An improved method to spot-weld difficult junctions

Abstract

Recent advances in spot-welding technology such as high frequency direct current inverter welders provide an improved and reproducible method to spot-weld difficult junctions. The importance of removing the oxide layers on metal surfaces, accurately delivering the weld pulse profile, and controlling the force applied to the materials during the welding process are discussed in the context of resistance spot-welding a molybdenum crystal to a tantalum loop and attaching a tungstenrhenium thermocouple to the crystal.

Optimization of resistance spot welding on the assembly of refractory alloy 50Mo–50Re thin sheet

“…During welding, it was also observed that molten metal expulsion occurred significantly at 0 ms ramp time, whereas there was almost no expulsion taking place at a weld current of 500 A and a ramp time of 8 ms. The upslope, relatively slowly introducing current to the workpieces to be joined, not only minimized the metal expulsion but also reduced the variation in contact resistance between the electrodes and workpieces [13]. Hence, it resulted in a more uniform melting between the faying workpieces and improved the quality of welding of Mo-Re sheet.…”

“…Higher cooling rate could also engender a smaller heat affected zone (HAZ), which is normally the weakest region in weldments, and accordingly benefit the quality of welding [13]. Based on the result, the hold time of 999 ms was set in the next experiments.…”

“…5(b)). The weld joints in alloys produced by powder metallurgy often contain voids which are produced by residual volatile materials [13]. In this project, 50Mo-50Re sheets were synthesized by a powder metallurgy method, thus it might not be surprising to observe pores frequently in the weld zone of this alloy.…”

The small-scale resistance spot welding of refractory alloy 50Mo-50Re thin sheet

“…The upslope, gradually introducing current to the workpieces to be joined, not only minimized the metal expulsion but also reduced the variation in contact resistance between the electrodes and workpieces. 8 Therefore, it was preferable to use a weld current profile with a ramp time of several milliseconds to improve welding of this alloy. Figure 1 shows the effect of weld time with 8 ms ramp time and other default welding parameters, as shown in Table A.…”

Application of W–Re thermocouples for in situ ultrahigh vacuum use over a wide temperature range

“…On the other hand, high-temperature thermocouples can be firmly attached to difficult samples either mechanically or by means of a spot-welder, 5 and are relatively inert. However, this solution is unsatisfactory because it is necessary to mechanically break and make the contact of the low-temperature thermocouple in situ.…”