Proceedings of SerbiaTrib '13

Figure 5. Flank wear land width versus number of cutsin various cases of face and peripheral millingMoreover, as it is demonstrated in Figure 5b,when up milling is applied, the flank weardevelopment is less intense compared to downperipheral or face milling at a chip length of about40 mm. The attained accumulative tool life in upmilling is approximately three times highercompared to those ones in down milling. Thisbehaviour can be explained, based on the developedcutting edge entry impact duration in the previouslydescribed cases.To highlight this effect, in Figure 6, the obtainedaccumulative tool life in the investigated peripheraland face milling cases is displayed versus thecutting edge entry impact duration t e . The curve inthis chart describes the effect of the cutting entryimpact duration on the accumulated tool life. Therelevant results were obtained in milling, at varioustool geometries, cutting kinematics and conditions[3, 9, 10, 11].In down milling, face or peripheral, atundeformed chip lengths l cu of ca. 40 mm, thecutting edge entry impact durations t e amount toapproximately 0.1 ms leading to the accumulativetool life diminishing.Furthermore, in up milling at an undeformedchip length l cu of ca. 40 mm, due to the smootherchip thickness growth at chip formation start, thecutting edge entry impact duration t e isapproximately 2.2 ms and the accumulative tool lifeincreases significantly compared to thecorresponding one in down milling.In contrary, in down and up milling, face orperipheral, at undeformed chip lengths l cu of about80 mm, the entry impact duration varies from 3.1 to5.4 ms and the accumulative life remains almost onthe same level.Considering Figure 6, it can be concluded thatentry impact duration larger than 2 ms leadpractically to almost the same accumulative toollife. Furthermore, it is obvious, that short entryimpact durations correspond to comparably lowercoating fatigue critical forces (see Figure 4) anddiminishes the coated tool life. Longer entrydurations improve the film fatigue behaviour, thusenhancing the coated tool life.The accumulated tool life in milling of theemployed hardened steel IMPAX versus the entryimpact duration at various cutting speeds isdisplayed in Figure 7. The accumulated tool life inmilling of the employed hardened steel IMPAXversus the entry impact duration, displayed in Figure7, can be described by the equations, displayed inFigure 7b, for the cutting speeds of 100, 200 and 300m/min.Similar experiments were conducted for allemployed hardened steels. Figure 8 illustrates theaccumulated tool life in milling of NIMAX, AISI304 L and the 42CrMo4 versus the entry impactduration at various cutting speeds. The obtainedaccumulated tool life of NIMAX is substantiallylower than the corresponding of IMPAX at thesame cutting speed and almost equal to 1/3 of that.Figure 6. Accumulated tool life in milling versus theentry impact duration16 13 th International Conference on Tribology – Serbiatrib’13