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  • 1. Bernspång, Lars
    et al.
    Hammam, T.
    Mattiasson, K.
    Schedin, E.
    Melander, A.
    Samuelsson, A.
    Verification of an explicit finite-element code for the simulation of the press forming of rectangular boxes of coated sheet steels1993Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 39, nr 3-4, s. 431-453Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The industrial aim for shorter lead times in the development process for new products has encouraged a fast development of finite-element procedures for the simulation of sheet-metal forming. These procedures can shorten the design stage for new sheet-forming tools and the try-out period. In order to reach these goals robust calculation procedures and extensive verification of results are required. This paper presents a detailed validation of one promising type of finite-element code, namely the explicit code DYNA3D. Experiments for verification were performed on a zinc-coated sheet steel with a hot-dip galvanized coating. Stretch forming and deep drawing of cylindrical cups were performed. Rectangular boxes were formed from rectangular blanks and blanks with cut corners. Dies both with and without draw beads were used. Punch forces, flange draw-in and strain distributions were measured. The pressings with cylindrical shape were used to determine coefficients of friction with a fitting procedure based on comparison of data from pressings and from the DYNA3D calculations. These tribological data and constitutive data of the steels were used in the simulation of pressings of rectangular boxes. The calculations with DYNA3D gave a good description of flange draw-in and the strain distributions in the pressings. In most of the cases studied the punch-force curves were well reproduced. It is concluded that the present code is well suited for the simulation of sheet-forming operations.

  • 2.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Industrial and Mechanical Engineering.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser-arc hybrid welding of thick HSLA steel2018Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 259, s. 75-87Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A standard laser-arc hybrid welding (S-LAHW) and LAHW with preplaced cut wire inside the groove before welding were studied and compared. The S-LAHW setup revealed problems with filler wire delivery to the root, resulting in substantial hardness increase due to bainitic-martensitic transformation. The applied finite element modelling confirmed significant cooling rate increase in the root area for deep penetration welds. Preplacement of cut wire prior to welding reduced hardness providing improved welds with higher homogeneity. This method was subsequently applied for multi-pass welding that revealed insufficient nucleation of acicular ferrite on non-metallic inclusions (NMIs). It is implied that a critical cooling rate has been exceeded where the NMIs become inactive, resulting in a microstructure consisting of a martensite and bainite mixture. This kind of microstructure is clearly harmful for the weld metal toughness.

  • 3.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Industrial and Mechanical Engineering.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F.H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Deep penetration fiber laser-arc hybrid welding of thick HSLA steel2018Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 256, s. 216-228Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present investigation addresses laser-arc hybrid welding of 45 mm thick steel with variation in a wide range of process parameters. High volume fraction of acicular ferrite formed in the upper part of the weld metal regardless process parameters. Significantly lower fraction of acicular ferrite was found in the root due to substantially increased cooling rates and the inability to deliver filler wire to this region, resulting in bainite-martensite microstructures in the root. The delivery of filler wire to the root can be enhanced by increasing the air gap between the plates. Higher heat inputs reduce cooling rates in the root which create softer and ductile microstructures, at the expense of a much wider and coarser grained HAZ. The results obtained showed high fusion line and weld metal toughness at low temperature (−50 °C).

  • 4.
    Edberg, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Wedge rolling test1994Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 42, nr 2, s. 227-238Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method for the evaluation of friction models is described. A wedge is rolled to uniform thickness, a range of reductions being investigated thereby in one experiment. Finite-element simulations are performed in order to estimate the friction parameters that can be used in the simulation of hot rolling. The influence of the material parameters and the friction parameters on the calculated results are investigated and the latter are compared with experimental results. It is shown that it is possible to separate the influence of the material parameters and the friction parameters, thus enabling the friction parameters to be evaluated from a minimum number of experiments.

  • 5.
    Golling, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Östlund, Rickard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A study on homogenization methods for steels with varying content of ferrite, bainite and martensite2016Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 228, s. 88-97Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The demand of ultra high strength steel (UHSS) components increased in the last decade due to their high strength to weight ratio. The driving force in this development is the automotive industry and regulations concerning passenger safety and fuel consumption. The use of ultra high strength steel enables design of lighter car bodies with equal or better passenger safety compared to earlier car generations. The automotive industry and their suppliers need predictive tools in the development of components with tailored material properties. Components with tailored material properties are produced by hot stamping, in this process a blank is austenitized before it is formed and quenched in one step. By use of sequential heated or cooled tools, different mechanical properties distributed within the same component are achieved.In order to develop a constitutive model for components consisting of regions with varying phase content, a suitable method to describe the elasto-plastic part of the yield curve is needed. The focus of this work is on the description of the elasto-plastic constitutive model of an ultra high strength steel depending on the phase content in the material. Different volume fractions of ferrite, bainite and martensite are experimentally formed. In this study the capability of different homogenization methods on the prediction of the material response of a multi-phase steel depending on the volume fraction of formed phases is investigated. The modeling results are compared to experimental results.The prediction of the composite response using the micromechanical based double-inclusion model and pure phase measured data as well as experimentally obtained phase volume fractions of present phases showed good agreement throughout all samples tested in this study.

  • 6.
    Gustafsson, E.
    et al.
    Dalarna University, Borlänge.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jansson, A.
    SSAB EMEA AB, SE-781 84 Borlänge.
    Design and validation of a sheet metal shearing experimental procedure2014Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, nr 11, s. 2468-2477Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Throughout the industrial processes of sheet metal manufacturing and refining, shear cutting is widely used for its speed and cost advantages over competing cutting methods. Industrial shears may include some force measurement possibilities, but the force is most likely influenced by friction losses between shear tool and the point of measurement, and are in general not showing the actual force applied to the sheet. Well defined shears and accurate measurements of force and shear tool position are important for understanding the influence of shear parameters. Accurate experimental data are also necessary for calibration of numerical shear models. Here, a dedicated laboratory set-up with well defined geometry and movement in the shear, and high measurability in terms of force and geometry is designed, built and verified. Parameters important to the shear process are studied with perturbation analysis techniques and requirements on input parameter accuracy are formulated to meet experimental output demands. Input parameters in shearing are mostly geometric parameters, but also material properties and contact conditions. Based on the accuracy requirements, a symmetric experiment with internal balancing of forces, is constructed to avoid guides and corresponding friction losses. Finally, the experimental procedure is validated through shearing of a medium grade steel. With the obtained experimental set-up performance, force changes as result of changes in studied input parameters are distinguishable down to a level of one percent.

  • 7.
    Gustafsson, E.
    et al.
    Dalarna University, Borlänge.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jansson, A.
    SSAB EMEA AB, SE-781 84 Borlänge.
    Experimental study on the effects of clearance and clamping in steel sheet metal shearing2016Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 229, s. 172-180Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Shear cutting is common within several sheet metal industry processing steps, e.g. in cut to length lines, slitting lines, end cropping. Shearing is fast and cheap relative to competing cutting methods like laser and plasma cutting, but involves large forces on the equipment that increase with increased sheet material strength. Accurate shear experiments are a prerequisite to increase the knowledge of shearing parameters, improve industrial shearing, and provide data for validation of numerical shear models. Here, the two shear parameters clearance and clamp configuration, identified as important to the shear results, were studied in an experimental set-up with well defined tool movement and high measurability of tool position and force. In addition to force measurements, the sheared edge geometry was characterized. Steels of low, medium, and high strength were selected for the study. Throughout the experimental study, the shear tool penetration before fracture decreased with increased material strength. The required shear force decreased and the force attempting to separate the two shear tools increased when one side of the sheet was left unclamped and free to move. Further, the maximum shear force increased with decreased clearance. Clearance changes were small and moreover continuously measured during all shear experiments.

  • 8.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Antti, Lena
    The effect of drying method and temperature level on the hardness of wood2006Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 171, nr 3, s. 467-470Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The purpose of the present work was to investigate whether wood hardness is affected by temperature level during microwave (MW) drying and whether the response is different from that of conventionally dried wood. Matched samples of Norway spruce (Picea abies) were therefore dried from green state to different moisture content (mc) at different temperature levels, both conventionally by air circulation and by MW. The results show that specimens dried by any of the two methods at a temperature level of 100 or 60°C there is a significant difference in wood hardness parallel to the grain between the methods when drying progresses to relatively lower level of moisture content, i.e. wood hardness becomes higher during MW drying. Temperature level in the range 60-110°C during MW drying has no significant influence on wood hardness. Variables such as density and mc have a greater influence on wood hardness than does the drying method or the drying temperature. Since wood is a biological material, its strength varies within the specimens as well as between different samples. For this reason it is important to use matched samples when performing this type of comparative investigation.

  • 9.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Antti, Lena
    The effect of microwave drying on Norway spruce woods strength: a comparison with conventional drying2003Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 141, nr 1, s. 41-50Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The purpose of the present work was to investigate whether the drying method itself affects strength of wood apart from fibre direction, density, temperature in the wood, moisture content and with which angle the microfibril is placed in the middle layer at the secondary cell wall S2. The drying methods compared were microwave drying and conventional air-circulation drying, and the species tested was Norway spruce. The result shows that it is not possible to demonstrate any difference between the two drying methods with respect to the strength of the wood. What affects wood strength are such variables as moisture content, number of annual rings and the density properties weight, width and thickness

  • 10. Hansson, Sofia
    et al.
    Jansson, T.
    Sandvik Materials Technology.
    Sensitivity analysis of a finite element model for the simulation of stainless steel tube extrusion2010Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 210, nr 10, s. 1386-1396Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, a sensitivity analysis has been performed on a finite element model of glass-lubricated extrusion of stainless steel tubes. Fifteen model parameters, including ram speed, billet and tool temperatures, friction coefficients and heat transfer coefficients, were considered. The aim of the study was to determine the parameters that are most important for the response of the extrusion force. The relationship between the model parameters and the responses was analyzed by a calculation of two different regression models: one linear polynomial model and one model that includes interaction terms. Additional simulations were then carried out to validate the regression models. The results show that the initial billet temperature is the factor that has the strongest impact on the extrusion force within the parameter ranges studied in this work. The goodness of prediction and goodness of fit are very good for both regression models.

  • 11.
    Hedayati, Ali
    et al.
    Department of Materials Engineering, Isfahan University of Technology.
    Najafizadeh, Abbas
    Department of Materials Engineering, Isfahan University of Technology.
    Kermanpur, Ahmad
    Department of Materials Engineering, Isfahan University of Technology.
    Forouzan, Farnoosh
    Department of Materials Engineering, Isfahan University of Technology.
    The effect of cold rolling regime on microstructure and mechanical properties of AISI 304L stainless steel2010Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 210, nr 8, s. 1017-1022Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the effect of different thickness reductions by cold rolling on the microstructure and mechanical properties of AISI 304L austenitic stainless steel were investigated. The hot rolled steel strips were subjected to cold rolling at 0 °C from 10 to 90% thickness reduction. Microstructures, strain-induced martensitic transformation and mechanical properties of the cold-rolled specimens were characterized by X-ray diffraction, Feritscope measurements, optical metallography, hardness and tensile tests. The resulting transformation curve showed a sigmoidal shape with the saturation value of strain-induced martensite of approximately 100%. A good agreement was found between the experimental results and the Olsen-Cohen model. The results indicated that formation of strain-induced martensite clearly resulted in a significant strengthening of the steel

  • 12. Ion, John
    et al.
    Ainsdahl, L.M.
    SINTEF.
    A PC-based system for procedure developement in laser transformation hardening1997Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 65, nr 1-3, s. 261-267Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A PC-based software package has been developed which facilitates the generation of procedures for laser transformation hardening. The package comprises a model-based process simulation module, a graphical user interface based on a standarized parameter record, a database of completed procedures, and a processing cost analysis. Analytical models of heat flow and phase transformations are used to predict the depth of the transformed zone and the maximum hardness developed, in terms of the principal process variables (the laser beam parameters and material properties). Good agreement between experimental data and model predictions is demonstrated for a range of alloy steels. Realistic sets of processing parameters can thus be obtained for experimental evaluation, reducing the amount of trial-and-error testing significantly. Archived procedures can be retrieved for editing and further development. Processing costs can be compared readily with those for conventional surface-hardening techniques.

  • 13.
    Ivarson, Anders
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kamalu, J.
    University of Dundee, Department of APEME.
    Magnusson, Claes
    Oxidation dynamics of laser cutting of mild steel and the generation of striations on the cut edge1994Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 40, nr 3-4, s. 359-374Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Over the past two decades CO2 laser cutting has grown from an obscure laboratory technique into an important branch of manufacturing engineering. The most commonly cut materials are steels and a great deal of industrial and scientific research has been carried out on the laser-material interactions that generate a cut. This paper concentrates on the phenomena which give rise to a cyclic cutting event when a CO2 laser in conjunction with an oxygen jet is used to cut mild steel. The nature of the cut edge striation produced by the cyclic oxidation reaction is explained thoroughly and a possible oxidation cycle is postulated. It is demonstrated that the key to understanding the cyclic nature of the cutting event is the self-limiting nature of the oxidation of the steel in the cut zone

  • 14.
    Kajberg, Jörgen
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Material characterisation using high-temperature Split Hopkinson pressure bar2013Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 213, nr 4, s. 522-531Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In order to characterise the mechanical response of materials in manufacturing processes, such as wire and bar rolling involving very high strain rates, temperatures and level of straining, an experimental device is presented. The device is suitable for testing at strain rates up to approximately 4000 s−1, temperatures up to 1200 °C (≈1500 K) and strains around 0.5. It is based on the classical split Hopkinson pressure bar and is complemented with an inductive heating source for achieving requested temperatures. By keeping the specimen separated from the Hopkinson bars just until an instant before impact (50 ms) considerable cooling and temperature gradients in the specimen are avoided. Three steel grades, two stainless steels and a high-speed steel, were tested. Four different material models whose parameters were fitted to the obtained experimental data were used for mechanical characterisation: two empirically based and two physically based. Overall, one of the physically based models showed the best agreement between experimental results and the predicted flow stresses.

  • 15.
    Keskitalo, M.
    et al.
    University of Oulu, University of Oulu, Oulu Southern Institute.
    Mentyjärvi, K.
    University of Oulu.
    Sundqvist, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser Welding Of Duplex Stainless Steel With Nitrogen As Shielding Gas2015Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 216, s. 381-384Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nitrogen loss from laser welding melt pools and can have a deleterious effect on weld toughness for duplex stainless steels. This effect can be alleviated by using nitrogen as the shielding gas during laser welding. The use of Nitrogen results in increased austenite levels in the weld metal and improved toughness levels.

  • 16.
    Kim, Kyounghak
    et al.
    Department of Welding and Joining Science Engineering, Graduate School, Chosun University.
    Bang, Heeseon
    Department of Welding and Joining Science Engineering, Chosun University.
    Bang, Hansur
    Department of Welding and Joining Science Engineering, Chosun University.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Joint properties of ultra thin 430M2 ferritic stainless steel sheets by friction stir welding using pinless tool2017Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 243, s. 381-386Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, friction stir butt welding of ultra thin 430M2 ferritic stainless steel sheets with satisfactory joint properties has been achieved using a pinless WC-Co tool. Friction stir welding was carried out at a tool rotational speed of 900 rpm and a travel speed of 96 mm/min. FSW joints were welded completely without any unwelded zone resulting from smooth material flow, despite of being adopted pinless tool. It was revealed that the maximum tensile strength of FSW welds was 468 MPa, equivalent to the tensile strength of base metal. Notably, it was found that sigma phase formation in FSW welds is suppressed compared with that of arc welds, resulting in improving joint strength. These results suggest that the low input process of FSW is an effective substitute for the conventional fusion welding GTAW in ultra thin ferritic stainless steel plate.

  • 17.
    Lamas, Javier
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Gap bridging for two modes of laser arc hybrid welding2015Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 224, s. 73-79Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The topology of welds is an important quality criterion for which the mechanisms behind are only partially understood. The impact of gap width on the resulting weld shape produced by laser-arc hybrid welding was studied for two arc modes: pulsed arc and cold metal transfer. The weld bead and root topology were scanned and analysed. For widening gaps below a limiting width, top reinforcement turns into underfill. Above a certain gap width (0.8 mm in this case), a bridge of melt is created across the weld zone. Although high speed imaging shows very different drop transfer and weld pool formation for the two arc modes, the bridging behaviour shows the same trend for both modes. This bridging effect is important from an industrial point of view because, when viewed from the top, it gives the misleading impression that a good weld has been produced. For even wider gaps the melt collapses into the gap. These different regimes are analysed and discussed for both modes.

  • 18.
    Lindgren, Lars-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Edberg, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Explicit versus implicit finite element formulation in simulation of rolling1990Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 24, s. 85-94Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The computational efficiency of the explicity finite element code DYNA2D and the implicit code NIKE2D are compared in the case of simulation of rolling. It is found that the explicit code is preferable. The advantages of the explicit formulation will be even more pronounced in three-dimensional simulations

  • 19. Lindgren, Michael
    Cold roll forming of a U-channel made of high strength steel2006Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 186, nr 5, s. 77-81Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cold roll forming is a bending process where the bending occurs gradually in several forming steps from an undeformed strip to a finished profile. The process is very interesting for the sheet metal industry due to the high speed in which the profile can be produced. High strength steel has, in recent years, become more common in cold roll forming. These materials have advantages but also disadvantages that affect the design of the process.Simple models in literature [K.F. Chiang, Cold roll forming, ME Thesis, University of Auckland, August 1984] predict that the longitudinal peak membrane strain in the flange of a profile is independent of the material properties. However, Ingvarsson [L. Ingvarsson, Förenklad teori för rullforming av elementär v-profil, jämförelse mellan normalt och höghållfast stål, VAMP 15- rullforming 23 april 2001] compared mild and ultra high strength in a roll forming experiment and the conclusion was that the material properties will affect the finished profile. This paper is a fundamental study performed in order to understand the observation by Ingvarsson [L. Ingvarsson, Förenklad teori för rullforming av elementär v-profil, jämförelse mellan normalt och höghållfast stål, VAMP 15- rullforming 23 april 2001].The objectives of this study are to investigate the change in the longitudinal peak membrane strain at the flange edge and the deformation length when the yield strength increases. These are important since they can be used to determine the number of forming steps and the distance between them when designing the cold roll forming machine. The result from the simulations show that the longitudinal peak membrane strain decreases and the deformation length increases when the yield strength is increased.

  • 20. Lindgren, Michael
    Experimental investigations of the roll load and roll torque when high strength steel is roll formed2007Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 191, nr 1-3, s. 44-47Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The cold roll forming process is a highly efficient process used to produce profiles for many applications, for example vehicles, buildings, domestic machines, etc. Therefore, its market share is increasing every year. Many of the above products are already today made of high strength steel and the usage of these materials will likely continue to increase.The objectives of this project are to find how the roll load and roll torque are influenced by the yield strength of the material. Full-scale experiments have been performed. U-channels made of different materials from mild to ultra high strength steels have been formed. The roll torque is measured during the process using a torque sensor mounted between the tool and the power transmission. Used power is also calculated with help of the motor current. The roll load is measured with load cells mounted on both side of the roll forming tool.The experimental result will increase the understanding of the specific conditions for roll forming steels with increasing yield strength. The result can be used to support the roll machine designer to choose machine elements and power unit for these applications. Furthermore, the result can also be compared with finite element simulations in order to improve and validate simulation models

  • 21. Lindgren, Michael
    et al.
    Bexell, Ulf
    Dalarna University.
    Wikström, Lars
    Dalarna University.
    Roll forming of partially heated cold rolled stainless steel2009Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 209, nr 4, s. 3117-3124Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Today you will find roll formed details in many different products, for example buildings, household appliances and vehicles. The industry, in order to save weight, tends to use more and more high strength steel. The disadvantage with these materials is that they can be difficult to form due to reduced ductility. A way to increase the ductility in the forming areas is by partially heat the steel.It is shown that partial heating substantially increases the ductility of high strength steel and make it possible to roll form large bend angles. When roll forming, the material will work hardening almost to the as-received condition in the outer and inner radius of the roll formed profile. Furthermore, the heating power decides the bend angle obtained. Finally, the mechanical properties after heating and roll forming are discussed.

  • 22.
    Mangalaraja, R.V.
    et al.
    University of Concepción.
    Mouzon, Johanne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Hedström, Peter
    Kero, Ida
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Ramam, K.V.S.
    University of Concepción.
    Camurri, C.P.
    University of Concepción.
    Odén, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Combustion synthesis of Y2O3 and Yb-Y2O3: Part 1: Nanopowders and their characterization2008Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 208, nr 1-3, s. 415-422Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanosized yttrium oxide and ytterbium doped yttrium oxide powders were prepared by ceramic combustion techniques such as flash combustion, citrate gel decomposition and glycine combustion using urea, citric acid and glycine respectively as fuels. As synthesized precursors and calcined powders were characterized for their structural, particle size and morphology, and the optimization of calcination process by differential scanning calorimetry and thermal gravimetry. The thermal analyses together with XRD results demonstrate the effectiveness of the combustion process for the synthesis of pure phase nanocrystalline powders. Nanocrystalline pure yttria powders were obtained by the calcination of as-prepared precursors at 1100 °C for 4 h.

  • 23.
    Marth, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Östlund, Rickard
    Post necking characterisation for sheet metal materials using full field measurement2016Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 238, s. 315-324Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    precise prediction of the post-necking behaviour of materials is needed to increase the precision of computer simulations with large deformations. Applications in which this need is encountered include crash, forming, and failure simulations. By using an optical full-field measurement of the localised deformation field, an effective and computationally fast method is presented to determine the relationship between true stress and true plastic strain, including post-necking behaviour. The presented stepwise modelling method is used to characterise heat-treated boron steel using thin sheet metal specimens. These results are validated with the results determined by a method based on inverse modelling. It can be concluded that the stepwise modelling method is considerably faster than the compared inverse modelling method. The method is also suitable for effectively determining element size dependency due to regularisation of the hardening behaviour needed for finite element analysis with strain localisation, e.g., for crash simulations

  • 24.
    Nilsson, Annika
    et al.
    Luleå tekniska universitet.
    Melin, Lars
    Luleå tekniska universitet.
    Magnusson, Claes
    Finite-element simulation of V-die bending: a comparison with experimental results1997Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 65, nr 1-3, s. 52-58Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A major problem in sheet bending is to compensate for springback. Analytical descriptions are not sufficiently general to accommodate influences from the material and the geometry due to the simplifications that have to be made. Practical experiments are still needed to be able to compensate for springback. The aim of this work has been to test the finite-element method on its abilities to predict springback for free bending in a V-die. The work shows that the finite-element method can be used to predict springback off-line. The true stress-true strain curve from a tensile test is used as the material description. Springback has been studied for eight different materials of varying thickness. The process has been simulated with the code Nike2d and the results from the simulations compared with those from experiments, good correlation between the simulations and the experiments being achieved.

  • 25.
    Odenberger, Eva-Lis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thilderkvist, P.
    Forming Group, OSAS, Industrial Development Centre in Olofström AB.
    Stoehr, T.
    Manufacturing Technology, University of Erlangen-Nuremberg.
    Lechler, J.
    Manufacturing Technology, University of Erlangen-Nuremberg.
    Merklein, M.
    Manufacturing Technology, University of Erlangen-Nuremberg.
    Tool development based on modelling and simulation of hot sheet metal forming of Ti-6Al-4 V titanium alloy2011Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 211, nr 8, s. 1324-1335Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the aero engine industry alternative manufacturing processes for load carrying aero engine structures imply fabrication. The concept of fabrication involves simple forgings, sheet metals and small ingots of e.g. titanium alloys which are welded together and heat treated. In the concept phase of the product development process, accurate evaluations of candidate manufacturing processes with short lead times are crucial. In the design of sheet metal forming processes, the manual die try out of deep drawing tools is traditionally a time consuming, expensive and inexact process. The present work investigates the possibility to design hot forming tools, with acceptable accuracy at short lead times and with minimal need for the costly die try out, using finite element (FE) analyses of hot sheet metal forming in the titanium alloy Ti-6Al-4 V. A rather straightforward and inexpensive approach of material modelling and methods for material characterisation are chosen, suitable for early evaluations in the concept phase. Numerical predictions of punch force, draw-in and shape deviation are compared with data from separate forming experiments performed at moderately elevated temperatures. The computed responses show promising agreement with experimental measurements and the predicted shape deviation is within the sheet thickness when applying an anisotropic yield criterion. Solutions for the hot forming tool concept regarding heating and regulation, insulation, blank holding and tool material selection are evaluated within the present work.

  • 26.
    Pelcastre, Leonardo
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Rolland, Anthony
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Influence of microstructural evolution of Al-Si coated UHSS on its tribological behaviour against tool steel at elevated temperatures2016Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 228, s. 117-124Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The usage of the hot stamping process is of great importance due to the high demands for production of ultra-high strength steels (UHSS). An Al-Si coating is normally applied to the steel to prevent decarburisation and scaling during heating and to improve the corrosion resistance of the final component. During heating, the Al and the Si from the coating combine with the Fe from the steel substrate to form hard intermetallic phases. Little is known about the influence of the heating conditions on the tribological behaviour of the Al-Si coating during interaction with tool steels. The present work investigated different heat treatment parameters and the influence they had on the microstructure of the coating and the galling behaviour. With low alloying temperatures (700˚C), severe galling occurred and increasing the alloying temperature to 900˚C resulted in almost negligible material transfer. The reduction in galling was associated to the development of Fe2Al5 and FeAl2 at the surface.

  • 27.
    Robertson, Stephanie
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Ramasamy, Anandkumar
    Lincoln electric europe.
    Kalfsbeek, Bert
    Lincoln electric europe.
    Volpp, Jörg
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F.H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Microstructures of high strength steel welding consumables from directed thermal cycles by shaped laser pulsesIngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Filler wire metallurgy was modified through temporally shaped laser pulses, controlling cooling cycles in a recently developed method. Trends were identified through efficient mapping while maintaining representative thermal cycles of welding processes. A primary pulse melted preplaced filler wires in a cavity, forming a nugget. A secondary ramp-down pulse elevated the nugget temperatures to re-austenisation followed by linear temperature decay, guiding the temperature through a regime to a desired microstructure. For three very high strength steel wire chemistries, quenching yielded smaller plates with cross-hatched microstructures, accompanied by grain boundary ferrite. Finer bainite microstructures started forming for fast linear temperature decay, about 250°C/s. Slower decay or a weaker third cycle led to less cross-hatching, coarser microstructure and coalescent sheaves.

  • 28.
    Siva Prasad, Himani
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    The stability of laser welding with an off-axis wire feed2019Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 264, s. 84-90Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The concept using an off-axis filler wire during laser welding is introduced here in order to provide added process robustness considering gap width variations. Its stability is investigated with respect to gap width, welding speeds and powers. Geometry of the welds is analysed by tracing of weld cap edges and joint cross sections, connecting trends to weld parameters. High speed imaging and streak images are used to further study and describe sequences of events, including undercut formation. Formation of imperfections are found to be mainly correlated to wire feed position variations at the surface due to irregular melting of the wire tip.

  • 29.
    Sundqvist, Jesper
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Shachaf, L.
    Holo/Or Ltd.
    Kong, Choon Yen
    TWI Ltd, Granta Park, Great Abington, Cambridge .
    Analytical heat conduction modelling for shaped laser beams2017Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 247, s. 48-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Conduction mode laser spot welding and laser spot hardening usually employ Gaussian or top-hat-like beam modes. One main requirement of these techniques is the avoidance of overheating in the centre of the laser-material interaction zone. Process flexibility can be improved by spatially and/or temporally shaping the beam, which can enable higher process quality, robustness or speed. A desired spatial beam shape can be achieved by a suitably designed diffractive optical element. However, the prediction of a suitable beam shape for a particular process can be complex. A simplified analytical heat conduction model has been developed that can rapidly calculate the temperature field and cooling behaviour for almost any spatial and temporal beam shape. The potential and limits of the model are demonstrated and discussed by calculating and analysing temperature profiles for several cases of multi-spot welding

  • 30.
    Tan, Z.
    et al.
    Luleå tekniska universitet.
    Persson, Bengt
    Magnusson, Claes
    Empiric model for controlling springback in V-die bending of sheet metals1992Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 34, nr 1-4, s. 449-455Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A process model is presented for v-die bending of sheet metals. This model is especially valuable to control a press brake equipped with a computer integrated controlling and planning system. A bent part recovers elastically on release of load, and the springback varies with both material and process parameters. A desired bend angle is obtained by controlling the punch insertion depth so that the springback can be compensated by right amount of overbending. The model combines analytical method with trial and error work to establish the relationship of punch insertion depths and corresponding unloaded bend angles. To apply this model, three trial bendings are required for sheet metal and tool combination, so that three coefficients in the half-empiric model can be obtained in a regressive way. Experiments have shown that process parameters affect springback more obviously than material properties do, and the model predicts accurate punch insertion depths for desired angles in air bending. The model is simple, so it can easily be used for real time control

  • 31.
    Tan, Zheng
    et al.
    Luleå tekniska universitet.
    Melin, Lars
    Luleå tekniska universitet.
    Magnusson, Claes
    Application of an image processing technique in strain measurement in sheet metal forming1992Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 33, nr 3, s. 299-310Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In sheet metal forming, strains or strain increments are evaluated usually from the shape change of grids marked previously on the surface of the workpiece, the present understanding of formability in a forming process being based largely on the knowledge gained from the strain measurement. The theory of square-grid analysis is a great help in gaining knowledge of sheet metal forming. In the application of this theory, nodal points on a sheet metal surface etched with square-grids have to be measured. Conventional grid measurements are performed manually, which is either time-consuming or of low accuracy. It is known that the image processing technique is very powerful in digitizing the image of an object. A newly developed image processing device which consists of a video camera, a monitor and a personal computer, has therefore been introduced into strain measurement. The computer is equipped with an AD card and with data processing software. With such a device, the measurement of a gridded surface can be performed conveniently, with accuracy and efficiency. The combination of the image processing technique and the theory of square-grid strain analysis permits rapid measurement and strain analysis over the surface of a workpiece marked with a large number of nodal points.

  • 32.
    Torres, Hector
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement. AC2T research GmbH, Wiener Neustadt, Austria.
    Rodriguez Ripoll, M.
    AC2T research GmbH, Wiener Neustadt, Austria.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Self-lubricating laser claddings for friction control during press hardening of Al-Si-coated boron steel2019Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 269, s. 79-90Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In recent years, the use of Al/Si coatings has become widespread in hot stamping in order to protect the work piece from detrimental mechanisms such as scale formation or decarburisation affecting the quality of the finished product. However, the formation of Al-Fe intermetallics due to diffusion at high temperature can lead to unstable friction and damage both the tool and the work piece.

    In the present study, self-lubricating coatings with the addition of silver and MoS2 have been prepared by means of laser cladding deposition, aiming at their use in hot stamping in order to decrease friction and wear. The coatings were evaluated at high temperatures against Al-Si-treated boron steel using two different testing configurations featuring open and closed tribosystems. A significant reduction in friction for the self-lubricating claddings were observed along with decreased material transfer. This could be beneficial for hot stamping applications as it can ensure the stability of the process while preventing surface damage to the work piece. Additionally, closed configuration tribotesting has been found to underestimate friction and wear of the tool/work piece system, thus making it less suited for the lab-scale simulation of hot metal forming compared to open configuration tribometers. This finding has been considered relevant as many references in the available literature still report the use of closed configuration tribometers.

  • 33. Åkerström, Paul
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Austenite decomposition during press hardening of a boron steel: computer simulation and test2006Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 174, nr 1-3, s. 399-406Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work a model to predict the austenite decomposition into ferrite, pearlite, bainite and martensite during arbitrary cooling paths for thin sheet boron steel is used. The model is based on Kirkaldy's rate equations. The basic rate equations has been modified to account for the austenite stabilization effect from the added boron. The model is implemented as part of a material subroutine in the Finite Element Program LS-DYNA 970. Both the obtained simulated volume fractions microconstituents and hardness profiles shows promising agreement to the corresponding experimental observations.

  • 34.
    Östlund, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Berglund, D.
    Gestamp R&D.
    Evaluation of localization and failure of boron alloyed steels with different microstructure compositions2014Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, nr 3, s. 592-598Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Within the press hardening technology, where hot sheet blanks are simultaneously formed fixed and quenched, new methods with differential thermal treatment come to light. With controlled tool temperature variation, components with tailored properties can be produced. Automotive components combining high energy absorption and intrusion protection in a crash situation are feasible. In the present work the mechanical properties of three different material qualities, beginning with the same base sheet metal subjected to different thermal histories, are investigated. A strategy for modelling post-necking response and crack initiation using shell elements larger then the typical bandwidth of the localized neck is used. The model relies on a sequence of full field measurements throughout a tensile test; i.e. Digital Speckle Photography(DSP). The full field experimental method allows for evaluation of mechanical and failure properties at different analysis lengths, providing parameters for a model which accounts for shell element size. Additionally the model contains a strain based failure criteria as a function of stress triaxiality. Good correlations between a simulated tensile test and experimental results were found. A detailed metallographic study of the three grades was performed and is presented.

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