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Adhesive wear testing and modelling of tool steels sliding against sheet metals
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.ORCID iD: 0000-0002-1225-0598
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sheet metal forming is a manufacturing method used because of its versatility. Sheets are plastically deformed by a tool to create a product. A tool is expected to last for several 100,000 forming operations and efforts are made to optimize the tools. A common type of wear referred to as galling is the adhesion of sheet material to the tools. This problem has become more prevalent as new high strength sheet materials have been developed at the same time as lubricants have become heavily regulated. This has forced the development of new tool steels with improved resistance to galling. There are many parameters influencing the response to galling. In this work the influence of surface preparation, contact geometry, material selection and lubrication has been investigated. The surface of the forming tools has a large influence on the tools effective life. To refurbish a forming tool is expensive and often requires special shops and hand polishing. The influence on galling of different surface preparations suited for sheet metal forming was investigated using a strip-reduction equipment. The contact conditions of a tool sliding against metal sheets were investigated using FE models. The contact conditions were calculated for a U-bending test and for a sliding-on-flat-surface wear tester. The results were compared to those found in literature. One model incorporated the surface roughness of a sheet as measured by optical profilometry. The strength of the interface between the tool and the sheet material determine if material can be transferred onto the tool. The interface between the tool and adhered sheet material was closely studied using transmission electron microscopy of thin lamellas produced by focused ion beam milling. This showed sheet material adhering to the tool without the formation of an interlayer. Finally, several different combinations of tool steels and sheet materials were tested with regards to their ability to withstand galling.

Abstract [en]

Baksidestext:

Sheet metal forming can be used to produce a wide range of products but the initial costs are high as the forming tools are expensive. Wear of the tools in the form of galling i.e. the adhesion of tiny pieces of sheet material to the tools has become more prevalent as high strength sheet materials have been developed and lubricants have become heavily regulated.

In this work the influence on galling of surface preparation, contact geometry, material selection and lubrication has been investigated. It was found that tool surfaces should be polished as rougher surfaces quickly picked up material that adhered to the tools and subsequently scratched the sheets. The strength of the interface between the tool and the sheet material determine if material can be transferred onto the tool. The interface was studied using bright field transmission electron microscopy and the sheet material was found to adhere to the tool without the formation of an interlayer. The conditions under which galling occurs were studied using a slider on flat surface wear tester and several different material combinations were tested with regards to their galling resistance. The contact conditions of the test equipment were also modeled using FE models to better understand the strains of the materials involved.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2014. , 64 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2014:25
Keyword [en]
Adhesive wear
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-31793ISBN: 978-91-7063-556-4 (print)OAI: oai:DiVA.org:kau-31793DiVA: diva2:708845
Public defence
2014-05-09, 21A342, Eva Erikssonsalen, Karlstad, 10:15 (English)
Opponent
Supervisors
Available from: 2014-05-05 Created: 2014-03-30 Last updated: 2014-05-05Bibliographically approved
List of papers
1. Tool steel and contact geometry influence on galling initiation in lubricated sliding on carbon steel sheets
Open this publication in new window or tab >>Tool steel and contact geometry influence on galling initiation in lubricated sliding on carbon steel sheets
2009 (English)In: Proceedings of the 8th International Tooling Conference, Vol 1, 2009, 189-198 p.Conference paper, Published paper (Refereed)
Abstract [en]

In sheet metal forming operations, sliding contact may cause adhesive wear of sheet materials with transfer of worn material to the tool surface, a wear damage process named galling. It results in loss of product quality, process performance and tool lifetime. The industrial experience of the optimal combination of sheet metal grades, tool steel grades, tool geometry and lubrication to increase the tool performance is not clearly understood. Accordingly, simulation of wear of sheet metal forming operation in laboratory conditions in order to quantify tendency of a tool material to galling is not a trivial problem neither. In the present study two tool steel grades, an ESR made 8%Cr cold work tool steel and a superior PM made high speed steel, were tested with different test tool geometries to obtain different contact pressure conditions. A slider on flat sheet (SOFS) test equipment was utilized, where a disc made of tool steel was slid along lubricated carbon steel sheets of different strengths. The sliding tool discs were prepared so that one elliptical and two linear contacts were simulated, in order to study their influence on distance to galling initiation. Normal and friction force data were collected, galling initiation was detected by analysis of the friction curve and verified by SEM and OP analysis of the tool surfaces and sheet sliding tracks. It was found that under selected test conditions, galling initiation was remarkably dependent on tool material as well as geometry.

Keyword
Galling, sheet metal forming, wear, tool steel
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-8968 (URN)
Conference
The 8th International Tooling Conference, June 4th 2009, Aachen
Available from: 2011-12-19 Created: 2011-12-19 Last updated: 2017-12-06Bibliographically approved
2. The effect of grinding and polishing procedure of tool steels in sheet metal forming
Open this publication in new window or tab >>The effect of grinding and polishing procedure of tool steels in sheet metal forming
2010 (English)In: ICTPM 2010, 2010, 603-612 p.Conference paper, Published paper (Refereed)
Abstract [en]

The surface finish of tools in sheet metal forming has a large influence on the performance of the forming tool. Galling, concern of wear in sheet metal forming, is a severe form of adhesive wear where sheet material is transferred on to the tool surface. By polishing the tools to a fine surface finish, material pick-up has traditionally been reduced, but some surface preparations withstand adhesive wear better. To investigate the effect on galling performance of different surface preparations lubricated tests have been performed using a strip reduction rig. Two different tool materials, Vancron 40 and Vanadis 6 and up to ten different grinding and polishing treatments were tested against AISI 316 stainless steel. The tests showed that an optimum surface preparation might be found at the transition between abrasive and adhesive wear.

Keyword
galling, sheet metal forming, wear, sheet surface treatment
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-8969 (URN)
Conference
The 4th International Conference on Tribology in Manufacturing Processes, June 15th 2010, Nice
Available from: 2011-12-19 Created: 2011-12-19 Last updated: 2017-12-06Bibliographically approved
3. Study of the influence of contact geometry and contact pressure on sliding distance to galling in the Slider-On-Flat-Surface wear tester
Open this publication in new window or tab >>Study of the influence of contact geometry and contact pressure on sliding distance to galling in the Slider-On-Flat-Surface wear tester
2013 (English)In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 56, no 6, 1137-1145 p.Article in journal (Refereed) Published
Abstract [en]

One of the major causes of tool failure in sheet metal forming is wear in the form of galling. Galling is gradual buildup of adhered sheet material on the tool and leads to unacceptable scratches on the sheet surface and to components that fail to meet tolerances. Because it is difficult to reproduce operational and interactional conditions in laboratory test equipments it is hard to test, model, and predict galling initiation.Here the authors examine how changes from elliptical to line contact geometry influenced galling initiation under dry sliding by using a slider-on-flat surface (SOFS) wear tester. A micro clean tool steel was tested against ferritic low-strength and martensitic high-strength steel sheets.The sliding distance to galling initiation was extracted from friction data and verified by scanning electron microscopy (SEM) observations. The presence of adhesive wear on worn tools after completed tests was used as a criterion. Experimental results showed that the elliptical contact causes galling quicker than the line contact.Applicability of experimental results depends on the relevance of test conditions, so contact pressures calculated for the described tests were compared to calculated contact pressures in a semi-industrial U-bending test and to literature data relevant to industrial applications. Good agreement between values observed for SOFS and for most selected industrial applications was found, which assume that contact pressures typical for most common industrial applications can be successfully simulated by selection of tool geometry and normal load in the SOFS tester.

Place, publisher, year, edition, pages
London: Taylor & Francis, 2013
Keyword
galling, wear, sheet metal forming, friction
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-8970 (URN)10.1080/10402004.2013.827766 (DOI)000324614500023 ()
Available from: 2011-12-19 Created: 2011-12-19 Last updated: 2017-12-08Bibliographically approved
4. Assessment of galling performance of tools steel andsheets metals used in forming
Open this publication in new window or tab >>Assessment of galling performance of tools steel andsheets metals used in forming
(English)Manuscript (preprint) (Other academic)
Abstract [en]

A number of tool steel and sheet metal combinations were tested with respect to gallingbehaviour. Tests were performed both in dry and lubricated sliding. The tested sheet gradeswere three carbon steels, Docol 1200 M, Docol 1000 DP and DC01 two stainless steels,EN 1.4301 and EN 1.4509 one aluminium grade, AA 1193 and one titanium grade ti6al4vor EN 3.7164. The tool steels were two high speed steels and three powder metallurgicaltool steel grades.It was found that the tool steels performed equally well on dry sheets and the gradescould not be adequately separated. Under lubricated sliding on the Docol 1200 M sheetsthe difference between two PM materials was however notable.The addition of lubrication increased the tool life significantly for all materials excepttitanium. Titanium showed signs of galling immediately even if the sheets were lubricated.

Keyword
Galling, Wear, sheet metal forming
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-31841 (URN)
Available from: 2014-04-04 Created: 2014-04-04 Last updated: 2014-11-19Bibliographically approved
5. Study of the interface between adhered sheet metaland tool steel subjected to adhesive wear
Open this publication in new window or tab >>Study of the interface between adhered sheet metaland tool steel subjected to adhesive wear
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Many products used every day have at least some parts manufactured by sheet metal forming.Sheet metal forming is well suited for mass production and many machines perform aforming step in a matter of seconds. A common and severe form of wear is called gallingand occurs as small amounts of the sheet material is transferred on to the tool.In the present study the interface between three different sheet materials and a powdermetallurgical tool steel was investigated based on morphology and chemical composition.The sheets used were a high strength carbon steel sheet CS, a stainless steel grade, SS andtitanium, Ti. The tool steel, Vancron 40, was selected based on previously shown resistanceto galling. The microstructure of the tool steel contains three major constituents, the steelmatrix, M6C carbides and MCN carbonitrides, each constituent with potentially differentadhesive properties.To investigate the interfaces between the tool and the adhered material cross sectionlamellas was cut using a focused ion beam and studied in a transmission electron microscope.The chemical compositions of the interfaces were also investigated using electronenergy-loss spectroscopyThe presence of an interlayer between the tool and the adhered material would be ofhigh interest as the adhesion in the interface governs galling. The study did not reveal anyinterlayer between tool constituents and adhered material, for Vancron 40 worn against CSand SS but for one combination. SS sheet showed a ≃ 10 nm morphological interlayeragainst a MCN carbonitride. The lubricant was removed from the contact area and no traceof it was left in the interface between tool and adhered sheet. This shows that adhesive wearoccurs during direct tool to sheet contact comparative to dry sliding in SOFS tests.

Keyword
Galling, Interface, Micro structure
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-31842 (URN)
Available from: 2014-04-04 Created: 2014-04-04 Last updated: 2014-11-19Bibliographically approved
6. FE calculations of contact conditions of a doublecurved disc pressed and slid against a metal sheet
Open this publication in new window or tab >>FE calculations of contact conditions of a doublecurved disc pressed and slid against a metal sheet
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Many products are manufactured using sheet metal forming, as it has a high productionrate and a low cost when producing large series. However wear of sheet metal formingtools in the form of galling can severely limit the production. The sliding-on-flat-surfacewear tester, SOFS, has been used to reproduce the wear process leading up to galling in alaboratory environment.The contact conditions of the SOFS wear tester were investigated by several differentFE models. The contact conditions during static loading were accurately and preciselypredicted for the contact geometry found in the Sliding on flat surface wear tester. Thepressures were validated against the analytical Hertzian solution. During sliding the contactgeometry was shown to change predictably into a semi elliptical shape. At high friction, = 0.6, the contact pressure distribution changed to be heavier in the front and to the sides,leaving a slightly lower pressure in the center of the contact.An attempt was also made to model a sheet with surface roughness as measures byan optical profilometer. The attempt was successful in that a working FE model could becreated but there still remains work before the model con be used to accurately predict thecontact conditions. The model showed the formation of potential lubrication pockets on a

Keyword
Contact pressure, Surface roughness, Friction
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-31843 (URN)
Available from: 2014-04-04 Created: 2014-04-04 Last updated: 2014-11-19Bibliographically approved

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