Picosecond Laser Machining Research Articles

Understanding the self-limiting effect in picosecond laser single and multiple parallel pass drilling/machining of CFRP composite and mild steel

The availability of ultra-short laser pulse sources such as picosecond lasers makes it possible to improve the quality (e.g. heat affected zone <10μm) in laser machining engineering materials such as metals and carbon fibre reinforced polymer (CFRP) composites. However, the processing rate and the machining depths of such lasers are very low and thus demands better understanding of process limitations and machining strategy. This paper identifies a self-limiting effect in high power picosecond laser machining and compares single and multiple parallel pass strategies during drilling/machining of CFRP composite and mild steel sheets. Electromagnetic (EM) simulation was performed to understand the taper formations and the self-limiting effects in ps-pulsed laser drilling and to determine the maximum cutting/drilling depths. The work shows that the machining depth and material removal rate were significantly improved by increasing the number of parallel passes under the same energy delivery and machining time. A new machining mechanism is proposed. This applies to both the CFRP and the mild steel investigated.

Removal of the Heat Affect Zone created by EDM with Pico-second LASER Machining

Metallurgical modifications of machined metal surfaces are created by nearly all machining processes based on thermal and or mechanical processes. The EDM – electro-discharge machining –creates a so called “white layer” or “heat affected zone” (HAZ) having a thickness ranging from a few hundred micro-meters (for roughing operation) down to a few micrometers (for finishing). This remaining HAZ is a problem for many industrial applications: the presence of micro-cracks and metallurgic inhomogeneity inherent to thermal stresses reduces part lifetime of tools, etc. due to fatigue stress.The study presents a method to remove the HAZ created by Die-sinking EDM on warm working steel (W300) by cold ablation with a pico-second LASER. Technologies & strategies for Laser machining have been developed. The laser machined samples have been metallurgical analysed to prove the removal of the white layer and assure that no heat impact due the LASER machining was created, eg. only cold ablation took place. Fatigue test samples have been prepared by EDM machining and either EDM finished or finished by pico-second LASER in order to compare the lifetime both kind of samples

Experimental study on picosecond pulsed laser various materials micro-structure processing

A picosecond laser machining system is designed and constructed so that it is able to output 355, 532 and 1064 nm picosecond pulsed lasers. Through the axial aberration compensation design, the maximum distance of axial focus compensation reaches 0.4 mm with the focus spot size of 3 μm in diameter. The experimental studies of picosecond pulsed laser micro-machining are performed with this system. The results show that the picosecond laser micro-machining is able to reach the precision of microns with good quality.

Effect of energy density and feeding speed on micro-holes drilling in SiC/SiC composites by picosecond laser

Picosecond laser machining is an important modern technology for materials with high hardness. In this paper, micro-holes with several hundred micrometer diameter were drilled in SiC/SiC composite using picosecond laser, and the quality of the micro-holes under different machining parameters was investigated in detail. The results indicated that energy density and feeding speed had remarkable effect on the micro-hole quality. The roundness of the micro-holes on the laser entry side was rarely affected by energy density and feeding speed. However, the roundness of the micro-holes on the laser exit side and micro-hole diameters along processing direction were quite sensitive to the energy density and feeding speed. Feeding speed had little influence on the quality of drilling holes, except for more debris on the entry side with 11.2 μm/s feeding speed.

Picosecond laser machining of deep holes in silicon infiltrated silicon carbide ceramics

Silicon infiltrated silicon carbide (Si-SiC) ceramics, as high hardness materials, are difficult to machine, especially drilling micro-holes. In this study, the interaction of picosecond laser pulses (1 ps at 1 030 nm) with Si-SiC ceramics was investigated. Variations of the diameter and depth of circular holes with the growth of the laser energy density were obtained. The results indicate that the increase of machining depth follows a nonlinear relation with the increasing of laser energy density, while the diameter has little change with that. Moreover, it is found that some debris and particles are deposited around and inside the holes and waviness is in the entrance and at walls of the holes after laser processing.

Special Issue on Non-Traditional Manufacturing Processes Study at Micro- and Nano-Scales

Micro- and nano-fabrication processes are increasingly important in modern technology and economy. Basic fabrication methods include additive, subtractive and deformation-based processes. In recent years, novel fabrication processes such as laser micro/nano machining, 3D printing of miniature features, etc., have undergone significant growth and have reduced the manufacturing cost and enabled new designs for emerging markets such as smart phones, photovoltaics (PVs), and advanced batteries.This special issue focuses on the established and emerging nontraditional manufacturing technologies with various energy sources (mechanical, thermal, optical, etc.) at micro- and nano-scales. It consists of several invited papers and papers presented at the symposium on micro-/nano-scale fabrication processes at the manufacturing science and engineering conference, held on June 9–13, 2014 at the University of Michigan, organized by the Manufacturing Engineering Division of the American Society of Mechanical Engineers (ASME). The included papers consist of a variety of non-traditional manufacturing processes at small scales, ranging from novel process development and innovative simulation method, to broad application examples for different industries.Among different micro- and nano-processes, laser manufacturing brings significant attention from both academia and industry with its special capability of creating small features in a fast production rate. One contribution discusses the different capabilities of two processes to produce microchannels in stainless steel using laser induced plasma micromachining and ultrashort pulsed laser ablation processes; and then the superior capability of the former process for machining different materials is addressed in another paper in this special issue. The optimum scribing conditions of a picosecond laser machining process are determined thin-film solar cells and the potential processing speed is increased. One comprehensive comparison of micro-scale rapid prototyping techniques is presented for three different processes (laser ablation, micromilling, and 3D printing) to fabricate a sample part with features representative of microfluidic devices. In simulation method, a model of the plasmonic lithography process is developed, which is another promising way for nano-fabrication and can produce feature size with 22 nm resolution. On the application side, several contributions covering very diverse fields are also part of the special issue. Examples include synthesis of CdS nanoparticle using a reverse oscillatory flow method, laser diagnostics of plasma in synthesis of grapheme-based materials, and fabricating a hemodialysis device. Finally, a novel approach to “3D print” polymer nanocomposite structures brings us to the additive manufacturing world at nanoscales. It also has great potential for low cost, large scale fabrication with its inkjet printing and reel-to-reel fiber alignment techniques.There are still challenges ahead as well as application domains where such methods are yet to have an impact. This special issue is published with the hope to provide the readers with a small window to discern the recent trends and the capability of different micro- and nano-manufacturing processes and encourage expansion in new application areas. The Editors of this special issue would like to thank all the authors for the effort in preparing their contributions and to thank all the reviewers for their help in reviewing these papers. We would also like to thank Associate Editor Nicholas Fang who contributed his Editorial support for some of the papers submitted in this issue. Last but not least, we would like to thank the Journal of Micro- and Nano-Manufacturing Editorial Office and the Production Coordinator at the ASME for their encouragement and help during the course of the special issue publication.

Fabricating optical fibre-top cantilevers for temperature sensing

In this paper, we propose techniques to fabricate micro-cantilevers onto the end of standard single mode optical fibres using a combination of picosecond laser machining and focused ion beam milling techniques and demonstrate their use as temperature sensors. Using this approach the cantilever can be pre-aligned with the core of the fibre during fabrication, therefore offering a stable and straightforward means of optically addressing the cantilever. The cantilever is designed to measure deflection over a range of 10 µm using a simple readout technique. A phase recovery algorithm is employed to reduce the interrogation error to around 2–3 nm. Finally, a temperature cycling experiment demonstrates that the cantilever could be used as a temperature sensor from room temperature to 500 °C with an average rms temperature error from 20 °C to 500 °C of ∼±1.4 °C.

Femtosecond versus picosecond laser machining of nano-gratings and micro-channels in silica glass

The ability of 8 picosecond pulse lasers for three dimensional direct-writing in the bulk of transparent dielectrics is assessed through a comparative study with a femtosecond laser delivering 600 fs pulses. The comparison addresses two main applications: the fabrication of birefringent optical elements and two-step machining by laser exposure and post-processing by chemical etching. Formation of self-organized nano-gratings in glass by ps-pulses is demonstrated. Differential etching between ps-laser exposed regions and unexposed silica is observed. Despite attaining values of retardance (>100 nm) and etching rate (2 μm/min) similar to fs pulses, ps pulses are found unsuitable for bulk machining in silica glass primarily due to the build-up of a stress field causing scattering, cracks and non-homogeneous etching. Additionally, we show that the so-called "quill-effect", that is the dependence of the laser damage from the direction of writing, occurs also for ps-pulse laser machining. Finally, an opposite dependence of the retardance from the intra-pulse distance is observed for fs- and ps-laser direct writing.

Micro-Texturing onto Amorphous Carbon Materials as a Mold-Die for Micro-Forming

Among various kinds of carbon materials, two types of amorphous carbon were employed as a mold-die material for micro-forming. Diamond like carbon (DLC) has sufficient strength and toughness as a protective coating onto the steel and WC (Co) substrates. Glassy carbon is a solid material which also has high strength even at the elevated temperature under inert gas atmosphere. These two materials are selected to fabricate the micro-textured mold-die as a mother tool to duplicate this micro-textured pattern onto the metallic and polymer sheets via table-top CNC micro-forming systems. High density oxygen-plasma etching and pico-second laser machining were developed to make micro-texturing onto the above two mold-die materials. In the former, micro-groove and micro-grid patterns were formed on the DLC coating; table-top CNC stamping system with CNC-feeder and cropper was used to duplicate these patterns onto the aluminum sheets in dry and at the room temperature. In the latter, micro-wedge patterns were imprinted onto the glassy carbon substrate; table-top CNC mold-stamping system with heating equipment was utilized for duplication of these patterns onto thermoplastic polymer sheets above the glass transition temperature. Formation of micro-textures onto these amorphous carbon materials provides us a new tool to fabricate the micro-patterned parts and devices in mass production via cold and hot stamping processes.

Onset of void coalescence in uniaxial tension studied by continuous X-ray tomography

Void growth and coalescence in model materials containing a pre-existing three-dimensional void array were studied by X-ray computed tomography coupled with in situ uniaxial tensile deformation. A newly developed continuous tomography technique was employed to capture the onset of coalescence. Using a picosecond laser machining system and a diffusion bonding technique, model materials with different void geometries were prepared. By implementing continuous tomography, the plastic strain at the onset of void coalescence was measured (instead of simple linkage) for the first time. The plastic strains at the onset of void coalescence were compared with the existing void coalescence models. Finite-element (FE) simulations were performed to study the influences of void shape (sphere, cylinder, tapered-cylinder) on the void growth behavior. This study shows that the coalescence models developed by Thomason and later extended by Pardoen and Hutchinson provide accurate predictions of coalescence strain when the voids are aligned normal to the tensile axis. However, offsets can induce shear effects that lower the coalescence strain in a manner not predicted by the models. Two-dimensional plane-strain FE simulations were also used to explore the influence of shear localization between two misaligned coalescing voids on ductility. These demonstrate the nature of the effect.

Picosecond Laser Machining of Metallic and Polymer Substrates for Fluidic Driven Self-Alignment

Fluidic self-alignment of micro-components relies on creating a receptor site that is able to confine a liquid droplet. When a micro-component is brought in contact with the droplet, capillary forces move the component to its final position. A method to stop the advancing of a liquid from a receptor site, consists of creating geometrical features, such as edges around the site. A picosecond pulsed laser source was used to create suitable edges in a metallic and a polyimide substrate. Subsequently, the self-alignment capabilities of these sites were tested. The receptor sites in polyimide showed the highest success rate.

Picosecond and Femtosecond Laser Machining May Cause Health Risks Related to Nanoparticle Emission

Picosecond and Femtosecond Laser Machining May Cause Health Risks Related to Nanoparticle Emission