A building intercom is a communication and intercom control device installed at the entrance of a building anti-theft door. Host is generally installed on anti-theft door of each unit or near wall. Host consists of panel, bottom box, operation part, audio part, video part, and control part.
Maximum external dimensions of building intercom shell products are 227.76 mm * 173.0 mm * 41.90 mm, average thickness of plastic parts is 2.50 mm, material of plastic parts is ABS, shrinkage is 1.005, weight of plastic parts is 111.35 grams. Technical requirements of plastic parts are are that there must be no defects such as peaks, dissatisfaction with injection molding, flow lines, pores, warpage, silver lines, cold materials, spray lines, air bubbles and so on.

 

It can be seen from Figure 1 that plastic parts belong to small household electrical appliances with smooth surfaces. A sunken circular arc surface exists locally on the top. Place intercom handset in this position. There are two raised posts at the front end of sinking arc surface, with through holes inside, which need to be formed by front mold slider. There is a cylinder on the edge of large curved surface of plastic part and a through hole in the inside, and this hole needs to be designed with a sloping top inside plastic part. Three bone position are designed on the inner edge of plastic part for assembly with product bottom shell. All of these bone positions need to design inner slider (or inclined top) to be demolded. One of bones is close to inner hole that needs to be demolded, see Figure 1.
There are 15 button holes on the top surface of plastic part, and corresponding arc bone positions are designed on the back side for button guidance. These bones tend to form trapped air during injection molding. These parts require cutting inserts for exhaust. On the other hand, these parts must have high processing accuracy to avoid influence of pincers on the function of button. In addition, attention should be paid to demolding slope of bone position of button. If demolding slope is too large, gap between button and hole is too large, there is a possibility that button may tip over during movement, and there may be a phenomenon of seizure. If gap between button and hole is too small, button will also be stuck. Therefore, button and key hole clearance must be selected reasonably.
Plastic parts are large in size and complex in structure, and there are many places in inner slider, front mold slider and lifter. Mold design cavity layout is 1 cavity, and mold base is standard mold base DCI4045 A=100 B=120; use of a standard fine nozzle mold base can facilitate core pulling of front mold slider and at the same time facilitate gate to inject. Four corners of front and rear mold cores are positioned with tiger's mouth to ensure accurate mold clamping.
Plastic parts belong to larger appearance parts, and gates are designed on the top surface to facilitate injection molding. Ideal situation is to design gate in a hidden position, where product can be covered after assembly. Due to large plastic parts, especially deep bones on the back of 15 key holes, it is difficult for plastic to flow and fill, so a gating system with a small nozzle to a large nozzle is designed, that is, after molten plastic is injected into center of square hole using a point gate, it is changed to a two-point side gate to inject. Runner system

 

Figure 1 Product picture of building intercom face shell

 

Design parameters are shown in mold design drawing 2. Because nozzle material is on the side of machine nozzle, in order to balance material and facilitate storage of cold material, a tapered inverted material pulling mechanism is designed at the end of large machine nozzle. See enlargement U.
Front die slider is driven by a T-slot. Inner slider is driven by a shovel 33. There is a cylinder on the edge of large curved surface of plastic part, and there is a through hole in the inside, this hole needs to be designed with a lifter inside plastic part. In this part, a mold structure in which rear mold slider and lifter collide with each other is designed. When designing mold of rear die slider and lifter, it is necessary to carefully observe the form of collision between two, whether there is interference, and how much interference is, how to solve it. Lifter of this set of mold is under slider, so it is necessary to design the first reset mechanism. Various situations and solutions of interference between slider and lifter are shown in Figure 3.

 

 

 

 

 

 

 

 

 

 

Figure 2 Mould drawing of building intercom face shell products

 

Figure 3 Various situations of interference between slider and inclined top