Drazen Veselovac

Developments in Wire-EDM for the Manufacturing of Fir Tree Slots in Turbine Discs Made of Inconel 718

This paper deals with developments of Wire-EDM technologies for fir tree slot production. The aim of these developments is to substitute certain conventional processes within turbine manufacturing that have been identified as non-optimal like the critical broaching process. Thereby the negative characteristics like inflexible manufacturing processes, high machine tool investment costs and huge energy consumption can be abolished. The objective targets of the conducted research are to meet all safety requirements of the critical components and get an economic manufacturing process. In the first step a special brass wire technology for cutting Ni-based super alloys was developed. Main focus was to meet the requirements of fir tree production concerning aspects of surface integrity and geometry. To measure these aspects on the one hand non-destructive analyses have been performed to guarantee surface roughness and accuracy. On the other hand destructive analyses in terms of cross section polishing for showing thermal influenced rim zones have been prepared. A capable Wire-EDM process is presented.

Broaching of Inconel 718 with cemented carbide

Broaching is the standard process for machining complex-shaped slots in turbine discs. More flexible processes such as milling, wire EDM machining and water-jet cutting are under investigation and show promising results. In order to further use existing resources and process knowledge, the broaching process has to be improved towards higher material removal rates. Taking into account that the state-of-the-art broaching process is working with high-speed-steel tools, the higher thermal resistant cemented carbide cutting materials offer the potential to significantly increase cutting speeds, which lead to increased process productivity. The following article presents a broad study on broaching with cemented carbide tools. Different cutting edge geometries are discussed on the basis of process forces, chip formation and tool wear mechanisms. Furthermore, a detailed comparison to the standard process is drawn.

Influence of Tool Coating, Tool Material, and Cutting Speed on the Machinability of Low-Leaded Brass Alloys in Turning

The influence of tool coating and material on the machinability of low-leaded brass alloys (Pb < 0.2%) was analyzed in external turning. Carbide tools with various coatings as well as polycrystalline diamond (PCD) tools were applied. As workpiece materials, three low-leaded brass alloys CuZn38As, CuZn42, and CuZn21Si3P were used. Their machining behavior was compared to the leaded (Pb < 3.32%) brass CuZn39Pb3. CuZn38As showed the worst machinability in terms of process forces, chip formation, and workpiece quality. This is due to the high volume fraction of α-phase with face-centered cubic lattice structure. The machining problems were reduced by the use of tool coatings, in particular by a diamond-like carbon coating. The latter is characterized by high hardness, diamond-like cubic-crystalline lattice structure, and low chemical affinity to brass, which reduced friction in the secondary shear zone. CuZn42 exhibited an improved machinability compared to CuZn38As due to the lower volume fraction of α-phase. The positive influence of the tool coating was similar to CuZn38As. Main machining problem of CuZn21Si3P is tool wear because of the hard silicon-rich κ-phase. In tool life tests, PCD showed higher performance than uncoated and coated carbide tools due to its high abrasive wear resistance and low adhesion tendency.

Investigation on Force Sensor Dynamics and Their Measurement Characteristics

Cutting force is a common monitoring parameter reflecting the behaviour of a production process. As monitored cutting conditions are used to adjust a process’s performance to its highest feasible level, control strategies for machining operations are claimed. To ensure a control’s functionality, an accurate measurement of the cutting conditions is required. In this paper the impact of a work piece’s mass onto a sensor’s dynamic behaviour is presented. For this purpose, at different setups the measurement characteristics of piezoelectric force sensors are researched and verified. Different trials are carried out, not only taking the natural frequencies of the sensors, but also the vibration characteristics of the whole machinery into account. Based on this, methods to improve and condition a measurement system’s dynamic accuracy are approached.Copyright

Concept for Temperature Control in Broaching Nickel-Based Alloys

In production of safety critical components in aero engine manufacture, to date broaching is the most efficient process machining fir-tree slots in turbine discs. Machining highly thermal resistant Nickel-based alloys, manufacturers commonly use High Speed Steel (HSS) tools and work at low cutting speeds in order to stay at rather low tool wear rates and avoid part quality defects. The key variable affecting tool wear as well as part quality, as in most machining processes, is the temperature. Excessive temperatures in the cutting zone lead to enhanced tool wear on the one hand, and surface defects such as white layer formation and residual tensile stresses on the other hand. In this article, the temperature development is investigated for typical tool geometries and cutting parameters in broaching. Furthermore, the possibility of a temperature control using intermediate variables such as process forces is discussed, and potentials employing a control are explained.

Self-optimizing Production Technologies

Customer demands have become more individual and complex, requiring a highly flexible production. In high-wage countries, efficient and robust manufacturing processes are vital to ensure global competitiveness. One approach to solve the conflict between individualized products and high automation is Model-based Self-optimization (MBSO). It uses surrogate models to combine process measures and expert knowledge, enabling the technical system to determine its current operating point and thus optimize it accordingly. The objective is an autonomous and reliable process at its productivity limit. The MBSO concept is implemented in eight demonstrators of different production technologies such as metal cutting, plastics processing, textile processing and inspection. They all have a different focus according to their specific production process, but share in common the use of models for optimization. Different approaches to generate suitable models are developed. With respect to implementation of MBSO, the challenge is the broad range of technologies, materials, scales and optimization variables. The results encourage further examination regarding industry applications.

DESIGN APPROACH FOR ADAPTIVE AXIAL FORCE CONTROL IN GUN DRILLING

In this paper an adaptive axial force control for g un drilling of small drilling diameters is presented. The system i s applicable to CNC drilling and gun drilling machine tools, whi ch are equipped with a fast analog NC input and an axial f orce measurement system. An online identification algori thm discretely investigates the actual transfer functio n of the control path. Based on this information proper controller p arameters are allocated. Experimental tests of the adaptive contr ol system show the functionality in drilling a material trans ition from steel 100Cr6 into cast iron ADI 800 and exemplary illustr ate the disturbance reaction, introduced by activated chang es of the path behavior.

Approaches of Self-optimising Systems in Manufacturing

Within the Cluster of Excellence “Integrative Production Technology for High-Wage Countries” one major focus is the research and development of self-optimising systems for manufacturing processes. Self-optimising systems with their ability to analyse data, to model processes and to take decisions offer an approach to master processes without explicit control functions. After a brief introduction, two approaches of self-optimising strategies are presented. The first example demonstrates the autonomous generation of technology models for a milling operation. Process knowledge is a key factor in manufacturing and is also an integral part of the self-optimisation approach. In this context, process knowledge in a machine readable format is required in order to provide the self-optimising manufacturing systems a basis for decision making and optimisation strategies. The second example shows a model based self-optimised injection moulding manufacturing system. To compensate process fluctuations and guarantee a constant part quality the manufactured products, the self-optimising approach uses a model, which describes the pvT-behaviour and controls the injection process by a determination of the process optimised trajectory of temperature and pressure in the mould.

Model and Method for the Determination and Distribution of Converted Energies in Milling Processes

This paper summarises the current state of project research focussing on the energy model for milling processes. The general methodology of heat flux determination is described in detail. An analytical temperature distribution model that has been engineered in a subproject is presented as an initial result. The potential theory provides complex solutions for the differential equation of thermal conduction that make available temperature field and heat flux field at the same time. The models were validated by means of the temperature fields measured. An online calibration method combining an infrared camera with a two-colour pyrometer was developed to ensure the quality of the captured data. Finally, the principal paradigm of determining heat fluxes from the temperature models is briefly introduced.

Einfluss des Regelstreckenmodells auf die erzielbare Güte einer Axialkraftregelung für das Tiefbohren

Kurzfassung Inwieweit der Modellansatz für die Regelstrecke eines Fertigungsprozesses Einfluss auf die erzielbare Regelgüte nimmt, belegen die Ergebnisse am Werkzeugmaschinenlabor in Aachen (WZL). Am Beispiel eines adaptiven Regelungssystems für das Tiefbohren werden zwei Regelstreckenmodelle hinsichtlich ihrer Eignung zur modellbasierten Reglerparametrierung untersucht. Die Ergebnisse zeigen, mit welchen Qualitätseinbußen hinsichtlich der erzielbaren Regelgüte zu rechnen ist, wenn das reale Streckenverhalten abstrahiert wird. Die Wahl des Modellansatzes ist entscheidend für den Aufbau eines adaptiven Regelungssystems, da die freien Modellparameter durch geeignete Algorithmen während des Bohrprozesses (online) zu identifizieren sind. Dies führt zu einem klassischen Optimierungsproblem zwischen Identifikationsaufwand und Adaptionsqualität.