Tomas Forsman - Academia.edu (original) (raw)

Papers by Tomas Forsman

This thesis presents the development of laser welding of aluminium and describes what can be perf... more This thesis presents the development of laser welding of aluminium and describes what can be performed with modern Nd:YAG lasers in the wide range of commercial aluminium alloys available. Specific process and quality problems during aluminium welding have been approached and studied experimentally. In some cases analytical models have been developed in order to help explain the process and to support the conclusions. Paper one is a literature review comprising laser welding of low density structural materials, i.e. aluminium alloys, magnesium alloys, titanium alloys and polymers. The paper describes the properties of the different materials and explains how the properties influence the laser welding process and the weld results. For some of the materials laser welding was found to be the only successful fusion welding process. Paper two investigates Nd:YAG laser lap welding between sheets of two different coated aluminium alloys. Successful welds were produced using a certain gap w...

This paper investigates the factors affecting the absorptivity during Nd:YAG laser keyhole weldin... more This paper investigates the factors affecting the absorptivity during Nd:YAG laser keyhole welding of a 6xxx aluminum alloy. The influence of surface condition on absorption is shown to be negligib ...

A review of laser welding of low density structural materials : (Alloys of titanium, aluminium, m... more A review of laser welding of low density structural materials : (Alloys of titanium, aluminium, magnesium and polymers)

Nd:YAG-lasersvetsning av aluminium belagt med torrsmorjmedel : Delrapport i projektet Applikation... more Nd:YAG-lasersvetsning av aluminium belagt med torrsmorjmedel : Delrapport i projektet Applikationsutveckling av YAG-laser med hog effekt for flexibel svetsning och skarning: en nyckelprocess vid fordonstillverkning

Trials are reported of the Nd:YAG laser welding of sheet of thickness about 1 mm in two aluminium... more Trials are reported of the Nd:YAG laser welding of sheet of thickness about 1 mm in two aluminium alloys (AA-5182 (Al, 4.0-5.0%Mg) and AA-6016 (Al, 0.3-0.6%Mg, 1.0-1.5%Si)) coated with "Drylube" dr ...

Laser welding is emerging as one of the most interesting methods for joining of metals. The proce... more Laser welding is emerging as one of the most interesting methods for joining of metals. The process has already been proven in both high quality welding in aerospace, electronics and medical engine ...

A new method to fabricate cross-ply laminates by RTM was developed. Glass-fibre roving was wound ... more A new method to fabricate cross-ply laminates by RTM was developed. Glass-fibre roving was wound on a steel sheet using a turning machine to produce 90 degree layers and Lyvertex 21130 "woven" rovi ...

International Congress on Applications of Lasers & Electro-Optics, 2002

ABSTRACT Laser welding has an incrising role in the automotive industry, namely on the sub-assemb... more ABSTRACT Laser welding has an incrising role in the automotive industry, namely on the sub-assemblies manufacturing. Several sheet-shape parts are laser welded, on a dissimilar combination of thicknesses and materials, and are afterwards formed (stamped) being transformed in a vehicle body component. In this paper low carbon CO2 laser welding, on the thicknesses of 1,25 and 0,75 mm, formability investigation is described. There will be a description of how the laser welded blanks behave in different forming tests, and the influence of misalignment and undercut on the formibility. The quality is evaluated by measuring the limit strain and limit effective strain for the laser welded sheets and the base material, which will be presented in a forming limit diagram.A soldadura laser assume um papel cada vez mais importante na indústria automóvel, principalmente para a fabricação de sub-conjuntos constituídos por varias partes de chapa de diferentes espessuras (e diferentes materiais), que depois de estampados constituem um componente para integrar num veículo. Descreve-se neste artigo o trabalho de investigação de enformabilidade de chapa de ac.o de baixo carbono soldada por laser de CO2, nas espessuras de 1,25 e 0,75 mm. Apresenta-se uma descrição do comportamento das chapas soldadas por laser em diferentes testes de enformação, e a influência dos defeitos das soldaduras (desalinhamento e queda do banho-undercut) no comportamento à enformação. A qualidade é avaliada pela medição da extensão limite e da extensão limite efectiva no material base e no material soldado, que serão representadas num diagrama de limite de enformabilidade.

International Congress on Applications of Lasers & Electro-Optics, 1999

This paper describes an analytical model for determining the geometry of laser welds. An earlier ... more This paper describes an analytical model for determining the geometry of laser welds. An earlier model by Lampa and Kaplan, for CO2 laser welding of stainless steel, has been further developed to cover Nd:YAG laser welding of aluminium alloys. This analytical work was followed by experimental verification using a 4 kW Nd:YAG laser. The model was found to be accurate over a wide range of process parameters.This paper describes an analytical model for determining the geometry of laser welds. An earlier model by Lampa and Kaplan, for CO2 laser welding of stainless steel, has been further developed to cover Nd:YAG laser welding of aluminium alloys. This analytical work was followed by experimental verification using a 4 kW Nd:YAG laser. The model was found to be accurate over a wide range of process parameters.

International Congress on Applications of Lasers & Electro-Optics, 1997

This experimental program investigated the production of lap welds between 1 mm thick sheets of a... more This experimental program investigated the production of lap welds between 1 mm thick sheets of aluminium alloys 5182 and 6016 which had previously been coated with Drylube. (Drylube is a polymer based coating approximately 1 μm thick which improves the formability of the aluminium alloy sheet). Successful welds were produced using a 2.5 kW Nd:YAG laser in conjunction with a 0.6 mm optical fibre. It was discovered that there is an optimum gap width between the two sheets which gives the best weld quality and strength. Pulsed and CW laser welds were produced and compared with respect to porosity and surface profile, etc.This experimental program investigated the production of lap welds between 1 mm thick sheets of aluminium alloys 5182 and 6016 which had previously been coated with Drylube. (Drylube is a polymer based coating approximately 1 μm thick which improves the formability of the aluminium alloy sheet). Successful welds were produced using a 2.5 kW Nd:YAG laser in conjunction with a 0.6 mm optical fibre. It was discovered that there is an optimum gap width between the two sheets which gives the best weld quality and strength. Pulsed and CW laser welds were produced and compared with respect to porosity and surface profile, etc.

International Journal of Fatigue, 2016

''Fish eye" is a typical phenomenon of fatigue crack initiation at a subsurface defect such as in... more ''Fish eye" is a typical phenomenon of fatigue crack initiation at a subsurface defect such as inclusion during very high cycle fatigue. The formation of a fine grained area and micro-debonding is believed to cause fatigue crack initiation. This paper provides a basic study on the formation of the fine grained area in a martensitic stainless steel during very high cycle fatigue using scanning electron microscopy, SEM, focused ion beam technique, FIB, electron backscatter diffraction, EBSD, and electron channeling contrast imaging, ECCI. The results show that the formation of a fine grained zone is a local behavior. The fine grained zone is very near the fatigue crack initiation origin. In the transversal direction (cross section), the depth of the fine grained zone is only few micrometers. In the longitudinal direction (crack propagation direction), the depth of the fine grain zone is about one micrometer. ECCI analysis shows that in the fine grained area with high retained strain, high plastic deformation can be found. Dislocation slip bands can be observed. They interact with grain boundaries and cause the formation of damage due to impingement cracking. The results indicate that occurrence of plastic deformation in metallic material during very high cycle fatigue is very localized, mainly near the front of the crack tip or a defect.

Journal of Laser Applications, 2000

ABSTRACT