Performance Testing of Cutting Fluids and Tool Holders in Metal Cutting

Licentiate thesis, 2009

ABSTRACT The metal cutting industry has evolved over the last century to the point where an increasing range and complexity of tool holding systems and cutting fluids are available for metal machining in the market. Most of the companies report their cutting fluid cost to be between 7 -17 % of the manufacturing cost. This is more than the tooling cost. The cutting fluids still have been used because of their better cutting performance. The proper selection of a cutting fluid and tool holding system is a factor that is sometime neglected in the machining practice. This has highlighted a need to provide an intelligent, user-friendly system of selection and recommendation that can also provide performance data for engineers and end-users. This can be achieved by testing in metal cutting operations. This work involves the performance testing of different type of cutting fluids and a findings regarding new type of hydrostatic tool-holding system. For cutting fluids testing, drilling and tapping tests were performed into aluminium alloy (AlSi9Cu3) and alloy steel (SAE 52100), which are the materials extensively used in automotive industry. The objective of the experiments is to determine the function of cutting fluid in these machining operations. Tap forming (deformation of metal) operations were performed on aluminium alloy and tap cutting drilling was performed on both types of material. To investigate the role of cutting fluids seven different fluids were used. The results reveal that type and concentration of cutting fluids have effect on the torque, thrust force, tool life and surface quality. Face turning test was also performed for Build up Edge (BUE) formation and it has been seen that concentration has also an effect on BUE formation. For chip analysis, tests were performed on alloy steel with assistance of emulsion, MQL (minimum quantity lubrication) and compressed air. The results were compared to dry machining in terms of chip colour, microstructure, white-etching band formation and contact area. It was observed that both chip upper free side and chip back side had a heat- and deformation-affected zone with a thickness that varied between 10-20 μm. The microstructure in the white-etching band (chip back side) had a grain size varying between 50 and 400 nm for the chips that were produced by machining with emulsion. This grain size range for the emulsion-assisted cutting was smaller compared to those when machining with MQL, compressed air and dry machining. The reason is supposed to be faster cooling of the chip surfaces in contact with the cutting media. Tool-holder performance tests were done for two types of tool-holding systems in boring, hydrostatic and bolt type. It was observed that better machining stability can be achieved by hydrostatic clamping of boring bar. Such kind of solution improves quality of machining and it can contribute to increasing the productivity and reliability of the boring process. Tool life can be increased by using the hydrostatic tool-holding system for same machining parameters as compared to bolt type system.