الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Computer numerically controlled (CNC) multi-pass conventional spinning process is considered state-of-the-art in many modern industrial applications such as aerospace, automotive, chemical, petroleum and defense industries. Critical components including jet engines, large scale tanks, pressure vessels, propulsion nozzles, blowers, fans, aerospace bearing cages, and turbine engines are being produced using multi-pass conventional spinning. However, a large research lag exists behind these technological advances in terms of quality and performance measures of the spun components due to the high flexibility of the process. Geometrical and dimensional accuracy of the spun parts besides the surface finish are demanding requirements for the operational functions of important mechanical components. Residual stresses, microstructure evolution and hardness affect the service life and mechanical performance of high-pressure vessels and jet engines. This investigation is based on building a new CNC spinning machine by retrofitting of a traditional center lathe and using it in performing extensive experimental study to reveal the effect of process variables on the spun part quality characteristics including thickness reduction, springback, surface finish, roundness, cylindericity, formed cup height, hardness and microstructure. The retrofitting process involved preliminary static acceptance testing of the center lathe followed by selection of actuators (motors) and sensors, establishing the control circuits using motor drives and a CNC controller integrated with software to generate the code required to generate the spinning tool path. Some mechanical components were added to the lathe to perform the spinning process such as the roller, mandrel, and sheet holder. Calibration of the displacement axes was conducted for accurate tool paths and mechanical system errors such as backlash in power screws were considered and treated in the control system. The machine performance was verified experimentally against the published research data. Two series of experiments were designed and analyzed statistically using Design Expert 7 software and conducted on the CNC retrofitted spinning machine using the involute tool path on pure aluminum sheet blanks. The first was a screening experiment based on six factors namely, feed ratio, mandrel speed, sheet thickness, number of spinning passes, spinning ratio, and lubrication to determine the most significant process parameters. Based on the screening experiment results, a full factorial experiment was carried out in order to improve the quality in terms of both geometrical accuracy and productivity. Finite element (FE) simulations were employed using the commercial software ABAQUS/CAE 6.13 under variable coefficient of friction to predict the residual stresses and geometrical characteristics particularly springback at higher feed ratios than that used in the experimental work to assure higher productivity for large scale spun components. The finite element analysis was based on explicit codes for the spinning process and implicit codes for the relaxation time after processing. Although, the incremental nature of this sheet metal forming process and the localized plastic deformation made it challenging to control the geometrical accuracy and mechanical performance of the spun parts during both the experimental and numerical studies, better quality and performance levels were achieved at low friction (under lubricated condition) using relatively large number of spin-forming passes (10 passes) and a feed ratio of 1 mm/rev. implying reasonable productivity. Spinning ratio had a striking effect on all quality characteristics and is preferred to be small as possible. Interesting relationships among wall thinning, microstructure, and hardness were revealed. Correlations found between springback and both wall thinning and out-of-roundness are critical contributions of this study. The major contributions of this study include low cost CNC upgrading solution of older machine tools to improve both quality and productivity which is beneficial for the research community and manufacturers especially in developing countries like Egypt. Secondly, bridging many research gaps in the geometrical accuracy of spun products and the effect of critical parameters such as spinning ratio, and number of passes. Additionally, lubrication proved to have significant impact on enhancing both the quality and productivity of spun parts at the same time. Effect of wall thinning during the process on microstructure, hardness and springback was an original finding of this research as well as revealing the dependence of geometrical accuracy on the amount of springback. Finally, prediction of residual stresses in the spun cups with their controlling parameters is an originality aspect of this study.