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On the wear of PVD-coated HSS hobs in dry gear cutting
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap. (Tribomaterial)
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap. (Tribomaterial)
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap. (Tribomaterial)
Vise andre og tillknytning
2009 (engelsk)Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 266, nr 3-4, s. 444-452Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

A hob is an advanced gear cutting tool usually made of homogenous high-speed steel (HSS) and coated by physical vapour deposition (PVD). It is designed for regrinding and recoating many times. However, hobs of today suffer from unpredictable wear making it difficult to schedule when they should be taken out for reconditioning. This investigation is aimed to contribute to the fundamental knowledge of the wear mechanisms and wear propagation of hobs used in dry gear cutting. Two AlCrN-coated hobs, used in actual gear cutting, were investigated by scanning electron microscopy (SEM) to study the tool topography, light optical microscopy (LOM) to study metallographic cross-sections and by X-ray photoelectron spectroscopy (XPS) for surface analyses.

It is concluded that the high potential of PVD-coated HSS as tool material is not taken full advantage of. The main reason is a combination of a poor surface preparation prior to coating and excessively high compressive residual stresses, making parts of the coating detach along the edge line even on unused cutting teeth. During cutting, the high intrinsic stresses in combination with droplets and defects in the coating facilitated its fragmentation through decohesion and detachment. Simultaneously, the rake face is gradually covered by a thin oxide layer dominated by Fe, Cr and Mn in about equal amounts, and also with a significant content of Si. It is believed but not proved that this layer is beneficial.

To improve service life and reliability of gear cutting hobs, precautions should be taken for the grinding–polishing preparation prior to PVD-coating to ensure a smooth substrate free from burning damage and other defects. Also, the edge radius and coating thickness has to be matched with the magnitude of compressive residual stresses in the coating.

sted, utgiver, år, opplag, sider
2009. Vol. 266, nr 3-4, s. 444-452
Emneord [en]
Gear hobbing, High-speed steel, PVD-coating, Wear propagation
HSV kategori
Forskningsprogram
Materialvetenskap
Identifikatorer
URN: urn:nbn:se:uu:diva-111756DOI: 10.1016/j.wear.2008.04.014ISI: 000263217300011OAI: oai:DiVA.org:uu-111756DiVA, id: diva2:282655
Prosjekter
KUGGTilgjengelig fra: 2009-12-21 Laget: 2009-12-21 Sist oppdatert: 2017-12-12
Inngår i avhandling
1. Tribology at the Cutting Edge: A Study of Material Transfer and Damage Mechanisms in Metal Cutting
Åpne denne publikasjonen i ny fane eller vindu >>Tribology at the Cutting Edge: A Study of Material Transfer and Damage Mechanisms in Metal Cutting
2012 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

The vision of this thesis is to improve the metal cutting process, with emphasis on the cutting tool, to enable stable and economical industrial production while using expensive tools such as hobs. The aim is to increase the tribological understanding of the mechanisms operating at a cutting edge and of how these can be controlled using different tool parameters. Such understanding will facilitate the development and implementation of future, tribologically designed, cutting tools.

Common wear and failure mechanisms in gear hobbing have been identified and focused studies of the material transferred to the tool, in both metal cutting operations and in simplified tribological tests, have been conducted. Interactions between residual stresses in the tool coating and the shape of the cutting edge have also been studied.

It was concluded that tool failure is often initiated via small defects in the coated tool system, and it is necessary to eliminate, or minimize, these defects in order to manufacture more reliable and efficient gear cutting tools. Furthermore, the geometry of a cutting edge should be optimized with the residual stress state in the coating, in mind. The interaction between a compressive stress and the geometry of the cutting edge will affect the stress state at the cutting edge and thus affect the practical toughness and the wear resistance of the coating in that area.

An intermittent sliding contact test is presented and shown to be of high relevance for studying the interaction between the tool rake face and the chip in milling. It was also demonstrated that material transfer, that can have large effects on the cutting performance, commences already after very short contact times. The nature of the transfer may differ in different areas on the tool. It may include glassy layers, with accumulations of specific elements from the workpiece, and transfer of steel in more or less oxidized form. Both tool coating material, its surface roughness, and the relative speed between the tool surface and the chip, may influence the extent to which the different transfer will occur.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2012. s. 77
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 988
Emneord
Tribology, Metal cutting, Gear hobbing, Wear, Coating, Residual stress, Material transfer, Steel
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot tribomaterial
Identifikatorer
urn:nbn:se:uu:diva-183186 (URN)978-91-554-8514-6 (ISBN)
Disputas
2012-12-07, 2005, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (svensk)
Veileder
Tilgjengelig fra: 2012-11-16 Laget: 2012-10-23 Sist oppdatert: 2013-01-23bibliografisk kontrollert

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