On design and tribological behaviour of laser textured surfaces

The paper reports an investigation into the functional response of textured surfaces with different designs that incorporated arrays of micro-dimples and grooves (40 μm diameter/width and 15 μm depth for both patterns) produced on tungsten carbide (WC) blocks by employing nanosecond (ns) and femtosecond (fs) lasers. In particular, the tribological performance of the textured WC blocks against stainless steel (SS316L) counterbody was evaluated in terms of friction and wear under dry condition compared to an untextured specimen. Friction tests were carried out on a reciprocating sliding tester while unidirectional ball-on-disc method was utilised to assess wear on the mating surfaces. The untextured surface exhibited a continuous rise in the friction coefficient from 0.15 to 0.5 from the start of the cycle to the end while the specimens textured with ns and fs lasers reached steady-state condition after 100 and 200 cycles with values between 0.35-0.45 and 0.3-0.4, respectively. Energy dispersive spectroscopy following wear tests showed a pronounced material transfer from the balls to the textured surfaces with stainless steel filling up some of the dimple and groove cavities; however, the reverse phenomenon was not apparent. Additionally, texturing with the fs laser exhibited formation of nano-ripples/structures in the produced dimples and grooves that can be further studied for creating nano-textured cutting tools or surfaces with super-hydrophobic/anti-ice properties

Ultrasonic assisted creep feed grinding of Inconel 718

AbstractThe paper details the effects of depth of cut and vibration amplitude when ultrasonic assisted (US) creep feed grinding Inconel 718 with an open structured alumina based wheel. The workpiece was actuated at a constant frequency (∼20.5kHz) via a block sonotrode attached to a 1kW piezoelectric transducer-generator system. A full factorial experimental array comprising 12 tests was conducted involving variation in depth of cut (0.1, 0.5 and 1.0mm), amplitude of vibration (high and low) and grinding condition (with and without vibration). Wheel speed and table feed were fixed at 30m/s and 600mm/min respectively for all tests. Application of ultrasonic vibration resulted in reductions in vertical (Fv) and horizontal (Fh) force components by up to 28% and 37% respectively, however greater wheel wear (30-60% lower G-ratio) occurred under hybrid operation due to increased grit/bond fracture. SEM micrographs of the slots machined with US assistance revealed higher levels of side flow/ploughing in comparison to standard creep feed ground specimens. Additionally, more overlapping grit marks were visible on surfaces subject to ultrasonic assisted grinding. Increasing amplitude of vibration produced lower grinding forces (up to 30% for Fv and 43% for Fh) but higher workpiece surface roughness (up to 24%). Topographic maps of grinding wheel surface replicas indicated that use of US vibration generally led to an increase in the number of active cutting points on the wheel

Experimental study on heat transfer enhancement during condensation using microstructured surfaces

Microstructured surfaces have been found to be energy efficient and cost effective through enhancement of heat transfer, drag reduction and anti-fouling in areas such as thermal engineering, fluid mechanics, microelectronics and transportation. However, their use with the condensation phenomenon has yet to receive considerable attention. Therefore, based on a new approach to recover energy in humid environments, the influence of different geometries manufactured on stainless steel inserts via micro-wire electro discharge machining (µ-WEDM) on condensation was analysed. The experimental work was carried out in a chamber with a high percentage of relative humidity (% RH) comparing the geometries against an unstructured surface. The experimental results showed a differential temperature (ΔT), 26% higher than the unstructured surface. Thus, it is reasonable to believe that this experimental study could be used in the design of energy recovery systems to enhance condensation heat transfer

Effects of laser microtextured surfaces in condensation heat transfer

Some major application areas of microtextured surfaces are found in the energy, biomedical, transportation and aerospace sectors. In relation to the energy sector, microtextured surfaces provide an energy efficient and cost-effective passive mechanism for increased heat transfer during matter’s phase change in energy recovery systems. This study explores the viability of laser microprocessing as an attractive manufacturing route for generating textured surfaces and compares with the results from a previous study involving microgeometries created by micro-wire electro discharge machining (µWEDM). Two types of stainless steel SS316L insert, produced via casting followed by machining, as well as by selective laser melting (SLM), were used as the workpieces. A number of microtextured geometries were produced on the workpieces’ planar top faces using a nanosecond fibre laser (1064 nm wavelength) operating with 0.066 and 0.25 mJ laser energy, 10 and 80 kHz frequencies, 400, 600 and 700 mm/s beam scanning speeds, and 25 and 60 µm set distances between the unidirectional textured grooves/laser tracks. The textured surfaces were subsequently scanned using a 3D optical scanner for evaluating the depth and width of the geometries. The scanning electron micrographs showed comparable groove geometries produced via both laser and µWEDM. During condensation experiments, the laser textured surfaces typically exhibited higher differential temperature, ΔT (~11.9-28.9%) with respect to the unstructured specimens. Additionally, the textured SLM samples generally showed greater heat transfer quality (~3.7-5.7% higher ΔT) than their cast and machined counterparts