(V) Case study- The Effect of Steel Inclusion on Fatigue Life of Hypoid Drive Pinion
The Primary Function of Drive Pinion is to Transmit the Power from Propeller Shaft to Crown Wheel (Ring Gear). Being a Prime member in Rear Axle, the Quality is inevitable parameter in the Pinion. In this case The Axles is tested for Hypoid Gear Set Fatigue validation on Test Rig. Out of 3 Axle Samples, the SN2 sample did not meet the acceptance criteria but SN1 & SN3 are met. SN2 failed at 66191 cycles & SN1, SN2 failed at 93910 & 91267 cycles. The Drop in Fatigue life cycles is 28.5% which is significant. The Fractography revealed that SN2 drive pinion is fractured due to Inclusion segregation found at the subsurface of tooth Flank. SEM EDS analysis conducted & identified inclusion as Predominantly Al oxides clusters AL2O3. The Steel Process reviewed, Ishikawa diagram plotted to understand the Root cause. The Cast Billet End Cutting operation found suspicious as it has Manual intervention at Hot Condition. To generate the Defect DOE conducted on 3 Heats. Heat H1 with 1.2mter end cut length, HeatH2 & Heat H3 are with 1.5 meter & 2 meter respectively. Multiple samples drawn at these locations to analyze for Micro & Macro Inclusion behavior of the heats. The outcome shows the heat 3 samples are having the Micro & Macro inclusion lesser than that of Heat 1 & Heat 2. This indicates Longer the End Cut better the last Billet Quality of the Caster particularly for inclusion. As a corrective action Automation Introduced for Billet Cutting operation. End Discard length Fixed. Additionally First & Last Billet of Each Heat is identified & rolled separately & multiple inclusion samples are analyzed as a quality control Pokayoke. This study shows, The Presence of small inclusion could reduce the Fatigue Life of Part 28.5%.