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Title:Development of temperature and feed rate controllers for a hybrid thermoplastic forming of surgical blades from bulk metallic glass
Author(s):Dancholvichit, Nattasit
Advisor(s):Kapoor, Shiv
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):bulk metallic glass, feedback control, fuzzy logic control, ARX model, thermoplastic, linear motors, blade sharpness
Abstract:Bulk metallic glasses (BMG) are multi-component alloys that have an amorphous atomic structure. This new family of alloys exhibits a unique combination of high strength/hardness and high elastic limit, which is ideal for the formation and retention of a sharp edge. At a high temperature above glass transition temperature, BMG transitions to a supercooled liquid regime, so that thermoplastic forming process can be applied. BMG has therefore been identified as an alternative material for precision surgical blades with the potential of tremendous cost savings. Zhu [8] has recently developed a controller of the testbed that successfully manufactures high-quality sharp edge surgical blades from BMG in terms of surface roughness, straightness and edge radius. However, the controllers employed in the testbed lack repeatability and the process is not predictable and consistent due to large errors of the controlled process settings including temperature and feed rate. This error is critical to the BMG thermoplastic forming since both parameters can significantly affect the type of deformation of BMG, which ultimately result in blade edge shape. In this research, temperature control, using Fuzzy logic is implemented along with Auto-Regressive eXogenous, ARX model to the test bed, which can maintain the steady state temperature within the range of ± 2.5 K. In terms of the thermoplastic drawing process, a cascade P-PI controller is deployed. This controller improves the consistency of the position tracking performance while controlling the feed rate. Both precise temperature and feed rate control can lead to more consistent surgical blades manufacturing. Experiments have shown similar or better results of multi-facet blade geometries manufactured by Zhu [8] with type 3 deformation process settings. The blade samples are successfully manufactured with surface roughness of 18.9 nm with a standard deviation (SD) of 3.78 nm. The straightness of the blade is on the average of 18.9 nm with a SD of 3.78 nm. The average edge radius is found to be 25.7 nm with a SD of 6.3 nm. Further, the position, velocity, and force profiles during the blade manufacturing are found to be consistent with better tracking. As a result, the process parameters can be predicted with certainty to manufacture blade edges with less defects.
Issue Date:2018-04-26
Rights Information:Copyright 2018 Nattasit Dancholvichit
Date Available in IDEALS:2018-09-04
Date Deposited:2018-05

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