Maximum size of scanner shutter product is 121.80 mm * 88.86 mm * 25.77 mm, average thickness of plastic part is 2.70 mm, the material of the plastic part is PC+ABS, shrinkage rate is 1.005, weight of plastic part is 18.35 grams. Technical requirements of plastic part are that there must be no defects such as peaking, unfillling injection molding, flow lines, pores, warpage deformation, silver lines, cold materials, jet lines, bubbles and so on.

 

Through hole, need to design core pulling mechanism. Product diagram of scanner shutter is shown in Figure 1. Plastic part is a complex bracket. Although there is no complicated curved surface, height fluctuation is large and shape is complicated. Another feature of plastic parts is that shape is symmetrical. In the product, plastic part assumes a functional supporting role and is a key part of product. There are 4 vertical vertical walls in the middle of plastic part, each of which has a ø3.2 through hole. 4 holes here must ensure concentricity requirements to facilitate flexible rotation of other related parts after assembly. At the openings at both ends of U-shaped plastic part, there is a piercing hook for assembling other original parts. There is a hook at the bottom of U-shaped part. All these installation positions require accurate dimensions. Therefore, plastic parts have higher requirements for geometric tolerances. Plastic part material PC+ABS, commonly known as plastic alloy, combines excellent properties of two materials, namely formability of ABS material and mechanical properties of PC, impact strength, temperature resistance, and ultraviolet (UV) resistance. Difficulty of mold design is selection of mold opening direction, design of parting surface and sliding core pulling mechanism with 4 through holes. Parting surface analysis of plastic part is shown in Figure 2. Due to large size and complex structure of plastic part, parting surface is undulating, and there are many rubbing positions. Mold layout is 1 cavity. Mold base is standard mold base CI3035 A70B110C90. Design diagram is shown in Figure 3. For this set of molds, choice of mold opening direction is very important. Qualitative analysis shows that there is not much difference between plastic part's tightening force on the front mold and back mold. No matter which side of plastic part is designed on the front mold, there is a risk of sticking to front mold. In actual mold design drawing, side with more bones was chosen to be fixed mold. Advantage of this design is that stroke of slider is small. But four holes in the middle of plastic part are easier to stick to front mold. For this reason, a core-pulling method combining rear mold slider and front mold oblique elastic slider is designed. Front mold oblique elastic slider can overcome tightness of front mold by plastic part while pulling core. Front mold oblique elastic slider is limited by limit block 21, see cross-sectional view M-M. Injection method of mold is a large nozzle mold, gate is a side gate, 3 points injection, see mold design diagram 3.

 

Figure 1 Scanner shutter product picture

Design of ejection system of plastic part is very critical. Two ends of plastic part are symmetrical along center line. Therefore, ejection system design is also completely symmetrical. Ejection force at both ends is exactly same. Ejection system all use pin to eject. Thimble hole is cut with a slow-moving thread, diameter of hole and unilateral clearance of thimble are 0.01, which can effectively exhaust air without flare. Method of detecting thimble gap is to insert thimble from back mold core and it can be easily rotated without jamming. Depth tolerance of thimble on thimble board is 0.02 to prevent thimble from jamming, maintain ejection force balance, and avoid ejection deformation of plastic part.

 

Figure 2 Analysis of parting surface of scanner shutter