What is the difference between extrusion molding and injection molding?

1, Structural differences and working principles
Extrusion molding
Extrusion molding, also known as extrusion molding, is a continuous processing method. It mainly relies on the internal screw and barrel of the extruder to plasticize the material under the action of heating and shear force, and continuously extrude it through the die head to form a continuous profile with a constant cross-section. This process usually includes key steps such as feeding, melt plasticization, extrusion molding, shaping, and cooling. The structure of an extruder mainly includes key components such as feeding device, material cylinder, screw, and die head.
injection molding
Injection molding is an intermittent processing method. It uses an injection molding machine to inject molten plastic into a closed mold cavity under high pressure, and after cooling and solidification, opens the mold to remove the product. The structure of an injection molding machine is relatively complex, including key parts such as injection system, mold locking system, hydraulic transmission and electrical control system, and injection mold. The process of injection molding mainly includes stages such as mold closing, injection, pressure holding, cooling, and mold opening.
2, Raw material adaptability
Extrusion molding
Extrusion molding has a relatively wide adaptability to raw materials, suitable for most thermoplastic plastics such as polyethylene, polypropylene, polyvinyl chloride, etc., as well as some thermosetting plastics such as phenolic plastics. Extrusion molding requires relatively low flowability of raw materials because the extrusion process is open and there is no significant resistance from the reverse direction of the mold. However, extrusion molding has certain requirements for the strength of the melt, especially in the case of incomplete solidification after the export mold, low melt strength may lead to poor product molding.
injection molding
Injection molding requires high fluidity of raw materials, especially for thin-walled and large products. The injection molding process is completed in a mold, and the geometric constraints of the mold composition do not require high melt strength, but have high requirements for the flowability and filling performance of the raw materials. Injection molding is almost applicable to all thermoplastic materials, and can also process certain thermosetting plastics such as phenolic plastics.
3, Product Features and Quality
Extrusion molding
Products formed by extrusion are usually continuous profiles, such as pipes, sheets, profiles, films, etc. These products have the characteristics of balanced and tight internal organization, stable and accurate size. Extrusion molding can be continuously produced with high production efficiency, simple mold structure, easy manufacturing and maintenance, low investment, and fast results. However, extruded products are limited in terms of shape complexity, making it difficult to produce products with complex structures.
injection molding
Injection molded products are more diverse and can produce various complex shaped plastic products. The structural dimensions of injection molded products are relatively accurate, the surface quality is good, and they can be standardized, normalized, and serialized. The injection molding operation is relatively simple, and the molding mold is easy to adjust and update. It can adopt fully automated production with high production efficiency. In addition, injection molding can also achieve high-precision and high-quality product production, meeting consumers' high requirements for product appearance and performance.
4, Application Fields and Limitations
Extrusion molding
Extrusion molding is widely used in the plastic processing industry, such as the production of continuous products such as pipes, profiles, sheets, and films. In addition, extrusion molding is commonly used in processes such as batching, granulation, rubber filtration, as well as manufacturing various thermoplastic elastomers, rubber products, etc. Extrusion molding has the advantages of high production efficiency, strong adaptability, and wide application range, but it is also limited by the complexity of product shape.
injection molding
Injection molding is widely used in fields such as automotive parts, household appliances, daily necessities, medical equipment, toys, etc. Injection molding can produce products with complex shapes and precise dimensions, and has a wide range of material choices to meet the performance requirements of different fields. However, injection molding equipment requires significant investment, high initial costs, and high precision requirements for molds and equipment.