Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures

The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2½D structures [2–4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 µm at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. Piqué and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. Piqué (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513–519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ‘t Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087–4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553

Laser Machining by short and ultrashort pulses, state of the art and new opportunities in the age of the photons

An overview is given of the applications of short and ultrashort lasers in material processing. Shorter pulses reduce heat-affected damage of the material and opens new ways for nanometer accuracy. Even forty years after the development of the laser there is a lot of effort in developing new and better performing lasers. The driving force is higher accuracy at reasonable cost, which is realised by compact systems delivering short laser pulses of high beam quality. Another trend is the shift towards shorter wavelengths, which are better absorbed by the material and which allows smaller feature sizes to be produced. Examples of new products, which became possible by this technique, are given. The trends in miniaturization as predicted by Moore and Taniguchi are expected to continue over the next decade too thanks to short and ultrashort laser machining techniques. After the age of steam and the age of electricity we have entered the age of photons now

Laser processing of carbon fibre reinforced plastic (CFRP)

Carbon fibre reinforced plastic (CFRP) is extensively used in automotive and aerospace industries with the aim to achieve reduction on emission by reducing weight and consequently fuel usage. Due to high demand and governmental regulations to reduce the environmental impact, the need for re-using CFRP is becoming an interesting area of application with economic benefits to industry. Cutting CFRP to meet large manufacturing demands with fast cutting speeds and high-quality cuts can impose significant problems for conventional cutting methods. High power lasers can provide fast and efficient cutting speed, but if not controlled effectively can cause excessive fibre damage that has significant impact on the mechanical strength. Secondly, the joining technology is one of the major obstacles in composite parts application. Traditional joining techniques such as screwing and riveting damage the fibres, leading to major stresses due to drilled holes. One way to achieve higher degree of material application is to use adhesive bonding between two surfaces. However, a good adhesion between two surfaces is necessary to achieve strong and high resistance bonds. A surface pre-treatment is essential before the adhesive bonding to bring reproducibility a clean, slightly rough, and preferably active surface. One of the approaches is to use laser as a method of cleaning. Currently lasers are only used to clean the surface of virgin material for surface contamination. This thesis presents a research work using a 1.5 kW single mode fibre laser to investigate the effects of process parameters such as cutting speed, multi-pass, stand-off, large diameter aperture, double aperture and trenching on the reduction of fibre damage to under 100 μm. The fibre damage was observed using scanning electron microscope. Thermal cameras were used to observe the temperature throughout the cutting process. Regression analysis was carried out to develop five models for CAD/CAM interface for quick adaptation of the laser cutting process – in addition, contour plots have been developed for analysis of process parameters on the fibre damage. For laser cleaning a novel approach was used that employs a flash pumped Nd:YAG laser to clean the glue remained on separated CFRP parts, previously joined with PU and EP adhesive with the aim to reduce the CFRP waste by limiting the damage fibre and composite material substrate as a whole and for re-joining purposes. A feasibility study was conducted to assess the developed laser cleaning process in removing adhesive residue from internal curvatures of 3D CFRP components.Carbon fibre reinforced plastic (CFRP) is extensively used in automotive and aerospace industries with the aim to achieve reduction on emission by reducing weight and consequently fuel usage. Due to high demand and governmental regulations to reduce the environmental impact, the need for re-using CFRP is becoming an interesting area of application with economic benefits to industry. Cutting CFRP to meet large manufacturing demands with fast cutting speeds and high-quality cuts can impose significant problems for conventional cutting methods. High power lasers can provide fast and efficient cutting speed, but if not controlled effectively can cause excessive fibre damage that has significant impact on the mechanical strength. Secondly, the joining technology is one of the major obstacles in composite parts application. Traditional joining techniques such as screwing and riveting damage the fibres, leading to major stresses due to drilled holes. One way to achieve higher degree of material application is to use adhesive bonding between two surfaces. However, a good adhesion between two surfaces is necessary to achieve strong and high resistance bonds. A surface pre-treatment is essential before the adhesive bonding to bring reproducibility a clean, slightly rough, and preferably active surface. One of the approaches is to use laser as a method of cleaning. Currently lasers are only used to clean the surface of virgin material for surface contamination. This thesis presents a research work using a 1.5 kW single mode fibre laser to investigate the effects of process parameters such as cutting speed, multi-pass, stand-off, large diameter aperture, double aperture and trenching on the reduction of fibre damage to under 100 μm. The fibre damage was observed using scanning electron microscope. Thermal cameras were used to observe the temperature throughout the cutting process. Regression analysis was carried out to develop five models for CAD/CAM interface for quick adaptation of the laser cutting process – in addition, contour plots have been developed for analysis of process parameters on the fibre damage. For laser cleaning a novel approach was used that employs a flash pumped Nd:YAG laser to clean the glue remained on separated CFRP parts, previously joined with PU and EP adhesive with the aim to reduce the CFRP waste by limiting the damage fibre and composite material substrate as a whole and for re-joining purposes. A feasibility study was conducted to assess the developed laser cleaning process in removing adhesive residue from internal curvatures of 3D CFRP components

Laser welding of metallic glass to crystalline metal in laser-foil-printing additive manufacturing

The application of metallic glasses has been traditionally limited to parts with small dimensions and simple geometries, due to the requirement of fast cooling during the conventional process of casting. In addition, joining metallic glass to crystalline metal is of interest for many applications that require locally tailored functions and properties, but it is challenging. This research describes a promising additive manufacturing technology, i.e., laser-foil-printing, to make high-quality metallic glass parts with large dimensions and complex geometries and to fabricate multi-material components from metallic glass and crystalline metal. In this research, Zr52.5Ti5Al10Ni14.6Cu17.9 metallic glass parts are fabricated on different crystalline metal substrates, including pure Zr metal, Ti-6Al-4V alloy, and 304L stainless steel. The dissimilar bonding between the metallic glass part and the crystalline metal substrate is studied and then improved through the use of appropriate intermediate layers. The microstructure and properties of the fabricated metallic glass parts are also investigated. The results show that Zr can form a crack-free bonding with Zr-based metallic glass owing to the formation of ductile α-Zr phase, whereas direct joining of Zr-based metallic glass to Ti alloy or stainless steel fails due to the formation of various brittle intermetallic compounds. By using Zr intermediate layers for Ti substrates and V/Ti/Zr intermediate layers for stainless steel substrates, the formation of deleterious intermetallics is suppressed and thus the bonding between metallic glass and crystalline metal is significantly improved. Additionally, fully amorphous and nearly fully dense (~99.9%) metallic glass parts with comparable mechanical properties to as-cast parts have been successfully fabricated --Abstract, page iv

Laser processing of materials

Light amplification by stimulated emission of radiation (laser) is a coherent and monochromatic beam of electromagnetic radiation that can propagate in a straight line with negligible divergence and occur in a wide range of wave-length, energy/power and beam-modes/configurations. As a result, lasers find wide applications in the mundane to the most sophisticated devices, in commercial to purely scientific purposes, and in life-saving as well as life-threatening causes. In the present contribution, we provide an overview of the application of lasers for material processing. The processes covered are broadly divided into four major categories; namely, laser-assisted forming, joining, machining and surface engineering. Apart from briefly introducing the fundamentals of these operations, we present an updated review of the relevant literature to highlight the recent advances and open questions. We begin our discussion with the general applications of lasers, fundamentals of laser-matter interaction and classification of laser material processing. A major part of the discussion focuses on laser surface engineering that has attracted a good deal of attention from the scientific community for its technological significance and scientific challenges. In this regard, a special mention is made about laser surface vitrification or amorphization that remains a very attractive but unaccomplished proposition

Pulsed gas laser

A review of pulsed laser discharge systems based on CO2, N2 and excimer gas mixtures is given. The design of a double discharge self-preionized TE laser system is described. [Continues.

New Trends and Applications in Femtosecond Laser Micromachining

This book contains the scientific contributions to the Special Issue entitled: "New Trends and Applications in Femtosecond Laser Micromachining". It covers an array of subjects, from the basics of femtosecond laser micromachining to specific applications in a broad spectra of fields such biology, photonics and medicine

Laser Ablation Technique for Synthesis of Metal Nanoparticle in Liquid

Recently, the synthesis and application of metal and ceramic nanoparticle are significant subject in science and engineering. The metal nanoparticles such as silver, gold, and copper nanoparticles have more application in material science, nanomedicine, electronic, photonic, and art. One of the green methods for preparation of metal nanoparticles is laser ablation technique that offers a unique tool for nanofabrication of nanoparticles. In this technique, the high-power laser ablates the metal plate and the nanoparticles are formed in the liquid. The properties of nanoparticles using laser ablation are unique, and they are not reproducible by any other method such as chemical methods. The important parameters to produce the metal nanoparticles are energy, wavelength, repetition rate of laser, ablation time, and absorption of an aqueous solution. Laser ablation is a simple method for fabricating the metal nanoparticles without surfactant or chemical addition. In this chapter, the mechanism of formation of metal nanoparticles in liquid, significant parameters for using the laser ablation technique to prepare the metal nanoparticles, and the preparation of silver, gold and copper nanoparticles will be reviewed