Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Precision Finishing of Additive Manufactured Ti-Al-components Using Diamond Slide Burnishing
    ( 2022)
    Polte, Julian
    ;
    Polte, Mitchel
    ;
    Lahoda, Christian
    ;
    Uhlmann, Eckart
    Due to the increasing importance of lightweight design in terms of resource management, titanium aluminium (Ti-AI) alloys are gaining more and more significance. To fully exploit light weight design potentials additive manufacturing (AM) has the ability to shift state of the art product design towards maximised resource efficiency and physically minimized weight. Next to material standardization and qualification processes, major limitations for mass scale industrialization of additive manufacturing are high surface roughness values in a range of 5 μm ≤ Ra ≤ 15 urn and remaining tensile residual stress states. A promising approach to overcome these challenges shows a process chain consisting of near-net-shape laser powder bed fusion (LPBF) and subsequent finishing using a dedicate diamond slide burnishing (DSB) process [1]. Within this work plastic deformation induced by DSB and the effects on the workpiece material properties were investigated.
  • Publication
    Zirconium dioxide-reinforced aluminium oxide ceramic for micro-milling of graphite
    ( 2022)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Polte, Julian
    ;
    Hocke, T.
    ;
    Wendt, M.
    Tool and mould making is one of the most important sectors for production of complex parts with highest economic efficiency. Particularly the milling process is a key technology for the manufacturing of tool electrodes for electrical discharge machining (EDM). Beside copper, graphite is the most industrial relevant tool electrode material for sinking-EDM. According to the state of the art the machining of graphite results in high tool wear in consequence of strong chemical and abrasive effects. Currently, uncoated and cost intensive diamond coated cemented carbide tools are used for industrial applications. High tool costs and short tool life have a negative impact on the economic efficiency of the manufacturing process and increase the overall production costs. To reduce the production costs, the needs for innovative cutting materials and dedicated manufacturing processes are high. The zirconium dioxide-reinforced aluminium oxide ceramic used in this investigation shows a great potential because of the high hardness H, the missing binder phase and the covalent bond. The aim of this investigation is the examination of the application behaviour of ceramic cutting tools during the machining process of graphite. Therefore, dedicated milling tests in partial and full cut were carried out. For evaluation of the application behaviour of the ceramic tools, the surface quality of the machined graphite depending on the wear of the tools was considered. The results show that a minimum surface roughness of Ra = 0.80 µm and average surface roughness of Rz = 6.55 µm could be achieved in first milling tests. Due to a strong sharpening effect of the cutting edge during the machining, the possibility was provided to produce complex components with highest precision and without chipping behaviour. The machining of graphite using ceramic milling tools shows extensive advantages compared to conventional milling tools, which may positively affect the economic efficiency of machining graphite in the future.
  • Publication
    High-Performance Electro-Discharge Drilling with a Novel Type of Oxidized Tool Electrode
    ( 2022)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Streckenbach, Jan
    ;
    Dinh, Ngoc Chuong
    ;
    Yabroudi, Sami
    ;
    Polte, Mitchel
    ;
    Börnstein, Julian
    Electro-discharge drilling is a key technology for manufacturing sophisticated nozzles in a broad range of automotive and aerospace applications. The formation of debris in the working gap leads to arcs and short circuits on the lateral surface when state-of-the-art tool electrodes are used. As a result, limited drilling depth, increased linear tool wear, and the conicity of boreholes are still challenges. In this work, a new approach for the passivation of the lateral surface of copper tool electrodes by oxidation is shown. The comparison with state-of-the-art tool electrodes showed a reduction in the erosion duration by 48% for machining hardened steel. Promising improvements could be achieved by the thermal oxidation of the tool electrodes with the aim of increasing the electrical resistivity of the lateral surface of the tool electrode. However, due to the loss of strength, the high oxide layer thickness, and the partial delamination of the oxide layer, further comprehensive investigations on the influence of the oxidation temperature need to be conducted. Future adjustments with lower oxidation temperatures will be carried out.
  • Publication
    Residual stresses in additive manufactured precision cemented carbide parts
    ( 2022)
    Polte, Julian
    ;
    Polte, Mitchel
    ;
    Hocke, T.
    ;
    Blankenburg, Malte
    ;
    Lahoda, Christian
    ;
    Uhlmann, Eckart
    Due to the good strength properties and high hardness, components made of cemented carbide are used in various industrial sectors as key components, e.g. mould making and matrices. Precision cemented carbide parts are mainly machined by milling and electrical discharge machining (EDM). Nevertheless, long machining times and excessive tool wear are remaining challenges at the state of the art. A promising approach to overcome these challenges is the machining of precise cemented carbide parts using a process chain consisting of near-net-shape laser powder bed fusion (LPBF) and subsequent finishing using a dedicate diamond slide burnishing process. Within previous investigations a geometrical accuracy of ag ≤ 10 µm and a reduction of the surface roughness by Ra = 89 % could be achieved. Within this work plastic deformation induced by the diamond slide burnishing and the effects on the material properties in the surface area were investigated, e.g. residual stresses. For this purpose, the lattice distortion of the metallic cobalt phase was measured by X-ray diffraction using high-energy synchrotron radiation. In addition, the height profile of the residual stresses was also recorded in distances of d = 3 µm to obtain information about the depth effect of the diamond slide burnishing process. Based on the investigations an increase of the residual compressive stresses could be obtained. This shows a particularly positive effect especially for additively manufactured components, as these often show a slight porosity and higher surface roughness as conventional manufactured components. In this way, crack propagation can be prevented and the fatigue strength can be increased.
  • Publication
    Characterization and investigation of binderless nanopolycrystalline diamond turning tools for precision machining
    ( 2022)
    Uhlmann, Eckart
    ;
    Sturm, Heinz
    ;
    Polte, Mitchel
    ;
    Hocke, T.
    ;
    Polte, C.
    ;
    Polte, Julian
    Cemented carbide is used in a wide range of industrial applications as a wear-resistant material, e.g. in mould making and forming industry. At state of the art, the machining of cemented carbide is severely limited because of the hardness, high strength and the resulting wear resistance of the material. Due to the brittle-hard character cemented carbide materials suffer from surface cracks during the machining. The brittle-hard character and the related phenomena result in high tool wear. A promising approach for the machining of cemented carbide is the use of the novel cutting material binderless nanopolycrystalline diamond (NPD) with a dedicated cutting edge design. Within this work, laser machined tools with a corner radius of rε = 400 µm are fully characterized, investigated by Raman spectroscopy regarding the condition of the diamond and applied for first cutting experiments. Cutting investigations were carried out using specimens with a tungsten carbide content of cC = 88 %, a cobalt content of cCo= 12 % and a grain size of dg= 0.5 µm. Prior to these investigations, the condition of the diamonds and possible changes due to the lasered cutting edges were examined by Raman spectroscopy. During the cutting investigations, the brittle-ductile transition as well as the minimum chip thickness were identified by scratching tests. It could be shown that a hydrostatic stress state can be used to achieve ductile chip formation using cemented carbide as workpiece material.
  • Publication
    Additive manufacturing of precision cemented carbide parts
    ( 2021)
    Polte, Julian
    ;
    Polte, Mitchel
    ;
    Lahoda, Christian
    ;
    Hocke, Toni
    ;
    Uhlmann, Eckart
    Cemented carbide parts are commonly used as wear resistance components in a broad range of industry, e.g. for forming, mould making and matrices. At state of the art the machining of precision cemented carbide components by milling is strongly limited due to excessive tool wear and long machining times. Promising approaches for precision machining of cemented carbide components are dedicated cutting tool coatings, new cutting materials like binderless polycrystalline diamond and ultrasonic-assisted machining. Nevertheless, for all these approaches the components need to be machined of monolithic materials. The new approach addresses an innovative manufacturing process chain composed of near net shape Additive Manufacturing followed by a precision finishing process. Within this investigations for the manufacturing of precision cemented carbide parts, cemented carbide with a cobalt content of 17 % and a grain size in a range of 23 µm ⤠gs ⤠40 µm were used. As Addit ive Manufacturing technology laser powder bed fusion was used. Diamond slide burnishing and immersed tumbling were investigated as finishing technologies. Based on the investigations, a dedicated process chain for the manufacturing of precision cemented carbide parts could be realised. The findings show that the developed process chain composed of near net shape Additive Manufacturing and the finishing process diamond slide burnishing enables the manufacturing of precision cemented carbide parts with a geometrical accuracy of ag ⤠10 µm. Due to the finishing process the initial surface roughness after Additive Manufacturing could reduce by Ra = 89 %.
  • Publication
    Cutting edge preparation of monolithic ceramic milling tools
    ( 2021)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Polte, Julian
    ;
    Hocke, Toni
    Due to international competition, continuous increases in productivity, product quality and reduction of production costs are required. Especially, the development of milling tools made of innovative cutting materials and application-specific tool geometries for the machining of brittle materials are in focus to overcome these challenges. One approach to improve the performance and the tool behaviour concerning milling of graphite is the use of monolithic ceramic milling tools. Unfortunately, the high brittleness of the ceramic leads to breakouts on the cutting edge during the grinding process. This results in an increased maximum chipping of the cutting edge, which has a significant influence on the milling process. To improve the breakout behaviour, a cutting edge preparation with the immersed tumbling process was applied. To enable a process reliable cutting edge preparation, a suitable lapping medium, the influence of the processing time as well as the depth of imme rsion were investigated. Besides the maximum chipping of the cutting edge, the rounded cutting edge radius was also analysed. The results show that a process reliable cutting edge preparation of monolithic ceramic milling tools with a maximum chipping of the cutting edge RS,max ⤠3 µm and a rounded cutting edge radius of rβ ⤠7 µm could be realised. In future investigations, the experimental applicability of monolithic ceramic milling tools will be proved.
  • Publication
    Modeling of the wet immersed tumbling process with the Discrete Element Method (DEM)
    ( 2021)
    Uhlmann, Eckart
    ;
    Fürstenau, J.-P.
    ;
    Kuche, Yves
    ;
    Yabroudi, Sami
    ;
    Polte, Julian
    ;
    Polte, Mitchel
    Immersed tumbling is an industrially established process for finishing of components made of metal, ceramic or plastic. In this process, the components are completely surrounded by a wet, abrasive medium, which allows burrs to be removed and surfaces to be polished. In order to gain specific insights into the influence and flow properties of the abrasive media used in this process, numerical approaches using the Discrete Element Method (DEM) with the Rocky DEM software are presented within these investigations. A complete process simulation could be realised by means of a digital machine tool. The immersed tumbling process with cone-shaped polymer abrasive media is implemented by use of a liquid bridge model. The results were validated by experiments with an industrially used immersed tumbling machine tool and for the first time allow sound statements about the contact conditions and interactions of the abrasive media with the workpiece.
  • Publication
    Precision finishing of additively manufactured components using the immersed tumbling process
    ( 2021)
    Polte, Julian
    ;
    Polte, Mitchel
    ;
    Hocke, Toni
    ;
    Lahoda, Christian
    ;
    Uhlmann, Eckart
    Additive manufacturing enables the production of highly complex metallic components with highest geometrical flexibility in dedicated lightweight construction. For titanium-aluminium alloys, which are used in particular in the aviation industry, powder bed based processes such as the laser powder bed fusion are established. Nevertheless, laser powder bed fusion is limited with regard to the producible surface roughness in a range of 5 µm ⤠Ra ⤠15 µm. According to the state of the art, the increase of the geometrical accuracy and the reduction of the surface roughness values of the additive manufactured components are realised by different cutting and non-conventional processes. In this investigation, a new approach for the reduction of the surface roughness values by immersed tumbling was realised. Therefore, additively manufactured square bars made of the titanium alloy Ti-5Al-5Mo-5V-3Cr were used as sample geometries. An immersed tumbling machine tool with plan etary kinematics for post-processing was applied and the lapping media QZ, HSC 1/500 and M5/400 were evaluated. In addition, the influence of the rotor speed and the holder as well as the depth of immersion were considered as influencing factors. As target values the surface roughness values as well as the rounded edge radius were examined. Within this investigations the surface roughness values could be reduced by more than 90 %. In addition, a targeted rounding of the edges could be obtained, which removed the excess edge height at the part resulting from the laser powder bed fusion process. As a result the immersed tumbling process shows a great suitability as a finishing process for additively manufactured components and is particularly suitable for automated and serial finishing processes.
  • Publication
    Micro-milling of a sprue structure in tungsten carbide-based metal matrix composite
    ( 2021)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Polte, Mitchel
    ;
    Hein, Christoph
    ;
    Hocke, Toni
    ;
    Jahnke, Christian
    Many industries rely on plastic components manufactured by micro-injection moulding. There is a high potential to further increase the cost-effectiveness by machining the moulds needed for this process from non-ferrous metals and reinforcing the parts of the mould, which experience high loads during the micro-injection moulding. Inserting tungsten carbide particles locally into the surface of these non-ferrous metals is one possibility of reinforcement. The resulting metal-matrix-composites (MMC) exhibit the needed wear resistance, while the ground material can be machined very effectively through micro-milling. In contrast, the Micro-milling of these MMC-materials is challenging and so far not state of the art. Thus, this investigation is concerned with the development and qualification of micro-milling parameters for tungsten carbide-based MMC-materials. Binderless polycrystalline diamond as innovative cutting material was applied for this purpose. The goal of the mil ling parameter development was to optimize the surface roughness and the form accuracy for machining an aluminium bronze workpiece reinforced with tungsten carbide particles through laser injection. Based on an analysis of a wide range of process parameters, an optimised milling strategy was applied to machine a sprue structure from the described MMC-material. Different parameter sets are evaluated by analysing the form accuracy and measuring the surface roughness of machined structures. A surface roughness of Ra = 80 nm and form accuracy of a = 3 µm could be achieved with optimized micro-milling parameters and qualified the developed parameters for industrial applications.