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On Transfer of Work Material to Tools
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap. (Tribomaterial)
2012 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Bulk forming and cutting are widely used to shape metals in industrial production. Bulk forming is characterized by large strains, extensive plastic deformation and large surface expansions. Cutting is characterized by high speeds, high pressures and high temperatures. The prevailing conditions during these processes lead to transfer of work material to tools. In bulk forming this is a significant problem. The transferred work material is hardened and becomes harder than the work material, causing galling. This leads to high friction and high forming forces, bad surface finish of the formed products and significant difficulties to produce complicated geometries. In cutting, transfer of work material can be desired for protection of the tool surface. However, the transfer film has to be of the correct type to provide a stable and predictive behaviour during operation.

In this thesis the influence from tool material and surface treatment on work material transfer has been studied for both applications, with the use of simplified laboratory test methods followed by extensive surface studies. Both the tendency to, appearance of and chemical composition of work material transfer is evaluated. The results are compared with real industrial examples, to ensure that the correct mechanisms are mimicked.

In forming, the problems arise when poor lubrication prevails, due to high forming forces or large surface expansions. The transfer of work material can then be avoided with the use of a galling resistant coating, offering low adhesion. However, the coating has to be as smooth as possible, to avoid activation of the work material and subsequent transfer.

In cutting, the desired transfer film can be obtained by choosing the correct cutting parameters. The geometry and material of the fabricated component is often predetermined, setting the general cutting conditions, but the cutting speed influences the formation of the transfer film. Too low speed or too high speed leads to an unstable cutting process and poor surface finish of the piece. The speed intervals for each mechanism are partly determined by the tool material and thus by the tool coating.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Uppsaliensis , 2012. , s. 68
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 894
Emneord [en]
Tribology, Friction, Forming, Cutting, Galling, Material transfer, Tribological coatings, Surface finish, Micro mechanisms, Aluminium
HSV kategori
Forskningsprogram
Materialvetenskap
Identifikatorer
URN: urn:nbn:se:uu:diva-165828ISBN: 978-91-554-8261-9 (tryckt)OAI: oai:DiVA.org:uu-165828DiVA, id: diva2:480657
Disputas
2012-03-02, Häggsalen, Lägerhyddsvägen 1, Uppsala, 10:15 (svensk)
Veileder
Tilgjengelig fra: 2012-02-10 Laget: 2012-01-10 Sist oppdatert: 2013-04-08
Delarbeid
1. Laboratory test simulation of galling in cold forming of aluminium
Åpne denne publikasjonen i ny fane eller vindu >>Laboratory test simulation of galling in cold forming of aluminium
2009 (engelsk)Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, nr 12, s. 2278-2286Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Cold forming of aluminium is a group of very efficient methods, which are successfully used in a number of industrial applications. Two of the major factors limiting the tool life and restricting the shapes and sizes possible to produce, are galling, i.e. transfer of work material to the tool surface, and high stresses occurring when forming complex shapes. Both phenomena are closely related to the friction and adhesion in the tool to workpiece interface.

The present paper investigates the influence of several surface parameters to the tendency to galling. This is done by forming aluminium using tool steel in a geometrically simplified lab test. The test scans over a wide load interval while monitoring the coefficient of friction. The corresponding transfer of work material to the tool surface is studied in the SEM after testing. The test is focused on the initial tool contact and also on the number of contacts before a critical friction level is reached.

The test set-up comprises two crossed cylinders in sliding contact, one made of tool steel and one of work material. Three commercial tool materials were included, each prepared to two surface finishes. The aluminium workpiece cylinders of AA6082 were prepared by two different pre-treatments, solid lubrication followed by soft annealing and pickling, respectively.

The respective importance of the tool material, preparation of the tool surface finish and the aluminium surface pre-treatment are compared with respect to initial galling tendencies and friction stability. The practical implications for real forming applications are discussed.

HSV kategori
Forskningsprogram
Materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-111808 (URN)10.1016/j.wear.2009.04.006 (DOI)000272810200017 ()
Tilgjengelig fra: 2009-12-22 Laget: 2009-12-22 Sist oppdatert: 2017-12-12
2. Laboratory test simulation of aluminium cold forming – influence from PVD tool coatings on the tendency to galling
Åpne denne publikasjonen i ny fane eller vindu >>Laboratory test simulation of aluminium cold forming – influence from PVD tool coatings on the tendency to galling
2010 (engelsk)Inngår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 204, nr 21-22, s. 3606-3613Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Cold forming of aluminium is a group of very efficient methods used in a number of industrial applications. Two of the major factors limiting the tool life and restricting the complexity of the shapes produced, are galling, i.e. transfer of aluminium to the tool surface, which leads to problems in successive forming, and high stresses occurring when forming complex shapes. Both phenomena are closely related to friction and adhesion in the tool to workpiece interface. Earlier investigations have shown that aluminium is transferred to the tool steel surface regardless of the surface roughness of the tool. This has been proposed to be due to the hard native oxide on the soft aluminium leading to a mechanical gripping in the tool surface.The present paper investigates the influence of ceramic coatings on the tendency to galling. This is done by plastic forming of aluminium against coated tool steel rods in a lab test. The test scans over a wide load interval while monitoring the coefficient of friction. The transfer of work material to the tool is studied in the SEM. The test is focused on the friction level and on the number of contacts before a critical friction level is reached.The test set-up comprises two crossed cylinders in sliding contact, one made of coated tool material and the other of work material. Eight commercial coatings were included; DLC, TiAlN, TiN and TiCN as single layer or as multilayer combinations, with hardness values ranging from 800 HV to 3500. HV. All substrates were the same tool steel material (H13), prepared to two different surface finishes. The aluminium work piece cylinders of AA6082 were prepared by two different pre-treatments, soft-annealing followed by industrially used solid lubrication and pickling, respectively.The coating material, preparation of the tool surface finish and the aluminium surface pre-treatment all proved important with respect to galling tendencies and friction levels. Three of the DLC coatings showed very promising behaviour, also without lubricant, but surface roughness deteriorates the galling resistance. The other low-friction coatings tested neither improved the galling resistance nor reduced the friction significantly, compared to the uncoated tool steel.

Emneord
Aluminium alloy, Ceramic coating, Friction, Galling
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-134845 (URN)10.1016/j.surfcoat.2010.04.025 (DOI)000279696400036 ()
Tilgjengelig fra: 2010-12-02 Laget: 2010-12-02 Sist oppdatert: 2017-12-12bibliografisk kontrollert
3. Mechanisms of transfer of aluminium to PVD-coated forming tools
Åpne denne publikasjonen i ny fane eller vindu >>Mechanisms of transfer of aluminium to PVD-coated forming tools
2012 (engelsk)Inngår i: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 46, nr 3, s. 299-312Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Cold forging is a group of methods effectively used in a number of industrial applications to form aluminium. Tool life and complexity of the possible shapes are mainly restricted by galling; the uneven tool surfaces caused by lumps of transferred material lead to surface damage on successive parts formed and/or problems in successive forming operations, and high stresses occurring when forming complex shapes. Earlier investigations have shown that improved surface roughness of an uncoated steel tool decreases the amount of adhered aluminium on the tool, but does not decrease the friction in the long run. Testing has also shown that when using conventional forming tools it is very important to have sufficient lubrication to avoid galling. Addition of an optimized low-friction PVD-coating decreases the galling tendency and increases the tolerance to insufficient lubrication and lubricant film breakthrough, as long as the coating surface is smooth, whilst other similar coatings have little or no effect. The present article further investigates the mechanism behind the transfer of aluminium to the coatings. All coatings were found to be intact after testing, and so the differences were concluded to lie in the chemical properties of the coating and, if these are favourable, then in surface roughness on the micro scale.

Emneord
Galling, Friction mechanisms, Friction-reducing coatings, Aluminium
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot tribomaterial; Teknisk fysik med inriktning mot materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-167057 (URN)10.1007/s11249-012-9952-5 (DOI)000303876300009 ()
Tilgjengelig fra: 2012-01-19 Laget: 2012-01-19 Sist oppdatert: 2017-12-08bibliografisk kontrollert
4. Evaluation of TiB2 coatings in cold forming of aluminium
Åpne denne publikasjonen i ny fane eller vindu >>Evaluation of TiB2 coatings in cold forming of aluminium
2012 (engelsk)Inngår i: Surface Engineering, ISSN 0267-0844, E-ISSN 1743-2944, Vol. 28, nr 7, s. 517-525Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Aluminium alloy parts are often formed using cold forming. The transfer of aluminium to the tool is a major problem in these operations. TiB2 has low reactivity with aluminium and has shown promising results in other forming tests. Here, cold forming is simulated in equipment comprising a TiB2 coated tool cylinder and an aluminium cylinder in sliding contact. The coated surfaces are prepared to two surface finishes, and the aluminium cylinders were prelubricated or unlubricated respectively. The test is focused on friction level and number of contacts to reach a threshold friction level. The aluminium surface pretreatment was found to be the most important factor; lubrication lowers the friction significantly. The tool surface finish is also important; polishing lowers and stabilises the friction. The TiB2 coating offered 20‐30% better galling performance than the uncoated steel. However, this improvement was far from that of the best available diamond-like carbon coatings.

HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-167056 (URN)10.1179/1743294412Y.0000000017 (DOI)000307963500009 ()
Tilgjengelig fra: 2012-01-19 Laget: 2012-01-19 Sist oppdatert: 2017-12-08bibliografisk kontrollert
5. The influence from shape and size of tool surface defects on the occurrence of galling in cold forming of aluminium
Åpne denne publikasjonen i ny fane eller vindu >>The influence from shape and size of tool surface defects on the occurrence of galling in cold forming of aluminium
2011 (engelsk)Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, nr 9-10, s. 2517-2524Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Aluminium alloys are shaped in cold condition in a large number of industrial applications. Simple geometries can be produced to net shape in a single operation. Galling is an important factor limiting the tool life, the complexity of the shapes and the number of processing steps. A selection of ceramic coatings gives a strongly reduced tendency to galling, even without lubricant, as long as the coating surface is smooth. With rough coating surfaces there is no significant improvement compared to the conventionally used uncoated tool steels. The present investigation concentrates on the character of the surface roughness and its influence on galling. Here, surface defects including pyramidal indents and elongated scratches are introduced in a controlled manner and then characterised with optical microscopy and electron microscopy. After testing, the transfer of work material to the tool is studied using electron microscopy and surface analysis. The influence of the various types of local defects is studied with respect to galling tendencies and friction. The shape and extent of the surface roughness is important for galling resistance. Single indents, symbolizing occasional dents in the coating, initially pick up more aluminium than the surrounding coating but do not influence the galling and friction in total. This implies that the forming tools need fine polishing and gentle handling to avoid dents and initial aluminium pick up. The overall surface roughness level is of higher importance for galling and friction.

Emneord
Galling, Surface preparation, Friction, Tool steel, Ceramic coating, Aluminium alloy
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot materialvetenskap; Teknisk fysik med inriktning mot tribomaterial
Identifikatorer
urn:nbn:se:uu:diva-162393 (URN)10.1016/j.wear.2011.01.077 (DOI)000294590200167 ()
Tilgjengelig fra: 2011-11-30 Laget: 2011-11-30 Sist oppdatert: 2017-12-08bibliografisk kontrollert
6. New understanding of the initiation of material transfer and transfer layer build-up in metal forming: In situ studies in the SEM
Åpne denne publikasjonen i ny fane eller vindu >>New understanding of the initiation of material transfer and transfer layer build-up in metal forming: In situ studies in the SEM
2012 (engelsk)Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 292-293, s. 61-73Artikkel i tidsskrift (Fagfellevurdert) Published
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-167047 (URN)10.1016/j.wear.2012.05.032 (DOI)000308628400008 ()
Tilgjengelig fra: 2012-01-19 Laget: 2012-01-19 Sist oppdatert: 2017-12-08bibliografisk kontrollert
7. Mechanisms of material transfer studied in situ in the SEM: Explanations to the success of DLC coated tools in aluminium forming
Åpne denne publikasjonen i ny fane eller vindu >>Mechanisms of material transfer studied in situ in the SEM: Explanations to the success of DLC coated tools in aluminium forming
2012 (engelsk)Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, nr 292, s. 49-60Artikkel i tidsskrift (Fagfellevurdert) Published
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-167050 (URN)10.1016/j.wear.2012.05.033 (DOI)000308628400007 ()
Tilgjengelig fra: 2012-01-19 Laget: 2012-01-19 Sist oppdatert: 2017-12-08bibliografisk kontrollert
8. Evaluation of an intermittent sliding test for reproducing work material transfer in milling operations
Åpne denne publikasjonen i ny fane eller vindu >>Evaluation of an intermittent sliding test for reproducing work material transfer in milling operations
Vise andre…
2012 (engelsk)Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 52, s. 153-160Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

TiN coated HSS test cylinders from an intermittent sliding test were compared with TiN coated HSS milling inserts from a single insert milling test. A 20NiCrMo2 case hardening steel was used as counter material and work material in the two tests. HSS test cylinders, coated with AlCrN, TiAlN and Al2O3, were also tested in the intermittent sliding test and evaluated with regard to material adhesion. Two distinctly different tribofilms were formed on test cylinders as well as on cutting inserts. One consisting of Mn, Si, Al and O and one consisting of Fe, Mn, Cr, Si and O. The transferred material was similar in appearance and composition, both when comparing the two test methods and when comparing the different tool coatings.

Emneord
Transfer, Coating, Chip, Sliding
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot tribomaterial; Teknisk fysik med inriktning mot materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-167051 (URN)10.1016/j.triboint.2012.03.015 (DOI)000304798900015 ()
Tilgjengelig fra: 2012-01-19 Laget: 2012-01-19 Sist oppdatert: 2017-12-08bibliografisk kontrollert
9. Influence of sliding speed on modes of material transfer as steel slides against PVD tool coatings
Åpne denne publikasjonen i ny fane eller vindu >>Influence of sliding speed on modes of material transfer as steel slides against PVD tool coatings
Vise andre…
2013 (engelsk)Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 58, s. 55-64Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

An intermittent sliding test was used in order to study the formation and build-up of tribofilms during intermittent sliding of PVD coated HSS against case hardening steel (20NiCrMo2). Two cutting tool coatings were tested, TIN and AlCrN, and the influence of sliding speed was evaluated. With moderate speed, two tribofilms were formed separately, one consisting of Mn, Si, Al and O on an intermediate layer of Fe and one consisting of Fe, Mn, Cr and O on an intermediate layer of Cr and Mn. At low sliding speeds an uneven transfer of steel occured while high sliding speeds resulted in thermal softening of the substrate leading to coating failure. AlCrN provided better substrate protection at high speeds than TiN did.

sted, utgiver, år, opplag, sider
Elsevier, 2013
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-167053 (URN)10.1016/j.triboint.2012.09.012 (DOI)000312610600008 ()
Tilgjengelig fra: 2012-01-19 Laget: 2012-01-19 Sist oppdatert: 2017-12-08bibliografisk kontrollert
10. Influence from surface roughness on steel transfer to PVD tool coatings in continuous and intermittent sliding contacts
Åpne denne publikasjonen i ny fane eller vindu >>Influence from surface roughness on steel transfer to PVD tool coatings in continuous and intermittent sliding contacts
Vise andre…
2012 (engelsk)Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 56, s. 9-18Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

A sliding test is used in order to evaluate the influence of tool surface roughness on the material transfer in intermittent and continuous sliding of PVD coated HSS against case hardening steel (20NiCrMo2). Two cutting tool coatings, TiN and AlCrN, and three different surface roughnesses are tested. For polished surfaces the same types of material transfer are obtained irrespective of sliding mode and coating type. If the surfaces are too rough, the tribofilms do not grow thick enough to separate the surfaces and the work material is abrasively worn in both sliding modes. With increased sliding distance, cracking of the TiN coating occurs while the AlCrN coating remains intact.

Emneord
Transfer, coating, sliding, roughness
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-167054 (URN)10.1016/j.triboint.2012.06.013 (DOI)000308284000002 ()
Forskningsfinansiär
VINNOVA
Tilgjengelig fra: 2012-01-19 Laget: 2012-01-19 Sist oppdatert: 2017-12-08bibliografisk kontrollert

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