AMP_06_September_2021

A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 2 1 1 9 A study was carried out to measure the behavior of a heavy-truck axle housing banjo at its brake flange weld location. This region was chosen as the focus because it is one of the major loading areas during service, and it experiences bending, torsional, and braking loads. The brake flange is attached using MIG welding on the sur- face of the housing banjo. The weld- ing process induces thermal stresses in the welded parts, resulting in warp- age or bending [1] . A number of brack- ets, spring seats, and spindles are also welded to the housing banjo, which means it experiences much thermal stress, even though the material used for welding is a high-strength low-alloy (HSLA) low carbon equivalent. These thermal cycles lead to warping and so a straightening process is necessary [1] . The straightening process involves me- chanical cold working on the housing banjo to forcibly push it into an accept- able runout specification and ensure maximum performance during service. Figure 1 shows the housing banjo and brake flange region. HOUSING BANJO FABRICATION The typical major process flow for manufacturing a housing banjo is: Raw material  Hot press stamping  Shot blasting  MIG welding  Straight- ening  Machining  Final inspection  Ready to assemble In this flow, shot blasting, which is mechanical bombardment of steel shots on the surface of the housing, is used to clean the part surface by remov- ing the scales and debris [2] . The shot blasting operation induces an amount of low-magnitude residual stress on the housing banjo surface. The stress is re- duced by the straightening process later on, and because the stresses are com- pressive in nature, they could help im- prove performance of the housing banjo. STRAIGHTENING OPERATION After MIGwelding is the straighten- ing step. The runout of the job is mea- sured using a dial gauge and the load is applied where the runout is out of spec- ification. The runout is checked again and, if necessary, corrected by apply- ing the load through the ram. These steps are repeated multiple times un- til the runout is within the acceptable limit. During this operation there is me- chanical cold working on the surface of the banjo locally. This repeated cold working alters the local strain thereby changing the residual stress near the brake flange area. Both the magnitude and nature of the stress can change. RESIDUAL STRESS MEASUREMENT Two samples identified as SN1 and SN2 were processed through the straightening step then taken for resid- ual stress measurement. The residual stress is measured using x-ray diffrac- tion [3] . The measurement location is identified around the brake flange weld region as shown in Fig. 2. The housing banjo is not sectioned and the whole banjo is exposed to the machine. The brake flange outer diameter is turned to access the collimator of the diffraction machine at the measurement location. This does not alter the residual stress on the housing banjo as the machining operation is far away. Measurements are taken at the brake flange weld start, middle, end of the weld, and in the no weld zone. They BEFORE AND AFTER: EFFECTS OF STRAIGHTENING ON RESIDUAL STRESS This case study measures residual stress on a truck axle housing as it goes through the manufacturing process. Yathish Rao,* Industry Professional, Pune, India *Member of ASM International Fig. 1 —Housing banjo showing the brake flange region. Brake flange region