Predicting the evolution of electrochemical trepanning for inner blisks with a chamfer structure at blade tip

Electrochemical trepanning(ECTr)is an effective electrochemical machining(ECM)technique that can be used to manufacture the integral components of aero-engine compressors.This study focused on the dynamic evolution of ECTr for production of inner blisks(bladed disks)with a special chamfer structure at blade tip.Due to the existence of chamfer,the ECTr process of inner blades is in a non-equilibrium state during the early stages,and the physical field changes in the machining gap are complex,making it difficult to predict the forming process.In this paper,a dynamic evolution model(DEM)of inner blade ECTr with a special chamfer at blade tip structure is proposed,and an ECTr multi-physical fields simulation study was carried out.The evolution of the chamfer at blade tip was analyzed and data related to chamfer were predicted based on the dependence of anode boundary properties with machining time and feed rate.In addition,the dis-tributions of current density,electrolyte flow rate,bubble volume fraction,temperature rise,and electrolyte conductivity in the machining area at different times were obtained by combining them with the multi-physical fields simulation results.Subsequently,a series of ECTr experiments were conducted,in which,as the feed rate increased,the surface quality and machining accuracy of the inner blades were improved.Compared with the simulation results,the error in machining accu-racy of the chamfer profile is controlled within±2%,and the machining accuracy of the blade full profile was controlled within±0.2 mm,indicating that the model proposed in this study was effec-tive in predicting the evolution of inner blades ECTr with chamfer structures at blade tip.

Recurrence of chronic subdural hematoma after trepanation and drainage

Objective: To sum up the causes of recurrence of chronic subdural hematoma (CSDH) from failure of trepanation and drainage and explore its prevention and treatment. Methods: From October 1988 to June 2002 a total of 358 patients with CSDH were treated with trepanation and drainage in our hospital. Among them 15 patients had recurrence of CSDH after operation. The data of the 15 patients were reviewed retrospectively. Results: Of the 15 patients, 13 were cured by retrepanation and redrainage, one cured by removal of hematoma by craniotomy with bone flap, and one, a 1 year old child, gave up reoperation due to severe encephalatrophy. Conclusions: Most CSDHs which recur after trepanation and drainage can be cured by retrepanation and redrainage. For the patients with repeated recurrence of CSDH removal of hematoma capsule can be considered. The causes of recurrence of CSDH are related to disease course, the thickness of hematoma capsule, the severity of encephalatraphy and whether the hematoma cavity is drained or irrigated completely, and operation methods.

Optimization of flow field in electrochemical trepanning of integral cascades(Ti6Al4V)

Ti6Al4V is widely applied in the integral cascades of aero engines.As an effective machining method,electrochemical trepanning(ECTr)has unique advantages in processing surface parts made of hard-to-cut materials.In ECTr,the state of the flow field has a significant effect on processing stability and machining quality.To improve the uniformity of the flow field when ECTr is applied to Ti6Al4V,two different flow modes are designed,namely full-profile electrolyte supply(FPES)and edges electrolyte supply(EES).Different from the traditional forward flow mode,the flow directions of the electrolyte in the proposed modes are controlled by inlet channels.Simulations show that the flow field under EES is more uniform than that under FPES.To further enhance the uniformity of the flow field,the structure of EES is optimized by modifying the insulating sleeve.In the optimized configuration,the longitudinal distance between the center of the inlet hole and the center of the blade is 6.0 mm,the lateral distance between the centers of the inlet holes on both sides is 16.5 mm,the length to which the electrolyte enters the machining area is 1.5 mm,and the height of the insulating sleeve is 13.5 mm.A series of ECTr experiments are performed under the two flow modes.Compared with EES,the blade machined by FPES is less accurate and has poorer surface quality,with a surface roughness(R_(a))of 3.346μm.Under the optimized EES,the machining quality is effectively enhanced,with the surface quality improved from R_(a)=2.621μm to R_(a)=1.815μm,thus confirming the efficacy of the proposed methods.

Electrochemical trepanning with an auxiliary electrode

Electrochemical trepanning(ET)is one of the main methods for processing the blisks in aero-engines.However,stray corrosion in ET has a very negative impact on the machining quality of the blades.This paper proposes an innovative ET method with an auxiliary electrode surrounding the inner wall of the cavity above the cathode.Two-dimensional electric-field models are established and simulations are carried out with the auxiliary electrode at different positions and different electric potentials.The electric-field simulations show that adding the auxiliary electrode reverses the directions of the current lines in the processed area,thereby protecting it.The results show that when the distance from the bottom of the auxiliary electrode to the top of the cathode tool is 3 mm and the potential difference between the auxiliary electrode and the anode workpiece is 5 V,the area corroded by stray current is decreased.Experiments are performed under the parameter values determined by the simulations,and they confirm that this method is effective at reducing stray corrosion.Specifically,at a feed rate of 2.5 mm/min,the blade taper angle is decreased from 1.37°to-0.09°,the thickness of the leading and trailing edges is increased from 0.307 mm to 0.704 mm,and the average surface roughness is decreased from S_(a)=8.239μm to S_(a)=7.028μm.