Performance and Wear Behaviour of Diamond Fibre Grinding Wheels when Grinding Glass

Diamond coated fibres have been produced by a hot filament CVD technique, where the surface of the fibres has a faceted structure making them suitable for use as an abrasive medium. Grinding trials to determine the performance of a metal bonded diamond fibre grinding wheel have been carried out using a ‘state of the art’ machining centre developed for the high precision ductile regime grinding of optics. Further work has been undertaken using a single fibre placed radially in a titanium disc to assess wear. Ductile ground surfaces were produced in BK7 glass with a surface roughness figure of 70nm Ra, and less than 2μm sub-surface damage. The wear behaviour of the single fibre mounted in a disc wheel was monitored. Measurements showed that the initially sharp leading edge broke down to form a chamfered wear face, the profile produced by the fibre remaining similar. Diamond fibre grinding wheels have been shown to be capable of ductile grinding. These initial trials suggest that diamond fibres have the potential for longer wheel life, when grinding in the ductile region, compared with existing resin bond wheels. Introduction Diamond fibres are produced by a CVD technique in which a mixture of 0.85% methane in hydrogen gas is passed over a wire at 900°C [1,2]. Diamond is deposited onto the wire and the resulting crystal structure is shown in Fig. 1. This clearly shows facets, which suggests that these fibres can be used in an abrasive machining process. Fig. 1 View of Diamond Fibre showing Facets Tests have been carried out using diamond fibres of 150 m diameter, formed on a tungsten wire of 50 m diameter. A single fibre was embedded in a titanium matrix, with the fibre aligned radially. Earlier tests have shown that a diamond fibre can cut glass in a ductile manner and the ductile to brittle transition has been investigated [3]. Under these conditions the wear of a single fibre was Key Engineering Materials Online: 2004-02-15 ISSN: 1662-9795, Vols. 257-258, pp 245-250 doi:10.4028/www.scientific.net/KEM.257-258.245 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,19:19:40) high. This current paper presents the results of an analysis of the wear of a single fibre, when the removal rate is constrained to be always in the ductile mode. For the next stage of grinding trials a metal bonded grinding wheel with randomly oriented diamond fibres was manufactured. Tests were carried out on a ‘state of the art’ machining centre – Nanocentre – which was developed for the high precision ductile regime grinding of optics [4]. The aim was to evaluate the performance of the newly developed wheel against conventional resin bond grinding wheels typically used for the production of precision optics by ductile grinding. Experimental Conditions The single fibre was mounted radially in a 40mm diameter titanium disc. The periphery of the disc was subjected to a hydrofluoric acid etch in order to expose the cutting surface of the diamond fibre. The disc was mounted in the chuck of an air bearing spindle. Six separate tracks were ground into a silica glass specimen, the test conditions being given in Table 1. Table 1 Test Conditions for Diamond Fibre Wear Tests Wheel speed 10,000 rpm Feed rate 5 2m/s Depth of cut 1 2m Length of traverse 500 μm No of passes 6 The metal bonded wheel was mounted onto the Nanocentre and initially trued using an electroplated diamond-forming disc, with the set-up as shown by the image on the left in Fig. 2. Grinding was carried out as shown by the right image in Fig.2. Fig. 2 Truing and Grinding Set-up on Nanocentre Parameters are given in Table 2 for both the truing and grinding operations. Water based coolant was used in both cases. Table 2 – Truing & Grinding Parameters for Nanocentre Truing Grinding Grinding Wheel 3600-4800rpm Grinding Wheel 900rpm Workhead 60-100rpm DOC 5-10μm Truing Wheel 5000rpm Rough Grind Feed-rate 0.1-0.4mm/s DOC 1μm DOC 10μm Finish Grind Feed-rate 0.05mm/s 246 Advances in Abrasive Technology VI