Page 37 - MetalForming-Oct-2018-issue

need a smoother surface finish than other parts might require. “We’ve had to make significant changes to the lubricity of our formulas to be able to work in those environments,” he says.
Zhao says that working with lighter, stronger metals increases the need for boundary/EP lubrication additives. The hard surfaces of HSS, aluminum alloys and the titanium alloys used in the aerospace industry require a different lubrication mechanism. “We test addi- tives by themselves and as parts of for- mulation packages for specific appli- cations, and we use design of experiments to optimize our formula- tions,” he says.
Taming Rogue Ions
Hard-water cations (positively charged ions) can cause emulsions to separate, and they can leave mineral deposits on tools and workpieces. Cal- cium and magnesium are the usual suspects, but aluminum ions can cause hard water as well. Cast aluminum alloys contain magnesium, notes McClure, and magnesium is particu- larly hard on water-soluble cutting flu- ids. Formulations must contain addi- tives that can stabilize emulsions in this environment.
Lightweight metals such as alu- minum and magnesium corrode more easily than steel, and their protective oxide coatings are stable over a much narrower pH range than iron oxides. Semi-stable emulsions that deposit an oil coating on the workpiece are one option for preventing corrosion, though cleaning off the oil film is nec- essary before applying coatings or paints.
Even a small amount of corrosion can present a problem in the form of staining. Aluminum, magnesium and their alloys are prone to staining. Alu- minum is a more reactive metal than steel, so processing fluids must contain corrosion inhibitors to prevent staining, says Hoon Kim, senior principal R&D scientist with Chemetall, Jackson, MI (see Corrosion Inhibitors: A Primer).
Ferrous alloys corrode in neutral to acidic environments, but not in highly
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