Overview in PDF format - Tallinna Tehnikaülikool

Figure 2.3 Noise recognition in machiningAs the cutting process is in a continual state of change due to tool wear, it cannotbe considered time-invariable. Typical wear criteria are average wear land widthand maximum wear land width. Using these criteria it is possible to evaluate theaverage and maximum intensity of wear and implement these data in mathematicalequations or models predicting tool life. When it comes to the analysis of tool wear,it is recognised that the flank wear is of prime concern, so that all tool life testingtechniques have primarily considered this type of wear (Astakhov, 1999). It occurson the flank of the tool below the cutting edge and cannot be avoided. The size ofthe flank wear can be measured as the distance between the top of the cutting edgeand the bottom of the flank wear land. Modern cutting inserts have often chamferedcutting edges, enabling to extend the tool life (Fig. 2.4a). Therefore flank wear canbe recognised both on the cutting edge and on the flank face.At small cutting speeds flank wear is dominating. In Fig. 2.4b the flank wear isindicated by h αw , the width of chamfer by b γ , and the flank angle by a 0 . At the sametime chamfer width b γ decreases, and the corresponding decrease is indicated by b γwα .At average cutting speeds, over built-up edge formation limits, a notch is formedat the rake face. The depth of notch is small and the rake angles γ o1 and γ o2 remainthe same. The first phase is shortening both from rake and flank faces. The chamferwidth decreases during machining at the flank and rake faces. Usually cementedcarbide tools should be replaced when the average width of the flank wear landreaches 0.3 mm (by ISO 3685-1977) when wear land is uniform, or 0.6 mm whencutting edge is chipped.γo1bγγο2bγwαhαwαoFigure 2.4 An unworn cutter with chamfer honing (a), and a worn cutter at small cuttingspeeds (b)18