Laser Chemical Machining (LCM) is a non-conventional processing method, which enables very accurate and precise ablation of metallic surfaces. Material ablation results from laser-induced thermal activation of heterog...Laser Chemical Machining (LCM) is a non-conventional processing method, which enables very accurate and precise ablation of metallic surfaces. Material ablation results from laser-induced thermal activation of heterogeneous chemical reactions between electrolytes and a metallic surface. However, when processing metallic surfaces with LCM, large fluctuations in ablation quality can occur due to rising bubbles. The for-mation of bubbles during laser chemical machining and their influence on the ablation quality has not been investigated. For a more detailed investigation of the bubbles, ablation experiments on Titanium and Ce-ramic under different thermal process conditions were performed. The experiments were recorded by a high-speed camera. The evaluation of the video sequences was performed using Matlab. The resulting bubbles were analyzed regarding their size and frequency. The results show that boil-ing bubbles formed on both materials during processing. Titanium also produces smaller bubbles, which can be identified as process bubbles ac-cording to their size. Furthermore, it was found that undisturbed laser chemical ablation can be achieved in the presence of a boiling process, since both boiling bubbles and process bubbles were detected during machining within the process window.展开更多
Laser Chemical Machining (LCM) is a non-conventional removal process, based on a precise thermal activation of heterogeneous chemical reactions between an electrolyte and a metallic surface. Due to local overheating d...Laser Chemical Machining (LCM) is a non-conventional removal process, based on a precise thermal activation of heterogeneous chemical reactions between an electrolyte and a metallic surface. Due to local overheating during the process, boiling bubbles occur, which can impair the removal quality. In order to reduce the amount of bubbles, the laser chemical process is performed at different process pressures. Removal experiments were performed on Titanium Grade 1 using the electrolyte phosphoric acid at various process pressures, machining speeds and laser powers in order to determine the limit of the process window by evaluating the characteristics of the removal cavities. As a result, the process window for non-disturbed laser chemical machining is widened at higher process pressures. The process pressures have no influence on the geometric shape of the removal. The expansion of the process window is attributed to the fact that at higher process pressures the saturation temperature of the electrolyte rises, so that bubble boiling starts at a higher surface temperature on the workpiece induced by the laser power. The removal rate could be increased by a factor of 2.48 by increasing the process pressures from ambient pressure to 6 bar, thus taking an important step towards the economic efficiency of the laser chemical machining.展开更多
Laser chemical machining(LCM)is a gentle metal removal technique with micrometer resolution.LCM involves laser-driven surface heating of the workpiece,which is subjected to a flowing acid bath,locally inducing a chemi...Laser chemical machining(LCM)is a gentle metal removal technique with micrometer resolution.LCM involves laser-driven surface heating of the workpiece,which is subjected to a flowing acid bath,locally inducing a chemical dissolution reaction.To ensure a high machining quality,the laser power is intentionally limited to avoid disturbances in material removal presumably caused by the shielding effect of boiling bubbles.To achieve both an increased removal rate and a high removal quality,the current understanding of surface removal mechanisms must be fundamentally expanded.Therefore,to create the basis of near-process quality control in the future,a near-process measurement approach is needed for the machined workpiece geometry inside the machine and the temperature in the process fluid as an important process quantity.This study introduces a fluorescence-based measurement approach capable of assessing both quantities in-situ.An experimental feasibility study demonstrated the robustness of the approach in measuring the three-dimensional geometry of a structure produced by LCM,even in the presence of streaming air bubbles in the optical path,thereby validating its near-process capability.However,systematic measurement errors,such as edge artifacts,were observed in the geometry measurements,indicating the need for a revision of the signal model.In addition,precise temperature measurements of the electrolyte solution within the LCM environment were achieved,with a random error of 1℃ and a systematic error of 1.4℃.展开更多
Suitable approaches are needed for rapid and cost-efficient materials development.High-throughput experimentation reduces the identification time of suitable material compositions.One approach is to use small specimen...Suitable approaches are needed for rapid and cost-efficient materials development.High-throughput experimentation reduces the identification time of suitable material compositions.One approach is to use small specimen geometries to save additional production costs.Hence,research is continuously being conducted on a new hardness test based on laser-induced shock waves.Thus far,characteristic values from the induced indentations have been extracted,which correlate with hardness and tensile strength.However,the indentation result varies in dependence of the specimen size and mass.This condition hinders the correlation between characteristic values and material properties.Thus,the goal was to induce similar indentation results to minimum specimen size.Herein,different mounting materials and methods were investigated.The created indentations were compared with those induced in large specimens.Essential mounting parameters were derived from the findings.Consequently,small specimens can be used for material characterization by considering these mounting parameters.展开更多
文摘Laser Chemical Machining (LCM) is a non-conventional processing method, which enables very accurate and precise ablation of metallic surfaces. Material ablation results from laser-induced thermal activation of heterogeneous chemical reactions between electrolytes and a metallic surface. However, when processing metallic surfaces with LCM, large fluctuations in ablation quality can occur due to rising bubbles. The for-mation of bubbles during laser chemical machining and their influence on the ablation quality has not been investigated. For a more detailed investigation of the bubbles, ablation experiments on Titanium and Ce-ramic under different thermal process conditions were performed. The experiments were recorded by a high-speed camera. The evaluation of the video sequences was performed using Matlab. The resulting bubbles were analyzed regarding their size and frequency. The results show that boil-ing bubbles formed on both materials during processing. Titanium also produces smaller bubbles, which can be identified as process bubbles ac-cording to their size. Furthermore, it was found that undisturbed laser chemical ablation can be achieved in the presence of a boiling process, since both boiling bubbles and process bubbles were detected during machining within the process window.
文摘Laser Chemical Machining (LCM) is a non-conventional removal process, based on a precise thermal activation of heterogeneous chemical reactions between an electrolyte and a metallic surface. Due to local overheating during the process, boiling bubbles occur, which can impair the removal quality. In order to reduce the amount of bubbles, the laser chemical process is performed at different process pressures. Removal experiments were performed on Titanium Grade 1 using the electrolyte phosphoric acid at various process pressures, machining speeds and laser powers in order to determine the limit of the process window by evaluating the characteristics of the removal cavities. As a result, the process window for non-disturbed laser chemical machining is widened at higher process pressures. The process pressures have no influence on the geometric shape of the removal. The expansion of the process window is attributed to the fact that at higher process pressures the saturation temperature of the electrolyte rises, so that bubble boiling starts at a higher surface temperature on the workpiece induced by the laser power. The removal rate could be increased by a factor of 2.48 by increasing the process pressures from ambient pressure to 6 bar, thus taking an important step towards the economic efficiency of the laser chemical machining.
基金Contributions by Claudia Niehaves,Yasmine Bouraoui,Yang Lu and Tim Radel are funded by the German Research Foundation(DFG),project number 451385285(Process-oriented characterization of temperature field and ablation changes during laser chemical processing)Andreas Tausendfreund was funded by the European Research Council(ERC),project number 101044046-InOGeM(Indirect Optical Geometry Measurement).
文摘Laser chemical machining(LCM)is a gentle metal removal technique with micrometer resolution.LCM involves laser-driven surface heating of the workpiece,which is subjected to a flowing acid bath,locally inducing a chemical dissolution reaction.To ensure a high machining quality,the laser power is intentionally limited to avoid disturbances in material removal presumably caused by the shielding effect of boiling bubbles.To achieve both an increased removal rate and a high removal quality,the current understanding of surface removal mechanisms must be fundamentally expanded.Therefore,to create the basis of near-process quality control in the future,a near-process measurement approach is needed for the machined workpiece geometry inside the machine and the temperature in the process fluid as an important process quantity.This study introduces a fluorescence-based measurement approach capable of assessing both quantities in-situ.An experimental feasibility study demonstrated the robustness of the approach in measuring the three-dimensional geometry of a structure produced by LCM,even in the presence of streaming air bubbles in the optical path,thereby validating its near-process capability.However,systematic measurement errors,such as edge artifacts,were observed in the geometry measurements,indicating the need for a revision of the signal model.In addition,precise temperature measurements of the electrolyte solution within the LCM environment were achieved,with a random error of 1℃ and a systematic error of 1.4℃.
基金Financial support of the subprojeet D02"Laser induced hardness measurements"funded by the Deutsche Forschun-gsgemeinschaft(DFG,German Rescarch Foundation)-Project number 276397488-SFB 1232 .
文摘Suitable approaches are needed for rapid and cost-efficient materials development.High-throughput experimentation reduces the identification time of suitable material compositions.One approach is to use small specimen geometries to save additional production costs.Hence,research is continuously being conducted on a new hardness test based on laser-induced shock waves.Thus far,characteristic values from the induced indentations have been extracted,which correlate with hardness and tensile strength.However,the indentation result varies in dependence of the specimen size and mass.This condition hinders the correlation between characteristic values and material properties.Thus,the goal was to induce similar indentation results to minimum specimen size.Herein,different mounting materials and methods were investigated.The created indentations were compared with those induced in large specimens.Essential mounting parameters were derived from the findings.Consequently,small specimens can be used for material characterization by considering these mounting parameters.
