Mobile phone shell product is shown in Figure 1. Maximum size of product is 97.62 mm * 43.76mm * 11.80 mm, average thickness of plastic part is 1.10 mm, material of plastic part is ABS+PC, shrinkage rate is 1.006, and weight of plastic part is 5.80 Grams. Technical requirements for plastic parts are that there must be no defects such as peaks, underfilling of injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, and jet lines.

 

Figure 1 Product Picture of Mobile Phone Case
This is an old-fashioned mobile phone case. This mobile phone has been eliminated, but its mold structure can still be studied. It can be seen from Figure 1 that plastic part structure is a flat shell, with 13 large and small button holes on the front, a rectangular display window on upper part.

 

Mobile phone shell is composed of upper and lower shells. After upper and lower shells are assembled, joint surface is required to be smooth without scratching, and appearance is beautiful. Mobile phone shell is a very demanding plastic part with high appearance, which has high requirements on mold. Plastic part of mobile phone shell is made of ABS+PC, commonly known as plastic alloy, which has high toughness and strength, as well as good injection performance. The most important thing is plastic alloy products, which will not crack when dropped on the ground, which can meet requirements of mobile phone products.
According to accuracy requirements of mobile phone case, mold design cavity rank is 1 cavity. Mold base is standard mold base CI2330, cavity rank is 1 cavity not because production batch of mobile phone case is small, but accuracy is determined. Mold design drawing is shown in Figure 2. Gate position of mobile phone shell is selected in the middle of two windows on the top surface of shell, and a single hot nozzle is used to inject glue at one point. After plastic part is assembled, gate position is covered by lens, which will not affect appearance of plastic part.
There are 4 hooks for assembling on the edge of plastic part. See attached 3D drawing. It is necessary to design movable mold slider. There are 3 undercuts on inside that need to be designed for inclined ejection. Because movable die slider is very small, a barb is designed on slider to replace inclined guide post. Three inclined roofs all adopt inclined roof of MLM sub-structure. Minimum pin diameter here is ø4. There is a key point in mold design, middle insert of movable mold (blue insert), insert must be designed here and cannot be made into original structure. Because original body is left, electrical discharge processing is required, which will make edges of plastic parts of mold not clear enough, and it is difficult to vent during injection molding.

 

Movable and fixed molds are designed with sufficient cooling and water transportation. Fixed mold has a set of water transportation IN5 and OUT5 close to parting surface. This group of water transportation needs to be connected to hot oil during injection molding to increase cavity mold temperature, improve appearance quality of plastic parts, avoid welding marks outside each button hole. Hot oil has a high temperature, a long throat nozzle is required to be directly connected to mold core, and it is not suitable to use a rubber ring to seal.
Ejector of plastic parts adopts a thimble and a cylinder. Because diameter of cylinder is small and there are 3 lifters, ejector plate of mold must be guided by center to avoid failure of ejection mechanism. An inclined top guide block is also designed on the bottom surface of B board.

 

 

 

 

 

 

Figure 2 Mould diagram of mobile phone shell