Laser Micromilling Research Articles

Laser micro-milling under a thin and flowing water layer: A new concept of liquid-assisted laser machining process

This study proposes a new laser micro-milling technique for minimizing the thermal damage and gaining a higher material removal rate than using the laser alone. A low-pressure waterjet was used to impinge on the workpiece surface in order to form a thin water film, where the laser ablation was made underneath the water layer created. According to the findings, the presented technique can introduce a great reduction in heat-affected zone and significantly increase the cavity depth compared to the other laser milling processes. Experimental analyses and potential use of this new machining technique were also given and discussed.

WITHDRAWN: Laser micro-milling under a thin and flowing water layer: A new concept of liquid-assisted laser machining process

WITHDRAWN: Laser micro-milling under a thin and flowing water layer: A new concept of liquid-assisted laser machining process

Laser micro-milling of microchannel on copper sheet as catalyst support used in microreactor for hydrogen production

Microchannel structure as catalyst support has been widely used to construct numerous microreactors for hydrogen production. In this work, the laser micro-milling technique was introduced into the fabrication process of microchannels with different geometry and dimensions. The effects of varying scanning speed, laser output power and number of scans on the surface morphology and geometrical dimension of microchannels have been investigated based on SEM observations. It is found that the change of scanning speed and laser output power significantly affected the surface morphology of microchannel. Moreover, the depth of microchannel was increased when the laser output power and number of scans were increased. Subsequently, the microchannels on copper sheet fabricated by the laser micro-milling technique were used as catalyst support to conduct the methanol steam reforming reaction. The better reaction performance of methanol steam reforming in microchannels indicates that laser micro-milling process is probably suitable to fabricate the microchannel reactor for the commercial application.

Laser micromilling of convex microfluidic channels onto glassy carbon for glass molding dies

This study reports the fabrication of convex microfluidic channels on glassy carbon using an ultraviolet laser processing system to produce glass molding dies. The laser processing parameters, including various laser fluences and scanning speeds of galvanometers, were adjusted to mill a convex microchannel on a glassy carbon substrate to identify the effects of material removal. The machined glassy carbon substrate was then applied as a glass molding die to fabricate a glass-based microfluidic biochip. The surface morphology, milled width and depth, and surface roughness of the microchannel die after laser micromilling were examined using a three-dimensional confocal laser scanning microscope. This study also investigates the transcription rate of microchannels after the glass molding process. To produce a 180μm high microchannel on the GC substrate, the optimal number of milled cycles, laser fluence, and scanning speed were 25, 4.9J/cm2, and 200mm/s, respectively. The width, height, and surface roughness of milled convex microchannels were 119.6±0.217μm, 180.26±0.01μm, and 0.672±0.08μm, respectively. These measured values were close to the predicted values and suitable for a glass molding die. After the glass molding process, a typical glass-based microchannel chip was formed at a molding temperature of 660°C and the molding force of 0.45kN. The transcription rates of the microchannel width and depth were 100% and 99.6%, respectively. Thus, the proposed approach is suitable for performing in chemical, biochemical, or medical reactions.

Closed-loop control in ultrafast laser milling process using laser triggered plasma

The derived light from laser triggered plasma is used as an indicator for a closed-loop control in the femtosecond pulse laser micro-milling. The relationship between the brightness of derived light and the defocusing distance is pre-measured as a basic curve for the closed-loop control milling to assure the machining accuracy. The two elements, i.e. the defocusing distance and the size of the laser affected volume, are analyzed to predict the final machining result. By monitoring the brightness of the derived light, the ablation depth during a femtosecond pulse laser micro-machining process can be controlled in a real-time manner. A micro-milling experiment as reported in this paper demonstrates the feasibility and efficiency of this novel closed-loop micro-machining method.

Prediction of depth of cut for single-pass laser micro-milling process using semi-analytical, ANN and GP approaches

The present study is aimed to investigate micro-milling performance of thermoplastics with different parameters, namely laser beam absorptivity, latent heat of vaporization, laser power and cutting speed. The 25-W CO2 (CW) laser engraving machine is used for the investigation. In total 50 different combinations of laser power and cutting speed with four categories of thermoplastics, namely poly-methyl-methacrylate, poly-propylene, acrylonitrile butadiene styrene and nylon 6, are used in this study. Experimental results suggest that laser beam absorptivity, cutting power and cutting speed are the major influencing parameters on depth of cut. Theoretical model for the prediction of depth of cut in terms of material properties, cutting power and cutting speed has been proposed. Two correction parameters have been introduced in this analysis using non-linear regression method to improve the theoretical model. Comparison has been made between prediction capabilities of theoretical model, model based on multi-gene genetic programming and artificial neural network. The comparison clearly indicates that all the three models provide accurate prediction of depth of cut. The details of experimentation, model development, testing and the performance comparison are presented in this paper.

Determination of process parameters in the laser micromilling application using Taguchi method: A case study for AISI H13 tool steel

Laser micromilling technique is a thermal machining process which is used to remove material on the target geometry and has been widely employed in mold and die making industry. In this technique, the control factors of process such as scan speed, scan direction, frequency, and fill spacing play major affect on the surface quality. The selected quality characteristics are the mean surface roughness and milling depth. The main objective of this study is to determine the optimal milling conditions based on machining direction for minimizing the surface roughness and maximizing the milling depth. Therefore, L18 orthogonal array is constituted and subsequently signal/noise ratio and analysis of variance were employed to investigate the optimal levels of process parameters. The analysis results show that the scan speed has the highest effect on the surface roughness of which percentage contribution is 39.68% and also the beam scan direction and fill spacing have significant effects which contribute 19.67% and 16.09%, respectively. The experimental result for optimal condition is 2.23 μm. The results for milling depth show that only scan speed and fill spacing have significant effects which contribute 69.08% and 19.21%, respectively. Moreover, the scan direction has the least effect on the milling depth which can be neglected. The frequency has no effect on both surface roughness and milling depth. The result obtained from experiment at the optimal condition is 121.4 μm.

Femtosecond laser micromilling of Si wafers

Femtosecond laser micromilling of silicon is investigated using a regeneratively amplified 775 nm Ti:Sapphire laser with a pulse duration of 150 fs operating at 1 kHz repetition rate. The morphological observation and topological analysis of craters fabricated by single-shot laser irradiation indicated that the material removal is thermal in nature and there are two distinct ablation regimes of low fluence and higher fluence with logarithmical relations between the ablation depth and the laser fluence. Crater patterns were categorized into four characteristic groups and their formation mechanisms were investigated. Femtosecond laser micromilling of pockets in silicon was performed. The effect of process parameters such as pulse energy, translation speed, and the number of passes on the material removal rate and the formation of cone-shaped microstructures were investigated. The results indicate that the microstructuring mechanism has a strong dependence on the polarization, the number of passes and laser fluence. The optimal laser fluence range for Si micromilling was found to be 2–8 J/cm 2 and the milling efficiency attains its maximum between 10 and 20 J/cm 2.