Details Of The Production Of Automotive Plastics Components

• Posted by autoparts dongfa 13 February 2022 - Filed in Business - #automobiles stamping supplier  #automotive plastics components  - 21 views

   

  1. automotive plastics components molding cycle

  The time required to complete an injection molding process is called the molding cycle, also known as the molding cycle. It actually includes the following parts: Molding cycle: The molding cycle directly affects labor productivity and equipment utilization. Therefore, in the production process, the relevant time in the molding cycle should be shortened as much as possible under the premise of ensuring the quality. In the whole molding cycle, the injection time and cooling time are the most important, and they have a decisive influence on the quality of the product. The filling time in the injection time is directly inversely proportional to the filling rate, and the filling time in production is generally about 3-5 seconds. The pressure holding time in the injection time is the pressure time for the plastic in the cavity, which accounts for a large proportion of the entire injection time, generally about 20-120 seconds (the extra thick parts can be as high as 5-10 minutes). Before the molten material at the gate is frozen, the holding pressure time has an impact on the dimensional accuracy of the product, and if it is later, it has no effect. The dwell time also has a Z value, which is known to depend on the material temperature, mold temperature, and the size of the sprue and gate. If the dimensions of the sprue and gate and the process conditions are normal, usually the pressure value with the smallest fluctuation range of the product shrinkage rate shall prevail. The cooling time is mainly determined by the thickness of the product, the thermal and crystalline properties of the plastic, and the mold temperature. The end of the cooling time should be based on the principle of ensuring that the product does not change when the product is demolded. The cooling time is generally between 30 and 120 seconds. If the cooling time is too long, it is not necessary, which not only reduces the production efficiency, but also affects the complex parts. Difficulty in demolding, and even demolding stress will be generated when demoulding is forced. The other time in the molding cycle is related to whether the production process is continuous and automated, and the degree of continuous and automated.

  
  2. Pressure control

  The pressure in the injection molding process includes plasticizing pressure and injection pressure, and directly affects the plasticization of plastics and the quality of products.

  1. Injection pressure: In the current production, the injection pressure of almost all injection machines is based on the pressure exerted on the plastic by the top of the plunger or screw (converted from the pressure of the oil circuit). The role of injection pressure in injection molding is to overcome the flow resistance of plastic flowing from the barrel to the cavity, to give the melt filling rate and to compact the melt.

  2. Plasticizing pressure: (back pressure) When a screw injection machine is used, the pressure on the top of the screw when the screw rotates and retreats is called plasticizing pressure, also known as back pressure. The magnitude of this pressure can be adjusted by the relief valve in the hydraulic system. In injection, the size of the plasticizing pressure is unchanged with the speed of the screw, so when the plasticizing pressure is increased, the temperature of the melt will be increased, but the speed of plasticizing will be reduced.

  After a period of production, the melted glue continuously takes away the heat, resulting in insufficient melted glue, high viscosity and poor fluidity, resulting in a lack of glue in the product. Increase the tube temperature to solve.

  In addition, increasing the plasticizing pressure can often make the temperature of the melt uniform, the mixing of the colorant is uniform, and the gas in the melt can be discharged. In general operation, the decision of plasticizing pressure should be as low as possible on the premise of ensuring the quality of the product. The specific value varies with the variety of plastic used, but usually rarely exceeds 20 kg/cm 2 .

  3. Temperature control

  1. Nozzle temperature: The nozzle temperature is usually slightly lower than the highest temperature of the barrel, which is to prevent the "drooling phenomenon" that may occur in the straight-through nozzle. The temperature of the nozzle should not be too low, otherwise it will cause the premature solidification of the melt to block the nozzle, or the performance of the product will be affected due to the injection of the early solidified material into the mold cavity.

  2. Mold temperature: The mold temperature has a great influence on the intrinsic performance and apparent quality of the product. The temperature of the mold depends on the presence or absence of plastic crystallinity, the size and structure of the product, performance requirements, and other process conditions (melt temperature, injection speed and injection pressure, molding cycle, etc.).

  3. automobiles stamping supplier barrel temperature: The temperature that needs to be controlled in the injection molding process includes barrel temperature, nozzle temperature and mold temperature. The first two temperatures mainly affect the plasticization and flow of the plastic, while the latter temperature mainly affects the flow and cooling of the plastic. Each plastic has a different flow temperature. For the same plastic, due to different sources or grades, its flow temperature and decomposition temperature are different. This is due to the difference in average molecular weight and molecular weight distribution. The plasticizing process in the machine is also different, so the selection of the barrel temperature is also different.