Machinery's Handbook, 31st Edition
GRINDING FEEDS AND SPEEDS 1263 conditions are obtained by increasing the work speed 5 to 10 times higher than the above recommendations indicate. These higher work speeds will create compressive stresses that are not detrimental to the surface. The by-product of higher work speeds is much higher SMRR values and thereby much shorter grinding times. Compressive stresses are also obtained by reducing the depth of cut a r . Wheel Life Relationships and Optimum Grinding Data.— Fig. 2a, Fig. 2b, and Fig. 2c show, in three planes, the 3-dimensional variation of wheel-life T with wheel speed V and ECT when grinding a hardened tool steel. Fig. 2a depicts wheel-life versus wheel speed (the T - V plane) with constant ECT appearing as approximately straight lines when plotted in log-log coordinates. In grinding, the wheel-life variation follows curves similar to those obtained for conventional metal cutting processes, including a bend-off of the Taylor lines ( T - V graph) towards shorter life and lower cutting speeds when a certain maximum life is achieved for each value of ECT . In the two other planes ( T - ECT , and V - ECT ) we usually find smooth curves in which the maximum values of wheel-life are defined by points along a curve called the H -curve.
100
ECT = 17 ECT = 33 ECT = 50 ECT = 75 ECT × 10 − 5
10
1
100
1000
10000
V m/min
Fig. 2a. Taylor Lines: T versus V , ECT Plotted for Grinding M4 Tool Steel, Hardness 64 RC Example 2: The variation of SMRR = V 3 ECT 3 1000 and wheel-life at various wheel speeds can be obtained from Fig. 2a. Using sample values of ECT = 33 3 10 − 5 mm and V = 1300 and 1900 m/min, SMRR = 1300 3 33 3 10 − 5 3 1000= 429, and 1900 3 33 3 10 − 5 3 1000 = 627 mm 3 /mm width/min, respectively; the corresponding wheel lives are read off as approximately 70 and 30 minutes, respectively.
1000
V = 4600 V = 3600 V = 2907 V = 2220 V = 1800 V = 1500
G-CURVE
H-CURVE
100
10
1
0.00001
0.0001
0.001
ECT, mm
Fig. 2b. T versus ECT , V Plotted Fig. 2b depicts wheel-life T versus ECT with constant wheel speed V shown as curves plotted in log-log coordinates, similar to those for the other cutting operations.
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