It would be interesting to know our opinion about the evolution of keyhole depth during prolonged (with infinite time) spot welding by laser beam . Will the keyhole exist as long as the laser action with some fluctuations or it will completely disappear as a result of the final collapse without the following new formation? What is the reason of such behavior by your opinion? Maybe you have seen it in the experiment?
In my opinion the keyhole will also fluctuate if the laser action have some fluctuation. For prolonged spot the size of spot will enlarge. Because due to heat dissipation, conduction the molten zone size will increase.
The car companies have avoided spot welding using lasers. instead, they have chosen to go with stitch welding with stitch lengths that provide the same, or better, adhesion results of spot welds. Pooling using lasers have shown to cause localized martensitic formation, alloy segregation and zinc contamination if joining galvanized material. Very important to concentrate on heat management.
Dear Prof Biswas. Many thanks for the answer. You're absolutely right when you talk about the solid-melt interface. But interesting to understand the behavior of the cavity (gas-melt interface). Will the cavity exist as long as the laser action or it will completely disappear at last despite laser action?
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