Tribology on Cutting lubricated with minimal quantity of Lubricant

采用间歇车削工艺和摩擦试验仪研究了MQL的切削效果和机理，该装置是为测量塑性接触条件下新成形表面与刀具材料之间的摩擦而设计的。采用润滑性不同、速度在100~400m/min范围内的两种润滑剂进行了切削试验。实验结果表明，在铝合金车削加工中，微量润滑的润滑机理随润滑剂种类和刀具表面温度的不同而有较大变化。如果使用酯型润滑剂，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，则可以在断续切割的初始阶段获得较大的摩擦力降低。这一结果还支持这样的事实，即在使用酯型…的MQL切割中，如果同时向切削点供应水雾润滑剂种类多，切削力大大降低。也就是说，在铝合金车削加工中，对良好润滑性的要求是将刀面冷却到摩擦转变温度，并使用具有较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加工材料的情况下，酯类润滑剂仅表现出MQL方法的润滑效果。在这种情况下，即使在MQL切割中，也可能需要另一种在高温条件下起作用的润滑机制。一般情况下，难加工材料的金属加工液中含有氯型、硫型或磷型添加剂，以便在界面上与加工材料发生反应。在常用的添加剂中，即使使用环境负担相对较小的硫化脂肪油作为MQL切割添加剂，也不能得到很大的改善。在MQL中，由于添加剂的总量很小，可以认为硫化脂肪油的反应层不足以降低摩擦，要获得良好的润滑效果，解决方案之一是增加表面的吸附和反应位置。结果表明，氧化铁促进了铁与硫型添加剂之间的吸附和反应。因此，表面强化氧化是一种改善润滑性的好方法。从强化氧化的观点来看，对难加工材料的MQL切割采用同时供给细水雾的方法，在这种情况下，细水雾容易因切割热而蒸发和过热，从而促进表面氧化。EPMA分析支持表面氧化，摩擦试验表明具有良好的润滑性。在实际切割试验中，加入细水雾可使切削力降低10%左右。较少

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