Structure of printer cover plastic part is shown in Figure 1. Its top view has a "convex" shape, width of convex position is 99mm, maximum external dimension is 296mm * 173mm, wall thickness is 2.5mm, and plastic part material is ABS.

 

Three-dimensional structure of plastic part is shown in Figure 2. There is a ring-shaped buckle on both sides of raised position of plastic part. There is a cylindrical hole in the center of ring. Diameter of cylindrical hole is φ5mm and depth is 18mm, and are formed using an inclined guide column + slider structure; there is also a buckle on inner surface of raised position of plastic part. Since buckle position is located above parting surface, it is formed using a fixed mold and inclined push structure. There is a cylindrical hole next to buckle. Diameter of cylindrical hole is φ3.2mm and depth is 5mm. Since axis direction of cylindrical hole is inconsistent with direction of parting surface, it cannot be designed according to conventional demoulding structure. The two cylindrical holes are also demoulded using a fixed mold oblique pushing structure. There are several buckles on inner surface of plastic part, and buckles on inner surface are formed using a movable die tilt push structure. There is a side hole on plastic part, inner and outer surfaces of side hole are transitioned by arcs. In order to form an arc on plastic part, inner surface of side hole is formed by an oblique push structure, and outer surface is formed by a slider.

 

In order to make buckle demoulding on molded plastic parts smooth, designed demoulding structure is shown in Figure 3, including 3 inclined guide pillars + slider structures, 4 fixed mold inclined push structures and several movable mold inclined push structures.

 

For ring buckles on both sides of raised position of molded plastic part, there is a cylindrical hole in the center, there are 4 reinforcing ribs between cylindrical hole and ring buckle. In order to prevent slider from forming a vacuum when demoulding, core of cylindrical hole is designed as an insert, as shown in Figure 4.

 

1. Chute seat 2. Insert seat 3. Pressure plate 4. Inclined slider 5. Slider 6. Insert 7. Elastic tube
Figure 4 Slider release structure with side core inserts
In order to facilitate processing and modification of mold parts, core of cylindrical hole is divided into two sections: insert and insert seat. In order to make insert have a delayed mold opening function, a vertical surface is set on insert seat, and height of vertical surface is 6 mm. When mold opening distance between fixed mold and movable mold is 0 to 6 mm, slider retreats backwards. However, since contact surface between insert seat and wedge is vertical, insert cannot follow retreat of slide block and protrude from slide block, pressing against molded plastic part. At this time, insert has function of a push rod, and air enters from around insert, effectively preventing formation of a vacuum between ring buckle and slider.
When mold opening distance between fixed mold and movable mold is greater than 6mm, contact surface between insert and wedge is no longer a vertical surface, but an inclined surface. At this time, insert and slider perform demoulding motion. Due to limited space of mold, it is not suitable to open chute on both sides of slider. Instead, a T-shaped slot is opened in the middle of slider, springs are set on both sides of slider to assist movement of slider, and an insert is set on one side of slider as a core for side hole.

In order to demould inner buckle and inner cylindrical hole in molded plastic parts, a fixed mold tilt push structure is used, and four nitrogen gas springs are set on fixed mold tilt push seat, as shown in Figure 5(a). Nitrogen gas springs control movement of fixed die tilt push assembly. Set a cylindrical pin on inner inclined push rod, as shown in Figure 5(b), and install cylindrical pin in horizontal groove of inner inclined push rod. When inner inclined push rod is driven by inner inclined push rod to move up and down, cylindrical pin slides in horizontal direction in horizontal groove of inner inclined push rod.

 

For side holes in molded plastic parts and external buckles next to side holes, inclined guide pillar + slider structure is used for demoulding. Depth of side hole is about 12mm. In order to facilitate processing of mold parts and prevent material leakage when forming side hole, side hole core is designed as an insert, as shown in Figure 6(a). Due to long length of slider, in order to increase stability of slider movement, 2 guide bars are added to the bottom of slider and 4 springs are set, as shown in Figure 6(b).

 

For inner buckle of molded plastic parts, movable mold oblique push structure is used for demoulding, as shown in Figure 7. Because inclined push rod is thin, its cross-section is only 10mm*6.5mm. In order to enhance rigidity and strength of inclined push rod and prevent inclined push rod from breaking, length of inclined push rod is shortened. Method adopted is increase height of inclined push seat to 132mm. Inner surface of side hole in molded plastic part is transitioned by an arc, must be formed and demolded using an inclined push structure.

 

In order to overcome shortcomings of ordinary runner pouring, one hot runner is converted into two ordinary runners for pouring, and a latent gate is used for pouring, as shown in Figure 8, where ordinary runner is a circular runner. Since there are two reinforcing ribs on both sides of protruding position of plastic part, there is a large square hole in the middle of main part of plastic part, and two inlets are used to meet molding requirements of plastic part. This pouring method produces smaller weld lines.

 

In order to quickly cool and shape molded plastic parts and prevent plastic parts from deforming, a cooling system with good cooling effect should be designed according to structure of mold. Since cooling water path of fixed mold needs to avoid 2 slide blocks and 4 fixed mold inclined push components, designed cooling water path adopts a straight water path + a transverse water well water path, in which transverse well water path is located between fixed mold inclined push components, as shown in Figure 9 (a). Generally, water wells in mold are placed vertically, but water wells in this mold are placed horizontally and are used to cool parts between fixed mold and inclined push assembly. Cooling water path of movable mold adopts a straight water channel + a water well water channel. In order to make mold temperature uniform and prevent heat from being brought in from other areas, a one-way straight water channel is used, that is, cold water flows in from one end and flows out from the other end. A well waterway is set between the two slide chute, as shown in Figure 9(b).

 

Mold structure is shown in Figure 10. Its working process: After injection material is heated in hot runner tube, it enters mold cavity through hot nozzle, ordinary runner, and latent gate. After filling, pressure maintaining, solidification, and shaping, mold is opened at PL. When mold is opened, nitrogen spring expands, pushing fixed mold tilt push assembly to perform demoulding movement, and inclined guide pillar drives slider to perform demoulding movement at the same time. When mold is completely separated, push plate pushes ejection structure to push out molded plastic part. After plastic part is taken out, mold is closed. Mold closing process is opposite to mold opening process.

 

1. Moving mold seat plate 2. Push plate 3. Push rod fixed plate 4. Moving mold plate 5. Moving mold insert 6. Slider guide rail 7. Slider 8. Guide column 9. Fixed mold insert 10. Fixed mold plate 11 .Hot runner plate 12. Fixed mold seat plate 13. Heat insulation plate 14 Inclined push rod 15. Fixed mold inclined push seat 16. Nitrogen gas spring 17. Positioning ring 18. Pad 19. Inclined push seat 20. Inclined push rod 21. Guide pillar 22. Slider 23. Hot runner plate 24. Insert 25. Hot runner tube 26. Core

Mold adopts 4 demoulding structures. For buckles on both sides of protruding position of plastic part, inclined guide pillar + slider demoulding structure is used for demoulding; for buckling on inner surfaces of both sides of protruding position of plastic part, fixed mold tilt push structure is used for demoulding. A fixed mold tilting push seat is installed in hot runner plate, and fixed mold tilting push assembly is driven by a nitrogen spring to demould, so that two-plate mold has function of a three-plate mold; for outer arc surface of side hole of plastic part and outer buckle next to it, use inclined guide pillar + slider demoulding structure to demould; for arc transition surface on inner surface of side hole of plastic part and internal buckle position next to it, movable mold tilt push assembly is used to demould. Actual production has proven that mold structure is reasonable, quality of molded plastic parts is stable, and it has a certain reference effect on molding of similar plastic parts.