Modern aircraft engines are nowadays designed with the aim of reducing fuel consumption and emission of pollutant gases as well as increasing reliability and competitiveness in the manufacturing and ...repair costs. These requirements on the engines result in new requirements on components and manufacturing processes, to know: application of new engineering materials, higher component temperatures, increased demands on tightness, 3-D complex shapes as well as new manufacturing technologies. EDM-machining is typically chosen for applications including complex geometries like high aspect ratio cavities in high-temperature resistant materials, since the EDM-process is independent from the mechanical properties of the processed material. This paper addresses the design and utilization of a unit composed of piezoelectric actuators for machining seal slots in turbine components. This aims the optimization of the flushing mechanisms through vertical vibration of the tool electrodes while manufacturing high aspect ratios cavities and therewith the optimization and/or reduction of both process time and electrode wear. Firstly, the piezo-unit was designed and components like piezoelectric actuators and charge amplifier were chosen, in accordance to previous defined requirements regarding vibration frequencies and amplitudes. During the experimental investigations graphite electrodes were applied. A total of twelve cavities with an aspect ratio of 12 are simultaneously machined in the material MAR-247. During the process, a harmonic longitudinal vibration of the electrodes overlapped to the machine's feed movement is realized. Both vibration amplitude and frequency were varied during the experiments, ranging from 2μm to 16μm and from 50Hz to 1kHz, respectively. The results are compared to the conventional process without vibration, while the EDM-parameters remain unaltered. By applying longitudinal vibration to the tool electrodes the material removal rate was increased by 11%. The relative tool electrode wear was reduced by 21%.
The die-sinking EDM is applied in the aerospace industry for the machining of seal slots in blades and in structural components made of nickel-base alloys, normally applying graphite electrodes. The ...objective of this work was the development of a technology to dress the graphite electrodes inside the EDM machine tool, with the aim of rebuilding the original shape of the worn electrodes between EDM cycles. The milestones consisted on (I) understanding the wear behavior of the electrodes while machining the slots, (II) the development of the dressing technology applying the DoE-method and determination of statistically high influencing parameters, and finally (III) the integration of the dressing technology into the process chain.
This study investigates the wear on copper electrodes and the size of the micro-pits or micro-holes that are produced, after using an Electrical Discharge Machining (EDM) die sinking system. A copper ...electrode Ø 0.2 mm, and a model of an acetabular cup made from tool steel (SKD11), were used. The results show that electrode wear is greater when higher currents are applied. The current discharges applied were 0.5 A, 1.5 A, and 3.0 A, and they resulted in electrode wear of 0.236 mm, 0.246 mm, and 0.269 mm respectively. The highest mean area of the pits machined, at approximately 65901.9 μm2, was observed for the application of a 3.0 A current. Therefore, the EDM die sinking system could be a useful method for surface modification
Commonly, on Die Sinking Electrical Discharge Machining (DS EDM), a special generator enables current pulses in sinusoidal or triangular shapes, only in a single polarity. The duration and the ...amplitude are adapted to the machining sequence, allowing the achievement of different surface finishing. By using a new configuration, it is shown that if one applies pulses of current in both polarities, related together but with a certain ratio between the positive and the negative peaks current, machining results could be improved. The purpose of this new generator is the ability to control with great flexibility the generation of these pulses, in terms of durations, amplitudes and sequence. These parameters can be independently selected for the positive and negative polarity and modified during the machining. One can also choose a special predefined or settable sequence of pulses. The generator includes also the double polarity ignition and the high-speed gap breakdown detection. An embedded programmable circuit (FPGA) provides a high-speed control of the sequence. Machining tests have been performed in order to explore and quantify different sequences of pulses in terms of machining results and performances achieved, compared against the current situation.
CNC (computer numerical control) systems play an ultimately important role for controlling EDM (electrical discharge machining) machine tools and their machining processes. Till now, existing CNC ...systems do not offer sufficient openness that supports researchers and engineers to expend its capabilities and functionalities in response to the increasing demands of smart manufacturing; on the other hand, transforming an EDM machine made by small and medium-sized machine tool builders, into a smart manufacturing system has never been an easy job. To address the issues and overcome the difficulties which block the way towards smart manufacturing, this paper proposes an open architecture CNC platform for EDM machine tools. This platform utilizes the state-of-the-art technologies in implementation of the hardware and software without compromising with the constraints of obsolete techniques. For demonstrating the unique capabilities, the generalized unit arc length increment (GUALI) interpolation method and the Digitizer/Player system architecture are adopted. To exhibit the feasibilities of the newly developed platform, three kinds of EDM machine tools are applied associated with advanced functionalities such as machining process adaptive control, applications of machine learning, 6-axis EDM of shrouded turbine blisks etc. In addition, a small-scale smart manufacturing unit for drilling film cooling holes of turbine blades is built up into real production by applying the new CNC system and related software applications. From the practitioner’s viewpoint, openness and standardization are the keys that enable the people from academia and industry bringing in their domain knowledge to enrich the smart manufacturing ecosystem.
In this paper, a new dry die-sinking EDM polishing method using a mouldable polymer composite electrode as tool is presented. This EDM method involves two new concepts, namely: dry die sinking and ...the polymer composite tool. An experimental investigation was performed on the dry die-sinking EDM process to assess the feasibility of finishing down to 0.2–0.3 μm Sa, and polishing from 0.2 to 0.3 μm Sa down to the finest achievable surface finish. To simplify sample preparation, the methodology involved a reversal of the polishing process. Hence, the surface finish of a 13-mm diameter P20 tool steel disk was taken from a lapped 0.01-μm Sa surface finish up to a rougher steady-state surface finish value, assuming comparable results with conventional rough-to-fine polishing procedures. Several process parameters were evaluated such as: pulse current level
I
EP
, open-circuit voltage
V
OC
, pulse time on
T
ON
, pulse time off
T
OFF
, number of polishing cycles
N
C
and three pulse identification methods, for their effect on sample surface finish micrometre Sa, material removal rate MRR cubic millimetre per hour and electrode relative wear rate ERWR.
In this work, a comparative study of the electrical discharge machining (EDM) of three different conductive ceramics has been carried out. The ceramics used in the experiments were cobalt-bonded ...tungsten carbide (WCCo), hot-pressed boron carbide (B4C) and reaction-bonded silicon carbide (SiSiC). This study has been done only for the finishing stages and the selection of the above-mentioned conductive ceramics was motivated by their wide range of applications: machining and mining for WCCo, thermal-neutron absorber and nozzles for B4C and wear parts and heat exchangers for SiSiC, among others. The comparative study has been carried out on the influence of the design factors of intensity (I), pulse time (ti) and duty cycle (η) over response variables such as surface roughness (evaluated through the Ra parameter), volumetric electrode wear (EW) and material removal rate (MRR). This was accomplished through the technique of design of experiments (DOE), along with multiple linear regression techniques, which allowed us to carry out the analysis with only a small number of experiments.
The die-sinking EDM-technology, applied at the turbine industry for the fabrication of seal slots in turbine components, is addressed at this work. The objective was the development of a new ...technology to dress graphite electrodes inside the machine tool with the aim of reducing the set-up times and of enabling process automation with respect to all quality requirements. The wear pattern development of graphite electrodes during the EDM-machining of seal slots in nickel base alloy MAR-M247 was determined, followed by the analysis of the influence of dressing plate materials and dressing parameters. The process results analyzed were dressing time, dressing length and material removal rate. This enabled the understanding of tool electrode wear development, followed by the determination of influencing dressing parameters and their effects. The optimization of the dressing technology was conducted, including the variation of statistically high significant influencing dressing parameters. This enabled the determination of optimized dressing parameters applying the dressing plate materials graphite and cemented carbide. Finally, the dressing technology was integrated into the process chain, whereas five sets of 12 cavities were machined successively, with a dressing step between the EDM-machining steps. The analysis of all five sets of cavities proved that the form accuracy, arithmetical surface roughness and affected sub-surface remained within the tolerances for all pats.
In this paper, the results regarding the optimization of the die-sinking EDM-technology for the fabrication of turbine components are presented. The main objective of this work was the reduction of ...machining time while producing cavities with a depth of 11mm in the alloy MAR-M247, with respect to the requirements for surface roughness and sub-surface damage. The study was conducted using graphite electrodes of three different dimensions, totalizing 12 electrodes and a total electrode area of 89.50 mm2. The machine tool GENIUS 1000 THE CUBE was used in the experiments and IonoPlus IME-MH was used as dielectric fluid. The Design of Experiments Methods (DoE) were applied in the planning and execution of all experiments. Firstly, experiments were conducted to estimate the maximal discharge current that can be applied for fulfilling the quality criteria regarding both surface roughness and thickness of affected sub-surface, since discharge current is known as the main influencing process parameter affecting both factors. In the second stage, the process was optimized by varying following electrical parameters of the machine tool: discharge current (ie), discharge duration (ti), pause duration (t0), ignition voltage (V) and duty factor (τ). Finally, both process parameters as well as machine tool's control parameters were adjusted to achieve optimized results regarding the total machining time and electrode wear with respect to the surface requirements of produced parts. A total machining time reduction of more than 50% in comparison to the technology currently employed by the industry was achieved. Requirements on both arithmetical surface roughness as well as affected sub-surface thickness could be fulfilled. This robust technology was developed for producing the cavities in MAR-M247 and all applied methods, studied parameters as well as the results regarding machining time, electrode wear and the quality of the achieved work piece are presented.
High-strength copper alloys are used as materials for injection molding tools or as cores and inserts in steel molds because of their high thermal conductivity, corrosion and wear resistance. ...Unfortunately, there is little technological knowledge on the electrical discharge machining (EDM) of copper-beryllium ASTM C17200 alloy. In this work, rough and finish machining conditions were tested using copper and tungsten-copper as materials for the electrodes. Cross-sectional micrographic and hardness examinations as well as surface roughness measurements were also carried out on workpieces after machining in order to study the thermally affected zones. Appropriate parameters settings for EDM of the investigated alloy are suggested.
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