Abstract Simulation systems are used to optimize milling processes by analyzing surface location ... more Abstract Simulation systems are used to optimize milling processes by analyzing surface location errors, which can be predicted by combining various modeling techniques in a multi-scale way. In order to visualize surface location errors, a multi-dexel representation of the workpiece can be used. The application of a triangle mesh representation of the tools to cut the workpiece model is presented, which results in a higher accuracy of the predicted surface location errors in comparison to a Constructive-Solid-Geometry-(CSG)-based approach. Both models are evaluated by simulating a milling process and the simulation results are validated by comparing them to experimental results.
The wear-resistance of sheet metal forming tools can be increased by thermally sprayed coatings. ... more The wear-resistance of sheet metal forming tools can be increased by thermally sprayed coatings. However, without further treatment, the high roughness of the coatings leads to poor qualities of the deep drawn sheet surfaces. In order to increase the surface quality of deep drawing tools, grinding on machining centers is a suitable solution. Due to the varying engagement situations of the grinding tools on free-formed surfaces, the process forces vary as well, resulting in inaccuracies of the ground surface shape. The grinding process can be optimized by means of a simulative prediction of the occurring forces. In this paper, a geometric-kinematic simulation coupled with a finite element analysis is presented. Considering the influence of individual grains, an additional approximation to the resulting topography of the ground surface is possible. By using constructive solid geometry and dexel modeling techniques, multiple grains can be simulated with the geometric-kinematic approach simultaneously. The process forces are predicted with the finite element method based on an elasto-plastic material model. Single grain engagement experiments were conducted to validate the simulation results.
AbstractThe abrasive wear resistance of tribologically stressed free-formed surfaces can be incre... more AbstractThe abrasive wear resistance of tribologically stressed free-formed surfaces can be increased with thermally sprayed tungsten carbide coatings. In order to improve the surface topographies and shape accuracies, the workpieces must be finished prior to industrial application. A suitable machining process is NC grinding on five-axis machining centres using abrasive mounted points. However, the high hardness of the applied coatings and the small diameter of the utilized tools pose a great challenge for the process design. In this paper both, the results of fundamental investigations on the grinding of tungsten carbide coatings as well as a process optimization for the finishing of a coated forming tool are presented. This includes the heat transfer into the coating and the tool wear during the grinding process as well as the wear behaviour of the coating in dependence of the generated surface topography. In order to achieve a smooth surface, elastic-bonded diamond tools were used during polishing in a multi-stage machining process.
The necessity to approximate dynamic contact problems arises in many engineering processes. Becau... more The necessity to approximate dynamic contact problems arises in many engineering processes. Because of the local effects in the contact zone, adaptive techniques are suited to improve the finite element discretisation of such problems. In this article, the Newmark method in time and finite elements in space are used to approximate the solution numerically. A spatial error estimator is derived from the semidiscretised problem. The approach relies on an auxiliary problem, which is a variational equation. An adaptive refinement process is based on this error control. Numerical results illustrate the performance of the presented method.
Microfinishing, also known as superfinishing or short-stroke honing, is a commonly used process f... more Microfinishing, also known as superfinishing or short-stroke honing, is a commonly used process for generating technical surfaces focusing on tribological applications. Due to microfinishing processes high surface qualities are manufacturable regarding the surface roughness and bearing area ratio. While the required characteristics for tribological loaded workpieces are changing with their rising significance, the surface structuring is becoming more and more important. With the use of defined abrasive belts, the possibilities of surface structuring by microfinishing are enhanced. The possibilities and challenges concerning surface structuring by microfinishing applying defined abrasive belts are described in this research study. Therefore, a geometrical-kinematic simulation is used to predict the theoretical structures generated by microfinishing, while in experimental investigations the influences of kinematic parameters and a multi-stage process sequence are considered.
Abstract This study investigates the influence of the pre-drilling diameter on hardness and tensi... more Abstract This study investigates the influence of the pre-drilling diameter on hardness and tensile failure of the formed internal threads (M6), manufactured perpendicular to the profile thickness of thin-walled AZ91 magnesium casting alloys. Previous investigations have shown that introducing a pre-drilling before friction drilling prevents the failure of the bore’s outer wall during the friction drilling process. Considering the oversizing of core bore (friction drilled bore) as an effective factor that can contribute to an incomplete formation of the threads profile through thread forming process, the influence of the pre-drilling diameter was investigated on the hardness and tensile failure of the formed M6 threads. Computed tomography of the friction drilled bores indicated an increase in oversizing of the friction drilled bore with increasing the pre-drilling diameter. Metallographic investigations of the manufactured samples by friction drilling and thread forming process revealed a rhombus-shaped deformation region around the manufactured thread, which provides an enhanced hardness especially at the subsurface of threads profile. The resulting hardness was decreased insignificantly in thickness direction with an increase in pre-drilling diameter. The failure mode of the M6 threads was analysed by means of quasistatic tensile tests. Due to incomplete formation of the threads profile, variation of the pre-drilling diameter did not declare a concrete trend in measured tensile strengths. Fractographic failure analysis by scanning electron microscopy on threads before and after tensile tests showed that the cold-formed threads were mostly sheared off in load direction (thread stripping) by tensile tests implying an internal thread failure caused by shear stresses because of the incomplete formed threads profile, especially along the cross section corresponding profile thickness direction.
Abstract When machining the titanium alloy Ti6Al4V, segmented chip formation is a major challenge... more Abstract When machining the titanium alloy Ti6Al4V, segmented chip formation is a major challenge as it leads to chatter-vibrations of the tool-machine-system. In this paper a counter element to suppress segmentation, the constraint, is designed by simulations. Therefore, the segmented chip formation of Ti6Al4V has been modelled in a finite element simulation using different approaches for flow stress modelling. The simulation results were validated with the help of orthogonal cutting experiments. Based on a suitable choice of a flow stress model, different geometries and positions of the constraint are analysed and discussed in this paper.
Abstract In the machining process, both the tool wear and the surface integrity of the machined w... more Abstract In the machining process, both the tool wear and the surface integrity of the machined workpiece are significantly influenced by the friction. For this reason, the reliable prediction of friction behavior is of great importance for simulation-based tool and process design. It is known from previous investigations that the relative speed is a significant factor influencing the friction behavior between metallic materials and cemented carbide. The exact relationship, particularly in relation to the topography of the tool surfaces, is mainly unexplored. In the context of this publication, results from a friction characterization under machining-similar conditions for AISI 1045 and differently prepared cemented carbide surfaces are presented. The focus of the paper is to develop models for the friction coefficient, based on these results, which take the relative speed and the surface topography into account. Within a Finite-Element chip formation simulation, these models are compared to conventional models that assume the friction coefficient to be constant. For the validation of the simulations, results are used, which were determined from orthogonal cutting tests with differently prepared rake faces. Within the scope of these cutting tests, knowledge was gained about the influence of the rake face topography and the cutting parameters on the friction in the secondary shear zone.
Study on machinability of additively manufactured and conventional titanium alloys in micro-milli... more Study on machinability of additively manufactured and conventional titanium alloys in micro-milling process,
Due to the increased requirements on machining of metallic and non-metallic materials, the pre-an... more Due to the increased requirements on machining of metallic and non-metallic materials, the pre-and post-treatment of hard thin films has been an important topic in several researches in the past decade. The main improvement in tool properties by a reduction of surface inhomogeneities is reached by an additional mechanical or chemical treatment before and/or after the coating process. Especially the cleaning before coating has to be considered to reduce the amount of debris of the pre-treatment which may negatively effect surface quality after the coating process. The mainly used processes of mechanical treatment to enhance surface topography before and after coating are several machining processes such as abrasive jet machining or drag finishing. This paper introduces a novel process for the pre-and post-treatment of coated cutting tools by elastically bonded diamond grinding wheels. Both the removal rate of surface inhomogeneities, the influence of surface topography before and after coating and the influence of the initial tool surfaces regarding coating adhesion strength were investigated to underline the potential of this pre-and post-treatment. Additionally, a new method for characterizing and describing the number of coating defects and proportion area of coating defects per mm 2 is presented.
Sheet-bulk metal forming (SBMF) processes are characterized by a successive and/or simultaneous o... more Sheet-bulk metal forming (SBMF) processes are characterized by a successive and/or simultaneous occurrence of different load conditions such as the stress and strain states. These conditions influence the material flow and often lead to a reduced geometrical accuracy of the produced components. To improve the product quality, a control of the material flow is required. One suitable approach, the local adaption of tribological conditions by means of surface modifications of tool or workpiece, so-called tailored surfaces. To control the material flow and thus to improve the component accuracy, methods to reduce and to increase friction are needed. The aim of this study is to determine requirements for necessary adaptions of the friction, the identification of tribological mechanisms for different types of tool-sided tailored surfaces as well as the verification of the effectiveness of these surface modifications to improve the results of a specific SBMF process. The numerical analysis of a combined deep drawing and upsetting process revealed that this process is characterized by two areas of varying tribological load conditions. Using a numerical analysis, the friction factor gradient between these two areas was identified as a main influencing factor on the material flow. Based on this finding, Chromium-based hard coatings for the reduction of the friction and high-feed milled surfaces for an increase of the friction were investigated regarding their frictional behaviour. The results of the ring-compression tests revealed that the carbon content and the post treatment of coated tool surfaces are relevant to reduce the friction. The increased profile depth of the milled surfaces was identified as the main influencing factor on the tribological behaviour of this kind of tailored surfaces. The effectiveness of both types of tailored surfaces was verified for the combined deep drawing and upsetting process.
Surface structures are used for several applications in industry to enhance the characteristics o... more Surface structures are used for several applications in industry to enhance the characteristics of surfaces and therefore processes. One example is the Sheet-bulk metal forming process which combines the advantages of bulk and sheet metal forming. Due to the complex material flow and load, the tool surfaces do need adapted tribological properties. High feed milled surface structures have been used in the past to control the material flow of the sheets. But due the high stresses appearing, the surfaces show a running-in behavior which altereds the tribological conditions. Within this study, a pressurized air wet abrasive jet machining (PAWAJM) process is used for adapting the high feed milled surface in order to manipulate the tribological conditions. Therefore, the surfaces characteristics, residual stresses as well as the tribological effects were investigated. It is shown that the PAWAJM process can be used to modify the surface characteristics and thus the friction of the surface. In addition, it can be seen that residual compressive stresses are applied during the PAWAJM.
The cutting edge preparation is a common process in the production chain of cemented carbide macr... more The cutting edge preparation is a common process in the production chain of cemented carbide macro tools. It is used to reduce failures resulting from grinding and to generate a specific cutting edge geometry that is appropriate for the application of the cutting tool. The adhesion of a subsequently applied coating is also increased due to the rounded and more regular shape of a prepared cutting edge. Even though cutting edge preparation is able to significantly increase the life of macro tools, it is not state of the art in the production of micro tools since common preparation processes have not been developed and established for this case of application. Within the investigations, the feasibility of the wet abrasive jet machining process for the preparation of micromilling tools is analysed. For this purpose, the preparation process is refined which allows an effective reduction of the defects and a successful adjustment of different rounding sizes of the cutting edge in a relatively short preparation time. In addition, a high-quality statistical model is achieved to describe the interdependency of the process parameters. In conclusion, TiAlN layers are applied on the rounded cutting edges by a PVD-process without obstructive droplets.
Steel strips are frequently used in the metal working industry for the manufacturing of tubes and... more Steel strips are frequently used in the metal working industry for the manufacturing of tubes and bearing sleeves. These steel strips are produced by cold and warm rolling and are commonly coiled up for transportation purposes. Moreover, the obtained coils are split into customized sizes. In order to use the steel strips for further processing the edges need to be machined with respect to deburring and joint preparation. Therefore, specialized machine tools are used which apply common turning inserts with a translational cutting motion. On the one hand this process is high efficient but on the other hand the process reliability is affected by the formation of long continuous chips. In order to meet the requirements for an increased process reliability investigations on chip flow control are carried out with the aid of the finite element method (FEM). The acquired results are presented in this article.
Kurzfassung In der vorliegenden Arbeit wird der Einfluss der Prozessparameter auf die Eigenspannu... more Kurzfassung In der vorliegenden Arbeit wird der Einfluss der Prozessparameter auf die Eigenspannungsausbildung bei der Drehbearbeitung eines Bauteils mit einer funktional gradierten Eigenschaftsverteilung untersucht. Es handelt sich um eine in einem thermo-mechanischen Umformprozess hergestellte Flanschwelle aus dem Werkstoff 51CrV4, bei der eine charakteristische ortsabhängige Gefügeverteilung vorliegt. Als Folge der daraus resultierenden Härte- bzw. Festigkeitsverteilung stellen sich durch die spanende Bearbeitung ortsabhängige Eigenspannungsverteilungen mit unterschiedlichen Tiefenverläufen ein, deren Ursachen in Abhängigkeit der Prozessparameter diskutiert werden.▪
The mechanical wear behavior of forming tools is the limiting factor during an incremental gear-f... more The mechanical wear behavior of forming tools is the limiting factor during an incremental gear-forming process. These forming tools with a simply shaped geometry are exposed to high forming forces. Additionally, the necessary workpiece chambering, which is characteristic for this incremental process restricts the dimensioning of the tools. Thereby, the geometrical design of the forming tools is limited, which leads to a decreased lifetime. Functional structures on the tool surfaces can influence the occurring loading and wear behavior by reducing the contact area, the supply of lubricant pockets, and by a controlled influence and adjustment of the occurring material flow. For the extension of the tool's lifetime, different surface concepts and combinations with CrAlN PVD-coatings are investigated. To offer conditions with a high tool load, the investigations are focused on an incremental gear forming process with a simple one-wedge forming tool. The results show abrasive and adhesive wear characteristics, as well as outbreaks, and crack formations. The crack propagation on the flank leads to a chipping of the tool tip, hence limiting the tool life. Compared to the reference tool, a surface structure combined with a PVD-coating provides a significant increase of the tool life of 84%.
A growing demand for fibre-reinforced ceramics necessitates effective ways for machining these ma... more A growing demand for fibre-reinforced ceramics necessitates effective ways for machining these materials. In this paper, different tool concepts are presented for an efficient machining of carbon fibre-reinforced silicon carbide. Drill hole machining, slot machining and first investigations of free-form surface machining are presented.
Abstract Simulation systems are used to optimize milling processes by analyzing surface location ... more Abstract Simulation systems are used to optimize milling processes by analyzing surface location errors, which can be predicted by combining various modeling techniques in a multi-scale way. In order to visualize surface location errors, a multi-dexel representation of the workpiece can be used. The application of a triangle mesh representation of the tools to cut the workpiece model is presented, which results in a higher accuracy of the predicted surface location errors in comparison to a Constructive-Solid-Geometry-(CSG)-based approach. Both models are evaluated by simulating a milling process and the simulation results are validated by comparing them to experimental results.
The wear-resistance of sheet metal forming tools can be increased by thermally sprayed coatings. ... more The wear-resistance of sheet metal forming tools can be increased by thermally sprayed coatings. However, without further treatment, the high roughness of the coatings leads to poor qualities of the deep drawn sheet surfaces. In order to increase the surface quality of deep drawing tools, grinding on machining centers is a suitable solution. Due to the varying engagement situations of the grinding tools on free-formed surfaces, the process forces vary as well, resulting in inaccuracies of the ground surface shape. The grinding process can be optimized by means of a simulative prediction of the occurring forces. In this paper, a geometric-kinematic simulation coupled with a finite element analysis is presented. Considering the influence of individual grains, an additional approximation to the resulting topography of the ground surface is possible. By using constructive solid geometry and dexel modeling techniques, multiple grains can be simulated with the geometric-kinematic approach simultaneously. The process forces are predicted with the finite element method based on an elasto-plastic material model. Single grain engagement experiments were conducted to validate the simulation results.
AbstractThe abrasive wear resistance of tribologically stressed free-formed surfaces can be incre... more AbstractThe abrasive wear resistance of tribologically stressed free-formed surfaces can be increased with thermally sprayed tungsten carbide coatings. In order to improve the surface topographies and shape accuracies, the workpieces must be finished prior to industrial application. A suitable machining process is NC grinding on five-axis machining centres using abrasive mounted points. However, the high hardness of the applied coatings and the small diameter of the utilized tools pose a great challenge for the process design. In this paper both, the results of fundamental investigations on the grinding of tungsten carbide coatings as well as a process optimization for the finishing of a coated forming tool are presented. This includes the heat transfer into the coating and the tool wear during the grinding process as well as the wear behaviour of the coating in dependence of the generated surface topography. In order to achieve a smooth surface, elastic-bonded diamond tools were used during polishing in a multi-stage machining process.
The necessity to approximate dynamic contact problems arises in many engineering processes. Becau... more The necessity to approximate dynamic contact problems arises in many engineering processes. Because of the local effects in the contact zone, adaptive techniques are suited to improve the finite element discretisation of such problems. In this article, the Newmark method in time and finite elements in space are used to approximate the solution numerically. A spatial error estimator is derived from the semidiscretised problem. The approach relies on an auxiliary problem, which is a variational equation. An adaptive refinement process is based on this error control. Numerical results illustrate the performance of the presented method.
Microfinishing, also known as superfinishing or short-stroke honing, is a commonly used process f... more Microfinishing, also known as superfinishing or short-stroke honing, is a commonly used process for generating technical surfaces focusing on tribological applications. Due to microfinishing processes high surface qualities are manufacturable regarding the surface roughness and bearing area ratio. While the required characteristics for tribological loaded workpieces are changing with their rising significance, the surface structuring is becoming more and more important. With the use of defined abrasive belts, the possibilities of surface structuring by microfinishing are enhanced. The possibilities and challenges concerning surface structuring by microfinishing applying defined abrasive belts are described in this research study. Therefore, a geometrical-kinematic simulation is used to predict the theoretical structures generated by microfinishing, while in experimental investigations the influences of kinematic parameters and a multi-stage process sequence are considered.
Abstract This study investigates the influence of the pre-drilling diameter on hardness and tensi... more Abstract This study investigates the influence of the pre-drilling diameter on hardness and tensile failure of the formed internal threads (M6), manufactured perpendicular to the profile thickness of thin-walled AZ91 magnesium casting alloys. Previous investigations have shown that introducing a pre-drilling before friction drilling prevents the failure of the bore’s outer wall during the friction drilling process. Considering the oversizing of core bore (friction drilled bore) as an effective factor that can contribute to an incomplete formation of the threads profile through thread forming process, the influence of the pre-drilling diameter was investigated on the hardness and tensile failure of the formed M6 threads. Computed tomography of the friction drilled bores indicated an increase in oversizing of the friction drilled bore with increasing the pre-drilling diameter. Metallographic investigations of the manufactured samples by friction drilling and thread forming process revealed a rhombus-shaped deformation region around the manufactured thread, which provides an enhanced hardness especially at the subsurface of threads profile. The resulting hardness was decreased insignificantly in thickness direction with an increase in pre-drilling diameter. The failure mode of the M6 threads was analysed by means of quasistatic tensile tests. Due to incomplete formation of the threads profile, variation of the pre-drilling diameter did not declare a concrete trend in measured tensile strengths. Fractographic failure analysis by scanning electron microscopy on threads before and after tensile tests showed that the cold-formed threads were mostly sheared off in load direction (thread stripping) by tensile tests implying an internal thread failure caused by shear stresses because of the incomplete formed threads profile, especially along the cross section corresponding profile thickness direction.
Abstract When machining the titanium alloy Ti6Al4V, segmented chip formation is a major challenge... more Abstract When machining the titanium alloy Ti6Al4V, segmented chip formation is a major challenge as it leads to chatter-vibrations of the tool-machine-system. In this paper a counter element to suppress segmentation, the constraint, is designed by simulations. Therefore, the segmented chip formation of Ti6Al4V has been modelled in a finite element simulation using different approaches for flow stress modelling. The simulation results were validated with the help of orthogonal cutting experiments. Based on a suitable choice of a flow stress model, different geometries and positions of the constraint are analysed and discussed in this paper.
Abstract In the machining process, both the tool wear and the surface integrity of the machined w... more Abstract In the machining process, both the tool wear and the surface integrity of the machined workpiece are significantly influenced by the friction. For this reason, the reliable prediction of friction behavior is of great importance for simulation-based tool and process design. It is known from previous investigations that the relative speed is a significant factor influencing the friction behavior between metallic materials and cemented carbide. The exact relationship, particularly in relation to the topography of the tool surfaces, is mainly unexplored. In the context of this publication, results from a friction characterization under machining-similar conditions for AISI 1045 and differently prepared cemented carbide surfaces are presented. The focus of the paper is to develop models for the friction coefficient, based on these results, which take the relative speed and the surface topography into account. Within a Finite-Element chip formation simulation, these models are compared to conventional models that assume the friction coefficient to be constant. For the validation of the simulations, results are used, which were determined from orthogonal cutting tests with differently prepared rake faces. Within the scope of these cutting tests, knowledge was gained about the influence of the rake face topography and the cutting parameters on the friction in the secondary shear zone.
Study on machinability of additively manufactured and conventional titanium alloys in micro-milli... more Study on machinability of additively manufactured and conventional titanium alloys in micro-milling process,
Due to the increased requirements on machining of metallic and non-metallic materials, the pre-an... more Due to the increased requirements on machining of metallic and non-metallic materials, the pre-and post-treatment of hard thin films has been an important topic in several researches in the past decade. The main improvement in tool properties by a reduction of surface inhomogeneities is reached by an additional mechanical or chemical treatment before and/or after the coating process. Especially the cleaning before coating has to be considered to reduce the amount of debris of the pre-treatment which may negatively effect surface quality after the coating process. The mainly used processes of mechanical treatment to enhance surface topography before and after coating are several machining processes such as abrasive jet machining or drag finishing. This paper introduces a novel process for the pre-and post-treatment of coated cutting tools by elastically bonded diamond grinding wheels. Both the removal rate of surface inhomogeneities, the influence of surface topography before and after coating and the influence of the initial tool surfaces regarding coating adhesion strength were investigated to underline the potential of this pre-and post-treatment. Additionally, a new method for characterizing and describing the number of coating defects and proportion area of coating defects per mm 2 is presented.
Sheet-bulk metal forming (SBMF) processes are characterized by a successive and/or simultaneous o... more Sheet-bulk metal forming (SBMF) processes are characterized by a successive and/or simultaneous occurrence of different load conditions such as the stress and strain states. These conditions influence the material flow and often lead to a reduced geometrical accuracy of the produced components. To improve the product quality, a control of the material flow is required. One suitable approach, the local adaption of tribological conditions by means of surface modifications of tool or workpiece, so-called tailored surfaces. To control the material flow and thus to improve the component accuracy, methods to reduce and to increase friction are needed. The aim of this study is to determine requirements for necessary adaptions of the friction, the identification of tribological mechanisms for different types of tool-sided tailored surfaces as well as the verification of the effectiveness of these surface modifications to improve the results of a specific SBMF process. The numerical analysis of a combined deep drawing and upsetting process revealed that this process is characterized by two areas of varying tribological load conditions. Using a numerical analysis, the friction factor gradient between these two areas was identified as a main influencing factor on the material flow. Based on this finding, Chromium-based hard coatings for the reduction of the friction and high-feed milled surfaces for an increase of the friction were investigated regarding their frictional behaviour. The results of the ring-compression tests revealed that the carbon content and the post treatment of coated tool surfaces are relevant to reduce the friction. The increased profile depth of the milled surfaces was identified as the main influencing factor on the tribological behaviour of this kind of tailored surfaces. The effectiveness of both types of tailored surfaces was verified for the combined deep drawing and upsetting process.
Surface structures are used for several applications in industry to enhance the characteristics o... more Surface structures are used for several applications in industry to enhance the characteristics of surfaces and therefore processes. One example is the Sheet-bulk metal forming process which combines the advantages of bulk and sheet metal forming. Due to the complex material flow and load, the tool surfaces do need adapted tribological properties. High feed milled surface structures have been used in the past to control the material flow of the sheets. But due the high stresses appearing, the surfaces show a running-in behavior which altereds the tribological conditions. Within this study, a pressurized air wet abrasive jet machining (PAWAJM) process is used for adapting the high feed milled surface in order to manipulate the tribological conditions. Therefore, the surfaces characteristics, residual stresses as well as the tribological effects were investigated. It is shown that the PAWAJM process can be used to modify the surface characteristics and thus the friction of the surface. In addition, it can be seen that residual compressive stresses are applied during the PAWAJM.
The cutting edge preparation is a common process in the production chain of cemented carbide macr... more The cutting edge preparation is a common process in the production chain of cemented carbide macro tools. It is used to reduce failures resulting from grinding and to generate a specific cutting edge geometry that is appropriate for the application of the cutting tool. The adhesion of a subsequently applied coating is also increased due to the rounded and more regular shape of a prepared cutting edge. Even though cutting edge preparation is able to significantly increase the life of macro tools, it is not state of the art in the production of micro tools since common preparation processes have not been developed and established for this case of application. Within the investigations, the feasibility of the wet abrasive jet machining process for the preparation of micromilling tools is analysed. For this purpose, the preparation process is refined which allows an effective reduction of the defects and a successful adjustment of different rounding sizes of the cutting edge in a relatively short preparation time. In addition, a high-quality statistical model is achieved to describe the interdependency of the process parameters. In conclusion, TiAlN layers are applied on the rounded cutting edges by a PVD-process without obstructive droplets.
Steel strips are frequently used in the metal working industry for the manufacturing of tubes and... more Steel strips are frequently used in the metal working industry for the manufacturing of tubes and bearing sleeves. These steel strips are produced by cold and warm rolling and are commonly coiled up for transportation purposes. Moreover, the obtained coils are split into customized sizes. In order to use the steel strips for further processing the edges need to be machined with respect to deburring and joint preparation. Therefore, specialized machine tools are used which apply common turning inserts with a translational cutting motion. On the one hand this process is high efficient but on the other hand the process reliability is affected by the formation of long continuous chips. In order to meet the requirements for an increased process reliability investigations on chip flow control are carried out with the aid of the finite element method (FEM). The acquired results are presented in this article.
Kurzfassung In der vorliegenden Arbeit wird der Einfluss der Prozessparameter auf die Eigenspannu... more Kurzfassung In der vorliegenden Arbeit wird der Einfluss der Prozessparameter auf die Eigenspannungsausbildung bei der Drehbearbeitung eines Bauteils mit einer funktional gradierten Eigenschaftsverteilung untersucht. Es handelt sich um eine in einem thermo-mechanischen Umformprozess hergestellte Flanschwelle aus dem Werkstoff 51CrV4, bei der eine charakteristische ortsabhängige Gefügeverteilung vorliegt. Als Folge der daraus resultierenden Härte- bzw. Festigkeitsverteilung stellen sich durch die spanende Bearbeitung ortsabhängige Eigenspannungsverteilungen mit unterschiedlichen Tiefenverläufen ein, deren Ursachen in Abhängigkeit der Prozessparameter diskutiert werden.▪
The mechanical wear behavior of forming tools is the limiting factor during an incremental gear-f... more The mechanical wear behavior of forming tools is the limiting factor during an incremental gear-forming process. These forming tools with a simply shaped geometry are exposed to high forming forces. Additionally, the necessary workpiece chambering, which is characteristic for this incremental process restricts the dimensioning of the tools. Thereby, the geometrical design of the forming tools is limited, which leads to a decreased lifetime. Functional structures on the tool surfaces can influence the occurring loading and wear behavior by reducing the contact area, the supply of lubricant pockets, and by a controlled influence and adjustment of the occurring material flow. For the extension of the tool's lifetime, different surface concepts and combinations with CrAlN PVD-coatings are investigated. To offer conditions with a high tool load, the investigations are focused on an incremental gear forming process with a simple one-wedge forming tool. The results show abrasive and adhesive wear characteristics, as well as outbreaks, and crack formations. The crack propagation on the flank leads to a chipping of the tool tip, hence limiting the tool life. Compared to the reference tool, a surface structure combined with a PVD-coating provides a significant increase of the tool life of 84%.
A growing demand for fibre-reinforced ceramics necessitates effective ways for machining these ma... more A growing demand for fibre-reinforced ceramics necessitates effective ways for machining these materials. In this paper, different tool concepts are presented for an efficient machining of carbon fibre-reinforced silicon carbide. Drill hole machining, slot machining and first investigations of free-form surface machining are presented.
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Papers by D. Biermann