Influence of a High-Pressure Lubricoolant Supply on Thermo-Mechanical Tool Load and Tool Wear Behaviour in the Turning of Aerospace Materials

Abstract

In the field of machining difficult-to-cut materials like titanium or nickel-based alloys, the use of a high-pressure lubricoolant supply may result in a significant increase of productivity and process stability. Due to enhanced cooling and lubrication of the cutting zone and thus reduced thermal tool load, tool wear can be decreased which allows higher applicable cutting speeds. Furthermore, the process stability can be increased as a result of effective chip breaking and chip evacuation. The present paper investigates the effect of high-pressure lubricoolant jets, directed into the tool—chip interface, in a longitudinal turning process with cemented carbide tools. For this type of lubricoolant supply the reduction of the contact length between tool and chip is an important detail. In turning of Inconel 718 and Ti6Al4V, the cutting tool temperature, tool wear, and resulting chip forms as well as the ratio of cutting forces and tool—chip contact area were analysed as a function of the lubricoolant supply pressure and flowrate (up to 300 bar, 55 l/min). To study the effect of the high-pressure lubricoolant supply, reference tests were carried out using conventional flood cooling. The results suggest that the tool temperature can be decreased by almost 25 per cent by the use of a high-pressure lubricoolant supply for both machined workpiece materials. However, due to the different tool wear mechanisms of the presented materials and the change in the specific load on the cutting edge during machining, the resulting tool wear was influenced differently. In the best case, tool wear could be reduced in an order of magnitude of 50 per cent, while in other cases tool wear even increased significantly due to the use of a high-pressure lubricoolant supply.

High performance cutting of advanced aerospace alloys and composite materials

“…The positive results of a ''high-pressure lubricoolant supply'' [114] during cutting of aerospace alloys, mainly nickel based and titanium alloys, has been confirmed by numerous researchers in the past. The main effects are improved chip breakage, reduced friction and tool temperature, higher tool life, process stability and productivity.…”

“…The understanding of the basic mechanisms is fundamental to improve the systematic use of the highpressure lubricoolant supply and its optimal adjustments to maximize profitability and energy efficiency [114]. In this regard, the appropriate ratio of pressure and flow rate has to be carefully coordinated in combination with the cutting parameters and the tool design.…”

“…Even though numerous research studies have been conducted in the past, the scientific relations of the high-pressure lubricoolant supply has not been completely analyzed yet and further research is necessary [113,114]. The understanding of the basic mechanisms is fundamental to improve the systematic use of the highpressure lubricoolant supply and its optimal adjustments to maximize profitability and energy efficiency [114].…”

High performance cutting of gamma titanium aluminides: Influence of lubricoolant strategy on tool wear and surface integrity

“…This is due to the reduction of the tool temperature consequent to the better cooling, and to the enhanced lubrication close to the cutting edge due to the reduction of tool-chip contact area [10]. As reported by Klocke et al [9], the effects are coherent with the vapour bubble theory: an increase of lubricant supply pressure raises the mechanical pressure of the lubricoolant jet acting on the vapour bubble formed by the boiling fluid close to the cutting edge, which insulate the cutting zone. As a result, the increased breaching of the cold lubricoolant leads to achieve better outcomes.…”

“…One approach to extend tool lifetime in high performance cutting of difficult to cut materials was identified in advanced lubricoolant strategies. In this context, the effectiveness of the cooling is improved by the usage of high pressure lubricoolant supply, leading to tool temperature and wear reduction [9][10][11][12]. One alternative to improve process cooling is cryogenic cooling [13][14][15], leading to a further reduction of tool temperature by using media with extremely low temperatures when expanding, as liquid hydrogen (boiling point: À253 1C), liquid nitrogen (boiling point: À196 1C), liquid oxygen (boiling point: À 183 1C) and dry ice/CO 2 snow (sublimation point: À 79 1C).…”