Abstract
Laser chemical machining (LCM) is a non-conventional processing method that enables a smooth and precise micro structuring of metallic surfaces. However, a high-quality removal is limited to a laser power window of some 100 mW. This is due to the high sensibility to removal disturbances, such as the deposition of metallic salts and oxides. In this work, the dynamic process behavior around the transition from a disturbance-free to a disturbed removal is investigated for the laser chemical machining of titanium (3.7024) and stainless steel (AISI 304) in different phosphoric acid solutions. Therefore, the removal cavities are recorded using confocal scanning microscopy and characterized regarding width, depth and quality in dependence of the laser power, feed velocity and electrolyte concentration. While the removal characteristics within the disturbance-free regime are found to be material-independent, the disturbed regime is strongly dependent on the tendency of the material to gas bubble adherence. Additional CCD records of the interaction zone reveal that the transition to the disturbed regime is accompanied by significant light reflections and thereby indicate the influence of adhering gas bubbles on disturbing the removal process. Moreover, typical removal disturbances are presented and discussed with regard to the responsible mechanisms for their occurrence.
Highlights
The ever-increasing demand for miniaturized components and devices requires the qualification of novel manufacturing methods that fulfill high expectations of flexible and individualized production [1]
The dynamic process behavior around the transition from a disturbance-free to a disturbed removal is investigated for the laser chemical machining of titanium (3.7024) and stainless steel (AISI 304) in different phosphoric acid solutions
Self-passivating metals lose their natural passivation property, allowing an electrochemical etching of the base material [5]. This material dissolution occurs under the formation of hydrogen and water soluble metallic salts [2], as has been observed for different self-passivating metals, e.g., stainless steel, titanium alloys [6] and tool steels (Cr–Co alloys) [7]
Summary
The ever-increasing demand for miniaturized components and devices requires the qualification of novel manufacturing methods that fulfill high expectations of flexible and individualized production [1]. Among other non-conventional processes, laser chemical machining (LCM) presents a promising method towards a gentle and precise micro machining of especially metallic parts [2]. It unifies the advantages of laser machining with its precise and localized energy deposition [3] and the electrochemical machining with its smooth processing without affecting the material microstructure [4]. Robert et al have used stainless steel (1.4310) micro molds, which were laser chemically machined, for the structuring of monocrystalline diamond by an ultrasonic-assisted friction polishing [11] Another application presents the surface finishing of metallic surfaces, as is shown by Eckert et al [12]
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