Ear thermometer bottom shell product is shown in Figure 1. Maximum dimensions of product are 145.30 mm * 28.83 mm * 31.64 mm; average thickness of plastic part is 1.60 mm, material of plastic part is ABS, shrinkage rate is 1.005, and weight of plastic part is 18.45 grams. Technical requirements for plastic parts are that there should be no defects such as peaking, injection dissatisfaction, flow lines, pores, warping deformation, silver streaks, cold material, and jetting lines, and meet ROSH environmental protection requirements.

 

Figure 1 Product picture of ear thermometer bottom case

 

Figure 2 Mold 3D drawing (sketch)
Shell of ear thermometer product generally consists of 4 large parts. Upper and lower shells are assembled into one body. The front end is designed with a sensor head. Product must be temporarily stored in storage box when it is in use. There are various shapes of ear thermometer products, and there are a variety of products, but basically the outer shell is composed of four parts: upper and lower shells, storage box cover and sensor head. Basic structure of upper and lower shells is a slender and curved structure, and edges are connected by multiple buckles. After upper and lower shells are assembled, art lines are required to be neat and beautiful. Therefore, molds of these four plastic parts generally have following characteristics:
1. Parting surface of upper and lower shell molds is not a plane, and often includes inclined slopes or curves. Most of complex parting surfaces are on the head of plastic part, that is, part where sensor head is assembled. Parting surface here determines quality of assembled art line of upper and lower shells, and also determines appearance quality of assembled sensor head. Therefore, parting surface needs to improve processing quality. Parting surface can be processed and formed by a high-speed machine at one time, and some are formed by wire cutting. Which processing technology to use depends on structure of mold and conditions of processing machine tool. To produce high-quality plastic parts, one of the most basic principles is that processing quality of curved parting surface is high, and manual filing cannot be used. Parts after manual filing lose processing standard, product is deformed, and quality cannot be guaranteed.
2. Mold for storing box cover has been introduced in previous article. Shape of storage box cover is similar to that of shoes, and its mold structure often has an inclined slider of front mold. Design of slider of front mold here is somewhat difficult.
3. Mold of sensor head also has a typical structure, which was also introduced in previous article. Plastic part is a rotating body or an approximate polygonal shape, mold structure is a Huff mold structure, and arrangement is a linear arrangement.
4. Upper and lower shell molds of ear thermometer, slider or slanted top design space is small, and small slanted top needs to be well guided. For small slanted roofs, matching clearance should not be too small on the basis of ensuring that rubber can be sealed, so that service life of slanted roof can be appropriately extended.
5. For bottom shell shown in this set of molds, due to structural reasons of plastic parts, care must be taken not to deform plastic parts when ejecting.
It can be seen from Figure 1 that structural shape of plastic part is U-shaped with one end closed, and there are two undercuts on inner side of edge. It is necessary to design core-pulling of inner slider. Design structure of inner slider is shown in Figure 3. Since inner sliders need to be designed on both sides of plastic part, which will occupy a large mold space, mold design cavity arrangement is 1 cavity, and inner sliders are dynamic tunnel sliders. Mold base is fine nozzle DCI2330, and gate is a point gate to inject glue one by one.

 

Figure 3 Analysis diagram of mold structure
Typical sliding block core-pulling mechanism in moving mold is shown in Figure 4. In order to facilitate processing, this set of molds divides moving mold core into 2 pieces to form a tunnel-type slider structure.

 

Figure 4 Slider core-pulling mechanism in the moving mold
1. A plate 2. Spring 3. Inclined guide post 4. Inner slider 5. B plate 6. Core 7. Backing plate
Plastic parts are ejected using cylinder and thimble. Since thimble and cylinder are small, in order to ensure stable ejection, ejector plate needs to be designed with a center guide. Front and rear molds of the whole set of molds need to be cooled and transported to ensure that injection molding operation can continue normally.