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.
There are many parts on the car that are plastic products
Many of the household appliances are also plastic parts
The common processing methods of plastic parts generally have the following 8 kinds:
1. Injection molding
This plastic processing method is one of the most common methods. The main steps in this approach are
The mold → filled → the packing → cooled→ the mold is opened → released, the plastic product is removed, and the next cycle is cycled according to the previous steps.
Generally speaking, this method has five major elements to pay attention to, namely:
1. Temperature: barrel temperature, material temperature, mold temperature, drying temperature, oil temperature, ambient temperature, etc
2. Pressure: injection pressure, holding pressure, back pressure, release pressure, mold opening pressure, mold locking pressure, etc
3. Time: injection molding time, holding time, cooling time, drying time, measurement delay time, etc
4. Speed: injection speed, carriage return speed, opening and closing mold speed, mold release speed, etc
5. Position: metering position, ejection position, mold opening position, etc
Adjusting and changing the parameters in these 5 elements will directly affect the effect of injection molded parts. When we analyze the defects of injection molded parts, we generally consider which aspect of the problem is in these aspects.
Schematic diagram of the injection molding process
This processing technology has derived other methods due to material, mechanical design and product requirements, such as plug-in molding of pre-embedded metal parts, multi-color and mixed-color injection molding, structural foam injection molding, etc.
Second, extrusion molding
The thermoplastics are heated in the extruder, pressurized, and then extruded with screws, and the cross-sectional shape of the extruded product depends on the head, which can be rod-shaped, tubular, flat-shaped, heterogeneous and so on.
Schematic of the extrusion molding process
Third, molding
This is a kind of thermosetting plastic molding method, the thermosetting plastic is preheated first, placed in an open cavity, and heat and pressure are applied after closing the mold until the material hardens. This processing method is often used to make home appliance shells, parts, gears, furniture, tableware, etc.
Schematic of compression molding
Fourth, hollow molding
This method is to first extrude the thermoplastic from the head of the extruder to make it a thin tube, called a blank, and then close the mold, blow air and then form. The use of this method is more and more extensive, such as the automotive industry, the materials used are also from the traditional PE, PP, PVC, PET, etc., to high-performance engineering plastics.
The advantage of this method is that it is convenient to manufacture large products and one-time molding, and the disadvantage is mainly that the wall thickness of each part of the plastic product is not easy to control.
Hollow molding (commonly known as blow molding)
Fifth, rotational molding
The principle of rotational molding is to inject the normal temperature powder or liquid molding material into the rotational molding mold, use heating and centrifugal force to make the plastic evenly distributed on the mold wall, and the hollow molded product can be obtained after cooling. This method is suitable for the molding of large items, but the disadvantage is that the wall thickness is difficult to control.
Schematic diagram of rotational molding
Barrels made by the rotomolded finished product process
Sixth, thermoforming
This method is to heat and soften the thermoplastic sheets and then pressurize them with vacuum, air, or jacketed metal. Its strength is related to the thickness of the plastic plate, and the product needs to be cut, and the excess edge material is recycled.
Thermoforming schematic
8. Extrusion molding
The principle of this method is to use a punch or punch to pressurize the blank placed in the die to produce a plastic flow, so as to obtain a pressure processing method corresponding to the shape of the mold or the shape of the die. When extruded, the blank generates a three-way compressive stress, and even the less plastic blank can be extruded into shape.
Schematic of extrusion molding
As mentioned above, there are 8 methods commonly used for plastic molding, and there are more than 8 methods of plastic molding, which are limited in space and are not listed one by one, with the progress and development of the times, there are many new molding methods. We usually need to pay more attention and learn more. Among these 8 methods, the most common is still the first, which can be said to occupy half of the plastic molding products, so we must thoroughly understand the process difficulties of our commonly used processing methods in our ordinary work, so that we can be targeted and comfortable in our work.
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