Forehead temperature gun bracket belongs to PCB bracket inside portable forehead temperature measuring instrument. Product diagram is shown in Figure 1. Maximum external dimensions of product are 65.00mm * 10.09 mm * 42.20 mm, average thickness of plastic parts is 0.86 mm, and material of plastic parts is ABS, shrinkage rate is 1.005, weight of plastic part is 11.2 grams. Technical requirements for plastic parts are that there shall be no defects such as peaks, underfilling, flow lines, pores, warpage deformation, silver lines, cold materials, and spray lines.

 

Figure 1 Product Diagram of Forehead Thermometer Bracket
As can be seen from Figure 1, appearance of forehead temperature gun bracket is a saddle-shaped curved surface, glue position of head and tail is inclined. Difficulty of mold design is design of two slider core-pulling mechanisms. In addition, shape of plastic part is an irregular shape, and column position of rear mold of plastic part needs to be placed vertically in order to be demolded smoothly.
Mold design is shown in Figure 2, cavity ranking is 1 cavity, mold base is GC1823 80 60 70 OH230, parting surface is a steep curved surface, cavity is subjected to a large lateral force during injection molding. In order to avoid force deviation of cavity, tiger mouth positioning is designed at four corners of front and rear mold cores, as shown in Figure 3. When milling curved surface, it is necessary to use a milling cutter with a larger diameter. Distance D between raised positioning tab on parting surface and curved surface needs to satisfy D>d+1, where d is diameter of milling cutter. Size here needs to be larger than tool diameter to facilitate CNC machining. This is a problem of mold processing technology and is often ignored. Cutting amount of tool with too small diameter is very small, which is time-consuming and labor-intensive, and quality of machined surface is not high, so more attention should be paid to surface machining.
Parting surface of this curved surface needs to be directly milled and formed by a high-speed machining center during processing, and manual trimming process is avoided. When front and rear mold cores are flying, a gap of 0.01 should be left on parting surface to facilitate exhaust. Middle glue position of rear mold core is divided into inserts, which are installed on rear mold core with a hanging table, which is convenient for exhausting and avoids workload of sparking.
Small inserts in the center of movable die are of irregular shape, and it is very important to choose a reasonable processing technology. Because this insert has a small width and a large height dimension, it is not rigid enough for CNC machining. Processing process diagram is shown in Figure 4. After processing technology is material preparation, wire cutting is performed first, and excess steel material on the top of insert is first cut off. Then CNC processing, after CNC processing, hanging table is set aside, and shape is processed in place by wire cutting.
Gating system is designed with side gate and one-point injection. Due to design of front mold slider at head of mold, panel and A plate need to be separated when mold is opened. Therefore, gate sleeve is fixed on the back of A plate with screws. Positioning ring is fixed on panel and is designed separately from sprue sleeve.
Slider at head of plastic part is designed with a core-pulling structure for slider of front mold. Horizontal sliding block is driven by curved pin, and horizontal sliding block drives inclined sliding block through T-slot to complete core pulling. Separation of panel and A plate is limited by a small tie rod, and a spring is set on small tie rod to assist mold opening. A resin shutter is designed between A and B plates of mold to assist sequential parting of mold. Head of bent pin is beveled, insert is designed on the back of A plate to be inclined, and backhoe is designed to match head of bent pin. Rear mold slider at tail of plastic part is an oblique core-pulling and is driven by an oblique guide column.
Ejection of plastic parts is ejected by flat thimble and thimble.
Mold is a small mold, two straight-through water transports are designed in the front and rear molds, which effectively ensures normal progress of injection molding.

 

 

 

Figure 2 Forehead temperature gun bracket mold diagram

 

Figure 3 Machining of parting surface of front and rear mold cores

 

Figure 4 Process diagram of movable die inserts