Normal > Accurate plastic products, and the high degree of automation of the molding process, has a wide range of applications in plastic molding processing. However, with the increasing application of plastic products for hearing, people have put forward higher requirements for the accuracy, shape, function, and cost of plastic products. The traditional injection molding process has been difficult to meet this requirement, mainly in the production of a large area structure. When making parts, high melt viscosity requires high injection pressure, high injection pressure requires large clamping force, thereby increasing the cost of the machine and mold; 2 production of thick-walled parts, it is difficult to avoid surface sink marks and internal Shrinkage hole, poor dimensional accuracy of plastic parts; 3 When the processing fiber increases the composite material, it lacks the ability to control the orientation of the fiber, the fiber distribution in the matrix is random, and the reinforcing effect cannot be fully exerted. Thus, on the basis of traditional injection molding technology, some new injection molding processes have been developed, such as gas-assisted injection, shear control orientation injection, laminar injection, melt core injection, low pressure injection, etc., to meet the needs of different application fields. .
Normal > 1. Gas (water) assisted injection molding
Normal > Gas-assisted injection molding is one of the most important developments in injection molding technology since the introduction of reciprocating screw injection molding machines. It produces a hollow cross-section through the high-pressure gas inside the injection-molded parts, uses the volumetric pressure of the gas to reduce the residual internal stress of the products, eliminates the surface sink marks of the products, reduces the use of materials, and shows the superiority that can not be compared with the traditional injection molding. Gas-assisted injection process includes three stages:
Normal > The initial stage is melt injection. At this stage, the plastic melt injection cavity is the same as conventional injection molding, but the melt only fills 60%-95% of the cavity , and the specific injection volume varies with the product.
Normal > The second stage is gas injection. At this stage, high-pressure inert gas is injected into the melt core, and the melt front continues to flow forward under the pressure of the gas until it fills the entire cavity. Gas-assisted injection melt flow distance significantly shortened melt injection pressure can be greatly reduced. Gas can enter the workpiece through the gas injection element from the main flow path or directly from the cavity. Since the gas has the property of always selecting the direction of the least resistance (high temperature, low viscosity) penetration, it is necessary to specially design the gas passage in the mold.
Normal > The third stage is gas pressure maintenance. This stage cools the part while keeping the gas pressure. Further use the isotropic pressure transmission characteristics of the gas to press outward uniformly inside the part, and supplement the volume shrinkage (secondary penetration) caused by the cooling and solidification of the melt through gas expansion to ensure that the outer surface of the product adheres tightly Mold wall.
Normal > Gas-assisted technology has enabled the injection molding of many parts that could not be traditionally injection-molded, and has been possible in almost all plastic parts of automobiles, home appliances, furniture, electronic devices, daily necessities, office automation equipment, building materials, etc. Has been widely used, and as a challenging new process for plastic molding opened up entirely new applications. Gas-assisted technology is particularly suitable for making injection-molded products in the following areas:
Normal > 1) Tubular, rod-shaped products
Normal> such as handles, hooks, chair armrests, shower heads, etc. The hollow structure can be used without affecting the function and performance of the product. The raw material can be greatly saved and the cooling time and production cycle can be shortened.
Normal > 2) Large flatware
Normal > Such as automotive dashboards, interior grilles, commercial military and parabolic satellite antennas. By installing the air passage in the product, the rigidity and surface quality of the product can be significantly improved, the warping deformation and the surface depression can be reduced, the clamping force can be greatly reduced, and the larger parts can be formed with smaller equipment.
Normal > 3) Thick, thin-walled complex structure products
Normal> Such as televisions, computers, printer shells, and internal supports and exterior trims. Such products can not be molded once by conventional injection molding processes. The use of gas transmission technology improves the freedom of mold design and facilitates the integration of accessories. For example , the internal support and the number of external decorative parts required for Panasonic 74cm TV sets are from the conventional injection molding process. The reduction of 17 to 18 can significantly reduce assembly time.
Normal > Water-assisted injection molding is a new technology developed by IKV on the basis of gas-assisted injection molding technology. It uses water instead of nitrogen to assist the flow of the pavilion, and finally uses compressed air to press water out of the parts. Compared with gas-assisted injection molding, water-assisted injection molding can significantly reduce the molding time and reduce the wall thickness of the product. It can be applied to any thermoplastic plastics, including those with low molecular weight and easily blown through, and can produce large diameters ( More than 40mm) rod or tubular hollow parts, for example, for parts with a diameter of 10mm, the production cycle can be reduced from 60s to 10s (wall thickness l-1.5mm); and the diameter of 30mm parts, the production cycle can be 180s Reduced to 40s (wall thickness 2.5 to 30mm).
Normal > IKV and Ferromatik Milacron are currently working on prototypes. Other gas injection molding companies such as Baitenfeld and Engel have recently joined the development team. Water-assisted injection molding is mainly used to produce smooth, important media conduits with internal surfaces; its quality and economic benefits are inferior to gas-assisted injection techniques.
Normal > 2. Mold sliding injection molding
Normal > Mold sliding injection molding is a two-step injection molding method developed by Japan Steel Works and is mainly used for the manufacture of hollow products. The principle is to first divide the hollow product into two, two parts are injected to form a semi-finished product, and then the two parts of the semi-finished product and the mold are slid to the mating position, the two molds are closed, and the two parts of the product are combined and injected into the plastic melt ( 2 (Note), and finally get a complete hollow product. Compared with blow-molded products, this French-made product has the advantages of good surface precision, high dimensional accuracy, uniform wall thickness, and large design freedom.
