(V) Case study- Effect of welding heat input on Fatigue Life of Axle Housing Banjo

Truck Axle Housing Banjo is manufactured by Fabrication Method that involves lots of welding. Typically MIG welding is followed either using Semi Automatic Machine OR Robotic weld Cell. In this case study, the Axle Housing banjo is fabricated at Two Different locations. Location A & Location B. Both the Housing banjos are Bench validated for Vertical Beaming test with same boundary loading condition as defined. Location A Banjos fractured at 510000 cycles & Location B failed at 425000 cycles. The Location A Banjos meets the life expectation but Location B are Not. The fracture analysis shows the location A Banjo fractured away from the weld & Location B fractured at the HAZ area of brake flange weld. Ishikawa Diagram plotted & Welding parameters are reviewed. Heat input is calculated using ASM Hand Book Vol6 Formula. Observed that the Location B has 3 times higher Heat input than location A banjos. Heat input of Location A is 180Jouls/mm & that of Location B is 548 jouls/mm. These higher heat Energy input induces the Thermal Stresses causing the earlier failure of Location B Housing Banjo. This was evidenced by the higher HAZ Hardness in Location B banjo than Location A. 340 HV on Location B & 255 HV on Location A indicates 33% increase in the Hardness. Microstructure at HAZ of Location A banjos are typical to MIG welding but Location B banjos has Bainitic Microstructure. The Higher Heat input would induce tremendous thermal stress, causing the heterogeneity in heat transfer rate between the weldment & Parent Material resulting in Higher HAZ hardness, thereby reducing the Vertical Beaming Fatigue life of Axle Housing to almost 16%. Location B Banjos re-manufactured using Location A Heat energy inputs & weld process parameters & met the life requirement similar to Location A Banjos.