The wall thickness of the sheath of this thermocouple lies between
0.18 and 0.2 mm. Thermocouples are made by cold drawing process which results in minor ovalities in the outer
sheath. This variation in the cross-section can give rise to weld defects during laser welding. A special fixture has
been designed and fabricated to remove the ovalities from the thermocouple locally in the weld location. Using this
fixture, the thermocouple wire is held between the head stock and the tail stock of a lathe and fine machining is done
using a diamond tool. The laser welding parameters selected are to be such that the sheath material is not punctured
and at the same time sufficient weld penetration is achieved. This paper discusses the challenges involved, and the
standardization of laser welding parameters to successfully fabricate pressurized capsule with attachment of
thermocouple.
2. Experimental Arrangement
The normal operating temperature range in a reactor lies between 400ºC and 550ºC. K-type thermocouple