Page 18 - MetalForming June 2015

Lubrinomics
testing as possible to form a reasonable opinion on the end result. When ready- ing a test for water-extendible products, first determine the quality of the water used to mix the finished lubricant. A 10- percent mixture contains 90 percent water, so a poor water source gives your end product a bad start.
All stampers should know their water-source characteristics: pH of the water; water hardness, and if it derived from calcium or magnesium; and chlo- ride and sulfide levels, as these can affect the mixed product’s stability and corrosion control. Also, know the con- ductivity, as high conductivity can destabilize the mixed lubricant and lead to corrosion issues. Knowing water characteristics helps determine how to best mix a water-extendible product and what, if any, considerations to make to improve water quality or deal with it in the process.
Residue characteristics of the test lubricants can be evaluated on material coupons long before stamping out the
first piece-part.
Gather a sample
lot of all materi-
als used, and
apply the mixed
lubricant to the
material. This gives
a representative
sample of the type
of residue the lubri-
cant will leave once
it dries. Is the
residue oily, sticky,
tacky, dry to the
touch or waxy?
These material
coupons then can be transferred to applicable secondary processes for the parts. Send them through cleaning, deburring, welding and sample pack- aging to determine the interaction of the proposed lubricant. Perform tests at a few predetermined ratios, such as 25-, 15- and 10-percent dilutions, to see how each dilution affects the process.
Refractometers give accurate readings of the process fluids, leading to proper cal- culation of lubricant-to-water ratios.
Scientific laboratory
tests also provide a real-world lubricant comparison. For example, the twist compression test uses a rotat- ing tool-steel cylinder and a material coupon, along with a hydraulic force, to measure friction and provide a lubri- cant comparison. Pressures and speeds can be adjusted to mimic the stamping process. The test does not simulate the actual stamping processes, but the results derived correlate well with field- testing performed on actual stamping dies. This preliminary testing can give confidence to proceed with the trial,
16 MetalForming/June 2015
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