在刀具磨损机制中， ” 穿” 其本身并不是工具故障的唯一原因。相当， “高温” 才是切削刀具真正的大敌。由于高温的影响，切削刀具的轻微磨损可能 “自我放大”. That is to say, when the cutting edge of the tool becomes slightly blunt, the increased frictional forces during cutting may lead to increased cutting heat, thus raising the temperature of the tool and softening the tool material. This will cause the cutting edge to become even more blunt at an accelerated rate. As the tool becomes blunter, the cutting friction increases, as does the tool temperature, forming a vicious cycle. Eventually, under the driving force of cutting heat, the tool will fail in a “self-accelerating” manner.Therefore, the advantages of using liquid nitrogen as trim cutting fluid are discussed next.
conventional wet machining
In conventional wet machining, the main role of cutting fluids is lubrication and splashing on the tool and workpiece to remove heat. In cryogenic machining, the role of the cutting fluid (liquid nitrogen) is refrigeration. The temperature of the flooded coolant may be +20°C, whereas liquid nitrogen is -196°C, a difference of almost 220°C. Such a large temperature differential is sufficient to turn the tool into a heat sink. Due to its extremely low temperature, the tool can absorb cutting heat from the cutting edge like a sponge absorbing water, ensuring the cutting performance and tool life will not degrade prematurely due to high cutting temperatures.
liquid nitrogen as Metal cutting fluid
The cutting fluids we call “coolants” are not completely successful in providing cooling functionality. Flood cooling can remove some of the heat generated during machining, but its cooling effect is intermittent and cannot reach the actual heat source (i.e. the cutting zone under the chips where the tool shears the workpiece material). Delivering coolant through the spindle’s internal channels attempts to bring the coolant closer to the cutting zone, while new through-tool coolant delivery technologies do manage to get the coolant very close to the cutting zone.
Cryogenic machining using liquid nitrogen involves cooling the workpiece, cutting tool or cutting zone to low temperatures using liquid nitrogen during machining. Nitrogen gas is the most abundant component in the atmosphere, and liquid nitrogen is widely available as a by-product of the industrial production of oxygen. When used as a cutting fluid, liquid nitrogen evaporates into a gas and returns to the atmosphere after application, without generating any pollutants. From an environmental perspective, it is a promising alternative cutting fluid. This machining method greatly extends the tool life of cutting tools.
In addition to superior machining performance, after cryogenic machining, no slippery cutting fluids remain on machine tool surfaces. Therefore, for operations where operators sometimes need to walk on large machine tool worktables, the risk of slipping and injury can be greatly reduced.
Some other benefits relate to environmental protection. Cryogenic machining does not require artificial coolants but uses nitrogen derived from air, which ultimately returns back to the atmosphere. Thus there is no wasteful fluid to dispose of. The nitrogen does not pollute the air, nor does it contaminate machined medical devices or other sensitive workpieces.
Why use liquid nitrogen as a trim cutting fluid?
Liquid nitrogen has an extremely low temperature (-196°C) which can significantly reduce cutting zone temperatures and prevent overheating. Also, no waste fluids require disposal, making it more eco-friendly.
Is liquid nitrogen cooling effective? Is it a significant improvement over traditional cutting fluids?
Yes, liquid nitrogen has an extremely powerful cooling effect, reducing cutting zone temperatures by about 200°C, far superior to conventional coolants.
What is the impact of using liquid nitrogen cooling on cutting tools?
It can significantly increase tool life and cutting performance while decreasing Built-up Edge formation.
Does liquid nitrogen cooling affect the mechanical properties of the material being machined?
No, the material returns to normal temperature rapidly after cooling, with no adverse effects.
What overall benefits can liquid nitrogen machining bring?
Improved machining efficiency, reduced cycle times, lower energy consumption, and more environmental friendliness.
In summary, liquid nitrogen as a trim cutting fluid can effectively improve the machining efficiency of difficult-to-cut materials such as titanium alloys and the service life of cutting tools. Although the price is relatively high, the cost will be further reduced with large-scale production.