Advantages and disadvantages between the extrusion and injection molding processes

Extrusion molding:

Extrusion is also known as extrusion in plastic processing, and is used in the processing of non-rubber extruders by using hydraulic press pressure to extrude the extrusion of the mold itself. It refers to a processing method in which the material passes through the action between the barrel and the screw of the extruder, is plasticized while being pushed forward by the screw, and continuously passes through the machine head to make various cross-section products or semi-products.

Injection molding:

After the plastic injection molding machine uses plastic to heat to a certain temperature, it can be melted into a liquid property, and the molten liquid is injected into the closed cavity by high pressure, and after cooling and setting, the mold body is ejected and the desired plastic product is obtained.

Raw material comparison:

1. Difference in liquidity

Injection molding requires high fluidity, especially for thin-walled products and large-scale products. Extrusion is a bit looser because the extrusion is open and there is no huge resistance to mold reversal.

2, melt strength

Injection molding is formed in the mold, and there are geometric constraints on the mold composition, which does not require high melt strength. Although there are also geometric limitations of the die, there is no complete cure after the exit die, and in this free state, sometimes it is not well formed (such as spinning) due to low melt strength.

After extrusion, it is often accompanied by subsequent processing in a free state, such as thermoforming, hollow blow molding, in which there are often different degrees of melt stretching, and if the melt strength is low, it is easy to break. Therefore, injection molding generally does not require high melt strength, and extrusion is generally required.

3. Export expansion

Injection molding generally does not have strict requirements on the expansion of the outlet, and the expansion of the extruded outlet can cause great problems. Therefore, the viscoelastic control of injection molding and extrusion materials will also be different.

4, applicable raw materials

Extrusion:

Most thermoplastics and some thermosetting plastics, such as PVC, PS, ABS, PC, PE, PP, PA, acrylic resin, epoxy resin and melamine resin.

Injection molding:

With the exception of a very small number of thermoplastics, almost all thermoplastics can be formed by this method. Injection molding can also process certain thermosetting plastics, such as phenolic plastics.

Feature comparison:

Extrusion

a. The production process is continuous, and the plastic parts of any length can be extruded, and the production efficiency is high;

b. The mold structure is also relatively simple, the manufacturing and maintenance are convenient, the investment is small, and the effect is fast;

c. The internal structure of the plastic parts is closely balanced, and the dimensions are relatively stable and accurate;

d. Adaptability, except for fluoroplastics, all thermoplastics can be extruded, and some thermosets can also be extruded. By changing the die of the machine head, the cross-sectional shape and size of the product can be changed accordingly, so that various plastic parts of different specifications can be produced;

e. Wide application range, simple operation equipment, low investment, quick effect, hygienic production environment, low labor intensity, suitable for mass production.

Injection molding

a. It can inject and shape various plastic products with complicated shapes;

b. The product structure size is relatively accurate and the surface quality is good;

c. Injection molded products can be standardized, standardized, and serialized;

d. The operation is relatively simple, the molding mold is convenient to adjust and update, and the whole automatic production can be adopted, and the production efficiency is high;

e. Injection molding equipment investment is relatively large, mold manufacturing costs are high, product molding process conditions need to be strictly controlled;

f. Short production cycle and high production efficiency.