An injection moulding machine
Paper clip mold opened in molding machine; the nozzle is visible at right
A 1300-ton injection molding machine with robotic arm
An Injection molding machine, or (Injection moulding machine BrE), also known as an injection press, is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, an injection unit and a clamping unit.
Types of injection molding machines
Machines are classified primarily by the type of driving systems they use:
injection molding machines hydraulic molding machine , mechanical molding machine , electrical molding machine , or hybrid molding machine
Hydraulic molding machine
Hydraulic presses have historically been the only option available.injection molding machine. Hydraulic machines, although not nearly as precise, are the predominant type in most of the world, with the exception of Japan.
Mechanical molding machine
Mechanical molding machines use the toggle system for building up tonnage on the clamp side of the machine. Tonnage is required on all machines so that the clamp side of the machine does not open (i.e. tool half mounted on the platen) due to the injection pressure. If the tool half opens up it will create flash in the plastic product.
Electric molding machine
The electric molding machine, also known as Electric Machine Technology (EMT), reduces operation costs by cutting energy consumption and also addresses some of the environmental concerns surrounding the hydraulic press. Electric presses have been shown to be quieter, faster, and have a higher accuracy, however the machines are more expensive.
Hybrid molding machine
Hybrid molding machine (sometimes referred to as “Servo-Hydraulic”) molding machines claim to take advantage of the best features of both hydraulic and electric systems, but in actuality use almost the same amount of electricity to operate as an electric injection molding machine depending on the manufacturer.
A robotic arm is often used to remove the molded components; either by side or top entry, but it is more common for parts to drop out of the mold, through a chute and into a container.
Main components of injection molding machine
Injection molding equipment originates from metal die casting processes. An injection molding machine has two main components.
- Plastic injection unit
- Mold clamping unit
Plastic Injection Unit
In essence, an injection unit’s primary functions are to melt and homogenize a polymer before injecting it into a mold cavity.
The injection is similar to an extruder. It contains a barrel that a hopper with a supply of plastic pellets feeds from one end. Inside the barrel is a screw that turns to mix and heat the polymer. The screw also acts as a ram that quickly moves forward to inject molten plastic into the mold. A non-return valve near the screw’s tip prevents the melted material from flowing backward along the screw’s threads.
Later in the molding cycle, the screw, or ram, returns to its former position. Because of the screw’s dual action, it’s referred to as a reciprocating screw, which also identifies the machine type. Older injection molding machines use a simple ram without screw flights. However, the reciprocating screw design’s superiority has promoted its widespread adoption in today’s custom injection molding companies.
Mold Clamping Unit
The clamping unit’s primary functions include:
Holding the two halves of the mold in proper alignment
Keeping the mold closed during the injection process by applying a clamping force strong enough to resist the injection force.
Opening and closing the mold at the appropriate times during the molding cycle
Clamping units have two platens—a fixed and movable platen—and a mechanism for translating the movable platen. The mechanism is like a power press that a hydraulic piston or mechanical toggle device operates. Larger machines have clamping forces of several thousand tons.