Ph. Bertrand

Experimental study of an oxygen plasma cutting torch: II. Arc–material interaction, energy transfer and anode attachment

A study of arc–material interaction and energy transfer in the case of plasma cutting is presented. A fast CCD camera moving with the torch is used to estimate the anodic arc root location inside the kerf. Temperature measurements on the cut-front surface and on the kerf edges are performed by infrared pyrometry. Temperature fields inside the workpiece obtained with inserted thermocouples are compared with the theoretical results of an analytical model to estimate heat conduction losses QHCL (W) dissipated in the plate. For various sets of operating parameters (voltage, inlet oxygen pressure and cutting speed), a complete energy balance of the process is performed with the calculation of the device efficiency on the basis of the various power terms implicated in the cutting tool: the power lost above the workpiece, heat conduction losses, the power involved in melting steel, the energy released by chemical oxidation reactions, the power available for cutting and losses under the plate in the extinguishing plasma.

Experimental design approach to optimize selective laser melting of martensitic 17‐4 PH powder: part I – single laser tracks and first layer

Purpose – The purpose of this paper is to investigate the effect of main process parameters of selective laser melting (SLM) technology on single lines and single layers manufactured from 17‐4 PH martensitic powder using the experimental design approach.Design/methodology/approach – A fractional factorial approach has been applied to vary and to identify the optimal set of process parameters using three different powder particle size distributions for 17‐4 PH steel. This paper assesses the impact of influence factors such as process and material parameters on objective factors such as dimension of single lines and single layers, as well as surface roughness.Findings – The influence of process parameters and materials properties on single line and single layer manufacture is shown and proved statistically. The effect of each process parameter and their interactions on single layer and single line stability and quality has been investigated, and a complex objective function analyzing geometrical stability o...

Studying the influence of initial powder characteristics on the properties of final parts manufactured by the selective laser melting technology

Selective laser melting (SLM) is an additive manufacturing process that enables direct manufacturing of 3D complex shape parts and internal architecture from powder materials. The SLM technology is characterised by high temperature gradients and solidification rates that have a significant effect on the microstructures and properties of final parts. The present paper aims at understanding the influence of the initial properties of various martensitic stainless steel powders on the final microstructures and mechanical properties of parts manufactured using the same optimised SLM process parameter settings. The results obtained show that for applied optimum process parameters, the thermal effects are the same for all martensitic powders used. Besides, the final microstructures and properties are different. The results clearly show the effect of the initial complex chemical composition of the martensitic precipitation hardening powder on the microstructures of final parts, and consequently, on their properties.

Modeling of temperature fields in the graphite target at pulsed laser deposition of CNx films

Abstract The pulsed laser deposition (PLD) technique is frequently applied to synthesize carbon nitride coatings having a general formula CNx. In previous experiments, the polycrystalline CNx films were deposited with the use of a CO2 TEA laser in a remote nitrogen atmosphere [1] . The x value was found to be approximately 0.6 and the grains, observed with SEM, were typically of a few hundreds of nanometers of size. This phenomenon was tentatively explained by the abundance of vapors generated by the action of the laser. It can be, in turn, related to the thermal fields in the graphite target. The numerical code ‘Fusion-2D’, describing laser/target interaction, was applied to model the temperature in two dimensions. The optical absorption data were taken for the wavelengths that corresponded to the typical lasers used in PLD processes, i.e. excimer, YAG and CO2. The evolutions in the graphite target temperature at the pulses generated by these lasers were then calculated for a given power density. The differences in these evolutions were related to the volume of produced vapors and helped to explain the morphology of the synthesized films.

Effect of Turning and Ball Burnishing on the Microstructure and Residual Stress Distribution in Stainless Steel Cold Spray Deposits

In this paper, an experimental study of influence of machining by turning and ball burnishing on the surface morphology, structure and residual stress distribution of cold spray 17-4 PH stainless steel deposits is provided. It is shown that cold spray deposits could be machined by turning under parameters closed to turning of bulk 17-4 PH stainless steel. Ball burnishing process permits to decrease surface roughness. Cross-sectional observation revealed that the turning and ball burnishing process allowed microstructure changes in the coating near-surface zone. In particular, significant particle deformation and particle boundary fragmentation is observed. Measurements of residual stresses showed that residual stresses in the as-spray deposit are compressive. After machining by turning, tensile residual stresses in the near-surface zone were induced. Further surface finishing of turned coating by ball burnishing allowed the establishment of the compressive residual stresses in the coating.

Temperature monitoring of Nd:YAG laser cladding (CW and PP) by advanced pyrometry and CCD-camera-based diagnostic tool

The set of original pyrometers and the special diagnostic CCD-camera were applied for monitoring of Nd:YAG laser cladding (Pulsed-Periodic and Continuous Wave) with coaxial powder injection and on-line measurement of cladded layer temperature. The experiments were carried out in course of elaboration of wear resistant coatings using various powder blends (WC-Co, CuSn, Mo, Stellite grade 12, etc.) applying variation of different process parameters: laser power, cladding velocity, powder feeding rate, etc. Surface temperature distribution to the cladding seam and the overall temperature mapping were registered. The CCD-camera based diagnostic tool was applied for: (1) monitoring of flux of hot particles and its instability; (2) measurement of particle-in-flight size and velocity; (3) monitoring of particle collision with the clad in the interaction zone.

Application of near-infrared pyrometry for monitoring of temperature evolution at contact surface of circuit breaker

Advanced pyrometers were applied for surface temperature monitoring during Nd:YAG laser pulsed and pulsed-periodic action on circuit breaker contacts (Ag based composite material with graphite inclusions). Temperature evolution, heating and cooling rates, melting threshold are measured and discussed.

Application of near infrared pyrometry for CW Nd:YAG laser welding of stainless steel and laser cladding of stellite

A bi-dimensional monochromatic and a 1-spot multiwavelengths pyrometers were applied for surface temperature monitoring in Nd:YAG continuous laser welding. The experiments were performed for stainless steel and titanium alloy applying variation of laser parameters: power, welding velocity, focalisation distance, shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between the dissimilar plates. Surface temperature evolution along and perpendicular to the welding seam and full temperature image versus laser action parameters were measured with the help of the bi-dimensional pyrometer. The dynamics of temperature gradients, transient periods and steady-state temperature distributions are analysed. The same approach is applied for Nd:YAG laser cladding of stellite on steel substrate. A new type of CCD based optical diagnostic tool has been applied for monitoring the particle in flight size and velocity.