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Title: The Machining of Polymers
Author: Patel, Yatish
ISNI:       0000 0004 2678 2418
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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Machining is a non-linear process and involves the consideration of variables such as inelasticdeformation, high temperatures and contact conditions. This thesis focuses on investigating thecontact conditions between cutting tools and polymeric materials during orthogonal cutting. Atest rig has been developed to allow cuts to be taken from a rectangular workpiece, such that therake angle (the angle of inclination of the tool surface) can be varied. In this work the rake angle was varied from -20o to 30o, and the cutting was performed at ratesof 0.01ms-1 and 0.1ms-1 on PMMA, nylon 4/6 and nylon 6/12. As part of a round robininvestigation, tests were also performed on HIPS, ABS and LLDPE.The experimental method developed required the measurement of forces in two directions (thedirection of cutting, Fc and transverse to the direction of cutting, Ft). The rig allowed for thecareful control of the depth of cut, h. After each cut, the thickness of the off-cut chip hc wasalso measured. A series of cuts were taken at depths varying between the range of 0.02mm to 0.25mm and theforces were measured. A cutting theory has been applied to the experimental data to determinethe fracture toughness Gc, and the yield stress ?Y of the material. The Coulomb friction ? andan adhesion term, Ga representing sticking at the tool-chip interface, were also deduced. Independent fracture mechanics tests were performed at a range of temperatures and rates on thedifferent polymers. Tensile tests were also performed, to compare standard values to thematerial parameters determined in cutting. The values of Gc and ?Y deduced were independentof the rake angle however, ? and Ga were not. The calculated values of Gc were typicallywithin 5% of the standard values however, ?Y was found to be up to 5 times higher. Theexistence of work hardening is believed to be the cause of these elevated values. The cutting analysis was also applied to some previously published metal cutting data andproduced constant values of Gc.
Supervisor: Blackman, Bamber ; Williams, J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral