8 Common Methods For Molding Plastic Products
Earlier we introduced the design principles of plastic products, so from the perspective of processing methods, how can plastic parts be processed? This article will briefly introduce it.
Many parts on cars are made of plastic products
Many household appliances are made of plastic parts
There are generally 8 common processing methods for plastic parts:
1. Injection molding
This plastic processing method is one of the most common. The main steps of this method are
Mold closing → filling → pressure holding → cooling → mold opening → demoulding, take out the plastic product, and repeat the above steps in the next cycle.
Generally speaking, there are five main elements that need to be paid attention to in this method, namely:
1. Temperature: barrel temperature, material temperature, mold temperature, drying temperature, oil temperature, ambient temperature, etc.
2. Pressure: injection pressure, holding pressure, back pressure, demoulding pressure, mold opening pressure, mold clamping pressure, etc.
3. Time: injection time, holding time, cooling time, drying time, measurement delay time, etc.
4. Speed: injection speed, carriage return speed, mold opening and closing speed, demoulding speed, etc.
5. Position: measurement position, ejection position, mold opening position, etc.
Adjusting and changing the parameters in these five elements will directly affect the effect of the injection molded parts. When we analyze the defects of injection molded parts, we generally consider where the problem lies from these aspects.
Injection molding process flow chart
This processing technology has spawned other methods depending on materials, machine design and product requirements, such as insert molding of embedded metal parts, multi-color and mixed-color injection molding, structural foam injection molding, etc.
2. Extrusion molding
The thermoplastic is heated and pressured in an extruder and then extruded using a screw. The cross-sectional shape of the extruded product depends on the machine head and can be rod-shaped, tubular, flat, special-shaped, etc.
Schematic diagram of extrusion molding process
3. Forming
This is a thermoset plastic molding method. The thermoset is first preheated and placed into the open mold cavity. After the mold is closed, heat and pressure are applied until the material hardens. This processing method is often used to manufacture home appliance casings, parts, gears, furniture, tableware, etc.
Molding drawing
4. Blow molding
In this method, the thermoplastic plastic is first extruded through the extruder head to form a thin tube, called a parison, and then the mold is closed and blow molded. This method is more and more widely used. For example, in the automotive industry, the materials used have also shifted from traditional PE, PP, PVC, PET, etc. to high-performance engineering plastics.
The advantage of this method is that it facilitates the manufacture of large products and molds them in one go. The main disadvantage is that the wall thickness of each part of the plastic product is difficult to control.
Hollow molding (commonly known as blow molding)
5. Rotational molding
The principle of rotational molding is to inject powdered or liquid molding materials at room temperature into the rotational mold, and use heating and centrifugal force to evenly distribute the plastic on the mold wall. After cooling, the hollow molded product can be obtained. This method is suitable for molding large products, but the disadvantage is that the wall thickness is difficult to control.
Rotational molding diagram
Medicine bucket made by rotomolding finished product process
6. Thermoforming
This method involves heating and softening thermoplastic sheets, which are then pressed into shape using vacuum, air or metal. Its strength is related to the thickness of the plastic board. The finished product needs to be cut and the excess corners recycled.
Thermoforming diagram
8. Extrusion molding
The principle of this method is to use a punch or die to pressurize the blank placed in the die to cause plastic flow, thereby obtaining parts corresponding to the shape of the die hole or concave and convex die. . During extrusion, the billet generates three-dimensional compressive stress, and even billets with low plasticity can be extruded.
Extrusion molding diagram
The above are 8 commonly used methods for plastic molding. There are more than 8 methods of plastic molding. Due to limited space, we will not list them one by one. With the progress and development of the times, many new molding methods have emerged. We usually need to pay more attention and learn more. Among these 8 methods, the most common is the first one. It can be said that it accounts for half of the plastic molded products. Therefore, in our daily work, we must fully understand the technical difficulties and difficulties of our commonly used processing methods, so that we can play a role in our work. Aim and relax.
