Injection Molding - How Does It Work?

Marcin Napierała

September 9, 2025

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5 min czytania

The importance of injection molding technology in industry is not to be overestimated. By using the appropriate machining methods, very detailed details with the desired shapes and performance characteristics can be obtained. It is not surprising that more and more companies are declaring their desire to use this process to improve the production of plastic components. Check out what injection molding is all about and how the whole procedure goes.

Plastic Injection Molding

The injection molding process is widely used in industry, among others in the plastics processing industry, automotive sector or construction. Today, more than 80% of the polymer materials that hit the market come from plastic injection. This process offers many benefits that address both budgetary and environmental issues. The high quality and precision of the components and the automation of production, make plastic injection molding readily used by enterprises that deal with serial or large series production.

Regarding the ecological aspect, it is worth paying attention to issues such as low emissions of harmful substances into the atmosphere and the generation of a small amount of waste. The use of injection molds also supports the development of the recycling industry, as the resulting components can be reprocessed.

Liquefaction of plastic under the influence of heat

Plastic injection molding is a process in which temperature control is crucial for excellent effect. In this process, a huge role is played by various types of heaters. These are, for example, ceramic band heaters, which are specially designed to maintain a constant and precise temperature inside the forming tool. Thanks to them, it is possible to achieve uniform heat distribution, which is extremely important in the process of creating precise and durable components. In turn ceramic band heaters are distinguished by excellent insulation and the ability to reach high temperatures.

In some cases, especially in the plastics processing industry, hot nozzles play a key role in the injection molding process. They use heaters to heat and dissolve the plastic, which allows the material to be injected into the mold smoothly and evenly.

Conditions for carrying out the injection molding process

The central unit of the injection molding system is an injection molding machine - a multifunctional machine that allows the production of workpieces. Thanks to it, you can get a lot of repetitive elements with the required physical properties.

A prerequisite for the process to be carried out correctly is the correct injection temperature, which allows to maintain adequate fluidity. If it is too low, the mass will remain solid or will not be flexible enough to allow the injection process to be carried out. In turn, too high values will lead to damage to the polymers and loss of their properties, as a result of which the finished components may not meet the required production standards of the parts.

An equally important parameter is the injection pressure in the cylinder of the machine, which is exerted on the plastic mass, which is injected into the injection mold. If its values are too low, its surface will not be filled with plastic. Too high pressure can, in turn, cause the plastic to spill out.

Injection moulding — how does this process work?

The plastic molding process is based on heating the material in the form of granules until a plastic mold is obtained. Then the plastic is transferred to the mold socket, the dimensions and shape of which are designed for individual order. After lowering the temperature, hardening of the introduced plastic occurs, which is then removed from the forming sockets. Depending on the dimensions of the manufactured elements, the whole procedure can take from several minutes to even several hours.

Injection Molding Cycle:

Introduction of plastic into injection molding machine

The rotational movement of the screw, a special spiral located in the cylinder of the injection molding machine, causes the plasticized plastic to move along the inner walls of the machine. Thanks to the use of heating elements in the cylinder, such as ceramic band heaters and constant stirring, the mass maintains the right temperature. The combination of high pressure and the required temperature ensures that the molten plastic retains its liquefied form.

Also check out other types of heating elements: ring heaters, coil heaters, band heaters

Specific injection

The auger forehead presses the plastic mass into the mold through special nozzles and a system of channels hollowed out in the mold. The design of the tool facilitates fast and precise filling in the shortest possible time.

Chilling

When the plastic is already in a closed injection mold, it is cooled or heated. Cooled molds are used for thermoplastics, and heated - thermosetting.

Injection mold emptying

The injection mold usually consists of two parts. After cooling, the fitting is released from the mold (automatically or manually).

Injection Mould Closure

After the mass is extracted, the injection molds are closed again and the injection cycle can be realized again.

Purification of the finished product

It happens that the finished product has an excess of material. In this case, it is necessary to mechanically remove the excess and polish the surface in the place of the joints.

Plastic injection techniques, that is, injection molding methods

The topic of injection molding is very broad. The multitude of polymer materials available on the market has resulted in the dynamic development of technologies used in the processing of plastics. Today, there are more than a dozen unconventional machining methods that make it possible to create elements of complex shapes and complex construction. Choosing the right one depends on the type of plastic. Among the most popular of them are:

SUEDE (Water Assist Injection Molding) — water-assisted molding process,
GUM (Gas Assist Injection Moldingin the presence of gas,
Multicomponent Injection Molding — multi-component or multi-color injection.

All of these methods make it possible to produce mouldings with specific characteristics and achieve high dimensional stability.

summary

Although plastic injection molding seems to be a relatively simple and intuitive process, it requires a lot of knowledge in the field of materials science. Polymers have different technical parameters, e.g. melt flow rate or thermal conductivity. Understanding these characteristics allows you to choose a material that will work for specific applications. For this reason, it is better to entrust the production process of plastic parts to companies that have the appropriate technical background and construction experience.