Geyontech · Daily Learning Notes

2026-07-02 | Gear Transmission & Precision Manufacturing

Part I: Industry News — Shot Peening Technology Becomes Key Means for Gear Fatigue Life

Shot Peening continues to rise in importance in gear manufacturing. Knowledge base data shows carburized gears (20CrMnTi) have fatigue life of approximately 2×10⁶ cycles before peening, improving to 1×10⁷ cycles after peening — a 5× improvement. Medium-carbon Q&T gears (40Cr) improve from 1×10⁶ to 6×10⁶, a 6× improvement.

This effect is not theoretical prediction but measured data. The results are most stable when Almen intensity is controlled at 0.35~0.60 A mm and coverage ≥100%. But note: No heat treatment >250°C after peening, otherwise the residual compressive stress dissipates and the treatment is wasted.

Trend Assessment: In 2026, the gear industry’s demand for longer life is increasingly intense. Shot peening has become a standard process rather than an optional one. For transmission parts exported to Europe, SAE J443 / MIL-S-13165 certification is almost a hard requirement.

Part II: Technical Knowledge Points

Knowledge 1: Three Levels of Heat Treatment Distortion Control

Gear heat treatment distortion is the biggest killer of transmission part yield. The knowledge base organizes 5 types of distortion:

• Ovality distortion — bore becomes elliptical, mainly due to uneven heating/cooling
• Taper distortion — diameter differences at ends, mainly due to cooling sequence
• Bending/warping — axis bending, residual stress release
• Tooth profile/lead distortion — precision grade downgrade
• Shrinkage/expansion — phase transformation volume effect

Control measures target three aspects:

① Design Stage: Uniform wall thickness, choose stable hardenability material (20CrMnTi), reserve grinding allowance, symmetrical structure ② Process Control: Pre-oxidation 400500°C → stepped heating → martempering (near Ms point) → oil temperature 6080°C → tempering ≥2 times each ≥2h → deep freezing -60~-80°C ③ Tooling: Shaft parts vertical hanging, disc parts flat on support, thin-walled ring gears use dedicated quenching dies

Practical Significance: With good heat treatment distortion control, DIN Grade 7 first-pass yield can increase from 60% to over 85%. Less rework means pure profit.

Knowledge 2: DIN Precision Grades & Export Gear Standard Matching

DIN 3961~3967 series standards cover: precision grade → individual tolerances → composite tolerances → gear pair tolerances → backlash tolerances.

For transmission parts exported to Europe, recommended standard matching:

Before quoting for export, the DIN/ISO/AGMA grade correspondence required by the customer must be confirmed. Otherwise, even if the gears are well-made, if the precision grades don’t match, the return cost is extremely high.

Part III: Today’s Reflection

Shot peening + heat treatment distortion control — these two processes are actually a pair of opposites:

Heat treatment aims to control distortion, while shot peening is also cold working deformation (just controlled plastic deformation). In actual production, shot peening is arranged after heat treatment and before finish grinding — first heat treatment to ensure matrix hardness, then shot peening for surface strengthening, finally finish grinding to size. If the sequence is wrong, the parts are scrapped.

This makes me rethink: When we prepare proposals for customers, the sequence of the process route is more important than the specific parameters. Parameters can be adjusted if wrong, but if the sequence is wrong, the cost of redoing is too high. In future proposal documents, the “process route diagram” should be on the first page, with parameter details in the appendix.

Keywords: Gear precision manufacturing · Shot peening · Heat treatment distortion control · DIN gear standards · Fatigue life improvement

Knowledge Tags: #GearTransmission #PrecisionManufacturing #ShotPeening #HeatTreatment #DINStandard #Geyontech