Injection molding machines are rated mainly by clamping force (tonnage) and shot size. Picking the right size is the key decision.
1. Size by tonnage
Clamping force must match your part's projected area and the plastic used. As a rough guide:
- Small parts (caps, fittings): 50 to 120 tons.
- Medium parts (housings, containers): 150 to 350 tons.
- Large parts (crates, automotive): 400 tons and up.
2. Hydraulic vs servo
Servo (energy-saving) machines cut electricity cost significantly versus older hydraulic machines, important given Pakistan's power tariffs. Hydraulic machines are cheaper upfront and still common on the used market.
3. Inspect a used machine
- Check the clamping unit, tie bars and platens for wear or cracks.
- Test the screw and barrel, look for wear and consistent shots.
- Confirm the heaters, thermocouples and controller all work.
- Watch for hydraulic leaks and oil condition.
- Run a few cycles and check repeatability.
4. Total cost
Budget for the mould(s), a chiller/cooling, a hopper dryer, transport and installation alongside the machine itself. Power-saving servo models pay back over time.
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