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The use of cutting fluid has a great influence on tool life and processing quality. Even the best cutting fluid can not play its proper role if it cannot be effectively transported to the cutting area. Therefore, when using a lubricating fluid based on lubrication (such as cutting oil), it should be transported to a location where an oil film can be formed on the friction surface. Conversely, if the cutting fluid selected is primarily cooled (eg, water-based cutting fluid), the cutting fluid should be brought close to the blade of the tool. Under such conditions, the pressure method is usually used to force the cutting fluid into the cutting area, thereby taking away the heat generated by the tool, the workpiece and the chip due to friction and deformation. Continuous application of cutting fluids is better than intermittent application of cutting fluids. Intermittent application of cutting fluids can cause thermal cycling, which can result in cracks and chipping of hard and brittle tool materials such as carbide tools. Intermittent use of cutting fluid not only shortens the tool life, but also makes the working surface rough and uneven.
Another benefit of proper use of cutting fluids is the effective removal of chips, which also contributes to the extended tool life. If the nozzle of the cutting fluid is properly placed, the chip removal groove of the milling cutter and the drill bit can be prevented from being blocked by chips or the chip removal is not smooth. For the processing of some large workpieces, or the powerful cutting and grinding of large feeds, two or more rows of coolant nozzles are used to fully cool, which is beneficial to improve processing efficiency and ensure processing quality.
1, manual refueling method:
Solid or paste lubricants can be applied or dripped onto a tool or workpiece with a brush or brush (mainly when tapping threads and die sleeve threads). Recently, a portable liquid dispenser has been developed to atomize the lubricant by pressure and spray it onto the tool and the workpiece.
On machines without a metering cooling system, if the number of drilled or tapped threads is small, manual oiling is an effective method. When two different processes are to be performed on the same machine, manual oil can be used in conjunction with the overflow cooling system on the machine.
2. Overflow method:
The most common method of using cutting fluids is the overflow method. The cutting fluid is pumped into the pipe by a low pressure pump and flows out of the nozzle through the valve, and the nozzle is mounted close to the cutting area. The cutting fluid flows through the cutting zone and then flows to different parts of the machine tool, and then collects it into the oil collecting pan, and then flows back from the oil collecting pan to the cutting fluid tank for recycling. Therefore, the cutting fluid tank should have sufficient volume to allow the cutting fluid to cool for a while and to set fine chips and abrasive grains. Depending on the type of processing, the volume of the cutting fluid tank is about 20-200L, and the individual processing is larger, such as drilling deep holes and strong grinding, etc., the cutting fluid tank can reach 500-1000L or more. A coarse filter should be provided in the oil pan to prevent large cutting from entering the cutting fluid tank and a fine filter at the suction port of the pump. For grinding, honing and deep hole drilling, deep hole boring and other machine tools, due to the high surface quality requirements of the machined workpiece, it is necessary to remove finer grinding debris, grinding wheel particles and cutting particles, such as gun drilling deep hole processing, 10um The filter paper is filtered. The use of filtration equipment can avoid excessive contaminants or excessive metal particles in the cutting fluid, which helps to keep the cutting fluid clean and prolong the cutting fluid life cycle. Modern automated machine tools generally have cutting fluid filtration, separation and purification devices.
The overflow method allows the cutting fluid to continuously flow to the cutting area and wash away the chips. The flow rate of the cutting fluid is larger to allow the tool and workpiece to be submerged by the cutting fluid. In addition to providing the cutting fluid with the proper cutting fluid, there is enough cutting fluid to prevent abnormal temperature rise. In the deep hole drilling process, if the cutting fluid tank is too small, the temperature rise of the cutting fluid is very fast. When the oil temperature exceeds 60 °C, the cutting cannot be continued, so the deep hole drilling machine is generally equipped with a larger cooling oil tank.
The following is the typical cutting fluid dosage recommended by the American Machining and Cutting Manual: Turning, cutting fluid flow rate 19L/min; thread cutting, diameter 25mm cutting fluid flow rate 132L/min, diameter 50mm cutting fluid flow rate 170L/min, diameter 75mm cutting Flow rate of liquid 227L/min; milling, flow rate of cutting fluid of small milling cutter 19l/min (tool), flow rate of cutting fluid of large milling cutter 227 (tool) L/min; drilling, reaming, cutting fluid with diameter 25mm The flow rate is 7.6-11L/min, the flow rate of the cutting fluid of the large drill hole is 0.3-0.43L/min (diameter/mm); the deep hole drilling, the external chip type diameter 4.6-9.4mm cutting fluid flow rate 7.6-23L /min, 9.4-19mm cutting fluid flow rate 19-64L/min, 19-32mm cutting fluid flow rate 38-151L/min, 32-38mm cutting fluid flow rate 64-189L/min, internal chip removal type 7.9-9.4mm The cutting fluid flow rate is 19-30L/min, the cutting fluid flow rate of 9.4-19mm is 30-98L/min, the cutting fluid flow rate of 19-30mm is 98-250L/min, and the cutting fluid flow rate of 30-60mm is 250-490L/min. With a precision filter, the deeper the hole, the larger the diameter, the larger the flow rate used (for the drill bit in the same series); the hole drilling, the outer chip type, the diameter 5 1-89mm cutting fluid flow rate 30-182L/min, 89-152mm cutting fluid flow rate 61-303L/min, 152-203mm cutting fluid flow rate 121-394L/min, internal chip removal type 60-152mm cutting fluid flow 416-814L/min, 152-305mm cutting fluid flow rate 814-1287L/min, 305-475mm cutting fluid flow rate 1287-1741L/min, 475-610mm cutting fluid flow rate 1741-2158L/min, requires precision filter In the same series of drill bits, the larger the diameter and the deeper the hole, the larger the flow rate; the grinding, the flow rate of the cutting fluid of the small hole is 11L/min (per hole), and the flow rate of the cutting fluid of the large hole is 19L/min (per hole) , requires precision filter; broaching, small hole cutting fluid flow rate 38L / mm (stroke), large hole cutting fluid flow rate 0.45L / mm (stroke) * cutting length; centerless grinding, small workpiece cutting fluid flow 76L/min,
The cutting fluid flow rate of the large workpiece is 151 L/min, and the cutting fluid flow rate of other grinding (grinding wheel width/mm) is 0.75 L/min, and a precision filter screen is required.
The distribution of the cutting fluid flow directly affects the efficiency of the cutting fluid. The nozzle should be placed at a position where the cutting fluid is not thrown away from the tool or workpiece by the action of centrifugal force. Preferably, two or more nozzles are used, one to feed the cutting fluid to the cutting zone and the other to assist in cooling and flushing the chips.
In turning and boring, it is required to send the cutting fluid directly to the cutting area, so that the cutting fluid covers the blade of the tool and the workpiece to provide a good cooling effect. Practical experience has shown that the diameter of the nozzle of the cutting fluid is at least three-quarters of the width of the turning tool.
For heavy-duty turning and boring, a second nozzle is required to feed the cutting fluid along the underside of the tool. The cutting fluid supplied by the lower nozzle can be smoothly sent between the tool and the workpiece without being blocked by the cutting, which helps to lubricate at low speed.
When drilling and reaming horizontally, it is best to send the cutting fluid to the cutting area through the inner hole of the hollow cutter to ensure that the cutting blade has enough cutting fluid and punches the chips out of the hole. Since the spiral groove of the drill bit (in order to discharge the chip) functions to discharge the cutting fluid from the cutting zone, even if it is a vertical drill, the cutting fluid entering the cutting zone is small, and only the hollow drill bit can solve the problem. At present, most of the boreholes in China use twist drills. The cutting fluid enters the opposite direction of the chip removal, so the cutting fluid is difficult to enter the cutting edge, which affects the cooling and lubricating effect of the cutting fluid, resulting in easy burn of the drill bit, serious wear and durability. Low degree. How to improve the supply of cutting fluid is a problem worth studying.
When milling, it is best to have two nozzles to feed the cutting fluid to the inlet and outlet sides of the milling cutter. The cutting fluid from one nozzle is sent to the cutting area by the cutter teeth, and the cutting fluid from the other nozzle takes the chips from the cutter. Chong out. A narrow circular cutter can be used with a standard round nozzle, and a wide cutter requires a flat nozzle with a width of at least 3/4 of the width of the tool for good coverage.
For face milling, an annular sprayer made of a tube with many small holes is preferred. This allows the cutting fluid to be sent to each cutting edge, so that the tool is completely immersed in the cutting fluid for uniform cooling. If a face milling cutter of a particular size is used, preferably a fan-shaped annular injector, the curve at the opening matches the radius of the tool.
Grinding fluid with low pressure and large flow rate during grinding can generally receive good results. However, when the flow rate is too large, unnecessary splashing will occur, especially for the synthetic cutting fluid with poor defoaming performance, which is more likely to cause the overflow of the grinding fluid. It can be solved by installing a splash-proof plate and adding a defoaming agent. .
If the general spraying method is used, the effect is very poor. The grinding fluid can hardly take away any heat before the grinding heat spreads to the whole workpiece. This is because the surface speed of the grinding wheel is very high, and there is always a layer around the surface of the grinding wheel. The air film prevents the cutting fluid from penetrating into the cutting area. A special nozzle should be designed to force the cutting fluid to pass through the air film to the grinding wheel. This nozzle should be as close as possible to the workpiece to prevent the cutting fluid from being completely lost due to the centrifugal force of the grinding wheel. Another way to overcome the creation of an air film on the grinding wheel is to install a baffle near the nozzle to block the flow of air so that a partial vacuum is created between the grinding wheel and the workpiece to draw the grinding fluid.
3. High pressure method:
For some machining operations, such as deep hole drilling and socket drilling, high pressure (pressure 0.69-13.79 MPa) cutting fluid system is commonly used for oil supply. The deep hole drill uses a single-edged drill bit, similar to the borehole, except that there is a passage for cutting fluid inside the drill bit. Hole drilling is a method of drilling a cylindrical hole in a workpiece but leaving a solid cylinder. When the tool enters the workpiece, the solid cylinder that is drilled passes through the hollow cylindrical tip, and the cutting fluid is sent to the tool by the pressure pump, forcing the chips to flow out of the center of the tool. The cutting fluid for hole drilling must have good extreme pressure and sinter resistance, the viscosity should be low, and it can flow freely around the tool. It should also have good oiliness to reduce the relationship between the tool and the workpiece, between the tool and the chip. Coefficient of friction.
The main problem with deep hole drilling is how to maintain sufficient cutting fluid flow in the cutting area. One method is to use the cuttings groove as the passage of the cutting fluid. The cutting fluid pressure is 0.35-0.69 MPa. The rotating sealing sleeve flows into the drill bit and then directly enters the cutting zone. The cutting fluid flowing out of the hole helps to remove the chips. In deep hole drilling, the use of oil hole drilling is a big improvement over the overflow method, and the life and productivity of the drill bit are greatly improved.
The high pressure method facilitates the cutting fluid to reach the cutting area and is sometimes used on other machine tools. Grinding allows the high pressure nozzle to facilitate the cleaning of the grinding wheel.
4, spray method:
The cutting fluid can be sprayed onto the tool and the workpiece in the form of an airborne oil mist. The cutting fluid is passed through a small nozzle, using compressed air at a pressure of 0.069-0.552 MPa to disperse the cutting fluid into small droplets that are injected into the cutting zone. In this case, the water-based cutting fluid is better than the oil-based cutting fluid because the oil mist of the oil-based cutting fluid pollutes the environment, hinders health, and is easy to integrate large oil droplets. The spray method is best suited for machining with high cutting speeds and low cutting areas (eg end milling). The cutting fluid with good cooling performance is selected, and the small droplets are in contact with hot tools, workpieces or chips, and can quickly evaporate and take the tropics away. Spray cooling does not require the use of splash guards, oil pans and return lines, only a small spherical shape, and the workpiece is dry, even if a little oil is easy to dry.
The spray method has the following advantages: 1) the tool life is longer than the dry cut; 2) it can be used to provide cooling when there is no or no overflow system; 3) the cutting fluid can reach places that other methods cannot access; 4) Between the workpiece and the tool, the flow rate of the cutting fluid is higher than the overflow method, and the cooling efficiency is calculated by the same volume of cutting fluid, which is many times higher than the overflow method; 5) the cost can be reduced under certain conditions; 6) See the workpiece being cut. Disadvantages of the spray method are limited cooling capacity and the need for ventilation.
There are three ways of spraying: 1) suction type, the principle is the same as that of household sprayer, mainly using the principle of thin waist tube, compressed air draws the cutting fluid out of the liquid tank and mixes and atomizes in the air flow. It has a tube for compressed air and another tube for siphon cutting fluid and is attached to the mixing joint, which is suitable for spraying low viscosity cutting oils and emulsions. 2) Pneumatic type (pressurization method), the principle is that the cutting fluid is installed in the sealing liquid cylinder and pressurized with compressed air of 0.2-0.4 MPa. When the electromagnetic valve is opened, the cutting fluid is pressed out, and the mixing valve is passed through The compressed air stream is mixed and atomized. This device is suitable for the spraying of water-based synthetic fluids and emulsions, but the aqueous solutions and emulsions must not contain fatty oils or suspended solids. The atomization mixing ratio can be adjusted by a mixing valve and a pressure regulating valve. 3) Jet type, the principle is that the cutting fluid is pressurized by a gear pump, and is directly sprayed into the compressed air flow through the mixing valve to atomize it. This device is suitable for atomizing transparent cooling water and low viscosity cutting oil.
Spraying can be applied to end milling, turning, automatic machining, CNC machining. The spray device with solenoid valve control is suitable for tapping and reaming on CNC machines.
5, cooling liquid cooling method:
There are many types of cooling liquid cooling methods. For example, nitrogen, argon, carbon dioxide and other gases can be compressed into liquids and placed in steel cylinders. Fluorine gas can be compressed into liquid by mechanical means. It is released during use and is directly injected into the cutting area through a regulating valve. Cooling tools, workpieces and chips by gasification and heat absorption. This method has a very good cooling effect and is suitable for the cutting of difficult-to-machine materials such as stainless steel, heat-resistant steel and high-strength alloy steel, which can greatly improve the durability of the tool.
6. Centralized supply system of cutting fluid:
For large and medium-sized mechanical processing plants, where possible, a centralized circulation system should be considered to supply cutting fluids to multiple machines, but each machine must use the same cutting fluid. Several grinders can handle wear debris with a conveyor system that is linked together. Focusing on the fine chips and wear debris wetted by the cutting fluid can reduce manpower and improve working conditions.
The concentrated supply of cutting fluid allows the plant to better maintain the cutting fluid. The cutting fluid is concentrated in a large pool, and the raw liquid or water is periodically replenished according to the inspection result by regular sampling inspection, which is convenient for controlling the concentration of the cutting fluid. The number of sampling inspections can be reduced, so that more items can be inspected to ensure the quality of the cutting fluid during use. Compared with many separate multi-cutting fluid supply systems that are separately provided, the cost is also relatively reduced due to the reduced maintenance work of the cutting fluid.
The main advantage of the centralized supply system is that it can effectively remove the oil and metal particles in the cutting fluid by centrifugal treatment, and also removes half of the bacteria in the cutting fluid (because the bacteria are easily floating in the cutting fluid) Growth at the interface with metal particles). Continuous removal of these contaminants, periodic inspection of quality and, based on these inspection results, planned use of additives or addition of stock solutions are important factors in making concentrated systems very effective in extending the life of cutting fluids. This also reduces the waste liquid treatment of the water-soluble cutting fluid.
　　 Metal processing experts teach you how to tell the difference between cutting fluid:
　　 Take a small amount of emulsified oil with mineral water bottle for 10~30 times water, shake it and let it stand for a while:
　　 1. There is no oil scum in the upper layer.
　　 2. There is no wall hanging on the wall of the bottle without milk residue.
　　 3. The stock solution and the diluent are left to stand for a long time without stratification (the stratification of the stock solution is mostly caused by the use of an emulsifier to increase the alkali value and strengthen the alkali, and the stratification of the diluent is mostly caused by the imbalance of the emulsifier).
　　 4. The original liquid has no irritating odor (formaldehyde, phenol and ammonia smell, etc.), and it is a transparent or slightly turbid liquid observed in the light transmission place.
　　 5. The hand feels non-heating, lubricious and easy to wash off. The dilution is applied to the back of the hand and the pores of the arm without itching redness or redness. 5. The condition is good. The concentration can be measured by a simple refractometer (the price is very low) .
　　 6. The processed parts can be used to compare the anti-rust performance of the product, and then the dough is soaked in the diluted solution and placed on the white paper, and the tea bowl is used to hold the humidity. It is better that there is no rust on the white paper in two or three days.