The shaping and processing methods for plastic products used in household appliances mainly include injection molding, extrusion molding, thermoforming, blow molding, laminating, compression molding, transfer molding, foam plastic molding, casting molding, embedding casting, and encapsulation casting, with injection molding being the primary method.
In recent years, a range of new plastic processing techniques and equipment have found significant application in molding plastic products for household appliances. These include precision injection molding, rapid prototyping techniques, melt-core injection molding, gas-assisted/water-assisted injection molding, electromagnetic dynamic injection molding, and film overlay injection molding.
1、Precision Injection Molding:
This technique ensures high precision and repeatability in terms of product dimensions and weight. Injection molding machines using this technology can achieve high-pressure, high-speed injection. With control typically in open-loop or closed-loop mode, high-precision control of injection process parameters is achievable. Precision injection molding often requires high mold precision.
2、Rapid Prototyping Techniques:
Developed alongside the diversification of household appliance types and ongoing upgrades, this technology is primarily used for producing plastic housings for appliances. An advantage of this technology is that it allows small-batch production of plastic parts without the need for molds.
Currently, mature rapid prototyping methods include laser scanning and liquid photopolymerization, with laser scanning being more prevalent. Laser scanning equipment consists of a laser source, scanning device, powder spraying device, and computer. The process involves computer-controlled laser scanning along a defined path. At points where the laser passes, plastic micro-powder is heated and fused, and after each scan, a thin powder layer is applied. Through repeated scanning, a product with specific shape and size is formed.
3、Melt-Core Injection Molding
This technique is usually applied for forming irregular cavity products with high requirements for cavity roughness and accuracy, which cannot be processed using hollow or rotational molding methods. While this technology is mature in other countries, it is still in limited use in China. The process involves first molding a core that forms the cavity and then using this core as an insert for injection molding. The core melts and flows out under the heat of the injection part, forming the cavity.
4、Gas-Assisted/Water-Assisted Injection Molding
This technique is versatile and can be used to form various types of injection-molded parts, with TV casings being a prime example. During injection molding, gas or superheated water is injected into the mold cavity nearly simultaneously with the plastic melt. The plastic melt envelops the gas or water, resulting in a sandwich-like structure in the formed plastic product. After solidification, the gas or water is released, allowing for easy demolding. These products have the advantages of material savings, minimal shrinkage, excellent appearance, and good rigidity. Key components of the molding equipment are gas-assisted or water-assisted devices and their control software.
5、Electromagnetic Dynamic Injection Molding Technology
This technology induces reciprocating vibration in the screw through electromagnetic forces. By achieving micro-plasticization during pre-plasticization, the structural density of molded parts during the holding phase is improved, reducing internal stress. This technology is used for high-quality products like optical discs and can also enhance the quality of regular products.
6、Film Overlay Injection Molding Technology
This technique involves placing a specialized printed decorative plastic film in the mold before injection molding. The film adheres to the product’s surface after heat deformation, providing both aesthetics and durability, and eliminating the need for post-decoration steps.
In general, there is a high demand for plastic molds for household appliance manufacturing. For instance, a refrigerator or fully automatic washing machine may require over 100 sets of molds, while an air conditioner requires more than 20 sets, and a color television requires 50-70 sets of plastic molds. The technical requirements for plastic molds are relatively high, often requiring shorter mold processing cycles, promoting the development of mold design and modern mold manufacturing technology. Additionally, more challenging molds like hot runner molds and multi-layer injection molds are gradually gaining traction in China.
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