Bottom case of mobile phone is shown in Figure 1. Maximum size of product is 97.50 mm * 43.85mm * 10.10 mm, average thickness of plastic part is 1.00 mm, material of plastic part is ABS+PC, shrinkage rate is 1.006, and weight of plastic part is 7.16 Grams. Technical requirements of 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, jet lines, etc.

 

Figure 1 Product Picture of Mobile Phone Bottom Case
Mobile phone shell is composed of upper and lower shells. After upper and lower shells are assembled, joint surface is required to be smooth and not scratchy, appearance is beautiful. Mobile phone shell is a very demanding plastic part with high appearance, which has high requirements on mold. Plastic parts of mobile phone shell are made of ABS+PC. Last article has analyzed key points of mold design of face shell, this issue will continue to analyze and introduce key points of bottom shell mold design.
Mobile phone shell mold is a precision mold. Mold cavity is ranked 1 cavity. Mold base is a standard mold base CI2330. Left and right sides of mold base are designed with a slope positioning block to facilitate precise mold clamping and resistance to lateral force during injection molding. Glue feeding method of mold is to feed glue at one point at a point, using a single hot nozzle to feed glue, and glue feeding position is on the top surface of plastic part.
Mobile phone shell is divided into a front shell and a bottom shell, the two are usually assembled tightly with a buckle. Therefore, key points in design and production of mobile phone shell mold are design of lateral core pulling mechanism and design of lifters. Generally, cross-section size of inclined roof of mobile phone shell mold is small. Therefore, lifter needs to be paid attention to when making:
(1) It is made of better steel, which needs to have higher toughness and wear resistance.
(2) Wire cutting accuracy should be high, medium wire or slow wire wire cutting is often used.
(3) There must be an oil groove on non-glue position of lifter. Oil tank is more than 10mm away from glue position.
(4) For long-life molds produced for a long time, lifter surface needs to be nitrided, PVD treated, and DLC treated. DLC film not only has excellent wear resistance, but also has a very low friction coefficient, generally lower than 0.2, which is an excellent surface anti-wear modified film.

 

(5) Clearance. There should be a large gap between small lifter of mobile phone shell mold and back mold core to have a long life. As saying goes, lifter should be looser.
(6) For lifter, make a guide block on the back of B plate, and use guide block to guide to avoid damage. For guide block, see part 5 and part 33 in mold design diagram 2.
Plastic part structure is a flat shell, and there are three places around it that need to be designed with lateral core pulling, one of which is front mold slider. For hot runner or hot nozzle molds, since fixed mold plate is fixed, no mold plate can be separated, so it is difficult to design front mold core. In this set of molds, front mold slider 21 of cylinder core is designed. For front mold slider of oil cylinder core-pulling, if area of core-pulling is small, lateral force of slider expansion is not large, and oil cylinder can be used directly without need for wedge locking. This is the case of this set of molds, and core is drawn directly with an oil cylinder. Two outer slides are movable mold slides, which are driven by oblique guide posts.
Both front and rear molds are designed with a wrap-around direct water transport, which effectively guarantees normal progress of injection molding. Water transported around front mold is hot oil, water transported around hot nozzle is cold water, and water transported by rear mold is cold water. Main purpose of passing a set of hot oil to front mold is to increase surface temperature during injection molding and improve appearance quality of surface of plastic part.
In addition to lifter, ejector of plastic part is also designed with a thimble.

 

 

 

 

 

 

 

 

Figure 2 Mould diagram of mobile phone bottom case