Hydraulic, servo-hydraulic and all-electric injection machines: which one, when?
A comparison of machine types in terms of energy, precision, speed and maintenance, and the criteria for choosing one.
The most notable shift in injection machines in recent years is the move from classic fixed-pump hydraulic machines to servo-hydraulic and all-electric machines. When choosing, "which is better" is the wrong question; "which for which job" is the right one.
Three main types
- Hydraulic (fixed/variable pump): Simple, powerful, common for thick parts and high tonnage. Energy consumption is high; oil heating and temperature swings can affect repeatability.
- Servo-hydraulic: The pump is driven by a servo motor; it uses no energy while idle. Energy savings are noticeable, and it's compatible with existing hydraulic infrastructure.
- All-electric: Every axis is servo-motor driven. High repeatability, fast and precise motion, clean operation (no oil); stands out in fields like medical, optical and electronics. Investment cost is generally high.
- Hybrid: Combinations such as an electric screw with hydraulic clamping.
Selection criteria
| Criterion | Hydraulic | Servo-hydraulic | Electric |
|---|---|---|---|
| Initial investment | Low | Medium | High |
| Energy consumption | High | Medium-low | Lowest |
| Repeatability | Medium | Good | Very good |
| Very high tonnage | Suitable | Suitable | Limited options |
| Clean room | Difficult | Medium | Suitable |
| Maintenance | Oil, seals, pump | Less oil | Bearings, belt, screw |
Actual savings and price difference vary by manufacturer, machine size and cycle time; use this table as a guide, not an absolute.
What changes in the calculation?
- Speed and pressure setting: On electric machines, injection pressure is often shown directly as polymer pressure (force/screw area); on hydraulic machines, hydraulic pressure is shown on the screen and is converted to polymer pressure via the intensification ratio (IR). Pay attention to your machine's units when working with the values on screen.
- Cycle: Because servo machines can perform mold open/close and screw motions quickly, the "other" times in the cycle can shorten.
- Clamping force: The tonnage requirement is independent of machine type; it depends on cavity pressure and projected area.
Questions to ask when deciding
- Production volume and cycle time; in what time does the energy savings calculation pay for itself?
- Part precision and repeatability requirements (medical, optical, connectors).
- Existing spare parts, service and operator familiarity.
- Mold variety and clamping/screw requirements.
Note: The final decision on machine choice should be made with the manufacturer's technical data and your own cycle/energy figures.
Pick your machine in the calculation tool (or enter your own machine's screw diameter and pressure values) to get starting values.
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