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  • 1.
    Asnafi, Nader
    Swedish Institute for Metals Research, Stockholm, Sweden .
    On strength, stiffness and dent resistance of car body panels1995In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 49, no 1-2, p. 13-31Article in journal (Refereed)
    Abstract [en]

    There are cases in which practitioners wish to be able to predict the properties of a panel, should they replace one material by another. In this study, the yield strength, stiffness and dent resistance of double-curvature car body panels are treated both theoretically and experimentally. The results of the investigation show that the above-mentioned properties of a pressed panel can be predicted provided that the magnitude of the principal surface strains and the magnitude of the panel radii at the panel centre are known.

  • 2.
    Asnafi, Nader
    Gränges Technology, Finspång, Sweden.
    On stretch and shrink flanging of sheet aluminium by fluid forming1999In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 96, no 1-3, p. 198-214Article in journal (Refereed)
    Abstract [en]

    In this investigation, vertical stretch and shrink flanging of sheet aluminium by fluid forming are studied experimentally and theoretically. The theoretical part comprises both analytical modelling and finite-element simulations.

    The fracture limit in stretch flanging is determined by the plastic strain ratio, the strain hardening exponent, and the uniform strain. The greater the magnitude of these parameters, the greater will be the fracture limit.

    The maximum applied pressure determines the ’wrinkling’ limit in shrink flanging by fluid forming. The greater is this pressure, the greater ’wrinkling’ limit. This limit is certainly several times greater in magnitude than that in shrink flanging by conventional tools (a rigid punch and die).

  • 3.
    Asnafi, Nader
    et al.
    Volvo Car Corporation, Olofström, Sweden.
    Nilsson, Tomas
    Sapa Profile Bending, Vetlanda, Sweden.
    Lassl, Gunnar
    Volvo Car Corporation, Göteborg, Sweden.
    Tubular hydroforming of automotive side members with extruded aluminium profiles2003In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 142, no 1, p. 93-101Article in journal (Refereed)
    Abstract [en]

    Side member left and side member right, which go from bumper to bumper in a car body, were at the focus in the present study. These side members were produced using straight round (hollow with a circular cross-section) extruded aluminium profiles as tube material. The tubes were bent and hydroformed. Rotary-draw bending yielded the best result. A spread within 8mm after bending was found to be acceptable provided that the bent tube was hydroformed with a high maximum internal pressure (1300bar in this study). Pressure-assisted tool closure (hydroforming tool) should be preferred. Such a tool closure prevents formation of buckles, which may be difficult to straighten out completely during hydroforming. Planeness and parallelity of the press tables and adapters play a significant role, as far as the spread and inplaneness of hydroformed components are concerned. The hydroforming tool must be matched in the press that actually will be used. Proper evacuation (of particularly air) is essential, especially in long hydroforming tools. All cross-sections must be deformed at least 2% (average perimeter enlargement) if the hydroformed components are to exhibit a reasonable spread. The critical (fracture) cross-sections predicted by finite-element simulation corresponded to those found in practice. However, the finite-element simulation was not able to predict formation of wrinkles at the tube ends caused by excessively large strokes. Such wrinkles were obtained in practice.

  • 4.
    El-Amine, Karim
    et al.
    Örebro University, School of Science and Technology. Suzuki Garphyttan AB, Garphyttan, Sweden.
    Larsson, Joakim
    Örebro University, School of Science and Technology. Department of Mechanical Engineering.
    Pejryd, Lars
    Örebro University, School of Science and Technology. Department of Mechanical Engineering.
    Experimental comparison of roller die and conventional wire drawing2018In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 257, p. 7-14Article in journal (Refereed)
    Abstract [en]

    In this work, the application of roller dies as an alternative to conventional dies in the wire drawing process – claimed in earlier works to offer many advantageous improvements – is evaluated. To this end, experimental procedures using a single stage drawing machine were conducted, drawing low and medium carbon steel wires using both roller dies and conventional dies. The two reduction processes were compared with respect to drawing force and the resulting wire temperature. Also the mechanical properties of the drawn wires were investigated. The obtained results have not shown any large differences between the two processes, and the main improvement using the roller die method was a better wire surface. This advantage was counteracted with downsides including higher wire temperature and lower strain at fracture.

    Moreover, a formula to theoretically calculate drawing force for the conventional drawing process was modified and used to calculate drawing force for the two reduction steps in the roller die cassette. The results showed that the proportion of inhomogeneous deformation was much higher in the rolling process as compared to the conventional process.

    In view of the outcomes in this work, the alternative of drawing wire through roller dies was not considered to be offering more improvements with respect to the conventional drawing method.

  • 5.
    Gillström, Peter
    et al.
    Örebro University, Department of Technology.
    Jarl, Magnus
    Örebro University, Department of Technology.
    Mechanical descaling of wire rod using reverse bending and brushing2006In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 172, no 3, p. 332-340Article in journal (Refereed)
    Abstract [en]

    Wire rods are covered with an oxide layer, which must be removed before wire drawing. This paper presents an investigation of mechanical descaling by reverse bending and brushing as replacement for pickling. Steel grades studied were low carbon steel and silicon chromium steel. Brushing was done with steel brushes and nylon brushes with SiC. The amount of scale remaining after reverse bending of the low carbon steel depended on the roller diameter. After brushing traces of scale remained in valleys on the surface. Surface damage was observed after brushing with steel brushes but not after SiC-nylon brushing. Silicon chromium alloyed steel was not possible to clean by bending and brushing with the roller diameters studied. The electrical energy required for the mechanical descaling of low C steel may be estimated to be 7kWh/tonne with SiC-nylon brushes and 14kWh/tonne with steel brushes. [All rights reserved Elsevier]

  • 6.
    Gunnarsson, Lars
    et al.
    Swedish Institute for Metals Research, Stockholm, Sweden.
    Asnafi, Nader
    Swedish Institute for Metals Research, Stockholm, Sweden.
    Schedin, Erik
    Swedish Institute for Metals Research, Stockholm, Sweden.
    In-process control of blank holder force in axi-symmetric deep drawing with degressive gas springs1998In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 73, no 1-3, p. 89-96Article in journal (Refereed)
    Abstract [en]

    A new blank-holder system with degressive gas springs has been developed and evaluated for axi-symmetric deep drawing. In contrast to most published works in this field, in which hydraulic systems are utilized, the new system is integrated with the tool body instead of with the press, the advantage with this approach being that the system is independent of press facilities. The new system consists of inter-connected active and passive gas springs, moving parallel during forming. With the new system, degressive, constant and progressive blank-holder force (BHF) trajectories can be obtained. The BHF-trajectories were pre-determined with a specially developed software. Two materials, an ordinary deep drawing steel and a high-strength rephosphorized steel, have been analysed. The thickness was 0.7 mm and a water emulsion was used as lubricant. The blank holder force, punch force, total force and the separation of the blank holder (wrinkle detection) were recorded continuously during the pressing operation. With a degressive BHF-trajectory the process window between fracture and wrinkling in axi-symmetric deep drawing is larger compared to those obtained with constant and progressive trajectories, and also, the LDR is higher.

  • 7.
    Gustafsson, Erik
    et al.
    Väderstad-Verken AB, Väderstad, Sweden.
    Hofwing, Magnus
    Department of Mechanical Engineering, Jönköping University, Jönköping, Sweden.
    Strömberg, Niclas
    Department of Mechanical Engineering, Jönköping University, Jönköping, Sweden.
    Residual stresses in a stress lattice: experiments and finite element simulations2009In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 209, no 9, p. 4320-4328Article in journal (Refereed)
    Abstract [en]

    In this work residual stresses in a stress lattice are studied. The residual stresses are both measured and simulated. The stress lattice is casted of low alloyed grey cast iron. In fact, nine similar lattices are casted and measured. The geometry of the lattice consists of three sections in parallel. The diameter of the two outer sections are thinner than the section in the middle. When the stress lattice cools down, this difference in geometry yields that the outer sections start to solidify and contract before the section in the middle. Finally, an equilibrium state, with tensile stresses in the middle and compressive stresses in the outer sections, is reached. The thermo-mechanical simulation of the experiments is performed by using Abaqus. The thermo-mechanical solidification is assumed to be uncoupled. First a thermal analysis, where the lattice is cooled down to room temperature, is performed. Latent heat is included in the analysis by letting the fraction of solid be a linear function of the temperature in the mushy zone. After the thermal analysis a quasi-static mechanical analysis is performed where the temperature history is considered to be the external force. A rate independent J2-plasticity model with isotropic hardening is considered, where the material data depend on the temperature. Tensile tests are performed at room temperature, 200°C, 400°C, 600°C and 800°C in order to evaluate the Young´s modulus, the yield strength and the hardening accurate. In addition, the thermal expansion coefficient is evaluated for temperatures between room temperature and 1000°C. The state of residual stresses is measured by cutting the mid section or the outer section. The corresponding elastic spring-back reveals the state of residual stresses. The measured stresses are compared to the numerical simulations. The simulations show good agreement with the results from the experiments.

  • 8.
    Larsson, Joakim
    et al.
    Örebro University, School of Science and Technology.
    Jansson, Anton
    Örebro University, School of Science and Technology.
    Pejryd, Lars
    Örebro University, School of Science and Technology.
    Process monitoring of the wire drawing process using a web camera based vision system2017In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 249, p. 512-521Article in journal (Refereed)
    Abstract [en]

    Wire drawing is a cold metal forming process where a wire is drawn through a series of dies, reducing the wire dimension, and enhancing the material properties. The wire drawing process requires lubrication to function, as discrepancies in the lubrication can cause failure of the entire process. Such incidents can be costly and there is a need to monitor the process so that changes in the lubrication can be detected, and addressed, before failures occur. The aim of this work was to determine whether a CCD-camera could be used to monitor the wire drawing process. The purpose of the monitoring was to detect if the process was about to fail. In this work the failure of the process was initiated by removal of the lubricant, causing galling between the wire and the die. The signal from the CCD-camera was compared to the signal from a drawing force measurement that clearly indicates when the friction in the die increases, which in turn indicates imminent failure of the process. It was found that the CCD-camera signal clearly indicated the removal of lubricant, and thus failure. In this work, the CCD-camera was tested on two different wire materials and two different lubricant, both with positive results. All tests were performed in an industrial wire drawing setup.

  • 9.
    Överstam, Henrik
    Örebro University, Department of Technology.
    The influence of bearing geometry on the residual stress state in cold drawn wire, analysed by the FEM2006In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 171, no 3, p. 446-450Article in journal (Refereed)
    Abstract [en]

    Finite element simulations have been performed in order to study the influence of bearing geometry on the residual stress-state in cold drawn wires. Experiments in full industrial scale have been performed in order to verify the FEM results. The residual stresses were measured with X-ray diffraction in both the axial and tangential direction. The material used was a high carbon steel for roller bearings, 100Cr6. It was found that the geometry of the bearing has a large influence of the residual stress-state. When the bearing is somewhat tapered, a gap in the beginning of the bearing is formed. This "double contact" reduces the axial and tangential residual stress to minimum or even to a compressive state. A cylindrical bearing gave no contact in the bearing at all due to elastic deformation. This resulted in a large axial and tangential residual stress. It was shown that even a small divergence from the desired bearing geometry due to the grinding of the die could affect the residual stress immensely.

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