TYPES OF INJECTION MOLDING MACHINE
There is various type of injection molding machine available based on their function and utilization. The cost of the machine is increased depending on their functions and size. The simplest injection molding machine is a hand injection molding machine with a very low cost and the costliest machine may be a screw type automatic microprocessor injection molding machine.
Drawing: Vertical hand injection machine
The simplest mode of injection molding machine may be considered as a hand operated mold which is apt equipment to understand the interaction of major operating parameters. The machine consists of a barrel, plunger, bend heaters, along with energy regulators, rack and pinion system for injecting the material by the plunger a torpedo and nozzle. The clamping is done manually on a working table. The machine is fitted on the working table. Heating is set manually. The capacity of the machine is available from 0.5 Oz 02 Oz. Once heating is achieved the production starts manually. The quality of the product completely depends upon the skill of the operator. The heating set point is achieved by heat and trial method. Although the temperature controller may be fitted on the machine the set point completely depends on the quantity of product produced by the operator. The cycle time is completely variable and it depends on the competent of the operator. The function of torpedo is to help the material for proper melting and create back pressure to help him mixing.
Plunger type injection molding machine:
The plunger type injection molding machine is the available horizontal or vertical type and operated pneumatically or hydraulically. The clamping and injection may be semi or automatic.
Drawing: Vertical and Horizontal plunger type injection molding machine
In a semi-automatic type, the clamping cylinder and the injection cylinder are operated by levers which is connected the pneumatic or hydraulic cylinder. In automatic type, the cylinder is actuated automatically to set times.
Screw type injection molding machine:
The screw type injection molding machine consists of a hopper, a reciprocating screw & barrel assembly, and injection nozzle. This system confines and transports the plastic as it progresses through the fittings, compressing, degassing, melting, injection and packing stage.
Drawing: Screw type injection molding machine
A single screw injection molding machine for thermoplastic, showing the plastic sizing screw, a barrel, band heaters to heat the barrel, a stationary platen, and a movable platen.
Plunger-Plunger Injection Molding machine:
As the plastic industry developed a second type plunger machine appeared, known as to two-stage plunger. This type of equipment involved two plunger units set on top of other the one-two plasticize the material and feed it to another cylinder that consists of a chamber to heat the plastic material by conduction and plunger that operates as a shooting plunger and push the plasticize material into the mold.
- Faster than the conventional machine (single plunger)
- No pressure loss and countered in compacting the granules
- Allow larger parts with a more projected area
- Extra construction for pre-plasticizing so cost is more
Screw Plunger Injection Molding Machine:
Later still variation appeared in which first plunger stage (also known as a pre-plasticizer) was replaced by a rotating screw. In this case, the action of the screw serves to work and melt the resin and feed it into the second plunger unit where the injection ram forces it towards mold.
- Better mixing and shear action of the plastic melt
- The broader range of stiffer flow
- Heat sensitive material can be the processor
- The color change can be handled in shorter time
- Lower stresses are obtained in the molded form
- Higher cost in extra construction for pre plasticizing unit
- Longer cycle time then reciprocating screw type machine