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Author:Hirn, Justus
Title:Suitability of resistance spot welding and laser welding for the production of all steel sandwich panels with ultra high-strength thin faces and the high-strength core
Vastuspistehitsauksen ja laserhitsauksen soveltuvuus kerroslevyrakenteiden valmistukseen käytettäessä ultra-lujateräksisiä ohuita pintalevyjä ja lujateräksisiä ytimiä
Publication type:Master's thesis
Publication year:2010
Pages:110 + [19]      Language:   eng
Department/School:Insinööritieteiden ja arkkitehtuurin tiedekunta
Main subject:Koneenrakennuksen materiaalitekniikka   (Kon-67)
Supervisor:Hänninen, Hannu
Instructor:Suomi, Markus
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto     | Archive
Keywords:all steel sandwich panels
resistance spot welding
laser welding
teräksiset kerroslevyt
vastuspistehitsaus
laserhitsaus
Abstract (eng):The objective of this Master's thesis was to study the suitability of different joining methods to the production of all steel sandwich panels. The joining methods studied were laser welding, resistance spot welding, electron beam welding, plasma welding and friction stir welding. Test materials were martensitic RAEX 400 ultra high-strength steel and ferritic HC380LA cold rolled high-strength steel.

In the literature part of the thesis, the different types of sandwich panels, the joining methods used at the present and possibly in the future were discussed. The different welding methods were compared, and based on that, the resistance spot welding and laser welding were discussed in more detail. The strength properties of all steel sandwich panels and the LCA of sandwich panel production were discussed.

Experimental part of the thesis consisted of the shear and fatigue tests of the test specimens. Test specimens were small-scale specimens from the lap joints with dissimilar and similar material. Different laser welding directions and penetrations and direct resistance spot welding were compared. In addition, the mechanized peel tests were conducted in resistance spot welding case. All different welding cases were investigated with optical microscopy and the hardness profiles of joints were measured.

The shear strength of the tested lap joints in all dissimilar joined cases was approximately the same. In cases, where the welding direction was from HC380LA to RAEX 400, the fracture occurred in the base material of HC380LA. In other test cases the fracture occurred in the cross-section area of the joint. In shear strength tests the biggest factor was the cross-section area of the joint, which varied because of the air gap between the plates, heat input, welding speed and welding direction. Fatigue strength of the tested lap joints showed that the lap joints which were laser welded by full penetration had better fatigue resistance compared to the joints which were laser welded with partial penetration. Tests revealed that DRSW cases had lower fatigue resistance compared to the laser welded test cases. In addition, the fatigue properties of the laser welded lap joints depended mostly on the geometry of the joint, whereas the cross-section area of the joint, that is the length and the width of the joint, were the most important factors affecting the shear strength.
Abstract (fin):Tämän diplomityön tavoitteena oli tutkia eri liittämismenetelmien soveltuvuutta teräksisten kerroslevyrakenteiden valmistamiseen. Tutkitut menetelmät olivat laserhitsaus, vastuspistehitsaus, elektronisuihkuhitsaus, plasmahitsaus ja kitkahitsaus. Tutkittavat materiaalit olivat martensiittinen RAEX 400 ultra-luja teräs ja ferriittinen HC380LA kylmämuokattu teräs.

Kirjallisuusosassa käsiteltiin erilaiset kennotyypit, mahdolliset nykyiset liittämismenetelmät, sekä mahdolliset liittämismenetelmät tulevaisuudessa. Erilaisia liittämismenetelmiä verrattiin keskenään, jonka perusteella vastuspistehitsaus ja laserhitsaus käsiteltiin yksityiskohtaisemmin. Lisäksi käsiteltiin teräksisten kerroslevyrakenteiden lujuus ominaisuudet ja teräksisten kerroslevyrakenteiden tuotannon elinkaarianalyysi.

Kokeellisessa osuudessa käsiteltiin koekappaleiden leikkaus- ja väsymislujuuksia. Koekappaleet olivat pienimittakaavaisia eripari- ja samamateriaalisia limiliitoksia. Erilaisia laserhitsaussuuntia ja -tunkeumia, sekä suoraa vastuspistehitsausta verrattiin keskenään. Lisäksi mekaaninen aukirullauskoe suoritettiin vastuspistehitsaustapauksen yhteydessä. Kaikkien eri hitsaustapausten hitsit tutkittiin mikroskooppisesti, sekä niiden kovuusprofiili mitattiin.

Tutkittujen limiliitosten leikkauslujuus oli suunnilleen samanlainen kaikissa eripariliitoksissa. Tapauksissa, joissa hitsaussuunta oli HC380LA:sta RAEX 400:n, murtuma tapahtui perusaineessa HC380LA:n puolella. Muissa tapauksissa murtuma tapahtui hitsin poikkipinta-alassa. Leikkauslujuus-kokeissa suurin vaikuttava tekijä oli hitsin pinta-ala, joka vaihteli hitsauksen aikana olleen ilmaraon, lämmöntuonnin, hitsausnopeuden ja hitsaussuunnan vuoksi. Läpitunkeumalla laserhitsattujen limiliitosten väsymislujuus osoittautui testeissä osittaistunkeumaa paremmaksi. Suoritetut kokeet paljastivat suoran vastuspistehitsauksen väsymislujuudet huonommiksi verrattuna laserhitsattuihin koetapauksiin. Lisäksi laserhitsattujen limiliitosten väsymisominaisuudet riippuivat enimmäkseen liitoksen geometriasta, kun taas tärkein tekijä leikkauslujuudessa on hitsin poikkipinta-ala, joka muodostuu hitsin leveydestä ja pituudesta.
ED:2010-10-18
INSSI record number: 41118
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