Bracket structure is shown in Figure 1, shape is "Y" shape, main body is a cylindrical rod, center of cylindrical rod is a tapered round hole, top of round hole has an internal thread hole, and thread is a pipe thread. The lower end of cylindrical rod is two branches, which are symmetrically arranged in a mirror image, and an undercut hole with a depth of 2mm is provided on inner side. Plastic part material is nylon PA66, and shrinkage rate is 0.8%~2.1%.

 

Difficulties in forming plastic parts: ①Wall thickness of plastic parts is unevenly distributed, the thickest is 4.5mm, the thinnest is 2.6mm, and average wall thickness is 3.55mm. It is necessary to adopt a reasonable gate position and gate size to make cavity obtain. It is fully filled and is conducive to adjustment of injection process, especially adjustment of pressure-holding process parameters; ②Internal thread stripping at upper end of cylindrical rod of plastic part needs to be equipped with a special thread removal mechanism; ③For forming of tapered hole in the center of cylindrical rod, only smaller diameter molding parts can be used, which need to take certain strengthening measures to prevent impact deformation caused by injection pressure during injection; ④ For demoulding of 2 undercut holes inside 2 branches, space for installing core-pulling mechanism in mold is narrow, so a special mechanism needs to be designed for demoulding.

The overall structural layout of mold is shown in Figure 2, and a three-plate mold is used for injection molding, with a structure of 8 cavities. Gating system uses point gate to side gate, and each cavity is poured from side gate. Runners of point gate are R1 and R2, and runner of side gate is R3. Molded parts adopt an insert-jointed structure, and exhaust of each cavity is completed by gap between molded inserts, and gap δ≤0.015mm. For cooling of cavity, φ8mm cooling pipes are opened in some larger molding inserts for cooling. Mechanisms used for demolding molded plastic parts: ①Hydraulic cylinder piston rod drives rack and thread stripping mechanism M1; ②Push plate pushes out demoulding mechanism M2; ③Fixed mold Huff slider core-pulling mechanism S1, S2, S4, S5;④ Fixed mold locking block drives the first core-pulling mechanism S3. In view of stability needs when multi-cavity multi-plate mold is closed, mold uses a standard three-plate mold base, and 8 pairs of guide pillars/guide sleeves are set in mold base, of which 4 sets of main columns/guide sleeves are used for closing guide of mold base mold plate. 4 pairs of auxiliary guide pillars/guide sleeves are used for reset guidance of each mold plate when cavity is closed.

 

1. Wear-resistant plate 2, auxiliary guide column 3, push plate 4, insert push block 5, main column 6, nozzle
Cooling of a single cavity mainly includes cooling of slider assembly of mechanisms S1 and S2 and insert push block 4 at the bottom of mechanism M2. Wear-resistant plate 1 is used for support of two groups of Huff sliders of mechanism S1/S2, S4/S5, and push plate 3 is equipped with 8 insert push blocks 4 for pushing out molded plastic parts.

Mold structure is shown in Figure 3. Parts of molded plastic part include front undercut hole insert 7, rear undercut hole insert 48, outer wall left slider 8, outer wall right slider 9, insert push block 4 and threaded insert Part 11, wherein upper end of threaded insert 11 is a center hole insert, and the lower end is an internal thread forming part. Outer wall left slider 8 and outer wall right slider 9 are sliders of Huff slider mechanism S1, S2, which are installed in fixed mold base groove. Both front undercut hole insert 7 and rear undercut hole insert 48 are processed into form of a slider, which needs to implement side hole retraction and core pulling. Insert push block 4 is processed into a ring shape, which is convenient to adopt ring groove type waterway to cool it.

 

2, Auxiliary guide post 4, insert push block 5, main post 7, front undercut hole insert 8, outer wall left slider 9, outer wall right slider 10, cooling water pipe 11, threaded insert 12, wear-resistant block 13 , rotating wear-resistant sleeve 14, gear 15, threaded rod at tail end 16, thread guide sleeve 17, lock nut at tail end of thread sleeve 18, secondary driving gear 19, primary driven gear 20, primary central shaft 21, bearing 22 , gear 23, gear key 24, tertiary driving gear 25, secondary central shaft 26, bearing 27, key 28, movable mold seat plate 29, second backing plate 30, third backing plate 31, rack guide plate 32, support Seat 33, hydraulic cylinder 34, first backing plate 35, movable platen 36, push rod 37, push plate 38, fixed platen 39, stripper plate 40, fixed plate seat plate 41, pull rod 42, bushing 43, positioning ring 44 , pulling material rod 45, spring 46, inclined guide post 47, locking block 48, rear buttonhole insert 49, fixed template pull rod 50, S Huff slider 51, spring core rod 52, spring 53, guide bar 54 , limit block 55, stripper rod R4, vertical main runner R5, horizontal runner P1-P4, parting surface

Figure 3 Mold Structure
In cooling setting of single cavity of mold, three waterways are set up for cooling, which are C1 waterway on left slider 8 of outer wall, C2 waterway on right slider 9 of outer wall, and C3 waterway at lower end of insert pusher 4.

(1) Piston rod of hydraulic cylinder drives rack dethreading mechanism M1. There are 8 threaded cores (threaded inserts 11) driven by mechanism M1. In structural composition of a single threaded insert 11, it is necessary to set up a rotating wear-resistant sleeve 13 and a gear 14 (number of teeth Z=15, modulus m=1.5 mm), threaded rod at tail end 15, threaded guide sleeve 16, lock nut at the end of threaded sleeve 17 (2 pieces). Threaded guide sleeve 16 is used for rotation core pulling and reset guide of threaded insert 11 .
Combined with top view structure of movable mold shown in FIG. 2 , rack 22 drives threaded insert 11 of a single cavity through three-stage gear transmission. In order to realize three-stage gear transmission, two-stage intermediate transmission gear assemblies for power transmission are respectively: the first-stage two sets of intermediate transmission assemblies, single-group assembly includes I-stage passive gear 19, I-stage central shaft 20, II-stage driving gear 18 , bearing 21 and gear key 23; 4th group of intermediate transmission assemblies of II stage, its single group assembly includes III stage driving gear 24, II stage center shaft 25, bearing 26, key 27. Power drive assembly of mechanism includes a rack 22 , a rack guide 31 , a support 32 , and a hydraulic cylinder 33 . Hydraulic cylinder 33 is used to drive rack 22 to move, driving gear 14 drives threaded insert 11 to rotate and pull core or reset.
Power transmission path of threaded insert 11: rack 22 → class I driven gear 19 (number of teeth Z=15) → class II driving gear 18 (number of teeth Z=50) → class III driving gear 24 (number of teeth Z=60) → gear 14 (number of teeth Z=15).
(2) Push plate ejection and demoulding mechanism M2 is used to finally push molded plastic parts from threaded insert 11, components include 6 push rods 36, push plates 37 and 8 insert push blocks installed on push plates 37 4.
(3) Core-pulling mechanism S1 and S2 of fixed-mold Huff slider are a group, S4 and S5 are a group. Each group of Huff sliders forms outer walls of 4 plastic parts. In composition of a single half slider mechanism, taking mechanism S4 as an example, its components include a guide bar 53 , an S4 half slider 50 , a spring core rod 51 , a spring 52 , and a limit block 54 .
(4) There are 8 core-pulling mechanisms S3 driven by fixed mold locking block, one for each cavity. Mechanism is synchronously driven by locking block 47. Retractable side core-pulling, taking reverse button hole insert 48 as an example, its structure is designed in the form of a special-shaped slider. When inclined guide post 46 is driven, spring 45 jointly acts as a push. When slider is in closed position, it is locked block 47 is locked.
(5) Mold base uses an improved three-plate mold non-standard mold base. Mold base mold plate includes a fixed mold seat plate 40, a stripper plate 39, a fixed template 38, a push plate 37, a movable mold plate 35, a first backing plate 34, a second backing plate 29, third backing plate 30, movable mold seat plate 28. Different from three-plate mold standard mold base, there are no pads, push plate, push plate cover and other components on movable mold side of mold. Instead, push plate is used to push out demoulding mechanism M2 to push out; first backing plate 34, the second backing plate 29, and third backing plate 30 are added to movable mold side for hydraulic cylinder piston rod to drive rack stripping mechanism M1 assembly installation.
(6) Mold opening is divided into 4 times, and opening sequence is P1→P2→P3→P4. Control principle is same as common three-plate mold structure, distance control parts of mold plate opening and closing include a pull rod 41, a stripper plate pull rod 55 and its spring, a fixed mold plate pull rod 49 and its spring. A nylon buckle is set between fixed mold plate 38 and push plate 37.
(7) Vertical main runner R4 and horizontal runner R5 of side gate in gating system are set on parting surface of same group of Huff sliders, so that design enables side gate to have an opening position and can realize filling sequence from top to bottom.

Combined with mold structure shown in Figure 3, working principle of mold is as follows.
(1) Clamping injection. After mold is successfully installed and debugged on injection molding machine, injection is completed after mold is closed, and after cooling, mold is ready to be opened.
(2) Thread removal. Before mold is opened, piston rod of hydraulic cylinder drives rack stripping mechanism M1 to act, and at the same time drives threaded inserts 11 in 8 cavities to complete thread core pulling.
(3) P1 side is open. Sliding block of injection molding machine drives movable mold back, and P1 surface is opened to complete two actions, one is separation of point gate runner condensate from side gate runner condensate; the other is mechanism S3 to complete core pulling.
(4) P2 side is opened. Movable mold continues to retreat, stripping plate 39 releases point gate runner condensate from pull rod 44 and comes off automatically.
(5) P3 surface is opened. Movable mold continues to retreat, and springs of four Huff sliders in mechanisms S1, S2, S4, and S5 push out respective sliders to realize demoulding of outer wall of molded plastic part.
(6) P4 side is opened. As moving mold continues to retreat, ejector rod of injection molding machine pushes 8 insert push blocks 4 to push 8 molded plastic parts out from threaded insert 11, so as to realize complete demoulding of plastic parts.
(7) RESET. Before reset, hydraulic cylinder piston rod drives rack thread removal mechanism M1 to act first, and drives threaded inserts 11 in 8 cavities to complete reset, then mold is closed in the order of P4→P3→P2→P1 to prepare for next injection cycle.