The difference between blow molding and injection molding

Blow molding and injection molding are two common plastic molding processes that differ significantly in multiple aspects. The following is a detailed comparison of these two molding processes:

1、 Forming process

Blow molding:

Blow molding, also known as hollow blow molding, is a rapidly developing plastic processing method.

The tubular plastic preform obtained by extrusion or injection molding of thermoplastic resin is placed in a split mold while it is hot (or heated to a softened state). After closing the mold, compressed air is immediately introduced into the preform to inflate it and tightly adhere to the inner wall of the mold. After cooling and demolding, various hollow products are obtained.

According to the production method of preforms, blow molding can be divided into extrusion blow molding and injection blow molding, with newly developed methods including multi-layer blow molding and stretch blow molding.

Injection molding:

Injection molding refers to the injection molding of thermoplastic materials.

Injection molding is the process of melting plastic material and then injecting it into a film cavity. Once molten plastic enters the mold, it is cooled and molded into a certain shape according to the mold cavity sample, and the resulting shape is often the finished product, which does not require any further processing before installation or use as the final product.

The injection molding machine has two basic components: an injection device for melting and feeding plastic into the mold, and a mold closing device. The function of the mold clamping device is to close the mold under injection pressure and remove the product. The injection device melts the plastic before injecting it into the mold, and then controls the pressure and speed to inject the melt into the mold. There are currently two designs of injection devices used: screw pre plasticizers or two-stage devices, and reciprocating screws.

2、 Raw material usage

Blow molding:

The raw materials for blow molding are usually polyethylene, polyvinyl chloride, polypropylene, polystyrene, thermoplastic polyester, polycarbonate, polyamide, cellulose acetate, and polyacetal resin, among which polyethylene is the most widely used.

Injection molding:

The raw materials for injection molding are usually thermoplastic or thermosetting plastics.

3、 Product application

Blow molding:

Blow molding is widely used in industries such as bottles, cans, baby products, sports goods, chemical product packaging, lubricant packaging, and bulk material packaging. The obtained hollow containers are also widely used as industrial packaging containers.

Injection molding:

Injection molding is widely used in fields such as automotive parts, household appliances, mobile phones, laptops, various plastic casings, communications, micro motors, computers, appliances, electronics, toys, clocks, lighting fixtures, locomotives, medical equipment, daily necessities, etc. Its efficient production method and diverse product forms have made injection molding technology the mainstream production method in the plastic products industry.

4、 Product Features

Blow molding:

Blow molded products are usually hollow structures, with uneven surfaces and air vents.

Injection molding:

Injection molded products are usually solid cores with high appearance quality, dimensional accuracy, positional accuracy, and functionality. However, injection molded products may also have defects such as silver discoloration, weld marks, flash edges, shrinkage, missing glue, warping, and brittleness.

In summary, blow molding and injection molding have significant differences in molding processes, raw material usage, product applications, and product characteristics. The choice of molding process mainly depends on the specific needs and design requirements of the product.