Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Determining the density distribution in cemented carbide powder compacts using 3D neutron imaging
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). Sandvik Coromant, Stockholm, SE-126 80, Sweden.ORCID iD: 0000-0001-8653-393X
Show others and affiliations
2019 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 354, p. 584-590Article in journal (Refereed) Published
Abstract [en]

Spray-dried refractory carbide and metal powder mixtures, containing tungsten carbide, is compacted and sintered during the production of conventional cutting tool inserts. Since friction between the pressing tool and the powder gives rise to density gradients in the powder compact, shrinkage during sintering is uneven. The shape of the sintered blank is important and can be predicted with finite element (FE) simulations. To validate the simulation of the pressing procedure, the density gradients in the powder compacts must be measured with a high spatial resolution. Since tungsten has a high atomic number, it is hard to penetrate with X-rays and even cold neutrons. We show here that by using a polychromatic beam of thermal neutrons, along with beam-hardening correction, such measurements can be successfully realized. The obtained results show good agreement with corresponding FE-simulations. Also, deliberate differences in the compaction process could be verified with the neutron measurements.

Place, publisher, year, edition, pages
Elsevier, 2019. Vol. 354, p. 584-590
Keywords [en]
Carbide and metal powder mixtures, Density distribution, FEM simulations, Polychromatic thermal neutrons, Powder compaction, Tungsten carbides
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-262514DOI: 10.1016/j.powtec.2019.06.033ISI: 000490625500056Scopus ID: 2-s2.0-85068007493OAI: oai:DiVA.org:kth-262514DiVA, id: diva2:1366143
Note

QC 20191028

Available from: 2019-10-28 Created: 2019-10-28 Last updated: 2020-02-18Bibliographically approved
In thesis
1. Mechanical Modelling of Powder Compaction: Due to Corona is not possible to attend this defense in person, instead attend via this link: https://play.kth.se/media/t/0_mbkr2jhi​
Open this publication in new window or tab >>Mechanical Modelling of Powder Compaction: Due to Corona is not possible to attend this defense in person, instead attend via this link: https://play.kth.se/media/t/0_mbkr2jhi​
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cutting tool inserts, for instance used in steel machining, have the requirement to be toughand are therefore most often manufactured out of cemented carbides, using powdermetallurgy. Manufacturing components with powder metallurgy has its advantages in highproductivity and good net shape. The powder is spray dried and compacted to half itssintered volume. Because of friction between the powder and the pressing tool, the densityafter compaction is uneven, leading to uneven shrinkage during sintering. To get the rightshape after pressing and sintering, the pressing tool must often be compensated, which isboth expensive and time consuming. By doing computer simulations of the manufacturingprocess, the shape after sintering can be predicted and used to compensate the pressing toolbefore it is manufactured, thus saving both time and money. Also cracks and porosity in thepowder blank can be predicted with such simulations.

This thesis studies mechanical modelling of powder compaction in general and compactionof cemented tungsten carbide powders in particular. Because of the amount of powdergranules in a typical geometry, the mechanical behavior is modelled with a continuumapproach, using the finite element method (FEM). Accuracy is important in the presentapplication and therefore a detailed elastic-plastic material model with a density dependentyield surface of Drucker-Prager CAP kind is used.

For accurate material modelling it is important to include relevant features and to excludeunimportant physical effects. In Paper A sensitivity studies are therefore performed inorder to conclude which properties in the material model that have a significant influence onthe result. The studies show that anisotropy can be disregarded in the current application.

In Paper B the effects from creep and compaction speed are studied. It is concluded thatcreep has no influence on the density after compaction, which also is confirmed by densitymeasurements using a neutron source in Paper D. The compaction speed on the other handinfluences the friction coefficient between powder and pressing tool, lower at increasedspeed. In Paper C frictional behavior is scrutinized experimentally with the aid of aninstrumented die. The friction coefficient is determined and analyzed, and it is shown that itdepends on the normal pressure.

The sensitivity studies in Paper A show that measurements of the local density are neededin order to determine and verify material properties. Since the analyzed powder containstungsten (W), which has a high atomic number, a polychromatic beam of thermal neutronsis needed. In Paper D it is shown that the local density can be measured with 3D imagingand a thermal neutron source.

From the results and conclusions in the above-mentioned papers, a material description forpowder compaction is suggested. This description is implemented in FEM in Paper E andapplied to reverse engineering in order to determine important material parameters.Experiments in a pressing machine with a pressing method that includes multiple unloadingsteps is used. The material description with the determined parameters is verified withdensity measurements using a neutron source.

Abstract [sv]

Inom skärande bearbetning av exempelvis stål, där skärspetsen måste vara hård ochhållfast, används oftast hårdmetallskär, tillverkade med pulvermetallurgi. Att tillverkakomponenter med pulvermetallurgi har fördelen att hög produktivitet nära den slutgiltigaformen kan uppnås. Pulvret sprejtorkas och kompakteras till halva den sintrade volymen.Eftersom det uppstår friktion mellan pulver och pressverktyg är densiteten i det pressadeämnet ojämn och därmed krymper ämnet ojämnt under sintring. För att få rätt form efterpressning och sintring måste därför pressverktyget ofta kompenseras, vilket är både dyrtoch tidskrävande. Genom att göra datorsimuleringar av framställningsprocessen kanformen efter pressning och sintring istället predikteras, och pressverktyget kankompenseras före tillverkning, vilket sparar både tid och pengar. Även sprickor ochporositet efter pressning kan förutsägas med sådana simuleringar.

I denna avhandling studeras mekanisk modellering av pulverkompaktering, generellt ochspecifikt för hårdmetall. På grund av mängden granuler i en typisk skärgeometri modellerasde mekaniska egenskaperna med en kontinuumansats och finita elementmetoden (FEM).Eftersom noggrannhet är viktig i denna applikation, används en detaljerad elastisk-plastiskmaterialmodell med en densitetsberoende Drucker-Prager CAP flytyta.

Grundläggande för relevant materialmodellering är att inkludera viktiga egenskaper och attutelämna oviktiga fysikaliska effekter. I Artikel A görs därför känslighetsanalyser för attundersöka vilka delar i materialmodellen som har en signifikant påverkan på resultatet.Slutsatsen är att anisotropi inte behöver modelleras för denna applikation.

I Artikel B studeras effekten av kompakteringshastighet och kryp. Slutsatsen är att krypinte har någon inverkan på densiteten efter pressning, vilket också valideras medneutronmätningar i Artikel D. Presshastigheten påverkar däremot friktionskoefficientenmellan pulver och pressverktyg, lägre vid högre hastighet. I Artikel C analyserasfriktionsbeteendet experimentellt med hjälp av en instrumenterad dyna.Friktionskoefficienten bestäms och analyseras, och slutsatsen är att den beror pånormaltrycket.

Känslighetsanalysen i Artikel A visar att mätningar av den lokala densiteten är nödvändigaför att bestämma och verifiera materialegenskaper. Eftersom det analyserade pulvretinnehåller wolfram (W), som har ett högt atomnummer, krävs en polykromatisk stråle avtermiska neutroner. I Artikel D visas att den lokala densiteten kan mätas med 3D-bildanalysoch termiska neutroner.

Utifrån resultaten och slutsatserna i ovannämnda artiklar föreslås en materialbeskrivningför pulverkompaktering. Beskrivningen är implementerad i FEM i Artikel E och användsmed baklängesoptimering för att bestämma viktiga materialparametrar. Experiment i enpressmaskin och en pressmetod som inkluderar flera avlastningar används.Materialbeskrivningen verifieras med densitetsmätningar där en neutronkälla används.

Place, publisher, year, edition, pages
Kungliga Tekniska högskolan, 2020. p. 30
Series
TRITA-SCI-FOU ; 2019:63
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:kth:diva-268185 (URN)978-91-7873-420-7 (ISBN)
Public defence
2020-03-20, Live streaming, 10:00 (Swedish)
Opponent
Supervisors
Note

QC 20200218

Available from: 2020-02-18 Created: 2020-02-17 Last updated: 2020-03-18Bibliographically approved

Open Access in DiVA

No full text in DiVA

Other links

Publisher's full textScopus

Authority records BETA

Staf, HjalmarOlsson, ErikLarsson, Per-Lennart

Search in DiVA

By author/editor
Staf, HjalmarOlsson, ErikLarsson, Per-Lennart
By organisation
Solid Mechanics (Dept.)
In the same journal
Powder Technology
Materials Engineering

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 37 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf