Instrument window panel product is shown in Figure 1. Maximum size of product is 317.93 mm * 167.80 mm * 118.80 mm, average thickness of plastic part is 1.50 mm, material of plastic part is PP TD20, shrinkage rate is 1.012, and weight of plastic part is 161.18 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, jet lines, etc.

 

 

Instrument window panel is internal bracket of front instrument panel of a Japanese car's cab. According to requirements of use of plastic parts, it is made of PP TD20. This material is made by adding calcium carbonate (talc) to PP to improve physical properties of plastic by adding fillers. Common use of PP material to add calcium carbonate is to manufacture refrigerator drawers and car bumpers. It can be seen from Figure 1 that structure of plastic part is complex. Plastic parts have large fluctuations in height and many small scratches on edges. Main difficulties in mold design of this plastic part are gate design, plastic part filling, how to ensure dimensional tolerances and how to prevent ejection deformation. On the other hand, mold structure of plastic part is simple, and there is no complicated structure such as a slider. Two inclined roofs are designed for ejection needs, to avoid clamping plastic parts during ejection.
Size of plastic part is relatively large, and mold design cavity rank is 1 cavity. Mold design drawing is shown in Figure 2. Mold base is a non-standard mold base CI 5075 that imitates standard mold base design. In order to adapt to coding method of Japanese injection molding machine, mold base is chamfered on one side, and there is no design positioning ring. A large area sinking code mold slot is opened on panel and bottom plate. At the same time, design screw holes for code patterns on the sides of panel and bottom plate. Code pattern slots of panel and bottom plate are shown in Figure 4 and Figure 5 respectively. Parting surface spacing of AB board is designed to be 15, and two balance blocks 21 are designed on movable mold side of parting surface to balance force of the mold. In movable part of mold, positioning pins are designed between plates of mold base to increase rigidity of mold.
Gating system is designed with a latent gate design. Enlarged view of sprue bushing design is shown in Figure 6. Here, bushing is 0.2 to 0.25 larger than sprue bushing on one side, so as not to form an undercut and affect removal of sprue material. After molten plastic enters parting surface from main runner in small mouth 01, it sneaks into cavity from center of large round window through latent gate.

 

Size of plastic part is larger, so size of front and rear mold cores is correspondingly larger. Therefore, the lower frame of mold core is positioned and pressed by squeezing block. Four corners of front and back molds are locked with tiger mouths. For front mold core, combined with structural characteristics of plastic part, front mold core is divided into two parts, two parts are locked with each other with an inclined plane, and locked together with screws. Piercing position of edge of plastic part is all made of inserts.
Height of plastic part is large, tightening force on back mold is large, and force is uneven. Two ends of plastic part (side of mold world) are designed with an inclined roof. For rear mold, ejection mechanism must be designed. If it is designed for a straight top, it will clamp plastic part, so inclined top is designed. Three semi-circular raised edges have the largest ejection force, and are designed with a straight top, and the other parts are designed with a thimble to eject.
In order to make ejection mechanism smooth, a guiding mechanism must be designed for ejector plate. Guide post 08 and guide sleeve 09 adopt MISUMI standard parts to guide ejection mechanism. This kind of guide post is directly inlaid on the back of B board and bottom plate, accuracy is higher than that of guide post directly fixed on bottom plate, and at the same time, it plays role of supporting head. Travel switch 16 is designed to ensure mold return. Ejector rod in ejector hole is also designed with a special ejector rod.

 

 

 

 

 

 

 

 

Figure 2 Mould diagram of instrument window panel

 

Figure 3 3D mold diagram

 

Figure 4 Design of code die slot of panel

 

Figure 5 Design of code die slot of bottom plate

 

Figure 6 Gate sleeve design