In addition to tasks such as chip removal, the main functions of cooling lubricant are to reduce friction in the process and to dissipate heat. In previous research work, IFW has shown that the control of volume flow has considerable potential for improving machining processes. In this case, it was even possible to achieve gains in tool life with a significant reduction in the electrical power consumption of the cooling lubricant pump when the volume flow was reduced – without affecting the machining result. The design of cooling lubricant volume flows can therefore increase sustainability and efficiency in manufacturing technology.
However, the design cannot be based on the appropriate basic knowledge, since the mechanisms by which the cooling lubricant works in the contact between tool-chip-workpiece are not sufficiently known. For this reason, there is also no methodology that allows a targeted design of the cooling lubricant supply conditions. One approach to this are simulation methods that consider the tribological, tribochemical and mechanical influences of the cooling lubricant. In a subproject of the DFG-funded priority program 2231 FluSimPro – Efficient Cooling, Lubrication and Transport, IFW is conducting multi-scale research into the mechanisms of cooling lubrication strategies in machining processes. This involves close collaboration with the Institute of Machine Design and Tribology (IMKT).
The project aims to generate basic knowledge of the tribology of the workpiece-chip-tool contact. A particular challenge here is the poor accessibility of the cutting zone. To meet this challenge, IFW has a unique planing test rig. This allows, due to the stationary tool, the high-speed analysis of the chip formation process at cutting speeds of up to 500 m/min. For this purpose, state-of-the-art camera technology is used, which enables the analysis of the material separation mechanisms at frame rates of up to 200,000 FPS at exposure times of 1'000 ns. This makes it possible, for example, to calculate the mechanical load on the cutting wedge or to analyze the material compression and cutting behavior. By adding a high-pressure cooling lubricant supply, in-situ insights can also be gained during wet machining. The modular design of the cooling lubricant supply allows the targeted variation of the parameters of the cooling lubricant supply, such as nozzle diameter, angle and distances. The hand pump and pressure accumulator can be used to examine pressures up to p = 70 bar and the influence of various cooling lubricants.
In the previous funding phase of the project, an increase in the normal stress in the area of the cutting edge was observed at constant process forces. This resulted mainly from a reduction in the contact length due to a high-pressure cooling lubricant supply. The cause of the decrease in contact length is the focus of the current investigations. “With the help of high-speed microcinematography, it is possible to systematically analyze the mechanical influence of the fluid on chip formation and to model the effects,” says project engineer Jan Schenzel. This mechanical influence could be implemented in a FE chip formation simulation using a subroutine. In the future, it can be used for process and tool design and for efficiency optimization.
However, the current research has shown that the thermal influence during machining with cooling lubricant has a significant effect on the tribology at the cutting wedge. Consequently, the effect of temperature in the steady state is to be examined in depth in order to also research tribochemical effects and take them into account in the simulation environment. In addition, the existing findings are to be extended to the entire cutting wedge. In particular, the flank face of the cutting wedge, which is important for the formation of the component, is to be investigated with regard to the effect of cooling lubrication.
We would like to thank the German Research Foundation (DFG), which provided funding as part of the project SPP2231 FLUSIMPRO “Efficient Cooling, Lubrication and Transport - Coupled mechanical and fluid-dynamic simulation methods for realizing efficient production processes”.
Contact:
For further information please contact Jan Schenzel, Institute of Production Engineering and Machine Tools at Leibniz Universität Hannover, on +49 511 762 4299 or by e-mail (schenzel@ifw.uni-hannover.de).
