Upper cover of scanner is shown in Figure 1. Maximum size of product is 276.43 mm * 57.29mm * 30.63mm, average thickness of plastic part is 2.50 mm, material of plastic part is HIPS, shrinkage rate is 1.004, and weight of plastic part is 35.19 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 scanner cover
This is upper cover of a certain brand scanner of NEC Corporation. Plastic part is shaped as a flat long shell, and there are 4 undercuts on back bone. It is necessary to design lifter to release mold. Outer end surface of the deepest bone position on the back is a vertical surface, and it is necessary to design back mold slider core to solve demolding problem. See attached file 3D diagram.
Production batch of plastic parts is large, combined with structural characteristics of plastic parts, mold design cavity is ranked as 1. Mold base is standard mold base CI3550, edge code position of mold panel and bottom plate is milled and thinned, only thickness of 25 is retained, which is convenient for code molding. In domestic mold design, general code mold parts are not processed for I-shaped mold bases. For large molds, where panel or bottom plate is thick, press plate code mold may be used directly, which may be difficult to compact, which may cause safety hazards. Japanese customers' code molds, for large and medium-sized, especially large molds, are mostly horizontal code molds, that is, molds are not hoisted in from air, but are moved horizontally. It is basic requirement to mill code mold part to be thin. See mold design shown in Figure 2.
Precise positioning of mold adopts 4 conical positioning parts on the edge of mold base to offset lateral force generated during injection molding. Mold alignment direction is relative alignment of two holes. Head and tail are arranged crosswise, which is convenient to maintain balance of injection force. Glue feeding method is a latent gate, a ø2.5 thimble is inserted into glue, and each hole has a gate.
Ejection of plastic parts adopts inclined ejector and thimble ejection. There are many structural design methods for inclined roofs. This set of mold adopts lifter with a pin structure. Lifter structure is shown in Figure 3. Two rounded corners are made on the bottom edge of lifter. Note that bottom of lifter is in smooth contact with thimble bottom plate, pin is in close contact with inclined top groove on the top of thimble, and circumference is tangent. Another point to note is pin diameter. Pin diameter cannot be less than ø4. Pin material is generally modified by SKD61 thimble.
Another small detail of Japanese molds is handling of small inserts. Small insert is shown in Figure 4. Japanese molds require small inserts to be designed with a hanging table, and screw connections are not allowed. The biggest disadvantage of fixing small inserts with screws is that it is easy to cause missed installation errors. Because of small screws on the back of mold plate, when mold plate is thicker, counterbore of screw will be deeper, it is difficult to see clearly if screw is installed or not, which brings trouble to mold assembler. This kind of error can be avoided by using hanging station connection.
Standard parts of Japanese molds mostly use MISUMI brand, and there is a domestic standard. Steel mostly adopts NAK80, movable mold can also adopt NAK55. Etching pattern needs to adopt Nihong standard.

 

 

 

 

 

 

Figure 2 Diagram of upper cover mold of scanner

 

Figure 3 Lifter

 

Figure 4 Hanging platform