Correlation Between Machinability Index and Gray Iron Structural ...

nnnB. NEDELJKOVICUDK 621.9.0L:621.7.01C)xLIJat!tn nCorrelation Between Machinability Indexand Gray Iron Structural ParametersGray iron machinabitity is one of its most important characterisfics. A complex approach to theaim assumes respecfing of the direct inJluence of the casfing process to the machinabilityparameters of the castings. Basic parameters machinability is, before all, gray iron structure whichdepends on its chemical composition, melting condifions, modifcation, rctw material quality andother fectors.The paper present research results between machinability and gray iron qualitatrve andquanti tafive micros tructure parometers.Keywords: machinability, gray iron, microstructure, casting1. INTRODUCTIONGray iron machinability, as one of more importantgray characteristics, has always been watched fromthe aspect of cutting control, cutting speed, cuttingblade structure, type of hard coating and othertechnological factors and very rarely, or almostnever, from the aspects of structure and materialcharacteristics is, in fact, the basic point of this paper.Highly productive automatic transfer machines forcastings, as it is the case with breaking drums, at highcutting speeds require constant cutting resistancesand any variation represents a serious problem atlarge castrng series. For that reason, the target aim ofthis paper \\'as to promote casting technology in thefunction of machinability casting advancement.2. RESEARCH PROGRAMMEThe preparation and casting of the test batches wascarried out in four ton induction furnaces, using thefollowing charge make up:. steel motor car body sheet packed in bales,oreturned grey iron (scrap castings, runners andrisers),. carburising and alloying agents.Dr B. Nedeljkovii,"Zastava automobili"Ce ntralni laboratoii umKragujevacAll the charge conditioning and alloying materialswere pre-analyzed and were added to the charge inthe furnace.After the first batch of castings, was poured, the meltunderwent chemical analysis on a Philips PV 8300emi ssion spectrometer.Previously modified liquid metal, prepared in thisw&y, was cast into moulds with a 0.1% SiCa basedinoculant. The first cast was followed by batchcorrection inside the induction furnace and chemicalanalysis repeated.Table I shows the results of chemical compositiontests.Table I. Chemical composition of liquid metalNoElementFirst batchContentSecond batchI Carbon 3.00 3102. Silicon 1.80 L903. Manganese 0.50 0854. Boron 0.076 0.0325 Phosphorus 0.045 0.0546. Sulphur 0.042 0.0607. Aluminium 0.030 0 028Before castrng into the moulds, the liquid metal fromthe second batch was also modified with 0.1%SiCa.t0Tribolog,,in industry, Volume 22, No. I&2,2000.

2.2. Drum machinability testsCuttrng resistances Fl, F2 and F3 were measured asthe parameters to define the machinability indexwithout the application of a cooling agent.Operations on the test samples were carried out on auniversal lathe using accepted computer supportedregimes:Chemical composition of liquid metalCoromant SNMA: 120412 Sandvik plate,Number of revolutions: n:560rpmPitch: S:0.llZmmlrCutting depth: d:0.3mm3. MEASURING INSTRUMENTSA dynamometer, connected to the tool carner vicrtensiometrically resistant feeds, passing the signalthrough a measuring bridge to amplifier and arecorder (figure l) was used to measure Fl, F2 andF3 cutting resistances and machinability index.4. MIKROSTRUCTURE TEASTINGFigure L Three component dynamometer!UMetallographic tests were carried out on samplesobtained by cutting pieces from a ring shaped part ofthe drum which had had its machinabilitycharacteristics monitored :r qualitative microstructure tests. microstructure assay.Qualitative microstructure tests were performedaccording to DIN/6911964 standard for:oometal base microstructuregraphite shape, arrangement and size.Quantitative microstructure tests were carried fbrgraphite plates representative samples, obtained tiomall three batches.x!;a.a!!2t )) lJ 21 2J 20 2; 2E 29 JuDmmnurnber. graphite plates surface Aa, m m2r perimeter (circumference) La, m m. gap between graphite plates Lo,n m mr graphite plates width Lg,., rn rn.Other values important for cast microstructurequality assessment were calculated on the basis of theabove-mentioned measurement of physical values.E{l5. RESULTS OF TESTINGxc)hz,Figure 2. Mean values of machinability indexforseries | (top), series 2 (middle) and series 3 (bottom)The procedure for establishing materialmachinability characteristics by measuriugcorresponding cutting resistance components is basedon the differences that exist in the formula Fl:f(T)for the different series of machining tests when othermachining conditions are kept constant.Because of limited space, only the mean values of themachinability index for both passes of the nraincutting resistance (Fl) for all three batches are shown(figure 2).Tribolog,, in indust4y, Volum e 22, No. 1 &2r 2000.ll

Table 2. Structural graphite parameters of grey ironNoSamples 1chargDistance betweengraphite plateLosn (pm)AaLAGraphite plate width(um)1pm)2[GR) ((um)mln max sr nlln max sr mln max srRnrN/m1mHBN.xl0-3pnlSvpm/3nl41ll 0.58 I t.o 13.9 0.29 225 /.-1J 2.54 -1J I 19.53 0. l6 4.0 0.96 195.3 150.3 9.07 24.823I1 1.43 t'12 24.9 0.39 434 r9.8 5.1 362 J /U 0.25 4.75 t.4 290.1 207 3.48A1 13 29m 1.35 202 24 0.'17 295 I9.8 3.6 428 34.9 0.20 5.4 1.5 284.5 208 3.+> ++.JZArT{trl t.2l 150.3 16.6 0.05 257 tz.4 0.27 280 26.8 0.01 3.6 1.5 346.3 22s 4.91 34.04) l9lIU 1.43 153 2t.6 0.61 r82 12.8 5.13 2'll 28.6 0.07 4.08 r.27 366.6 227 5.68 JO.-)6. QUANTITATIVE METALLOGRAPHICTESTSTable 2 shows the results of measured values thatquantitatively define the microstructure of thecastings tested.Figs 3-7 show correlation between the measuredparameters of castings microstructure andmachinability index for representative samples fromall thrce batches:i-o 0.8xO.c 0.6:' ^Ao ..*.=.c.9 nt*FIE)+=--,Iii ;..:--fiI;.'----TIIiIT'IIIIIi-=#- -'-l_ ' '',l9 1l 13 5 t7 19Plote surfoce, Ao [pm']Figure 5. Correlation between machinability indexand the distance between grophite plates1I -o 0.8*i ii:ii, . } - t r I I Ix 0).c 0.6-:ou.e.C .c.8 o.2!1620242tThe distance beh.veen graphite plates L. [pm ]U26 30 34 38 42 46Surfoce densfi, S, [pm'/pm']Figure 3. Correlation between machinability indexand plate surfbceFigure 6. Correlafion between machinability indexdependence of graphite plate width>aoD.c 0.6=€.C.COo0.4aav14 5 6 7 I 9 r0Numenkol density, N. xl0'[pm'lFigure 1. Correlatton between mochinobilityindexand surfaceFigure 7. Machinability index dependence onnumericol densitvt2TribologS,, in industry, Volume 22, No. l&2,2000.

7. CONCLUSIONo Obtained results point out the existence of non -unified machinability of tested drums within thesame charge.. It is observed that value machinability index atthe third charge is slightly worse than at thesecond one regardless of increased mechanicalproperties (Rm and HB results are not presentedin this paper). This is the consequence of betterinoculation of liquid metal of the third chargerelative to the second one.. With the increase of numeric density No, surfaceof lamella Ae surface density Sv and width ofgraphite lamellas LcR, also the machinabilityindex is increased if metal base is the same.. Significantly bigger index of machinability ofcastings from the first charge relative to thesecond and the third charee is the result ofpresence of larger share of fenite in metal base.REFERENCES|.lfrlfunovic D., Master of Degree paperwork -Energetic aspect of machinability by scrapingof gray iron with multiple coated cutting toolsmade of hard metal, Kragujevac 1991.12.l Babic M., Nedeljkovic 8., Milit //. .Modertitation of machinability andtribological properties of casting from grayiron, study on project realization 1.3.0668,Kragujevac 1994.[3.]Nedeljkovic B, Ph. D. thesis, Effect of microstructure on machinability of gray iron,Beograd 1995.Tribologt in industry, Volum e 22, No. 1 &2, 2000.l3