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Introduction Of Injection Molding Screw Barrel
Injection Molding Screw Barrel is one of the most important processes in this industry. It allows complex structures to be produced with good accuracy and reproducibility. Its application extends to the fields of microelectronics, biomedicine, automotive and aerospace. The ideal property of materials such as metals and plastics is the way they are formed. When cooled, they maintain the new structure they formed. Injection molding is also suitable for thermoset materials. These are materials that will not melt when heated. Instead, they change from a viscous liquid to a solid through a cross-linking process. Materials such as metal, rubber, plastic and glass can be injection molded. It allows mass production of products in repeated cycles.
The injection molding machine is the injection and clamping part. The injection part includes screw, barrel, valve and control unit. The clamping part includes gate, runner, gate, mold and cooling device. The materials are mixed and melted in the injection section. The melt is then compressed and cooled in the clamping part. The process can be fully automatic, semi-automatic or manual. The fully automated system will include temperature controllers, automatic ejectors and metering. Manual processes may require opening the mold manually. In the manual type, the ejection of the cooling product can also be manual.
The following paragraphs describe the injection molding machine. Then the process of injection molding is described. The following paragraphs discuss the different types, advantages and disadvantages. This basic understanding of injection molding aids operation and design.
Injection molding 1
Injection molding machine
A typical injection molding machine consists of the following parts:
Tighten
Barrell
Heater
Limit switch
Check valve
Gate
Runner
Door
Mould
Cooling line
The injection molding machine plays the role of melting, injection and pressure maintaining. The main component that accomplishes most of the work is the screw. In injection molding, the screw is a reciprocating screw. It moves forward and backward at specific points in the loop. It applies shear torque as it rotates. The screw is in the barrel, and the plastic particles forming the new product enter the barrel from the hopper. The barrel is heated by an electric heater. These along its length, the heat reaches the pellets and screw. The product is formed in a mold cavity, which is connected to the nozzle of the barrel through a gate. The runner feeds the runner, and then the molten material is fed into the mold cavity through the gate.
Injection molding 2
The mold shapes the molten material into the desired shape. Steel is often used to produce injection molded parts. The mold cavity size includes consideration of shrinkage. Shrinkage is a characteristic of the material used. For example, the shrinkage rate of high-density polyethylene is 3%, while the shrinkage rate of polypropylene is 2%, and the shrinkage rate of PET is 0.4%. Shrinkage occurs due to the rearrangement of the molecular crystal structure. This reordering occurs when the material changes from the molten phase to the solid phase. Shrinkage is also the result of changes in enthalpy and entropy in the material.
Process overview
Injection molding is a cyclic process. This means that the process will occur as a series of events repeated in the same way. A cycle starts when the mold is closed. The granular material enters the hopper. The screw rotates and moves backward. The pellets are melted, and the melt is pushed forward along the barrel into the melt chamber.
The melting of the pellets is caused by the heating of the barrel wall. The heat generated by the friction between the rotating screw and the barrel also contributes. This continues until the screw reaches the limit switch. The limit switch indicates that the required injection volume is in the melting chamber. Injection volume refers to the amount of molten material required to fill the mold cavity in one cycle. This includes shrinkage, flow channels and retention in the chamber. The melt chamber refers to the space between the end of the screw and the nozzle. The nozzle sends the melt into the runner and mold.
The screw reaches the limit switch and stops moving backward. Then it moves forward with high speed and pressure by hydraulic pressure. This injects the melt from the melt cavity into the mold cavity. The check valve prevents the melt from flowing back through the check valve. The mold is then kept under this pressure and cooled. Cooling is performed by the cooling fluid provided by the cooling line. Pre-cooling molds can achieve faster cooling and more effective product molding. After cooling, the mold is opened and the product is ejected from the cavity through the ejector pin. The release of the product is also partly assisted by contraction. Especially in plastics, the cooled product can shrink to 3% of the s melt volume. As the mold cools, the screw begins to move backward and the next cycle begins.
Injection molding 3
The goal of injection molding is to achieve controlled heating, molding, and cooling. This should be the best efficiency and defect-free in the shortest time. This is the use of multiple control systems. Parameters include speed, temperature, speed, time, etc. The rotation speed of the screw is in revolutions per minute (rpm). The temperature in the barrel and the temperature in the mold. Filling pressure and speed. The holding pressure and temperature in the mold cavity. The control of process parameters is essential to achieve the best quality and productivity. Auxiliary equipment includes motor, gear reducer and temperature control unit.
Advantages of injection molding method
The advantages of injection molding include the production of complex structures with good precision. The scalability of the process is also very important. The process is scaled up by increasing the number of molds per cycle. The process is also repeatable. This allows mass production of the same product.
Otherwise, the complexity of injection molding takes several hours per piece. Common processing and engraving techniques cannot achieve the same output. There are many examples of items that can be produced by injection molding. These include knobs, screws, chairs, buckets, flower pots, medical tools, and footwear.
Injection molding also has the advantage of short cycle time. This allows mass production rates. The typical cycle time is between 10 and 30 seconds, or even shorter. The cycle time starts from the moment the mold closes and the screw starts to fill the melting chamber. When the mold is filled again, the cycle ends.
The versatility of injection molding is also an advantage. This machine is suitable for producing different products by changing molds. The size of the product changes according to needs. This can range from small items such as screws and bolts to larger items such as chairs and vehicle parts. Injection molding can realize complex 3-dimensional structures with high detail accuracy. Compared with processes such as compression molding, it does a better job in this regard.
Disadvantages of injection molding method
Like other processes, injection molding has its disadvantages. One of the inherent disadvantages is that it is a cyclic rather than a continuous process. This brings some restrictions, such as the time required for cooling. The well-designed process and machine reduce the time of demolding and cooling...Nevertheless, this will increase the process time.
The use of molds minimizes the loss of materials. This is different from compression molding in which the mold is overfilled. This is to ensure that the product is fully formed. Excessive amounts lead to the formation of waste. Injection molding also generates waste in the runner and runner. Especially in the cold runner type.
The mold plays an important role in the injection molding process. The design capital cost of the injection mold is high. This is because the mold requires high-quality metal. This is to maintain the pressure required for injection and to keep the melt in place during the cooling process. Compression molding uses cheaper materials, such as wood. However, these have not reached the 3-dimensional accuracy of the injection molding process.
Types of injection molding
The difference in injection molding lies in the characteristics of the materials used. Melting point, melt viscosity, glass transition temperature, shrinkage and density are some. Injection molding is classified in different ways. One is based on the number of molds. Injection molding can be a single-cavity or multi-cavity system. The single cavity system is used for injection molding of very large parts. For example, large equipment or vehicle parts. For smaller products, use a multi-cavity system. These pieces are produced every cycle. This allows economies of scale to manufacture many pieces in a few seconds
It can also be classified by material type. Such as thermoplastics, thermosetting plastics, metal, powder or glass injection molding. Although they use the same basic injection molding process, there are still some differences. In plastic injection molding, both melting and molding are performed with heat and pressure. In thermosetting injection molding, molding is through cross-linking in the mold. Thermosetting crosslinking can be carried out at room temperature or high temperature. Some need conditions such as ultraviolet radiation may be possible. Thermoplastic injection molding is not as complicated as thermoset injection molding. The latter is difficult to ensure that crosslinking only occurs in the mold. If the polymer solidifies and reaches the cavity, equipment and products may be damaged.
Injection molding 5 molding. Respectively referred to as PIM or MIM. The metal injection molding process uses finer metal particles. A smaller particle size results in a higher surface area. A larger surface area leads to more efficient heat exchange and distribution. This means that less heat energy input is required to reach the melting point of the metal. In addition, a smaller particle size will allow for better compaction. This leads to a higher density of the product. Finer powders require harsher processing. Therefore, MIM is often more expensive than the PIM process. In addition, the PIM process can be a combination of metals, ceramics and adhesives. The binder degrades during debindering and sintering. This also leads to a decrease in volume and an increase in density. Metals, such as steel, aluminum, copper, tungsten, and titanium.
Another category of injection molding is related to porosity. Such methods include gas-assisted injection molding and structural foam molding. The former involves passing high-pressure air through the mold cavity. This creates a hollow center and a dense wall. The latter involves the uniform distribution of gas in the molded article to create holes.
It can also be injection molded according to the type of runner system used. These are cold runner and hot runner injection molding. The type of cooling system used in the clamping part of the injection molding machine. Other articles discuss hot runner and cold runner systems in more detail in other articles. All of this helps to determine the correct injection molding process and machinery required. The processor must have a good understanding of the material. Target product design, application and budget are also important factors to consider.
in conclusion
In short, the injection molding process is a universal process. It processes various materials into a wide range of products. It realizes the high-volume, high-speed and low-cost production of complex parts. In injection molding, the material undergoes high shear and high temperature. The processing temperature is usually close to the melting point of the material.
Metal is also processed using injection molding. This can be through powder injection molding or metal injection.
Single Screw Extruder Screw Barrel also has a similar principle. If you want to know more about it, you can contact us.
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