Laser surface treatment of grey cast iron by high power diode laser

AbstractA grey cast iron surface was heat treated by a 1kW diode laser to improve the hardness and wear resistance of the surface. Based on a temperature measurement and control system, different levels of surface temperature and scan speed were investigated for single and multi-pass hardening processes. A homogeneous hardened zone with hardness 700–800 HV0.3 was obtained in cross section regardless to the process temperature and scan speed during single pass laser hardening. Considering the process productivity, the optimal combination of high temperature and high scan speed was used to identify the process condition to be used in the multi-pass laser hardening. The selected parameters were then applied in large surface treatment to investigate the effect of the overlapping procedure on the surface properties. Different overlapping lengths were investigated to produce a large hardened area with uniform hardening depth and hardness

Laser dimpling and remote welding of zinc-coated steels for automotive applications

"The flexibility in terms of beam shapebility and amplitude in the range of process parameters offered by the emerging high power and quality active fiber lasers can be advantageously used in overcoming the well-known problems in remote laser welding of zinc-coated steel components in the car mass production. The paper explores the potentiality offered by the combination of the scanner technology with high brilliance fiber lasers when laser dimpling and remote welding are executed in a successive order: the first one to realize gap spacers and the second one to weld together clamped sheets in zinc-coated steels. In particular, the substitution of the traditional mechanical dimpling with the laser dimpling is investigated in order to highlight the potentiality of a solution that is flexible, unaffected by tool wear and highly productive.

Remote cutting of Li-ion battery electrodes with infrared and green ns-pulsed fibre lasers

"Thin sheet anode and cathode materials made in composite structures constitute some of the most important components of a Li-ion battery. These materials are currently cut by punching technology, which shows degrading behaviour as the tool wears out. A viable option for Li-ion battery electrode manufacturing is the use of remote laser cutting. However, the operation requires fulfilling both productivity and quality aspects to substitute the conventional production method. One of the most critical aspects in quality is the clearance width, which is defined as the extent of the exposed middle layer of the sandwich at the laser cut kerf. This work investigates the quality aspects of laser cutting of Li-ion electrodes when a green fibre laser source (λ=532 nm, τ= 1 ns) is used rather than the more traditional infrared (IR) fibre laser source (λ=1,064 nm, τ=250 ns). The processing conditions were investigated to reveal the technological feasibility zones. Clearance width was studied within the technological feasibility zones for all the material-laser combinations. Results showed that high productivity criterion is met by the IR system, since cutting speed could reach 30 m/min with 54Waverage laser power on both anode and cathode. On the other hand, the green laser provided clearance width below 20 μm. In the best case, the clearance on anode could be eliminated with the green laser system. Although the maximum cutting speed was 4.5 m/min, upscaling of green laser power can provide required productivity.

Lasers in the manufacturing of cardiovascular metallic stents: Subtractive and additive processes with a digital tool

Laser beams can be manipulated to achieve different types of interaction mechanisms with metals allowing them to heat, melt, vaporize, or ablate them. Today's laser sources are robust, fast-addressable optoelectronic devices, easily integrated into automation systems along with sophisticated CAD/CAM solutions. Being a photonic digital tool, the laser beam is a fundamental tool for Industry 4.0 and is already widely exploited in the manufacturing of metallic stents. The conventional manufacturing method of laser cutting employs a subtractive method to cut the stent mesh on tubular feedstock. On the other hand, laser beams can be exploited to melt metallic powders to produce stent geometries in a layer-by-layer fashion. The present work provides a short state of the art review concerning the works focusing on the two laser-based manufacturing processes underlining the evolution of the laser source types and used materials. The work provides insights into the future opportunities and challenges that should be faced by the manufacturing research communities in the light of improving the biomedical device performance by exploiting the possibilities provided by the digital tool

Microcutting of multi-layer foils with IR and green ns-pulsed fibre lasers for Li-Ion batteries

open2noLi-Ion batteries are crucial components in mobile devices that range from cellular phones to electrical vehicles. With the increasing demand in the market for these devices, manufacturers are required to reduce production cycle times. The main components of the Li-Ion batteries are anode and cathode foils, which are cut in required forms by punching. These materials consist of Cu sheets sandwiched between graphite layers for anode, and Al sheets sandwiched between Li metal oxide layers for cathode. In punching, the process quality degrades in time due to tool wear. This eventually causes machine down times for tool repair or change, which can increase the whole process cycle time drastically. Laser remote cutting based on ablation can be adequate solution to substitute the current technology, if the cutting edge quality and productivity can be matched to punching. This paper investigates laser microcutting of Li-Ion battery anode and cathode thin foils with ns-pulsed fibre lasers. These laser sources are cost effective and provide industrially robust operation. Two systems operating with 1 μm and 0.5 μm wavelength and 250 ns and 1 ns pulse durations respectively were compared. The cut kerfs were evaluated in terms of clearance, which is defined as the extent of the exposed middle layer of the sandwich (i.e. Cu or Al) at the laser cut kerf.Demir, Ali Gökhan; Previtali, BarbaraDemir, ALI GOKHAN; Previtali, Barbar

Probing multipulse laser ablation by means of self-mixing interferometry

In this work, self-mixing interferometry (SMI) is implemented inline to a laser microdrilling system to monitor the machining process by probing the ablation-induced plume. An analytical model based on the Sedov-Taylor blast wave equation is developed for the expansion of the process plume under multiple-pulse laser percussion drilling conditions. Signals were acquired during laser microdrilling of blind holes on stainless steel, copper alloy, pure titanium, and titanium nitride ceramic coating. The maximum optical path difference was measured from the signals to estimate the refractive index changes. An amplitude coefficient was derived by fitting the analytical model to the measured optical path differences. The morphology of the drilled holes was investigated in terms of maximum hole depth and dross height. The results indicate that the SMI signal rises when the ablation process is dominated by vaporization, changing the refractive index of the processing zone significantly. Such ablation conditions correspond to limited formation of dross. The results imply that SMI can be used as a nonintrusive tool in laser micromachining applications for monitoring the process quality in an indirect way

On the use of areal roughness parameters to assess surface quality in laser cutting of stainless steel with CO2 and fiber sources

"Laser cutting provides various advantages such as high flexibility in terms of process parameters and cut material type, as well as the possibility to obtain complex geometry in different dimensions with high precision. From industrial point of view, the two more competitive laser cutting technologies are based on the use of CO2 and active fiber sources, which produce samples visually different, with non-uniform surface and different depth of the striations. The quality assessment between the two laser systems within the industry is commonly based on standard ISO 9013; that covers several aspects of quality, the most used are the surface roughness and edge perpendicularity; however 2D profilometers adopted for measures are not able to analyze the complex 3D surface topography of the cutting edge. As a result, despite the fact that the differences are visually appreciated, measured 2D roughness values of different CO2 and fiber laser cutting conditions are very similar. Recently, a greater diffusion of 3D surface profilometry devices is present. These devices allow areal surface roughness parameters to be defined, which are potentially suitable to better quantify the laser cut quality. This work points out the use of a focus-variation microscopy to acquire 3D surfaces and evaluate analytically the surface quality of laser cut edges using areal surface roughness parameters. In particular, the purpose is to define a simple and repeatable method to identify the type of cutting process analyzed through the reconstruction of surface characteristics and quality of the cut-edge. As a case study, two stainless steel samples with the same geometry obtained with different laser sources, CO2 and active, fiber is presented. For comparison purposes the cutting conditions were fixed to represent the state of the art of respective laser cutting technologies, which actually show distinct cutting edge characteristics.

Comparative study of CW, nanosecond- and femtosecond-pulsed laser microcutting of AZ31 magnesium alloy stents

Magnesium alloys constitute an interesting solution for cardiovascular stents due to their biocompatibility and biodegradability in human body. Laser microcutting is the industrially accepted method for stent manufacturing. However, the laser-material interaction should be well investigated to control the quality characteristics of the microcutting process that concern the surface roughness, chemical composition, and microstructure of the final device. Despite the recent developments in industrial laser systems, a universal laser source that can be manipulated flexibly in terms of process parameters is far from reality. Therefore, comparative studies are required to demonstrate processing capabilities. In particular, the laser pulse duration is a key factor determining the processing regime. This work approaches the laser microcutting of AZ31 Mg alloy from the perspective of a comparative study to evaluate the machining capabilities in continuous wave (CW), ns- and fs-pulsed regimes. Three industrial grade machining systems were compared to reach a benchmark in machining quality, productivity, and ease of postprocessing. The results confirmed that moving toward the ultrashort pulse domain the machining quality increases, but the need for postprocessing remains. The real advantage of ultrashort pulsed machining was the ease in postprocessing and maintaining geometrical integrity of the stent mesh after chemical etching. Resultantly, the overall production cycle time was shortest for fs-pulsed laser system, despite the fact that CW laser system provided highest cutting speed

Fibre Laser Cutting and Chemical Etching of AZ31 for Manufacturing Biodegradable Stents

The use of magnesium-alloy stents shows promise as a less intrusive solution for the treatment of cardiovascular pathologies as a result of the high biocompatibility of the material and its intrinsic dissolution in body fluids. However, in addition to requiring innovative solutions in material choice and design, these stents also require a greater understanding of the manufacturing process to achieve the desired quality with improved productivity. The present study demonstrates the manufacturing steps for the realisation of biodegradable stents in AZ31 magnesium alloy. These steps include laser microcutting with a Q-switched fibre laser for the generation of the stent mesh and subsequent chemical etching for the cleaning of kerf and surface finish. Specifically, for the laser microcutting step, inert and reactive gas cutting conditions were compared. The effect of chemical etching on the reduction in material thickness, as well as on spatter removal, was also evaluated. Prototype stents were produced, and the material composition and surface quality were characterised. The potentialities of combining nanosecond laser microcutting and chemical etching are shown and discussed