demoulded using a push tube structure. A pull rod is set for each of two branch channel solids. Push-out system is shown in Figure 9.

 

Figure 9 Ejection system

Water channel of cooling system must avoid sliders, push rods, inserts, etc., must not reduce strength of mold parts, and must ensure uniform mold temperature. A hollow tube is set inside higher part of core, and a threaded cooling water channel is set outside. A straight-through water channel is set at other positions of movable mold, as shown in Figure 10 (a). Cooling water enters along hollow tube in the middle of threaded tube and then exits along threaded tube to form a cooling circuit. Fixed mold plate is suitable for a straight-through water channel. In order to avoid fixed mold slider 1 (see Figure 3 (a)), no cooling water channel is set at position where fixed mold slider 1 is located, and only cooling water channels are set on different sides of cavity plate, as shown in Figure 10 (b).

 

Figure 10 Cooling water channel arrangement

Mold adopts a two-plate mold structure. In order to demold fixed mold slider and inner slider mechanism, two mold openings are designed. The first mold opening is set between fixed mold base plate and fixed mold plate, and a limit screw is set between the two to make mold opening distance 12 mm. Mold cross-sectional structure is shown in Figure 11.
Mold working process: After injection is completed, mold is first separated between fixed mold plate 8 and fixed mold base plate 9. Inclined wedges 7, 15, inclined guide pillars 24 and 25 drive their respective sliders to perform demolding movements. When separation distance between fixed mold plate 8 and fixed mold base plate 9 is 12 mm, movement stops under action of limit screw 18, and the first mold opening is completed. Then mold is separated between movable mold plate 5 and fixed mold plate 8 for second mold opening. When mold is completely separated, injection molding machine slider drives mold's ejection mechanism (including push plate 2, push rod fixing plate 3, inclined push rod 11, pull rod 19, push rod 28, etc.) to perform ejection movements. After plastic part is taken out, ejection mechanism of mold automatically resets under elastic force of reset spring, and slider of injection molding machine drives movable mold part of mold to reset with fixed mold. Reset step is completely opposite to mold opening step. During reset process, surface of fixed mold plate presses against end surface of reset rod 22, driving ejection mechanism of mold to completely reset. When mold is completely reset, next production can be carried out.