Coolant boiling and cavitation wear - a new tool wear mechanism on WC tools in machining Alloy 718 with high-pressure coolant
Coolant boiling and cavitation wear - a new tool wear mechanism on WC tools in machining Alloy 718 with high-pressure coolant
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DOI：
10.1016/j.wear.2020.203284
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发表时间：
2020-07-15
期刊：
影响因子：
5
通讯作者：
Wretland, Anders
中科院分区：
文献类型：
--
作者：
Alagan, Nageswaran Tamil;Hoier, Philipp;Wretland, Anders
近年来，对应用于工具-工件界面（第三剪切区）的液体冷却介质的研究兴趣显著增长。特别是，人们更加注意在高压下使用介质的工作。这很可能是由类似应用中报告的积极结果引发的，但冷却剂介质指向切削刀具的前刀面（二次剪切区）。最典型的应用并不令人惊讶地涉及耐热超级合金（HRSA）或其他“难以加工”的合金的加工，其中主要目的是通过降低剪切区温度来延长工具寿命并改善表面光洁度。这些成果揭示了一个知识空白，并打开了一个新的研究领域，以了解冷却介质应用于超临界流体的效果和影响，在高压条件下加热表面。本研究的目的是调查的“冷却剂沸腾和空化”的现象，出现在应用程序的冷却剂在高压下的未涂覆的WC刀具的后刀面，而车削合金718。通过改变后刀面（冷却介质）压力、改变螺旋切削长度（SCL）和改变切削速度三个方面的实验，研究了后刀面磨损、冷却介质压力和冷却介质蒸汽压与冷却沸腾区的位置和大小的关系。此外，结果表明，以低于冷却剂本身的蒸汽压的压力施加的冷却剂引起“莱顿弗罗斯特”效应。此外，在切削刀具的小区域上观察到侵蚀坑，类似于典型的气穴现象（通常在泵和螺旋桨等不同的应用中发现）。所发现的磨损机制表示为“空蚀磨损”被用作讨论的基础，旨在加深对刀具和工件之间的滑动界面附近的条件的理解。尽管“气蚀磨损”在泵和水轮机等液压系统中已被广泛报道，但在使用高压后刀面冷却时，这是一种在切削刀具上看到的新现象。
In recent years, research interest in liquid coolant media applied to the tool-workpiece interface (the tertiary shear zone) has grown considerably. In particular, attention has increased for work where the media has been applied under high-pressure. This is most likely triggered by the positive results reported on similar applications, but with coolant media directed towards the rake face of the cutting tool (the secondary shear zone). The most typical applications have not surprisingly been related to the machining of Heat Resistant Super Alloys (HRSA) or other "difficult to machine" alloys where the main intention has been to extend tool life and improve surface finish through reduced shear zone temperatures.Concurrently, these achievements have revealed a knowledge gap and unlocked a new research area in understanding the effects and influences of coolant media applied on super-heated surfaces under high-pressure conditions. The aim of this study is to investigate the "coolant boiling and cavitation" phenomena that emerges during the application of coolant under high-pressure to the flank face of an uncoated WC tool while turning Alloy 718. The experimental campaign was conducted in three aspects: varying flank (coolant media) pressure; varying spiral cutting length (SCL); and varying cutting speed.The results revealed that the location and size of the coolant-boiling region correlated with flank wear, coolant pressure and vapour pressure of the coolant at the investigated pressure levels. Further, the results showed that coolant applied with a lower pressure than the vapour pressure of the coolant itself caused the "Leidenfrost" effect. This then acts as a coolant media barrier and effectively reduces the heat transport from the cutting zone.Further, erosion pits were observed on small areas of the cutting tool, resembling the typical signs of cavitation (usually found in much different applications such as pumps and propellers). The discovered wear mechanism denoted as "Cavitation Wear" was used as base for the discussion aimed to deepen the understanding of the conditions close to the sliding interface between the tool and the workpiece. Even though "Cavitation Wear" has been widely reported in hydraulic systems like pumps and water turbines, it is a new phenomenon to be seen on cutting tools while using high-pressure flank cooling.