Ph.D programme

After passing the Russian language exam which was conducted six months after joining the course, I was allowed to join the Department of Technology of Metals for my Ph.D programme. Taking in to account my background Prof.Olshanskii suggested that I study the temperature distribution during Electron Beam Welding and correlate the metallurgical changes that take place in the metal with measured temperature distribution. In addition he suggested that I should develop a method of predicting depth of penetration for a given welding parameter.

At first instance the problem appeared to be simple. But experimentally determining the temperature distribution had its own problems. Platinum-Platinum Rhodium thermocouples were used for measuring the temperature. The Heat affected Zone in Electron Beam welds are extremely narrow and to locate the thermocouples precisely in that zone was very tricky. Initial experiments were done to measure the width of the heat affected zone for various weld parameters. The welding chamber was equipped with a precision table which can move in the X and Y direction. The table was adjusted such that the electron beam passed through the centre of the table in the Y-direction. A jig was prepared such that the electron beam passes through the centre of the jig. The jig was bolted to the traverse table. Test specimens were machined such the they fit snugly in to the jig. Holes were drilled in the test plate and thermocouples were embedded to measure the temperature in the heat affected zone.The location of thermocouples was decided by the earlier experiments done to measure the width of the heat affected zone. The thermocouples were taken out of the welding chamber and connected to a high speed strip chart recorder. Welding was started and the temperatures were recorded. These experiments look simple but it was very difficult ensure that the electron beam traverses precisely where you want. Slightest changes in parameters or alignment of the test plate will result in the electron beam going over the thermocouples or going far from the thermocouples. The recorded temperature distribution was compared with the theoretical temperature distribution considering the heat transfer is two dimensional, The specimens were sectioned and were subjected to metallurgical tests.Several test specimens were welded to establish the repeatability. The first portion of the assignment was finished and the next was to find a method of predicting depth of penetration for a given welding parameter.