Browsing by Author "Comley, Paul"

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    Brittle ductile transition during diamond turning of single crystal silicon carbide
    (Elsevier Science B.V., Amsterdam., 2013-02-28T00:00:00Z) Goel, Saurav; Luo, Xichun; Comley, Paul; Reuben, Robert L.; Cox, Andrew
    In this experimental study, diamond turning of single crystal 6H-SiC was performed at a cutting speed of 1 m/sec on an ultra precision diamond turning machine (Moore Nanotech 350 UPL) to elucidate the microscopic origin of ductile-regime machining. Distilled water (pH value 7) was used as a preferred coolant during the course of machining in order to improve the tribological performance. A high magnification scanning electron microscope (SEM) (FIB- FEI Quanta 3D FEG) was used to examine the cutting tool. A surface finish of Ra 9.2 nm, better than any previously reported value on SiC was obtained. Also, tremendously high cutting resistance was offered by SiC resulting in the observation of significant wear marks on the cutting tool just after 1 Km of cutting length. It was found out through a DXR Raman microscope that similar to other classical brittle materials (silicon and germanium etc.) an occurrence of brittle-ductile transition is responsible for the ductile-regime machining of 6H-SiC. It has also been demonstrated that the structural phase transformations associated with the diamond turning of brittle materials which is normally considered as a prerequisite to ductile-regime machining, may not well be realized during machining of polycrystalline materials, yet, ductile-regime exploitation is possible.
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    A comparison of polymer film and glass collectors for concentrating solar power
    (Elsevier, 2014-06-02T00:00:00Z) Sansom, Christopher L.; Comley, Paul; Bhattacharyya, Debabrata; Macerol, Nastja
    This paper describes work to compare the optical properties and surface texture of glass and polymer film collectors. We also present the results of experiments designed to simulate collector cleaning processes (both contact and non-contact), and the degradation of glass and polymer reflecting surfaces owing to sand and dust abrasion. Finally we present initial results on the applicability of anti-soiling and self-cleaning coatings on glass and polymer film collector surfaces. Measurements, which include specular and hemispherical reflectance, surface roughness, and electron microscopy, indicate the excellent performance of currently available polymer film in terms of its optical performance and robustness in comparison with traditional glass collectors in CSP applications.
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    Form measurement and durability of mirror surfaces for concentrating solar power applications
    (Cranfield University, 2014-11) King, Peter; Sansom, Christopher L.; Comley, Paul
    Concentrating solar power systems currently have a high capital cost when compared with other energy generating systems. The solar energy is captured in the form of thermal energy rather than directly electrical, which is attractive as thermal energy is easier and currently cheaper to store in large amounts. It is also used directly as processing heat including desalination and water purification. For the technology to compete against other generating systems it is important to reduce the electrical energy cost to the $0.05 per kilowatt-hour level. One of the significant capital costs is the solar field, which contains the concentrators. To reduce the cost of this field, novel constructions and improvements to the durability and lifetime of the concentrators are required. Techniques for characterising the shape, durability and optical properties of such novel mirrors are the focus of this thesis. The thesis describes the development and validation of an inexpensive, highly portable photogrammetry technique, which has been used to measure the shape of large mirror facets for solar collectors. Photogrammetry has demonstrated its versatility and portability by successful measurements across concentrating solar power sites globally. The accuracy of the technique has been validated to show a measurement capability of better than 100 µm using a large coordinate measuring machine. Measurements performed on novel thin glass mirrors and their comparison with conventional thick glass mirrors are presented, showing that the increased flexibility of thin mirrors is an important consideration during installation, but that it is possible for such novel mirrors to perform to the same level. ...[cont.]
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    Grinding metre scale mirror segments for the E-ELT ground based telescope
    (Technische Rundschau, Hallwag Publishers; 1999, 2011-04-21T00:00:00Z) Comley, Paul; Morantz, Paul; Shore, Paul; Tonnellier, Xavier
    The next generation of ground based telescopes require many hundreds of metre scale off-axis mirrors. In this paper the grinding of a 1.45m scale Zerodur® mirror segment for the European Extremely Large Telescope (E-ELT) is introduced. Employing an R-theta grinding mode with a multi stage grinding process material removal rates of up to 187.5mm3/s are achieved, whilst typically removing up to 1mm depth of material in total. Results show a RMS form error of <1μm, with subsurface damage <10μm, and a production cycle time under 2
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    Grinding processes and their effects on surface integrity
    (Cranfield University, 2005-03) Comley, Paul; Corbett, John; Stephenson, David J.
    The introduction of high performance grinding machines in combination with the latest superabrasive technology has the potential to impact significantly on existing process chains. The aim of the research was to look at both the high and low rate removal grinding processes and their effects on the surface integrity, as a means to exploit the above technologies. A major objective was to determine the feasibility of High Efficiency Deep Grinding (HEDG) in cylindrical plunge grinding. HEDG is a high speed removal process which differs from conventional forms of grinding in that it uses large depths of cut together with high feedrates. Together, these changes affect the thermal energy partitioning within the work zone. Through this work an understanding of the process conditions enabled the development of this process, such that prevention of thermal damage to the finished workpiece surface is achievable. At the opposite extreme to the high material removal rates of HEDG, kvdrk was carried out in the high precision finish grinding regime. Developments *ere undertaken to look at the implementation of a modified path into the normal cylindrical plunge grinding action, in a process referred to as Superfinish Grinding. The aim of this process being to demonstrate an improvement to the surface texture primarily through a reduction in grinding directionality. Surface integrity is an important consideration in the development of any grinding process. Damage as a result of grinding is predominately of a thermal nature and results in changes to the material properties in the near surface region. One such change is the residual stress, which was measured using Barkhausen Noise intensity instrumentation, which provided a reliable early indication to a build up in thermal energy. Developments in thermal modelling supported by temperature measurements provided a better understanding of the HEDG regime. The model employed new energy partitioning theories together with circular arc modelling of conditions along the contact length. A model was derived to predict the surface finish produced with the Superfinish Grinding approach, this again provided an increased understanding of the grinding process. Industrial trials have shown how HEDG can be implemented on standard production machine tools for the cylindrical plunge grinding of crankshaft components. The process demonstrated the potential for improved surface integrity, whilst maintaining surface finish and form accuracy. The same grinding machine was also used to generate high quality surfaces using a Superfinish Grinding process. Roughness values of the order of 0.11um RQ were routinely obtained exhibiting reduced levels of grinding directionality. Thus, using a single machine tool and a single set-up, exceptionally high stock removal rates are achievable in a roughing cycle followed by superfinishing to generate the required surface characteristics and profile.
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    Photogrammetry for concentrating solar collector form measurement, validated using a coordinate measuring machine
    (MDPI, 2019-12-25) King, Peter; Sansom, Christopher L.; Comley, Paul
    Concentrating solar power systems currently have a high capital cost when compared with other energy generating systems. The solar energy is captured in the form of thermal energy rather than direct electrical, which is attractive as thermal energy is more straightforward and currently more cost-effective to store in the amounts required for extended plant operation. It is also used directly as industrial process heat, including desalination and water purification. For the technology to compete against other generating systems, it is crucial to reduce the electrical energy cost to less than $0.10 per kilowatt-hour. One of the significant capital costs is the solar field, which contains the concentrators. Novel constructions and improvements to the durability and lifetime of the concentrators are required to reduce the cost of this field. This paper describes the development and validation of an inexpensive, highly portable photogrammetry technique, which has been used to measure the shape of large mirror facets for solar collectors. The accuracy of the technique has been validated to show a whole surface measurement capability of better than 100 mm using a large coordinate measuring machine. Qualification of facets of the MATS plant was performed during its installation phase, giving results of the shape, slope and intercept errors over each facet.
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    Poster presentation: Ultra-precision control of a reel-to-reel process
    (Cranfield University, 2017-11-08 08:41) Graham, Andrew; Morantz, Paul; Comley, Paul
    Poster presentation of research work at the EPSRC Centre for innovative manufacturing in ultra precision.
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    Precision grinding for rapid fabrication of segments for extremely large telescopes using the Cranfield BoX
    (International Society for Optical Engineering; 1999, 2012-07-11) Tonnellier, Xavier; Morantz, Paul; Shore, Paul; Comley, Paul; Eli, Atad-Ettedgui; Dietrich, Lemke
    An ultra precision large optics grinding machine, BoX®, was developed and produced at Cranfield University. BoX® offers a rapid and economic solution for grinding large off-axis aspherical and free-form optical components. Grinding high accuracy surfaces with low subsurface damage reduces subsequent polishing time. This efficient grinding process provides the capacity to grind 1.5 m parts. This paper presents an analysis of Astrositall® optical ground parts: a hexagonal 84 m radius of curvature mirror of 1 m across corners and an off-axis 350 mm diameter mirror. The 1 m hexagonal part is representative of segments under study for making extremely large telescope (ELT) segmented mirrors. The second part was machined off-axis to demonstrate free-form fabrication capability. These operations demonstrate the scalability of the rapid grinding process developed for large free-form optics. The use of an error compensation procedure improved an initial ground form accuracy to +/- 1 μm p-v over 1 metre surface. The results highlighted the effect of grinding parameters and machine dynamics on form accuracy and fabrication t
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    Predicting the effects of sand erosion on collector surfaces in CSP plants
    (Elsevier, 2015-06-05) Sansom, Christopher L.; Comley, Paul; King, Peter; Almond, Heather; Atkinson, C.; Endaya, E.
    This paper presents a methodology to predict the optical performance and physical topography of the glass collector surfaces of any given CSP plant in the presence of sand and dust storms, providing that local climate conditions are known and representative sand and dust particles samples are available. Using existing meteorological data for a defined CSP plant in Egypt, plus sand and dust samples from two desert locations in Libya, we describe how to derive air speed, duration, and sand concentrations to use within the Global CSP Laboratory sand erosion simulation rig at Cranfield University. This then allows us to predict the optical performance of parabolic trough collector glass after an extended period by the use of accelerated ageing. However the behavior of particles in sandstorms is complex and has prompted a theoretical analysis of sand particle dynamics which is also described in this paper.
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    Production of electronics and photovoltaics using a reel-to-reel process
    (European Society for Precision Engineering and Nanotechnology, 2016-06-30) Graham, A.; Morantz, Paul; Comley, Paul
    Reel to reel manufacturing is a mature technology that involves the passing of a flexible substrate or web continuously through one or more processes. The web is typically much longer than it is wide, and the width in turn is much greater than its thickness. It is a continuous process that results in high output at a low unit cost when compared with other production methods. Historically this has included newspaper printing and textile manufacture, but more recent research is being conducted in developing printed electronics, such as solar cells (Organic Photo-Voltaic or OPV), and wearable tech and flexible screens (Polymer LEDs or PLEDs). These devices consist of up to five layers, with a separate printing or coating process needed for each. Greater accuracy is necessary than for traditional industries and advances are required in three areas: control of the web; measurement and registration of the printed web; and flexible semi-conductor materials. In this paper we present a new methodology to improve printing accuracy by combining an advanced metrology system with an innovative process design.
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    Robotic polishing of large optical components
    (Cranfield University, 2014-08) Chen, Sulei; Tonnellier, Xavier P.; Comley, Paul
    Lightweight space mirrors have been widely used in earth observation and astronomy applications. Many organizations and companies, such as NASA in America, ESA in Europe, SSTL in UK as well as CASC in China, have spent a lot of money and effort on researching new materials for larger size space mirrors to meet both the payload weight constraints of launch and the increased advanced manufacturing process demanded for higher observations quality. This project is aimed at robot neutral polishing of lapped, ground and polished optical substrates using an industrial FANUC robot system. The project focused on three main fields which were: robot polishing with polyurethane tool and cerium oxide, pitch polishing with pitch tool and cerium oxide, as well as polishing of a 400mm ULE component. The polishing process targets were to achieve: 1) a surface roughness (Ra) of 10 nm and a surface profile (Pt) of 6 µm and 2µm on lapped and ground substrates respectively with polyurethane based tools and 2) a surface roughness (Ra) of 2nm with a surface profile (Pt) unchanged on robot neutral polished substrates using pitch based tools. This thesis comprises four main sections: a literature review, an experimental implementation, metrology and analysis, and the final conclusions. The experiment results measured with the metrology equipment selected were analysed. Conclusions of the relationship between the polishing performance of a specific sample and the selected polishing tool, polishing slurry, tool pressure, polishing time and other parameters were drawn. Results obtained from robot neutral polishing were surface roughness (Ra) of 8-10nm and surface profile (Pt) of 6µm for 100mm square lapped and ground parts. The process scalability was demonstrated from robot neutral polishing in 45hours, a 400mm square ground component from a surface roughness (Ra) of 200nm to 10nm. There is additional work to be implemented in the future, such as the development of robot pitch polishing of robot neutral polished parts to achieve 2nm Ra.
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    Thermal Performance of a Multi-Axis Smoothing Cell
    (Cranfield University, 2011-05) Georgiou, Charalambos Andrew; Comley, Paul; Shore, Paul
    Multi Axis Robots have traditionally been used in industry for pick and place, de-burring, and welding operations. Increasing technological advances have broadened their application and today robots are increasingly being used for higher precision applications in the medical and nuclear sectors. In order to use robots in such roles it is important to understand their performance. Thermal effects in machine tools are acknowledged to account for up to 70% of all errors (Bryan J. , 1990) and therefore need to be considered. This research investigates thermal influences on the accuracy and repeatability of a six degree of freedom robotic arm, which forms an integral part of a smoothing cell. The cell forms part of a process chain currently being developed for the processing of high accuracy freeform surfaces, intended for use on the next generation of ground based telescopes. The robot studied was a FANUC 710i/50 with a lapping spindle the end effector. The robot geometric motions were characterised and the structure was thermally mapped at the latter velocity. The thermal mapping identified the key areas of the robot structure requiring more detailed analysis. Further investigation looked into thermal variations in conjunction with geometric measurements in order to characterise the robot thermal performance. Results showed thermal variations of up to 13ºC over a period of six hours, these produced errors of up to 100μm over the 1300mm working stroke slow. Thermal modelling carried out predicted geometric variation of 70μm to 122μm for thermal variations up to 13ºC over a period of six hours. The modelling was 50% to 75% efficient in predicting thermal error magnitudes in the X axis. With the geometric and modelling data a recommendation for offline compensation would enable significant improvement in the robots positioning capability to be achieved.