Guide
Powder Metal or Machined Gears: What Do You Give Up and Gain at 10,000 a Year?
Powder metal or machined gears is a choice between pressing and sintering a gear from metal powder in a hard tool, and cutting it from wrought steel. Sintered gears give up some strength and accuracy headroom and gain material use, built-in features and a repeatable tooth form; at about 10,000 a year the deciding questions are load, accuracy class and how much machining is left after sintering.
By Saola Manufacturing engineering team · Published · Updated
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What do powder metal gears give up against machined gears?
Some strength headroom and some accuracy headroom. One powder maker’s review says high performance sintered gears match wrought gears in strength and geometry except in high-end automotive and aerospace transmissions, but that strength comes from added density and surface densification, not from ordinary pressed-and-sintered steel.
The review (Dizdar, Höganäs, 2010) states that, apart from high-end gear applications in automotive and aerospace transmissions, high performance sintered steel gears meet wrought steel gears in gear strength and geometrical quality. Its own test conclusions are more specific: pitting resistance of the sintered gears reached over 70 percent of the wrought reference, and tooth-root strength and roller contact fatigue met it. Note the source: Höganäs sells the powder, and the gears tested were prototypes of small module.
An older, independent view comes from Sanderow, Gear Technology, 1996, written in 1996 and so predating the density gains in the review. It states that, compared with wrought steel gears, powder metal gears have lower impact resistance, fatigue strength and contact stress capability because of porosity, which may limit a same-size replacement. It lists double press and double sinter, warm compaction, higher sintering temperature and case hardening as ways to recover part of the gap, and notes that a larger gear or a better fillet radius can recover bending strength where the design space allows.
Two geometric limits also appear. Sanderow, Gear Technology, 1996 says helical and bevel teeth cannot be compacted to the density possible in spur teeth, because part of the pressure is lost to friction, and that the face width of powder metal gears is limited to well under 3 in. with the lowest density at the midpoint of the width. Both limits matter for a gear carrier or a wide helical gear.
| Measure | Wrought, machined, case hardened, ground | Sintered, shot-peened or gear rolled, case hardened |
|---|---|---|
| Tooth-root strength (MPa) | 1000 at P0.99; 1300 at P0.50 for module 1.5875 mm | 1100 to 1300 at P0.50 (module 1.5875 mm) |
| Gear quality | DIN 7 | DIN 7 to 8 |
| Flank roughness | Ra below 0.25 µm | Ra below 0.20 µm |
What do powder metal gears gain?
Material utilization, built-in features and a repeatable tooth form. Powder metal also damps noise through residual porosity, and true involute forms are easier to make by pressing than by other fabrication methods.
The Höganäs paper quotes a Metal Powder Industries Federation study of a truck transmission notch segment, a gear-like part: powder metal used 95 percent of its raw material against 40 to 50 percent for machining, needed 6 manufacturing steps against 17, and used 1.243 kWh per piece against 2.847 kWh (Dizdar, Höganäs, 2010). The author says the numbers for gears will not be much different. Treat this as supplier-quoted and as a different part from yours, but the direction is plain: the chips machined from bar are what powder metal avoids.
PickPM, Typical Powder Metallurgy Parts says true involute gear forms are easier to produce through powder metallurgy than by other fabrication methods, that blind corners are possible so no undercut relief is needed, that carbide dies give long tool life and accuracy, and that residual porosity helps damp noise. Sanderow, Gear Technology, 1996 adds keyways, drive lugs, splines, cam contours and lightening holes formed in the compaction step, and a consistent tooth form and surface finish over long runs.Those features are where the cost goes when the same gear is machined: a hub, a spline or a cam profile that a press forms in one stroke is separate machining operations on a bar. If your gear has several of them, the powder route removes more machining than a plain spur gear would suggest.
How accurate can each route make the gear teeth?
As pressed and hardened, sintered gears usually reach a coarser class than ground wrought gears; with gear rolling they can reach the same range. Accuracy class is where cost climbs on the powder route, because tighter classes need secondary operations.
The Höganäs paper says gears of about 7.1 g/cm³ made by pressing, sintering and hardening usually reach no better than DIN 10, and that gear rolling can improve all deviations to DIN 6 to 7, with DIN 8 enveloping all tooth deviations (Dizdar, Höganäs, 2010). It adds that case hardening can drag the teeth back to DIN 10 unless the pressing and rolling dies compensate. The ground wrought reference in its summary table is DIN 7.
Sanderow, Gear Technology, 1996 gives the same picture on the AGMA scale: an AGMA Q7 gear is feasible with no extra processing for small and medium-size gears, a sizing or boring operation is needed to reach Q8 or Q9, and very large gears of 4 to 6 in. pitch diameter come out at Q6 without secondary operations. Do not convert between the two scales by feel: AGMA Q numbers rise as quality improves, while DIN class numbers fall. PickPM, Typical Powder Metallurgy Parts states that cost rises with the AGMA class because of the secondary operations needed for tighter tolerances, and that close total indicator readings are harder to hold than with arbor-cut gears, since hole location depends on the running tolerances of the tool members. Grinding the gear bore true to the pitch diameter reduces the runout.What changes when the volume is about 10,000 a year?
Volume decides whether a hard tool is worth building, but at this level the better question is how much machining is left after the gear is sintered. If sintering replaces most of the cutting and little is added back, the powder route wins; if not, the tool buys little.
A pressing die is dedicated tooling, so the tool cost is spread over the gears it makes. A machined gear needs no such tool, and its cost is machine time on every piece. At about 10,000 a year the tool is spread over fewer pieces than in an automotive program, so the case for powder metal rests on real machining removed: the tooth form, the hub, splines and lightening holes in one stroke, not a plain disc with teeth.
There is also a hybrid. The Höganäs review describes a clever blank concept: press and sinter the gear blank, densify the surface, harden it, and then send it for hard finishing to reach the final geometric quality (Dizdar, Höganäs, 2010). It keeps most of the material and energy benefit and leaves the final accuracy to a finishing step. For a gear carrier or a hub-and-gear part, the finishing of bores and cross features is ordinary CNC work.
A caution on conversions. The same review says that many gears in service have never had a load-capacity calculation or experimental verification, so any change of design or process raises questions and uncertainty, and conversion to sintered gears is a particular uncertainty (Dizdar, Höganäs, 2010). Plan a gearbox life test on sintered samples before committing the program; do not decide from the tables alone.
Which route fits which gear?
Powder metal fits spur and planet gears with features along the pressing axis, moderate to high load and an accuracy class the process reaches. Machined gears fit the top accuracy classes, wide or complex helical forms, and designs not yet frozen.
The grid below summarizes the sources in one place. It is a screening aid, not a standard: your load case and gearbox test decide the final answer.
| Condition | Leans powder metal | Leans machined |
|---|---|---|
| Load and life | Moderate to high, with high density and surface densification, proven in a life test | High-end automotive or aerospace transmissions; no time or budget to validate |
| Accuracy class | As pressed and hardened about DIN 10; DIN 6 to 7 with gear rolling | Ground teeth at the top classes; tight runout from arbor-cut gears |
| Geometry | Spur and planet gears; steps, hubs, splines and cams along the pressing direction; blind corners | Wide face width; helical or bevel teeth needing uniform density; undercuts |
| Features | Several features formed in one pressing | Plain gear on bar |
| Noise | Residual porosity damps noise | No porosity damping; quiet running depends on tooth accuracy |
| Volume and design stability | Frozen design, enough pieces to carry a die | Design still changing, or too few pieces for a die |
What should an RFQ for a gear that could go either way contain?
The full gear data, the load and life requirement, the accuracy class with its standard named, the finish-machining scope, and a request to quote both routes on the same basis.
List module, number of teeth, pressure angle, helix angle, face width, material and heat treatment, the accuracy class and which standard it comes from (DIN or AGMA), and the surface roughness on the flanks. Add the gearbox duty: torque, speed, life, noise target. Without the duty, no supplier can say whether sintered material is enough.
Ask for the powder route to state its density, its surface densification and its case depth, and ask for the same finish machining on both routes so the quotes compare. Our guide on density, sizing and roll densification for powder metal gear strength covers what to write for those. Quality of either route can be inspected with the same equipment: Sanderow, Gear Technology, 1996 says a rolling or composite gear checker suits fine pitch gears and an involute or element checker suits coarser ones, with tooth torque or tooth breaking tests on a sample from each lot.
Saola places powder metal and MIM work through a partner plant it manages and does not name, and the quote states the production site and country of origin. The lead CNC plant’s CNC turning and CNC milling cover the machining around the gear: blanks, bores, hubs and cross features. Where the teeth are cut or formed is stated on the quote, route by route.
Frequently asked
Are sintered gears as strong as machined gears?
In the Höganäs tests, sintered prototypes matched the wrought tooth-root reference and reached over 70 percent of the pitting reference, except for high-end automotive and aerospace applications. Ordinary pressed-and-sintered gears are weaker; the strength depends on density and surface densification.
Can powder metal make helical gears?
Yes, per PickPM, and copper infiltration is sometimes used to raise tooth density. Sanderow notes that helical and bevel teeth cannot reach the density of spur teeth, so check the strength case with the supplier.
What accuracy class does powder metal reach?
About DIN 10 as pressed and hardened at 7.1 g/cm³, and DIN 6 to 7 with gear rolling, per the Höganäs paper. On the AGMA scale, Q7 is feasible without extra processing for small and medium gears, per Sanderow (1996).
Is powder metal worth it at 10,000 gears a year?
It is when sintering removes substantial machining and little is added back. Judge by the machining content of your gear, not by volume alone, and quote both routes on the same scope.
How old is the Gear Technology source, and does it still apply?
It was published in 1996, before the density gains described in the 2010 review, so use it for the mechanisms and the geometry limits, not as a current performance ceiling.
Sources
- Dizdar, S., High performance sintered steel gears for use in transmissions and machinery: a critical review, Höganäs AB, presented at the International Conference on Gears, Munich, October 2010 (a powder supplier’s paper)
- Sanderow, H. I., Gear Design and Inspection (powder metal gears), Gear Technology, September/October 1996 (old; read for mechanisms, not current limits)
- PickPM, Typical Powder Metallurgy Parts, MPIF powder metallurgy design center, accessed October 2026 (2026)