Quasi-dry cutting: compared with dry cutting and wet cutting, it sprays a layer of lubricating oil on the cutting edge of cutting tool. When cutting, lubricating oil forms a layer of oil film between cutting tool and workpiece, protects cutting tool and workpiece, avoids heat generation, and improves machining precision of workpiece, especially in precision machining.
Micro-lubrication system: Simply speaking, the precise control of fuel injection device, usually divided into external injection and internal injection device. The lubricating oil and compressed air are regulated independently by the external injection device. The compressed air blows the lubricating oil to the cutting edge through the high-speed air flow at the nozzle exit to realize the lubrication.
The mechanism of spray cooling
Cutting fluid plays two main roles in metal cutting, one is lubrication and the other two is cooling. Whether cutting fluid can give full play to effective lubrication is an important factor. The penetration of conventional gating cutting fluids in cutting process can be carried out in two ways: liquid penetration and gas penetration: the liquid penetration efficiency of gating is lower than that of high speed cutting; gas penetration is due to the vaporization of the liquid poured into the chip surface crack with the increase of cutting temperature and seeping into the rake face. It's clear. Experiments show that the permeability of conventional cutting fluid is not strong, and the amount of liquid that can be vaporized is very small, which limits the lubrication effect. The two phase fluid formed by spray cooling can make up for the lack of penetration capacity of cutting fluid. When gas-liquid two-phase fluid is injected into the cutting zone, it has higher velocity and kinetic energy, so the permeability is stronger. In addition, the size of micro-liquid in gas-liquid two-phase jet is very small, and the metal with high temperature is easy to vaporize, which can penetrate into the tool rake face from many aspects. Although the amount of liquid in the jet is very small, the vaporized part is more than the continuous casting of cutting fluid, so the lubrication effect is better. In metal processing, the heat of cutting mainly comes from the plastic deformation of metal, and the cooling process in the cutting zone is the heat transfer process between solid and fluid. Because of the attraction between the fluid and the solid molecules and the fluid viscosity, there is a fluid stagnation layer on the solid surface, thus increasing the thermal resistance. The thicker the stagnant layer, the greater the thermal resistance, and the thickness of the stagnant layer is mainly determined by the fluid viscosity. The cooling effect of the small viscosity fluid is better than that of the viscous fluid.
When the gas-liquid two-phase fluid is ejected, the volume suddenly expands to do work outside, consuming internal energy, and lowering the temperature by about 10 degrees Celsius. In the spray cooling, the two phase fluid has a higher speed, it can wash away the iron scraps in time and take away a lot of heat, which further enhances the cooling effect. Therefore, spray cooling actually combines the cooling effect and advantages of two fluids.
Two working principle of spray cooling device
Spray cooling is to mix the trace liquid into the pressure gas flow and form a mist like gas-liquid two-phase fluid. The jet is generated by spraying, and the jet is injected into the cutting area, so that the workpiece and the cutter are fully cooled and lubricated.
When the spray cooling device works, compressed air is filtered by water separator to remove impurities such as water. After a small part of compressed air is entered into the coolant box through the electromagnetic valve, the cooling hydraulic pressure is discharged to the nozzles. Most of the compressed air is adjusted to 0.32 to 0.35MPa by the pressure regulating valve, and the compressed air hose is mixed with the cooling liquid through the compressed air hose. Spray to the cutting area after atomization.
The key of spray cooling technology is whether the coolant can be atomized sufficiently. Since the pressure of the coolant is slightly greater than that of the compressed air, the two are mixed in the gas-liquid mixing chamber and then ejected from the nozzle head through the snake skin tube cooling tube 5. Conversely, if the pressure of the coolant is less than the pressure of compressed air, the coolant will be pressed back into the coolant tank. In some spray cooling devices for imported machine tools, compressed air enters the coolant tank from the pressure regulating valve, so there is often a "gasping" phenomenon when ejecting the coolant. If the compressed air is changed directly into the coolant box from the solenoid valve, the phenomenon of "panting" can be avoided.
In order to adjust the discharge of the cooling liquid, the coolant flow control valve is installed on the nozzle. The spray cooling device adopted by some imported machine tools is cone shaped, and the adjusting flow of the coolant is adjusted by adjusting the size of the conical surface to match the clearance. Because it is difficult to process the nozzle regulating valve with this structure, the concentricity between the stem and the cone surface of the valve body is not easy to be guaranteed, so the flow rate of coolant can not be effectively regulated. The test proves that if the cone valve is changed into a flat valve, the cone surface is changed into a plane, and a sealing ring is added, the flow rate of coolant can be adjusted arbitrarily.
Three selection of spray coolant
Because the cooling liquid sprayed from the nozzle is misty, most of it is sprayed into the cutting area, and a small part is dispersed in the air. In order to avoid environmental pollution and harm to operators, the choice of coolant is very important. Environmental costs are significantly reduced by using non-traditional cutting fluid vegetable oils, including lipids. The technical advantages of these products include cleaner, dispersant performance, low foaming, rapid deflation, relatively high ignition point and surface compatibility. Vegetable-based lubricants can be quickly biodegraded, and in most cases, they break down within 21 days, leaving no long-term cleanliness worries. These lubricants have also been improved, with low atomization characteristics, and help to clean for a short time.
Requirements for lubricants:
First, lubricants require lower viscosity.
Secondly, lubricants have good permeability and surface adhesion coefficient.