Structure of elbow wire slot is shown in Figure 1. Its main body consists of a section of elbow and a section of straight pipe. Centerline radius of elbow is R64.5mm, bending angle is 75°, inner diameter of elbow is φ39.5mm, wall thickness is 1.8mm, and length of straight pipe section is 71.8mm. Its inner diameter and wall thickness are same as those of elbow section. There are 8 small holes U2 and 8 large holes U1 on outer wall of plastic part. Diameter of small hole U2 is φ3.0mm, and diameter of large hole U1 is φ6.0mm. Outer wall is also provided with 4 different sizes of slot ribs U3~U6 and 4 rectangular through holes U7. Wall thickness of slot rib is 2.0mm. Plastic part material is PC+ABS, and shrinkage rate is 0.52%~0.56%.

 

Combined with structural characteristics of plastic part, a single cavity layout is proposed to design mold structure. Mold adopts a two-plate mold, single cavity parting and molding part design is shown in Figure 2. Plastic part to be molded is arranged horizontally in cavity, and outer wall parting surface PL1 is set according to maximum outer edge contour line of its horizontal state. Main molding parts are divided into C1 upper main insert and C2 lower main insert, which are also main molding parts of outer wall of plastic part. Then, inner wall is parted by interface PL2 between straight pipe section and curved pipe section in inner wall of plastic part to be molded, then B1 straight pipe core and B2 curved pipe core are set. To facilitate processing of molded parts, main insert on C1 is further divided into 4 partial inserts I1 for molding of 4 small holes U2, 4 partial inserts I2 for molding of 4 large holes U1, 2 partial inserts I3 for molding of 2 rectangular through holes U7; main insert on C2 is also divided in same way, and obtained inserts are I1′, I2′, and I3′.

 

After obtaining molded parts of plastic parts, demoulding settings of molded plastic parts are: ① B2 curved tube core is pulled out first; ② Straight tube core is pulled out; ③ Main insert on C1 and partial inserts I1, I2, and I3 are separated from plastic parts; ④ Plastic parts are pushed out from main insert on C2 by push rod and completely demolded. According to experience of mold design for bent tube plastic parts, two latent side gates are planned to be used for pouring mold cavity. In view of small space of B1 straight tube core and B2 bent tube core, it is difficult to set cooling water channels in these two molded parts. Only cooling water channels are designed for outer wall molded parts C1 upper main insert and C2 lower main insert, and cooling pipe diameter is φ10mm.

Mold adopts a 1-mold 1-cavity two-plate mold structure, as shown in Figure 3. Structural parts arranged on fixed mold side mainly include C1 upper main insert 1, which is locked and positioned using Y-direction wedge block 2 and X-direction wedge block 5 to ensure that C1 upper main insert 1 and C2 lower main insert 8 are accurately closed. Since both ends of molded plastic parts need to be cored out, in order to ensure service life of mold, 4 positioning side locks 3 are additionally set in 4 directions of mold.

 

1.C1 upper main insert 2. Wedge block 3. Side lock 4. Guide sleeve 5. Wedge block 6. L insert 7. I2 insert 8.C2 lower main insert 9. Wedge block 10.I2’ Insert 11.I1' insert 12.B1 straight tube core 13. Straight tube core slider 14. Guide column 15. Hydraulic cylinder 16. Wedge block 17.B, bent tube core 18. Arc slider 19. Cylindrical pin 20. Swing arm 21. Screw 22. Cylindrical pin 23. Positioning pin 24. Arc slider seat 25. Arc guide strip 26. Pull rod 27. Cylindrical pin 28. Bend tube linear slider 29. Hydraulic cylinder
Figure 3 Arrangement of mold structure parts
Movable mold side is mainly arranged with C2 lower main insert 8 and two hydraulic cylinder-driven slider core-pulling mechanisms. The first mechanism is hydraulic cylinder 15 driving B1 straight tube core 12 core-pulling; second mechanism is hydraulic cylinder 29 driving B2 curved tube core 17 core-pulling, and its main parts include parts 17~29. Working principle of second mechanism: piston rod of hydraulic cylinder 29 drives straight slider 28 of bent tube to pull core. Cylindrical pin 27 is used on straight slider 28 of bent tube to connect lower end of pull rod 26. Pull rod 26 pulls cylindrical pin 19 to follow movement through pin hole at its front end. Cylindrical pin 19 is also equipped with a pin hole at upper end of swing arm 20. Lower end of swing arm 20 is positioned on C2 lower main insert 8 using a cylindrical pin 22. Under traction of pull rod 26, arc slider 18 rotates in an arc in arc slider seat 24 under arc guidance of arc guide bar 25 to pull core, and B2 bent tube core 17 is pulled out of plastic part, as shown in Figure 4 (a). Core pulling action of first mechanism is directly driven by piston rod of hydraulic cylinder 15 to drive B1 straight tube core 12 to complete core pulling, as shown in Figure 4 (b).

 

1.C1 upper main insert 8.C2 lower main insert 13.Straight tube core slider 15.Hydraulic cylinder 17.B, bent tube core 26.Tie rod 27.Cylindrical pin 28.Bent tube linear slider 29.Hydraulic cylinder 30.Fixed mold base plate 31.Fixed mold plate 32.Moving mold plate 33.Pad 34.Push rod fixing plate 35.Push plate 36.Moving mold base plate 37.Push plate guide column 38.Mold foot 39.Location ring 40.Gate bushing 41.Pull rod 42.Push rod: 43.Support column
Figure 4 Installation of core pulling mechanism
Two latent gates G1 and G2 are set for casting of cavity to ensure that straight pipe end and curved pipe end of cavity are filled sufficiently and evenly. Main insert 1 on C1 is cooled by water channels W1 and W2, main insert 8 on C2 is cooled by water channels W3 and W4. Water channel is sealed by a sealing ring 45 when it passes between molded part and mold plate, as shown in Figure 5. Guide pin 14 of mold needs to be vented in time when it is inserted into guide sleeve. A venting groove needs to be opened at its top to prevent guide pin from burning. Wedge angle of wedge blocks 2 and 16 is 5°. Mold parting surface is PL surface. When push rod fixing plate 34 and push plate 35 are reset after pushing out plastic part, a travel switch 44 needs to be set to detect whether it is completely reset to avoid interference between push rod and slider of core pulling mechanism.

Mold working principle is as follows.
(1) Mold is closed, and injection molding machine completes filling, pressure holding and cooling of cavity by melt, and waits for mold to be opened.
(2) Piston rod of hydraulic cylinder 29 moves first to complete core pulling of B2 curved tube core 17.
(3) Piston rod of hydraulic cylinder 15 moves to complete core pulling of B1 straight tube core 12.
(4) Slider of injection molding machine drives mold parts below PL surface to move, mold opens at PL surface, and plastic part remains on C2 lower main insert 8.
(5) After movable mold moves to a certain position, slider of injection molding machine supports push plate 35, pushes push rod 42, pull rod 41, etc. to push plastic part out of C2 lower main insert 8, realizes synchronous demolding of plastic part and runner condensate.
(6) Mold is reset and closed, push plate 35 and others are reset first.
(7) Mold is closed at PL, and next injection cycle starts after mold is completely closed.