Stage identification and process optimization for fast drilling EDM of film cooling holes using KBSI method

Fast drilling electrical discharge machining(EDM)is widely used in the manufacture of film cooling holes of turbine blades.However,due to the various hole orientations and severe electrode wear,it is relatively intricate to accurately and timely identify the critical moments such as breakout,hole completion in the drilling process,and adjust the machining strategy properly.Existing breakout detection and hole completion determination methods are not suitable for the high-efficiency and fully automatic production of film cooling holes,for they almost all depend on preset thresholds or training data and become less appropriate when machining condition changes.As the breakout and hole completion detection problems can be abstracted to an online stage identification problem,in this paper,a kurtosis-based stage identification(KBSI)method,which uses a novel normalized kurtosis to denote the recent changing trends of gap voltage signals,is developed for online stage identification.The identification accuracy and generalization ability of the KBSI method have been verified in various machining conditions.To improve the overall machining efficiency,the influence of servo control parameters on machining efficiency of each machining stage was analyzed experimentally,and a new stage-wise adaptive control strategy was then proposed to dynamically adjust the servo control parameters according to the online identification results.The performance of the new strategy is evaluated by drilling film cooling holes at different hole orientations.Experimental results show that with the new control strategy,machining efficiency and the machining quality can be significantly improved.

Equivalent model of close-packed film cooling holes in nickel-based single crystal cooled blade based on crystallographic theory

The mechanical properties of nickel-based single crystal thin-walled plate with close-packed film cooling holes were studied based on the equivalent solid material concept. The effective plastic parameters inversion method based on crystallographic theory were proposed. A simplification method for close-packed film cooling hole plates with square and triangular penetration patterns was presented. A large number of finite element analysis results covering different ligament efficiencies and penetration patterns were provided to verify the feasibility of the plastic equivalent principle and simplification method. The results show that the stress–strain curve and resolved shear stresses of simplification models are in consistence with the plate models with close-packed film cooling holes. The equivalent errors of yield strength are all within the error band and the values of equivalent errors are all less than 10%. In addition, the equivalent errors of the positions where maximum resolved shear stress occurs are all less than 15°, indicating the accuracy of plastic equivalent model and simplification method.

Hybrid RANS-LES of Shaped Hole Film Cooling on an Adiabatic Flat Plate at Low Reynolds Number

Hybrid RANS-LES methods offer a means of reducing computational cost and setup time to simulate transitional flows. Several methods are evaluated in ANSYS CFX, including Scale-Adaptive Simulation (SAS), Shielded Detached Eddy Simulation (SDES), Stress-Blended Eddy Simulation (SBES), and Zonal Large Eddy Simulation (ZLES), along with a no-model laminar simulation. Each is used to simulate an adiabatic flat plate film cooling experiment of a shaped hole at low Reynolds number. Adiabatic effectiveness is calculated for Blowing Ratio (BR) = 1.5 and Density Ratio (DR) = 1.5. The ZLES method and laminar simulation most accurately match experimental lateral-average adiabatic effectiveness along the streamwise direction from the trailing edge of the hole to 35 hole diameters downstream of the hole (X/D = 0 to X/D = 35), with RMS deviations of 5.1% and 4.2%, and maximum deviations of 8% and 11%, respectively. The accuracy of these models is attributed to the resolution of turbulent structures in not only the mixing region but in the upstream boundary layer as well, where the other methods utilize RANS and do not switch to LES.

Observation of Atomic Dynamic Behaviors in the Evaporative Cooling by In-Situ Imaging the Plugged Hole of Ultracold Atoms

We experimentally observe the dynamic evolution of atoms in the evaporative cooling, by in-situ imaging the plugged hole of ultracold atoms. Ultracold rubidium atoms confined in a magnetic trap are plugged using a blue-detuned laser beam with a waist of 20 m at a wavelength of 767 nm. We probe the variation of the atomic temperature and width versus the radio frequency in the evaporative cooling. Both the behaviors are in good agreement with the calculation of the trapping potential dressed by the rf signal above the threshold temperature,while deviating from the calculation near the phase transition. To accurately obtain the atomic width, we use the plugged hole as the reference to optimize the optical imaging system by precisely minimizing the artificial structures due to the defocus effect.

Comparative Study on Different Methods for Prediction of Thermal Insulation Performance of Thermal Barrier Coating Used on Turbine Blades

As turbine inlet temperature gets higher and higher,thermal barrier coating(TBC) is more and more widely used in turbine blades.For turbine blades with TBC,it is of great significance to evaluate the temperature distribution of its substrate metal quickly and accurately,especially during the design stage.With different degrees of simplification such as whether to consider the change of the geometric size of the fluid domain by TBC and whether to consider the planar heat conduction in TBC,three different methods used in conjugate heat transfer(CHT) simulation to model the TBC of the turbine blades have been developed and widely used by researchers.However,little research has been conducted to investigate the influence of the three methods on the temperature distribution of turbine blade.To fill this gap,three geometric models were designed.They are a solid conduction model with a substrate metal layer and a TBC layer,a transonic turbine vane with internal cooling and TBC,and a plate cylindrical film hole cooling model with TBC.Different methods were used in these geometric models and their differences were carefully analyzed and discussed.The result shows that for the conduction model used in this paper,with the same TBC surface temperature distribution,the difference between the three methods is very small and can be ignored.For a transonic turbine vane with internal cooling,regarding the local maximum temperature of the substrate-TBC interface,the largest difference between the method in which TBC is considered as a thermal resistance or a virtual layer of cells and the method in which three-dimensional heat conduction equation of TBC is solved occurs at the trailing edge.The difference near the leading edge is below 2K.When employed to the film cooling model,the difference of the laterally averaged temperature of the substrate-TBC interface can be 8 K which is mainly due to the change of the length to diameter ratio of the film cooling hole by TBC.If the substrate thickness is reduced by the thickness of TBC when three-dimensional heat conduction equation of TBC is solved,the temperature difference between the three methods will be quite limited.

Breakthrough detection in electrochemical discharge drilling to enhance machining stability

Film cooling holes are widely used in aero-engine turbine blades.These blades feature large numbers of holes with complex angles and require a high level of surface integrity.Electrochemical discharge drilling(ECDD)combines the high efficiency of electrical discharge drilling(EDD)with high quality of electrochemical drilling(ECD).However,due to the existence of a variety of energy for material removal,accurate and timely detection of breakthroughs is fraught with difficulties.An insufficient preset setting distance results in a tiny exit aperture,influencing the structure's shape.In addition,the electrode is prone to bending at a large overfeeding distance,causing secondary discharge damaging sidewall surface integrity.This paper compares and analyzes the characteristics of processing waveforms using EDD and ECDD.A novel breakthrough detection method is proposed based on the variance signal of average voltage(VSAV)to increase machining stability and achieve fabrication without a recast layer.This method extracts the fluctuation transformation by calculating the variance of the average.Following signal detection,the overfeeding distance is quantified.An experiment is used to validate the breakthrough detection with 100%accuracy in all tests.The optimum overfeeding distances for hole angles of 0°,30°,and 60° are obtained,and the stable removal of the recast layer is realized.Finally,the effectiveness of the method is verified on a typical workpiece with a double-wall structure and a nickel-based single crystal blade.