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Item type:Publication, Access status: with files , Model based assessment of maximal surface temperatures and heat flow in edge trimming of UD CFRP with tools of different type(Elsevier, 2025-04-04); ; ; ; Excessive heating during edge trimming of CFRP components leads to matrix degradation impairing their quality. The thermal response of unidirectional CFRP when machining with different tool types is studied: PCD cutters, coated carbide routers, and diamond grinding pins. Temperature and torque were measured at various fibre orientation angles Φ and cutting conditions. Based on an analytical model, key thermal parameters were identified from experimental data. For all tools, temperatures exceeded the matrix glass transition temperature under most conditions. Maximum of temperature changes was observed at Φ = 135°, minimum at Φ = 90° was most pronounced for the cutter, less noticeable for the router, and almost absent for the grinding pin. At Φ = 90°, the thermal contact length and heat flow ratio typically reached maximum values, while the heat flux was at its lowest. Regarding cutting conditions for both the cutter and router, an increase in cutting speed led to higher equivalent heat flux, heat flow, and temperature change. In contrast, for grinding pins, temperature change increased at the lower cutting speed or feed rate. In grinding, heat flow, equivalent heat flux and thermal contact length were primarily influenced by the fibre orientation symmetry angle, whereas heat flow and equivalent heat flux were nearly independent of the cutting conditions. Thus, the tool types exhibit different thermal parameters and patterns of their dependencies on the machining conditions, which are differentiated by the model and can be explained by pulsed point, pulsed linear or continuous surface contact of individual cutting edges.Publicationtype: Journal Article38 32 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , The role of material properties in modeling maximal surface temperatures and heat distribution in milling of UD CFRP(Elsevier, 2025); ; ; ; In order to meet the precision requirements for components made of carbon fibre reinforced plastics (CFRP), the edges are often trimmed by milling. However, this can lead to detrimental thermal damage to the machined surface. The aim of the study was to investigate in detail the maximum temperatures and characteristic thermal parameters for various unidirectional CFRP materials under different cutting conditions. During upcut milling using a PCD cutter an infrared camera, thermocouples and a dynamometer were employed to monitor temperatures and the cutting power. An analytical heat flow model suitable for arbitrary fibre orientation angles was used to determine, based on thermal material properties, the temperature change at the machined surface and the heat flow parameters from experiments. Material influence on the cutting power was considered by its specific elastic energy at fracture depending on the volume content and mechanical properties of the fibres. At the machined surface, the resin glass transition temperatures were frequently exceeded, and the highest temperature changes were observed at a fibre orientation angle of Φ = 135◦. In most cases, higher cutting speeds were accompanied by greater temperature changes. Phenomenological models of the thermal parameters of the machining process were developed, which take into account both the thermal and mechanical CFRP properties and show a good correlation with the experimental results. They provide benefits in order to predict the temperature fields for materials with differing properties and under varying cutting conditions.Publicationtype: Review Article42 11 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Modeling of temperature fields in milling of unidirectionally reinforced CFRP depending on the fibre orientation angle and the effective width of cut(Elsevier, 2025); ; ; ; CFRP parts are conventionally used within various industries; however, during machining these components, the generated heat is a very relevant limiting factor. Exceeding the glass transition temperature can lead to workpiece degradation, reduced strength, and shorter lifetime. During up-cut milling of unidirectional (UD) CFRP with PCD cutters, the temperature was measured using thermocouples and a thermographic camera, while the cutting torque was measured with a rotating dynamometer. The maximum temperature increase at the machined surface, the heat flow from the machining zone into the material, and the ratio of heat flow to cutting power were simulated. An analytical model developed earlier for the temperature field in machining orthotropic composites with arbitrary fibre orientation was used. The results indicate that cutting power, heat flow, and the ratio of heat flow to cutting power exhibit approximate symmetry relative to the fibre orientation angle Φ = 90°. Introducing the concept of the fibre orientation symmetry angle is useful. Unexpected fractures of larger segments of remaining UD CFRP material occur at all feeds at higher fibre orientation and engagement angles within a small range of fibre cutting angles near 45°, significantly reducing the nominal width of cut and impairing results. The effective width of cut was evaluated based on the drop in cutting torque, measured at various fibre orientation angles, cutting speeds, feeds, and nominal widths of cut. The highest maximum temperature increase consistently occurs at Φ = 135°. As an overall effect, higher cutting speeds lead to increased cutting power, heat flow, and maximum temperature at the machined surface, but result in a smaller depth of the heat-affected zone. The simulations conclude that a higher fibre orientation symmetry angle leads to a higher equivalent heat flux, shorter thermal contact length, and reduced heat flow, and vice versa. In the future, the influence of different tools and composite materials needs to be investigated.Publicationtype: Conference Paper52 14 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Oxidation and wear behavior of CrAlMoN with varied Mo-content for cutting Ti6Al4V(Springer, 2023-08-03); ; ; ; The cutting of difficult to machine materials such as titanium alloys is challenging for the machining industry. In case of the titanium alloy Ti6Al4V, the properties of the material cause high temperatures, mechanical loads as well as high frequency vibrations at the cutting edge, leading to premature tool failure. The use of uncoated carbide tools is very common for machining of Ti based alloys. However, temperature active, self-lubricating physical vapor deposition (PVD) coatings like CrAlMoN showed promising results to reduce friction and wear during turning of Ti6Al4V. In the present study, self-lubricating (Cr34Al41Mo25)N, (Cr29Al36Mo35)N and (Cr25Al31Mo44)N coatings were investigated on cemented carbide tools. These were deposited by a hybrid process combining direct current Magnetron Sputtering and High Power Pulsed Magnetron Sputtering. Coating morphology, thickness, chemical composition, indentation hardness and modulus at ϑ = 20 °C, ϑ = 200 °C, ϑ = 400 °C and ϑ = 600 °C as well as the oxidation behavior were analyzed. Moreover, wear development after cutting tests using a CNC-lathe was investigated. Independent of Mo-content, all coating variants possessed a dense morphology and a smooth surface topography, as well as a coating adhesion class of HF1 to the cemented carbide substrate in Rockwell indentation tests according to DIN 4856. With an increasing amount of Mo, heat treatment temperature and time, more self-lubricating molybdenum oxides such as MoO3 and Mo4O11 were detected by Raman spectroscopy. Therefore, the coating with the highest amount of Mo possessed the highest amount of molybdenum oxides. After cutting tests, molybdenum oxides were also found on the tool flank face by Raman spectroscopy. The level of flank wear land width decreased with increasing amount of Mo.Publicationtype: Journal Article50 11 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Self-lubricating CrAlMoN high performance tool coatings for machining of TiAl6V4TiAl6V4 allows significant performance improvements in industrial applications. However, the machining is a considerable challenge due to low thermal conductivity, Young’s modulus and strong adhesion tendency. This leads to high thermal and mechanical loads on the cutting edge resulting in early tool failure. Today, uncoated cemented carbide tools are commonly used. However, temperature active physical vapor deposition (PVD) coatings like CrAlVN and CrAlMoN provide a promising approach to increase tool life. For this, the coating’s ability to form lubricating oxide phases is vital. In the present study, CrAlVN and CrAlMoN coatings were investigated to determine the more suitable version for increasing the economic efficiency of machining TiAl6V4. The coatings were deposited by hybrid direct current magnetron sputtering/high power pulsed magnetron sputtering (dcMS/HPPMS) processes. Morphology, thickness, chemical composition, indentation hardness, indentation modulus and oxide phase composition were analyzed. Moreover, friction and wear behavior of the coated tools were determined using a pin on disc (PoD) tribometer at various temperatures. Additionally, tool life and deformation behavior were analyzed after turning TiAl6V4. The CrAlVN and CrAlMoN coatings show a dense morphology and a smooth surface topography. Both variants have a good adhesion to the cemented carbide tools. For increased temperatures, the tribological analyses showed a reduction in the coefficient of friction. In case of CrAlMoN coated samples, a friction reduction compared to CrAlVN was observed at lower temperatures. Due to this, an increased tool life was achieved for CrAlMoN coated cutting inserts during turning of TiAl6V4.Publicationtype: Journal ArticleScopus© Citations 1 79 74 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Effect of DED process parameters on distortion and residual stress state of additively manufactured Ti-6Al-4V components during machining(Elsevier, 2022-09); ; ; ; One of the major challenges in high-deposition rate Directed Energy Deposition processes is the resultant residual stresses generated during material deposition, often leading to distortion and poor material characteristics. Important part families suitable for DED process in aerospace sector are thin-wall components, characterized by a large base surface area with rib-like strengthening structures. Here, the substrate plate can be designed to be a part of the final component. The integration of substrate plate into final component results in possible deformation due to residual stress release during machining. This paper therefore investigates the effect of various powder-based Laser Metal Deposition process parameters and strategies on the residual stress state of the additively manufactured Ti-6Al-4V components and the resulting stress release during machining process. The analysis has been carried out during the machining process by including in-process strain measurements of the substrate. The embraced layer removal method allows the determination of machining zone specific stress release mapping, based on an analytical and FEM-model. Hence, the initial residual stress state of the builds was calculated, which revealed that although the heat treatment resolved most of the residual stresses, also in heat treated parts residues were identified depending on the part clamping during the treatment. Furthermore, the study revealed that the significant residual stresses are present in the layers close to the substrate.Publicationtype: Journal ArticleScopus© Citations 5 108 542 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 53 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Self-lubricating CrAlVN coatings for turning of Ti6Al4V: oxidation and wear behavior(Wiley-VCH, 2021-12-15); ; ; ; The titanium alloy Ti6Al4V enables significant performance increases in various branches of industry. Nevertheless, it is difficult to machine, because of its material properties. Due to the low thermal conductivity of titanium, the heat generated while turning Ti6Al4V mainly flows into the tool leading to high temperature loads. In addition, the comparatively low Young’s modulus and high yield strength contributes to high mechanical stresses during machining. Temperatureactive, self-lubricating physical vapor deposition hard coatings appear to be suitable for reducing friction and tool wear during turning of Ti6Al4V compared to the most commonly used uncoated carbide tools. The ability of the coating to form lubricating oxide phases at high temperatures is crucial for this purpose. This paper investigates the oxidation and diffusion behavior of vanadium doped chromiumaluminium nitride (CrAlN) coatings after heat treatment at ϑ=600°C, ϑ=700°C and ϑ=800°C in atmosphere as well as the resulting coating properties. The wear behavior of certain coating variants while turning of Ti6Al4V is analyzed.Publicationtype: Journal ArticleScopus© Citations 1 94 194 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Wear development of self-lubricating CrAlVN coatings during turning Ti6Al4V(Social Science Electronic Publ., 2021-12); ; ; ; Interactions between cutting tool and workpiece material are crucial to tool wear at the cutting edge. In particular difficult to machine materials like the titanium alloy Ti6Al4V require tailored solutions to avoid extensive tool wear. Temperature-active, self- lubricating chromium-aluminium-vanadium-nitride (CrAlVN) coatings deposited by physical vapor deposition (PVD) have shown the potential to reduce tool wear during Ti6Al4V turning. These coatings form lubricating oxide phases at temperatures between 700 °C ≤ θ ≤ 800 °C which might be suitable to reduce thermal and mechanical loads during cutting. However, the initial wear development as well as the formation of lubricating oxide phases during Ti6Al4V turning while using cooling lubricant have not been adequately investigated. Consequentially, it is unclear whether the lubricating oxide phases form during the turning operation with flood cooling. Nevertheless, this is of interest, because the use of cooling lubricant is state of the art in turning of Ti6Al4V in order to reach an increased tool life. That is why, the initial tool wear within the first two minutes of turning with flood cooling was investigated in this study. For this purpose, two different CrAlVN coatings with varying V/Al ratios were deposited on cemented carbide inserts by a hybrid direct current magnetron sputtering (dcMS) / high power pulsed magnetron sputtering (HPPMS) process using an industrial coating unit. Subsequently, cutting tests with a depth of cut ap = 1.2 mm, feed rate f = 0.12 mm, setting angle κr = 95° and cutting velocity vc = 80 m/min were conducted at defined cutting intervals of tc = 5 s, 10 s, 20 s, 40 s, 80 s and 120 s using a computer numerical controlled (CNC) lathe machine. The initial tool wear development, prevailing wear mechanisms as well as the formed oxide phases during the intervals were analyzed. Uncoated cemented carbide inserts were used as a reference. The results highlight that the formation of lubricating vanadium oxides is possible in turning process with cooling lubricant. Furthermore, it seems that adhesion processes are the main causes of tool failure. The results offer the possibility to adapt the CrAlVN coatings for Ti6Al4V turning.Publicationtype: Journal Article105 220 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Impact separation of support structures from laser powder bed fusion generated LPBF partsPublicationtype: Conference Paper108