Performance evaluation of WC-12wt%Co as grinding wheel abrasive material by machining a titanium alloy

Enever, Anton Alexander (2016-03)

Thesis

ENGLISH ABSTRACT: Grinding has been the most common machining process for material removal in manufacturing for many decades. The process originated from the realization that harder materials have the ability to abrasively alter the geometry and surface finish of softer materials. It was originally used in construction of buildings by abrasively forming limestone building bricks into desired shapes and sizes. This process has evolved over time to the high precision manufacturing industries of the modern era. High quality and high precision parts are manufactured with the use of grinding wheels, from rough part forming or part cutting to precision automotive engine components such as cam shafts. Most abrasives in modern grinding processes have been developed for general applications, while others are intended for specialised applications. The use of tungsten carbide as abrasive for both general and specialised grinding wheels is not generally implemented in industrial applications or used in published research work. This carbide falls in the refractory group of materials. When it is mixed and sintered with a ductile metal such as cobalt, molybdenum or nickel, its classification changes to a cemented carbide or cermet (ceramic metal). The amount of metal incorporated in a cermet mainly influences the ductility and transverse rupture strength. A metal content of about 12 wt% (12 weight %) is roughly the midway between a hard and brittle and a ductile cermet, giving tungsten carbide a unique hardness to ductile ratio. The metal that works best with tungsten carbide is cobalt, thus producing the cermet WC-12wt%Co. This specific cermet is commonly used as the base material for machining tools (for lathes and milling machines) due to its high hardness to toughness ratio that is needed for machining hard metals such as tool steels or titanium alloys. The base WC-12wt%Co material can be used as is for machining, but it is commonly coated with layers of other high wear resistant materials (such as titanium nitride, TiN, or titanium carbo-nitride, TiCN). This study focuses on the custom manufacture of a grinding wheel containing WC-12wt%Co as abrasive material, bonded together by an epoxy resin binder. This type of grinding wheel is not in use in industrial applications and must thus be specially designed and produced. The resin is used as binder, which is the case for many industrially implemented grinding wheels, to ease the production process and make it safer. The grinding wheels that were produced in this study are the smaller variant called mounted points. The performance of these mounted points was determined by the grinding of a titanium alloy and measuring the rate of wear, the surface finish the points produce on the titanium alloy and the surface hardness of the alloy.

AFRIKAANSE OPSOMMING: Die slyp proses is die mees algemene bewerkingsproses vir die verwydering van materiaal in vervaardigingsprosesse vir baie dekades. Die proses het ontstaan uit die besef dat harder materiale die vermoë het om die geometrie en oppervlakafwerking van sagter material te verander deur slyping. Dit was oorspronklik gebruik in die konstruksie van geboue deur slyp vorming van kalksteen boustene in die benodigde groottes en vorms. Hierdie proses het ontwikkel met verloop van tyd tot die hoë presisie vervaardigingsnywerhede van die moderne era. Hoë gehalte en hoë presisie onderdele word vervaardig met die gebruik van slypwiele wat strek van growwe onderdeel vorming tot presisie motor enjin komponent vervaardiging. Die mees algemene skuurpartikels in moderne slyp prosesse is ontwikkel vir algemene toepassings, terwyl ander bedoel is vir gespesialiseerde toepassings. Die gebruik van wolframkarbied vir beide algemene en gespesialiseerde slyp wiele word nie gewoonlik geïmplimenteer in industrie nie, asook nie in gepubliseerde navorsingswerk nie. Hierdie karbied materiaal val in die vuurvaste groep van materiale. Wanneer dit gemeng en gebind word met 'n smeebare metaal soos kobalt, molibdeen of nikkel, word die klassifikasie verander na 'n gesementeerde karbied of kermet (keramiek metaal). Die hoeveelheid van die metaal wat gebruik word in die kermet beïnvloed die smeebaarheid daarvan. ‘n Metaal inhoud van sowat 12 gw% (12 gewig %) is rofweg die middeweg wat lei tot 'n unieke hardheid tot taaiheid verhouding. Die metaal wat die beste werk met wolfram karbied is kobalt, dus WC-12gw%Co. Hierdie spesifieke kermet word algemeen gebruik as basis materiaal in bewerking gereedskap (vir draaibanke en freesmasjiene) te danke aan die hoë hardheid en taaiheid verhouding benodig vir die bewerking van harde metale soos verharde staal of titaan allooie. Hierdie basis WC-12gw%Co materiaal kan net so gebruik word vir masjinering, maar word gewoonlik bedek met lae van ander slytwerende materiale (soos titaan nitried, TiN, of karbonitried, TiCN). Hierdie studie fokus op die spesiale vervaardiging van 'n slypwiel wat WC-12gw%Co as skuurmiddel bevat en wat gebind word met 'n epoksie hars binder. Hierdie tipe slypwiel is nie in gebruik in industriële toepassings nie en moet dus spesiaal ontwerp en vervaardig word. Die hars word gebruik as binder, wat die geval is vir baie industrieel geïmplementeerde slypwiele, om die produksie proses te vereenvoudig en hoër veiligheid te verseker. Die slypwiele wat in hierdie studie geproduseer is, is die kleiner weergawe wat ‘n gemonteer punt genoem word. Die werksverrigtinge van hierdie gemonteerde punte word bepaal deur die slyp van 'n titaan allooi. Die werks verrigtinge is bepaal deur die meting van die tempo van slytasie, die oppervlakafwerking wat die punte produseer op die titaan allooi en die oppervlak hardheid van die allooi aangesien dit gewoonlik deur die slyp proses beïnvloed word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98569
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