Design and development of an on-machine profile measurement system for an ELID grinding machine

Master'sMASTER OF ENGINEERIN

Modeling and analyses of electrolytic in-process dressing (ELID) and grinding

Ph.DDOCTOR OF PHILOSOPH

Fundamental Studies on Wheel Wear in ELID Grinding

Ph.DDOCTOR OF PHILOSOPH

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

Elid superfinishing of spherical bearings

Driven by a requirement to extend the lifespan of self-aligning lined spherical bearings, this research investigates the use of Elid (electrolytic in-process dressing) as a method of improving ball surface finish. Elid is a continuous and self-regulating electrochemical dressing process that modifies the surface of a grinding, lapping, or superfinishing wheel. It provides improved grit protrusion, impedes wheel loading / glazing and promotes effective cutting. The characteristics of the newly-developed Elid superfinishing process are in many ways fundamentally different to conventional superfinishing. The main difference is that the use of super-abrasives prevents the wheel from self-sharpening; the normal mechanism by which dulled conventional abrasives are removed and a wheel’s surface refreshed. Because the wheel’s performance and condition is continually maintained inprocess by the Elid system, metal resin bonded (MRB) wheels containing very small super-abrasives can be used. It is the utilization of these fine abrasives (30 to 0.12 μm) that enables surface roughness values below 5 nm Ra to be consistently produced on the spherical surface of corrosion-resistant steel balls. This research provides an in-depth understanding of the Elid spherical superfinishing process; investigating the most effective use of the Elid system, wheel dressing requirements and process performance. Optimisation is provided in terms of evaluating the critical operating parameters, the most effective superfinishing cycle and the implications to the complete ball production chain. A range of techniques are used to evaluate processing performance and ball output quality. These include in-process monitoring of Elid and wheel spindle power levels, analysis of wheel condition, rates of ball surface generation and material removal, ball finish and form. Although predominantly concentrated on corrosion-resistant steel, testing is also conducted on titanium and various ball coatings. In investigating various ways of using the Elid system, this work considers electrodischarge truing, pre-process dressing, Elid 1, Elid 2, Elid 3, and Elid combined with electrolytically assisted superfinishing. The initial process solution of Elid 3 (electrodeless) superfinishing provides the capability of working on all standard size balls, however the dressing system lacks stability. The development of a fixturing system that has a small separate electrode enables Elid 1 (conventional) to be used on the majority of ball sizes. Elid 1 allows more aggressive and consistent dressing, a faster rate of ball material removal and thus a substantially reduced processing time. Results with a #12,000 wheel show that surface quality is vastly improved through the use of Elid whilst maintaining current production standards of form accuracy. Surface finishes of 2nm Ra are achieved, which is an order of magnitude better than balls currently produced using barrelling / polishing. Processing times are equivalent or faster when using Elid 1. Alternatively, consistently sub 10 nm Ra finishes can be reached with a #2,000 wheel using Elid 2 (interval dressing). Generally MRB-CBN wheels provide a more effective carbide cutting action than conventional superfinishing wheels. Controlling wheel condition and achieving full and even ball to wheel conformity are the two most significant contributory factors to the success of Elid spherical superfinishing. Insufficient control of these factors results in poor output quality. Monitoring of wheel spindle and Elid power usage provides useful information in assessing the condition of the wheel and identifying potential problems. High spindle power correlates with fast material removal and is a result of high loads and a free cutting action. Elid processing can be employed for improving surface finish after the conventional honing stage, or after cylindrical grinding for improving both ball form and finish.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Precision grinding for rapid manufacturing of large optics

Large scale nuclear fusion and astronomy scientific programmes have increased the demand for large freeform mirrors and lenses. Thousands of one metre class, high quality aspherical optical components are required within the next five to ten years. Current manufacturing process chains production time need to be reduced from hundred hours to ten hours. As part of a new process chain for making large optics, an efficient low damage precision grinding process has been proposed. This grinding process aims to shorten the subsequent manufacturing operations. The BoX R grinding machine, built by Cranfield University, provides a rapid and economic solution for grinding large off-axis aspherical and free-form optical components. This thesis reports the development of a precision grinding process for rapid manufacturing of large optics using this grinding mode. Grinding process targets were; form accuracy of 1 m over 1 metre, surface roughness 150 nm (Ra) and subsurface damage below 5 m. Process time target aims to remove 1 mm thickness of material over a metre in ten hours. Grinding experiments were conducted on a 5 axes Edgetek high speed grinding machine and BoX R grinding machine. The surface characteristics obtained on optical materials (ULE, SiC and Zerodur) are investigated. Grinding machine influence on surface roughness, surface profile, subsurface damage, grinding forces and grinding power are discussed. This precision grinding process was validated on large spherical parts, 400 mm ULE and SiC parts and a 1 m Zerodur hexagonal part. A process time of ten hours was achieved using maximum removal rate of 187.5 mm 3 /s on ULE and Zerodur and 112.5 mm 3 /s on SiC. The subsurface damage distribution is shown to be "process" related and "machine dynamics" related. The research proves that a stiffer grinding machine, BoX, induces low subsurface damage depth in glass and glass ceramic.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Исследования пластичного режима резания хрупких материалов (обзор)

Рассмотрены теоретические и экспериментальные исследования пластичного режима резания хрупких материалов (полупроводников, керамики и стекла). Пластичный режим резания основан на осуществлении фазовых переходов под давлением в обрабатываемом материале с последующим срезом трансформированного аморфного слоя, что позволяет избежать образования трещин. Рассмотрены работы по изучению фазовых переходов в хрупких материалах при индентировании, царапании, трении и резании. Показано, что глубина резания, радиус округления кромки резца, толщина формируемой стружки, угол наклона режущей грани резца, кристаллографическая ориентация обрабатываемого материала и алмазного инструмента, тип смазочно-охлаждающей жидкости являются определяющими параметрами для реализации пластичного режима резания.Розглянуто теоретичні та експериментальні дослідження пластичного режиму різання крихких матеріалів (напівпровідників, кераміки та скла). Пластичнийрежим різання базується на здійсненні фазових переходів під тиском в оброблюваному матеріалі з подальшим зрізанням трансформованого аморфного шару, що дозволяє уникнути утворення тріщин. Розглянуто роботи з вивчення фазових переходів у крихких матеріалах при індентуванні, дряпанні, терті і різанні. Показано, що глибина різання, радіус округлення різальної кромки різця, товщина стружки, кут нахилу ріжучої грані різця, кристалографічна орієнтація оброблюваного матеріалу і алмазного інструменту, тип мастильно-охолоджувальної рідини і деякі інші параметри є визначальними для реалізації пластичного режиму різання.Theoretical and experimental studies of ductile regime cutting of brittle materials (semiconductors, ceramics and glass) were considered. The ductile mode cutting is connected with implementation high-pressure phase transformations that occur in the machined brittle materials with following removal of the transformed amorphous layer, which permits to avoid cracking. The investigations of phase transformation in brittle materials at indentation, scratching, friction and cutting were reviewed. It is shown that the cutting depth, the tool cutting edge radius, the undeformed chip thickness, the tool rake angle, crystallographic orientation of the machined material and the diamond tool, the cutting lubricants and some others parameters are critical for maintaining the ductile mode

Wear-adaptive optimization of in-process conditioning parameters during face plunge grinding of PcBN

Polycrystalline cubic boron nitride is a very hard material. Machining of this material is performed by grinding with diamond tools. Due to its high hardness, grinding tools are subjected to severe microscopic and macroscopic tool wear. This wear leads to short tool life and results in high effort in conditioning the abrasive layer. Contrary to the usual conditioning of diamond grinding wheels with diamond dressing tools, this study investigates a conditioning process based entirely on the use of white corundum cup rolls. These conditioning tools allow the in-process face plunge conditioning of vitrified bond diamond grinding tools. The circumferential speed of the conditioning tool and the average grain diameter of the corundum are identified as the main factors influencing the topography of the generated grinding layer. To describe the performance of the conditioning process, a specific conditioning removal rate Q′sd is derived. This parameter represents a cumulated variable that allows a comparison of different conditioning strategies. It is shown that an increase in Q′sd significantly counteracts microscopic wear on the abrasive layer. Therefore, optimized process parameters enable the process of in-process conditioning to significantly reduce wear on the grinding tool without increasing the process time or the non-productive time