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Träfflista för sökning "WFRF:(Dahlman Patrik 1971 ) "

Sökning: WFRF:(Dahlman Patrik 1971 )

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1.
  • Dahlman, Patrik, 1971- (författare)
  • High Pressure Jet Assistance in Steel Turning
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Steel turning is one of the most common industrial processes today. It is a very old process, where a lot of improvements and optimisations have been done throughout history. But, the struggle for further cost reductions pushes the process development into new areas. One of those is the use of pressurised cutting fluids in order to improve the machinability of the materials. This is a process predominantly used when turning high strength materials such as titanium and Inconel alloys. In this area the Ultra High Pressure Cooling (UHPC) process is accepted and used. But, when turning steel, the method has not been acknowledged to give enough benefits to be considered. Several tests showed that UHPC indeed could be a method giving substantial cost reductions when turning steels especially for long chipping grades. An extensive experimental investigation was therefore initiated with the purpose to increase the knowledge around UHPC in steel turning. From the start the research was focused upon quick industrial implementation, which has been done continuously for every new step in the development. Tests with high-pressure jets were done, both in laboratory and in industrial application. In combination with experiments available, diversified knowledge was collected into a coherent source of information to be used as a tool for implementation. Results show significant increase in chip control, its importance is sometimes overlooked in regard to production efficiency. In fact, chip control is more important than a long tool life. Improvements in tool life have been shown with possibilities to increase the cutting velocity with resulting improvement of productivity. To reach good results using UHPC in turning, certain rules of application are required. These have been defined. Especially important is the way the jet is applied into the cutting zone. It is not possible to achieve the benefits if the jet has an erroneous direction. Jet momentum has been found as the most comprehensive way to evaluate the effect on the chip form as a function of pressure and flow.
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3.
  • Ryttberg, Kristina, 1977-, et al. (författare)
  • High strain rate deformation induced by high-velocity forming of 100Cr6 steel
  • 2008
  • Ingår i: proceedings of The 9th International Conference on Technology of Plasticity (ICTP), Gyeongju, Korea, September 7-11, 2008. - 978-89-5708-152-5
  • Konferensbidrag (refereegranskat)abstract
    • This paper concerns the development of the near-net-shape manufacturing technique of high-velocity forming. The microstructural response to the high strain-rate deformation was evaluated for 100Cr6 steel in two differently heat treated conditions: spheroidise annealed (hardness 250 HV) and quenched and tempered (330 HV). A high-velocity pressing machine was used to conduct the forming tests on cylindrical specimens. By applying different impact velocities on samples with varying sizes deformation mechanisms could be related to strain and strain rate. Extreme localization of deformation resulting in white etching bands was seen in quenched and tempered samples but not in spheroidise annealed samples. Furthermore, the strain and strain rates were shown to affect the tendency for extreme localization. No white etching bands were found in samples strained to less than 1. Appearance of white etching bands could be seen in the macroscopic shape of the samples where the more homogeneously deformed samples showed a typical barrel shape while the strongly localized samples were slightly more bell shaped. It can be concluded that for high-velocity forming to be applicable to 100Cr6 steel a careful choice of the combination strain/strain rate needs to be made.
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4.
  • Ryttberg, Kristina, 1977-, et al. (författare)
  • Microstructural evolution during fracture induced by high strain rate deformation of 100Cr6 steel
  • 2009
  • Ingår i: journal of materials processing technology. - 0924-0136. ; 209:7, s. 3325-3334
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper investigates the influence on parting-off mechanisms of a significantly higher impact velocity compared to commercial methods. A specially developed method, allowing for parting-off velocities ranging from 38 to 285 m/s has been applied to 100Cr6 steel bars. Two different heat treatments; spheroidise annealing (SA) and quench and tempering (QT) were employed to produce two different microstructures of a hardness of 255 and 310HV, respectively. It appears that the failure mechanisms active in the current process are virtually identical to failure occurring during high-velocity parting-off using commercially available machines, which displays shear fracture and adiabatic shear banding. It was also concluded that the estimated energy consumed during parting-off is not dependent on microstructure. Prior to parting-off, impact results in shear localisation, which is somewhat increased with increased impact speed. Furthermore, shear strains at fracture also increases with impact speed, from a value of about 2.2 at the lowest impact velocity to almost 3.5 at an impact velocity of 285 m/s. The heavy deformation causes a grain refinement. Right below the fracture surface three subzones can be found in the microstructure; a white etching band (WEB) (only present on some locations), equiaxed grains and then elongated subgrains. The grain size within these zones varies between 50 and 150 nm. The findings of elongated subgrains of a mutual orientation, adjacent subgrains having {110} type of planes in parallel, support the theory of formation of white etching bands being a mechanically rate controlled process.
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5.
  • Ryttberg, Kristina, 1977-, et al. (författare)
  • Microstructure and texture development during ring rolling of 100Cr6
  • 2008
  • Ingår i: proceedings of The 15th International Conference on the Textures of Materials (ICOTOM), Carnegie Mellon University, Pittsburgh, Pennsylvania, June 1-6, 2008, ed. by A.D..Rollett (American Ceramic Society 2008). - 978-1-57498-296-1
  • Konferensbidrag (refereegranskat)abstract
    • Pre-turned 100Cr6 steel rings with spheroidised annealed microstructure have been cold ring rolled to two levels: expanding the outer diameter by 10 and 20%. The final microstructure was shown to be varying throughout the cross-section of the ring, where the largest deformation was found close to the surface of the inner diameter. This was reflected in the hardness profile showing the highest hardness values close to the inner surface. Scanning electron microscopy showed that the microstructure below the surface of the outer diameter consisted of a greatly refined ferrite. Close to the surface of the inner diameter the structure was even more refined. Electron back scatter diffraction together with X-ray diffractometry showed that cold ring rolling changed the existing texture of the ring blanks, where {110}-planes were parallel to the axial direction of the rings, towards {110}-planes becoming parallel to the rolling direction. This resulted in a weak {110}-texture. Close to the surface of the outer diameter the greatly refined ferrite had decomposed into a more random orientation distribution.
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7.
  • Ryttberg, Kristina, 1977-, et al. (författare)
  • The effect of cold ring rolling on the evolution of microstructure and texture in 100Cr6 steel
  • 2010
  • Ingår i: Materials Science and Engineering A. - 0921-5093. ; 527:9, s. 2431-2436
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper concerns the development of microstructure and texture during cold ring rolling of 100Cr6 steel rings with starting rectangular cross-sections. By interrupting the rolling process at pre-defined intervals expansion ratios ranging from 1.05 to 1.5 were achieved resulting in varying degrees of deformation of the rings. Results for rings with a simple rectangular cross-section were compared with results for a cold rolled ring with a more complex cross-section. By combining results from optical and scanning electron microscopy with hardness measurements the two different ring shapes were shown to display similar material flow during cold ring rolling. The deformation was most severe near the inner diameter of the rings decreasing towards the area of the outer diameter. By employing electron back scatter diffraction (EBSD) the ring rolling process was shown to change the {111}-fibre texture of the ring blanks to a {110} texture. This implies a mixture of both shear and compressive deformation during rolling.
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