The real gains land where gears fail: the root fillet. We machine the tooth form, control the peening variables, and verify the compressive layer before parts ship.
Four complaints we hear from gearbox and drivetrain engineers before peening enters the drawing.
A ground flank leaves a thin, lightly stressed skin. Under repeated contact the subsurface stays in tension, micropits open, and the flank spalls. Field returns then carry a gearbox teardown and a full rebuild, not a rework of one tooth.
The fillet is the highest-stress zone on any loaded tooth. A visible machining mark or a sharp grind line there acts as a stress riser. Cracks start in service, usually well inside the warranty window, and the fix is a new gear set rather than a repair.
Carburizing and induction hardening build a hard case. That does not put the surface into compression. Two gears with the same case depth can differ by a wide margin in bending fatigue life once residual stress is measured instead of assumed.
Shot size, coverage, and intensity often go unrecorded. The part still looks peened. The compressive layer is thinner than the drawing assumed, and the first fatigue failure arrives at 40% of expected life. No paperwork means no traceable cause.
We treat peening as a measured process step, not a finishing afterthought.
Spherical media strike the surface at controlled velocity. Each impact yields a shallow dimple and stretches the metal around it. The stretched skin wants to return, but the material beneath holds it in place, so the surface ends up in compression with a balancing tension zone below.
That compression is what resists crack initiation. Cracks open under tension, and a compressive surface closes them again on every load cycle. On a gear tooth the effect is strongest exactly where bending stress peaks, at the root fillet, and that is where we aim coverage first.
Peening does not remove tool marks, it buries them. We cut the tooth form, blend the root fillet to the drawing radius, and control flank finish to Ra 0.8–1.6 μm on the 5-axis centers before any media touches the part. Distortion from heat treat is corrected in a separate step, so the geometry that gets peened is the geometry you specified.
After peening we do not grind the fillet. Grinding removes the compressive layer and puts a fresh tensile skin back on the highest-stress zone. If a flank needs final sizing, it happens before peening, and the peening follows as the last mechanical operation.
Use this to decide whether the process belongs on your part.
| Condition | Does peening help? | Reason |
|---|---|---|
| Bending fatigue at root fillet | Yes, main benefit | Compression opposes the peak tensile stress |
| Flank pitting under contact load | Yes, with good finish | Peening plus low Ra delays micropit growth |
| Already ground after peening | No, layer removed | Grinding strips the compressive skin |
| Sharp fillet, no radius | Fix geometry first | A stress riser defeats the peening |
| Soft plastic or low-strength alloy | Rarely worth it | Dimples flatten without holding stress |
| Thin wall, tight flatness | Plan for distortion | Peening can bow thin sections |
| Casting porosity near surface | Sometimes | Closes surface pores, does not fix deep voids |
| Shaft or spline in same drivetrain | Yes, same setup | Same fatigue logic applies to the shaft |
One shop for the geometry, the surface, and the paperwork.
16 simultaneous 5-axis centers cut tooth forms, helical flanks, and blended root fillets in one setup. Fewer setups means the fillet radius holds its tolerance.
27 three-axis machines, 12 four-axis mills, and 16 mill-turn centers handle gear blanks, hubs, shafts, and splines up to 4,000 mm.
Bead blasting, tumbling, brushing, and polishing prepare the flank before peening and clean up after. We keep the two operations in a fixed order.
One-off gears and test coupons before you commit to a run. No minimum order quantity, from a single prototype to 10,000+ parts.
Raw material check, in-process monitoring, final inspection. Dimensional and surface reports on request, with the peening parameters recorded.
4130, 4140, 4340, 17-4PH, and case-hardening steels behave differently under peening. We flag the grade before the process is fixed.
The numbers a fatigue engineer usually asks for.
| Variable | What we set | Why it matters |
|---|---|---|
| Media type | Cast steel, cut wire, glass, ceramic | Hardness match to part material |
| Media size | Selected to fillet radius | Too large bridges the fillet |
| Almen intensity | Per drawing or fatigue target | Sets the depth of compression |
| Coverage | 100% at fillet, documented | Uncovered zones stay in tension |
| Angle of impact | Normal to fillet surface | Oblique impact wastes energy |
| Nozzle distance | Fixed per fixture | Repeatability across the run |
| Fixture rotation | Uniform exposure | Prevents streaks and shadows |
| Post-peen step | No grinding on fillet | Protects the compressive layer |
Fifteen years in Dongguan, three plants, and a quality system built for drivetrain work.
Fifteen years of gear, shaft, and housing work across automotive, aerospace, robotics, and industrial machinery programs.
Held on machined features, or ±0.0002 in. Fillet radii and tooth geometry are checked against the drawing before peening starts.
Large gear blanks and shafts fit the travel envelope. Compact work down to 500 × 310 × 200 mm runs on the smaller centers.
Automotive quality management alongside ISO 9001:2015, ISO 13485:2016 for medical, and ISO 27001:2022 for data security.
Quotation and free DFM analysis within 12 hours. Production can start within 24 hours of approval, with parts shipping in 3–5 days.
100% inspection before shipment on every order, with reports available. Historical late-delivery probability stays below 2%.
Transmission and reducer gears where bending fatigue at the fillet sets the service interval. IATF 16949 process control from blank to final inspection.
Small, high-load gears in actuator and accessory drives. Tight fillet radii need smaller media so the shot reaches the root instead of bridging it.
Gears and shafts up to 4,000 mm where load capacity per tooth matters more than weight. Peening plus a corrected fillet radius raises the bending limit.
Cycloidal and planetary stages that see millions of cycles. Coverage at the fillet and a documented Almen intensity give the fatigue model a real input.
It changes the surface by a very small amount, typically a few thousandths of a millimeter on the dimpled skin. That is inside our machining tolerance for most gear features.
If your drawing has a tight flank tolerance, tell us. We can leave the pre-peen dimension at the top of the band so the finished part still lands in spec.
Yes, as long as the peening is the last mechanical step. Grinding after peening removes the compressive layer and leaves a fresh tensile surface at the fillet.
If a flank needs final sizing, finish the grind first, then peen. We will not grind the root fillet after peening.
Both, but for different reasons. Coverage decides whether the whole stressed zone is treated. Intensity sets how deep the compression reaches.
A part with 200% coverage at low intensity has a shallow layer. A part at full intensity with 80% coverage has untreated pockets that can start cracks. We record both.
It can. Peening puts one side of a thin section into compression and can bow it. Long, slender shafts are the usual risk.
We handle it with balanced peening on both sides, controlled rotation, and a straightness check after the process. For very thin webs we may recommend reducing the intensity.
The fillet is the priority because bending stress peaks there. Extending coverage across the full tooth face also helps flank pitting and oil retention.
For gears that only see bending load, fillet-only peening is a reasonable cost trade. For contact-fatigue-limited gears, cover the whole face.
Harder, higher-strength steels hold compressive stress better and hold it longer under load. 4140, 4340, and case-hardened grades respond well.
Soft, low-strength alloys and most plastics flatten the dimples without storing useful stress. We will tell you if peening is not worth the cost on your grade.
Yes, but we inspect first. If the fillet has a sharp grind line or the radius is under the drawing value, peening will not fix it.
In that case we quote a light machining pass to correct the fillet, then peen. That order matters more than the peening parameters themselves.
We record media type and size, intensity, coverage, and the process sequence for each lot. Dimensional and surface reports are available on request.
Raw material check, in-process monitoring, and final inspection run on every order. 100% inspection before shipment is standard, not an add-on.
Upload a gear drawing and we will come back with machining steps, peening parameters, and a quote within 12 hours.
12-hour quote100% inspectionNo minimum order quantityNDA on request
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