PDF | Light amplification by stimulated emission of radiation (laser) is a matter interaction and classification of laser material processing has been provided. W. M. Steen, J. Mazumder, Laser Material Processing. . advantage for the laser over electron beam processes, which require  Lambda Research Optics ( ) Radial polarizer for CO2 laser systems. aracer.mobi . pdf. Materials processing experts face a wide range of choices in determining the right laser we work with you to determine the right laser for your process needs.
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to the work piece. • Happens only if the material has high absorption at the wavelength corresponding to the laser beam. • Once the surface of the materials . INTRODUCTION TO LASER. MATERIALS PROCESSING. COURSE NOTES. RONALD SCHAEFFER, PhD. CEO, Photomachining, Inc. Pelham, NH. Printed in India. Laser processing of materials. J DUTTA MAJUMDAR and I MANNA. ∗. Metallurgical and Materials Engineering Department, Indian Institute of.
The precision of these manufacturing techniques relies on focusing a laser beam to a micron-sized spot onto the surface of the workpiece.
This tight lateral focusing comes at a price since it narrows the depth of field DOF along the axial direction, causing a concomitant drop in machining efficiency outside the reduced range.
Therefore, the surface of the workpiece has to be carefully maintained within the focal position of the laser beam to ensure a high efficiency; as material is removed, it is important to continue to adjust the location of the laser focus to follow the change in topography of the workpiece One common method used to mitigate a narrow vertical machining range consists of extending the DOF of the system by using, for example, a low focusing power lens or structured light.
However, such attempts lead to a significant loss in lateral resolution Alternatively, the focused beam can be adjusted with respect to the surface location throughout the material removal process, but this requires real-time knowledge of the surface location as well as a fast focusing method.
While some studies have attempted to acquire real-time surface location information to increase the machining efficiency, the complexity and inflexibility of the resulting machining system drastically reduces its potential for practical use Main types of high powered lasers 2.
CO2 lasers Carbon dioxide laser were the first generation in industrially used high powered lasers, Figure 1. The amplification of the light is achieved through molecular vibration rather than electronic translations as in other lasers.
The wave length of CO2 lasers varies between 9. The cost of these lasers is relatively low and there are applications which they are suited and will continue to find application. Neodynium — YAG lasers This type of laser is finding less and less application but there are still many of them in use in research and industrial sectors.
Abbreviated to Nd:YAG laser the amplification of light is achieved by triply ionised Nd as the lasant a material that can be stimulated to produce laser light and the crystal YAG yttrium-aluminium-garnet as the host.
The wavelength of this type of laser is 1. The light can be transport by optical fibre, which makes their application flexible and was responsible for their industrial uptake. Diode lasers Diode lasers are commonly used today and can be used in different configurations. Essentially as the name suggests diode lasers are didoes that have the ability to amplify light.
Diodes are semiconductor materials for which there are many types and the wavelength produced range from 0. Of the known diode materials there are 20 that will lase. The most common ones are GaAs and AlxGa1-x. This type of laser works by pumping a solid gain medium, like a ruby or a neodymium-doped YAG crystal, with a laser diode.
This configuration of laser is compact and very efficient and is finding wide spread industrial use. The industrially used version of theses lasers can have the light transported by optical fibre which is important to their application.
Figure 1. Fibre lasers Fibre lasers are the latest technology in high powered lasers and can be banked together to produce powers in the range of kW. Fibre lasers use a doped optical fibre to amplify the light.
The doping agents range from erbium, ytterbium, neodymium, dysprosium, praseodymium, and thulium. The high powers that can be generated with this technology are opening up new application for laser materials processing in the manufacturing sector and are currently the future of high powered lasers.
Laser optics Apart from the CO2 laser, which use mirrors, the major types of high power lasers use optical fibre to deliver the light.
Once near the region where the laser material processing is to occur, the light from the fibre needs to be collimated and then focused. Depending on the application the focal distance the distance can be varied by the choice of lenses for collimating and focusing. For most applications a Gaussian beam is used, but top hat profile gives a sharp thermal profile in the material, which has advantages.
Typically for laser materials processing applications the focal point is about 1mm in diameter and has a top hat profile.
Above focus the beam profile changes from top hat to bimodal, which increasing radius and below focus the beam is Gaussian with increasing diameter, Figure 2.
Figure 2. Laser optical configuration and resulting beam profile. Controlling the movement of the laser In the early days of laser materials processing the laser and optics were fixed to a CNC table and basic movement in X,Y and Z direction were possible. Nowadays robots are readily available and affordable, laser can be couple to the head of a robot allowing five-axis movement.
Also computer programs and CAD drawings can be used to develop paths for laser movement, which can allow complex geometries to be processed. This development has been crucial to the application of laser materials processing technology and has applications for treating manufactured component that required improved corrosion resistance. A sixth degree of movement can also be obtained through the use of a rotating chuck that can grip the component to be processed and is common on many commercial laser cladding systems.
Materials preparation Not all of the energy of the laser is transferred into heat in the substrate material. In fact the condition of the substrate plays a big role in how much energy is absorbed.
In the as machined state metallic materials are highly reflective and between 0. The range is because some metals absorb the laser energy better than others.
Coatings can be applied to the substrate to improve the absorption and in many cases the absorption can be as high as 0. Sand or grit blasting reduces the reflectiveness of metallic materials and the rough surface also improves absorption and absorption values as high as 0. It should also be noted that the angle of incidence also affects the absorption of the laser. This is known as the Brewster effect and needs to be considered when processing complex geometries.
Laser processing techniques for improving surface corrosion performance of alloys 3. Laser surface melting Laser surface melting LSM is performed by heating a metallic substrate using a laser with high enough power to create a melt pool.
The melt pool travels with laser movement, which when coupled with a raster pattern, an area of material can be melted.
The laser power level required to melt the material is dependent on the thermal diffusivity, conductivity and melting point of the substrate material as well as the rate at which the laser is being traversed. This can result in new types of microstructures formed, which are typically more homogeneous and exhibit improved corrosion performance. The geometry of the melt pool during LSM is dependent on the power density and hence laser traversing speed. With increasing laser traversing speed the melt pool geometry changes from hemispherical to flat-bottomed with increase of traversing speed as thermal diffusion becomes limited.
The flat-bottomed shape is the most desired for LSM. Improving the pitting potential of alloys By far most of the research into LSM for improved corrosion performance has been conducted on improving the pitting potential of commercial alloys. The general tendency of LSM to increase the homogeneity of the surface of a treated alloy is the reason for its application to increase pitting potentials. Low pitting potentials are associated with galvanic couples that can exist between second phase particles and the matrix which lower the potential for corrosion to occur and cause localised corrosion at the interface between the particles and the matrix, forming pits [ 2 ].
By dissolving the particles this mechanism is eliminated and the pitting potential is increased. The increase in the pitting potential is dependent of the potential of the galvanic couple of the particle and the matrix and the effect of the dissolved alloying element of the oxide layer formed and its ability to form a passivation film.
While for many alloys the pitting potential is improved in some cases the pitting potential can be reduced if the alloying elements are not completely dissolved and the increase in the number of grain boundaries and fine second phase particles increases the pitting potential by increase the number of regions for pitting to occur. Hit a particularly tricky question? Bookmark it to easily review again before an exam. The best part? As a Chegg Study subscriber, you can view available interactive solutions manuals for each of your classes for one low monthly price.
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