Machinery's Handbook, 31st Edition
1180 CUTTING FLUIDS IN MICROMACHINING The ratio P over V 1⁄3 is called the normalized diameter of the droplet. Using the nor malized diameter, the contact angle can be calculated using Equation (15), by looking up the value in a table (Table 8), or read from a graph (Fig. 22a and Fig. 22b). Fig. 21 shows the top view of some liquid droplets on stainless steel sheets from which contact angles are calculated and plotted for comparison. The cutting fluids are chosen from different commercially available oil-based lubricants: CL2200, CL2210, CL2210EP, and CL2300HD. Other coolants were also included for comparison: water, KM, and water-soluble coolants RL1:15, BC1:5, and CL1:30. The nomenclature x:yy indicates dilution ratio of concentrated coolant in water for the water soluble fluids.
1 mm
1 mm
1 mm
1 mm
1 mm
1 mm
Water CL12210 CL2210EP CL2300HD CL2200 Fig. 21. Wetting of Different Cutting Fluids on 316L Stainless Steel. Constant Drop Volume = 0.25 m L. Table 7 and Fig. 23 compare contact angles of these cutting fluids on different solids. The oil-based CL2210EP lubricant forms the lowest contact angle of 7° on 316L stainless steel, uncoated carbide, and titanium. This is in contrast to 60–70° from other water-based fluids. Surface tension of the CL2210EP lubricant is 26 mN/m, the lowest among others, thus it easily wets a carbide microtool and workpiece surfaces during machining. CL1:30
10 8 6 4 2 0
10 8 6
θ < 90° θ > 90°
A
B
4 2 0
C
0
5 10 15 20 25 Contact Angle θ (°)
0
45 90 135 180 Contact Angle θ (°)
Fig. 22a. Plot of Contact Angle versus Normalized Diameter for All Angles.
Fig. 22b. Plot of Contact Angle versus Normalized Diameter for Small Angles.
0 70 60 50 40 30 20 10
316 Stainless Steel Titanium Tungsten Carbide
Fig. 23. Average and Range of Contact Angles for Different Cutting Fluids on 316L Stainless Steel, Tungsten Carbide, and Titanium.
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