Injection Molding Machines: Design, Types and Applications
1 Oct 2026
A short overview of injection molding machines: how an injection molding machine works, the parameters used to select it, the available designs, drives and molds, and what is installed next to the machine. Prepared by the specialists of Plastic Expert.
What is an injection molding machine
An injection molding machine is a machine that works in cycles. This is what distinguishes it from an extruder: an extruder runs continuously and cannot be paused without restarting the whole process. On an injection molding machine, parts of a set size and shape are produced by injection molding.
Principle of operation
- Pellets enter the barrel through the feed hopper.
- The screw rotates, picks up a dose and moves back — the material melts and accumulates in front of the screw.
- The screw moves forward like a syringe plunger and injects the melt into the closed mold.
- The part cools in the mold.
- The mold opens, and the finished part drops into a container.
Key parameters
- Clamping force (in tons) — the force with which the two mold halves are closed before and during injection.
- Injection volume — the maximum amount of material in the barrel before injection.
- Injection speed and pressure — reference parameters.
- Platen working area and distance between tie bars — these determine which mold will fit on the machine.
Types of injection molding machines by clamping design
By the presence of tie bars:
- tie-bar machines — the mold size is limited by the distance between the tie bars;
- tie-bar-less machines — the tie bars do not limit the mold.
By clamping mechanism:
- with a toggle mechanism;
- with a plunger mechanism.
Types of drive
The main machines are hydraulic. They are easy to maintain and can produce almost any parts, including large ones. An electric drive gives smoother platen movement and higher speed: such machines are needed, for example, for making coffee lids. Hybrid machines also exist.
Molds: hot runner and cold runner
- Cold runner molds are cheaper, but when the mold opens the casting comes out together with the runner system. The sprue has to be separated and recycled.
- Hot runner molds have a manifold with heated material that is pushed out into the mold cavities. They are larger and more expensive, but work without sprues.
Hot runner molds are used for thin-walled items — preserves, salad packaging. For large items, such as buckets, cold runner molds are acceptable.
Auxiliary equipment
- chillers (industrial coolers) — circulate coolant through the molds;
- manipulators and robots — remove finished parts;
- enlarged feed hoppers with raw material drying;
- dosing units — add colorant.
What to read and watch next
- Injection molding machines in the catalog.
- How to choose an injection molding machine and not regret it.
- Buying an injection molding machine: mistakes that cost millions.
- What are chillers.
A Plastic Expert manager will help select a machine for your product and mold: 8 (800) 700-49-01.
