Project Ultraweld: Laser microwelding of dissimilar materials using industrial laser process toolsThursday (25.06.2020) 14:30 - 14:50 Room 1
Bonding of metals to transparent materials (glasses, crystals, etc.) is frequently used for several applications in modern manufacturing including for hermetic sealing and precision optics positioning. Common methods include the use of organic adhesives or glass frit interlayers as well as diffusion, anodic and arc bonding. Such techniques are either esoteric and operator skill dependent, introducing large heat input or are subject to post-process creep and volatile components outgassing leading to device degradation, all of which are highly undesirable. Apart from limiting the range of material combinations possible to join, such bonding often ends up as a lengthy, error prone process step. Recently  direct microwelding of glass to metal (BK7 and fused silica to Al) has been demonstrated utilising ultrafast lasers which offer high precision, high process speed and very small heat affected zones. Although the physical process is not fully understood yet, it relies on sub-10ps duration laser pulses, tightly focused through the glass near the metal interface. This triggers ionisation and plasma formation in a highly localised volume  which combined with heat accumulation from high repetition rates above 200kHz results in a narrowly confined melt zone of ~0.1mm around the irradiated region. Subsequent material solidification behind the translated laser beam forms a strong bond across a user-defined beam trajectory. Innovate UK-funded consortium (Ultraweld) led by Oxford Lasers was established in 2018 to upscale this process to TRL level 6 and resolve current manufacturing challenges relating to precision beam registration, part handling and throughput, beam distortion corrections. In this paper we will showcase a purpose-built ultrafast laser prototype (fig.1b) for laser microwelding of (i) 10-20mm thick bulk optics to flat aluminium or stainless steel parts and (ii) conductive layer coated 0.1mm thick flexible glass to thin flexible glass with sufficient bond strength for use in industrial applications. Case studies in aerospace electro-optics assembly and flexible electronics hermetic sealing for device encapsulation will be discussed in detail . This pre-commercial laser welding prototype is suitable for early adoption of this microwelding technology and process development in other optical material welding applications (e.g. glass to silicon; glass to ceramic, Nd:YAG to metal, etc.).
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