Remote control front and bottom shell products are shown in Figure 1. Maximum outer dimensions of face shell product are 100.00 mm * 50.00 mm * 10.00 mm; average glue thickness of plastic parts is 1.50 mm, plastic part material is ABS, shrinkage rate is 1.005, and weight of face shell plastic parts is 10.55 grams. Technical requirements for plastic parts are that there must be no defects such as peaks, underfilling, flow lines, pores, warping deformation, silver streaks, cold materials, jet lines, etc. and they must comply with ROSH environmental requirements.

 

Figure 1 Product picture of remote control front and bottom shell products

 

Figure 2 3D diagram of mold

 

Figure 3 Rear mold core and mold arrangement diagram

 

Figure 4 Mold parting surface and pouring system diagram
Remote control cover and bottom product contains 3 plastic parts. Front case is a whole, and bottom case contains a battery cover. As can be seen from Figure 1, the overall shape of plastic part is in the shape of a flat frame, front shell and bottom shell are connected by buckles on the side of circumference. These buckles require design of a lifter or lateral slider core-pulling mechanism. It can be seen from mold layout diagram that this set of molds is designed using a family-style mold design. Layout diagram includes front case, bottom case, battery cover and three internal small accessories. Putting plastic parts of same product model on same set of molds is called a family mold abroad. Family-style molds facilitate production organization and can reduce costs during product trial production or small batch production. However, in high-precision products, due to inconsistent shape and size of each plastic part, it is difficult to achieve flow channel balance, which brings difficulties to injection molding production. When producing plastic parts for a series of products, if quantity demand for a certain plastic part is small, production quantity can be adjusted by designing flow switching elements. Plastic part structure of this set of molds is relatively simple, which is especially suitable for beginners or college mold major students to use as a reference for graduation projects. Mold arrangement diagram is shown in Figure 3.
According to mold layout diagram, six plastic parts are arranged together, and flow channels need to be balanced as much as possible. Therefore, simplified fine nozzle standard mold base FCI3040 A60 B90 was selected for mold design. Front mold core was designed with S136 and rear mold core was designed with NAK80. Positioning of front and rear mold cores adopts tiger's mouth positioning at the four corners. Direction of tiger mouth protrusion must be adapted to structure of mold core, so as to save steel and processing time. Sometimes, direction of tiger's mouth needs to consider strength of cavity. Most of time, one side of cavity is recessed. Protrusion of core plays a role in tightening cavity and preventing cavity from expanding under action of injection pressure. Slope of side of tiger's mouth has a great influence on mold closing accuracy. Generally, angle is 5゜~10゜. The smaller angle, the better positioning accuracy. When friction angle of small friction insert is smaller than bevel angle on the side of tiger's mouth, tiger's mouth can protect friction insert from being damaged.

 

Figure 5 Rear mold core and insert structure
Side buckles of front case and bottom case are all solved by lifters. There are many structures for lifters. Common structures are T-shaped slot drive and roller drive at tail. Size of plastic parts is small and space location is limited. Guide block designed on the back of B board is a small lifter guide. Figure 6 shows a T-shaped lifter seat. Except for sliding fit between upper and lower sides of guide surface and lifter seat without any gaps, a 0.2 gap should be left on all other surfaces. Figure 7 shows structure of pin-through lifter and lifter base. Pin diameter is at least ø4mm, and slider seat hardness is HRC40 or above.

 

Figure 6 T-shaped lifter seat

 

Figure 7 Lifter seat with pin structure

 

Figure 8 Screw-connected lifter seat

 

Figure 9 Improved form of lifter seat with pin structure
Figure 8 shows structural form of screw-connected lifter seat. Tilted top seat is connected to the bottom of tilted top with screws, and spring washers are installed under screws to prevent loosening; a tilted top wear-resistant block is added to push plate to facilitate maintenance and replacement after wear.
Figure 9 shows improved form of lifter seat of through-pin structure. Diameter of pin is at least ø4mm, bottom plane of lifter bears injection pressure, and stress condition is significantly improved compared to Figure 7.