Micromachining Of Metals Research Articles

Micromachining of Metals with Copper Vapor Laser

Micromachining of Metals with Copper Vapor Laser

Analysis of the Heat-Affected Zone and Ablation Efficiency in Terms of Burst Mode Parameters During High Power Picosecond Laser Micromachining of Metals

Abstract This paper presents a systematic study on using the burst mode ablation to limit the heat-affected zone (HAZ) while maintaining a high ablation efficiency using a high-power industrial picosecond laser with burst fluence larger than 10 J/cm2. An extended three-dimensional two-temperature model (3D-TTM) was employed to study the mechanism of the HAZ development and to predict the ablation efficiency with experimental validation. The essentiality of including the lattice heat conduction to predict accurate HAZ was discussed. The effect of the number of pulses per burst and pulse-to-pulse separation time was investigated. The optimal number of pulses per burst was obtained by using the 3D-TTM for copper and stainless steel. The 3D-TTM suggested that by using the optimal number of pulses per burst, a maximum reduction of 77% and 61% in HAZ could be achieved for copper and stainless steel respectively. And the corresponding ablation efficiency will be increased by 24% and 163% for copper and stainless steel at the same time. This study showed that burst mode laser machining at high fluence is an effective way of increasing efficiency while limiting the HAZ.

Multi-Messenger Radio Frequency and Optical Diagnostics of Pulsed Laser Ablation Processes

In this report, a novel non-contact, non-invasive methodology for near and quasi real-time measurement of the structuring of metal surfaces using pulsed laser ablation is described. This methodology is based on the use of a multi-messenger data approach using data from Optical Emission Spectroscopy (OES) and Radio Emission Spectroscopy (RES) in parallel. In this research, radio frequency (RF) emission (in the range of 100–400 MHz) and optical emission (200–900 nm) were investigated and acquired in real-time. The RES and OES data were post-processed and visualized using heat maps, and, because of the large data sets acquired particularly using in RES, Principal Component Analysis (PCA) statistics were used for data analysis. A comparison between in-process RES-OES data and post-process 3D images of the different ablated holes generated by a picosecond laser with different powers (1.39 W, 1.018 W, and 0.625 W) on aluminum (Al) and copper (Cu) was performed. The real-time time-series data acquired using the Radio and Optical Emission Spectroscopy technique correlate well with post-process 3D microscopic images. The capability of RES-OES as an in operando near real-time diagnostic for the analysis of changes of ablation quality (cleanliness and symmetry), and morphology and aspect ratios (including the diameter of ablated holes) in the process was confirmed by PCA analysis and heat map visualization. This technique holds great promise for in-process quality detection in metal micromachining and laser-metal base manufacturing.

Analysis of dual-phase-lag heat conduction in a two-dimensional slab heated by a moving annular laser pulse

The controlled scan of a laser beam is at the core of the technology used for the micromachining of metals. To improve the laser micromachining of metal surfaces and reduce the thermal stress caused by the difference in temperature obtained in the process, a moving annular pulse laser heat source is introduced in present work. A mathematical model based on the dual-phase-lag (DPL) model is formulated to simulate the temperature response in a finite two-dimensional slab heated by the moving annular pulse laser heat source. Green's function approach and the superposition method are used to develop an analytical solution for the temperature field, and influences of the ratio of the thermalization time to the relaxation time of heat flux vector on the slab temperature distribution are investigated. The laser parameters that comprise the inner and outer radii are also examined to determine the induced temperature characteristics and advantages of the novel heat source.

A numerical study on influence of strain gradients on lattice rotation in micro-machining of a single crystal

In latest years small scale machining has been widely used in advanced engineering applications such as medical and optical devices, micro- and nano-electro-mechanical systems. In micromachining of metals, a depth of cut becomes usually smaller than an average crystal size of a polycrystalline structure; thus, the cutting process zone can be localized fully indoors of a single grain. Due to the crystallographic anisotropy, development of small scale machining models accounting for crystal plasticity are essential for a precise calculation of material removal under such circumstances. For this purpose, a 3D finite-element model of micro-cutting of a single grain was developed. A crystal-plasticity theory accounting for gradients of strain, implemented in ABAQUS/Explicit via a user-defined material subroutine VUMAT, was used in the computations. The deformation-induced lattice rotations in micro-cutting of a single crystal were analyzed extensively.

Review on Experimental and Theoretical Investigations of Ultra-Short Pulsed Laser Ablation of Metals with Burst Pulses.

Laser processing with ultra-short double pulses has gained attraction since the beginning of the 2000s. In the last decade, pulse bursts consisting of multiple pulses with a delay of several 10 ns and less found their way into the area of micromachining of metals, opening up completely new process regimes and allowing an increase in the structuring rates and surface quality of machined samples. Several physical effects such as shielding or re-deposition of material have led to a new understanding of the related machining strategies and processing regimes. Results of both experimental and numerical investigations are placed into context for different time scales during laser processing. This review is dedicated to the fundamental physical phenomena taking place during burst processing and their respective effects on machining results of metals in the ultra-short pulse regime for delays ranging from several 100 fs to several microseconds. Furthermore, technical applications based on these effects are reviewed.

WR‐1.5 (500–750 GHz) waveguide bandpass filter fabricated using high precision computer numerically controlled machining

AbstractIn this paper, a WR‐1.5 band (500–750 GHz) 3rd order waveguide bandpass filter has been designed and fabricated using high precision computer numerically controlled metal micromachining. The filter has been measured with a 7.29% (48.7 GHz) bandwidth at the center frequency of 667.5 GHz. The minimum passband insertion loss is measured to be 0.87 dB and the measured return loss is better than 10 dB across the whole passband. A yield percentage is analysed and estimated based on the fabrication tolerance.

Analysis of the Heat Affected Zone and Surface Roughness during Laser Micromachining of Metals

The current research focuses on the characterization of the produced heat affected zone when laser heats AISI H13 steel, AISI 1045 steel and Ti6Al4V alloy workpieces via finite element simulations and experimental investigation. The surface roughness designedly varies on the surface of the samples and its influence on the absorption of laser light is investigated. Experiments are conducted at 1-4 W laser power and for two scanning speeds of 2 and 100 mm/min. A 3D transient thermo-structural finite element model for a moving Gaussian laser heat source is developed to simulate the micromachining process and predict the depth and width of the heat affected zone. The Johnson-Cook material model that takes into account the effect of plastic strain, strain rate and temperature, along with a fracture model, is adapted to the simulations. A good agreement between the experimental data and the simulation results is found. The depth and width of the heat affected zone strongly depend on the laser parameters and material properties of the irradiated samples. This study constitutes the basis to the optimization and improvement of the laser assisted micromachining process parameters and provides key insights on the roughness-absorptivity relation for the three metallic materials.

Dynamic Process Behavior in Laser Chemical Micro Machining of Metals

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.

Micromachined Integrated Waveguide Transformers in THz Pickett–Potter Feedhorn Blocks

We present the design, fabrication technique, and performance of a circular-to-rectangular waveguide transformer integrated into a 1.9 THz Pickett-Potter feedhorn detector block. This design is applicable for instruments where circularly symmetric feedhorns are required to mate with rectangular waveguide-fed receiver devices that house the detector chip. The transformer was fabricated by direct metal micromachining, which offers significant advantages in reducing the complexity, timescale, and cost of manufacturing over competing techniques, such as transformer segments machined into separate blocks or machined into split-block segments. We simulate the tradeoff between the fabrication technique and the cost of rounding the edges of the rear rectangular waveguide. Simulations of the transformer circuitry using multiple electromagnetic software packages were used to finalize the dimensions of the optimized transformer. A single pixel feedhorntransformer module was manufactured on a three-axis milling machine to test the feasibility of the design and manufacturing technique. We tested the performance of the integrated feedhorn-transformer modules using waveguide-fed hot electron bolometer mixers designed and fabricated at the Jet Propulsion Laboratory. Radiation patterns of the Pickett-Potter modules were measured using a high-power 1.9 THz multiplication chain as the source. We find good agreement between the simulated and measured beam pattern.

Effect of laser beam conditioning on fabrication of clean micro-channel on stainless steel 316L using second harmonic of Q-switched Nd:YAG laser

Laser micromachining of metals for fabrication of micro-channels generate ridge formation along the edges accompanied by ripples along the channel bed. The ridge formation is due to the formation of interference pattern formed by back reflections from the beam splitter and other optical components involved before focusing on the work piece. This problem can be curtailed by using a suitable aperture or Iris diaphragm so as to cut the unwanted portion of the laser beam before illuminating the sample. This paper reports an experimental investigation on minimizing this problem by conditioning the laser beam using an Iris diaphragm and using optimum process parameters. In this work, systematic experiments have been carried out using the second harmonic of a Q-switched Nd:YAG laser to fabricate micro-channels. Initial experiments revealed that formation of ridges along the sides of micro-channel can easily be minimized with the help of Iris diaphragm. Further it is noted that a clean micro-channel of depth 43.39µm, width up to 64.49µm and of good surface quality with average surface roughness (Ra) value of 370nm can be machined on stainless steel (SS) 316L by employing optimum process condition: laser beam energy of 30mJ/pulse, 11 number of laser scans and scan speed of 169.54µm/s with an opening of 4mm diameter of Iris diaphragm in the path of the laser beam.

Melt Flow and Energy Limitation of Laser Cutting

Laser technology is a convertible technology for plenty of parts in most materials. Laser material processing for industrial manufacturing applications is today a widespread procedure for welding, cutting, marking and micro machining of metal and plastic parts and components. Involvement and support this huge mass-production industry of laser cutting, new technology and dry-process using lasers were and are being actively developed. Fundamentally, industrial laser cutting or other applications on industry should satisfy the four key practical application issues including “Quality or Performance”, “Throughput or Speed”, “Cost or Total Ownership Cost”, and “Reliability”. Laser requires for examples several complicated physical factors to be resolved including die strength to be enable good wire-bonding and survival of severe cycling test, clean cutting wall surface, good cutting of direct attach film, and proper speed of cutting for achieving economy of throughput. Some example of maximum cutting rate, wherewith is normally limited laser energy, cutting speed is depend on type laser, different of cutting with one laser beam and beam pattern and applied laser power/material thickness will be introduced in this paper.

Strain-gradient crystal-plasticity modelling of micro-cutting of b.c.c. single crystal

In recent years thanks to enhancements in design of advanced machines, laser metrology and computer control, ultra-precision machining has become increasingly important. In micromachining of metals the depth of cut is usually less than the average grain size of a polycrystalline aggregate; hence, a cutting process can occur entirely within a single crystal. The respective effect of crystallographic anisotropy requires development of machining models that incorporate crystal plasticity for an accurate prediction of micro-scale material removal under such conditions. To achieve this, a 3D finite-element model of orthogonal micro-cutting of a single crystal of b.c.c. brass was implemented in a commercial software ABAQUS/Explicit using a user-defined subroutine VUMAT. Strain-gradient crystal-plasticity theories were used to demonstrate the influence of evolved strain gradients on the cutting process for different cutting directions.

Abrasive enhanced electrochemical slurry jet micro-machining: Comparative experiments and synergistic effects

Abrasive enhanced electrochemical slurry-jet machining (ESJM) is presented as a new approach to the micro-machining of metals using a combination of abrasive slurry-jet machining (ASJM) and electrochemical jet machining (ECJM). A novel ESJM prototype was developed to generate a charged slurry jet consisting of a mixture of Al2O3 abrasive particles and an electrolytic solution of NaCl and NaNO3. A DC potential of 30V was applied between the nozzle and specimen. A series of micro-channels were machined in Stellite 12 using ASJM, ECJM and ESJM processes to investigate the relative effects of erosion and anodic dissolution on the material removal rate and surface finish in the combined process of ESJM. The results illustrated that the ESJM process results in significantly greater target mass loss rate than the separate erosion and corrosion processes. The magnitude of the synergistic effect on the rate of mass loss was found to vary from positive to negative as the erosion component increased with increasing particle kinetic energy (jet pressure) and particle concentration. The roughness of the channels machined using ESJM was between that obtained with ASJM and ECJM. The roughness decreased as the erosion component of the total mass loss increased.

Simulations and experiments on excimer laser micromachining of metal and polymer

Excimer laser at 248 nm has been used to micromachine holes and channels on stainless steel and polymethyl methacrylate using mask projection methods. The machining is numerically simulated considering the laser beam as a heat source only, thermal diffusion, and melt vaporization. The depth and width of the machined features at different pulse energies and number of pulses are measured by optical profilometry. Both the depth and the aspect ratio (depth-to-width) are found to increase with increasing number of pulses and pulse energies. The depth predicted by the simulations based on the thermal ablation model is closer to the experimental observations for steel as compared with that for the polymer. This allows for the quantification of the contribution of thermal ablation processes in the excimer laser machining of metals and polymers. High-energy pulses are found to have higher ablation efficiency in case of metal and lower ablation efficiency in case of polymer.

Compact machining module for laser chemical manufacturing

The size of machines for the manufacture of micro-components commonly stands in gross disproportion to the component size. The achievable accuracy is limited by inaccuracies of mechanical positioning elements and external disturbances. Micro-machining of metals can be realised in manifold ways by laser processes. In this paper, a compact module for laser chemical processing using continuous wave laser radiation is presented. For the laser-induced chemical machining the material removal is a result of thermochemical reactions between an etchant and the surface of a metallic workpiece at low laser power densities. Laser-induced chemical machining results in improved surface quality of the machined workpiece and it also avoids stress and strain of the material. Through the use of a micro-mirror array (DMD) for flexible beam shaping a 2-dimensional machining of the workpiece is possible. The laser chemical machining method now allow for the first time to connect the DMD technology with laser-based micro-machining for compaction of the machining module.

Prediction of machined surface evolution in the abrasive jet micro-machining of metals

Surface evolution models have been used in the past to accurately predict the cross-sectional profile of micro-channels resulting from the abrasive jet micro-machining (AJM) of glass and polymeric substrates. In the present paper, the models are suitably modified and applied for the first time to the AJM of metallic substrates. The dependence of erosion rate on abrasive jet inclination angle was measured for aluminum 6061-T6, Ti–6Al–4V alloy, and 316L stainless steel using 50μm Al2O3 abrasive powder launched at an average velocity of 106m/s. For all three systems the peak erosion rate was found to occur when the jet was inclined between 20° and 35° relative to the surface. The AJM etch rate was found to be much lower than that found in glass and polymers, and it was found that a significant amount of particle embedding occurred in the 316L stainless steel. When the erosion data were used in an AJM surface evolution model, the resulting predicted cross-sectional profiles of unmasked and masked channels were in reasonable agreement with the measured profiles up to an aspect ratio (channel depth/width) of 1.25. The results demonstrate that surface evolution during the abrasive jet micro-machining of metals can be predicted using existing models, originally developed for glass and polymers.

整形飞秒激光金属材料精细加工

整形飞秒激光金属材料精细加工

Novel optical f iber-based laser direct writing process for micromachining of metal

A laser micromachining technique for the fabrication of metallic microstructures is proposed. The fabrication of microstructures is done by laser-induced wet etching that adopts an optical fiber as a machining tool. The laser beam delivered through the multimode fiber directly irradiates on the workpiece while maintaining a proper gap to avoid fiber damage. The manufacture of microstructures with high surface quality and good size uniformity is realized. Microgrooves with aspect ratio over 10 and microholes with a nearly straight cross-section can be produced by the proposed technique. The overall etching results are examined closely with respect to process variables.

Conical emission in focused beams: analysis of contributing factors and elimination of scattering

We report a detailed analysis of experimental parameters and fundamental mechanisms contributing to the strong nonlinear scattering of femtosecond and short picosecond laser pulses (50–6000 fs) at focusing in ambient air and protecting gases. The experimental conditions under consideration are typical for a variety of applications: micromachining of metals and dielectrics, high power laser exposure of targets. Such scattering, being the most noticeable manifestation of the complex phenomenon of conical emission in the focusing geometry, puts fundamental limitations to the incident power of precision laser targeting, restricting in this way potential productivity of micromachining in this pulse width range. The phenomena analyzed here are: ionization, the optical Kerr effect, the distortion of spectra via self-phase modulation, and the refractive ability of microplasma, namely the scattering. Characteristics of the last were investigated with respect to the incident wavelength and pulse width, for focusing of Gaussian and flat-top beams of different diameters. The obtained extensive data allowed us to trace the clue trends and relationships of this phenomenon and to find several ways to reduce or even eliminate the scattering in a broad range of the incident energies.