Plastic injection molding process
There are two parts that create moldings:
- Injection molding machine
- Plastic injection tooling
Injection molding machine:
Injection molding is the process of transforming raw polymer into final complex plastic components through the aid the injection mold machine which heat plastic, then apply high pressure on the molten plastics to inject and fill the mold cavity.
An injection mold tool consists of two halves. One model half contains the sprue bushing and runner system. The other half houses the ejector system. The molded part is located at the parting line.
We will treat this in more further detail later on.
A mold tool is constructed from a number of sections but the three main section is:
- Fixed hall
This contains the cavity of the part to be molded
- Moving hall
This contains the care of the part to be molded
- Ejector plate
This contains the ejector pins which push the molded part of the core
One half of the mold tool will have the cavity or the female section of the mold, this half is also where the molten plastic is injected through the sprue runner system. This will be the fixed part of the mold.
The moving part at the mold will have the core or male part of the mold. This section will also include the ejection plate and pins.
The two halves of the molding are separated down a parting line. This is where the two halves of the tool match up.
The clamping unit is what holds the two halves of the mold together during the injection process.
There are three different types of clamp design:
Toggle clamp: is a mechanical device to amplify force. In a molding machine, which consists of two bars joined together with a pivot? The end of one bar is attached to a stationary platen; the other end of a second bar is attached to the moveable platen. When the pressure is applied to the pivot, the two bars form a straight line.
Hydraulic clamp: a clamping unit actuated by hydraulic cylinder, which is directly connected to the moving hall of the tool.
Hydromechanical clamp: this clamping system is a combination of mechanical and hydraulic clamping system to move the toggle a hydraulic cylinder is operated.You see the hydraulic ram closed the tool and the mechanical mechanism has locked the tool in place during the injection process.
Injection of polymer into the plastic mold
The molten polymer is pushed up to end of the injection cylinder by the use of a specially designed rotating screw. Once there are enough molten polymers at the end of the cylinder, the screw then forces it into the mold at a controlled speed and pressure. You can this part of the process here in the short clip.