We machine the gear, harden the teeth and control distortion before final inspection. Case depth, core hardness and runout are measured on the part, not assumed from a furnace chart.
Hardening makes or breaks the part. These are the failures we see most often.
Quenching moves the part. If the blank is machined to nominal and the quench is not fixtured, lead and profile drift past the drawing limit. The gear then needs hard finishing, which adds a second setup and days of schedule.
A 0.3 mm case on a gear that sees 1,500 Nm will pit before its rated life. Case depth has to match the contact stress at the pitch line. Too deep is also a problem: the core loses ductility and the tooth can crack at the root.
Hardened surfaces with no tempering relief hold residual stress that pulls the root open. Tempering temperature and time decide whether the gear survives shock loads or fails at the first jam.
Annealing, normalizing, hardening and stress relief can add up to roughly 30% of gear manufacturing cost. Specify the wrong sequence and you pay for two furnace runs plus the extra machining between them.
Machining, heat treating and inspection planned together so the hardening step does not undo the tolerances.
Carburizing suits gears that need a hard, wear-resistant surface over a tough core. We machine AISI 1018, 4320, 5120, 20MnCr5 and ZF-7B blanks to a controlled stock allowance, then diffuse carbon at temperature and quench. The result is a case that resists pitting while the core absorbs shock.
Nitriding skips the quench. It runs cooler, so there is far less distortion and no need for a post-hardening grind on many parts. That makes it a good fit for internal gears, thin webs and finished bores where a few hundredths of a millimeter matter.
A gear that leaves the furnace round and on-lead does not need hard finishing. We set stock allowance from the expected growth, fixture the part during quenching where the geometry allows, and check runout and lead on the first pieces before the batch continues.
When the drawing allows, we leave grinding stock on the bore and faces only. Teeth stay as-machined after hardening. That cuts one operation and keeps the case intact on the flank, which is where the pitting resistance actually lives.
Match the process to the failure mode you are trying to prevent.
| Process | Typical case depth | Best for | Watch out for |
|---|---|---|---|
| Carburizing | 0.5–1.5 mm | Transmission and drive gears under high contact stress | Quench distortion; needs stock allowance |
| Carbonitriding | 0.1–0.5 mm | Small gears, thin sections, mild wear duty | Shallow case; limited load capacity |
| Nitriding | 0.1–0.6 mm | Internal gears, finished bores, low distortion | Long cycle; needs alloy steel with nitride formers |
| Nitrocarburizing | 0.01–0.03 mm | Wear and scuffing resistance on finished parts | Thin compound layer; not for high load |
| Induction hardening | 0.8–3 mm | Large module teeth, shaft journals, local hardening | Coil design per tooth form |
| Through hardening | Full section | Pins, spacers, low-speed gears | Limited surface hardness; tempering needed |
One supplier for the machining, the hardening route and the inspection report.
Turning, hobbing, shaping and broaching on 127 CNC machines. Blanks held to ±0.005 mm so the hardening step starts from a known geometry.
We set the sequence, stock allowance and fixturing before the first chip. Annealing and normalizing when the part needs to be machinable first.
Carburizing and carbonitriding with case depth matched to pitch line stress. Core hardness and surface hardness both checked on the part.
Low-distortion options for internal teeth, thin webs and bores that are already finished to size.
Induction and flame hardening for large module teeth and shaft journals, with the rest of the part left soft.
Bore and face grinding, shot peening, black oxide and laser marking. Reports on request.
| Item | Range | Notes |
|---|---|---|
| Maximum part size | 4,000 mm | Large gears and shafts fit in one setup |
| Machining tolerance | ±0.005 mm | Before hardening; growth is added on top |
| Fine surface finish | Ra 0.2–0.8 μm | Where a finished bore or face is required |
| Standard finish | Ra 1.6–3.2 μm | Typical as-machined tooth flank |
| Gear steels | 1018, 1045, 4130, 4140, 4340 | Plus 20MnCr5, 4320, 5120, ZF-7B |
| Order size | One prototype to 10,000+ | No minimum order quantity |
The blank is cut and the treatment route planned by the same team. No finger-pointing between a machine shop and a heat treater when the teeth come back out of lead.
Pre-hardening geometry is machined to ±0.005 mm. Growth allowance is added deliberately, so the finished gear lands inside the print.
Send the drawing and material callout. You get a price, a process route and notes on where the hardening step is likely to fight the tolerance.
Raw material check, in-process monitoring and final inspection. Reports on request for case depth and hardness.
Production can start within 24 hours of release. Historical late-delivery probability is below 2%.
ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. NDA available on request.
High contact stress at the pitch line, quiet running, long fatigue life.
Large module gears and shaft journals hardened locally, rest of the part left machinable.
Thin webs and internal teeth where quench distortion would scrap the part.
Small gears with a shallow case and a clean surface, built in short runs.
There is no single best route. Carburizing fits gears that see high contact stress at the pitch line and need a hard case over a tough core. Nitriding fits internal teeth, thin webs and finished bores where distortion has to stay small. Induction hardening fits large module teeth or a single journal you want hard while the rest stays soft.
Send the load case and the drawing. We pick the process from the failure mode you are trying to avoid, then set the stock allowance to match.
It depends on section size, material hardenability and how the part is fixtured during the quench. Thin rims and unsupported rings move the most.
We machine the blank with growth allowance taken from the material and geometry, and we check runout and lead on the first pieces. If the drawing allows, we leave grinding stock on the bore and faces only.
Only for low-distortion processes. Nitriding and nitrocarburizing run cool enough that a finished bore usually stays in tolerance.
Carburizing involves a quench, so the part will move. Plan grinding stock on the bore and faces, or accept a hard-finishing operation after the furnace.
Match it to the contact stress at the pitch line and the module. A shallow case pits early under high load; an overly deep case leaves too little ductile core and raises root cracking risk.
Typical carburized gears run 0.5–1.5 mm, carbonitrided parts 0.1–0.5 mm, nitrided parts 0.1–0.6 mm. We confirm the target with you before the run starts.
Yes, on request. We inspect the part, not just the furnace chart. Surface hardness, core hardness and case depth can be documented, along with runout and lead measurements.
Raw material is checked on arrival, the process is monitored in run, and every part is inspected before shipment.
We machine 1018, 1045, 4130, 4140 and 4340, plus carburizing grades such as 4320, 5120, 20MnCr5 and ZF-7B. Stainless grades including 17-4PH are available for corrosion-resistant drives.
Tell us the drawing hardness callout and we will confirm the steel and the route.
There is none. We run from one prototype to 10,000+ part runs on the same process route.
Prototypes are useful for checking distortion before you commit to a production batch, because the hardening behavior is measured on your geometry.
Upload the drawing or a 3D file with the material, hardness callout and any case depth requirement. We return a quote and a DFM note within 12 hours.
Uploads stay confidential, and an NDA is available on request.
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