Injection molding is an industry with a wide range of knowledge, technology and practice. In the process of injection production, plastic raw materials, toner, nozzle materials, molds, injection molding machines, peripheral equipment, tooling clamps, sprays, various auxiliary materials and packaging materials, etc. are required to be used, which brings a lot of workload and certain difficulty to the management of injection molding workshop. Compared with other industries or departments, the requirements for management personnel at all levels of injection molding workshop are higher.
Injection molding production needs 24-hour continuous operation, generally in two-sided three knife shift or three shift working mode. There are many posts and complicated division of labor in the injection workshop, and the technical requirements for different posts are also different. In order to ensure the smooth production and operation of the injection workshop, it is necessary to manage the personnel, materials, equipment and tools involved in each link and each post, mainly including the operation and coordination management of the raw material room, crushing room, batching room, production site, post-processing area, tool room, semi-finished product area, office room and other areas.
Injection molding type
1. Rubber injection molding: rubber injection molding is a production method of injecting rubber directly from the barrel into the model for vulcanization. The advantages of rubber injection molding are: although it is intermittent operation, the molding cycle is short, the production efficiency is high, the preparation process of embryo is canceled, the labor intensity is small, and the product quality is excellent.
2. Plastic injection: plastic injection is a method of plastic products. The molten plastic is injected into the plastic product mould by pressure, and the desired plastic parts are obtained by cooling and forming. There are special mechanical injection machines for injection molding. At present, polystyrene is the most commonly used plastic. The resulting shape is often the final product, and no other processing is required before installation or use as the final product. Many details, such as bulges, ribs, and threads, can be molded in one step of injection molding.
influence factor
In the process of plastic injection molding, due to the volume change of crystallization, high pressure, small viscosity difference of molten material, small shearing stress between layers, and large elastic rebound after demoulding, the shrinkage of injection molding can also be reduced appropriately. The material temperature is high and the shrinkage is large, but the direction is small.
When the pressure is increased in injection molding, the molten material will be sheared greatly, and the fluidity will also increase, especially PE and POM are more sensitive. Therefore, the pressure during injection molding should be adjusted to control the fluidity. During molding, the material temperature, mold temperature, pressure during injection processing, injection speed and other factors can also be controlled to properly adjust the filling conditions to meet the molding needs .
Injection molding process
Injection molding is a kind of processing method used in mass production of some complex parts. Specifically, the material melted by heat is injected into the mold cavity by high pressure, and then cooled and solidified to obtain the formed product.
1, Temperature control
1. Barrel temperature: the temperature to be controlled in the injection molding process includes barrel temperature, nozzle temperature and mold temperature, etc. The first two temperatures mainly affect the plasticization and flow of plastics, while the second one mainly affects the flow and cooling of plastics. Each kind of plastic has different flow temperature. For the same kind of plastic, the flow temperature and decomposition temperature are different due to different sources or brands. This is due to different average molecular weight and molecular weight distribution. The plasticization process of plastic in different types of injection machines is also different, so the selection of barrel temperature is also different.
3. Nozzle temperature: the nozzle temperature is usually slightly lower than the maximum temperature of the barrel, which is to prevent the possible "salivation" of molten materials in the through nozzle. The temperature of the nozzle should not be too low, otherwise, the nozzle will be blocked due to the early setting of the melt, or the performance of the product will be affected due to the early setting material injected into the mold cavity.
4. Mold temperature: mold temperature has a great influence on the internal performance and apparent quality of products. The mold temperature depends on the crystallinity of the plastic, the size and structure of the product, performance requirements, and other process conditions (melt temperature, injection speed, injection pressure, molding cycle, etc.).
2, Pressure control
The pressure in the injection molding process includes plasticizing pressure and injection pressure, which directly affects the plasticizing of plastics and the quality of products.
1.Plasticizing pressure: (back pressure) when the screw injection machine is used, the pressure on the melt at the top of the screw when the screw rotates and retreats is called plasticizing pressure, also known as back pressure. This pressure can be adjusted by the relief valve in the hydraulic system. In the injection, the plasticizing pressure needs to change with the design of screw, the requirements of product quality and the type of plastic. If these conditions and the rotating speed of screw remain the same, increasing the plasticizing pressure will strengthen the shear effect, that is, it will increase the temperature of melt, but it will reduce the plasticizing efficiency, increase the countercurrent and leakage, and increase the driving power.
In addition, increasing the plasticizing pressure can make the melt temperature uniform, the color mixture uniform and the gas in the melt discharged. In general operation, the determination of plasticizing pressure should be as low as possible on the premise of ensuring good product quality. The specific value varies with the type of plastic used, but it is rarely more than 20 kg / cm2.
2. Injection pressure: in the current production, the injection pressure of almost all injection machines is based on the pressure (converted from the oil circuit pressure) applied to the plastic at the top of the plunger or screw. Injection pressure in injection molding
