DEVELOPMENT AND APPLICATION OF ON-MACHINE SURFACE MEASUREMENT FOR ULTRA-PRECISION TURNING PROCESS

Optical freeform components, featured with high functional performance, are of enormous demand in advanced imaging and illumination applications. However, the geometrical complexity and high accuracy demand impose considerable challenges on the existing ultra-precision freeform machining technologies. Surface measurement and characterisation become the key to further improving machining performance. In order to further increase the metrology availability and efficiency, a shift in the approach of surface metrology from offline lab-based solutions towards the use of metrology upon manufacturing platforms is needed. On-machine surface measurement (OMSM) will not only allow the assessment of manufactured surfaces just-in-time without transportation and repositioning, but also provide feedback for process optimization and post-process correction with consistent coordinate frame. In the thesis, a single point robust interferometer is integrated onto a diamond turning lathe to establish the metrology-embedded ultra-precision manufacturing platform. To extract a priori information for the subsequent OMSM, a theoretical and experimental study of surface generation was carried out for ultra-precision turning of optical freeform surfaces. With the proposed machining methodology and surface generation simulation, two freeform surfaces (sinusoidal grid and micro-lens arrays) were successfully fabricated using the slow tool servo technique. The machined topography of freeform surfaces was uniformly distributed and in agreement with simulated results. Since it operates in the manufacturing environment, the machine tool effects on the OMSM were comprehensively evaluated, including on-machine vibration test, machine kinematic error mapping and linearity error calibration. A systematic calibration methodology for single point OMSM was proposed. Both theoretical and experimental investigation have been conducted to prove the validity of the proposed calibration methodology and the effectiveness of OMSM. With the aid of OMSM, potential applications were explored to exploit the integration benefits to further enhance the ultra-precision machining performance. OMSM integration will increase the automation level of the manufacturing. As OMSM preserves the coordinate system between the machining and measurement, the process investigation can be carried out in a more deterministic manner. The effect of process parameters on the surface form errors was investigated for ultra-precision cylindrical turning process. An empirical model based on response surface methodology has been established and validated with the experimental results. Moreover, a corrective machining methodology was proposed to further improve the accuracy of diamond turned surfaces with OMSM. According to different correction tasks, corresponding OMSM data processing methods were presented. Profile and surface correction experiments were performed to validate the proposed corrective machining methodology and 40% improvement of surface accuracy was achieved

The Application of Zeeko Polishing Technology to Freeform Femoral Knee Replacement Component Manufacture

The purpose of this study was to develop an advanced 7-axis Computer Numerical Controlled (CNC) Polishing Machine from its successful original application of industrial optics manufacture into a process for the manufacture of femoral knee components to improve wear characteristics and prolong component lifetimes. It was indentified that the successful manufacture of optical components using a corrective polishing procedure to enhance their performance could be applied to femoral knee implant components. Current femoral knee implants mimic the natural shape of the joint and are freeform (no axis of symmetry) in nature hence an advanced CNC polishing machine that can follow the contours associated with such shapes could improve surface finish and conformity of replacement femoral knee bearing surfaces, leading to improved performance. The process involved generating machine parameters that would optimize the polishing procedure to minimize wear of materials used in femoral knee implant manufacture. Secondly a design of a Non-Uniform Refind B-Spline (NURBS) model for control of the Polishing Machine over the freeform contours of the femoral component. Completing the process involved development of a corrective polishing process that would improve form control of the components. Such developments would improve surface finish and conformity which are well documented contributors to wear and hence the lifeline of orthopaedic implants. By the means of comparison of this technique to that of a conventional finishing technique using pin-on-plate disc testing it was concluded that performance of the CNC polished components was an improvement on that of the conventional technique. In the case of form control their were slight indications through small decreases in peak to valley (PV) error that the process helped reduce form error and could increase the lifetime of femoral knee replacement components. The overall study provided results that indicate the the Zeeko process could be used in the application of polishing of hard-on-hard material combinations to improve form control without compromising surface finish hence improving lifetimes of the implant. The results have their limitations in the fact that the wear test performance was only carried out on orthopaedic implant materials using a pin-on-plate wear test rig. Due to the time limitations on the thesis it can be said that further analysis of correcting form without compromising surface finish on entire implant systems under full joint simulator testing which would provide mre realistic contitions would a more definitive answer be achieved

A gaussian process-based multi-sensor metrology system for precision measurement of freeform surfaces

Nowadays, precision freeform surfaces play an important role since they have superior performance and indispensable functionalities. Due to their geometrical complexity, high form accuracy and low surface roughness, precision freeform surfaces introduce a lot of research challenges in precision manufacturing and measurement processes. This is particularly true when the measurement is performed on traditional off-line single-sensor instruments such as white light interferometers (WLIs) and coordinate measuring machines (CMMs) whose measurement abilities are limited. For a single-sensor instrument, the measurement range and measurement resolution always need to strike a balance since the two terms appear to be contradictory. Moreover, when the workpiece is extremely large and error compensation procedure is needed to correct the form error of the workpiece, it is necessary to perform the measurement on machining facilities since repositioning error is unacceptable. However, off-line based measurement instruments cannot fulfil the in-situ measurement requirement. To address the above issues, this research firstly established a generic Gaussian process data modelling and image registration-based stitching method for the measurement of precision freeform surfaces based on traditional single-sensor surface measurement instruments using multiple measurement methods. With the proposed method, a dataset with a large measurement range and high resolution can be obtained. The proposed stitching method provides a turn-key solution for high dynamic range measurement using single-sensor instruments with a multiple measurement method. For multi-sensor instruments such as multi-sensor coordinate measuring machines (CMMs), this study proposes a Gaussian process-based data modelling and maximum likelihood data fusion method for the measurement of freeform surfaces for multi-sensor CMMs. The method utilizes an optical sensor such as laser sensor and a touch trigger probe mounted on the multi-sensor coordinate measuring machine for the measurement of freeform surfaces, and the measurement data are modelled using the Gaussian process modelling method. The combination of different kinds of sensors balances the measurement efficiency and accuracy since most optical sensors have a fast measurement speed and high density but low accuracy while contact sensors have an accurate measurement result but low efficiency. The measurement datasets from the laser sensor and touch trigger probe were fused with a maximum likelihood method so as to reduce the overall measurement uncertainty. To address the in-situ measurement issue, this thesis proposes an autonomous multi-sensor in-situ metrology system for high dynamic range measurement of freeform surfaces for precision machine tools. The system utilizes a laser scanner and a motion sensor together with a designed trajectory so as to perform in-situ measurement on the machining facilities. The proposed system is independent of the machining facilities which makes it extendable to a wide range of industrial applications. Based on the theory developed for the autonomous multi-sensor in-situ metrology system, a homogeneous multi-sensor in-situ measurement metrology system was developed equipped with a laser line sensor and laser point sensor. The laser line sensor provides high lateral resolution data while the laser point sensor gives accurate data. The measurement data from these two kinds of sensors are fused to obtain a more accurate result without losing the high lateral resolution. The present study has very large potential applications in industry. The successful development of the Gaussian process and image registration-based stitching method provides an important means for high dynamic range measurement, while the Gaussian process-based data modelling and maximum likelihood-based data fusion method establishes a generic measurement strategy for multi-sensor coordinate measuring machines so as to improve the measurement accuracy for precision freeform surfaces. The proposed in-situ multi-sensor high dynamic range measurement method and hence the homogeneous multi-sensor in-situ metrology system enable the measurement ability of machine tools so as to improve the efficiency and accuracy of the precision manufacture of complex freeform surfaces. The outcome of the research contributes significantly to the measurement science and technology, especially in the field of multi-sensor measurement and in-situ measurement of precision freeform surfaces

Ultra-high precision machining of rapidly solidified aluminium (RSA) alloys for optics

The advancement of ultra-precision is one of the most adaptable machining processes in the manufacturing of very complex and high-quality surface structures for optics, industrial, medical, aerospace and communication applications. Studies have shown that single-point diamond turning has an outstanding ability to machine high-quality optical components at a nanometric scale. However, in a responsive cutting process, the nanometric machinability of these optical components can easily be affected by several factors. The call for increasing needs of optical systems has recently led to the development of newly modified aluminium grades of non-ferrous alloys characterized by finer microstructures, defined mechanical and physical properties. To date, there has been a lack of sufficient research into these new aluminium alloys. In modern ultra-precision machining, the high demands for smart and inexpensive cutting tools are becoming more relevant in recent precision machines. In monitoring and predicting high-quality surface, cutting forces in single point diamond turning are believed to be as critical as other machining processes due to their potential effects on the quality of surface roughness. Undermining such an important factor is a compromise between the machining process's efficiency and the increased cost of production. Therefore, a comprehensive scientific understanding of the Nano-cutting mechanics is critical, particularly on modelling and analysis of cutting force, surface roughness, chip vii formation, acoustic emission, material removal rates, and molecular dynamic simulation of the rapidly solidified aluminium alloys to bridge the gap between fundamentals and industrial-scale application. The study is divided into three essential sections. First, the development of a force sensor. Secondly, investigation of the effect of cutting parameters (i.e., cutting speed, feed rate, and cutting depth) on cutting force, acoustic emission (AE), material removal rate (MRR), chip formation, Nose radius, and surface roughness (Ra), which play a leading role in the determination of machine productivity and efficiency of single-point diamond turning of rapidly solidified aluminium alloys. Thirdly, a 3-D molecular dynamic (MD) simulation of RSA 6061 is also carried out to further understand the nanometric mechanism and characterization of the alloy. The experiment was mainly conducted using Precitech Nanoform ultra-grind 250 lathe machines on three different advanced optical aluminium alloys materials; these are RSA 443, RSA 905, and RSA 6061.Thesis (PhD) -- Faculty of Engineering, the Built Environment and Information Technology, School of Engineering, 202

DEVELOPMENT OF A LOW COST PRECISION POLISHING MACHINE BASED ON PARALLEL KINEMATIC SYSTEM

The increasing demand on mass production of high precision parts, has pushed the precision manufacturing industry to develop reliable precision finishing processes such as Bonnet polishing to address market requirements. Indeed, the nature of the surface to be polished plays an important role in the design of a possible polishing machine. A gap within the research in polishing for precision industry needs has been identified. Small parts with <50mm x 50mm and possible freeform curvature containing small slopes cannot be polished with available bonnet polishing (BP) processes on market. This is caused by the tool head size and the tool holder being bigger than part curvature or the part itself. Although, the BP process has a huge potential for surface roughness improvement and form accuracy, it is generally seen in industry as an expensive solution for a non-deterministic finishing process. Therefore, this project has sought to develop a BP machine to cover the gap with an innovative and inexpensive design. In order to develop a machine which responded to the market expectations all possible requirements were listed from a customer point of view. Based on the requirement, a machine concept was produced. Market analysis helped to identify sub-systems of the machine. FEA analysis of the design was performed to check for stress distribution and displacement due to its own mass. Additional assembly parts are designed and a prototype of the machine was produced. The designed machine is tested for its ability as precision polishing machine. Flat surfaces of P20 tool steel were targets for polishing to nanometric surface finishes. Empirical experiments helped to identify parameters which influenced the surface roughness. Taguchi method were then used to optimise the parameters for better surface roughness. Optimum parameters conditions helped to reach less than 10 nm Ra systematically and repeatedly. The samples were also polished using re-circulating slurry techniques, and the obtained results were discussed. Further, pre polishing, Grolishing processes capable of improving surface roughness from ground finish to mirror like finish were developed for cost effective manufacturing procedures. The material removal was analysed to identify parameters capable of improving surface roughness over a step grolishing process. Two grolishing procedures were developed. Both processes produced nanometric range surface finishes. Other variations in results were compared and discussed. Although, machine axis has the ability to produce freeform movement, tool holders need to be improved to facilitate the identification of the distance between tool origin and workpiece origin. Therefore, a new spindle holder assembly is produced to hold the tool and an optical measurement device DRI used to evaluate accurately the distance separating the tool-workpiece origin and further align the workpiece inclination with respect to the machine axis. A CAD-CAM package is also developed to generate programme capable of performing freeform curvature

Ultra-high precision machining of rapidly solidified aluminium (RSA) alloys for optics

The advancement of ultra-precision is one of the most adaptable machining processes in the manufacturing of very complex and high-quality surface structures for optics, industrial, medical, aerospace and communication applications. Studies have shown that single-point diamond turning has an outstanding ability to machine high-quality optical components at a nanometric scale. However, in a responsive cutting process, the nanometric machinability of these optical components can easily be affected by several factors. The call for increasing needs of optical systems has recently led to the development of newly modified aluminium grades of non-ferrous alloys characterized by finer microstructures, defined mechanical and physical properties. To date, there has been a lack of sufficient research into these new aluminium alloys. In modern ultra-precision machining, the high demands for smart and inexpensive cutting tools are becoming more relevant in recent precision machines. In monitoring and predicting high-quality surface, cutting forces in single point diamond turning are believed to be as critical as other machining processes due to their potential effects on the quality of surface roughness. Undermining such an important factor is a compromise between the machining process's efficiency and the increased cost of production. Therefore, a comprehensive scientific understanding of the Nano-cutting mechanics is critical, particularly on modelling and analysis of cutting force, surface roughness, chip vii formation, acoustic emission, material removal rates, and molecular dynamic simulation of the rapidly solidified aluminium alloys to bridge the gap between fundamentals and industrial-scale application. The study is divided into three essential sections. First, the development of a force sensor. Secondly, investigation of the effect of cutting parameters (i.e., cutting speed, feed rate, and cutting depth) on cutting force, acoustic emission (AE), material removal rate (MRR), chip formation, Nose radius, and surface roughness (Ra), which play a leading role in the determination of machine productivity and efficiency of single-point diamond turning of rapidly solidified aluminium alloys. Thirdly, a 3-D molecular dynamic (MD) simulation of RSA 6061 is also carried out to further understand the nanometric mechanism and characterization of the alloy. The experiment was mainly conducted using Precitech Nanoform ultra-grind 250 lathe machines on three different advanced optical aluminium alloys materials; these are RSA 443, RSA 905, and RSA 6061.Thesis (PhD) -- Faculty of Engineering, the Built Environment and Information Technology, School of Engineering, 202

Frontiers in Ultra-Precision Machining

Ultra-precision machining is a multi-disciplinary research area that is an important branch of manufacturing technology. It targets achieving ultra-precision form or surface roughness accuracy, forming the backbone and support of today’s innovative technology industries in aerospace, semiconductors, optics, telecommunications, energy, etc. The increasing demand for components with ultra-precision accuracy has stimulated the development of ultra-precision machining technology in recent decades. Accordingly, this Special Issue includes reviews and regular research papers on the frontiers of ultra-precision machining and will serve as a platform for the communication of the latest development and innovations of ultra-precision machining technologies