Tribology on Cutting lubricated with minimal quantity of Lubricant

通过使用间歇车削过程和设计用于测量塑性接触条件下新成型表面与刀具材料之间摩擦闹剧的摩擦试验装置，研究了MQL切削的影响和机理。采用两种润滑性不同、转速在100m /min ~ 400m /min范围内的润滑油进行切削试验。在铝合金切削实验中，实验结果表明，根据润滑剂类型和刀面温度的不同，最小量润滑的润滑机理发生了很大的变化。如果使用酯类润滑剂，并且可以将刀具表面温度抑制在一定的摩擦转变温度以下，则在间歇切削间隔的初始阶段可以获得摩擦力的大幅度降低。这一结果也支持了在MQL切削时，如果水雾与酯类润滑剂同时供应到切削点，则可以获得切削力的大幅度降低。即铝合金切削对良好的润滑性的要求是将刀具面向下冷却到摩擦转变温度，并使用具有高摩擦转变温度的高极性润滑剂。另一方面，在加工奥氏体不锈钢等难切削材料时，酯类润滑剂仅通过MQL方法发挥润滑作用。这说明由于做热材料的低扩散率导致的较大的温升使酯类润滑剂吸附层的润滑作用失效，在这种情况下，即使在MQL切削中也可能需要另一种在高温条件下起作用的润滑机制。通常，用于难切削材料的金属加工液中含有氯、硫或磷酸盐类添加剂，以在界面处与工作材料发生反应。即使使用硫化脂肪油作为MQL切削添加剂，其环境负担在常用添加剂中相对较低，但也收效甚微。在MQL中，由于添加剂总量很小，可以认为硫化脂肪油的反应层不足以减少摩擦，获得良好润滑效果的解决方案之一是增加表面的吸附和反应位点。发现氧化铁增强了铁与硫型添加剂之间的吸附和反应。从增强氧化的角度出发，对难加工材料的MQL切削采用同时供给水雾的方法，在这种情况下，水雾容易因切削热而蒸发过热，进而促进表面氧化。EPMA分析支持表面氧化和摩擦测试表明良好的润滑性。在实际切削试验中，在MQL中加入水雾可使切削力减小10%左右。少

Effects and mechanisms in MQL cutting are investigated by use of an intermittent turning process and by a friction test apparatus which is designed for measuring friction farce between a freshly formed surface and tool material in plastic contact condition. Cutting tests are conducted using two types of lubricant which have difference in lubricity and in speed range from 100 m/min to 400 m/min. In the case of aluminum alloy cutting, experimental results suggest that the lubrication mechanism of the minimal quantity lubrication considerably changes depending upon the lubricant types and the temperature on the tool face. If ester type lubricant is used and tool surface temperature can be suppressed below certain transition temperature of friction, large reduction in a frictional force can be obtained at an initial stage of intervals of intermittent cutting This result also supports the fact that, if water mist simultaneously supply into the cutting point in the MQL cutting with the ester … More type lubricant, large reduction in cutting force can be obtain. That is, requirements for good lubricity in aluminum alloy cutting are chilling the tool face down to the transition temperature of friction and using the lubricant with high polarity which possesses high transition temperature of friction.On the other hand, in the case of machining difficult-to-cut material such as austenitic stainless steel, the ester type lubricant merely exhibits lubrication effect by the MQL method. This indicates that the considerable temperature rise due to low diffusivity of heat of work material disable the lubrication effect of adsorption layers of the ester type lubricant In this case, another mechanism of lubrication which acts at a high temperature condition might be needed even in the MQL cutting. Generally, metal working fluid for difficult-to-cut material contains chlorine-, sulfur-or phosphate-type additives to react with the work material at the interface. Even if using sulfurized fatty oil as additive in MQL cutting, which possesses relatively low environmental burden among them common additives, little improvement can be obtained. In the MQL, it can be considered that reaction layers from sulfurized fatty oil is insufficient to reduce the friction because total quantity of additive is very small One of the solutions to obtain the good lubrication effect is to increase the adsorption and reaction site on the surface. It was found that iron oxide enhances adsorption and reaction between iron and sulfur-type additive. accordingly enhancement of surface oxidation can be considered to be a good method to improve the lubricity Prom the viewpoint of the oxidation enhancement, to supply water mists simultaneously is adopted for the MQL cutting of the difficult-to-machine material In this situation, the water mists easily evaporate and be superheated due to cutting heat, and then, promote surface oxidation. EPMA analyses supports surface oxidation and friction test indicates good lubricity. In actual cutting test, cutting force reduction about 10% can be obtained with the water mists adding to the MQL. Less