What is the characteristics of injection molding?

Injection molding is a manufacturing process commonly used to manufacture items such as plastic toys, small accessories, auto parts, and mobile phones. Almost everything we use in our daily life is a by-product of the injection molding process.

The process involves the use of injection molding machines, and the materials used are thermoset or thermoplastic. In this process, the material is heated, melted and then placed in the mold cavity. The material is then allowed to cool down and finally ejected. The whole process includes the following 4 steps:

1. Clamping: The mold used for the process is divided into two halves. In this step, the two halves are clamped using a hydraulic clamping unit. One half of the mold is fixed on the injection molding machine, while the other half is allowed to slide. The clamping unit pushes the mold half and applies sufficient force to fix it during the injection of the material. The required clamping force is directly related to the performance of the resin and the injection pressure required to fill the cavity. Thicker resins have a low flow rate and require high pressure to discharge. However, thin resin has a high flow rate and therefore requires a smaller pressure.

2. Injection: The resin in the injection cylinder is liquefied under the action of pressure and heat. The barrel has a heating band to increase the temperature to the correct melting point. The accurate temperature is the most important feature of this process. If the temperature is too high, it will affect the shear stress and filling speed, thereby affecting product quality. On the other hand, if the temperature is too low, the product resin will not be liquefied properly. After the resin is liquefied, the screw in the injection barrel pushes the molten material through the nozzle and fills the mold cavity. The success of this stage depends on three factors: filling speed, filling and sink mark displacement, and shear stress.
3. Cooling: The liquefied plastic inside the mold will cool when it touches the inside of the mold. When the plastic cools, it will take up the shape of the desired part. Also, during the cooling process, some shrinkage may occur. The correct packaging of materials during the injection phase helps to reduce material shrinkage at this stage. The mold remains closed until the required cooling time has elapsed. The cooling time is determined by the thermodynamic properties of the resin and the thickness of the wall portion.
4. Ejection: Once the molded part is completely cured, it is ejected from the mold. During cooling, a lot of force is applied to the ejected parts. This helps prevent parts from sticking to the mold due to shrinkage. In order to promote smooth demolding, the mold release agent is sprayed on the surface of the cavity before injecting the material. After demolding, clamp it until the next injection.
I hope this makes everything about injection molding clear.

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