Fiber Laser Microcutting of AISI 316L Stainless Steel Tubes- influence of Pulse Energy and Spot Overlap on Back Wall Dross

AbstractThe design of coronary stents imposes high demands in terms of dimensional tolerance and surface finish. These devices are manufactured by laser microcutting of miniature tubes in materials such as stainless steel, cobalt chromium alloys and Nitinol. The work presented here is focused on fiber laser microcutting for coronary struts in AISI 316L stainless steel. This work studies the influence of gases such compressed air and argon passing through the tube in order to drag molten material while laser microcutting is performed. The experimental work studies the influence of beam spot overlap and pulse energy on back wall dross and average surface roughness, using response surface methodology. The results indicate that the introduction of compressed air or argon gas is a relevant method to reduce the amount of dross adhered in the back wall of the miniature tube

A CFD model of the laser, coaxial powder stream and substrate interaction in laser cladding

In laser cladding, the interaction of the substrate material, the laser beam and the powder stream play important roles in determining how the material is deposited. Previous models of the coaxial powder stream have concentrated either on mass flow dynamics or stream heating, neglecting the effect of the substrate. In this work, a comprehensive numerical model that considers the important parameters of the powder stream, the laser beam and the substrate material, is developed. It is clear from the work that the full three-way interaction of these elements, as in real processing situations, is necessary to accurately and reliably predict particle heating and effective fusion into the melt pool

A CFD model of laser cladding: From deposition head to melt pool dynamics

The laser metal deposition process continues to receive attention from researchers and industry due to its unique capabilities in applications such as surface coating or rapid manufacture. The development of numerical models has proven useful for improving the process. However, most models have focused on analyzing individual stages of the deposition process and have required the introduction of a number of assumptions at their limits. This paper describes a complete CFD model that, starting from particles in the deposition head, simulates all interactions that govern the dynamics of a deposition melt pool. Individual phenomena that are included in the gasphase stage of the model include the ricocheting of particles within the head, the flow of powder particles, their interaction with the laser and powder catchment/bouncing. Phenomena in the liquid phase (melt pool) stage of the model include particle enthalpy effects, buoyancy, temperature-dependant material properties and Marangoni forces. The model is demonstrated using the actual geometry and gas flows found in a typical coaxial nozzle. The method, using a single technique to capture all phenomena, allows simulation of the melt pool dynamics from input parameters in a single model

Experimental Study of Back Wall Dross and Surface Roughness in Fiber Laser Microcutting of 316L Miniature Tubes

Laser cutting is a key technology for the medical devices industry, providing the flexibility, and precision for the processing of sheets, and tubes with high quality features. In this study, extensive experimentation was used to evaluate the effect of fiber laser micro-cutting parameters over average surface roughness ( R a ) and back wall dross ( D bw ) in AISI 316L stainless steel miniature tubes. A factorial design analysis was carried out to investigate the laser process parameters: pulse frequency, pulse width, peak power, cutting speed, and gas pressure. A real laser beam radius of 32.1 μm was fixed in all experiments. Through the appropriate combination of process parameters (i.e., high level of pulse overlapping factor, and pulse energy below 32 mJ) it was possible to achieve less than 1 μm in surface roughness at the edge of the laser-cut tube, and less than 3.5% dross deposits at the back wall of the miniature tube

Experimental Study of Back Wall Dross and Surface Roughness in Fiber Laser Microcutting of 316L Miniature Tubes

This article uses extensive experimentation to evaluate the effect of fiber laser micro-cutting parameters over average surface roughness and back wall dross in AISI 316L stainless steel mixture tubes

Surface Finish and Back-Wall Dross Behavior during the Fiber Laser Cutting of AZ31 Magnesium Alloy

Magnesium alloys are of increasing interest in the medical industry due to their biodegradability properties and better mechanical properties as compared to biodegradable polymers. Fiber laser cutting of AZ31 magnesium alloy tubes was carried out to study the effect of cutting conditions on wall surface roughness and back-wall dross. During the experiments, an argon gas chamber was adapted in order to avoid material reactivity with oxygen and thus better control the part quality. A surface response methodology was applied to identify the significance of pulse overlapping and pulse energy. Our results indicate minimum values of surface roughness (Ra < 0.7 μm) when the spot overlapping is higher than 50%. A back-wall dross range of 0.24% to 0.94% was established. In addition, a reduction in back-wall dross accumulations was obtained after blowing away the dross particles from inside the tube using an argon gas jet, reaching values of 0.21%. Laser cutting experimental models show a quadratic model for back-wall dross related with the interaction of the pulse energy, and a linear model dependent on pulse overlapping factor for surface roughness