Query: Water Guided Laser

title: The cutting process and damage mechanism of large thickness CFRP based on water jet guided laser processing
abstract: Carbon fiber reinforced polymer composites (CFRP) is a composite material with resin as matrix and carbon fiber as reinforcement. It has been widely used in aerospace, military products, and automotive industries. However, CFRP is prone to damage because of its complex anisotropy and low interlayer strength, so it is a typical difficult to process material. Water jet guided laser processing technology is a combination of laser and water jet processing technology, which has the characteristics of no wear, no contact, flexible processing, and potential advantages of reducing HAZ and increasing cutting depth. In this paper, the water jet guided laser processing technology is used to perform cutting experiment for CFRP processing of low damage and large depth. In the experiment, the influencing law of the process parameters such as laser power, CFRP feed speed and water jet speed on the cutting results is obtained; then the cutting thickness of 1 mm, 2 mm, 4 mm and 10 mm CFRP is realized by adopting the parallel path layered scanning method. Moreover, the influences of carbon fiber arrangement direction and laser cutting path on the CFRP cutting damage mechanism are analyzed for the first time, and three damage mechanisms (exposing, falling off and pulling out) are summarized, which will provide the reference for the high precision cutting of large thickness CFRP.

title: Experimental study on water jet guided laser micro machining of mono crystalline silicon
abstract: Water jet guided laser micro machining is a novel micro machining technique for hard brittle materials. To investigate and evaluate the effects of water jet guided laser micro machining on the surface topography changes, highest aspect ratio evolution, and kerf edge variations, water jet guided laser micro machining experiment was undertaken using Nd: DPSS laser system with the repetition frequency of 20 120 kHz and max. power of 25 W. Surface topography measurements of the untreated and treated specimens were carried out with scanning electron microscope (SEM) The material composition of kerf edge and other area was achieved using energy dispersive spectrometer (EDS) The relationship between water jet guided laser micro machining parameters, surface topography changes, highest aspect ratio evolution, and kerf edge variations are presented and discussed. The experimental results show that there was no oxidation and cracks on the kerf edge and other surface, aspect ratio of kerf is up to 12.7, so the kerf is very steep, local edge breakage is rarely founded at 350x magnification, cutting speed can up to 1 mm/s. The results showed that performance of the water jet guided laser micro machining technology is excellent for mono crystalline silicon cutting.

title: Optically Guided Pyroelectric Manipulation of Water Droplet on a Superhydrophobic Surface.
abstract: Controlled droplet manipulation by light has tremendous technological potential. We report here a method based on photothermally induced pyroelectric effects that enables manipulation and maneuvering of a water droplet on a superhydrophobic surface fabricated on lithium tantalite (LiTaO3) In particular, we demonstrate that the pyroelectric charge distribution has an essential role in this process. Evenly distributed charges promote a rapid hydrophobic to hydrophilic transition featuring a very large water contact angle (WCA) change of ~76.5deg in air. This process becomes fully reversible in silicone oil. In contrast, the localized charge distribution induced by guided laser illumination leads to very different and versatile functionalities, including droplet shape control and motion manipulation. The influence of a saline solution is also investigated and compared to the deionized water droplet. The focusing effect of the water droplet, a phenomenon that widely exists in nature, is particularly of interest. Simple tuning of the laser incident angle results in droplet deformation, jetting, splitting, and guided motion. Potential applications, such as droplet pinning and transfer, are presented. This approach offers a wide range of versatile functionalities and ready controllability, including contactless, electrodeless, and precise spatial and fast temporal control, with tremendous potential for applications requiring remote droplet control.

title: Overview on the development and critical issues of water jet guided laser machining technology
abstract: There was no established literature or documentation regarding this due to the competition for the market and confidentiality issues. This article reviews the current status of waterjet guided laser (WJGL) processing. This paper addresses the state of the art development and knowledge in WJGL technology. The paper attempts to support researchers as well as practical engineers who are considering this non traditional manufacturing method for application in their field. The topic is developed following the history of the water jet guided laser technology. It outlines the primary aspects of industrial use, their relevant applications, and the variety of laser beam sources available. Here the principle, machine configuration and benefits of the WJGL technology are elaborated. The formation process of water jet, optical characteristics of water, the influence of different factors on the stability of jet are discussed. In this paper different aspect of laser waterjet coupling like coupling unit, parameters, loss, propagation modes and speckle etc. are discussed. The major factors which affect transmission efficiency are wavelength of laser, focal position and numerical aperture. After giving some more details on the operating principle and its realization, the following sections WJGL matter interaction, modeling of material removal, laser induced bubble and breakdown are presented. In this paper an attempt is made to present a literature survey on waterjet guided laser technology.

title: Research on water jet guided laser micro hole machining of 6061 aluminum alloy
abstract: With the rapid development of the information age, electronic components are developing toward miniaturization, which makes the manufacturing of chips more and more difficult. Water jet guided laser processing technology (WJGL) is a composite processing technology that combines pulsed laser and water jet, which can ensure the accuracy and efficiency of processing while small size parts machining. This paper is based on the "element birth and death" technique in the finite element method and the three dimensional transient temperature field and subsequent material removal model of 6061 aluminum alloy are established. The effects of laser average power, pulse repetition frequency, and pulse action time on the transient thermal distribution, aperture, taper, and other forming qualities with the two technologies of fixed point drilling and spiral drilling, respectively, are studied. Combining the experimental process, the general rule of morphology change of the micro hole is obtained. The results show that WJGL of micro hole is based on the combined effect of thermal ablation and real time cooling. Spiral drilling can maintain a better hole shape but fixed point drilling can achieve a smaller hole taper. With the increase of laser power, the hole taper increases, reaching saturation at 8 W. The repetition frequency is between 50 and 70 kHz to obtain better hole morphology while maintaining better processing efficiency, and the minimum hole taper is 8.21deg.

title: Water jet guided laser drilling of thermal barrier coated aerospace alloy
abstract: Drilling using quasi continuous wave (QCW) millisecond pulse fibre laser is the state of the art for producing film cooling holes over uncoated aero engine components. Laser drilling of coated components, including thermal barrier coated (TBC) components, is still a challenging task due to the risk of coating delamination. Water jet guided (WJG) laser is nowadays increasingly used for machining of advanced materials such as ceramics and composites. This paper aims to study the basic fundamental characteristics of WJG lasers drilling of acute angular holes over TBC coated nickel superalloy and compare it with the state of the art QCW millisecond fibre laser. Experiments were performed to investigate the characteristics of both QCW and WJG laser drilling in terms of TBC delamination, recast layer formation, hole surface topology and cycle time. Finite element analysis based numerical model was developed and used, to understand and confirm the mechanism of heat propagation and the subsequent material removal characteristics for both WJG and QCW laser. Experimental results show that the WJG laser drilling quality (in terms of thermal damages) is very similar to the process of cold ablation (i.e. machining without inducing any thermal defects within the substrate material) The numerical model confirms the hypothesis that the high temperature zone of WJG laser machining process is wholly confined within the small laser irradiation zone, which helps to avoid the TBC delamination typically observed with long pulse acute angle laser drilling process. The material removal mechanism of WJG laser machining seems to be the combination of melt ejection by vapour pressure, melt ejection by impulse shock pressure and by the action of water jet pressure.

title: Water jet guided laser microdrilling of aerospace alloys: Correlation of material properties to process time and quality
abstract: The hot section parts in a gas turbine are subject to high working temperatures and mechanical forces. In order to endure the harsh conditions, these parts are generally made of nickel based superalloys. Furthermore, microholes are drilled on them to help with cooling by allowing the air to pass through. These holes increase the allowable working temperature and service life of the parts as well. Water Jet Guided Laser is a technology that can be conveniently used for microdrilling operations on aerospace jet engine parts. It is a hybrid process, in which a laser beam is coupled with and guided through a thin cylindrical water jet. Pressurized water provides focusing, cooling, and cleaning on the cut region, eliminating undesired side effects of the laser. The technology has many advantages over traditional laser machining, such as consistent focusing, burr free cutting, minimized tapering, reduced heat affected zone, and recast layer. In this paper, using the Water Jet Guided Laser, variation in process time and quality are studied on different aerospace nickel based superalloys. The results depend mainly on the thermophysical properties of the processed materials. The experimental results are compared with calculations and correlated to the material properties.

title: Study on the mechanisms of curved water jet fiber guided laser technology
abstract: The emergence of a novel technology, curved water jet fiber (CWJF) guided laser, will broaden the application of water jet guided laser in surface high precision and no damage micromachining, such as micro texture treatment, drilling and grooving, etc. of inclined and curved workpiece, in particular, like some large and heavy parts that are difficult to move and rotate. In addition, the novel scheme of high precision, low damage, and circular section processing with the transmission laser and cooling effect of CWJF will be investigated. In this study, the parametric control of water jet deflection is explored using the model of the deflection trajectory of water jet discretized into continuously released water droplets under a nonuniform electric field, in which results show that large deflection angle and displacement can be obtained with high voltage, small distance, and low velocity. Optical transmission system models of CWJF guided laser under related parametric groups are established through 3D physical reconstruction models of CWJF by using the deflection trajectory. The theoretical calculation of meeting total reflection conditions of incident rays and visualization analyses of CWJF formed guided laser indicate laser beam can be transmitted effectively. The laser beam is still confined to CWJF and transmitted forward. The methods and results presented in this study will provide the theoretical support and reference for the control of CWJF formation and research of characteristics about CWJF guided laser during this novel technology development journey.

title: Experimental and Computational Investigation of Guided Waves in a Human Skull.
abstract: We investigate guided (Lamb) waves in a human cadaver skull through experiments and computational simulations. Ultrasonic wedge transducers and scanning laser Doppler vibrometry are used respectively to excite and measure Lamb waves propagating in the cranial bone of a degassed skull. Measurements are performed over a section of the parietal bone and temporal bone spanning the squamous suture. The experimental data are analyzed for the identification of wave modes and the characterization of dispersion properties. In the parietal bone, for instance, the A0 wave mode is excited between 200 and 600 kHz, and higher order Lamb waves are excited from 1 to 1.8 MHz. From the experimental dispersion curves and average thickness extracted from the skull computed tomography scan, we estimate average isotropic material properties that capture the essential dispersion characteristics using a semi analytical finite element model. We also explore the leaky and non leaky wave behavior of the degassed skull with water loading in the cranial cavity. Successful excitation of leaky Lamb waves is confirmed (for higher order wave modes with phase velocity faster than the speed of sound in water) from 500 kHz to 1.5 MHz, which may find applications in imaging and therapeutics at the brain periphery or skull brain interface (e.g. for metastases) The non leaky A0 Lamb wave mode propagates between 200 and 600 kHz, with or without fluid loading, for potential use in skull related diagnostics and imaging (e.g. for sutures)

title: Simulation and experimental investigation on energy distribution of water column in waterjet guided laser processing
abstract: Under the condition of limited laser energy, it is of great significance to understand and effectively control the laser distribution in the laminar flow column to solve the problem of depth capability decline caused by the taper effect of the slit in the thick plate material waterjet guided laser processing. In this paper, the distribution of laser energy in the water column is analyzed by means of simulation and experiment. In the simulation analysis, using ZEMAX software, the energy distribution of axial position and radial position (diameter section) in water column is simulated and analyzed for the different focal length and nozzle diameter. In addition, the simulation results are verified by experiments. The results show that: the laser energy in the laminar water column still presents the characteristics of Gaussian like distribution, which will make the material remove very difficult at the edge of the water column due to the insufficient power density. This is easy to produce machining taper effect. Finally, the energy distribution conditions of high efficiency material removal by water guided laser are given. This study provides a theoretical and technical basis for further understanding the law of energy transmission and distribution of water column in water guided laser.