Analysis of three plastic molding processes of injection molding, extrusion and blow molding

Plastic molding is an engineering technique that involves various processes for converting plastic into plastic products. This article will introduce you to the molding process of injection molding , extrusion, and blow molding. The details are as follows:

 

Injection molding, the principle is to add granular or powdery raw materials into the hopper of the injection machine, the raw material is heated and melted into a flowing state, and driven by the screw or piston of the injection machine, enters the mold cavity through the pouring system of the nozzle and the mold. , hardening and shaping in the mold cavity. Factors affecting the quality of injection molding: injection pressure, injection time, injection temperature.

advantage:

1. Short molding cycle, high production efficiency and easy automation

2, can form plastic parts with complex shapes, accurate dimensions, and metal or non-metal inserts

3, product quality is stable

4, a wide range of adaptation

Disadvantages:

1, the price of injection equipment is higher

2, the injection mold structure is complex

3. High production cost, long production cycle, and not suitable for the production of plastic parts in one small batch

application:

In industrial products, injection molded products include: kitchen utensils, housings for electrical equipment, toys and games, various products for the automotive industry, and parts for many other products.

 

Extrusion: Also known as extrusion molding, it is mainly suitable for the molding of thermoplastics, and is also suitable for the formation of thermosetting and reinforced plastics with better fluidity. The molding process uses a rotating screw to extrude the heated and melted thermoplastic material from a machine head having a desired cross-sectional shape, and then shaped by a sizing device, and then chilled and solidified by a cooler to obtain a desired cross section. product.

Process characteristics:

1. Low equipment cost;

2, the operation is simple, the process is easy to control, and it is convenient to realize continuous automatic production;

3, high production efficiency; product quality is uniform and compact;

4. By changing the die of the machine head, it can form products or semi-finished products of various sectional shapes.

application:

In the field of product design, extrusion molding has strong applicability. Extrusion products include tubing, film, bar, monofilament, flat belt, net, hollow container, window, door frame, sheet, cable cladding, monofilament and other profiles.

Blow molding: a molten thermoplastic raw material extruded from an extruder is sandwiched into a mold, and then air is blown into the raw material, and the molten raw material is expanded by air pressure to be bonded to the wall surface of the mold cavity, and finally cooled. A method of curing into the desired product shape. Blow molding is divided into two types: film blowing and hollow blowing:

Film blowing:

Film blow molding is to extrude molten plastic from a circular thin tube in the annular gap of the extruder die, while blowing compressed air from the center hole of the machine head into the inner cavity of the thin tube to inflate the thin tube into a diameter. A larger tubular film that is taken up after cooling.

Hollow blow molding:

Hollow blow molding is a secondary molding technique in which a rubber-like parison closed in a mold cavity is inflated into a hollow product by means of gas pressure, and is a method for producing a hollow plastic product. Hollow blow molding has different manufacturing methods for parisons, such as extrusion blow molding, injection blow molding, and stretch blow molding.

1) Extrusion blow molding: Extrusion blow molding is to extrude a tubular parison by an extruder, sandwich it in a mold cavity and heat the bottom, and then inject a compressed air into the inner cavity of the tube blank to form a blow molding.

2) Injection blow molding: The parison used was obtained by injection molding. The parison is left on the mandrel of the mold, and after the mold is closed by the blow mold, compressed air is introduced from the core mold to inflate the parison, and after cooling, the product is obtained after demolding.

3) stretch blow molding: the parison which has been heated to the stretching temperature is placed in a blow mold, longitudinally stretched with a stretching rod, and transversely stretched and inflated with blown compressed air to obtain a product. method.

advantage:

The product has uniform wall thickness, small weight tolerance, less post-processing and small waste corner; suitable for producing small-sized fine products with large batch size.

application:

Film blowing is mainly used to make plastic thin molds; hollow blow molding is mainly used to make hollow plastic products.