Glass welding by ultra-short pulsed (USP) lasers is a piece of technology that offers high strength joints with hermetic sealing. The joints are typically formed in glass that is transparent to the laser by exploiting nonlinear absorption effects that occur under extreme conditions. Though the temperature reached during the process is on the order of a few 1000 °C, the heat affected zone (HAZ) is confined to only tens of micrometers. It is this controlled confinement of the HAZ during the joining process that makes this technology so appealing to a multitude of applications because it allows the foregoing of a subsequent tempering step that is typically essential in other glass joining techniques, thus making it possible to effectively join highly heat sensitive components. In this work, we give an overview on the process, development and applications of glass welding by USP lasers.

Anisotropy is one central influencing factor on achievable ultimate machined surface integrity of metallic materials. Specifically, grain boundary has a strong impact on the deformation behaviour of polycrystalline materials and correlated material removal at the microscale. In the present work, we perform molecular dynamics simulations and experiments to elucidate the underlying grain boundaryassociated mechanisms and their correlations with machining results of a bi-crystal Cu under nanocutting using a Berkovich tool. Specifically, crystallographic orientations of simulated bi-crystal Cu with a misorientation angle of 44.1° are derived from electron backscatter diffraction characterization of utilized polycrystalline copper specimen. Simulation results reveal that blocking of dislocation motion at grain boundaries, absorption of dislocations by grain boundaries and dislocation nucleation from grain boundaries are operating deformation modes in nanocutting of the bi-crystal Cu. Furthermore, heterogeneous grain boundary-associated mechanisms in neighbouring grains lead to strong anisotropic machining behaviour in the vicinity of the grain boundary. Simulated machined surface morphology and machining force evolution in the vicinity of grain boundary qualitatively agree well with experimental results. It is also found that the geometry of Berkovich tool has a strong impact on grain boundary-associated mechanisms and resultant ploughing-induced surface pile-up phenomenon.

Great strides have been made over the past decade to establish femtosecond lasers in advanced manufacturing systems for enabling new forms of non-contact processing of transparent materials. Research advances have shown that a myriad of additive and subtractive techniques is now possible for flexible 2D and 3D structuring of such materials with micro- and nano-scale precision. In this paper, these techniques have been refined and scaled up to demonstrate the potential for 3D writing of high-density optical packaging components, specifically addressing the major bottleneck for efficiently connecting optical fibres to silicon photonic (SiP) processors for use in telecom and data centres. An 84-channel fused silica interposer was introduced for high-density edge coupling of multicore fibres (MCFs) to a SiP chip. Femtosecond laser irradiation followed by chemical etching was further harnessed to open alignment sockets, permitting rapid assembly with precise locking of MCF positions for efficient coupling to laser written optical waveguides in the interposer. A 3D waveguide fanout design provided an attractive balancing of low losses, modematching, high channel density, compact footprint, and low crosstalk. The 3D additive and subtractive processes thus demonstrated the potential for higher scale integration and rapid photonic assembly and packaging of micro-optic components for telecom interconnects, with possible broader applications in integrated biophotonic chips or micro-displays.

The 2024 aluminum alloy is used extensively in the aircraft and aerospace industries because of its excellent mechanical properties. However, the weldability of 2024 aluminum alloy is generally low because it contains a high number of solutes, such as copper (Cu), magnesium (Mg), and manganese (Mn), causing solidification cracking. If high speed welding of 2024 aluminum alloy without the use of filler is achieved, the applicability of 2024 aluminum alloys will expand. Grain refining is one of the methods used to prevent solidification cracking in weld metal, although it has never been achieved for high-speed laser welding of 2024 aluminum alloy without filler. Here, we propose a short-pulsed, laser-induced, grain-refining method during continuous wave laser welding without filler. Bead-on-plate welding was performed on a 2024- T3 aluminum alloy at a welding speed of 1 m min^-1 with a single mode fiber laser at a wavelength of 1070 nm and power of 1 kW. Areas in and around the molten pool were irradiated with nanosecond laser pulses at a wavelength of 1064 nm, pulse width of 10 ns, and pulse energy of 430 mJ. The grain-refinement effect was confirmed when laser pulses were irradiated on the molten pool. The grain-refinement region was formed in a semicircular shape along the solid– liquid interface. Results of the vertical section indicate that the grain-refinement region reached a depth of 1 mm along the solid–liquid interface. The Vickers hardness test results demonstrated that the hardness increased as a result of grain refinement and that the progress of solidification cracking was suppressed in the grain refinement region.

A computational fluid dynamics (CFD) study of the impact characteristics and stagnation formation on a solid target surface by an abrasive waterjet at supersonic velocities is presented to understand the impact process. A CFD model is developed and verified by experimental water and particle velocities and then used to simulate the jet impact process. The trends of the stagnation formation and its effect on the jet flow with respect to the jetting and impacting parameters are amply discussed. It is found that stagnation formation at the impact site increases with an increase in the impact time, nozzle standoff distance and nozzle diameter, while the initial peak velocity at the nozzle exit has little effect on the size of the stagnation zone. It is shown that stagnation markedly changes the water and particle flow direction, so that the particle impact angle is varied and the jet impact area is enlarged. The jet structure may be classified to have a free jet flow region, a jet deflection region with a stagnation zone and a wall jet region. Furthermore, the stagnation affects significantly the waterjet and particle energy transferred to the target surface. The average particle velocity across the jet is reduced by approximately one third due to the damping effect of the stagnation under the conditions considered in this study.