When selecting a lubricating-based cutting fluid (such as cutting oil), it should be transported to the part where an oil film can be formed on the friction surface. On the contrary, if the selected cutting fluid is mainly cooling (such as water-based cutting fluid), the cutting fluid should be close to the cutting edge of the tool. Under such conditions, the pressure method is usually used to force the cutting fluid into the cutting area, so as to take away the heat generated by the friction and deformation of the tool, workpiece and chips. Continuous application of cutting fluid is better than intermittent application of cutting fluid, which can create thermal cycling that can lead to cracks and chipping in hard and brittle tool materials such as carbide tools. In addition to shortening tool life, intermittent use of cutting fluid can also make the work surface rough and uneven.
Another benefit of proper use of cutting fluids is effective chip removal, which also contributes to longer tool life. If the nozzle of cutting fluid is properly placed, it can prevent the chip flutes of milling cutters and drills from being blocked by chips or poor chip evacuation. 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 allow them to be fully cooled, which is conducive to improving processing efficiency and ensuring processing quality.
1. Manual oiling method for cooling of cutting fluid
Solid or paste-like lubricants can be applied or dripped onto the tool or workpiece with a brush or brush (mainly when tapping threads and die sleeve threads). Recently, hand-held liquid feeders have also been developed, which atomize the lubricant through pressure and spray it onto the tool and workpiece. On machines without a metered cooling system, manual oiling is an effective method if the number of drilled or tapped threads is small. When two different operations are to be performed on the same machine tool, manual oil can be used in conjunction with the overflow cooling system on the machine tool.
2. Cutting fluid cooling overflow method
The most common method of using cutting fluid is the overflow method. The cutting fluid is pumped into the pipeline with a low-pressure pump, and flows out from the nozzle through the valve, which is installed close to the cutting area. The cutting fluid flows through the cutting area and then flows to different parts of the machine tool, and then collects in the oil collecting pan, and then flows back to the cutting fluid tank from the oil collecting pan for recycling. Therefore, the cutting fluid tank should have enough volume to allow time for the cutting fluid to cool and to settle fine chips and abrasive particles. Depending on the type of processing, the volume of the cutting fluid tank is about 20-200L, and 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 installed in the oil collecting pan to prevent large cuttings from entering the cutting fluid tank, and a fine filter should be installed at the oil suction port of the pump.
For grinding, grinding and deep hole drilling, deep hole boring and other machine tools, due to the high surface quality requirements of the processed workpiece, it is necessary to remove finer abrasive chips, grinding wheel particles and cutting particles, such as gun drilling deep hole processing, use 10um filter paper. The use of filtering equipment can avoid excessive contaminants or excessive metal particles in the cutting fluid, which helps to keep the cutting fluid clean and prolong the service life of the cutting fluid. Modern automated machine tools are generally equipped with cutting fluid filtration, separation and purification devices. With the overflow method, the cutting fluid can flow continuously to the cutting area and wash away the chips. The flow rate of the cutting fluid should be larger so that the tool and the workpiece can be submerged by the cutting fluid.
In addition to supplying the appropriate cutting fluid to the cutting zone, there must also be sufficient cutting fluid to prevent abnormal temperature rises. In deep hole drilling, if the cutting fluid tank is too small, the temperature of the cutting fluid will rise rapidly. 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 distribution of the cutting fluid flow directly affects the efficiency of the cutting fluid. The nozzle should be positioned so that the cutting fluid is not thrown away from the tool or workpiece by centrifugal force. It is best to use two or more nozzles, one to deliver the cutting fluid to the cutting area and the other to assist in cooling and flushing away chips. When turning and boring, it is required to send the cutting fluid directly to the cutting area, so that the cutting fluid covers the cutting edge of the tool and the workpiece and has a good cooling effect.
Practical experience has shown that the inner 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 supply 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 cutting obstruction, 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 tool to ensure that the cutting edge has enough cutting fluid and the chips are flushed out of the hole. Since the helical groove of the drill bit (in order to discharge the chips) has the function of discharging the cutting fluid from the cutting area, there is very little cutting fluid entering the cutting area even for a vertical drill. Only a hollow drill bit can solve this problem.
3. Cutting fluid cooling and high pressure method
For some processing, such as deep hole drilling and casing drilling, high pressure (pressure 0.69-13.79MPa) cutting fluid system is often used to supply oil. A single-edged drill is used for deep hole drilling, which is similar to boring, except that there is a passage for cutting fluid inside the drill. Trench drilling is a drilling method that drills a cylindrical hole in a workpiece but leaves a solid cylinder. When the tool enters the workpiece, the drilled solid cylinder passes through the hollow cylindrical cutter head, and a pressure pump is used to send the cutting fluid around the tool, forcing the chips to flow out of the center of the tool. The cutting fluid used for casing drilling must have good extreme pressure and anti-sintering properties. friction coefficient. The main problem in deep hole drilling is how to maintain adequate flow of cutting fluid in the cutting area. One way is to use the drill chip groove as the passage of the cutting fluid. The cutting fluid pressure is 0.35-0.69MPa. It flows into the drill bit through the rotating sealing sleeve, and then directly enters the cutting area. 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 compared with the overflow method, and the life and productivity of the drill bit are greatly improved. The high pressure method helps the cutting fluid reach the cutting area and is sometimes used on other machine tools. Grinding makes the high-pressure nozzles beneficial to the cleaning of the grinding wheel.
Fourth, cutting fluid cooling spray method
The cutting fluid can be sprayed onto the tool and workpiece in the form of an airborne oil mist. The cutting fluid is dispersed into small droplets and sprayed into the cutting area through a small nozzle and compressed air with a pressure of 0.069-0.552MPa. In this case, water-based cutting fluids are better than oil-based cutting fluids, because the oil mist of oil-based cutting fluids pollutes the environment, is unhealthy, and is easy to integrate larger oil droplets. The spray method is most suitable for machining with high cutting speed and low cutting area (such as end milling). Select the cutting fluid with good cooling performance, and the fine droplets contact with hot tools, workpieces or chips, which can quickly evaporate and remove the heat. Spray cooling does not need splash plates, oil collecting pans and oil return pipes, only small balls are used, and the workpiece is dry, even if there is a little oil, it is easy to wipe dry.
Using the spray method has the following advantages:
1. The tool life is longer than dry cutting; 2. When there is no or inappropriate use of the overflow system, it can be used to provide cooling; 3. The cutting fluid can reach places that cannot be accessed by other methods; 4. Between the workpiece and the tool, The flow rate of the cutting fluid is higher than that of the overflow method, and the cooling efficiency is calculated according to the same volume of cutting fluid, which is many times higher than that of the overflow method; 5. The cost can be reduced under certain conditions; 6. The workpiece being cut can be seen. Disadvantages of the spray method are the limited cooling capacity and also the need for ventilation.
There are three types of spray devices:
1. The principle of the suction type is the same as that of the household sprayer. It mainly uses the principle of the thin waist tube. The compressed air sucks the cutting fluid out of the liquid tank and mixes and atomizes it in the airflow. It has a pipe for compressed air and another pipe for siphoning cutting fluid, and is connected to the mixing joint. It is suitable for the spraying of low-viscosity cutting oil and emulsion. 2. The principle of pneumatic type (pressurization method) is that the cutting fluid is installed in the sealed liquid cylinder and pressurized with compressed air of 0.2-0.4MPa. When the solenoid valve is opened, the cutting fluid is pressed out, and the cutting fluid is pressed out through the mixing valve and compressed. Air flow mixed atomization. This device is suitable for spraying water-based synthetic liquids and emulsions, but the aqueous solutions and emulsions must not contain fatty oils or suspended solids. The atomization mixing ratio can be adjusted by mixing valve and pressure regulating valve. 3. The principle of spray type is to pressurize the cutting fluid with a gear pump, and spray it directly into the compressed air flow through the mixing valve to make it atomized. This unit is suitable for atomizing transparent cooling water and low viscosity cutting oils. Spraying can be applied to end milling, turning, automatic machine tool processing, and CNC machine tool processing. The spray device with solenoid valve control is suitable for tapping and reaming on CNC machine tools.
Five, cutting fluid cooling refrigeration liquid cooling method
There are many types of refrigeration liquid cooling methods, such as nitrogen, argon, carbon dioxide and other gases can be compressed into liquids and placed in steel cylinders, and freon gas can be compressed into liquids by mechanical devices, released during use, and injected directly into the cutting area through the regulating valve by the nozzle. , 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 for cutting fluid cooling and cutting fluid
For large and medium-sized machining plants, if possible, a centralized circulation system should be considered to supply cutting fluid to multiple machine tools, but each machine tool must use the same cutting fluid. Several grinding machines can handle abrasive debris with a linked conveyor system. Centralized treatment of fine chips and wear debris wetted by cutting fluid can reduce labor handling and improve working conditions.
Centralized coolant supply system allows factories to better maintain cutting fluid. The cutting fluid is concentrated in a large pool. Through regular sampling inspection, the stock solution or water is regularly replenished according to the inspection results, so as to control the concentration of the cutting fluid. The number of sampling inspections can be reduced, so that more inspections can be carried out to ensure the quality of the cutting fluid during the service period. Compared with many separate multi-cutting fluid supply systems, the cost is relatively lower due to the reduced maintenance work of cutting fluids. The main advantage of the centralized supply system is that it can effectively remove the floating oil and metal particles in the cutting fluid by centrifugal treatment, and also remove half of the bacteria in the cutting fluid (because the bacteria are easy to float in the cutting fluid oil. grown on the interface with metal particles). Continuous removal of these contaminants, regular quality inspections and, based on the results of these inspections, the planned use of additives or the addition of stock fluids are all important factors that make the centralized system very effective in extending the life of the cutting fluid. This also reduces waste disposal of water-soluble cutting fluids.