1. Due to volume change caused by crystallization during molding process of plastics, internal stress is strong, residual stress frozen in plastic parts is large, and molecular orientation is strong. Therefore, shrinkage rate is larger than that of thermosetting plastics, shrinkage range is wide, and directionality is obvious. In addition, shrinkage after molding, annealing or humidity adjustment treatment is generally larger than that of thermosetting plastics.
Structure of refrigerator drawer is shown in Figure 1. Dimensions are 434mm * 401mm * 134mm, average wall thickness is 3mm, volume is 902979mm³, material is transparent GPPS, and mold adopts a 1 cavity structure. Shape of plastic parts is relatively large, and there are undercuts on the outside and inside. Deepest undercut inside is 26mm, and outside is a circular arc.
Left end cover of vacuum cleaner is an important part of vacuum cleaner housing. Product picture is shown in Figure 1. Maximum size of product is 102.13 mm * 62.36 mm * 26.40 mm, average thickness of plastic part is 1.80 mm, material of plastic part is PC, shrinkage rate is 1.006, weight of plastic part is 90.82 grams. Technical requirements for plastic parts are that there must be no defects such as peaks, uncompleted injection, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, bubbles, etc.
Printer clamshell product is shown in Figure 1. Maximum external dimensions of product are 197.86 mm * 130.14 mm * 45.20 mm, average plastic position thickness of plastic parts is 2.0 mm, material of plastic parts is HI-PS, shrinkage rate is 1.005, weight of plastic parts is 60.62 grams. Technical requirements of plastic parts are that there must be no defects such as peaks, unfilling of injection molding, flow lines, pores, warpage, silver lines, cold materials, spray lines and other defects. Difficulty of mold design is that front and rear molds need to be designed with oblique core-pulling mechanism, and plastic parts must not be deformed after molding. Front and back molds of plastic parts are appearance surfaces, gate marks and eject marks cannot be produced.
Figure 1 shows emergency oxygen switch shell of an ambulance. Plastic part is composed of three parts. Main body is a cylindrical plastic part with a U-shaped opening in the middle. Upper and left ends are respectively semicircular shells. Total height of plastic part is 187mm. The largest fragment of cylindrical shell is ϕ76mm, and lower end of upper semicircular shell of plastic part is provided with a symmetrical concave on both sides. Plastic part is injection-molded. Difficulty in design of mold structure is demolding of two undercuts on inner wall of cylindrical shell of plastic part. Undercut has a width of 12mm, a depth of 3mm, and a height of 8mm. Design difficulty of demoulding mechanism with two undercuts is: if lifter mechanism is used to eject side core, head of lifter block is likely to interfere; if a relatively small lifter ejection angle and upper ejection distance are set, it exceeds total height of enlarged mold base and increases mold manufacturing costs.
High gloss injection molding is also known as rapid heat cycle molding (RHCM) and steam-assist injection technology (SAIT). High gloss injection molding can effectively eliminate defects such as weld marks, ripples, silver lines, and floating fibers on the surface of product, improve strength and quality of molded products. Products formed using this technology have higher gloss, can save secondary … Continue reading Numerical simulation analysis and process optimization of high gloss injection molding of complex structure products
Generally speaking, to determine whether a product can be mold-opened, one should follow this line of thinking: Product appearance and requirements → structure → gate → demoulding Why is it like this? Next, I will take a product as an example to illustrate that changes in thinking caused by various factors during entire design process lead to excessive changes in mold design results.
Interior of car glove box is used to store items. When glove box is closed, its appearance can be seen, as shown in Figure 1 (a). In order to make outer surface of glove box beautiful and comfortable, give users a good experience, an outer cover must be added to outer surface of glove box, as shown in FIG. 1 (b), outer cover and glove box are integrated by ultrasonic welding. Such a design scheme can be realized not only in process, but also in consideration of appearance requirements of product.
Under background of increasingly fierce market competition, various plastic products with peculiar shapes stand out, leading to more and more diversified injection mold structures. When making 3D data for large injection molds, it is necessary to assemble tens of thousands of parts together. There are often some interferences in the movement of certain parts. Such interference problems are difficult to discover in time, will be exposed during mold assembly and mold testing. Some corrective measures need to be taken, and sometimes even re-machining is required to eliminate problem. This increases manufacturing cost of mold, and at the same time extends manufacturing cycle, which affects reputation and long-term development of company. Therefore, it is particularly important to establish a motion simulation for large scale injection mold.
Black spots and impurity defects are the most important factors for rejection rate in normal production process. It mainly affects appearance of product and leads to scrap. Impurities and most black spots are foreign substances, have nothing to do with raw material itself, while a small part of black spots and impurities are caused by raw material itself.