Sensing of Drill Wear and Prediction of Drill Life

Abstract

High-speed steel drill life is found to be a strong function of the work material hardness (Tl α HB−16) when drilling cast iron. This strong dependence may account for the large variation in the life of the drills, which is observed in industrial conditions. Torque, thrust, and power are observed to be functions of drill wear. In the drilling of cast iron using H.S.S. drills of 10.32 mm (13/32 in.) dia at 690 rpm or 22.25 M/min (73 ft/min) maximum, the following relations were observed: torque(M)=0.125HBd2f+0.289HBd2r+0.0487HBd2w(3)thrust(T)=0.325HBdf+0.1242HBdw+0.755HBdr+0.0022HBd2(7) where HB = Brinell hardness of work material, d = diameter of the drill, f = feed per revolution, w = average flank wear, and r = radius at the cutting edge (0.01 mm or 0.0004 in.) all in consistent units. Flank wear of a drill increases rapidly at the end of its life. Torque and thrust reflect this change but are also influenced by workpiece hardness. Therefore, torque and thrust can be used as variables for drill wear sensing only when there is a close tolerance on the workpiece hardness, of the order of ±5 percent.

A summary of methods applied to tool condition monitoring in drilling

“…The simultaneous monitoring of thrust force and torque is rather common (see e.g. [2,6,[11][12][13][14][15][16][17][18][19]) and special electronics have been developed for this purpose [11].…”

“…Based on the tests with copper alloy and a model described in [19], formulas that define the thrust force and torque as a function of feed per revolution, drill diameter and flank wear have been developed and their applicability has also been tested [6]. It should be noted that the tests indicated that the increase in cutting speed over the range studied had no significant effect on work material strength, and hence it has no significant effect on cutting forces [6].…”

“…Based on tests with different workpiece material hardness, formulas for torque and thrust force have been developed as a function of Brinell hardness of work material, diameter of the drill, feed per revolution, average flank wear and radius at the cutting edge [19]. It is concluded that the variation in drill life is significantly influenced by the workpiece hardness.…”

“…the dynamics of the electric motor do not influence it to the same extent that they influence the current measurement. However, measuring torque is more complicated than measuring the current of the spindle motor and therefore the measurement of the current has also been widely tested and used [13,19,33,34].…”

Monitoring of Burr and Prefailure Phase Caused by Tool Wear in Micro-Drilling Operations Using Thrust Force Signals

“…The obtained average thrust force P av during peck drilling with the 0.1 mm drill shown in Fig. 11(a) rapidly increases in the early stage and then gradually increases at almost a constant rate with the increase in the number of drilled holes (8) . The characteristics of the average thrust force with the increase in the number of drilled holes is expected to be similar to the characteristics of the width of the flank wear land of the main cutting edge at the outer corner shown in Fig.…”