Merklein, Marion

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Merklein, Marion
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Merklein, Marion
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Merklein, M.
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2015 - 20204

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    Item-typ:Veröffentlichung,
    Development and Evaluation of Tool Sided Surface Modifications for Dry Deep Drawing of Steel and Aluminum Alloys
    (2015)
    Merklein, Marion
    ;
    Vollertsen, Frank
    ;
    Schmidt, Michael
    ;
    Wartzack, Sandro
    ;
    Tremmel, Stephan
    Avoiding negative effects of conventional lubrication in forming operations stimulates research on lubricant free forming processes. Increased friction and wear due to direct contact between tool and workpiece surface lead to insufficient forming results in dry forming operations. Dry deep drawing of rectangular cups with conventional tools reveals cracks and wrinkles. This necessitates the development of tool sided surface modifications which face the challenges of lubricant free forming. As former results of tribological investigations have shown, adhesion is the dominant friction and wear mechanism. Therefore, diamond-like carbon coatings are applied to decrease adhesion. The mechanical properties of a-C:H:W- and ta-C-coatings are systematically analyzed to reduce friction and wear. Additionally, micro features are generated by laser texturing of a-C:H:W coatings to control material flow by locally adapted frictional conditions. The effects of different feature edge geometries and the feature orientation are investigated in ring-on-disc tribometer tests. Depending on the deposition parameters some a-C:H:W coating variants show reduction of adhesion for DC04. However, in contact with aluminum alloys no improve of tribological conditions could be achieved. ta-C coatings affect the reduction of friction and wear in contact with DC04 and aluminum and show high potential for application in dry forming processes. Depending on adhesion affinity of the workpiece material, micro features can increase friction by adjusting their edge geometry, orientation and area coverage. The tribological behavior of selected surface modifications is finally analyzed in the strip drawing test. The obtained results gain basic knowledge for development of surface modifications towards realization of lubricant free deep drawing by a tailored tool concept.
    Wissenschaftlicher Artikel
      451  152
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    Item-typ:Veröffentlichung,
    Lubricant free forming with tailored tribological conditions
    (2020-06-12)
    Henneberg, Johannes
    ;
    Rothammer, Benedict
    ;
    Zhao, Rong
    ;
    Vorndran, Martin
    ;
    Tenner, Jennifer
    Changed ecological and economic situations motivate research into environmentally friendly and efficient manufacturing processes. Forming without lubricant has the potential to meet both requirements by avoiding the usage of environmentally harmful lubricants and shortening the process chain by omitting lubricant application and component cleaning. Within the scope of the project, an increase in friction and adhesive wear were identified as major challenges, resulting in failure of components due to cracking. Therefore, this project focused on the investigation of measures to meet these challenges. Amorphous carbon coatings, the reduction of roughness and the application of discrete microtextures were considered as potential measures. Hydrogen-containing amorphous carbon coating systems (a-C:H) fabricated by reactive physical vapor deposition (PVD), plasma-enhanced chemical vapor deposition (PECVD) and PVD/PECVD hybrid techniques, as well as a PVD-generated tetrahedral hydrogen-free amorphous carbon coating (ta-C) were investigated with respect to their properties and tribological performance Three specific profile requirements –a dopant free carbon network, smooth and defect-free surfaces and a high coating adhesion to substrate –are identified as requirements, in order to prolonger the service life of the coated tools. Moreover, to enable the steering of the material flow ultrafast laser based micro texturing for locally tailored tribological conditions were investigated. Thereby two wavelength dependent ablation regimes which differ in ablation mechanism and freedom of form were identified. Using these approaches the friction coefficient could either be reduced by up to 20 % or selectively increased. To improve the efficiency of the process, several beam shaping approaches were evaluated to provide a homogeneous beam profile for uniform modification. By applying ta-C and a-C:H coatings in forming tests, the findings of the laboratory tests were validated and the feasibility of lubricant free deep drawing was proven. In order to benefit from the forming-process-specific advantages, high quantities and therefore high durability of the measures are required. An application-oriented wear test rig has been designed to investigate their durability. By this, it was proven that 3 000 components can be produced from DC04 without wear with both a-C:H and ta-C coatings, and thus increasing tool life by a factor of 15 compared to unmodified tools. Even in the case of wear-critical AA5182, 3 000 parts were produced without wear using ta-C. Within the scope of the project, a fundamental understanding of lubricant free deep drawing processes and measures was created and proof of feasibility in form of a high number of components was achieved.
    Wissenschaftlicher Artikel
      378  286
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    Item-typ:Veröffentlichung,
    Tailored modifications of amorphous carbon based coatings for dry deep drawing
    (2016)
    Merklein, Marion
    ;
    Vollertsen, Frank
    ;
    Schmidt, Michael
    ;
    Tremmel, Stephan
    ;
    Andreas, Kolja
    Avoiding negative effects of conventional lubrication in forming operations stimulates research on lubricant-free sheet metal forming. Without lubricants, the direct contact between tool and workpiece leads to intensive interaction in terms of increasing friction and wear. Especially, when forming aluminum alloys, adhesion is detected as main wear mechanism propagating already at the initial contact between tool steel and sheet material. Thus, surface modifications need to be developed to substitute the functions of conventional lubricants. Former studies revealed that amorphous carbon based coatings improved the tribological conditions. Depending on the specific coating type adhesion and friction could be significantly reduced. Besides achieving a lower level of friction, a control of material flow is necessary to improve the forming results in deep drawing processes. Thus, there is a need for contact zones with higher and lower friction to locally accelerate or restrict the flow of the sheet material. In order to achieve these tailored tribological conditions a broad range of surface modifications needs to be developed and evaluated in a process-like environment. The tribological behavior is affected by coating properties and structure. By varying gas flow and ratio for a-C:H coatings the relationship between deposition parameters and coating properties are investigated. A further approach to realize a broader range of friction coefficients is the laser based texturing of coated tools. Additionally, a laser based heat treatment is investigated to control the sp2/sp3 ratio of ta-C coatings to affect friction and wear mechanisms. The tribological behavior of the investigated surface modifications is analyzed in ring-on-disc and flat strip drawing tests. A surface characterization is performed to identify about the wear mechanisms. Based on the modifications of a-C:H and ta-C coatings a correlation between chemical and mechanical properties and the tribological behavior in contact with zinc-coated deep drawing steel and aluminum alloys is found.
    Wissenschaftlicher Artikel
    Band:Volume 2
      1037  186
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    Item-typ:Veröffentlichung,
    Investigation of Tribological Systems for Dry Deep Drawing by Tailored Surfaces
    (2015)
    Merklein, Marion
    ;
    Schmidt, Michael
    ;
    Tremme, Stephan
    ;
    Wartzack, Sandro
    ;
    Andreas, Kolja
    Growing ambitions for efficient resource utilization and improving environmental standards stimulate the abandonment of environmentally harmful lubricants. However, dry forming leads to direct contact between tool and workpiece surface which causes increasing friction and wear. This paper presents a methodology for realization of lubricant free deep drawing processes. Dry deep drawing of a rectangular cup is investigated by a numerical simulation. First numerical results reveal the necessity of modifying the tribological system in order to realize dry deep drawing. Basic tribological investigations reveal increasing friction and intensive wear under dry conditions. Therefore, tailored surfaces are developed to improve the tribological properties without lubrication. By laser structuring various micro features were fabricated on the tool surface. Furthermore, tungsten doped hydrogenated amorphous carbon coatings (a-C:H:W) were deposited on the tool using unbalanced magnetron sputtering. The tribological behavior of these surface modifications were researched by a ring-on-disc-tribometer. The wear mechanisms during the dry sliding process are discussed depending on the micro features and coatings. The obtained test results help building the basic concept for generating tailored surfaces and subsequently to realize lubricant free deep drawing.
    Wissenschaftlicher Artikel
    Band:1
      462  235