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  • 1.
    Olofsson, Anders
    KTH, Skolan för industriell teknik och management (ITM).
    Hardening Distortions of Serial Produced Gears2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Hardening distortions are unwanted changes in shape and dimension that arise during hardening of steel components. Uncontrolled distortions induce random errors to the manufacturing process, and have a strong negative impact on manufacturing costs. The distortions are not only caused by the hardening process, several factors from previous manufacturing steps including the component geometry itself contribute to varying extent. The aim of the current work is to investigate the main influencing factors on hardening distortions for serial produced gears.

    The investigations were done on two different types of gears for heavy-duty transmissions, crown wheels for the rear axle central gear and main shaft gears for the gearbox. The steel was produced using either continuous casting or ingot casting. For rectangular continuously cast steel, the effect of disabling magnetic stirring of the steel melt during casting was investigated, finding a strong reduction of gear runout for crown wheels. Segregations in crown wheels produced from the top and bottom of ingots were shown to go in opposite directions, producing opposite back-face tilts.

    For crown wheels quenched one at a time, influences of stacking level on the hardening tray were found, indicating an impact from small variations in the carburizing process, despite identical quenching conditions. For main shaft gears, horizontal loading gave considerably less roundness and runout errors but increased flatness errors compared to vertical loading.

    This thesis shows the complexity of the distortion phenomenon and how several factors interact and contribute to the final result. It is shown that factors with significant impact on hardening distortions for one component may be less important for another component. With this in mind, each type of component to be hardened should be produced by a manufacturing chain where each process step is carefully chosen with respect to minimizing distortions.

  • 2.
    Olofsson, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM).
    Jonsson, Stefan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Hardening Distortions of Serial Produced Crown Wheels2017Inngår i: Materialwissenschaft und Werkstofftechnik, ISSN 0933-5137, E-ISSN 1521-4052Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    The hardening distortions of serial produced crown wheels are studied with respect to gear runout, inner diameter and back-face tilt. The data analysed originates from a production data base from ordinary production as well as from directed experiments carried out in production, resulting in a large set of data. Strong influences are found for steel plants, position of material in ingots and stacking levels on hardening trays. It could be concluded that rectangular strands have a detrimental effect on gear runout, which, however, can be strongly decreased by disabling the magnetic stirring during casting. Furthermore, the inner diameter after quenching is influenced by the stacking level on the hardening tray when free-hardening or when using a segmented central expander during press quenching. This influence is attributed to variations in hardening temperature. When press quenching using a fixed mandrel, the effect of stacking level disappears. Moreover, it is found that the back-face tilt strongly depends on the position in the ingot as well as on the stacking level on the hardening tray.

  • 3.
    Olofsson, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi. Scania CV, Södertälje, Sweden.
    Jonsson, Stefan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi. Scania CV, Södertälje, Sweden.
    Brash, Benjamin
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi. Scania CV, Södertälje, Sweden.
    Hardening distortions related to segregations in crown wheels2016Inngår i: HTM - Journal of Heat Treatment and Materials, ISSN 1867-2493, Vol. 71, nr 2, s. 68-74Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The back-face tilt of press-hardened crown wheels is investigated for continuous and ingot cast material. Two different geometries are studied, one with a flat back-face and one with a step. For two ingots, the original material position is tracked and coupled to back-face tilt, cross section hardness and chemical segregation. The chemical gradients are shifted from top to bottom of the ingot and are strongly coupled to the back-face tilt.

  • 4.
    Olofsson, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Köhn, Mikael
    Scania CV AB.
    Jonsson, Stefan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Identifying process parameters influencing gear runoutManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The hardening distortions with respect to base body, clutch teeth and helical gears are investigated for a serial-produced main shaft gear of a 20NiCrMoS6-4 steel. The influences of casting geometry, annealing heat treatment and stress relief annealing of blanks, as well as vertical and horizontal loading arrangements during case hardening, are studied. The concentricity, roundness and runout of clutch teeth and helical gears are measured in the soft machined, hardened and hard-machined conditions.

    The Brinell hardness is measured on blanks obtained from different manufacturing routes showing differences in hardness and scatter. Stress relief annealing lowers the hardness and the scatter for all groups, but has no significant effect on distortions. The case depth, core hardness and surface hardness are measured after hardening. The study shows that the surface hardness correlates with the oil flow measured in the quench tank.

    The effect of casting geometry is stronger for the clutch teeth compared to the helical gears. For the clutch-teeth roundness and runout, significantly lower values are found for square geometry compared to rectangular. It is also seen that the major part of the runout comes from roundness errors which are mainly induced by the hardening. Horizontal loading reduces roundness errors and runout but produces conical base-bodies with worse backplane flatness.

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