State of the Art of Laser Hardening and Cladding

In this paper an overview is given about laser surface modification processes, which are developed especially with the aim of hardness improvement for an enhanced fatigue and wear behaviour. The processes can be divided into such with and without filler material and in solid-state and melting processes. Actual work on shock hardening, transformation hardening, remelting, alloying and cladding is reviewed, where the main focus was on scientific work from the 21st century

Influence of different process parameters on deformation velocity in laser shock forming

In laser shock forming TEA-CO_2-laser induced shock waves are used to form metal foils, such as aluminum or copper. The process utilizes an initiated plasma shock wave on the target surface, which leads to a forming of the foil. Several pulses can be applied at one point in order to achieve a high forming degree without increasing the energy density beyond the ablation limit. During the process, pressure peaks in range of MPa can be achieved. In this article, the dependence of deformation velocity in laser shock forming on various materials as well as laser pulse intensities was determined experimentally for a laser shock bending process. In order to categorize these influences a theoretical model for deformation velocity based on the energy balance is proposed, which allows the evaluation of the influencing variables

Plasma Induced On Indenter Balls

There is an increasing demand to enable high throughput experimentation to characterize and develop new materials in a very short time. The investigated hardness measurement method differs from conventional hardness measurements in how the force is applied. The new method is based on laser-induced shockwaves. A shockwave is created with a nanosecond pulsed TEA CO2 laser on top of an indenter. The pressure of the shockwave is used to push an indenter inside a workpiece. A quadratic laser focus area of 4 mm², having a diagonal larger than the indenter diameter, leads to interactions of the laser beam with the surrounding material, which affects the plasma formation and results in heating of the material underneath. Material heating decreases the yield point and accordingly the hardness. Therefore, influence of pulse energy and plasma formation on heating of material are investigated to understand the interaction between the high intensity laser beam, the indenter and the material underneath. It is shown that a 3 mm indenter diameter reduces the maximum estimated temperature of the workpiece (X5CrNi18-10) underneath down to 64°C. With an additional positioning unit in combination with indenter diameter of 3 mm or larger no significant heat input was obtained anymore in the workpiece underneath

Non-thermal Laser Forming of Sheet Metal

In this paper the results of some preliminary experiments are presented on non-thermal microforming of thin metal sheets with laser induced optical breakdown shock waves. Three sheet metal forming processes are realized with this method. The most deeply investigated process is laser stretch-forming, since the influence of parameters like defocussing, power density, pulse energy, number of pulses, and material could be worked out. The results show that uniform shaped domes with a dome height over 250 µm with diameters of 1.4 mm could be produced. Additionally, first investigations on laser stamping and laser embossing have been carried out, but are not presented in this paper

Forming Behaviour in Laser Shock Drawing

Through the continuing trend of miniaturization new cost efficient and fast methods for processing small parts are required. In this paper a new non-mechanical process for the forming process of micro deep drawing is presented. This new deep drawing process utilizes a laser initiated plasma shock wave at the target, which forms the sheet. Several pulses can be applied at one point and therefore high forming degrees can be reached without increasing the energy density. In this paper the pressure of the shock wave is measured in order to enable optimizations of the process in future. Furthermore a distribution of the thickness over the deep drawn cups will be introduced. Finally laser deep drawing of samples made out of Al99.5, Cu and stainless steel sheet metal with thicknesses of 20 µm and 50 µm are shown

Determination of Forming Speed at a Laser Shock Stretch Drawing Process

Laser shock forming is a new high speed forming process based on TEA-CO2-laser induced shock waves. In former publications laser shock forming was already presented as a process which can be used for deep drawing, stretch drawing and cutting of thin copper and aluminum sheets. The process utilizes an initiated plasma shock wave on the target surface, which leads to the sheets forming. Several pulses can be applied at one point in order to achieve a high forming degree without increasing the energy density beyond the ablation limit. During the process, pressure peaks in the range of some MPa can be achieved. In order to classify the process in the framework of high speed forming processes, the temporal varying deformation velocity due to different materials have been identified based on a stretch drawing process by using different pulse energies. Therefore a new high speed measurement system based on the shadowing effects is designed and its suitability is shown. The determined strain rate of 520 s-1 meets one of the criteria for the classification of laser shock stretch drawing as a high-speed forming process

Novel Approach to Increase the Energy-related Process Efficiency and Performance of Laser Brazing

AbstractAlthough laser brazing is well established, the energy-related efficiency of this joining method is quite low. That is because of low absorptivity of solid-state laser radiation, especially when copper base braze metals are used. Conventionally the laser beam is set close to the vertical axis and the filler wire is delivered under a flat angle. Therefore, the most of the utilized laser power is reflected and thus left unexploited. To address this situation an alternative processing concept for laser brazing, where the laser beam is leading the filler wire, has been investigated intending to make use of reflected shares of the laser radiation. Process monitoring shows, that the reflection of the laser beam can be used purposefully to preheat the substrate which is supporting the wetting and furthermore increasing the efficiency of the process. Experiments address a standard application from the automotive industry joining zinc coated steels using CuSi3Mn1 filler wire. Feasibility of the alternative processing concept is demonstrated, showing that higher processing speeds can be attained, reducing the required energy per unit length while maintaining joint properties

Kolloquium Mikroproduktion und Abschlusskolloquium SFB 499 ; 11. - 12. Oktober 2011, Karlsruhe (KIT Scientific Reports ; 7591)

In diesem Tagungsband werden aktuelle Ergebnisse der angewandten Grundlagenforschung auf dem Gebiet der Mikroproduktion vorgestellt. Die dargestellten Arbeiten und Ergebnisse stammen vom SFB 499 "Mikrourformen", dem SFB 747 "Mikrokaltumformen", der FOR 702 "Maschinen-, Werkzeug- und Prozessentwicklung für neue Verfahren zur Herstellung von Mikrobauteilen über flüssige Phasen" und aus dem Umfeld des 2010 abgeschlossenen SFB 516 "Konstruktion und Fertigung aktiver Mikrosysteme"

Comportamento ad alta temperatura di rivestimenti NiCrAlY prodotti mediante tecnica Laser Cladding

La tecnica Laser Cladding è un metodo alternativo alla spruzzatura termica per la produzione di rivestimentiresistenti alle alte temperature con una porosità molto bassa o addirittura nulla.Il presente studio ha riguardato il comportamento ad ossidazione di rivestimenti NiCrAlY ottenuti medianteLaser Cladding su substrati di Hastelloy X. Il comportamento ad ossidazione dei campioni rivestiti è statovalutato mediante prove in forno a circolazione d’aria alla temperatura di 1100°C con durate fino a 450 ore.I rivestimenti sono stati analizzati, prima e dopo le prove di ossidazione, mediante tecniche di microscopiaottica ed elettronica, microanalisi e diffrazione di raggi X. Dopo la deposizione il rivestimento ha mostratouna struttura dendritica con grani colonnari e porosità pressoché nulla. Dopo le prove di ossidazione l’analisimicroscopica ha mostrato la presenza di due distinti strati di ossidi, uno più esterno costituitoprevalentemente da ossidi di tipo spinello e uno strato più interno, continuo, costituito principalmenteda allumina. I risultati ottenuti suggeriscono che il rivestimento di NiCrAlY preparato per Laser Claddingè in grado di formare, ad alte temperature ed in atmosfera ossidativa, uno strato continuo di alluminache può proteggere il substrato dall’ossidazione

A comparison between ultraviolet disinfection and copper alginate beads within a vortex bioreactor for the deactivation of bacteria in simulated waste streams with high levels of colour, humic acid and suspended solids.

We show in this study that the combination of a swirl flow reactor and an antimicrobial agent (in this case copper alginate beads) is a promising technique for the remediation of contaminated water in waste streams recalcitrant to UV-C treatment. This is demonstrated by comparing the viability of both common and UV-C resistant organisms in operating conditions where UV-C proves ineffective - notably high levels of solids and compounds which deflect UV-C. The swirl flow reactor is easy to construct from commonly available plumbing parts and may prove a versatile and powerful tool in waste water treatment in developing countries