Designing plastic parts is a complex task, involving many factors and a series of requirements for the application. "How to use the part?" "How does it match with other parts in the assembly?" "What load will it bear during use?" In addition to functional and structural issues, the problem of injection molding in Shijiazhuang lies in the design of injection molded plastic parts. China also plays a big role. How molten plastic enters, fills and cools the cavity to form a part, which largely determines the characteristics that the part must have. Following some basic rules of injection molded part design will result in parts that are generally stronger in use, in addition to being easier to manufacture and assemble. Dividing parts into basic groups will help you build parts in a reasonable way while minimizing molding problems. When a part is developed, remember how the part is formed and what you can do to reduce stress.
Plastic injection molding is a good process for manufacturing plastic parts. Injection molding is used to make many things, such as electronic housings, containers, bottle caps, car interiors, combs, and most other plastic products today. It is ideal for the production of large numbers of plastic parts, because multiple parts can be produced in each cycle using a multi-cavity injection mold. Some of the advantages of injection molding are high tolerance accuracy, good repeatability, many material choices, low labor costs, low waste loss Z, and almost no need to complete parts after molding. Some of the disadvantages of this process are expensive upfront tool investment and process limitations.
Most polymers can be used, including all thermoplastics and some elastomers. There are thousands of different materials available for injection molding. Available materials are mixed with alloys or mixtures of previously developed materials, which means that product designers can find a material with the right properties from a large selection of materials. The material is selected according to the required strength and function of the part; and each material has different molding parameters that must be considered. Common polymers like nylon, polyethylene, and polystyrene are thermoplastic.
Injection molding machine, also known as a press, consists of a hopper, an injection head or screw plunger and a heating device. The Shijiazhuang injection mold is clamped on the pressure plate of the molding machine, and the plastic is injected into the mold through the injection port. The press is evaluated according to the tonnage, which is the calculated value of the clamping force that the machine can exert. This force keeps the mold closed during the injection molding process. The tonnage can range from less than 5 tons to 6000 tons, although higher tonnage presses are rarely used. The total clamping force required is determined by the projected area of the custom part being molded. This projected area is multiplied by a clamping force of 2 to 8 tons per square inch of projected area. According to experience, 4 or 5 tons/inch can be used for most products. If the plastic material is very hard, more injection pressure will be required to fill the mold, so more clamp tonnage is needed to keep the mold closed. The required force can also be determined by the material used and the size of the larger plastic parts that require higher clamping forces.
Mold refers to the tool used to produce plastic parts during the molding process. Traditionally, injection molds are costly to manufacture and are only used in mass production applications where thousands of parts are produced. The mold is usually made of hardened steel, pre-hardened steel, aluminum and/or beryllium copper alloy. The choice of materials for making molds is mainly economic. Steel molds are generally more expensive, but have a longer service life, which will offset the higher initial cost of manufacturing more parts before wear. Pre-hardened steel molds have poor wear resistance and are mainly used for lower volume requirements or larger parts. The hardness of pre-hardened steel is usually 38-45 on the Rockwell hardness scale. The hardened steel mold is heat treated after processing to make it more superior in wear resistance and life. The typical hardness range is between 50 and 60 Rockwell.
The cost of aluminum molds is much lower than that of steel molds. When using better quality aluminum, such as QC-7 and QC-10 aircraft aluminum, and processing them with modern computer equipment, they can economically form hundreds of thousands of parts. Aluminum molds also provide quick turnaround and faster cycle times because of better heat dissipation. They can also be coated with a wear-resistant coating of glass fiber reinforced materials. Beryllium copper is used in areas that require rapid heat dissipation or areas that generate a lot of shear heat in Shijiazhuang plastic molds.
Through injection molding, granular plastic enters the heating barrel from the hopper under the action of gravity. When the pellets are slowly pushed forward by the spiral piston, the plastic is pushed into a heating chamber called a barrel, where it melts. With the advancement of the plunger, the molten plastic is forced to pass through the nozzle leaning on the mold sprue bushing, allowing it to enter the mold cavity through the gate and runner system. The mold is kept at a set temperature, so the plastic can solidify almost immediately after the mold is filled.
The sequence of events in the injection molding process of plastic parts is called the injection molding cycle. When the mold is closed, the cycle begins, and then the polymer is injected into the mold cavity. Once the cavity is filled, the pressure is maintained to compensate for material shrinkage. In the next step, the screw is rotated to feed the next lens into the front screw. This allows the screw to retract when preparing for the next injection. Once the part is sufficiently cooled, the mold opens and the part is pushed out.