When using a lubricating cutting fluid (such as cutting oil), it should be transported to a location where an oil film can be generated on the friction surface. On the contrary, if the cutting fluid selected is mainly for cooling (such as water-based cutting fluid), the cutting fluid should be close to the cutting edge of the tool. Under such conditions, pressure method is usually used to force the cutting fluid into the cutting area, thereby taking away the heat generated by friction and deformation of the tool, workpiece, and chips. Continuous application of cutting fluid is better than intermittent application of cutting fluid. Intermittent application of cutting fluid can produce thermal cycles, which can cause 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 using cutting fluid correctly is the effective removal of chips, which also helps extend tool life. Proper placement of cutting fluid nozzles can prevent the chip flutes of milling cutters and drill bits from being blocked by chips or causing poor chip discharge. For the processing of some large workpieces, or powerful cutting and grinding with large feed rates, two or more rows of coolant nozzles are used to fully cool them, which is beneficial to improving processing efficiency and ensuring processing quality.
1. Cutting fluid cooling and manual refueling method
Solid or paste lubricant can be applied or dripped onto the tool or workpiece with a brush or brush (mainly when tapping threads and die sets). Recently, a hand-held liquid supply device has been developed, which atomizes lubricant through pressurization and sprays it onto the cutting tools and workpieces. On machine tools without a metered cooling system, manual oiling is an effective method if the number of holes or threads to be drilled is small. When two different processes are to be completed 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 and overflow method
The most common method of using cutting fluid is the overflow method. Use a low-pressure pump to drive the cutting fluid into the pipeline, and then flow out from the nozzle through the valve. The nozzle 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 into the oil collection pan, and then flows from the oil collection pan back to the cutting fluid tank for recycling. Therefore, the cutting fluid tank should have sufficient volume to allow the cutting fluid time to cool and allow fine chips and abrasive particles to settle. Depending on the type of processing, the volume of the cutting fluid tank is about 20-200L. For individual processing, it is larger, such as deep hole drilling and powerful grinding. The cutting fluid tank can reach 500-1000L or larger. A coarse filter should be installed in the oil collection 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, deep hole drilling, deep hole boring and other machine tools, due to the high surface quality requirements of the workpiece being processed, finer grinding chips, grinding wheel particles and cutting particles must be removed. For example, for gun drilling deep hole processing, 10um must be used. filter paper. The use of filtration equipment can avoid excessive contaminants or excessive metal particles in the cutting fluid, helping to keep the cutting fluid clean and extend the service life of the cutting fluid. Modern automated machine tools are generally equipped with 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 must be larger so that the tool and workpiece can be submerged by the cutting fluid.
In addition to providing appropriate cutting fluid to the cutting area, there must be enough cutting fluid to prevent abnormal temperature rise. In deep hole drilling, if the cutting fluid tank is too small, the temperature of the cutting fluid rises quickly. When the oil temperature exceeds 60°C, cutting cannot continue. Therefore, deep hole drilling machines are generally equipped with larger cooling oil tanks.
The distribution pattern of cutting fluid flow directly affects the efficiency of cutting fluid. The nozzle should be placed so that the cutting fluid will not be thrown away from the tool or workpiece due to centrifugal force. It is best to use two or more nozzles, one to deliver the cutting fluid to the cutting area, while the others are used to assist cooling and flush 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 to provide a good cooling effect.
Practical experience has proven that the inner diameter of the cutting fluid nozzle is at least equivalent to three-quarters of the width of the turning tool. For heavy-duty turning and boring operations, 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 delivered between the tool and the workpiece without being blocked by cutting, which helps to lubricate at low speeds. 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 there is enough cutting fluid on the edge and to flush the chips out of the hole. Since the spiral groove of the drill bit (for the purpose of discharging chips) plays the role of discharging cutting fluid from the cutting area, even for vertical drills, very little cutting fluid enters the cutting area. Only hollow drill bits can solve this problem.
3. Cutting fluid cooling and high pressure method
For certain processing, such as deep hole drilling and casing drilling, high-pressure (pressure 0.69-13.79MPa) cutting fluid system is commonly used to supply oil. Deep hole drilling uses a single-edged drill bit, which is similar to boring, except that there is a passage for cutting fluid inside the drill bit. Trench drilling is a drilling method that drills a cylindrical hole in the workpiece but leaves a solid cylinder. When the tool enters the workpiece, the drilled solid cylinder passes through the hollow cylindrical tool head, and a pressure pump is used to send cutting fluid around the tool, forcing the chips to flow out from the center of the tool. The cutting fluid used for trepanning must have good extreme pressure and anti-sinter properties. The viscosity should be very low so that it can flow freely around the tool. It should also have good oil properties to reduce the friction between the tool and the workpiece, and between the tool and the chips. Friction coefficient. The main problem in deep hole drilling is how to maintain sufficient cutting fluid flow in the cutting area. One way is to use the chip flute as a passage for 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 remove chips. When drilling deep holes, the use of oil hole drilling is a big improvement compared with the overflow method, and the drill bit life and productivity are greatly improved. The high-pressure method helps the cutting fluid reach the cutting area and is sometimes used on other machine tools. Grinding enables high-pressure nozzles to facilitate cleaning of the grinding wheel.
4. Cutting fluid cooling spray method
Cutting fluid can be sprayed onto the tool and workpiece in the form of airborne oil mist. The cutting fluid passes through a small nozzle and uses compressed air with a pressure of 0.069-0.552MPa to disperse the cutting fluid into very small droplets and spray them into the cutting area. In this case, water-based cutting fluid is better than oil-based cutting fluid, because the oil mist of oil-based cutting fluid pollutes the environment, is harmful to health, 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). Choose a cutting fluid with good cooling performance. When small droplets come into contact with hot tools, workpieces or chips, they can quickly evaporate and take away the heat. Spray cooling does not require a splash guard, oil collection pan and oil return pipe. It only uses a small ball shape, and the workpiece is dry, even if there is a little oil, it can be easily wiped dry.
Using the spray method has the following advantages:
1. The tool life is longer than dry cutting; 2. When there is no overflow system or it is not suitable to use it, it can be used to provide cooling; 3. The cutting fluid can reach places that are inaccessible 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 based on the same volume of cutting fluid, which is many times higher than that of the overflow method; 5. Costs can be reduced under certain conditions; 6. The workpiece being cut can be seen. Disadvantages of the spray method are limited cooling capacity and the need for ventilation.
There are three types of spray devices:
1. The principle of the suction type is the same as that of a household sprayer. It mainly uses the principle of a thin waist tube. The compressed air draws the cutting fluid out of the tank and mixes and atomizes it in the air flow. 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 spraying low-viscosity cutting oil and emulsion. 2. Pneumatic type (pressurization method) The principle is that the cutting fluid is installed in the sealing fluid cylinder and pressurized with 0.2-0.4MPa compressed air. When the solenoid valve is opened, the cutting fluid is pressed out and passes through the mixing valve and compression. The air flow mixes and atomizes. 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 solid matter. The atomization mixing ratio can be adjusted by the mixing valve and pressure regulating valve. 3. The principle of the injection type is to use a gear pump to pressurize the cutting fluid, and spray it directly 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 used in 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 holes on CNC machine tools.
5. Cutting fluid cooling and refrigeration liquid cooling method
There are many types of refrigeration liquid cooling methods. Gases such as nitrogen, argon, carbon dioxide, etc. can be compressed into liquids and placed in cylinders. Freon gas can be compressed into liquids by mechanical devices and released during use. After passing through the regulating valve, the nozzles can be directly injected into the cutting area. , which relies on gasification and heat absorption to cool the tool, workpiece and chips. This method has a very good cooling effect and is suitable for cutting difficult-to-machine materials such as stainless steel, heat-resistant steel, and high-strength alloy steel. It can greatly improve the durability of the tool.
6. Cutting fluid cooling Centralized supply system for cutting fluid
For large and medium-sized mechanical processing plants, when possible, they should consider using a centralized circulation system to supply cutting fluid to multiple machine tools, but each machine tool must use the same cutting fluid. Several grinding machines can handle grinding chips using a linked conveyor system. Centralized processing of fine chips and grinding chips moistened by cutting fluid can reduce manual processing and improve working conditions.
The centralized cutting fluid supply system allows factories to better maintain cutting fluids. The cutting fluid is concentrated in a large pool. Through regular sampling inspection, the original solution or water is regularly replenished according to the inspection results to facilitate the control of the concentration of the cutting fluid. It can reduce the number of sampling inspections and conduct inspections on more items to ensure the quality of the cutting fluid during its service life. Compared with many separate multi-cutting fluid supply systems set up separately, the cost is also relatively reduced because the maintenance work of cutting fluid is reduced. The main advantage of the centralized supply system is that it can effectively remove floating oil and metal particles in the cutting fluid through centrifugal treatment. It also removes half of the bacteria in the cutting fluid (because bacteria can easily get into the floating oil in the cutting fluid). growth on the interface with metal particles). Continuous removal of these contaminants, regular quality inspections, and planned use of additives or addition of raw fluid based on these inspection results are all important factors that make a centralized system very effective in extending the service life of cutting fluids. This also reduces waste disposal of water-soluble cutting fluids.
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