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In the field of machining difficult-to-cut materials like titanium or nickel-based alloys, the use of a high-pressure lubricoolant supply may result in a significant increase of productivity and process stability. Due to enhanced cooling and lubrication of the cutting zone and thus reduced thermal tool load, tool wear can be decreased which allows higher applicable cutting speeds. Furthermore, the process stability can be increased as a result of effective chip breaking and chip evacuation. Since energy efficiency is very crucial, pressure and flow rate have to be adjusted carefully and in accordance with the cutting parameters to guarantee best results with less energy. For this purpose, experimental investigations were carried out under variation of the flow rate in order to find the minimum required value for a certain machining task with the overall aim to prevent waste of the media used. To maximize the positive effect of high pressure lubricoolant supply strategy on productivity and process stability, specially designed lubricoolant jet guidance geometry on the rake face was also investigated and compared to conventional turning inserts. To study the effect of high-pressure lubricoolant supply on tool temperature, reference tests also carried out using conventional overflood cooling (CoC). The results suggest that the tool temperature can be significantly decreased compared to CoC by applying the high pressure lubricoolant supply and using specially designed jet guidance geometry in turning the investigated aerospace materials TiAl6V4 and Inconel 718.

In metal cutting, unbroken chips may scratch the machined surface and hinder an efficient chip removal. Despite its relevance, the established methodologies of tool/process design with regard to chip breakage are still dominated by expensive empirical approaches. Valid predictive modeling helps to reduce the experimental effort and safe costs. Chip breakage initiates with ductile material fracture on the chip free surface. The fracture strain is influenced by the temperature and stress state, which is defined by the stress triaxiality and Lode angle. An introduction of fracture models considering these combined impacts to the finite element (FE) simulation of chip breakage is not available. In this work, a new model of final ductile fracture is proposed, calibrated, and applied for the 3D FE simulation of chip breakage in turning processes of AISI 1045 (C45E+N). The calculation of the fracture strain considers the stress triaxiality, Lode angle, and temperature. A new non-iterative calibration procedure is proposed, which describes the relationships between the chip geometry at breakage and the thermomechanical state variables on the chip free surface. By implementing experimentally obtained chip geometries into this methodology, the combinations of strain, stress triaxiality, Lode angle, and temperature are determined under which ductile fracture was observed in the cutting tests. Finally, a regression analysis delivers all material constants. The fracture model is implemented into a FE-chip formation model. The predicted locations of fracture are compared to high-speed videos of turning experiments while the direction of crack propagation is validated by scanning electron microscopical images of experimental chips.

Precise force measurements are often used for the development of machining processes. A key measure thereby is the specific cutting force, which comprises several factors such as cutting and work piece material as well as the cutting edge geometry. Therefore, it is vital for cutting tests to be as close to the real application as possible in order to guarantee a good alignment and transferability of the results. In many cutting tests carried out in a laboratory environment this cannot sufficiently be ensured. This paper presents two specific processes being applied in aeronautic industry for which force measurement systems were specially developed to satisfy the mentioned requirements. On the one hand, a 4-Component-High-Speed Rotating-Cutting-Force-Dynometer is employed for machining Aluminum parts on a machining center. On the other hand, a specially designed 3-Component Cutting-Force-Dynamometer was installed to an industrial broaching machine tool manufacturing slots in a nickel-based alloy. Besides an introduction of the new equipment, cutting tests being carried out with the piezo-electric sensor technology are analyzed and discussed regarding the achieved results.

Tool life is usually measured by end tool life tests, however, such experiments are costly and time consuming. Establishing correlation between these tests and shorter and cheaper tests is consequently of great interest. Experimental results from dry orthogonal cutting tests are reported and a good correlation between temperature reached at the tool and tool life test is shown.

15th CIRP Conference on Modelling of Machining Operations (15th CMMO) / Edited by Volker Schulze 15th CIRP Conference on Modelling of Machining Operations, 15th CMMO, Karlsruhe, Germany, 11 Jun 2015 - 12 Jun 2015; Amsterdam [u.a.] : Elsevier, Procedia CIRP, 31, 246-251 (2015). doi:10.1016/j.procir.2015.03.048, Published by Elsevier, Amsterdam [u.a.]

Tool geometry optimization, workpiece material characterization, process monitoring and optimization are based on the measurement of cutting forces by using machining dynamometers. Commercial dynamometers cover a wide range of machining applications, nevertheless there is a lack of measuring devices suitable for investigating milling and drilling applications with relatively small cutters and high spindle speeds. In this work, the development and testing of an innovative plate dynamometer designed for this purpose is discussed. The new measuring system was based on three high-sensitive triaxial piezoelectric force sensors arranged in a novel triangular configuration. Component design was optimized by using FE numerical approaches, according to the general guidelines derived from mathematical modeling of sensor dynamics. The prototype of the proposed device was manufactured and experimentally tested against two high-end commercial plate dynamometers by performing static calibration, modal analysis and cutting tests. Experimental results proved the excellent characteristics of the new device and its effectiveness for investigating advanced machining applications.

Surface Integrity standards for safety-critical aero engine components are very high. Besides the properties of the work piece material, the selected process parameters for machining have a significant impact on the achieved part quality. The present article identifies thermal induced Surface Integrity parameters such as micro-hardness, white-etching-layers and increased residual tensile stress as most critical when broaching Nickel-based alloys and presents a force-based concept for temperature prediction. The achieved results with the new model approach are compared to in-process temperature measurements.

This paper deals with a technological evaluation of wire electrode material and machining technologies for the production of fir tree slots by Wire-EDM to compete with the conventional broaching process. Meeting the high requirements on surface integrity and precision, new electrodes in combination with machining technologies have been developed in order to increase the productivity of this machining process. In particular three wire electrodes including a standard brass wire, a coated high-speed-cutting wire and a Ni-coated wire for zero contamination of Cu and Zn in combination with standard and specifically developed machining technologies for cutting Inconel 718 are presented. Evaluation criteria for the comparison are the demanding requirements on fir trees in turbine engine production like precision, surface roughness, minimization of white layer formation and contamination. Finally, an energy consumption analysis of the electrode/machining technology combination is shown. The analyzed processes show that Wire-EDM is a capable process for the fir tree slot production.

Kurzfassung Ein integraler Bestandteil von innovativen Systemansätzen für die Produktion von morgen ist digitales Technologiewissen. Dieses Wissen kann über Modelle, die prozessspezifische Zusammenhänge mathematisch beschreiben, bereit gestellt werden. Im vorliegenden Artikel wird das grundsätzliche Vorgehen zur Entwicklung solcher Modelle kurz erläutert. Darauf aufbauend wird ein Konzept zur autonomen Wissensgenerierung vorgestellt. Damit wird ein Fertigungssystem befähigt, digitales Technologiewissen selbstständig aufzubauen.

Due to their particular mechanical and thermal properties titanium- and nickel-based alloys such as Ti–6Al–4V or Inconel 718 are in common use as blisk materials. Besides conventional milling in this paper two alternative technologies for roughing operations in blisk manufacture – electro discharge machining (EDM) and electrochemical machining (ECM) – are presented. Therefore material removal rates in sinking-EDM (SEDM) and ECM as well as cutting rates in wire-EDM (WEDM) are determined for the above mentioned materials and class of geometries. With these results, an extensive cost-analysis is made where different production technologies are compared for analogical blisk geometries. It is demonstrated that for distinct geometries, materials and batch sizes unconventional manufacturing technologies are economic alternatives to existing milling strategies.

In order to increase the efficiency of jet engines hard to machine titanium- and nickel-based alloys are in common use for blade and disk materials. With Electrochemical Machining (ECM) highest material removal rates can be achieved at best surface qualities. However for tool design, knowledge of local material dissolution is indispensable. This paper deals with basic research on the electrochemical machinability of selected modern titanium- and nickel-based alloys for aero engine components. Therefor experimental results of feed rate as a function of current density for an ECM sinking operation with a cylindrical tool electrode and external flushing are compared to the theoretical dissolution behavior according to Faraday's law. Furthermore surface properties were examined in terms of SEM and EDX analysis of the rim zone.

In order to increase the efficiency of jet engines hard to machine nickel-based and titanium-based alloys are in common use for aero engine components such as blades and blisks (blade integrated disks). Here Electrochemical Machining (ECM) is a promising alternative to milling operations. Due to lack of appropriate process modeling capabilities beforehand still knowledge based and a cost intensive cathode design process is passed through. Therefore this paper presents a multi-physical approach for modeling the ECM material removal process by coupling all relevant conservation equations. The resulting simulation model is validated by the example of a compressor blade. Finally a new approach for an inverted cathode design process is introduced and discussed.

For industrial applications graphite is becoming more and more the electrode material of choice for sinking EDM. Especially f or roughing graphite offers great advantages compared to copper electrodes. Optimized parameters lead to a very low tool wear rate combined with a high material removal rate. As a result the number of tool electrodes for a certain EDM task can be reduced significantly leadin g to very short machining time. A satisfactory explanation for these benefits could not be found until now. Therefore the specific wear behavior and material removal rate is investigated in detail in this paper and linked to the physical characteristics of the graphite material. In total 5 different kinds of graphite were chosen with significantly different physical characteristics concerning their specific electric resistance, thermal conductivity and grain size. The performance of each grade was evaluated in terms of material removal rate and tool wear for roughing.

Kurzfassung Der vorliegende Artikel beleuchtet die aktuelle Situation der Fertigung von sicherheitskritischen Bauteilen in der Triebwerksindustrie. Entscheidend für die Bauteilqualität ist in erster Linie die Oberflächenintegrität. Diese wird in der Produktion derzeit mit Hilfe klassischer nicht-zerstörender Prüfverfahren verifiziert. Neue Ansätze bedienen sich der Prozessüberwachung, die ein großes Potenzial im Bereich der prozessbegleitenden Qualitätssicherung bietet. Ein erster Prototyp für eine industrienahe Lösung zur Prozessüberwachung beim Bohren wird in diesem Artikel vorgestellt.

Due to their particular mechanical and thermal properties titanium- and nickel-based alloys such as Ti-6Al-4 V or Inconel 718 are in common use as blisk materials. Besides conventional milling in this paper two alternative technologies for roughing operations in blisk manufacture – Electro Discharge Machining (EDM) and Electrochemical Machining (ECM) – are presented. Therefore material removal rates in Sinking-EDM (SEDM) and ECM are determined for the above mentioned materials and class of geometries. With these results, an extensive cost-analysis is made where different production technologies are compared for analogical blisk geometries. It is demonstrated that for distinct geometries, materials and batch sizes unconventional manufacturing technologies are economic alternatives to existing milling strategies.

Cutting force information may be used for several tasks, such as tool design and trajectory optimization, tool condition monitoring, machinability testing and many others. Accordingly, cutting force measuring has become a crucial activity aimed at enhancing process performance. In this work, the development of an innovative rotating dynamometer for cutting force measurement in milling is illustrated. The device is capable of providing independent triaxial cutting force information from each cutting edge with a good dynamic response. Static and dynamic behavior of a simplified single-edge device was first investigated through the static calibration procedure, pulse tests and preliminary cutting tests. Afterwards, the dynamic properties of the final prototype clamped on the spindle of a high speed milling machine were assessed by means of standard and rotating pulse tests – i.e. pulse tests performed during spindle rotation. Eventually, cutting tests were performed on a benchmark workpiece. The experimental tests highlighted the superior features of the new device.

Today’s process monitoring applications in the area of five-axis milling are based on strategies developed for machining operations of one or maximum three effective degrees of freedom. Applied static and dynamic threshold monitoring can be used to detect excessive loads, but do not enable the basic evaluation of process behaviour. As alternating machining conditions do not allow a determination of the machining characteristics, it becomes apparent that a machining position-oriented monitoring solution would reveal a basic opportunity to improve the monitoring abilities in a freeform cutting process. In this paper a metrological solution is introduced, which allows a position-oriented inspection of a five-axis milling process. Measurement chains which have been integrated into a machining centre are described. Experimental results of measuring the processes’ cutting forces in parallel to the machine’s axes position and the needed technological environment and software solutions are presented.

Turbine engine manufacturers permanently aim to improve the efficiency of their products. This is often accompanied by the development of new materials which have to be introduced to manufacturing. As a consequence, engineers responsible for machining process development are regularly confronted with the question, how to identify the optimal machining conditions in order to deal with the new constraints. Nowadays, the effort and success of such identification processes are to a significant degree depending on technology expert skills and experiences. From the process planning perspective, however, this circumstance is characterized by a significant degree of uncertainty. This article presents an innovative concept for a technology assistance system (TAS) for milling. The TAS supports the operator to determine optimal machining conditions by autonomously evaluating machinability criteria such as cutting force, tool wear or surface roughness for certain work piece material/ tool combinations. This includes the planning and organization of milling experiments, its standardized and automated execution as well as the generation of surrogate models to describe the machinability criteria for a given parameter range, serving as input for a future optimization. All functionalities of the TAS are conceptually described and first results achieved using a prototype solution are introduced and discussed.

Due to lightweight construction numerous parts in turbomachinery industry with aerodynamic properties exhibit thin-walled features. Typical examples are compressor blades or turbine blades. Finish-milling depicts a stage of the manufacturing process of these parts with significant value creation. A major limitation of productivity is process stability in terms of self-excited or forced vibration. Different simulation approaches attempt determining a priori the process stability to avoid a bad surface quality, accelerated tool wear, tool breakage or scrapped parts. One distinctive part of these simulations is a cutting force model which incorporates material and tool dependent coefficients. The simulation accuracy directly depends on the exactness of these coefficients. Usually, these coefficients are identified experimentally from cutting force measurements with piezoelectric sensors, whose transmissibility is nonlinear. In this paper a multidimensional stationary inverse filter for compensating the influence of the nonlinear transmissibility of force sensors is presented. In a subsequent step, a Levenberg–Marquardt algorithm is used to identify cutting force coefficients from filtered force measurements. The functionality of the filter is validated by comparing highly nonlinear and almost linear piezoelectric force measurement sensors connected in series during finish-milling experiments. The accuracy of the identified cutting force coefficients is assessed by comparing cutting force simulations to measurements.Copyright © 2015 by ASME

Mechanical sciences : MS 6(2), 89-94 (2015). doi:10.5194/ms-6-89-2015, Published by Copernicus Publ., Göttingen

Hardened bearing steel, M50, has been ultra-precision ground to produce an optical quality surface ( The development of optical quality surfaces is considered in terms of the processes occurring in the primary and secondary finishing zones of the cup-wheel, with the final surface finish enhanced by the burnishing action of worn CBN grits. It is shown that surface finish is limited by the pull-out of carbides in the secondary finishing zone. However, this can be overcome by using electrolytic in-process dressing (ELID), which maintains CBN grit protrusion and sharpness. This promotes cutting of the carbides at the ground surface and ensures a high level of surface integrity although the burnishing action of grits is reduced resulting in a slightly higher roughness for the steel matrix.

One of the central success factors for production in high-wage countries is the solution of the conflict that can be described with the term “planning efficiency”. Planning efficiency describes the relationship between the expenditure of planning and the profit generated by these expenditures. From the viewpoint of a successful business management, the challenge is to dynamically find the optimum between detailed planning and the immediate arrangement of the value stream. Planning-oriented approaches try to model the production system with as many of its characteristics and parameters as possible in order to avoid uncertainties and to allow rational decisions based on these models. The success of a planning-oriented approach depends on the transparency of business and production processes and on the quality of the applied models. Even though planning-oriented approaches are supported by a multitude of systems in industrial practice, an effective realisation is very intricate, so these models with their inherent structures tend to be matched to a current stationary condition of an enterprise. Every change within this enterprise, whether inherently structural or driven by altered input parameters, thus requires continuous updating and adjustment. This process is very cost-intensive and time-consuming; a direct transfer onto other enterprises or even other processes within the same enterprise is often impossible. This is also a result of the fact that planning usually occurs a priori and not in real-time. Therefore it is hard for completely planning-oriented systems to react to spontaneous deviations because the knowledge about those naturally only comes a posteriori.

Meta-modeling for manufacturing processes describes a procedure to create reduced numeric surrogates that describe cause-effect relationships between setting parameters as input and product quality variables as output for manufacturing processes. Within this method, expert knowledge, empiric data and physical process models are transformed such that machine readable, reduced models describe the behavior of the process with sufficient precision. Three phases comprising definition, generation of data and creation of the model are suggested and used iteratively to improve the model until a required model quality is reached. In manufacturing systems, such models allow the generation of starting values for setting parameters based on the manufacturing task and the requested product quality. In-process, such reduced models can be used to determine the operating point and to search for alternative setting parameters in order to optimize the objectives of the manufacturing process, the product quality. This opens up the path to self-optimization of manufacturing processes. The method is explained exemplarily at the gas metal arc welding process.

In the past few years, process monitoring of drilling processes using force and vibration signals has successfully been established. However, only few investigations were performed in the monitoring of chip breakage and chip transportation, while in gun drilling these properties are more relevant to ensure process robustness and performance than force and vibration. This paper presents a new monitoring approach of chip frequency and transportation for gun drilling processes using infrared light reflection next to the drilling bush. Gun drilling is a high performance cutting process used for small diameter and large aspect ratio drilling operations in the field of automotive, aeronautic, power generation and medical devices. The usage of new harder materials for future products increases the challenge of proper chip transportation and raises the need of chip monitoring being able to operate with economically acceptable parameters. The approach of optical chip detection highlights the opportunity of detecting chips smaller than 1 mm and velocities in axial direction of more than 16 m/s clearly and suggests new characteristic values to be used for process validation. For implementing the measurement principle a new sensor is designed. In addition, the opportunities of future data analysis and detection of characteristic values are explained.

The monitoring of high end material removal processes continues to develop to greater levels of technical sophistication which in turn enable greater levels of insight into the process phenomena occurring at the tool-chip interface. The broaching process is a traditional machining p rocess which is used extensively in the manufacture of some of the most expensive components of the aero engine. As a relatively slow cu tting process with low degrees of freedom, broaching could be a target for strain based monitoring. It is well known that strain gauges p rovide a rich source of data when installed close to the cutting process. This research provides insight into the resistive strain gauge measu rements during broaching. The paper also specifically focuses on the use of surface acoustic wave based strain measurement and p rovides some initial observations on the strain data available during tooth loading and cutting scenarios in broaching. © 2014 The Authors. Published by Elsevier B.V. Selection and peer-review under responsibility of the International Scientific Committee of the 6th CIRP International Conference on High P erformance Cutting.

15th CIRP Conference on Modelling of Machining Operations 2015 (15th CMMO) : Karlsruhe, Germany, 11 - 12 June 2015 / ed.: Volker Schulze 15th CIRP Conference on Modelling of Machining Operations 2015, 15th CMMO, Karlsruhe, Germany, 11 Jun 2015 - 12 Jun 2015; Red Hook, NY : Curran, Procedia CIRP, 31, 352-356 (2015). doi:10.1016/j.procir.2015.03.067, Published by Curran, Red Hook, NY

Components such as turbine discs in the high pressure turbine part of the aero engine suffer high mechanical and thermal loads during service and are critical to the safety of the aircraft. Therefore, in aero engine manufacture, the surface integrity has established as a complex quality measure regarding not only features on the surface but also the condition of the subsurface. The integrity at the machined surface on the one hand depends on the material properties of the part and on the other hand on the machining parameters as well as the condition of the cutting edge. This paper intends to contribute to the understanding of the physical effects during the cutting process and uses the temperature in the cutting zone as a measure to connect the cutting parameters and selected measures of the surface integrity.

Biodegradable implants are in the focus of recent research approaches in the medical engineering sector for the treatment of many different defects. In comparison to permanent implants the risk of inflammatory reactions is significantly reduced and no foreign material is left in the body using degradable materials. Due to the extraordinary biocompatibility and initial structural stability, similar to the human bone, magnesium alloys are best suited for degradable orthopedic implants. But up until now the degradation of magnesium inside the human body is too fast and therefore the structural stability is lost too early. Newest research suggests that the degradation kinematic as well as the cell response of the implant can be improved by adjusting certain surface properties, e.g. complex micro- and macrostructures. Since these structures are very difficult to be machined with conventional processes, especially for complex and filigree 3D-structures, alternative manufacturing processes need to be developed. Electro Discharge Machining in combination with a Plasma Electrolytic Conversion of the surface is very well suited for the creation of geometries with high aspect ratios and microstructures. The focus of this paper lies on the investigation of the influence of the production processes on the biocompatibility of the machined part. The process chain for such implants will therefore be analyzed in regard to macro and micro surface properties using SEM and EDX-analysis. These results are then compared to biocompatibility testing concerning cell viability and toxicity.