Design of Injection Mold for Notebook C Shell

Time:2020-07-18 08:29:33 / Popularity: / Source:

1 Introduction  

Notebook computer shell is divided into four major parts, A, B, C and D. Notebook A case: top cover of display, large cover is A shell, as shown in Figure 1(a). Notebook B case: frame inside display (side next to it when looking at screen), as shown in Figure 1(b). Notebook C case: Shell next to keyboard is C shell, position of hand rest, as shown in Figure 1(c). Notebook D case: Bottom of machine that contacts desktop is D case, as shown in Figure 1(d). Notebook case is carrier and protective case of functional operating components such as motherboard and processor. It integrates a series of importances such as process design, materials, volume control, weight control, heat dissipation control, rugged safety, and environmental protection. Notebook case materials include ABS engineering plastics, magnesium-aluminum alloys, titanium alloys, carbon fiber alloys, PC-GF (polycarbonate PC), etc. Among them, PC+ABS and aluminum-magnesium alloys are the most common, these two are also the most widely used notebook case materials. This article introduces mold design of notebook C shell made of PC+ABS.
Injection Mold 
Figure 1 Classification of laptop shells

2. Product analysis

Product picture of notebook C shell is shown in Figure 1. Maximum external dimensions of plastic parts are 276.50 mm * 228.30 mm * 9.30 mm, average thickness is 1.50 mm, thickness of button area is 1.20 mm, weight of plastic parts is 78.5 grams, material is PC+ABS, and shrinkage rate is 0.37%.
Appearance requirements of plastic parts are that there must not be any injection molding defects, and plastic parts must not be warped. PC+ABS combines advantages of PC and ABS. Compared with PC, PC+ABS alloy mainly improves melt flowability, moldability, electroplatability and appearance. Compared with ABS, it mainly improves heat resistance, impact resistance and rigidity of thin-walled products.
PC+ABS must be dried before forming to reduce moisture content of material to less than 0.05%, preferably less than 0.02%, in order to improve material processing stability and mechanical properties. When molding PC+ABS, a mold temperature machine is used to control mold temperature. Recommended mold temperature is 50-80℃. Higher mold temperature tends to produce good flow, higher weld line strength, and less product internal stress, but molding cycle will be extended. If mold temperature is lower than recommended, it will cause high internal stress and damage the best performance of part. As far as surface of workpiece and cycle time are concerned, when mold temperature is in the middle of recommended temperature range, good results are expected.
Plastic parts need to be designed with a slider core, and two button positions on the window edge of middle mouse touch screen need to be designed with a sloping top, as shown in Figure 2.
Injection Mold 
Injection Mold 
Figure 2 notebook C shell product diagram

3. Main points of mold design

3.1 Number of cavities

Size of plastic parts and tonnage of injection molding machine is large. Therefore, only one cavity layout can be designed. Mold design drawing is shown in Figure 3. Mold base is FCI4550A80B110C120. Four sides are equipped with zero-degree side locks for precise positioning. Injection molding machine selected is a 250-ton injection molding machine. After calculation, plasticizing ability and mold clamping force meet requirements.

3.2 Design of gating method

Plastic parts are large in size and belong to a flat thin-walled housing. Flow of plastic parts is relatively large. Therefore, it is critical to determine location and number of gates. In mold design, 8-point feeding is selected, see mold design drawing. Among them, gate position at keyboard position is 6 points, and gate parameters are shown in Figure 7. The other two points are large spout lap joint feeding, see Figure 8.

3.3 Design of lateral core pulling system

Two sliders are small in size, and rear die slider driven by inclined guide column is selected for core pulling. Both sloping tops are T-slotted sloping tops.

3.4 Insert design

Size of front and rear mold cores is larger, and it is more difficult to fit directly into fine frame of mold plate. Therefore, front and rear mold cores are respectively designed with squeezing blocks, with reference angle as reference, two sides away from reference angle, mold frame is enlarged by 1mm, and squeezing block is pressed. There are two types of inlays for rear mold core small inserts, one is hanging table and the other is taper, each with its own characteristics. Design of small insert hanging table has many advantages: first, it reduces drilling and tapping processing of mold base and inserts; second, it simplifies workload of mold assembly; third, it can avoid possibility of mistakes in missing screws. Main points of design of hanging platform are as follows: (1) Hanging platform of insert should be selected on the long side of insert, and at the same time avoid curved parts. (2) It must be ensured that hanging table and its location can be ground or wire cut. (3) Short hanging platform should avoid flat jack to avoid interference. (4) In short, design of hanging platform must consider processing technology, and it cannot be designed at will. (5) When there is a water-carrying rubber ring on the bottom of insert, do not use a hanging platform, but fix it with screws to prevent water leakage.
Injection Mold 
Injection Mold 
Injection Mold 
Injection Mold
Injection Mold 
Injection Mold 
Injection Mold

3.5 Cooling system design

Mold has a good cooling system, see mold design diagram 3.

3.6 Ejection system

In addition to eject, ejection of plastic parts is also designed to eject cylinder and eject pin, see mold design drawing 2.

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