Wind Turbine Gearbox Planet Gears: A DIN 5 Grinding Order Finished in 75 Days
In March 2026, a wind turbine gearbox maker in eastern China handed the planetary stage gears for its 2.X MW gearbox to GeyonTech: one sun gear and three planet gears per set, module 12, 18CrNiMo7-6 steel, DIN class 5 accuracy. From drawing approval to shipment took 75 days — 25 days less than the customer’s original 100-day plan. The first piece passed the customer’s full dimensional re-inspection on the first attempt, and all 12 pieces passed item-by-item checks with no out-of-tolerance readings. Tooth hardness was 58–62 HRC; effective case depth measured 1.8–2.2 mm. The gears have since completed the test-rig run-in and been accepted.
Background
The customer builds gearboxes for onshore wind farms, with a design life of 20 years. The planetary stage carries most of the torque through the gearbox. Tooth contact stresses run high, and under long-term alternating load the failure risk is real, so material, heat treatment, grinding accuracy and crack inspection all matter. Any weak link shows up in the field, years later.
This customer used to make these planetary gears in-house. When capacity tightened, the whole gearbox assembly waited. They wanted an outside supplier that could deliver to DIN tolerances and provide a full set of inspection reports.
The Challenge
The drawing was straightforward, but five conditions had to be met at once:
- Accuracy: DIN class 5 (DIN 3962) — cumulative pitch deviation, profile and helix deviation reported per piece, tooth surface roughness Ra ≤ 0.8 μm;
- Material: 18CrNiMo7-6, carburized and quenched, effective case depth 1.6–2.4 mm, tooth hardness 58–62 HRC, consistent within the batch;
- Distortion: at module 12, carburizing and quenching move the tooth flanks noticeably. Grinding stock must be left at the hobbing stage, and the grinding pass has to bring the distortion back inside tolerance;
- Inspection: ultrasonic (UT) plus magnetic particle (MT) testing on every piece, with reports;
- Lead time: the assembly slot was fixed. The customer’s original plan was about 100 days; the supplier was given less than 80.
The Solution
The process route came first, then the capacity plan.
- Engineering review: the drawings went through a strength check in KISSsoft to ISO 6336 — bending safety at the tooth root and contact safety on the flanks — before grinding parameters were locked in;
- Process route: forged blank → rough turning → hobbing (0.3–0.6 mm grinding stock left) → carburize and quench → finish-turn the locating faces → worm-wheel grinding → deburr → piece-by-piece inspection;
- Heat treatment: fixed furnace loading, furnace temperature and carbon potential set on the process card, so case depth and hardness stay consistent;
- Grinding: worm-wheel grinding machine, tooth roughness held within Ra 0.8 μm;
- Inspection: gear measuring center for profile/helix/pitch reports, CMM for bore position and form tolerances, UT + MT on every piece, hardness checks on flank and core;
- Lead time control: capacity for blanks, heat treatment and grinding was locked in advance; our own inspection data ran in parallel with the customer’s re-inspection instead of waiting for the full batch.
Results
| Item | Result |
|---|---|
| Lead time | 75 days (customer’s original plan: ~100 days) |
| Cumulative pitch deviation Fp | 0.019 mm measured, within DIN 5 |
| Profile deviation fα | 0.011 mm measured |
| Helix deviation Fβ | 0.010 mm measured |
| Tooth hardness | 58–62 HRC, batch spread ≤ 2 HRC |
| Effective case depth | 1.8–2.2 mm measured (drawing: 1.6–2.4 mm) |
| Crack inspection | 12/12 pieces passed UT and MT, no indications |
| First-piece re-inspection | Passed the customer’s full dimensional check on the first attempt |
| Assembly | Test-rig run-in completed and accepted |
Figures above come from the project’s inspection reports and the customer’s re-inspection records. Reference pricing for the sun gear (module 12, 20 teeth): roughly ¥5,000–15,000 per piece, depending on batch size and inspection scope.
What Worked
Distortion control came first. Grinding stock was graded by module and left at 0.3–0.6 mm at hobbing; the locating faces were finish-turned after heat treatment, and enough stock was kept for the grinding pass to correct the distortion.
Then lead time. The three bottleneck operations — blanks, heat treatment, grinding — had capacity locked in ahead of the order. Inspection reports travelled with the parts, so the customer’s re-inspection didn’t queue up. The batch cleared in 75 days.
And data transparency. Every piece shipped with its full report set: profile, helix, pitch, crack inspection, hardness, case depth. The customer’s first-article confirmation passed in one round.
Contact GeyonTech
Looking for a precision gear supplier for your gearbox, reducer or transmission project? Send us the drawings and the duty conditions — our engineering team will reply with a process proposal and a quotation. GeyonTech has 13 years of gear manufacturing experience, grinding capability to DIN class 3, and full inspection reporting to DIN, ISO and AGMA standards.
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