Laser surface texturing for high friction and other surface engineering applications
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The use of laser surface texturing (LST) for surface engineering, in particular the generation of high static friction surfaces, has been investigated. The niche nature of high friction surfaces has meant that the field has largely been discarded and forgotten, leaving an opening for novel and innovative research as a result. Several regimes for generating high friction surfaces were considered: exclusive use of LST on a single surface (as in a shim configuration), use of LST on both surfaces of a contact and LST of a single surface in conjunction with additional surface engineering processes. Each of these three regimes was found to operate by a different mechanism of high friction, namely adhesion, interlocking and embedding. The laser surface texturing was performed using a self-built, commercially available laser processing workstation encompassing a pulsed nanosecond fibre laser and galvanometric scanner. Analysis of the surface textures was performed using optical microscopy and profilometry with further investigations performed by cross-section, SEM and EDX analysis. Friction testing of the textured samples was performed by a custom made testing rig, with direct measurement of the applied normal force via an in-line load cell, and real-time measurement of the load force by a 100kN hydraulic press. A wide range of laser texturing parameters and material properties were investigated, with each of the three regimes exhibiting different optimal parameters. High friction coefficients (μs>0.8) can be repeatedly obtained at normal pressures of up to 100MPa when LST has been used in conjunction with additional surface engineering (hardening) processes and when both surfaces of the contact have been treated with laser surface texturing. In the latter case, static friction coefficients of μs~1 with processing rates of greater than 1cm2/s have been achieved. Several relevant applications for such high friction surfaces have also been discussed. The feasibility of integrating beam shaping optics into an industrial style laser processing workstation has also been demonstrated and possible applications for such shaped beams discussed.