Sintered Gears: Powder Metallurgy and MIM Gear Manufacturing
Hydroforce manufactures net-shape sintered gears by conventional powder metallurgy and metal injection molding: spur and helical gears, sprockets, pump gears and miniature MIM gearing, pressed and sintered on our own production line with final densities up to 97% and tolerances from ±0.05 mm as sintered down to ±0.02 mm for MIM parts.
When a gearbox, pump or actuator moves from prototype to volume production, the economics of gear making change completely. Cutting every tooth on a hobbing machine is the right answer for large, highly loaded reducer gears, and we described that route in our article on custom gears for industrial reducers. But for small and medium gears produced in thousands, pressing and sintering the gear directly to shape is usually faster, more repeatable and significantly cheaper. This article covers that second route: sintered gears made by powder metallurgy (PM) and metal injection molding (MIM) on our powder metallurgy line.
Why Sintered Gears
Powder metallurgy builds the gear from metal powder in a die instead of cutting it out of a blank. The tooth profile is formed by the compaction tool itself, so every part leaving the press carries the same geometry. For gear buyers this translates into concrete advantages:
- Net shape, no tooth cutting. The involute is pressed directly. Hobbing, shaping and deburring largely disappear from the routing.
- Material saving up to 30%. Powder goes into the part, not into chips. On volume orders this is a visible line in the piece price.
- High repeatability. One pressing tool, one sintering cycle, thousands of identical gears. Process control replaces part-by-part correction.
- Complex shapes in one cycle. Combination gears, gears with integrated cams, hubs, pockets and asymmetric webs are produced without assembly operations.
- Quieter running. Residual porosity of a sintered gear damps vibration, a property widely used in automotive and appliance drives.
The trade-off is size and loading: powder metallurgy is at its best on small and medium modules and medium torque. Where a drive needs a large, case-hardened and ground gear, the machining route wins, and we offer both under one roof.
From Powder to Precision Gear: Our Process
Our conventional PM route follows the sequence proven across the gear industry, with the process windows we run on our own equipment:
| Stage | What happens | Key parameters on our line |
|---|---|---|
| Powder preparation | Steel powder blended with alloying elements and lubricant | Carbon and alloy steels, stainless steel, copper alloys, titanium |
| Compaction | Tooth profile pressed in a rigid die | Pressing force up to 800 MPa, green density above 95% |
| Sintering | Metallurgical bonding in a controlled atmosphere | 1100 to 1400 °C held to ±5 °C, vacuum, argon or nitrogen |
| Sizing / calibration | Re-pressing to tighten geometry | Tolerances of ±0.05 mm after sintering, tighter after sizing |
| Heat treatment | Hardening where the drawing requires it | Quenching and tempering, case hardening, surface hardening |
| Finishing | Only where the application demands | CNC machining, grinding of bearing seats and bores |
Where tooth flanks need extra load capacity, the industry’s standard answers, sinter-hardening, case hardening and rolling densification of the flank, are applied per drawing after engineering review. Typical sintered gear densities run from 6.8 to 7.2 g/cm³ for conventionally pressed parts; our combined processes reach final densities up to 97% where the application calls for it.
MIM Gears: Miniature and Complex
For gears too small or too intricate for die compaction, we run metal injection molding. Ultra-fine powders below 20 μm are mixed with a polymer binder, injection molded like a plastic part, debound and sintered to a dense metal component:
- Final density above 97%, close to wrought material behaviour
- Standard tolerances of ±0.02 mm, calibrated features down to ±0.01 mm
- Wall thickness down to 0.3 mm, surface finish Ra 0.4 μm without additional finishing
- Stainless steels, tool steels, titanium and superalloys
This is the route for miniature planetary gears, pump internals, medical drive components and electronics actuators, the same technology base we described for MIM and PM lock components.
Gear Types We Produce by PM and MIM
- Spur gears, the classic sintered gear, from small pump pinions to appliance drives
- Helical gears, with helix angles typically up to about 20°, pressed with rotating tooling
- Sprockets and pulleys for chain and belt drives
- Pump gears and gerotors for oil pumps and hydraulic units, an application adjacent to our hydraulic motors and pumps
- Combination gears: gear plus cam, gear plus hub, two gear levels in one pressed part
- Miniature MIM gears for actuators, locks, medical and electronic devices
Internal gears, segment gears and non-standard profiles are quoted per drawing after engineering review.
Sintered or Machined? Choosing the Right Route
Because we operate both technologies, we advise customers on the split honestly. The short version:
| Criterion | Sintered (PM/MIM) gear | Machined gear |
|---|---|---|
| Batch size | From thousands upward | From one piece |
| Gear size | Small to medium, medium module | Up to 2000 mm diameter |
| Piece price at volume | Low, minimal scrap | Higher, chip removal |
| Tooling | Compaction or MIM tool required | No dedicated tooling |
| Accuracy route | As sintered, sized, optionally hard finished | Cut and ground to ISO 1328 classes |
| Typical use | Pumps, appliances, power tools, automotive drives | Reducers, heavy-duty and large drives |
Many of our customers use both: sintered gears for the volume stages of a drive and machined gears for the highly loaded output stage. One supplier, one quality system, one point of responsibility.
Quality Assurance
Every gear order runs through the same quality system as the rest of our production: metallographic analysis of sintered structure, hardness testing, dimensional and profile inspection with Zeiss Contura CMM and dedicated gear measurement tools, and material certificate verification. Hydroforce is certified to ISO 9001:2015, with TÜV and SGS audits confirming the system.
Why Hydroforce for Sintered Gears
Powder metallurgy at Hydroforce is our own production line, not a traded service: powder preparation, compaction, sintering, sizing, heat treatment and post-sintering machining all run under one roof. We support customers from design adaptation for PM (draft angles, density zones, tooth root geometry) through prototyping to full-scale production, with order volumes flexible in both directions.
If your product uses gears in the thousands, sintering them is very likely the most economical route available, and we can prove it with numbers on your own drawing.
Send your gear drawing or a sample part to office@hydroforce.ee or use the contact form. Our engineers will review the geometry, recommend PM, MIM or machining, and quote tooling and piece price for your volumes.