Abstract: Based on injection molding requirements for power plug-in housing, product required a single-piece, 2-1.5mm diameter holes. A mold parting scheme was proposed around these 2-1.5mm diameter holes. After analyzing and designing mold motion, mold structure design and manufacturing were completed. Production practice has verified that mold structure design is reasonable, operational, and product meets user requirements.
Power plug-in housing is made of nylon 66 + 20% reinforced glass fiber (PA66 + 20% GF). It is used as a connector for motorcycle wiring, as shown in Figure 1. To illustrate product's position within mold, main view of mold is shown. Six 0.6 x 3.5mm brass plates are horizontally arranged, and four 0.6 x 6mm brass plates are vertically arranged. These plates are inserted into brass plates immediately after injection molding. Plates are secured by shrinkage force of plastic part. After wiring is completed at left end of product, sealant is applied along inclined surface to form two plugs.

 

Figure 1 Power plug housing

Main view of product is used as basic idea for main view design of mold. Parting surface design uses horizontal center line as design reference for upper and lower (fixed and movable mold) parting surfaces, horizontal center line as core pulling axis on left and right sides to meet needs of product demoulding. 2-Φ1.5 holes in product are completed at one time, upper and lower molds are parted first.

(1) Structure of injection mold for power plug shell is shown in Figure 2.

 

1—Upper mold plate; 2—Fixed mold pad; 3—Locking block; 4—Core pull seat; 5—Core pull core (left); 6—Fixed mold insert; 7—Gate sleeve; 8—Upper Φ1.5 core; 9—Core pull core (right); 10—Fixed mold fixed plate; 11—Core pull connecting rod; 12—Hydraulic cylinder seat; 13—Hydraulic cylinder; 14—Die pull buckle assembly; 15—Moving mold frame; 16—Moving mold insert; 17—Lower Φ1.5 core; 18—Ejector rod; 19—Lower core fixing plate/pad; 20—Moving mold frame pad; 21—Pulling rod; 22—Moving mold guide pin; 23—Fixed mold guide pin; 24—Moving mold frame screw; 25—Fixed mold screw
Figure 2 Mold structure diagram

(2) Basic working principle of mold

After mold is installed on injection molding machine and hydraulic cylinder oil circuit is connected, oil circuit connection method must be determined before mold can be opened. When injection molding machine starts and injection is completed, movable mold moves backward. Under force of die buckle assembly 14, fixed mold pad 2, fixed mold fixed plate 10 and locking block 3 are parted for the first time. On fixed mold guide column 23, upper Φ1.5 core 8 is first separated from fixed mold insert 6. Separation distance is limited by fixed mold screw 25 and controlled at 12mm. At the same time as force of die buckle assembly 14, movable mold frame 15 and movable mold frame pad 20 are also separated from lower core fixed plate/pad 19 and mold base and other parts for second parting. On movable mold guide column 22, lower Φ1.5 core 17 is first separated from movable mold insert 16. Disengagement distance is limited by movable mold screw 24 and controlled at 10mm; when above-mentioned first and second partings are completed, mold movable mold continues to move backward to separate die buckle assembly 14, and third parting is achieved; left and right hydraulic cylinders 13 can start to move outward, core pulling connecting rod 11 respectively moves left and right core pulling seat 4, core pulling core (left) 5, core pulling core (right) 9 outward to separate from plastic part and complete core pulling work; injection molding machine starts ejection device, pushes ejector rod 18 and pulling rod 21, ejects product and gate from movable mold insert, and takes them out smoothly, completing process of injection molding product. Before second injection, ejector pin 18, pull rod 21, and ejector plate are pre-reset under force of a spring (not numbered in figure). Hydraulic cylinder 13 is first closed, causing core-pulling connecting rod 11 to move left and right core puller 4, left core puller 5, and right core puller 9 inward, completing reset. The entire mold can now be closed, upper Φ1.5 core 8 and lower Φ1.5 core 17 can be inserted into right core puller 9. Mold-pulling latch assembly 14 is also closed, completing mold closing process and allowing for second injection. During this process, hydraulic cylinder's opening and closing sequence must be adjusted to meet mold's operating requirements. Setting desired timing is crucial to ensuring fully automatic operation. Locking block 3 secures core puller and withstands lateral pressure required during injection.

(1) Fixed mold, movable mold inserts and left and right core pullers are all made of H13 mold steel. After rough machining and heat treatment (HRC44-48), fine machining is performed. Surface of product is directly processed by electric sparks and does not need to be polished. In this way, mold cavity and core pullers will not have flash on product due to deformation after heat treatment. Processing cost after heat treatment has increased and processing cycle is also longer, but service life is greatly improved, which still meets needs of economy.
(2) Core puller is made of 45 steel and connected to left and right core pullers with a dovetail. After mold is tested, pay attention to positioning them with pins on both sides. A 26×10 hole is cut on core puller, then a groove is milled. There is a certain gap with core puller connecting rod, which improves rigidity and strength of core puller. Core puller connecting rod on hydraulic cylinder can be removed from hydraulic cylinder for processing as needed. Pay attention to sealing. Core puller connecting rod in this series is Φ16 and is processed. Selection of hydraulic cylinders must ensure required core pulling distance. Core pulling distance of this series of hydraulic cylinders is greater than 30mm, and it is not necessary to have a core pulling distance that is too large. Basic structure of left core pulling seat and core pulling core is shown in Figure 3.

 

Figure 3 Basic structure of left core pulling seat and core pulling core
(3) Gate adopts a straight gate. When demoulding, pull rod is pulled down from fixed mold. A semicircular runner is made on movable mold insert. Feed port is made into a groove with a width of 2 and a depth of 1. Pouring bridge is 1~1.5mm away from cavity. Four Φ3 ejector rods are used to eject product on each cavity to ensure smooth ejection of product.
(4) Die buckle assembly 14 is generally sold in mold parts specialty stores, and can also be made by yourself according to your needs. Its diagram is shown in Figure 4. Die buckle seat is generally installed on fixed mold, and die buckle is generally installed on movable mold. Principle is that when die buckle is inserted into die buckle seat, cylinder on buckle seat coincides with arc groove on die buckle, and two springs press cylinder tightly to play a buckling role. During demolding, die clamp pulls die clamp seat and moves together until relevant parts are restricted. Die clamp continues to pull until they are pulled apart, completing die pulling function. Later, we also used nylon column die clamps, which had same effect.

 

Figure 4: Die buckle assembly
(5) Selection and adjustment of limit screws. Limit screws are generally hexagon socket screws. Pay attention to strength and number of screws. When adjusting limit distance, screw should be kept tightened. Distance is space between countersink and screw surface. When making countersinks, depth of countersink should be controlled. Keeping limit distance consistent can ensure smooth separation of mold plate.
(6) Cooling water channels must be made. Because water cannot flow on insert, cooling water channels can only be made on mold base to take away a certain amount of heat. Try to leave hole position in mold plate and make cooling water channels to ensure needs of molding process. This cooling water channel can be connected to oil temperature controller to control mold temperature.
(7) Use of guide pins and guide sleeves. Considering service life of mold and keeping mold in good use, use of guide pins and guide sleeves should be considered. At the same time, considering that ejector pin in ejector plate is relatively small, support guide pins and guide sleeves should be added to keep ejector plate stable during ejection process.

(1) There is a hook shape in lower part of view. There is not enough space in mold for design of inner core pulling. After obtaining user's consent, a movable insert structure is adopted. Insert is placed in mold before injection molding. Insert is ejected together with product when it is ejected from mold. Operator takes it out of product and puts it back into mold for next product injection molding. Two sets of inserts can be prepared in production.
(2) Mold shape (excluding hydraulic cylinder assembly) is 350×260×320 (mm) in length×width×height. Ningbo Haitian injection molding machine is selected. Its injection molding machine has a hydraulic core pulling connector that can be directly connected.
(3) Injection molding machine and mold temperature control. Temperature of rear section of barrel is 280~290℃, temperature of middle section is 275~300℃, temperature of front section is 270~280℃, and temperature of nozzle is 270~280℃; (20~30℃ higher than PA66 without reinforcement). Mold temperature is 80~90℃. Pay attention to temperature control during production to avoid weld marks.
(4) After verification by production practice, mold design structure is reasonable, operation is convenient, dimensional accuracy of injection molded parts can be controlled, and product quality has won satisfaction of users.