Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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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.

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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.

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Development of monolithic ceramic milling tools for machining graphite

2020 , Uhlmann, Eckart , Polte, Mitchel , Polte, Julian , Kuche, Yves , Hocke, Toni

Due to the 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 are in focus to overcome these challenges. Besides copper, graphite is the most important electrode material for electrical discharge machining (EDM). The machining of graphite leads to high tool wear due to a strong abrasive effect. Short tool life has a considerable influence on the economic efficiency of manufacturing processes. Currently, for the machining of graphite cost intensive diamond coated carbide tools are applied. In order to reduce machining costs, innovative cutting materials and dedicated manufacturing processes have to be applied. First results show a great potential of ceramics as tool material for machining graphite. The aim of this investigation is the characterisation and identification of novel ceramic cutting materials and the evaluation of an innovative tool micro-geometry especially designed for machining graphite. Therefore, the cutting material properties such as hardness, fracture toughness and wear resistance of four ceramic materials were investigated. Various hardness tests and particle blasting tests were carried out. Based on this investigations to manufacture the ceramic milling tools, a specific and innovative tool micro-geometry with defined angles was used. Thereby, a suitable cutting ceramic was identified, which represents a promising approach for an optimised machining of graphite.

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Influence of cutting edge micro-geometry in micro-milling of copper alloys with reduced lead content

2018 , Uhlmann, Eckart , Kuche, Yves , Polte, Julian , Polte, Mitchel

Especially copper-zinc alloys (CuZn) with good machining properties are used for electrical components and fittings. By using copper alloys with lead content of 1 % < Pb < 3 % an improved chip breakage can be achieved. Legal regulations require the reduction of lead and demand further knowledge about the effect of the material properties in interaction with the used micro-milling tools. In this contribution the cutting conditions of copper as well as four copper alloys were examined. The results show considerable differences in the resultant surface roughness and burr formation. Furthermore, the influence of two different tool geometries and variied cutting edge micro-geometries were investigated while machining CuZn21Si3P. Thereby, tools with increased cutting edge radii rv showed increased active forces Fa, burr height h0 and decreased surface roughness.

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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 %.

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Tool wear and surface roughness in micro-milling of aluminium and high-alloyed aluminium materials using cutting tools made of binderless carbide

2021 , Uhlmann, Eckart , Polte, Mitchel , Wiesner, H.M. , Polte, Julian , Hein, Christoph

Micro-milling can be applied for manufacturing in a wide range of materials and complex geometries. This process is especially important for the aerospace industry. High-alloyed aluminium is a common material for aerospace applications with complex micro- and macro-geometry due to its high wear resistance. The costs-effectiveness of producing these parts can be increased by using tools with improved wear behaviour and higher life times. However, wear-resistant tools are often associated with higher tool costs, which reduces the cost-effectivness of the whole production. An innovative solution is offered by the use of a cutting tool made of binderless tungsten carbide. The micro-milling of conventional and high-alloy aluminium with a new cutting material based on a binderless tungsten carbide is analysed in this investigation. The absence of a binding phase leads to an increased hardness and improves the wear behaviour of these tools. Therefore, tools with a tool diamete r of D = 10 mm were manufactured and there machinability was successfully proven. The feasibility of these innovative tools is demonstrated in a series of experiments. The experimental investigations were carried out on the five-axis high precision machine tool PFM 4024-5D PRIMACON GMBH, Peißenberg, Germany, with a workpiece made of TiAl 48-2-2. A surface roughness of Ra = 0.202 µm was detected after a path length due to primary motion lc = 70 m without any noticeable wear marks on the cutting tool. These results show the economic potential for milling tools based on binderless carbide for achieving high precision surfaces while reaching high lifetimes.

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DEM-simulation of particle behaviour during cutting edge preparation of micro-milling tools by immersed tumbling

2020 , Uhlmann, Eckart , Polte, Mitchel , Polte, Julian , Kuche, Yves

The micro-milling process is widely used in industry for the manufacturing of complex geometries for a wide range of materials. To increase the tool life and cutting length the cutting edge preparation could be successfully established. Within preliminary investigations the immersed tumbling process was identified as the most promising process for cutting edge preparation of micro-milling tools. The process enables a reproducible cutting edge preparation with constant cutting edge radii as well as low chipping of the cutting edges. For a profound understanding of the preparation process and the process mechanisms further knowledge about the particle interactions with cutting tools as well as the particle flow mechanisms needs to be obtained. Therefore, the process simulation using discrete element methods (DEM) offers the possibility of an improved understanding of the process behaviour. In this investigation simulation studies about the cutting edge preparation of micr o-milling tools using the immersed tumbling process will be presented. The DEM with the software ROCKY DEM from the company ESSS, Florianópolis, Brasil, was used and a process model was derived. The investigations show that the software can be successfully used for the visualisation of the immersed tumbling process and the flow mechanisms can be examined more closely.

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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.

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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.

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Development of a machining strategy for diamond slide burnishing burnishing tools made of polycrystalline diamond (PCD)

2020 , Uhlmann, Eckart , Polte, Mitchel , Polte, Julian , Kuche, Yves , Wendorf, S. , Siebel, D.

High demands on product quality force companies to reduce production costs. Due to the growing international competition, optical surfaces for tool and mould making need to be produced economically. These surfaces are commonly produced using ultra-precision cutting. However, the efficiency is limited due to low feed velocities vf, small depth of cut ap and associated long process times tPr. An innovative manufacturing process represents diamond burnishing, which can be carried out directly after the high-precision milling process. For this purpose, super-hard materials made of single crystalline diamond (SCD) are currently used as tool materials. Since the material costs are high and the availability is limited, SCD needs to be substituted. An innovative substitution material is polycrystalline diamond (PCD). Within this paper, a machining strategy for the high-precision production of PCD spheres for diamond slide burnishing tools is presented. The processes grinding, p olishing and electrical discharge machining (EDM) were applied. Therefore, the manufacturing costs, the surface roughness, the shape accuracy as well as the concentricity accuracy were analysed. Based on these investigations, an efficient and economical machining strategy for the production of high-precision spherical geometries made of PCD can be provided. First results showed that the prefered machining strategy uses a cross-process chain consisting of grinding and polishing. Thereby, the advantages of both processes with the fast manufacturing of the macro-geometry by the grinding process as well as the high surface qualities, which can be achieved by the polishing process, are combined.

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