Dissertations / Theses on the topic 'Laser assisted machining'

This research work assesses the effect of Laser Assisted Machining (LAM) on the machinability of Inconel 718 using a triple layer coated carbide and a sialon ceramic tool. This study was motivated by issues related to poor machinability of IN718 under conventional machining operations. In this work a focused Nd:YAG laser beam was used as a localized heat source to thermally soften the workpiece prior to material removal. Finishing operations were assumed throughout the experiments. Optimization screening tests were performed over a wide range of cutting speeds (ranging from 100 to 500 m/min) and feeds (ranging from 0.125 to 0.5 mm/rev). Results showed a significant drop in all three components of cutting force when thermal softening caused by the laser power was in effect. These tests yielded the optimum cutting speed and feed to be 200 m/min and 0.25 mm/rev for the coated carbide and 300 m/min and 0.4 mm/rev for the ceramic tool. Under these optimum conditions tool life tests were carried out. Drastic increase in terms of the material removal rate (MRR) was demonstrated under LAM conditions as compared to conventional machining. A nearly %300 increase in MRR was established for the coated carbide tool while slightly reducing tool life, mainly because the coatings offering thermal and wear protection could not withstand the high temperatures associated with LAM. Nearly %800 increase in MRR for the ceramic tool was achieved while improving tool life (about %50). In all cases, improvements in surface finish and surface integrity were observed. The dominant mode of tool failure was observed to be average flank wear for all tools tested. However, the coated carbide tool exhibited signs of chipping and flaking in the coatings. The morphology of the chips produced was analyzed and it was shown that temperature and increased chip thickness were the main causes of transition from steady state to shear localized chip structure. Shear localized or sawtooth chips tended to
Cette recherche évalue l'effet de l’usinage assisté par Laser (UAL) sur l’usinabilité d'Inconel 718 en utilisant deux outils : Le premier est enrobé d’une triple couche de carbure et le second est en céramique sialon. Cette étude a été motivée par la difficulté d’usiner IN718 conventionnellement. Dans ce travail, un rayon laser Nd:YAG a été utilisé comme une source de chaleur localisée pour adoucir thermiquement la pièce avant l'usinage. Les expériences représentaient les opérations de finitions. Une optimisation a été exécutée à travers une sélection unitaire pour une large gamme de vitesses de coupes (aux limites de 100 à 500 m/min) et de vitesses d’avance (aux limites de 0.125 à 0.5 mm/rév). Les résultats ont manifesté une réduction significative dans toutes les trois composantes de la force de coupe quand l'adoucissement thermique provoqué par le laser était mis en effet. D’après les tests, les valeurs optimales de vitesse de coupe et d’avance sont 200 m/min et 0.25 mm/rév pour l’outil avec la couche de carbure et 300 m/min et 0.4 mm/rév pour l’outil en céramique. Dans ces conditions optimales, des épreuves de tenue d’outils ont été réalisées. Une augmentation du taux d’enlèvement de matière a été démontrée lors de l’application de l’UAL en comparaison à l’usinage conventionnel. Une augmentation dans le taux d’enlèvement de matière de 300% a été établie pour l’outil enrobé de carbure avec une légère réduction en tenue d’outil. La raison de cette réduction est le fait que ces couches qui offrent une protection thermique et une résistance d’usure ne pouvaient pas résister aux températures élevées associées à l’UAL. Une augmentation de 800% dans le taux d’enlèvement de matière a été accomplie pour l’outil en céramique avec une amélioration de tenue d’outils d’environ 50%. Dans tous les cas, une amélioration de l’intégrité de la surface à ét

Laser-assisted machining has been considered as an alternative for difficult-to-machine materials such as metallic alloys and ceramics. Machining of some materials such as high chromium alloys and high strength steels is still a delicate and challenging task. Conventional machines or computer numerical control (CNC) machines and cutting tools cannot adapt easily to such materials and induce very high costs for operations of rough machining or finishing. If laser-assisted machining can be implemented successfully for such materials, it will offer several advantages over the traditional methods including longer tool life, shorter machining time and reduced overall costs. This thesis presents the results of the research conducted on laser assisted machining of hard to wear materials used in making heavy duty mineral processing equipment for the mining industry. Experimental set up using a high power Nd:YAG laser beam attached to a lathe has been developed to machine these materials using cubic boron nitride (CBN) based cutting tools. The laser beam was positioned so that it was heating a point on the surface of the workpiece directly before it passed under the cutting tool. Cutting forces were measured during laser assisted machining and were compared to those measured during conventional machining. Results from the experiments show that with the right cutting parameters and laser beam position, laser assisted machining results in a reduction in cutting forces compared to conventional machining. A mathematical thermal model was used to predict temperatures within the workpiece at depths under the laser beam spot. The model was used to determine the effect of various cutting and laser parameters on the temperature profile within the workpiece. This study shows that laser assisted machining of hard to wear materials such as high chromium white cast iron shows potential as a possible economical alternative to conventional machining methods. Further research is needed before it can be introduced in industry as an alternative to conventional machining.

Thesis (MEng) - Swinburne University of Technology, Industrial Research Institute Swinburne - 2006.
A thesis submitted in fulfillment of the requirement for the degree of Master of Engineering by Research, Industrial Research Institute Swinburne, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology - 2006. Typescript. Includes bibliographical references (p. 113-116).

There is growing demand for micro and meso scale devices with applications in the field of optics, semiconductor and bio-medical fields. In response to this demand, mechanical micro-cutting (e.g. micro-milling) is emerging as a viable alternative to lithography based micromachining techniques. Mechanical micromachining methods are capable of generating three-dimensional free-form surfaces to sub-micron level precision and micron level accuracies in a wide range of materials including common engineering alloys. However, certain factors limit the types of workpiece materials that can be processed using mechanical micromachining methods. For difficult-to-machine materials such as tool and die steels, limited machine-tool system stiffness and low tool flexural strength are major impediments to the use of mechanical micromachining methods. This thesis presents the design, fabrication and analysis of a novel Laser-assisted Mechanical Micromachining (LAMM) process that has the potential to overcome these limitations. The basic concept involves creating localized thermal softening of the hard material by focusing a solid-state continuous wave laser beam of diameter ranging from 70-120 microns directly in front of a miniature (300 microns-1 mm wide) cutting tool. By suitably controlling the laser power, spot size and speed, it is possible to produce a sufficiently large decrease in flow stress of the work material and, consequently, the cutting forces. This in turn will reduce machine/tool deflection and chances of catastrophic tool failure. The reduced machine/tool deflection yields improved accuracy in the machined feature. In order to use this process effectively, adequate thermal softening needs to be produced while keeping the heat affected zone in the machined surface to a minimum. This has been accomplished in the thesis via a detailed process characterization, modeling of process mechanics and optimization of process variables.

This thesis presents an investigation of novel laser assisted micromachining processes that addresses the limitations of micromachining of hard-to-machine materials. Two different laser assisted approaches are used to machine hard metals and high strength ceramics. For hard metals, the basic approach involves localized thermal softening of the workpiece material by focusing a solid-state continuous wave near infra-red laser beam in front of the micro milling tool (end mills of 0.1 to 0.5 mm diameter). By suitably controlling the laser power, spot size and scan speed, it is possible to produce a sufficiently large reduction in the flow strength of the work material and consequently the cutting forces and tool deflections. A force model is developed to predict the cutting forces in Laser Assisted Micro Milling (LAMM) of hard metals. For high strength ceramics, the approach involves use of a two step process. In the first step, thermal cracks are generated in a confined volume by the steep thermal gradients generated by laser irradiation of the workpiece. In the second step, the weakened region is removed by a micro grinding tool. The characterization and modeling of the process serve as bases for users of the two approaches to select optimal process parameters.

Cost-effective machining of hardened steel (>60 HRC) components such as a large wind turbine bearing poses a significant challenge. This thesis investigates a new laser tempering based hybrid turning approach to machine hardened AISI 52100 steel parts more efficiently and cost effectively. The approach consists of a two step process involving laser tempering of the hardened workpiece surface followed by conventional machining at higher material removal rates using lower cost ceramic tooling to efficiently cut the laser tempered material. The specific objectives of this work are to: (a) study the characteristics of laser tempering of hyper-eutectoid 52100 hardened steel, (b) model the laser tempering process to determine the resulting hardness, and (c) conduct machining experiments to evaluate the performance of the laser tempering based hybrid turning process in terms of forces, tools wear and surface finish. First, the microstructure alterations and phase content in the surface and subsurface layers are analyzed using metallography and x-ray diffraction (XRD) respectively. Laser tempering produces distinct regions consisting of - a tempered white layer and a dark layer- in the heat affected subsurface region of the workpiece. The depth of the tempered region is dependent on the laser scanning conditions. Larger overlap of laser scans and smaller scan speeds produce a thicker tempered region. Furthermore, the tempered region is composed of ferrite and martensite and weak traces of retained austenite (~ 1 %). Second, a laser tempering model consisting of a three dimensional analytical model to predict the temperature field generated by laser scanning of 52100 hardened steel and a phase change based hardness model to predict the hardness of the tempered region are developed. The thermal model is used to evaluate the temperature field induced in the subsurface region due to the thermal cycles produced by the laser scanning step. The computed temperature histories are then fed to the phase change model to predict the surface and subsurface hardness. The laser tempering model is used to select the laser scanning conditions that yield the desired hardness reduction at the maximum depth. This model is verified through laser scanning experiments wherein the hardness changes are compared with model predictions. The model is shown to yield predictions that are within 20 % of the measured hardness of the tempered region. Using the laser scanning parameters determined from the laser tempering model, cutting experiments using Cubic Boron Nitride (CBN) tools and low cost alumina ceramic tools are conducted to compare the performance of laser tempering based hybrid turning with the conventional hard turning process. The machining experiments demonstrate the possibility of higher material removal rates, lower cutting forces, improved tool wear behavior, and consequently improved tool life in the laser tempering based process. In addition, the laser tempered based hybrid turning process produce is shown to yield lower peak-to-valley surface roughness height than the conventional hard turning process. Furthermore, it is found that lower cost ceramic tools can be used in place of CBN tools without compromising the material removal rate.

Doctor of Philosophy
Department of Industrial & Manufacturing Systems Engineering
Shuting Lei
Laser-assisted machining (LAM) is a promising non-conventional machining technique for advanced ceramics. However, the fundamental machining mechanism which governs the LAM process is not well understood so far. Hence, the main objective of this study is to explore the machining mechanism and provide guidance for future LAM operations. In this study, laser-assisted milling (LAMill) of silicon nitride ceramics is focused. Experimental experience reveals that workpiece temperature in LAM of silicon nitride ceramics determines the surface quality of the machined workpiece. Thus, in order to know the thermal features of the workpiece in LAM, the laser-silicon nitride interaction mechanism is investigated via heating experiments. The trends of temperature affected by the key parameters (laser power, laser beam diameter, feed rate, and preheat time) are obtained through a parametric study. Experimental results show that high operating temperature leads to low cutting force, good surface finish, small edge chipping, and low residual stress. The temperature range for brittle-to-ductile transition should be avoided due to the rapid increase of fracture toughness. In order to know the temperature distribution at the cutting zone in the workpiece, a transient three-dimensional thermal model is developed using finite element analysis (FEA) and validated through experiments. Heat generation associated with machining is considered and demonstrated to have little impact on LAM. The model indicates that laser power is one critical parameter for successful operation of LAM. Feed and cutting speed can indirectly affect the operating temperatures. Furthermore, a machining model is established with the distinct element method (or discrete element method, DEM) to simulate the dynamic process of LAM. In the microstructural modeling of a β-type silicon nitride ceramic, clusters are used to simulate the rod-like grains of the silicon nitride ceramic and parallel bonds act as the intergranular glass phase between grains. The resulting temperature-dependent synthetic materials for LAM are calibrated through the numerical compression, bending and fracture toughness tests. The machining model is also validated through experiments in terms of cutting forces, chip size and depth of subsurface damage.

Master of Science
Industrial & Manufacturing Systems Engineering
Shuting Lei
Transparent brittle materials such as glass and silicon dioxide have begun to replace the conventional materials due to the advantageous properties including high strength and hardness, resistance to corrosion, wear, chemicals and heat, high electrical isolation, low optical absorption, large optical transmission range and biocompatibility. However because these materials are extremely hard and brittle, development of an ideal machining process has been a challenge for researchers. Non-traditional machining processes such as abrasive jet and ultrasonic machining have improved machining quality but these processes typically results with issues of poor surface integrity, high tool wear and low productivity. Therefore a machining technique that overcomes the disadvantages of existing methods must be developed. This study focused primarily on improving the machinability and attaining crack-free machined surfaces on transparent brittle materials by inducing micro cracks or seed damages on the subsurface of the materials. The hypothesis was that micro-cracks induced by femtosecond laser would synergistically assist the material removal process by a cutting tool by weakening or softening the material, followed by conventional machining process. Laser induced damages due to varying laser intensities and at different depths in bulk BK7 glass was studied in order to select the optimal laser machining conditions for the experiments. Dimensional and structural profiles of laser cracks are observed using an optical microscope. A comparative study of machined untreated BK7 samples and damage induced BK7 samples was conducted. Due to its simple process kinematics and tool geometry, orthogonal machining is used for the study. Results showed that machining laser-treated samples caused an average 75% force reduction on comparison to machining of untreated samples. Laser treated machined samples were produced without subsurface damages, and reduced tool wear was noted. Overall improved machinability of BK7 glass samples was achieved.

Predmet istraživanja ove disertacije predstavlja unapređenje, modelovanje i optimizacija procesa elektroerozivne obrade (EDM) savremenih inženjerskih materijala. Prvo su predstavljene dve inovativne metode: EDM u dielektrikumu sa pomešanim prahom i EDM sa pomoćnom elektrodom, a zatim i njihova kombinacija. Za generisanje matematičkih modela primenjene su metodologija odzivne površine i alati veštačke inteligencije. U nastavku su postavljeni optimizacioni procesi određivanja ulaznih parametara sa jednom i više funkcija cilja koji su rešeni primenom klasičnih metoda optimizacije. U završnom osvrtu sprovedena je verifikacija dobijenih modela i optimalnih ulaznih parametara elektroerozivne obrade.
The subject of the research of this dissertation is the improvement, modeling and optimization of the electrical discharge machining (EDM) of advanced engineering materials. First, two innovation methods are presented: EDM in powder mixed dielectric fluid and EDM with assisted electrode and that their combination. The method of response surface and artificial intelligence tools were applied to generate mathematical models. The optimization problems of determining the input parameters with single and multiple target functions are solved by the application of classical optimization methods. Finally, verification of the obtained models and optimal input parameters of electrical discharge machining was carried out.

碩士
國立中正大學
機械系
92
ABSTRACT This study focuses on the construction and development of the technique-- Laser-assisted-machining, LAM. It contains that verifies the feasibility of LAM and creates necessary theory. Laser-assisted-machining is a developing technique of processing hard-to-cutting materials. The main concept of machining utilizes the phenomena which a solid will be softened as located in a high temperature condition. While the laser ray is focused on the surface of workpiece, a tiny local part where is irradiated by laser will be heated to a high temperature region. At this instant, removing the heated and softened part of material by tool is more easily than conventional ways that the tool wear could be effectively reduced. Therefore, developing LAM technique makes the machining cost down. It’s hard-to-cutting metal and brittle ceramics that LAM skill wishes to cut, such as supper alloy--Inconel-718 or ceramic--Al2O3. Overseas, there are preliminary experimental results on LAM technique, but not any literature could be found domestically. Therefore, this study hopes to develop our own LAM technique in Taiwan. A finite element model has been created to compute temperature rising on workpiece due to laser irradiation and an orthogonal cutting model to estimate cutting force. The primary experimental result is able to ensure the feasibility of LAM on cutting ceramics. We hope this cutting technique can expand the method of machining ceramic beyond conventional grinding way. By LAM, ceramics with brittle and hard characteristic could be machined by milling or turning ways. The rise of processing efficiency and reduction of tool wear are the major benefit.

碩士
國立中正大學
機械工程所
98
In recent years, laser micromachining has excellent processing characteristics in related field. Micromachining technology has to become mainstream today. But the difficult thing in laser machining is the surface uneven. This is about a study of using a pulsed Nd-YAG laser to process the Cu assisted with gas and ultrasonic.Because the process of pulsed Nd-YAG laser ablating metal is a mechanism involved ultra-high temperature, so the HAZ (heat affected zone) is usually found around processed area. It was found that during the process of ablation, molten metal sprays out and forms the debris and recast layer on the edge. There are three auxiliary methods been proposed to reduce the HAZ, debris and recast problems of laser process: the nitrogen-assisted, ultrasonic-assisted and ultrasonic-assisted with nitrogen methods. We found the ultrasonic-assisted with nitrogen yielded the best result of the laser-processing Cu that the HAZ and recast layer are significantly reduced. The ultrasonic-assisted with nitrogen not only removes a large amount of the laser heat on the material substrate due to nitrogen cooling effect, so it is the best surface roughness.

碩士
國立虎尾科技大學
機械與電腦輔助工程系碩士班
103
Hardened and brittle material such as zirconia has gradually become the important materials for biomedical, precision instruments and aerospace technology industry applications in recent years. In which biomedical application is particularly active. As its demand is increased constantly, various requests on machining qualities of zirconia are also more stringent. At present, the main machining ways on zirconia are almost with engraving milling, grinding lapping or polishing and these machining processes are too complicated and too much wasted. Therefore, seeking a breakthrough for shortening the process and saving the cost effectively is an important issue for the machining workers. Because zirconia have the properties of high strength, high hardness, large brittleness, less malleability, low thermal conductivity and hence low machinability, it causes the cutting-tool wear quickly during the machining process. Also, the crack and damage, and edge-indentation are easily generated on the machined surface and outer edge, respectively. Therefore, enhancements of cutting performance and processing efficiency, and promotion of cutting-tool life for zirconia machining are the most concerned issues in industry for a long time. In this study, an integration of ultrasonically and laser assisted machining system is constructed for zirconia brittle material milling. This hybrid system is thus designed and fabricated, and mounted on a machine-tool system for working test. Three levels of three factors such as feed rate, radial depth of cut and spindle speed were selected in this study and orthogonal array of Taguchi method was applied for process parameter planning. General and extra-fine particle tungsten carbide cutting tools with diamond and TiSi coating, respectively, were used in the side-milling experiments of zirconia workpiece. The machined surface roughness and cutting force are used as objective function and subjecting constraint, respectively. The execution of different assisted machining types of milling experiments on zirconia were performed in series and Taguchi factor response and a numerical analysis on the simple response curves are applied together for accelerating the better process parameter determination. Various assisted machining types such as without assistance, ultrasonically assisted, laser-assisted and an integration of ultrasonically and laser-assisted milling were conducted sequentially in this study. Each experimental result obtained from the above assisted machining type is individually dealt with by factor response and numerical analysis of response curve at the same time, and the levels of each factor are alternatively switched to other values gradually. Two better levels of each factor are preserved preparing for the next assisted milling experiment while the worse level of the factor is replaced by the better one which is recommended by the numerical analysis of response curve. Follows up this rule of factor level substitution repeatedly in each type of assisted machining experiment, the better process parameters are determined accordingly. Dynamometer is used to monitor the variation of cutting force. Tool wear, edge-indentation, chip morphology and surface morphology of the zirconia will be measured by tool-microscope off-line. Surface roughness measurement through a non-contact optical instrument is also performed. The high spindle speed cutting experiment for zirconia will be undertaken to validate the two sets of better process parameter combination resulting from factor response and numerical analysis of response curve, respectively. The effects of each process parameter and their combinations on cutting performance and productivity of zirconia machining are also investigated in this hybrid assisted machining system of ultrasonic vibration and laser spot preheating. The results show that two better process parameters combinations both from Taguchi factor response and numerical analysis of response curve can obtain nearly the same preferred surface roughness and surface morphology, but the process parameter of the latter method exhibits a higher processing efficiency. Under the same process parameter combination, laser-assisted machining the cutting force may be reduced about 30 to 40% as compared with that without laser spot preheating assistance. The ultrasonically assisted machining system may not bring into full play on cutting performance improvement when a larger radial cutting depth is encountered. But a significant improvement on machined surface left mark and surface roughness is emerged from the hybrid assisted machining system of ultrasonic vibration and laser spot preheating under the cutting conditions obtained by a successive adjustment of the better process parameter determination just mentioned above. The overall cutting performance in the hybrid assisted machining system is better than those without assistance or with single assisted machining system only. Hence, this study verified the superiority of a hybrid system of the ultrasonically and later assisted machining on zirconia milling.

碩士
國立虎尾科技大學
機械與電腦輔助工程系碩士班在職專班
104
Hardened and brittle material such as quartz glass has gradually become the important materials for light source, electronic, optical communication, laser and aerospace technology industry applications in recent years. In which electro-optical system and semiconductor applications are particularly active. As its demand is increased constantly, various requests on machining qualities of quartz glass are also more stringent. At present, the main machining ways on quartz glass are almost with engraving milling, grinding lapping or polishing and these machining processes are too complicated and too much wasted. Therefore, seeking a breakthrough for shortening the process and saving the cost effectively is an important issue for the machining workers. Because quartz glass have the properties of high hardness, large brittleness, less malleability, low thermal conductivity and hence low machinability, it causes the cutting-tool wear quickly during the machining process. Also, the crack and damage, and edge-indentation are easily generated on the machined surface and around outer edge, respectively. In order to solve the above problems, this project applies the diamond cutting tool to conduct quartz glass machining through a combination of an ultrasonically assisted machining and laser assisted machining under the conditions of high cutting speed, low depth of cut and suitable feed rate. It is expected to handle the material removal process corresponding to different ductile-brittle transition modes properly for quartz glass machining and enhance the processing efficiency, improvement of surface quality and reduction of production cost consequently. The four stage experiments including without assistance, single and hybrid assisted machining systems on quartz glass milling were constructed in this study in order to verify the assisted effect on cutting performance and to compare the difference, merit and drawback among them. First of all, the milling experiment without assistance was performed to investigate the variations of cutting performance and the results were used for the suitable process parameter planning in the next stage experiments. Next, uniaxial ultrasonically assisted system, combination of laser assisted system and a biaxial ultrasonically assisted system with only one-axis oscillation (x or y direction), and combination of laser assisted system and a biaxial ultrasonically assisted system with simultaneous two-axis oscillations (x and y directions) were subsequently introduced at the second to the fourth stage experiments, respectively. At each stage experiment, the effects of process parameters on the variations of surface roughness, side-edge surface morphology and cutting-tool wear are investigated. It is expected that the machinability of this high brittle material can be promoted resulting in good cutting performance and better cutting-tool wear. Before the use of laser assistance, the laser preheating time related to the workpiece surface fragmentation should be tested in advance for a proper spacing distance setting between laser-spot and cutting-tool. Finally, a biaxial ultrasonically assisted machining system is designed, fabricated and mounted on a machine-tool work-table. At the meantime, a long-term oscillation test including calibration and detailed adjustment is conducted repeatedly until the whole normal manipulation of the system is assured. Thus, a hybrid assisted machining system can be established through the integration of this biaxial ultrasonically assisted system and a laser assisted system. Under these assistances, milling experiments of quartz glass by cutting-tool of extra-fine particle tungsten carbide with coating were conducted. And the full factorial experiments of process parameter combinations such as feed rate, cutting velocity and radial depth of cut were also planned. During the experiments, dynamometer is used to monitor the variation of cutting force. Tool wear, edge-indentation and side-edge surface morphology of the quartz glass will be measured by tool-microscope off-line. Surface roughness measurement through a probe contact type instrument is also performed. The results show that the milling experiment with both laser assisted system and an ultrasonically assisted system with simultaneous two-axis oscillations has the better results than those experiments without, with single assisted and the other hybrid assisted combinations. Because the use of this complete hybrid assisted system, the cutting performance of tool wear and surface roughness are improved significantly.

碩士
國立中正大學
機械工程所
94
This thesis is about a study of using a pulsed Nd: YAG laser to process the 304 stainless steel assisted with gas and liquid. We developed an image method to find the focus position of the laser beam. This image-based method is to analyze the size and shape of the captured images of the laser spot on the material surface. We had conducted several experiments to study the laser ablation mechanisms and the process parameters such as the laser pulse energy and the pulse rate. Because the laser machining is a single-point cutting mechanism, the three-dimension micro-structure is fabricated by using the scanning and layer-by-layer methods. The overlap effect of the laser spot has been studied to obtain the optimized surface roughness and geometrical accuracy. Finally, we developed a laser polishing method to smooth the processed surface. Because the process of pulsed Nd:YAG laser ablating the 304 stainless steel is a mechanism involved ultra-high temperature, so the HAZ (heat affected zone) is usually found around processed area. It was found that during the process of ablation, molten metal sprays out and forms the debris and recast layer on the edge. There are three auxiliary methods been proposed to reduce the HAZ, debris and recast problems of laser process: the argon-assisted, spray water-assisted and underwater methods. We found the spray water-assisted laser method yielded the best result of the laser-processing stainless steel that the HAZ and recast layer are significantly reduced. The spray-water not only removes a large amount of the laser heat on the material substrate due to water cooling effect, but also cleans the molten ashes and burned educts like carbons by the flushing effect. Because the single-point scanning laser process usually results a rough processed surface, so it is necessary to polish the processed surface. In the laser polishing method, we adapt a low laser power and a proper overlap factor to re-scan the substrate surface. In the laser polishing step, the asperity of the rough surface will be molted by the laser heat but without ablation. With a proper laser power and overlap factor, we had proved this laser polishing method can improve the surface roughness significantly.

碩士
國立虎尾科技大學
機械與電腦輔助工程系碩士班
105
The high temperature heat-resistant alloy such as Inconel 718 is a kind of Fe-Cr-Ni based super alloy through age-hardening treatment. It possesses high yield and ultimate strength, high fatigue strength, high working temperature, good corrosive resistance. It has been widely used for aerospace and other components that operate at high temperatures and hostile environments; such as, gas turbine, rocket engines, missile parts and hot extrusion tooling. However, these unique and desirable heat-resistant characteristics of super-alloys, on the other hand, impair their machinabilities greatly resulting in low material removal rate, short tool life and poor surface finish. Therefore, the cutting performance promotion and machined surface quality improvement of Inconel 718 resulting in extending the cutting-tool service life has long been the most concerned issue for related manufacturers. The five stage experiments including without assistance, single and hybrid assisted machining systems on Inconel 718 milling were constructed in this study in order to verify the assisted effect on cutting performance and to compare the difference, merit and drawback among them. First of all, the milling experiment without assistance was performed to investigate the variations of cutting performance and the results were used for the suitable process parameter planning in the subsequent stage experiments. Next, a laser assisted system was introduced in the second stage where the spacing distance between the laser spot and cutting-tool along the cutting direction was set to test whether laser preheating may effectively reduce the cutting force. A biaxial ultrasonically assisted system with only one-axis oscillation (x or y direction) and with simultaneous two-axis oscillations (x and y direction) were subsequently introduced at the third to fourth stage experiments, respectively. While a biaxial ultrasonically and the laser assisted systems are integrated together to construct a hybrid assisted cutting system at the last stage experiment. Under these assistances, milling experiments of Inconel 718 by cutting-tool of tungsten carbide with nano-Si® coating were conducted. And the full factorial experiments of process parameter combinations such as spindle speed, radial cutting depth and feed rate were also planned. During the experiments, dynamometer is used to monitor the variation of cutting force. Tool wear, machined surface and side-edge surface morphology of the workpiece were measured by tool-microscope off-line. Surface roughness measurement through a probe contact type instrument was also performed. The results indicated that the laser-preheating assisted system could effectively reduce the cutting force as well as enhance the cutting performance. The effect of the biaxial ultrasonic oscillation on tool service life could greatly be promoted. Furthermore, the cutting performance exhibited in the integrated hybrid assisted milling prevails over that in milling without assistance as well as with each single assisted system. Under this hybrid assisted, the better surface roughness of 0.216μm was obtained at spindle speed of 6000 rpm, radial cutting depth of 0.01 mm, and feed rate of 300mm/min, accompanied by a maximum cutting-tool wear of 13.849μm. Because the use of this integrated hybrid assisted system, the cutting performance of tool wear and surface roughness could be improved significantly.

博士
國立中正大學
機械工程所
95
Hybrid laser-assisted machining (HLAM) is evaluated for its potential to become an economically viable process for manufacturing precision aluminum oxide ceramic parts. It is locally heated by an intense laser source prior to material removal, HLAM leads to higher material removal rates, as well as improved control of workpiece properties and geometry. During HLAM process, an intense laser beam is used as the heat source to change the ceramic deformation behavior from brittle to ductile before material was removed, without melting or sublimation of the workpiece surface, and reduce the yield strength of the ceramic to a value below the fracture strength in order to avoid the destruction of subsurface. To assess the feasibility of the HLAM process and better understand its governing physical phenomena, experiments were conducted to obtain different measures of surface roughness for Al2O3 workpiece machined by laser-assisted turning using a Nd:YAG laser. It’s unable to measure the temperature inside workpiece material, so the lattice Boltzmann method(LBM) is developed to simulate the temperature rising on surface and interior temperature distribution. The temperature fields calculated by LBM are compared with those obtained from the analytical solution based on the Fourier’s law. Results indicate that the feed, depth of cut and rotational speed have the greatest impact on the surface roughness. HLAM’s most important advantage is its ability to produce much better workpiece surface quality than does conventional machining, together with larger material removal rates(M.R.R.) and moderate tool wear.

碩士
國立中正大學
機械工程所
95
Laser assisted machining have done many researchs not only in our country but also in foreigner.for example in many difficult machine materials such as Al2O3、SI3N4、PSZ、mullite、CGI、SKD11.the relative research in laser assisted machining have displayed the great improvement in the aspect of material removal rate,increase the tool life,improve the surface roughness,reduce the cost.we will separate the study into two conditions .one is static condition and the other is dynamic condition and then to build the surface temperature diagram and the contour diagram of the temperature field.we will also do the cutting force prediction when the temperature of the workpiece varied with the laser assisted machining.

碩士
國立中正大學
機械工程所
96
With the progress of industry, it is the priority that promoting the quality of industry materials, due to people have higher standard of that. We are looking forward to making the materials be strong, hard, and heat-resisting. However, using these ideal materials is usually accompanied by the shortage of having difficulty in dealing with them. Therefore, we are going to study how to process on the premise that keeping the original quality of the material and the rough after processing. As a result, people figured out advanced hybrid laser-assisted machining which makes use of preheating. Therefore, we also will add on experiment for 10 seconds preheating in the future to soften the materials before contacting with the cutter. It makes the materials from fragile to ductility, and reduces the yield strength of the ceramic to a value below the fracture strength to avoid destroying the subsurface of material. Utilizing laser to soften the materials, then may reduce material original high strength and high degree of hardness characteristic, therefore we can reduce the consumption of cutter and increase its lifespan, and let materials don’t broken easily when contacting with the cutter, further the surface roughness will also have a large scale improvement. In addition, in the efficiency which takes regarding the industry under, there is a great promotion of removal rates with the preheating of laser, undoubtedly it’s a good news for feasibility of materials which was cut hardly. The experiment shows that, compared with the traditional processing technique, it improves about 3 to 4 times on rough, and it reduces about half of the cutter’s consumption, and this all is an effect which the advanced hybrid laser-assisted machining brings.

碩士
國立中正大學
機械系
93
The material with high strength and good heat resistance has being used extensively on the industry. Other is than material performance. Manufactures also want materials with good accuracy and surface roughness after processing. This is a difficult problem in process technology, and the study hopes research can improve and overcome this problem. Laser Assisted Machining means using laser for the heat source in the material work piece on the surface in front of processing the component, Make some temperature rise and reach heat to soften, make mechanical nature of material and normal temperature different to some extent. Laser Assisted Machining utilizes materials to be heated the idea that softens, Then process with CBN cutter able to bear high temperature , high hardness by heating materials laserly first，It contributes to reducing the cutting force processing to heat on the material surface after softening. Reduce the wearing and tearing of the tools and increase tool-life, Increase the efficiency of processing and metal removal rate. This study has adopted the Heat Source Method to establish temperature, get the laser light source and shine the material temperature profile, use Taguchi method to process the parameter experiment. It will have direct relations with the spindle speed to shine in material surface temperature that laser. It is the spindle speed that the processing surface influences the factor mainly; the cutter enters to give leading and cuts the depth to take second place. Process the situation of wearing and tear with the Laser Assisted Machining than to the tradition cutting processed, prove Laser Assisted Machining the improvement cutter that can be effective and wear and tear.

碩士
國立成功大學
微機電系統工程研究所
94
Abstract Due to the rapid development of semiconductor technology, the optical photolithography is advanced constantly. Nevertheless, the feature size smaller than 100 nm has reached its physical limitation and the escalating cost has become a burden for many companies. As an alternative to photolithography, the Nano-imprinting lithography（NIL）is now a promising method for nano-patterning and nano-fabrication. In this study, we focused on silicon materials and utilized a single KrF excimer laser pulse which has a wavelength of 248 nm and a pulse duration of 30 ns as the heating source. The fused quartz mold for laser assisted nano-imprinting has nanometer-scaled features. A single KrF excimer laser passes through the quartz mould and melts a thin surface layer of the silicon substrate within picoseconds. The quartz mold bears some pre-fabricated nano-scald features on its contact side and is made of matericals transparent to the excimer laser. Upon radiating the excimer laser pulse on the sample surface, the near-surface silicon melt. Subsequent cooling and solidification of the molten layer will then complete the transformation of the nano-patterns from the mold to the silicon sample. This rapid technique for patterning nano-scale features in silicon does not require sping coating photo-resist, photolithography , and chemical etching. To fabricate nano-scaled feature quartz molds, this research utilizes condcting polymer ESPACER300 as conducting layer to dissipate charge effect and applied E-beam lithography technology to achieve 200 nm line width. Following by lift-off and inductively coupled plasma (ICP) etching we can get the nano-scale feature mold. A working platform based on an Excimer Laser Micro-Machining system is constructed for LADI process. The influence of laser fluence and the imprinted pressure on the resulting structures was verifying by varying the laser fluence (1.2～1.6 J/cm2) and the imprinted load (1.0～3.0 kg). The results have shown that the morphology and the imprinted depth were directly related to the laser fluence and the imprinted pressure.

碩士
國立中正大學
機械工程所
94
The present industry aims at pursuing for materials of great intensity and heat-resistant quality. However, the processing procedure is more difficult for materials of good mechanical quality than general one. The good mechanical quality puts a great challenge to the requirements of present industry which stress surface roughness, processing efficiency, and processing cost. Moreover, the common problem present industry faces is like enhanced processing cost as long as they use special processes. The present industry encounters difficulty in processing skill; that is, the processing time is usually more for special processing manner than general one. Return to reality, we don’t have to design additional machine; instead, by compound processing ideas, we just have to add laser device to the original machine. Therefore, we can soften the material by the LAM. Then, there is a reserved period before the cutting tool contacts the work piece. In the short period, the material absorbs heat to be soft. The form change makes sure that the work piece the cutting tool contacts with is soft. Hence, the abrasion of the cutting tool reduces relatively, and the roughness degree of work piece surface improves largely. By the result of this experiment, the roughness of the surface is four to five times difference on average due to use LAM or not. In addition, the abrasion of the cutting tool reduces largely by 40~60%. The effects mentioned above all result from LAM.