Failure analysis for gear tooth breakage: bending fatigue, overload, material defects. 5-Why and 8D corrective actions.
What Is Gear Tooth Breakage? Gear tooth breakage is the fracture of a tooth, usually at the root fillet, under bending fatigue or a single overload event. Fatigue breakage starts as a micro-crack at a stress concentration (a small fillet, a grinding mark or an inclusion) and grows until the remaining section cannot carry the load. Because it leaves characteristic beach marks on the fracture surface, breakage analysis can usually distinguish fatigue from overload. This is a D4 investigation where metallurgy, tooling and process control all come together. Symptoms Fracture at the root fillet, or partial spalling of the contact surface Metallic debris in the gearbox oil, captured by the magnetic plug Knocking or grinding noise during operation Gear mesh frequency (GMF) sidebands in the vibration spectrum Reduced gearbox efficiency and torque fluctuation at the output Affected Components Spur, helical, bevel and worm gears in automotive transmissions and industrial gearboxes Gear materials: case-hardening steels (20MnCr5, 8620), quenched and tempered steels, powder metallurgy Mating gears, shafts, bearings and the gearbox housing Lubrication system (oil pump, filter and oil grade) Detection Methods Vibration spectrum: increasing GMF sidebands and harmonics Oil debris monitoring: magnetic plug inspection and spectrometric Fe analysis Magnetic particle inspection...
