Philip Crouse

Elimination of striation in laser cutting of mild steel

High-power laser cutting is extensively used in many industrial applications. An important weakness of this process is the formation of striations (regular lines down the cut surface), which affect the quality of the surfaces produced. The elimination of striation formation is of considerable importance, since it could open up a variety of novel high-precision applications. This study presents the results of oxygen-assisted laser cutting of EN43 mild steel sheets, using a high-power fibre laser. Striation-free laser cuts are demonstrated for cutting 1 and 2 mm thick mild steel sheets. The optimal operating windows are presented and a mathematical method is proposed to estimate the critical speed at which striation-free cut can be obtained.

Comparison of MOF-5- and Cr-MOF-derived carbons for hydrogen storage application

AbstractNanoporous carbons which possess high surface areas and narrow pore size distributions have become one of the most important classes of porous materials with potential to be utilized for hydrogen storage. In recent times, several metal–organic frameworks (MOFs) have been shown to be promising precursors for creating nanoporous carbons due to their high surface areas and tunable pore sizes. The pore structure and surface area of the resultant carbon materials can be tuned simply by changing the calcination temperature. In this work, a zinc-based MOF (MOF-5) and a chromium-based MOF (Cr-MOF) were both used as precursors for syntheses of nanoporous carbons by the direct carbonization technique at different temperatures. The resultant carbon nanostructure from MOF-5 possessed higher surface area, higher pore volume and enhanced hydrogen storage capacity as compared to pristine MOF. Meanwhile, the derived carbons from Cr-MOF displayed lower surface areas, pore volumes and hydrogen uptake than the parent MOF due to the formation of chromium oxide and carbide species in the pores of the Cr-MOF-derived carbons.

A conversion electron mössbauer spectroscopic and gravimetric study of the hydrolytic oxidation of iron fluoride hydrate surface layers

Abstract The oxidation of FeF 2 -4H 2 O surface layers in an atmosphere saturated with water vapour was studied by means of Mossbauer spectroscopy as well as gravimetry. The major rust product is identified as β-FeOOH, and the reaction is shown to proceed as a front from the layer-atmosphere interface towards the substrate. The ratio of the initial amount of fluoride on the surface to the final amount of rust produced was found to be constant, with the fluoride present in 1 mole of FcF 2 -4H 2 O reacting further to yield more than 5 moles of oxyhydroxide. This constant and non-stoichiometric yield is explained in terms of an acid regeneration cycle.

Radical copolymerisation of chlorotrifluoroethylene with isobutyl vinyl ether initiated by the persistent perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical

Results of the radical copolymerisation of chlorotrifluoroethylene (CTFE) with isobutyl vinyl ether (iBuVE) initiated by ˙CF3 radicals generated by β-scission of perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical (PPFR) at 90 °C in a batch reactor are reported. 19F NMR spectroscopy enabled the assessment of the molecular weights of the poly(CTFE-alt-iBuVE) copolymer by end-group analysis. It was found that, at low initiator concentrations (≤10 mol%), the ˙CF3 radicals preferably attack the vinyl ether monomer to initiate chain propagation and produce alternating poly(CTFE-alt-iBuVE) copolymers. At initiator ratios of 20 mol%, 19F NMR signals in the CF3 region other than the expected CH2–CF3 are observed and are attributed to ˙CF3 addition patterns due to kinetic effects brought on by monomer solubility. The molecular weights for the copolymer produced from 1%, 5%, and 10% PPFR were found to be 340 000, 237 000 and 122 000 g mol−1, respectively. The copolymer produced from 20% PPFR was oligomeric in nature with a molecular weight of 18 000 g mol−1.

Laser surface texturing of Ti-6Al-4V and controlled oxide formation for improving biocompatibility

This paper reports the results of surface modification of Ti-6Al-4V using a 75 W Q-switched Nd:YAG (λ=1064 nm, τ=100 ns) laser in air with the ultimate aim of improving osseointegration and biocompatibility. Melting and rapid re-solidification develop new textures which mainly include molten, re-solidified droplets.Two types of samples were used. The first set of experiments was performed on samples with machined and polished surfaces. For the second set of samples a layer of oxide was formed on the laser treated surfaces. Oxide film growth was effected by laser heating in air. Analysis of the surface finish was done by XRD, SEM and surface roughness testing.The effects of process parameters (laser power, frequency, and scan speed) on surface finish are discussed. Surface finish is correlated with estimates of temperatures using simple analytical heat-transfer models.To evaluate the biocompatibility, contact angle measurement and SBF test were carried out. The effect of laser surface treatment and further oxide growth were discussed on the contact angle and formation of Ca and P-containing crystals on the surface.This paper reports the results of surface modification of Ti-6Al-4V using a 75 W Q-switched Nd:YAG (λ=1064 nm, τ=100 ns) laser in air with the ultimate aim of improving osseointegration and biocompatibility. Melting and rapid re-solidification develop new textures which mainly include molten, re-solidified droplets.Two types of samples were used. The first set of experiments was performed on samples with machined and polished surfaces. For the second set of samples a layer of oxide was formed on the laser treated surfaces. Oxide film growth was effected by laser heating in air. Analysis of the surface finish was done by XRD, SEM and surface roughness testing.The effects of process parameters (laser power, frequency, and scan speed) on surface finish are discussed. Surface finish is correlated with estimates of temperatures using simple analytical heat-transfer models.To evaluate the biocompatibility, contact angle measurement and SBF test were carried out. The effect of laser surface treatment and further...

Optimisation of TiN thin film synthesis by a novel combined laser/sol-gel processing technique

The authors recently reported a novel laser-based method for depositing hard TiN thin films. Results of process optimisation are given in this paper. The process chemical thermodynamics, laser interaction with the preplaced slurry that forms the coating and the heat transfer problem during the process are discussed. Surface morphology and microstructure of the deposited coatings and substrate surface layers were examined using optical microscopy, scanning electron microscope, and field emission gun scanning electron microscope which reveals the presence of sub-micron crystalline structure of TiN forming a metal matrix composite interlayer with the substrate below the film which suggest a good metallurgically bonding with the substrate. Chemical composition was determined by energy dispersive X-ray analysis. The phases were identified by X-ray diffraction which confirms the synthesis of TiN film for all the samples. Results of microhardness measurements revealed a hardness value of the order of 2700 HV(0.1).The authors recently reported a novel laser-based method for depositing hard TiN thin films. Results of process optimisation are given in this paper. The process chemical thermodynamics, laser interaction with the preplaced slurry that forms the coating and the heat transfer problem during the process are discussed. Surface morphology and microstructure of the deposited coatings and substrate surface layers were examined using optical microscopy, scanning electron microscope, and field emission gun scanning electron microscope which reveals the presence of sub-micron crystalline structure of TiN forming a metal matrix composite interlayer with the substrate below the film which suggest a good metallurgically bonding with the substrate. Chemical composition was determined by energy dispersive X-ray analysis. The phases were identified by X-ray diffraction which confirms the synthesis of TiN film for all the samples. Results of microhardness measurements revealed a hardness value of the order of 2700 HV(0.1).

Laser cutting of variable thickness materials - Understanding the problem

Laser cutting has been widely applied to materials with uniform thickness profiles. The aim of this study is to explore the problems and effects of cutting non-uniform metallic sheets. Mild steel sheets between 2-3 mm thickness with steps of 0.25 mm were cut using both CO2 and Nd:YAG lasers with equivalent cutting parameters and in 4 different cutting arrangements: a) thin-to-thick from the flat side; b) thick-to-thin from the flat side; c) thin-to-thick from the stepped side; and d) thick-to-thin from the stepped side. Quality of cut was examined in terms of dross attachment, surface roughness, perpendicularity, kerf width, and striation height. The work shows that variation in workpiece thickness affects the cut surface quality due to several factors related to irradiance and assist gas flow. In some situations these effects can be minimized within certain tolerances.Laser cutting has been widely applied to materials with uniform thickness profiles. The aim of this study is to explore the problems and effects of cutting non-uniform metallic sheets. Mild steel sheets between 2-3 mm thickness with steps of 0.25 mm were cut using both CO2 and Nd:YAG lasers with equivalent cutting parameters and in 4 different cutting arrangements: a) thin-to-thick from the flat side; b) thick-to-thin from the flat side; c) thin-to-thick from the stepped side; and d) thick-to-thin from the stepped side. Quality of cut was examined in terms of dross attachment, surface roughness, perpendicularity, kerf width, and striation height. The work shows that variation in workpiece thickness affects the cut surface quality due to several factors related to irradiance and assist gas flow. In some situations these effects can be minimized within certain tolerances.

Cutting 500 mm thick concrete using high-power lasers below 2 kW

Despite competing with several established conventional techniques, deep-section laser concrete cutting is foreseen to find a niche market in contaminated environments, such as in the decommissioning of nuclear power plants, where effective waste management is of critical importance. In a BNFL-sponsored development project at UMIST it has recently been shown that deep cuts of up to 500 mm – a new world record for concrete cutting depth – can be obtained fairly easily. A 1.2 kW CO2 laser and a 1.5 kW high-power diode laser were used in the investigation. In this paper details of the technique are discussed, along with typical problems that have to be overcome. Aspects of cutting reinforcing steel bars in the concrete matrix are also briefly discussed.Despite competing with several established conventional techniques, deep-section laser concrete cutting is foreseen to find a niche market in contaminated environments, such as in the decommissioning of nuclear power plants, where effective waste management is of critical importance. In a BNFL-sponsored development project at UMIST it has recently been shown that deep cuts of up to 500 mm – a new world record for concrete cutting depth – can be obtained fairly easily. A 1.2 kW CO2 laser and a 1.5 kW high-power diode laser were used in the investigation. In this paper details of the technique are discussed, along with typical problems that have to be overcome. Aspects of cutting reinforcing steel bars in the concrete matrix are also briefly discussed.

Generation of nickel-oxide nanoparticles by CW laser ablation in liquid

Pulsed laser ablation in liquid (PLAL) has been widely applied for the generation of nanoparticles (NPs). However, until now, there is no reported work on the successful generation of Ni oxide NPs by laser ablation of nickel target in aqueous environments. This paper reports our recent investigation on generation of Ni oxide NPs using a continuous wave (cw) high-power and high-brightness fibre laser source at wavelength of 1070nm. Characterisation of such NPs in terms of size distribution, shape, chemical composition and phase structure was carried out by transmission electron microscopy (TEM), high-resolution TEM equipped with energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). The results revealed the formation of NiO NPs in water with an average size of 12.6 nm. The addition of anionic surfactant sodium dodecyl sulphate (SDS) reduced the size of NiO NPs down to 10.4 nm. The shape of the NPs was also affected by the SDS, showing the change of shapes from spherical domination in water to tetragonal with increased SDS concentrations. In addition, the NiO NPs generated in water and SDS solutions were dual-phase containing both cubic and rhombohedral structures.Pulsed laser ablation in liquid (PLAL) has been widely applied for the generation of nanoparticles (NPs). However, until now, there is no reported work on the successful generation of Ni oxide NPs by laser ablation of nickel target in aqueous environments. This paper reports our recent investigation on generation of Ni oxide NPs using a continuous wave (cw) high-power and high-brightness fibre laser source at wavelength of 1070nm. Characterisation of such NPs in terms of size distribution, shape, chemical composition and phase structure was carried out by transmission electron microscopy (TEM), high-resolution TEM equipped with energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). The results revealed the formation of NiO NPs in water with an average size of 12.6 nm. The addition of anionic surfactant sodium dodecyl sulphate (SDS) reduced the size of NiO NPs down to 10.4 nm. The shape of the NPs was also affected by the SDS, showing the change of shapes from spherical domination in water to tetragon...

Efficient generation of titanium oxide nanomaterials using a continuous wave high-power fibre laser

We report, for the first time to our knowledge, the generation of titanium oxide nanoparticles in water using a high-power high-brightness continuous wave (CW) fibre laser source at 1070 nm (IPG Single mode YLR-1000-SM 1 kW fibre laser). Fibre laser sources are robust and easy-to-use. The output beam quality is determined by the waveguiding properties of the doped core and hence the output beam can be focused to a very small spot with relatively large depth of focus. Therefore the material processing/ablation/removal can be considerably directed/tailored as desired.