Comparison of methods for cutting fluid performance testing

A comparison is made of those methods for cutting fluid performance evaluation that involve metal cutting operations under controlled laboratory conditions. An analysis in terms of repeatability, resolution and cost is carried out, based on results from comprehensive experimental investigations in turning, drilling, milling, reaming, and tapping. Different workpiece materials, such as carbon steels, stainless steels, and aluminum alloys, as well as different kinds of cutting fluids, including water based products, straight mineral oils, and vegetable oil based formulations, are considered. The analysis is carried out grouping the tests according to the main measurand: tool life, cutting forces, and workpiece surface finish. The ratio σ/ρ, where σ is the standard deviation of measurements and ρ the range of variability of test results, was introduced to express the relative resolution of a test, and a cost model was developed. It was concluded from the analysis that tool life tests are connected with limited repeatability (σ = 10-50%) and resolution (σ/ρ ranging from 0.25-0.75), with costs ranging from 1000£ to 2000£. Tests based on cutting forces are connected with a much better repeatability and resolution, featuring values for σ in the range 0.5-6% and a σ/ρ ratio of approximately 0.2, with test costs of about 500£. Surface finish tests feature repeatabilities of approximately 50% and resolutions of 0.3-0.4, with costs of approximately 1000£.