Development and testing of novel mineral oil- and biocide-free glycerol- and propanediol-based fluids for drilling and tapping aluminium alloys

Abstract This research covers the development of novel metalworking fluids for machining of aluminium alloys which are based on renewable raw materials and do not contain mineral oil and conventional biocides. Glycerol/water and propanediol/water solutions were used as base fluids. The formulations were systematically optimized by the addition of performance enhancing additives. Thereby, the optimization steps were guided through laboratory investigations, like determinations of viscosities, corrosion protection properties, foaming characteristics, and microbiological stabilities. Furthermore, the fluids were investigated using tribological Brugger and tapping-torque tests. Finally, the metalworking fluids were applied in experiments on an industrial production machine with the processing routines deep drilling and thread forming. Two Al-alloys were used for the investigations: EN AW 6060 as a soft and EN AW 7075 as a hard alloy. For comparison purposes, a commercially available metalworking fluid for Al-machining, a mineral oil emulsion, was tested in parallel. As a result, a glycerol/water-based metalworking fluid was obtained that had a similar performance to the reference fluid. It is therefore already well suited for machining the Al-alloys. The propanediol/water-based metalworking fluid however was superior to the reference, especially concerning the surface qualities of the workpieces. No toxicological relevant emissions from the novel metalworking fluids were found by air samplings and measurements at the test machine. The concentrations of some identified carbonylic compounds were significantly below the occupational limit values, at least by a factor of 800.