Ultra-high precision grinding of BK7 glass

With the increase in the application of ultra-precision manufactured parts and the absence of much participation of researchers in ultra-high precision grinding of optical glasses which has a high rate of demand in the industries, it becomes imperative to garner a full understanding of the production of these precision optics using the above-listed technology. Single point inclined axes grinding configuration and Box-Behnken experimental design was developed and applied to the ultra-high precision grinding of BK7 glass. A high sampling acoustic emission monitoring system was implemented to monitor the process. The research tends to monitor the ultra-high precision grinding of BK7 glass using acoustic emission which has proven to be an effective sensing technique to monitor grinding processes. Response surface methodology was adopted to analyze the effect of the interaction between the machining parameters: feed, speed, depth of cut and the generated surface roughness. Furthermore, back propagation Artificial Neural Network was also implemented through careful feature extraction and selection process. The proposed models are aimed at creating a database guide to the ultra-high precision grinding of precision optics

Pulsed laser ablation of ultra-hard structures: generation of tolerant freeform surfaces for advanced machining applications

This thesis covers the laser generation of novel micro-cutting arrays in ultra-hard super-abrasive composites (e.g. polycrystalline diamond, PCD and polycrystalline cubic boron nitride, PCBN). Pulsed laser ablation (PLA) has been used to manufacture repeatable patterns of micro cutting/abrasive edges onto micro structurally different PCD/PCBN composites. The analysis on the influence of microstructural factors of the composite materials in the use of laser ablation technology has been carried out via a novel technique (Focused Ion Beam/High Resolution Transmission Electron Microscopy/Electron Energy Loss Spectroscopy) to identify the allotropic changes occurring in the composite as a consequence of PLA allowing the laser ablated PCD/PCBN surfaces to be characterized and the nanometric changes evaluated. The wear/failure characteristics/progression of the ultra-hard laser generated micro cutting/abrasive arrays has been studied in wear tests of Silicon Dioxide workpiece shafts and the influence of the microstructural factors in the wear properties of the super-abrasive micro cutting edges has been found. Opposing to these highly-engineered micro cutting/abrasive arrays, conventional electroplated abrasive pads containing diamond and CBN abrasives respectively have been chosen as benchmarks and tested under the same conditions. Contact profiling, Optical Microscopy and Environmental Scanning Electron Microscopy have been employed for the characterization of the abrasive arrays/electroplated tools before/during/after the wear/cutting tests. In the PCD abrasive micro-arrays, the type of grain and binder percentage proved to affect the wear performances due to the different extents of compressive stresses occurring at the grain boundaries. Mixed grained PCD arrays performed 25% better than fine grained arrays. All of the PCD laser manufactured arrays showed an increase up to 60% in the tool life when compared to the benchmarked pads. As for the PCBN abrasive micro-arrays, the laser manufactured arrays proved to perform 50% better than the electroplated ones in terms of wear resistance. This eThesis was first deposited on 6 November 2014

Modelling of grinding mechanics : a review

Grinding is one of the most widely used material removal methods at the end of many process chains. Grinding force is related to almost all grinding parameters, which has a great influence on material removal rate, dimensional and shape accuracy, surface and subsurface integrity, thermodynamics, dynamics, wheel durability, and machining system deformation. Considering that grinding force is related to almost all grinding parameters, grinding force can be used to detect grinding wheel wear, energy calculation, chatter suppression, force control and grinding process simulation. Accurate prediction of grinding forces is important for optimizing grinding parameters and the structure of grinding machines and fixtures. Although there are substantial research papers on grinding mechanics, a comprehensive review on the modeling of grinding mechanics is still absent from the literature. To fill this gap, this work reviews and introduces theoretical methods and applications of mechanics in grinding from the aspects of modeling principles, limitations and possible future trendencies

Revealing Prior Austenite Grain Boundaries of 4340 Steel

Grain growth during austenitization has a negative effect on fatigue strength. Several methods have been investigated in order to determine an accurate method of measuring the austenite grain size of 4340 steel. The McQuaid-Ehn method, an industry standard for evaluating austenite grain size, has been recognized to produce inaccurate results due to the coarsening of grains during extended austenitizing. A method utilized for hypoeutectoid steels, outlined by the ASTM-E112 standard, is investigated to potentially obtain more accurate results by reducing the duration of austenitizing. Studies regarding effective etching procedures for revealing austenite grains without austenitizing are also addressed. Samples are prepared by heat treating to induce temper embrittlement in order to improve etching at these grain boundaries. Although temper embrittlement is undesirable for components in service, the process proved to effectively delineate austenite grain boundaries when etched with a picric acid based reagent. This method may be utilized to acquire an accurate measurement of austenite grain size during processing. The picric acid reagent was unsuccessful when applied to the McQuaid-Ehn and Hypoeutectoid samples. The use of a nital etchant also proved to be ineffective for the McQuaid-Ehn, Hypoeutectoid and temper embrittlement methods utilized by this investigation

Materials review for improved automotive gas turbine engine

The potential role of superalloys, refractory alloys, and ceramics in the hottest sections of engines operating with turbine inlet temperatures as high as 1370 C is examined. The convential superalloys, directionally solidified eutectics, oxide dispersion strenghened alloys, and tungsten fiber reinforced superalloys are reviewed and compared on the basis of maximum turbine blade temperature capability. Improved high temperature protective coatings and special fabrication techniques for these advanced alloys are discussed. Chromium, columbium, molybdenum, tantalum, and tungsten alloys are also reviewed. Molbdenum alloys are found to be the most suitable for mass produced turbine wheels. Various forms and fabrication processes for silicon nitride, silicon carbide, and SIALON's are investigated for use in highstress and medium stress high temperature environments

Pulsed laser ablation of ultra-hard structures: generation of tolerant freeform surfaces for advanced machining applications

This thesis covers the laser generation of novel micro-cutting arrays in ultra-hard super-abrasive composites (e.g. polycrystalline diamond, PCD and polycrystalline cubic boron nitride, PCBN). Pulsed laser ablation (PLA) has been used to manufacture repeatable patterns of micro cutting/abrasive edges onto micro structurally different PCD/PCBN composites. The analysis on the influence of microstructural factors of the composite materials in the use of laser ablation technology has been carried out via a novel technique (Focused Ion Beam/High Resolution Transmission Electron Microscopy/Electron Energy Loss Spectroscopy) to identify the allotropic changes occurring in the composite as a consequence of PLA allowing the laser ablated PCD/PCBN surfaces to be characterized and the nanometric changes evaluated. The wear/failure characteristics/progression of the ultra-hard laser generated micro cutting/abrasive arrays has been studied in wear tests of Silicon Dioxide workpiece shafts and the influence of the microstructural factors in the wear properties of the super-abrasive micro cutting edges has been found. Opposing to these highly-engineered micro cutting/abrasive arrays, conventional electroplated abrasive pads containing diamond and CBN abrasives respectively have been chosen as benchmarks and tested under the same conditions. Contact profiling, Optical Microscopy and Environmental Scanning Electron Microscopy have been employed for the characterization of the abrasive arrays/electroplated tools before/during/after the wear/cutting tests. In the PCD abrasive micro-arrays, the type of grain and binder percentage proved to affect the wear performances due to the different extents of compressive stresses occurring at the grain boundaries. Mixed grained PCD arrays performed 25% better than fine grained arrays. All of the PCD laser manufactured arrays showed an increase up to 60% in the tool life when compared to the benchmarked pads. As for the PCBN abrasive micro-arrays, the laser manufactured arrays proved to perform 50% better than the electroplated ones in terms of wear resistance. This eThesis was first deposited on 6 November 2014

Influence of the surface and heat treatment on the flexural strength and reliability of Y-TZP dental ceramic

Ziel: Ziel dieser Studie war, den Einfluss verschiedener Oberflächenbehandlungen und der anschließenden Wärmebehandlung auf die Biegefestigkeit und die Zuverlässigkeit einer Y-TZP Keramik zu überprüfen. Materialien und Methoden: Sechs Gruppen mit 27 bis 30 Zirkoniumdioxid-Scheiben (LAVA ™ Frame, 3M ESPE, Seefeld, Deutschland) bekamen eine der folgenden Behandlungen : keine Behandlung, Sandstrahlen mit Aluminiumoxid-Partikeln (50 µm, 2 bar), Beschleifen mit feinkörnigen Diamanten (ISO-No. 806 314 111514 014, Komet Brasseler, Lemgo, Deutschland), Sandstrahlen und anschließendes Beschleifen, Sandstrahlen und anschließenden Brand oder Beschleifen und anschließenden Brand. Oberflächen von zufällig ausgewählten Proben wurden mit Raster-Elektronen-Mikroskopie untersucht und deren Rauheit wurde mit einem Profilometer gemessen. Nach der Behandlung wurde der biaxiale Biegeversuch zur Bestimmung der Biegefestigkeit der Scheiben verwendet und Röntgenbeugungsanalyse wurde angewendet, um den Einfluss der Oberflächen- und Wärmebehandlung auf die Phasenzusammensetzung zu beurteilen und das Auftreten von Phasenumwandlungen in der Y-TZP Keramik festzustellen. Die Daten wurden unter Verwendung von multiplen Welch-Tests und Anpassung der p-Werte mit der Bonferroni-Holm Methode analysiert, während die Überlebensfähigkeit mittels Weibull Analyse geschätzt wurde. Ergebnisse: Alle Oberflächenbehandlungen haben die Biegefestigkeit des Materials signifikant erhöht und die anschließende Wärmebehandlung hat sie verringert, jedoch zu einem von der Kontrollgruppe nicht signifikanten Niveau. Alle Gruppen hatten niedrigere m Werte als die Testproben mit der Ausnahme der beschliffenen und gebrannten Gruppe, die die höchste Zuverlässigkeit aufwies. Zwischen der Oberflächenrauhigkeit der Scheiben und der Biegefestigkeit wurde keine Korrelation gefunden. Schlussfolgerung: Die vorliegende Studie legt nahe, dass Sandstrahlen und Beschleifen verwendet werden können, um die Biegefestigkeit des Materials zu erhöhen, jedoch auf Kosten einer etwas niedrigeren Zuverlässigkeit. Sandstrahlen sollte nur nach dem Keramikbrand zur Verbesserung des Haftverbundes des Zementes an dem Material angewandt werden. Ein Regenerationsbrand sollte dem Beschleifen folgen, um die Zuverlässigkeit des Y-TZP Materials zu erhöhen, wobei auch eine hohe Biegefestigkeit bewahrt werden kann.Objective: The purpose of this study was to evaluate the influence of different surface treatments and subsequent annealing on the flexural strength and reliability of a Y-TZP dental ceramic. Materials and methods: Six groups of 27 to 30 zirconia discs (LAVA™ Frame; 3M ESPE, Seefeld, Germany) underwent one of the following treatments: no treatment, sandblasting with alumina particles (50 µm, 2 bar), grinding with fine grit diamond burs (ISO-No. 806 314 111514 014, Komet Brasseler, Lemgo, Germany), sandblasting and subsequent grinding, sandblasting and subsequent annealing or grinding and subsequent annealing. Surfaces of random specimens were observed with scanning electron microscopy and their roughness was measured with a profilometer. After treatment, the biaxial flexure test was used to calculate the flexural strength of the discs and X-Ray diffraction analysis was employed to assess the influence of the surface modifications and the firing procedures on the phase composition and the occurrence of phase transformations in the Y-TZP ceramic. The data was analyzed utilizing multiple Welch tests with adjustment of the p values with the Bonferroni-Holm method, whereas the survivability was estimated using Weibull analysis. Results: All surface treatments significantly increased the flexural strength of the material and subsequent heat treatment decreased it, but to a level not significantly different from the control group. All groups had lower m values than the test specimens, except for the ground and fired group, which had the highest reliability. No correlation was found between the surface roughness of the discs and the flexural strength. Conclusions: The present study suggests, that sandblasting and grinding can be used to increase the strength of the material in expense of somewhat lower reliability. Sandblasting should be employed only after the firing procedures to improve the adhesion of the cement to the material. Grinding procedures should be followed by a “regeneration firing”, in order to increase the reliability of the Y-TZP material, while also keeping a high flexural strength

Tungsten Carbide

Tungsten Carbide - Processing and Applications, provides fundamental and practical information of tungsten carbide from powder processing to machining technologies for industry to explore more potential applications. Tungsten carbide has attracted great interest to both engineers and academics for the sake of its excellent properties such as hard and wear-resistance, high melting point and chemically inert. It has been applied in numerous important industries including aerospace, oil and gas, automotive, semiconductor and marine as mining and cutting tools, mould and die, wear parts, etc., which also has a promising future particularly due to enabling to resist high temperature and are extremely hard