CAE-ECM system for electrochemical technology of parts and tools

J. Kozak et al. / Journal of Materials Processing Technology 107 (2000) 293±299 295of electrodes, are very important in ECM input parametersselection. The input parameters should always be chosensuch that the maximum temperature of electrolyte neverreaches its boiling point. One-dimensional model, in whichonly average values of T (Fig. 5b), and b across the gap canbe calculated, may not be accurate enough to properlyestimate the maximum temperature. Use of input parametersfrom simulation that underestimated electrolyte temperaturefor actual machining may lead to short-circuit betweenelectrodes, and what follows, to damage of tool and workpiece.Ability of CAE-ECM system to predict workpiece shapeafter machining was veri®ed experimentally. ECM sinkingof workpiece made of WNL tool steel (0.55% C, 0.7% Mn,2% Si, 0.7% Cr, 1.6% Ni, 0.25% Mo) was performed. Watersolution of NaNO 3 of 15% was used as electrolyte. Machiningwas performed for feed rates V f ˆ 0:6, 0.8, 1.0 mm/min,working voltage U ˆ 16 V and electrolyte gap inlet pressurep 0 ˆ 0:6 MPa. Tool-electrode used in experiment wasdesigned using the CAE-ECM system.In Fig. 6, actual and calculated workpiece shapes usingthe CAE-ECM are shown. The areas where the biggestdifference between the shapes was observed are magni®edin Fig. 7.Experimental veri®cation showed good agreementbetween theoretical and actual results. The analysis ofaccuracy of machined workpieces showed that maximumshape error is less than 0.02 mm or 5% of the gap size. Theerror is greater near the inlet of the electrolyte. This error canbe attributed to the approximate distribution of the electrolyte¯ow and electrical ®eld estimation at the electrolyteentrance region of the gap.3. Tool-electrode designFig. 3. Simulation algorithm.critical states with electrical discharges. The mathematicalmodel of the ECM process used in presented CAE-ECMsystem is described in [3]. Simulation algorithm is shown inFig. 3.Examples of simulation of ECM shaping are shown inFig. 4a and b. In Fig. 4a, results for simulation of ECM withconstant feed rate are shown. In Fig. 4b, results for machiningwith additional oscillations of tool-electrode are presented.Additional harmonic movement of tool-electrodesigni®cantly improves conditions in interelectrode gap thatresults in much greater dimensional accuracy of the process.In these ®gures, subsequent graphs illustrate anode-workpieceshape evolution in time.Electrolyte temperature distributions across the interelectrodegap at the point where electrolyte exits the gap (whereit reaches its highest temperature) are shown in Fig. 5a and b.The two maxima that can be observed in Fig. 5a in proximityIn order to obtain a desired shape of workpiece withincertain accuracy and for a given set of ECM input parametersthe tool-electrode needs to be properly designed andmanufactured. In such a design, ®nal interelectrode gapdistribution was uneven.In CAE-ECM system iterative trial-and-error method isused for tool-electrode design. At ®rst initial, approximatepro®le of tool-electrode is calculated on the basis of theso-called ``cosine law'', using constant electrochemicalproperties of material±electrolyte arrangement [1,2]. Next,simulation of ECM using the approximated shape of toolelectrodeis performed and errors obtained between F i anddesired F shapes of workpiece are calculated, DF ˆ F i F.Then, the tool shape is corrected using weighted valuesof the errors and another simulation is performed. Thisiteration cycle is repeated until some accuracy criterionis satis®ed. During iteration process software checks ifphysical conditions of machining are within imposed limitssuch as T < T max ; b < b max ; w < w max , etc. has to betaken into account.