Injection moulding is the process of injecting molten liquid plastic into a mold, while blow moulding is the process of blowing plastic into a mold.

Blow molding and injection molding are two types of processing for molded products, but their processing processes are different and have their characteristics.

In simple terms, blow molding vs injection molding: injection molds use the “injection+intense pressure” mode. Blow molding molds use the “injection+blow” mode, and injection mold generally makes a solid core body, while blow molding is an empty core body.

In addition, blow molding vs injection molding: the mold made by custom plastic injection molding process has a gate section, while the mold made by blow moulding process has an uneven surface with a blowing port. 

What is injection molding?

Injection molding is a molding method of producing the shape of an industrial product. Injection moulding is a method of cooling and solidifying hot plastic by pressing it into a metal model using pressure.

It has a short production cycle, little to no post-processing, and can form plastic products with complex shapes and precise dimensions in a single process.

It has high production efficiencies and easy to realize automatic operation, is cost-effective plastic parts, and is suitable for the injection molded production of external packaging plastic parts of household appliances and office automation equipment, etc. However, the molding equipment and molds are expensive.

Injection moulding requires both a custom plastic injection molding machine and an injection moulding tool to complete. The injection molding machine is the main molding equipment that uses plastic molds to make plastic products of various shapes from thermoplastic or thermosetting materials.

Main Types of Injection Molds

The common types of injection molds are two-platen molds, three-platen molds, hot runner molds.

Two-Plate Molds

It is the simplest and most basic type of mold and can be designed as a single cavity mold or multi-cavity mold according to product requirements.

Three plate mold

It is different from the single parting face injection mould in that it has a partially movable stripper plate on the fixed part of the completed mold.

In this design, the runner will be ejected between the first and second plates and the stripper plate will be ejected between the second and third plates to separate the part from the runner.

The double parting surface injection mould is not suitable for large injection parts because it has the characteristics of complex structure, high manufacturing cost and difficult parts machining.

Hot Runner Molds

The hot runner mold is similar to the traditional cold runner mold, the difference is that the hot runner mold injects the plastic material directly into the cavity through the nozzle, there is no runner in the manufacturing process, which greatly improves the utilization rate of raw material flow and avoids waste.

Generally, the plastic injection molding manufacturing cost of hot runner molds is higher than that of cold runner molds, but if the injection molded parts are very small, especially if the molded plastic parts are smaller than the runners, hot runner molds are a more economical choice.

There are many mechanical principles applied in the processing of hot runner molds, especially for multi-cavity molds, and the cycle time required to mold the parts can be reduced by processing through hot runner molds, which is suitable for high volume production and can reap more benefits.

What is blow moulding?

Blow moulding is a method used to process hollow plastic tube containers such as bottles by a blow molding machine. The thermoplastic resin is first extruded or injected and preformed into a tubular blank, which is then placed into a metal cavity and blown to fit snugly on the cavity’s own wall shape and sufficiently cooled and cured.

Blow moulding method of forming plastic bottles, cans, and boxes with the help of compressed air or vacuum, mainly includes blow moulding of hollow parts and film blow moulding. The blow molding process includes the manufacture of plastic blanks and the reshaping of the blanks.

Blow molding types

According to the different manufacturing methods of blanks, there are injection blow moulding and extrusion blow molding.

The difference between injection blow moulding and extrusion blow molding is that the former uses the injection method to manufacture the blanks, while the latter uses the extrusion method to manufacture the blanks.

In recent years, with the continuous development of plastic forming technology, there are new processes such as injection blow moulding, extrusion blow moulding and multi-layer blow moulding.

Characteristics of blow molding

Here are the characteristics of blow moulding from a macro perspective. Blow moulding of hollow products includes three main methods.

Extrusion blow moulding: mainly used for the processing of unsupported blanks. Injection blow moulding: mainly for the processing of blanks supported by metal cores.

Stretch blow moulding: including extrusion a stretch a blow moulding, injection a stretch a blow moulding two methods, can process biaxially oriented products, greatly reducing production costs and improve finished product performance.

In addition, there are multi-layer blow moulding, compression blow moulding, dipping and coating blow moulding, foam blow moulding, three-dimensional blow moulding, etc..

But 75% of the blow molded products with extrusion blow moulding, 24% with injection blow molding, 1% with other blow molding; in all the blow molded plastic parts , 75% belong to biaxially oriented products.

The advantage of extrusion blow moulding is high production efficiency, low equipment costs, a wide range of mold and machinery options, the disadvantage is the high rate of scrap, waste recycling, poor utilization, product thickness control, the dispersion of raw materials is limited, the molding must be trimmed after the operation.

The advantages of injection blow moulding are no scrap generation during processing, good quality control of product wall thickness variation and material dispersion, high molding accuracy of thin-necked molded products, smooth surface of products, and economic small batch production. The disadvantage is the high cost of pieces of equipment, and to a certain extent only suitable for small blow molded products.

The difference between injection mold and blow mold

Both injection moulding and blow molding need to be realized by molds. For injection, the plastic is sealed in the injection chamber and mold throughout the entire process.

On the other hand, the blow mold begins when the mold is removed from the plastic, which gives some more freedom for the blowing to expand the product to reach the necessary, final size. 

The major difference between injection molding and blow moulding is that injection moulding is often used for manufacturing solid components, such as tools, kitchen products, bottle caps, hair combs, and other solid parts.

Through the above introduction, I believe you have a certain understanding of these two processing processes.

The main difference between injection moulding and blow moulding molds lies in the form of product presentation. The injection molding process makes the product usually thicker, simpler to make and requires less raw materials. The high precision match of injection mould generally makes it more expensive than blow molds.

The blow molded product process is different, producing a wall thickness thin and transparent product with slight flaws that are easily visible. Because of this, the blow molding process is more demanding and requires a certain level of toughness and tensile properties from the raw material.

Injection molds and blow molds are widely used in daily life, each has its characteristics and advantages, and its processing technology is also improving year by year, there is a good prospect for future development.

Summary

The foundation of a successful project lies in the selection of the mold type. Generally, a professional injection molding partner and blow moulding partner will consider all factors, including part design, volume, molding environment, mounting system, resin usage, and customer-specific needs, to finally select the appropriate mold type.