Rozprawy doktorskie na temat „ABRASIVE JET MACHINING”

L'alliage de titane est généralement utilisé pour les pièces structurelles aéronautiques ayant une taille importante et ainsi que des parois minces tout en devant résister à des efforts considérables. L'usinage de ces pièces est difficile avec les méthodes classiques telles que le fraisage, car les forces de coupe sont élevées et les parois minces peuvent être facilement déformées. L'usinage de l'alliage de titane (Ti6Al4V) par un procédé utilisant un jet d'eau abrasif (AWJ) peut potentiellement être utilisé pour remplacer les méthodes d'usinage conventionnelles. Cependant, la compréhension des différents aspects de ce procédé est insuffisante pour autoriser son industrialisation. Cette thèse présente un modèle de prévision de la profondeur usinée dans deux cas de direction du jet : un jet perpendiculaire à la surface de la pièce et un jet incliné. Dans un premier temps, la compréhension du processus d'enlèvement de matière et de la qualité de surface obtenue est étudiée à travers l'observation de l'influence des paramètres du processus. Dans un second temps, un modèle basé sur la distribution gaussienne des particules abrasives dans le jet d'eau est proposé pour caractériser un passage élémentaire et pour prédire le profil du fond de poche obtenu par une succession de passages élémentaires. Ensuite, une méthodologie d'usinage des coins de poche utilisant un contrôle adaptatif de la vitesse d'avance est présentée. Enfin un nouveau modèle du profil du fond de poche prenant en compte l'angle d'inclinaison du jet est présenté. Tout au long de ce travail de thèse, la validation expérimentale a montré un bon accord entre les valeurs mesurées et modélisées et a ainsi démontré la capacité du jet d'eau abrasif à usiner à une profondeur contrôlée
Titanium alloy is generally used for aeronautical structural parts having a large size and as thin walls while having to withstand considerable effort. Machining these parts is difficult with conventional methods such as milling, because the high cutting forces can easily deform the part. Machining of titanium alloy (Ti6Al4V) by an abrasive water jet (AWJ) process can potentially be used to replace conventional machining methods. However, the understanding of the different aspects of this process is insufficient to allow its industrialization. This thesis presents a model of prediction of the machined depth in two cases of direction of the jet: a jet perpendicular to the surface of the part and an inclined jet. At first, the understanding of the removal material process and the obtained surface quality is studied through the observation of the influence of the process parameters. In a second step, a model based on the Gaussian distribution of abrasive particles in the water jet is proposed to characterize an elementary pass and to predict the pocket bottom profile obtained by a succession of elementary passes. Then, a method to machine pocket corners using an adaptive control of the feed rate is presented. Finally, a new model of the pocket bottom profile taking into account the angle of inclination of the jet is presented. Throughout this thesis work, the experimental validation showed a good agreement between the measured and modeled values and thus demonstrated the ability of the abrasive water jet milling to machine to a controlled depth

An experimental investigation has been undertaken to study the depth of cut in multipass abrasive waterjet (AWJ) cutting of an 87% alumina ceramic with controlled nozzle oscillation. The experimental data have been statistically analysed to study the trends of the depth of cut with respect to the process parameters. It has been found that multipass cutting with controlled nozzle oscillation can significantly increase the depth of cut. Within the same cutting time and using the same cutting parameters other than the jet traverse speed, it has been found that multipass cutting with nozzle oscillation can increase the depth of cut by an average of 74.6% as compared to single pass cutting without nozzle oscillation. Furthermore, a multipass cutting with higher nozzle traverse speeds can achieve a larger depth of cut than a single pass cutting at a low traverse speed within the same cutting time. A recommendation has been made for the selection of appropriate process parameters for multipass cutting with nozzle oscillation. In order to estimate the depth of cut on a mathematical basis, predictive models for the depth of cut in multipass cutting with and without nozzle oscillation have been developed using a dimensional analysis technique. The model development starts with the models for single pass cutting which are then extended to multipass cutting where considerations are given to the change of the actual standoff distance after each pass and the variation of kerf width. These predictive models has been numerically studied for their plausibility by assessing their predicted trends with respect to the various process variables, and verified qualitatively and quantitatively based on the experimental data. The model assessment reveals that the developed models correlate very well with the experimental results and can give adequate predictions of this cutting performance measure in process planning.

This thesis presents a design technology of forming a shaped lid focused on cutting, bending, drawing, as well as trimming and making the required holes. There is described several basic variants of sheet metal forming based on the literature. Production of holes of specified cover, for an annual production of 100 pieces of shaped lid, is solved by unconventional technologies. From subsequent economic evaluation of selected technologies is chosen an appropriate technology to minimize production costs.

In diploma thesis there is elaborated the analysis of assumed development of water jet technology and there is analyzed the level of water jet method in production. There are introduced the possibilities of new applications of water jet machining and the possibilities of it’s future development. There is think over the enlargement of this method in next 5 years. Simultaneously there is solved the question of techno economic operation severity of this technology.

Le procédé d'usinage par Jet d'eau Abrasif (JEA) est un processus polyvalent, largement employé pour découper une vaste gamme de matériaux. Récemment, quelques études ont démontré la capacité de ce procédé pour l'usinage non débouchant à profondeur contrôlée de matériaux composites, qui peuvent potentiellement être utilisés pour la réparation de structures aéronautiques composites endommagées. Plusieurs études scientifiques rapportent que ce procédé d'usinage induit divers types de défauts sur la surface usinée. S'agissant d'une application récente, l'usinage non débouchant de matériaux composites par JEA nécessite des investigations pour être compris sur de nombreux points. Cette thèse participe à combler ce manque en définissant trois objectifs : l'usinabilité du matériau composite par ce procédé, l'influence des défauts générés par l'usinage JEA sur le comportement mécanique, et l'influence de la qualité de surface et des défauts sur l'adhésion d'un collage dans un contexte de réparation. Premièrement, la compréhension de l'usinabilité des composites à renforts en fibres de carbone (CFRP) implique l'étude du taux d'enlèvement de matière, la morphologie de la surface usinée, et la caractérisation de la nature et de la taille des défauts générés par le procédé d'usinage. La qualité d'usinage est évaluée en utilisant des paramètres superficiels traditionnels comme la rugosité superficielle (Ra), et pour la première fois, la quantification des défauts est faite en utilisant un nouveau critère qui utilise un paramètre nommé " volume de cratères ". L'idée qui mène la deuxième partie de l'étude consiste à relier la qualité de la surface générée par l'usinage et le volume de défauts au comportement mécanique de la structure usinée. L'influence de la modification superficielle induite par l'usinage et l'influence des défauts sur la performance mécanique sont étudiées sous un chargement statique en traction, puis sous un chargement dynamique de fatigue traction/traction sur des spécimens usinés avec des niveaux de défauts variables. Les tests mécaniques statiques sont instrumentés avec un extensomètre et par de la corrélation d'images numériques, alors que les tests en fatigue sont instrumentés avec des extensomètres, des capteurs d'émissions acoustiques et par thermographie infrarouge.[...]
Controlled depth milling of carbon fiber reinforced plastic (CFRP) composites by abrasive water jet (AWJ) process is a recent advancement which can potentially be used for repairing composite structures. Aircraft composite structural repair is a costly affair owing to stringent requirements of skilled labor, time and regulatory certifications. Presently the aircraft maintenance industry lacks a reliable machining process for repair procedure. In comparison with conventional machining process AWJ milling could be a major advantage in the favor of the aircraft maintenance industry. However, knowledge on many aspects of this process is inadequate for reliable industrialization. Hence, this thesis focuses on narrowing this research gap by defining three objectives. Firstly, understanding the machinability of CFRPs, for this, the influence of process parameters on material removal rate, surface quality and nature and size of defects are studied. The machining quality is benchmarked using the traditional surface roughness criterion and a newly proposed criterion crater volume 'Cv' based on the quantification of the crater defects. The newly proposed machined surface quality criterion clears all the ambiguity that was previously present with the usage of surface roughness criterion. Secondly, the influence of machined surface quality and defects on static tensile and tension-tension fatigue behavior is studied for specimens with varying nature and levels of machining induced defects. The tensile strength and the endurance limits of various specimens are correlated with machining quality (Ra and Cv). The damage initiation and progression during loading and the role of defects in the promotion of the damage is studied using techniques like acoustic emission, thermography and X-ray tomography. Finally, the influence of machining quality on the quality of repair patch adhesion is examined by performing tensile tests on the specimens milled and bonded using an epoxy adhesive with new CFRP plies. These studies aid the industrial community to ascertain the usability of AWJ milling for composite repair and lay a strong foundation for industrialization of the AWJ milling process

博士
國立中央大學
機械工程研究所
96
This study introduces an Abrasive Jet Polishing (AJP) technique to improve the polishing performance. Furthermore, a Gas Atomization technique is employed to fabricate Wax-coated #3000SiC particles, investigations to establish the optimal AJP parameters for the surface finishing of different SKD61 mold steel specimens shape and processed. Taguchi design experiments are performed to identify the optimal AJP parameters when applied to the polishing of SKD61 mold steel specimens. Using #2000SiC particles were mixed with water wax and pure water in a ratio of 500: 1000: 1500 (Water Wax: SiC particles: Pure Water). Following 90 minutes of blasting, the surface roughness is improved from an initial value of 7.74 μm Rmax to 0.45 μm Rmax, thereby obtain a mirror-like surface finish. AJP polishing of the micro-grooving SKD61 surface, Linear type micro-channel SKD61 surface and Curvee type micro-channel SKD61 surface using #3000SiC particles mixed with water wax and pure water in the ratio 500:1000:1500 (Water Wax: SiC particles: Water) reduces the surface roughness from an initial value of Rmax = 2.32 μm, Rmax = 3.45 μm and Rmax = 3.58 μm to a final value of Rmax = 0.40 μm, Rmax = 0.43 μm and Rmax = 0.45 μm within 30 minutes, 60 minutes and 60 minutes, respectively. Gas Atomization system used in this study to fabricate the Wax-coated #3000SiC particles. AJP polishing of the ground SKD61 surface using wax-coated #3000SiC particles mixed with water wax and pure water in the ratio 500: 1000: 1500 (Water Wax: SiC particles: Water) reduces the surface roughness from an initial value of Rmax = 3.26 μm to a final value of Rmax = 0.31 μm within 45 minutes. In addition, using wax-coated #3000SiC particles of the micro-grooving SKD61 surface, Linear type micro-channel SKD61 surface and Curvee type micro-channel SKD61 surface reduces, the surface roughness from an initial value of Rmax = 2.32 μm, Rmax = 3.45 μm and Rmax = 3.58 μm to a final value of Rmax = 0.31 μm, Rmax = 0.35 μm and Rmax = 0.40 μm within 30 minutes, 60 minutes and 75 minutes, respectively. Overall, the results show that the use of wax-coated abrasive particles reduces the polishing time and achieves an improved surface finish.

碩士
淡江大學
機械與機電工程學系碩士班
104
Brittle materials such as glasses, silicon, silicon carbide are normally categorized as difficult to machine materials for its high hardness and brittleness s. However, they have attracted more and more attentions and been playing critical roles in many scientific/engineering applications for their advanced physic/optical/electronic properties. Micro-patterns such as micro-hole (array) of various sizes and shapes are frequently required to be generated on brittle materials. Many researchers have tried different approaches such as laser ablation, ultrasonic machining, rotary ultrasonic machining…. to produce micro-hole in brittle materials. This research applied abrasive jet machining to fabricate micro-hole array on glass. Efforts have been made to investigated the effect of grit-size, stand-off distance, pressure, scanning speed on the material removal rate and the obtained hole accuracy. Micro-holes of various shapes and with characteristic dimension ranged from 0.2mm to 2mm are successfully produced in glass plate of 0.4mm thickness.

碩士
淡江大學
機械與機電工程學系碩士班
100
Water abrasive jet (WAJ) is regarded as one of the very effective ways of machining difficult-to-machine materials such as steel, titanium alloys, composite and ceramic materials. Its applications can range from cutting/dicing/drilling when applying the AWJ with a high impact angle to micro-cutting/polishing/cleaning where the impact angle is kept very low. This research aimed to study the feasibility of using AWJ to cut the chemically toughened cover glasses and to polish the precision ground tungsten carbide (WC) materials. Alumina (Al2O3) and silicon carbide (SiC) particles of various sizes were used as the abrasives. Chemically toughened Gorilla (Corning) glass and WC of different cobalt concentrations were the tested materials. It is founded that, owing to the different removal rate between Co and WC, surface roughness of precision ground WC specimen of high Co concentration (18%) is more difficult to be improved than those of lower Co concentration (0~3%). SiC abrasives, having the higher hardness value, can achieve better material removal than Al2O3. As to the AWJ dicing process, a novel laser/AWJ hybrid dicing process where using laser to penetrate the toughened layer and AWJ to finish the dicing process was proposed and verified in this study.

The effect of particle size, velocity, and angle of attack was investigated on the roughness and erosion rate of unmasked channels machined in borosilicate glass using abrasive jet micro-machining (AJM). Single impact experiments were conducted to quantify the damage due to the individual alumina particles. Based on these observations, an analytical model from the literature was modified and used to predict the roughness and erosion rate. A numerical model was then developed to simulate the brittle erosion process leading to the creation of unmasked channels as a function of particle size, velocity, dose, impact angle and target material properties. For the first time, erosion was simulated using models of two damage mechanisms: crater removal due to the formation and growth of lateral cracks, and edge chipping. Accuracy was further enhanced by simulating the actual relationship between particle size, velocity and radial location within the jet using distributions measured with high-speed laser shadowgraphy. The process of post-blasting AJM channels with abrasive particles at a relatively low kinetic energy was also investigated in the present work by measuring the roughness reduction of a reference unmasked channel in borosilicate glass as a function of post-blasting particle size, velocity, dose, and impact angle. The numerical model was modified and used to simulate the post-blasting process leading to the creation of smooth channels as a function of particle size, velocity, dose, impact angle, and target material properties. Finally, the effect of alumina particle kinetic energy and jet impact angle on the roughness and erosion rate of channels machined in borosilicate glass using abrasive slurry jet micro-machining (ASJM) was investigated. The analytical and numerical models derived for AJM, were found to predict reasonably well the roughness and the erosion rate of ASJM channels, despite the large differences in the fluid media, flow patterns, and particle trajectories in AJM and ASJM.

碩士
南開科技大學
車輛與機電產業研究所
101
This study developed a hybrid process of abrasive jet machining (AJM) and electrical discharge machining (EDM). The effects of the hybrid process parameters on machining characteristics and surface modifications were comprehensively investigated to confirm the benefits of this hybrid process. The appropriate abrasives delivered by high speed gas medium were incorporated with an EDM in gas system to construct the hybrid process of AJM and EDM, and then the high speed abrasives could impinge on the machined surface to remove the recast layer caused by EDM process to increase the efficiency of material removal and reduce the surface roughness. In addition, the added abrasives could regard as the agents of surface modifications. In this study, the benefits of the hybrid process were determined as the machining performance of hybrid process was compared with that of the EDM in gas system. The main process parameters were varied to explore their effects on material removal rate (MRR), electrode wear rate (EWR), surface roughness (SR). The experiments were conducted based on Taguchi method. The experimental observed values were transferred to signal-to-noise (S/N) ratios, and then the significant machining parameters affecting obviously the machining performance were determined by analysis of variance (ANOVA). The optimal combination levels of machining parameters for each machining characteristic were obtained by the S/N ratio analysis according to Taguchi methodology. Moreover, the effects of surface modifications with relation to the machining parameters were also determined by the developed hybrid process. The experimental results show that the significant machining parameters affecting the MRR were machining polarity, peak current, and pulse duration; peak current was the significant parameter with relation to the EWR, and the peak current, pulse duration, and gas pressure were the significant in regard to the SR. In addition, The silicon content increased with increase in gas pressure, pulse duration, and peak current, as well the silicon content attained the value of 8.2 wt.% in the hybrid process with respect to surface modification. The developed hybrid process of AJM and EDM could enhance the machining efficiency and improve the surface modification. Consequently, the developed hybrid process could fit the requirements of modern manufacturing applications.This study developed a hybrid process of abrasive jet machining (AJM) and electrical discharge machining (EDM). The effects of the hybrid process parameters on machining characteristics and surface modifications were comprehensively investigated to confirm the benefits of this hybrid process. The appropriate abrasives delivered by high speed gas medium were incorporated with an EDM in gas system to construct the hybrid process of AJM and EDM, and then the high speed abrasives could impinge on the machined surface to remove the recast layer caused by EDM process to increase the efficiency of material removal and reduce the surface roughness. In addition, the added abrasives could regard as the agents of surface modifications. In this study, the benefits of the hybrid process were determined as the machining performance of hybrid process was compared with that of the EDM in gas system. The main process parameters were varied to explore their effects on material removal rate (MRR), electrode wear rate (EWR), surface roughness (SR). The experiments were conducted based on Taguchi method. The experimental observed values were transferred to signal-to-noise (S/N) ratios, and then the significant machining parameters affecting obviously the machining performance were determined by analysis of variance (ANOVA). The optimal combination levels of machining parameters for each machining characteristic were obtained by the S/N ratio analysis according to Taguchi methodology. Moreover, the effects of surface modifications with relation to the machining parameters were also determined by the developed hybrid process. The experimental results show that the significant machining parameters affecting the MRR were machining polarity, peak current, and pulse duration; peak current was the significant parameter with relation to the EWR, and the peak current, pulse duration, and gas pressure were the significant in regard to the SR. In addition, The silicon content increased with increase in gas pressure, pulse duration, and peak current, as well the silicon content attained the value of 8.2 wt.% in the hybrid process with respect to surface modification. The developed hybrid process of AJM and EDM could enhance the machining efficiency and improve the surface modification. Consequently, the developed hybrid process could fit the requirements of modern manufacturing applications.

博士
國立臺灣大學
機械工程學研究所
93
Abstract In the process of powder blasting, mask was closely stuck on the substrate to protect the area of substrate not to be powder blasted. The quality characteristics of this process depend completely on the erosion resistance of mask to the powder blasting and the accuracy of mask opening size. this paper will provides a new idea and methods to improve the precision and achieve a good quality of this process. Instead of one protective layer for mask that is conventionally used, two layers are coated on the surface of the substrate material. The inner layer is water-soluble resin with excellent adhesion to the substrate but having weak resistance to powder erosion, and the second layer is a photosensitive oligomer that is adhered well to the first layer and has very high resistance to powder erosion. Once the openings of the second layer are formed at the desired positions via a photo-etching method, a printing method, or other methods, the holes or grooves can be obtained by etching through the openings of the second layer to the first layer and the substrate by a powder blasting process. Then the whole protective coating is easily and smoothly stripped off without any damage to the substrate by dissolving the first layer with water. Such a protective coating possesses two contrary characteristics: high resistance to powder blasting and easy removal from substrate after powder erosion. Due to two layers are coated on the surface of the substrate material, the material of each layer can thus separately be developed to its utmost properties by researcher, and therefore, more space is created for developing in the powder blasting process. In creating a hole on brittle materials by double-side sand blasting, the rebounding sand particle flux during the process may result in underetching at the edge of the mask opening, and leads to a larger sized fluid hole than desired one. In practice, determination of the correct mask opening size was made mainly by trial and error or with fine-tuning of the masking process and compensation for mask wear. In this paper, relationships between the mask opening size and desired size of a hole on both the front and the back sides of the substrate are derived. For the front side, by taking into account the underetching effect, an equation is derived based on kinetic energy theory. For the back side, there is negligible rebounding sand particles, and the mask opening size is set to be equal to the desired size of the hole. Experiments were conducted to verify the derived relationships. It is found that the measured sizes of the eroded holes on both the front and the back sides of the wafer substrate are distributed normally. The desired hole sizes deviate slightly from the median of a normal distribution curve, and the maximum predicted errors are 2.4% and 3.0% for front side and the back side sand blasting, respectively. The very satisfactory result of the predicted errors for various hole size shows that the derived relationships is applicable for determination of mask opening size in powder blasting process. With this improvement of hole accuracy in size, it is expected that the powder blasting process will provide another choice for the process of machining holes on brittle materials.

碩士
國立中央大學
機械工程學系
104
Electrochemical jet machining (ECJM) is one of the non-traditional machining technologies, the technology is by metal material removing through electrochemical reaction, the dissolved metal were carried away via jet flow from machining region. However, The process of abrasive slurry-jet machining (ASJM) is that erodes material using abrasive particles by a steam of fluid impinging on a target. ECJM has several advantages, such as difficult to wear electrode, removing part of workpiece by dissolved via jet, no residual stress and Metamorphic layer, high machining rate and good smoothness on machining surface. In this thesis, the object of research is to combine ECJM and ASJM. Due to the unique technology of electrochemical machining, it is usually applied to other conditions which mechanics is hard to machine. However, when the electrochemical technology applies to machine carbon steel or the material which have been heat treatment, the black layer will be generated on the surface, that is Carbon-rich layer. This layer is not the products of the electrochemical reaction, but the iron in ions fall after leaves from the surface of workpiece. Because the carbon is active, it is easy to deposit to the surface of workpiece, and it is not easy to depart by electrolyte flow in general electrochemical machining method. Moreover, this layer will obstruct electrochemical machining, so it causes the lower rate of machining and more roughness on the surface after machining. In view of these, we proposed a project that is to machine and clear burr on SKD11 by ASJM. We can overcome the obstruction of blacklayer in the physical erosion and electrochemical corrosion, so as to increase the efficiency of machining and decrease the roughness of the surface. In this thesis, the hollow tube is used in 500 and 700μm, and the NaCl is chosen as the electrolyte to drill SKD11, and investigate the influence of different voltage, concentration, abrasive concentration, gap and flow. Moreover, we compare the effective height and aspect ratio to choose the best parameters, and make an object to machine a hole of 1000μm, and compare the difference if ECJM with abrasive or not. The results show that the best effective occurs when voltage in 70V and NaCl concentration in 20%, gap in 1mm and the flow in 340ml/min. And no matter roughness or material removal, ECJM assisted with abrasive is better than ECJM only.

碩士
國立臺灣科技大學
機械工程系
99
This thesis aims to investigate the optimal abrasive jet polishing parameters for Zr-based bulk metallic glass (BMG) material by using the Taguchi method. An abrasive jet polishing (AJP) system has been newly designed and installed on a machining center. In order to determine the optimal polishing parameters for the BMG sample, four polishing parameters, namely the hydraulic pressure, the impact angle, the stand-off distance, and the polishing time were chosen as the factors of experiments. The optimal AJP parameters have been determined after carrying out the experiments based on the Taguchi’s L9 orthogonal array experimental results. These optimal parameters are the combination of the hydraulic pressure of 2 kg/cm2, the impact angle of 50o, the stand-off distance of 15 mm, and the polishing time of 60 minutes. The surface roughness can be improved from about Ra 0.13 μm to 0.044 μm by using the AJP optimal parameters. Besides, an analysis of variation (ANOVA) of the experimental data indicated that the polishing time and hydraulic pressure was the dominant parameters of the AJP process for the BMG material.

The present study investigated the effect of dilute polymer solutions on the size, shape, and roughness of channels and holes, machined in metal and glass using a novel abrasive slurry-jet micro-machining (ASJM) apparatus. The apparatus consisted of a slurry pump and a pulsation damper connected to an open reservoir tank to generate a 140-micron turbulent jet containing 1 wt% 10-micron alumina particles. With the addition of 50 wppm of 8-M (million) molecular weight polyethylene oxide (PEO), the widths of the channels and diameters of holes machined in glass decreased by an average amount of 25%. These changes were accompanied by approximately a 20% decrease in depth and more V-shaped profiles compared with the U-shape of the reference channels and holes machined without additives. The present results demonstrate that a small amount of a high-molecular-weight polymer can significantly decrease the size of machined channels and holes for a given jet diameter.

碩士
建國科技大學
自動化工程系暨機電光系統研究所
101
In this study, the use of abrasive jet machining method (Abrasive Jet Machining,AJM) surface machining on milling explore on SKD61 mold steel processing and milling the surface of the polishing improvement. From the experimental results find that use the best combination of parameters by Taguchi Method ,the surface roughness value can drop from 0.76 μmRa to 0.21 μmRa and 4.57 μmRmax to 0.92 μmRmax, the improvement rate up to 72% and the surface is similar to a reflection mirror. Furthermore, study also investigated the surface characteristic of workpiece after machining. From EDX quantitative analysis result reveal that use the SiC abrasive after AJMPM, the SiC content on workpiece surface is going to increase obviously and micro hardness of surface will also increase because of the surface insertion effect (SiC particles).