Kolja Andreas

Analysis of Effectiveness of Locally Adapted Tribological Conditions for Improving Product Quality in Sheet-Bulk Metal Forming

Due to current ecological and economic developments there is a growing demand for functional components with complex and closely tolerated geometrical features. Conventional sheet and bulk metal forming operations leads to products which are often limited in their geometrical and functional variety. A promising approach is the process-class sheet-bulk metal forming (SBMF). SBMF is characterised by the application of bulk and sheet forming operations on sheet metals [1]. This combination leads to locally and temporally varying load conditions regarding stress as well as strain states. In order to get high quality parts, controlling the material flow is of major importance. Modified Surfaces, so-called tailored surfaces represent an innovative approach to control the material flow. The objective of the current study is the experimental investigation of the effectiveness of locally adapted tribological conditions using workpiece-and tool-sided tailored surfaces within SBMF processes. The study has shown that the local adaption of workpiece and tool surface increased the heights of functional elements. Thus, using locally adapted tribological conditions leads to an improvement of the quality of the produced gearing components. In a further step the influence of surface modifications on the surface properties of the manufactured components are analysed. Additionally, investigations regarding the wear behaviour of tool-sided surface adaptions lead to the assumption, that the effectiveness of tailored surfaces is reduced during the operating time of the tools.

Tribological measures for controlling material flow in sheet-bulk metal forming

Sheet-bulk metal forming (SBMF) is characterized by successive and/or simultaneous occurrence of quite different load conditions regarding stress and strain states. These conditions significantly influence the material flow and thus the geometrical accuracy of the components. To improve the product quality a control of the material flow is required. An appropriate approach is given by locally adapted tribological conditions due to surface modifications of tool and workpiece, so-called tailored surfaces. Within the present study different methods to adapt the surfaces are presented and investigated with respect to their tribological effectiveness in SBMF. In a first step, requirements regarding necessary adaptions of the friction values for two SBMF processes are numerically defined. Based on the requirements different tailored surfaces are presented and analyzed regarding their tribological influence. Finally, the potential of surface modifications to improve SBMF processes is shown.

Investigation of surface finishing of carbon based coated tools for dry deep drawing of aluminium alloys

Global trends like growing environmental awareness and demand for resource efficiency motivate an abandonment of lubricants in metal forming. However, dry forming evokes increased friction and wear. Especially, dry deep drawing of aluminum alloys leads to intensive interaction between tool and workpiece due to its high adhesion tendency. One approach to improve the tribological behavior is the application of carbon based coatings. These coatings are characterized by high wear resistance. In order to investigate the potential of carbon based coatings for dry deep drawing, friction and wear behavior of different coating compositions are evaluated in strip drawing tests. This setup is used to model the tribological conditions in the flange area of deep drawing operations. The tribological behavior of tetrahedral amorphous (ta-C) and hydrogenated amorphous carbon coatings with and without tungsten modification (a-C:H:W, a-C:H) is investigated. The influence of tool topography is analyzed by applying different surface finishing. The results show reduced friction with decreased roughness for coated tools. Besides tool topography the coating type determines the tribological conditions. Smooth tools with ta-C and a-C:H coatings reveal low friction and prevent adhesive wear. In contrast, smooth a-C:H:W coated tools only lead to slight improvement compared to rough, uncoated specimen.

Improvement of surface integrity of cold forging tools by adaption of tool making process

Cold forging enables mass production of steel based components. High loads within cold forging presuppose high loadable tool materials. This is why apart from tool steels cemented carbides are mainly used as tool materials. Due to brittleness of these materials, fatigue is one of the major limits of tool life. Tool manufacturing requires a combination of hard machining and subsequent machining steps. For hard machining of complex tool geometries electrical discharge machining (EDM) represents the industrial standard. The thermal influenced surface layer has to be removed by post and fine machining steps. The resulting surface integrity has a major influence on the internal strength of a tool. Correlations between tool manufacturing, surface properties and tool behavior will gain knowledge for an optimized tool production. In this context, scope of the present paper are the investigation and description of the interactions between tool manufacturing and resulting surface properties for tools made of cemented carbide and tool steel. Within the article, the surface properties caused by a conventional process chain consisting of EDM and polishing are quantified. In addition, these results are compared to an adapted process chain with an integrated peening process. The results reveal that the conventional and the adapted process chain lead to similar surface topographies and roughness values. However, the integration of a peening process shifts the residual stress level towards higher compressive stresses.

Modification of tribological conditions for influencing the material flow in bulk forming of microparts from sheet metal

In the present study, the influence of a global adaption of the tribological conditions for a bulk forming process of microparts from sheet metal was analyzed numerically. Based on numerical determined requirements, suitable experimental methods were investigated to modify tribological conditions. For a global adjustment of the friction the influence of a workpiece-sided surface modification and lubrication was investigated. Thus, a dry and lubricated condition as well as flat and abrasively blasted workpiece surfaces, of high-purity oxygen-free copper (Cu-OFE) were analyzed. To evaluate the influence of these measures on friction conditions, the pin extrusion test as a laboratory friction test was used. The friction factors for the different tribological conditions were determined using numerical identification. In a numerical feasibility study, it was shown that the height of the micropin in the investigated process can be influenced by an adaption of the friction. The height of the micropin and thus th...

Influence of Grinding on the Surface Properties of Cemented Carbides

The increased demand for manifold industrial goods requires superior manufacturing techniques. In the field of steel products, cold forging has gained importance for the last sixty years. Within cold forging the tool takes a key role as it determines both accuracy and efficiency of forming process. For forming processes with high demands regarding wear resistance WC-Co cemented carbides are increasingly used as tool materials. The manufacturing process of the tool requires a combination of hard and fine machining. In order to reduce the effort of subsequent fine machining process, surfaces with low roughness are preferred. As grinding leads to high surface qualities, it is a common method in tool machining. Grinding is accompanied by compressive residual stresses in the surface which have a positive influence on the tool life. The absolute value of residual stresses is determined by the machining parameters. The present study investigates the influence of feed and in-feed on the topography and the near surface residual stresses. While the surface roughness is correlated with both parameters, the feed has a major influence on the residual stresses in the surface of cemented carbides.