Bottom case of electronic sphygmomanometer is shown in Figure 1. Maximum external dimensions of product are 180.00 mm * 175.00 mm * 50.47 mm, average thickness of plastic parts is 2.50 mm, plastic parts are made of ABS, shrinkage rate is 1.005, and weight of plastic parts is 128.41 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 bottom case of electronic sphygmomanometer
Electronic sphygmomanometers are common medical devices and electronic products. Arm-type sphygmomanometers can be placed on desks or hung on indoor walls. Figure 1 shows typical design structure of bottom case of electronic sphygmomanometer. Bottom case has a sunken battery compartment. There are several small steps on the edge of battery compartment, which are used to match battery cover. There are small buttons on one side to facilitate assembly of battery cover hooks. Bottom of battery compartment is arc bone position for battery positioning, there are small and narrow grooves on edge to clamp spring of negative electrode of battery. For aesthetics and ease of mold manufacturing, battery compartment generally needs to be designed with fixed mold inserts. Label position also needs to be designed with inserts, so that edges and corners are sharp. Four corners of bottom case have pits for bonding soft foot pads. Usually, gates are designed in pits, and number of gates is 2~4. This set of molds is designed with two gates, which are arranged diagonally. See Figure 3. There are small holes or undercuts on three sides of plastic part, and a fixed mold slider needs to be designed. Generally speaking, there will be side holes on the side of bottom case of electronic sphygmomanometer, and a fixed die slider must be designed. Round hole on the side is hole for using hose inlet connector, and square hole is hole for data transmission USB connector. Most of electronic sphygmomanometer shells are made of ABS. For example, electronic sphygmomanometer of Citizen in Japan is often produced by ABS 757.

 

Figure 2 3D mold design

 

 

Figure 3 2D mold structure diagram
Edge of bottom case has a ring of notches, and another step is art line. Art line is gap specially reserved for top shell and bottom shell after assembly. At upper and lower contact points of plastic shell, in order to make contact points closely, upper shell is usually less than lower shell, and a part of lower shell extends into upper shell. In this way, even problem of insufficient straightness of shell edge due to injection molding process can be solved. During assembly, it can be seen that there is a uniform gap between upper and lower shells, which is called "art seam" or "art line".
Size of plastic part is large, three sides need to design fixed mold slider core pulling mechanism, mold design cavity layout is 1 cavity, mold base is DCH 4040 A80 B107.5 C120, mold parting surface is a curved surface, front and rear mold cores are positioned with four corners. Rear mold core cuts a large central insert at position of plastic part stop, which is convenient for exhaust and mold processing. Mold adopts 2-point injection of fine nozzles, 2-point gates are designed in pits for bonding soft foot pads and are arranged along diagonal. Some bottom shells have many back mold bones, and when bones are deep, it is necessary to design a point gate in each pit, that is, design 4 points of glue.
Three holes on the side of plastic part are all designed with fixed mold sliders. There are many structures of fixed die slider core pulling, the most basic is structure driven by T-slot. Most of T-slot drive sliders are used in situations where space is small or it is inconvenient to use bent pins or inclined guide posts. T-slots are usually processed by wire cutting. There is a buckle on the edge of plastic part, which is ejected by lifter. Ejection of plastic parts is mainly ejected by ejector pins.
Fixed mold of mold adopts straight-through water transportation, movable mold adopts combination of straight-through water transportation and pond for cooling.