This paper presents a comprehensive review of the concept of machinability by considering the dynamic, tribological, and thermo-mechanical interactions encountered at the tool-chip-machined surface interfaces. The paper provides a demonstration of the capabilities and gaps of the physics-based models for the characterization of the machining performance and the prediction of machinability of difficult-to-cut materials, including additively manufactured (AM) materials, nanocrystalline (NC) materials, fibre reinforced polymers (FRP), metal matrix composites reinforced with ceramic hard particles (MMC), and ceramic matrix composites (CMC). The utilization of efficient computation methods for accurate prediction of force, torque, power consumption, cutting temperature, deflection errors, vibration amplitudes, chatter stability, and thermomechanical interactions in the tool-workpiece system is discussed. The development of thermally-activated dissolution-diffusion wear models to describe the chemical reactions at the tool-chip-workpiece contact interfaces is also presented. These predictions are critical for identifying multi-objectives optimal machining conditions. The integration of predictive machining models within the framework of digital twins in cyber-physical spaces, for in-process monitoring and adaptive control, is demonstrated. Future research for developing new models that can characterize the machinability of AM and NC materials, by considering the effects of varying material microstructure and anisotropy, is presented for conventional and micro-machining operations.

Der Beitrag befasst sich mit Teilaspekten bei der Entwicklung von Methoden zur gezielten, bearbeitungsparallelen Oberflächenkonditionierung beim Tiefbohren. Konkret handelt es sich um messtechnische und simulationsbasierte Ansätze zur Identifikation von thermomechanischen Prozesszuständen beim BTA- und ELB-Verfahren. Hierbei werden Möglichkeiten zur Gewinnung von Prozessdaten sowohl mit einer in-situ eingesetzten Sensorik als auch mit begleitend durchgeführten FEM-Simulationen betrachtet. Diese Daten bilden die Grundlage einer Prozessregelung für die beiden Tiefbohrverfahren. Im ersten Teil werden zunächst die Arbeiten und Ergebnisse zum BTA-Tiefbohren behandelt.   The article deals with aspects of developing methods specifically for surface conditioning in deep hole drilling parallel to machining. This involves metrological and simulation-based approaches for identifying thermo-mechanical process conditions in both BTA and ELB process. Ways for obtaining process data both with sensor technology used in-situ and with FEM simulations performed concomitantly are investigated. These data form the basis of a deep hole process control. The first part presents the work and the results on BTA deep hole drilling.

Tool wear and borehole quality are two critical issues for high precision drilling processes. In this paper, several drilling experiments in terms of different drilling parameters and drill bit with and without coating are conducted according to the Taguchi orthogonal arrays. Thrust force and moment were measured during the drilling process. The cutting edge radius depending on the wear, roughness and roundness of the borehole were also aquired. By combining the experiment dataset with the expert knowledge, a Bayesian prediction network of tool wear radius, surface roughness and borehole roundness is established through structure learning and parameter learning algorithms based on GeNIe, a disposable software to create Bayesian networks. Up to 89 % accuracy were achieved using this approach. The research described in this paper can provide a new approach to multivariate prediction and parameter optimization in drilling.

Standzeittests an Kreissägewerkzeugen sind in der Regel zeit- und materialintensiv. Am Institut für Werkzeugmaschinen (IfW) der Universität Stuttgart wird der Aufwand mithilfe von Einzahnversuchen deutlich verringert. Die Versuche basieren auf einem Leistendrehtest, der sich an die ehemalige VDI-Richtlinie VDI 3324 anlehnt und auf Drehmaschinen durchgeführt werden kann. Durch einfach gestaltete, wechselbare Leisten entsteht eine für das Sägen typische Schnittunterbrechung und es können beliebige Werkstoffe berücksichtigt werden. Live time tests on circular saw tools are usually time-consuming and material-intensive. At the Institute for Machine Tools (IfW) of the University of Stuttgart, the required effort can be significantly reduced by conducting single tooth tests. The tests are based on a block turning test which adopts the former VDI guideline VDI 3324 and can be used on lathes. Simply designed and exchangeable blocks allow the typical cut interruption for sawing and consider any materials.

Die additive Fertigung eröffnet neue Gestaltungs- und Optimierungsfreiheitsgrade für oberflächen- und strukturoptimierte Bauteile. Mit diesen Verfahren lassen sich selbst komplexe räumliche Strukturen kostengünstig herstellen. Der vorliegende Artikel untersucht den Einfluss der Druckrichtung und des Füllgrads auf die mechanischen Eigenschaften, den Verzug sowie die erreichbaren Formgenauigkeiten am Beispiel von mit 3D-Druck über den FDM-Prozess erzeugten PLA-Bauteilen. Additive manufacturing opens up new possibilities for optimizing components with regard to surfaces and structures. These processes allow producing even the most complex three-dimensional structures at comparatively low cost. This paper analyzes how the print direction and the filling ratio affect the mechanical properties, the distortion, as well as the achievable geometrical accuracies, by using 3D-printed PLA components produced by FDM processes.

Die Reibungsbedingungen bei der Zerspanung von verstärkten Faserverbundkunststoffen werden durch die Oberflächengestalt der Werkzeugschneide beeinflusst. In dieser Studie wurde CFK-UD (unidirektional carbonfaserverstärkter Kunststoff) im Streifenziehversuch mit geschliffenen und gestrahlten Testwerkzeugen bei 5 MPa Flächenpressung untersucht. Die Oberflächen der Testwerkzeuge sind durch bestimmte Rauheits- und Funktionsparameter charakterisiert, die sich auf die Gleitreibung der tribologischen Paarung CFK – Werkzeugschneide auswirken. The friction conditions when cutting fiber-reinforced polymers are significantly influenced by the shape of the tool cutting surface. Hence, different strip drawing tests were carried out at a 5 MPa surface pressure to investigate the behavior of unidirectional CFRP with different test tool surface preparations. The tool surfaces were ground and blasted. The created surface topographies are characterized by particular parameters of roughness and function which affect the sliding friction of the CFRP / tool pair.

Die Zerspanung von Polymethylmethacrylat (PMMA) stellt höchste Anforderungen an die Qualität der Bauteile. Dies wird erschwert durch eine hohe Kerbempfindlichkeit, geringe Kratzfestigkeit und die Notwendigkeit Kühlschmierstoffen anzuwenden, um mögliche Aufschmelzungen aufgrund schlechter Wärmeleitung zu unterdrücken. Als alternative Lösung wurde die Anwendung von selbstklebenden Polymerfolien auf der Werkstückoberfläche beim Trockenbohren von PMMA untersucht. The cutting of polymethyl methacrylate (PMMA) puts high demands on parts quality. Good quality is hindered by notch sensitivity, low scratching resistance, and low thermal conductivity necessitating cooling lubricant to oppress the fuse of the material. Alternatively, this study researches self-adhesive polymer films for drilling without cooling lubricant.

Hybrid machining processes represent a potential approach to meeting the constantly increasing demands on cutting. In ultrasonic-assisted cutting, as a part of hybrid machining, the machining process is superimposed with a high-frequency vibration of small amplitude. This paper presents investigations on the drilling of stone materials, i.e. different granites and marble, in which this process is applied. It could be observed that the resultant forces and torques were reduced, which had already been discovered in investigations of various other materials. The influence of different parameters on the force reduction is shown, which is basically similar to the theoretical reduction of friction by ultrasound for small speed ratios δ, but is considerably increased. This increase must be due to other effects. Besides the force reduction, a reduction of cratering at the drill exit can be observed. Based on the present results, definite conclusions on tool wear cannot be drawn yet.

At present the machining of highly ductile electrolytic copper ECu 57 with gun drills is carried out at very low feed values, as the material tends to form very long and unfavourable chips. In addition, high frictional forces on the guide rails cause high torsional strain on the gun drill. This paper first reports on the results of ultrasonically assisted deep hole drilling in ECu 57 with tools of 5mm diameter. The actuator system for exciting axial vibrations in the ultrasonic range is described and experimental results which were obtained from cutting tests are reported. Particular emphasis is put on the improvements compared with the conventional drilling technology without superimposed vibrations. The effect of different input amplitudes is investigated in detail. The performance criteria are drilling moment, surface quality, chip form as well as the surface zone. By optimising the vibration amplitude, cutting speed and feed, the machining result was improved compared with conventional machining, and at the same time the stability of the machining process was simultaneously increased.

From different chipping machining processes it is known that a superposition of the cutting kinematics with additional vibration energy increases material removal rate and tool life. Concerning the deep drilling process in the scope of smallest diameters from 0.9 to 6 mm insights to this so called hybrid processes are still awaited. Preliminary investigations indicated that here is high, so far unused potential. The goal of current research is an increase in effectiveness of the deep hole drilling process by superimposing additional vibration energy in ultrasonic frequency range by means of a piezoelectric transducer and low-frequency vibrations in the range of acoustic frequencies as well. Positive effects can appear in a couple of areas, e.g. achievable surface quality, feeding force, drilling torque, shape and length of chips, feasibility of machining ceramic materials and tool wear. This paper describes mainly the ultrasound conform design of the vibration unit. Furthermore issues of contactless energy transfer into a rotating tool and model based design of piezoelectric transducers will be addressed.

Deep hole drilling with gun drills is the method of first choice for many cases of application, if small and smallest diameters, very large drilling depth to diameter (I/D) ratios and a high machining quality are required. At present, the developments are pushed ahead not only by the request of the user for a constant improvement in quality and effectiveness, but also by a growing competition due to deep-hole twist drilling. The latter is coming closer and closer to gun drilling regarding smallest possible diameters and the attainable quality of holes and, in addition, has a possible material removal rate which is many times higher. Applying approaches for optimisation in different areas, the lfW was able to show that there is still a great potential in gun drilling as well.

The following paper presents a method for the determination of the burr dimensions to be expected in short-hole drilling, simultaneously taking the parameters into consideration which influence the burr formation. These parameters are yield stress, forces and the geometry of the inserts. The method is based on empirical cutting examinations and takes account into the correlation between different burr parameters and the machining conditions such as cutting speed, feed and tool geometry. Using Schaefer's burr value g, it is possible to make a quantitative evaluation of the burr dimensions. The method was verified for the materials 16 MnCr 5 and Ck 45 in case of dry machining.

The machining of tough and high tensile materials with single-edge drilling tools of smallest diameter is only dissatifyingly mastered, because of the applied tools being very brittle and therefore fragile. The situation is made difficult by the opposed demands for higher productivity with respective cutting speed and rate of feed simultaniously to higher process security. At the moment, optimised cutting parameters for each individual application case have to be determined in expensive cutting tests. At the Institute for Machine Tools, University of Stuttgart, the cohesion between process parameters and their dependence on the control points are examined. The results enter a model of the machining process of single-edge drilling which in turn generates the basis for the optimisation model. By means of default conditions such as for example demanded machining quality, material to be machined, time of machining and so on, this leads to optimised values for the control points and moreover creates the precondition for the application of a process control system.