GlassWelding

Glasses are highly resistant materials used in a wide range of key applications from glass-ceramic plates to MEOMS encapsulation. Their assembly is usually done by bonding or by thermal processes (anodic discharge, brazing, etc.). However, for some applications these techniques have restrictive limits. Polymer adhesives do not withstand high temperatures and thermal processes are not suitable for making precise welds on small dimensions. Finally, when two thermally welded materials are dissimilar, a difference in thermal expansion is often a cause of failure. In this context, welding by ultra-short pulse lasers, spatially selective, without adding material is very promising. The project aims to develop a laser welding process for glass-to-glass and glass-to-metal that is compatible with current industrial requirements: precise (seam 30 MPa) and capable of withstanding high temperatures up to 700 K or a large number of thermal cycles. The improvement of the performances requires the understanding of the underlying multi-scale physical phenomena and, technologically, the development of a more efficient laser process. Our simulations have shown the possibility of using higher repetition frequencies (temporal shaping) to better control the thermal accumulation and to achieve a reduction of the thermal gradients, while reducing the required energy and the residual stresses. Experimental tests have also clearly shown the importance of the light pattern and the welding trajectory (spatial shaping) on the mechanical strength of the weld seam. In this project, a laser will be adapted by Amplitude to operate in burst mode with intra-burst frequency pulses of the order of GHz. The energies of the laser bursts will be up to ~200 µJ, sufficient to weld an extended pattern at once. An experimental design will be implemented by IREPA LASER to optimize the welding process parameters on a previously modified station. The station will indeed include a programmable beam shaping tool and a fast in situ vision system. Micro-macro scale characterizations (tensile tests, photoelasticity, transmission rate, hermiticity tests, etc.) will be systematically performed by the ICube laboratory to guide the experimental design. Characterizations at the micro-nano scale (AFM, nano-indentation, Raman spectroscopy) will be carried out by the Institute of Physics of Rennes on a selection of samples of interest, to better understand the physics of the welding process by confrontation with the multiphysics model that will be set up by ICube, (non-linear propagation and absorption, thermal accumulation, evolution of stress maps, role of microcracks, etc.). The process will first be tested for the assembly of optical components in the new range of ultra-short ultra-high power pulsed lasers from Amplitude. Other identified applications that will be investigated include assemblies for high-end watchmaking, encapsulation of MOEMS or micro-fluidic circuits, micro-assembly of optical components for smartphones, and aerospace assembly requirements for dissimilar materials (diamond on titanium, CaF2 on steel, glass on aluminum, material that do not create outgassing or epoxy contamination).