GRINDING FEEDS AND SPEEDS Machinery's Handbook, 31st Edition
1266
10
1
ECT = 0.00004 ECT = 0.000085 ECT = 0.00013 ECT = 0.00019 ECT = 0.005
0.1
1
10
100
1000
T, minutes
Fig. 5. Surface Roughness, Ra versus Wheel Life T , ECT Plotted Example 4, Specific Metal Removal Rates and Work Speeds in Rough and Finish Grind ing: The tabulated values in the following table indicate that a decreasing ECT combined with a higher wheel speed for 10 minutes wheel-life will decrease the metal removal rate and thereby increasing the grinding time. This change is accompanied by a better finish in both roughing and finishing operations. Note the high work speeds when finishing.
Roughing Depth a r = 0.025 mm
Finishing Depth a r = 0.0025 mm
Tool Life T = 10 minutes
Removal Rate
Wheel speed V 10 m/min
ECT mm 0.00050 0.00033 0.00017
SMRR 10 mm
3 /mm/ min
Work speed V
w m/min
1970 2580 2910
985 850 500
39 34 20
390 340
200 The grit size, however, is a major parameter. Fig. 6, shows that a high wheel speed, com bined with a small grit size, say 320 Mesh, can achieve Ra values as small as 0.03 micron.
10000
Ra = 0.03 Ra = 0.05 Ra = 0.25 Ra = 0.55 Ra = 1.1 Ra = 0.16
1000
100
10
100
1000
Mesh Fig. 6. Wheel Speed versus Wheel Mesh, Ra Plotted
Spark-Out Time.— Fig. 7 shows how spark-out time varies with system stiffness. As with surface finish, when wheel-life is short (high wear rate) the spark-out time decreases.
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