The application of new injection molding technology in injection molding processing, Dongguan Machiko injection molding manufacturer stated that with the increasingly widespread application of plastic injection molding products and the rapid development of plastic molding processes, people's requirements for plastic products are also increasing. In recent years, scientific and technological workers on the plastic molding front have conducted in-depth exploration, research, and practice on how to expand the application scope of injection molding, shorten the injection molding cycle, reduce molding defects, improve the quality of plastic injection molding, and reduce production costs. They have achieved gratifying results, and new technologies for molds and injection molding have emerged one after another. Here, we will only introduce the increasingly widely used thermosetting plastic injection molding, gas assisted injection molding, precision injection molding, low foam injection molding, co injection molding, exhaust injection molding, and reaction injection molding. The application of new injection molding technology in injection molding began in the 1960s. Prior to this, this type of plastic parts mainly relied on compression or injection molding methods. These two methods had complex process operations, high labor intensity, long molding cycles, low production efficiency, easy mold damage, and unstable product quality during injection molding. The injection molding of thermosetting plastic parts can be said to be a major reform of thermosetting plastic molding technology. It has the advantages of simplifying injection molding process, shortening injection molding cycle, improving production efficiency, reducing labor intensity, improving injection molding product quality, and longer mold life. However, this molding method requires high material requirements. Currently, phenolic plastics with wood powder or cellulose as fillers are commonly used, in addition to amino plastics, unsaturated polyester, epoxy resin, etc. 1、 Overview of Injection Molding Technology for Thermosetting Plastics Application of New Injection Molding Technology. Although there are many similarities in the injection molding principles and processes of thermosetting and thermoplastic plastics, there are also significant differences between them due to their different chemical properties. The principle of thermosetting plastic injection is to feed the formed material from the hopper of the injection machine into the material barrel for heating and melt and plasticize under the rotation of the screw, making it a uniform viscous flow state melt. Through the high-pressure push of the screw, these melts are injected into the high-temperature cavity through the nozzle at the front end of the barrel at a high flow rate. After a period of pressure maintaining, shrinking, and cross-linking reaction, they solidify and form into the shape of a plastic part, Then open the mold and take out the plastic part. It is obvious that in principle, the main difference in injection molding between thermosetting and thermoplastic plastics is manifested in the solidification molding stage after melt injection into the mold. The solidification of thermoplastic injection molded parts is essentially a physical process of transition from a high-temperature liquid phase to a low-temperature solid phase, while the solidification of thermosetting injection molded parts must rely on cross-linking chemical reactions under high temperature and pressure. It is precisely because of this difference that the injection molding processing conditions of the two are different.

（1） Temperature
(1) Material temperature: Similar to the thermoplastic injection molding process, material temperature includes plasticization temperature and injection temperature, which depend on the temperature of the material barrel and nozzle, respectively. However, due to the different properties of thermosetting and thermoplastic injection molding processes, there are differences in the temperature requirements for the material barrel and nozzle between the two. For thermosetting plastics, in order to prevent early hardening of the melt in the barrel and consider the impact of barrel temperature on plasticization less than the impact of shear friction within the material, Dongguan Machiko injection molding manufacturers tend to choose a lower barrel temperature. However, when the temperature of the material barrel is too low, the melting of the material is slower, and a large amount of frictional heat is generated between the screw and the raw material. This heat is actually more likely to cause early hardening of the melt than when the material barrel is at a higher temperature. Therefore, the temperature of the material barrel should be strictly controlled during production. Usually, the temperature of the material barrel is set in two or three stages. When set in two stages, for different materials, the temperature of the rear stage can be selected between 20~70 ℃, while the temperature of the front stage can be selected between 70~95 ℃, Posterior segment For example, when adding materials, consideration should be given to the frictional heat between the melt and the nozzle, which is generally a high temperature rise. In principle, it is usually required that the temperature of the melt after passing through the nozzle has good fluidity on one hand, and can be close to the critical value of the hardening temperature on the other hand, which not only ensures the filling mold but also facilitates the hardening and shaping. Therefore, the nozzle temperature is generally set higher than the material temperature. For different The temperature of the material and nozzle can be selected and controlled within the range of 75-100 ℃. At this temperature, the temperature of the melt passing through the nozzle can reach 100-130 ℃, which may meet the above two requirements.

(2) Mold temperature: Mold temperature is a key factor affecting the hardening and shaping of thermosetting plastic parts, directly related to the quality of molding and the level of production efficiency. If the mold temperature is too low and the hardening time is long, and if the mold temperature is too high, it will be difficult to discharge low molecular volatile gases due to the fast hardening speed, resulting in defects such as loose structure, foaming, and dark color in the plastic parts. Usually, for different materials, the selection and control range of mold temperature is 150-220 ℃. In addition, the dynamic mold temperature sometimes needs to be 10-15 ℃ higher than the fixed mold, which will be more conducive to the hardening and shaping of plastic parts.

（2） Pressure
(1) Injection pressure and injection speed: Similar to the injection molding process of thermoplastic injection molding, the injection pressure and injection speed of thermosetting injection molding process are also closely related. Due to the large number of fillers in the melt, high viscosity, and temperature rise requirements for the melt during the injection process, the injection pressure should generally be chosen higher. According to different materials, the commonly used injection pressure range is 100-170MPa, and a few materials can also have lower or higher values than this range. In principle, the injection speed related to the injection pressure should also be chosen higher, which is beneficial for shortening the flow filling and hardening setting time, while also avoiding early hardening of the melt in the flow channel and reducing the appearance of fusion marks and flow lines on the surface of the plastic part. But if the injection speed is too high, it is easy to draw air into the mold cavity and melt, resulting in defects such as bubbles on the surface of the plastic part. Based on current production experience, the injection speed of thermosetting plastics can be taken as 3-4. 5m/min
(2) Holding pressure and holding time: Holding pressure and holding time directly affect the cavity pressure, as well as the shrinkage and density of the plastic part. At present, due to the significant improvement in the hardening speed of thermosetting injection molten materials compared to before, and the fact that most molds use point gates, which freeze quickly, the commonly used holding pressure can be slightly lower than the injection pressure. The holding time is slightly less than that of injection thermoplastic, but it should be determined based on different materials, the thickness of the plastic part, and the freezing speed of the gate. Usually, it is taken as 5-20s. The cavity pressure for thermosetting injection molding is about 30-70MPa
(3) Back pressure and screw speed: When injecting thermosetting plastics, the back pressure of the screw should not be too high. Otherwise, the material will be compressed for a long distance in the screw, making injection difficult or causing the melt to harden prematurely. Therefore, the back pressure when injecting thermosetting plastics is generally lower than when injecting thermoplastic plastics, ranging from 3.4 to 5.2 MPa, and can be close to zero when the screw starts. In some cases, the back pressure valve can even be relaxed, using only the frictional resistance when the injection screw retreats as the back pressure. However, it should also be noted that when the back pressure is too small, the material is easily filled with air, the measurement is unstable, and the plasticization is uneven. When injecting thermosetting plastics, the screw speed related to back pressure should not be too high, otherwise the material is prone to uneven heating inside the barrel, resulting in poor plasticization. The speed of the screw is generally selected within the range of 30-70r/min.

（3） Forming cycle
The application of new injection molding technology in injection molding processing, the time content of thermosetting plastic injection molding cycle is basically the same as that of thermoplastic injection, but the cooling and setting time of thermosetting plastic parts should be changed to hardening and setting time corresponding to thermoplastic parts. The important factors in the molding cycle of thermosetting plastics are injection time and hardening setting time, and the holding time can belong to both injection time and hardening time, but it is often considered separately. In general, the injection time for domestically produced thermosetting injection materials needs to be 2-10s, the holding time needs to be 5-20s, and the hardening and setting time should be selected within 15-100s. The total injection molding cycle needs to be 45-120s. However, it should be pointed out that when determining the hardening and setting time for same-sex parts, it is not only necessary to consider the structure and requirements, but also the quality, especially according to the size of the parts. The hardening of the same domestically produced injection materials after mixing can be based on the size of the parts, It can be calculated based on the total deviation of injection, but with the continuous development of plastic production technology, the hardening rate of some thermosetting injection materials has basically reached the hardening rate of foreign rapid injection materials.

（4） Other process conditions
(1) The retention time and injection amount of materials in the material barrel. Every time the injection machine completes an injection action, there will be a portion of the plasticized melt left in the groove of the screw that cannot be injected out. Although these melts are gradually pushed out of the barrel in the future injection process, they are prone to cross-linking and hardening due to excessive retention time in the barrel, which can affect the molding quality of the plastic part at best and cause the injection machine to be unable to continue working, Therefore, it is necessary to control the retention time of thermosetting plastics in the material barrel. The residence time of the material in the barrel and m/m; It is related to the molding cycle t, but t. must not exceed the allowed plasticizing time of the material, otherwise the material will harden in the barrel. During production, empty injection is often required to prevent premature hardening of materials in the material barrel. It is obvious that this will result in significant waste of raw materials.
(2) Exhaust: Due to the large amount of reactive gas volatilization during the hardening and shaping process of thermosetting injection molded parts, exhaust issues are very important for injection of thermosetting materials. In addition to designing the necessary exhaust system in the mold, it is also necessary to consider whether pressure relief and mold opening measures need to be taken during injection molding operations. Usually, this measure is necessary for thick walled plastic parts, and the pressure relief mold opening time can be controlled within 0.2 seconds.
(3) Typical process conditions for thermosetting injection materials: The process conditions for thermosetting injection molding processing and injection molding were generally described earlier. Dongguan Machiko injection molding manufacturer has listed nine typical injection molding process conditions for thermosetting plastics, which can be used as a reference in production. However, it should be noted that the thermosetting injection molding process is still in the development stage, and the injection molding process will continue to be improved. In addition, the injection molding process of the same plastic may also vary due to different grades, plastic parts, or manufacturers.