What Are the Steps of Injection Molding


Injection molding is a manufacturing process which includes injecting liquid or molten material into the mold cavity to produce the parts. It is widely practiced to produce parts and components made of plastics, but not only for plastics but also for metals, glass, elastomers, and other materials. Molding begins with the preparation of a mold, commonly being of core and cavity halves, which together determine the shape of the final part. The material being used is typically in the shape of pellets or granules, which is melted down to a molten state first and then forced into the mold under high pressure.


After the material fills the mold and get its shape it is allowed to cool and solidify. The mold closes, then the molten material is injected into the mold cavity. It solidifies and the mold is opened, and the part is ejected. Injection molding is preferred in different industries as it has ability to design parts with the complex geometries, high precision, and a repeatable process. It is also one of the most inexpensive and most effective means of making parts by the hundreds and thousands.

What is injection molding process

Injection Molding Step

Injection molding is a process used in manufacturing to fabricate parts and products widely from plastic. It is a process where molten material usually a mixture of thermoplastic and thermosetting polymers is brought into the mold cavity and is injected under extremely high pressures. The process starts with the processing of the raw material which is usually in the form of small pellets or granules that are melted and then injected into the mold cavity through a nozzle. The mold cavity is normally machined out of steel and is often machine-tooled to the appropriate tolerances of the part.


Then the liquid material is poured into the mold cavity, cooled and set to take the shape of the cavity. The cooling rate of the process is accurately adjusted to prevent the formation of defects during the solidification process. Once the mold has adequately cooled and solidified, it opens and the part is ejected by means of ejector pins or other mechanisms. Only at the end of the mold open, the mold may close to begin a new cycle of injection.


The injection molding has some advantages in manufacturing compared to other processes. The other main feature is the ability to produce the more complex and intricate parts with higher precision and repeatability. This results in formation of plastic parts produced by an injection molding operation. Along with this, injection molding permits to use of an extensive variety of materials, comprising engineering grade plastics, that can be customized in accordance with particular functional requirements (for example, strength, flexibility or heat resistance).


In addition, injection molding is an excellent process in terms of efficiency, with fast cycle times and a small amount of waste. The automation of the production process itself contributes to the reduction of labor costs and achieves higher productivity. Yet, the capital for tooling and equipment is important, being totally required for high-volume runs.


Injection molding is a widely applied industrial process for massive trails of plastic parts. It has several processes done for making of accurate, and well-manufactured parts.

Here's an in-depth look at the injection molding process:

Clamping: The process is initiated with the closure of the mold respectively. The mold is composed of two halves, the static half (the "A" side) and the dynamic half (the "B" side). The two mold clamps injection molding halves are locked perfectly together by high pressure in order to keep them tight during the process.


Injection: While closing the mold, the molten plastic material is injected into the cavity via high-pressure injection. The raw plastic material is heated and liquified in a barrel by the injection molding machine which is usually in pellet or granular form. The screw installed inside the barrel then pushes melted plastic into the mold cavity using the nozzle.


Cooling: Following that, the cavity is filled up the molten plastic, the next process would cooling. The sealing process allows the molten plastic to harden into the final product and have the shape of mold cavity. Cooling can be achieved using different techniques, like circulating cooling water within the channels of the mold or simply waiting for it to cool down naturally.


Ejection: After the plastic component is cooled and stiffened to the required extent, the mold parts are separated, and the part is ejected out of the mold cavity. Assistance in the process can be provided by pins, ejector plates, or other such elements in the mold design. The relevant part, however, may be still attached to the sprue, runner, or gate, which is of excess plastic material that will be trimmed off only later.


Trimming: The flash (the excess plastic material like the sprue, runners, and gate) is trimmed from the plastic part either mechanically (using cutting, stamping, or cavity routing) or manually. This is the process to ensure that the final part meets the requirements in terms of its targeted specifications and looks.


Quality Control: A variety of quality control activities are undertaken along the molding process to make sure the parts produced are within the required specifications. This may be done through visual inspections, dimensional measurements, and any of the other tests that are used in checking for defects, which include warping, sink marks or surface imperfections.

Plastic parts quality control


Regrinding and Recycling: Trace parts of the resulting plastic generated during the injection molding process can be ground and reused. This translates into less wastage and improved sustainability because materials that would get disposed of are recycled.


Mold Maintenance: Maintenance of the injection mold is an important factor in extending the life of the molds and of the components it makes. The mold components can be kept in good operating condition by regular cleaning, lubrication and inspection which would prevent early wear and result in defects in the moulded parts.


Process Optimization: Through molding processes, process efficiency can be improved, cycle times can be reduced, and also material waste can be minimized. This can be done by changing many parameters, e.g. temperature, compression, injection rate, and cooling time, which are tuned to produce the result that is expected.


Documentation and Record-Keeping: Maintenance of the records which include the injection molding process parameters, quality control data and any modification made in the mold or process is crucial for the purpose of tracing, troubleshooting and continuous improvement.

Briefly, the injection molding process has the following components:

Clamping the mold, pumping in liquid plastic, cooling and solidifying the plastic, ejecting the part from the mold, cutting off the excess plastic, performing quality control, recycling scraps, maintaining the mold, optimizing the process, and keeping records throughout the manufacturing process.

How can you calculate the injection molding cycle time.

Accurate determination of the molding cycle time of injection molding is the main thing for reducing production inefficiencies and manufacturing cost calculation. The total period required to go through one complete cycle of injection molding (from closing the mold and then opening it again for the next shot) is called the cycle time. Here's how to calculate it:


Injection Time: Decide the time mold field will be fulfilled with molten plastic. This also includes the time occupied by the injection unit in such operations as the filling of the mold, application of packing pressure (if there is such a need), and maintaining of pressure to ensure proper part formation. The injection time can be calculated using the formula:The injection time can be calculated using the formula:


Tinjection=Vmold/Qinjection is the injection rate.


Cooling Time: Compute the time required for that plastic to cool down and harden within the mold cavity. This varies depending on the factors e.g. the material used, part geometry and mold design. This time can be determined by experimental data, the simulation software, the conducting of the tests.


Ejection Time: Measure the time while the mold is opening, parting, and closing to start the next shot. This also includes the operating time for the ejector and any added seconds spent on removal.


Clamping Time: Do you want to think about the time required for the mold to be clamped with maximum strength before commencement of injection? This also covers the period when the molding mechanism is closed and exerts enough pressure to clamp the two mold halves, to hold them together during injection.


Additional Factors: Consider the additional elements that may affect cycle time, such as raw material handling, mold temperature control and presets (e.g., part de-moulding and secondary operations).


Once you have determined the individual components of the cycle time, you can sum them up to calculate the total injection molding cycle time:


T cycle= T injection+T cooling+T ejection+T clamping+ Additional factors


Regular monitoring and optimizing these variables provides for reduction of cycle times, improvement of productivity and enhancement in the whole efficiency of the injection molding process.


In summary, injection molding is a key technique that is utilized for manufacturing purposes as it is very versatile and efficient. It offers a number of advantages including the high production rates, precision, repeatability, and cost-effectiveness. It is prevalent in different industries and extensively utilized for the high level of plastic parts and components production. As technological advances and materials go on further, the process of injection molding is always improving to allow the manufacturers to fulfill the conditions of current production requirements.

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