When using a cutting fluid that is mainly lubricating (such as cutting oil), it should be transported to the part that can form an oil film on the friction surface. Conversely, if the cutting fluid used is mainly cooling (such as water-based cutting fluid), the cutting fluid should be brought close to the cutting edge of the tool.
Under these conditions, the cutting fluid is usually forced into the cutting area by the pressure method, so as to remove the heat generated by the friction and deformation of the tool, work piece, and chip.
Continuous application of cutting fluid is better than intermittent application of cutting fluid.
Intermittent application of cutting fluids results in thermal cycling, which can cause cracking and chipping of hard and brittle tool materials (such as carbide tools). Intermittent use of cutting fluids not only shortens tool life, but also makes the work piece surface rough and uneven.
Another benefit of the correct use of cutting fluids is the effective removal of chips, which also helps extend tool life.
Properly placing the nozzle of the cutting fluid can prevent the chip discharge groove of the milling cutter and drill bit from being blocked or chipped by the chip.
For the processing of some large work pieces, or the powerful cutting and grinding of large feeds, two or more rows of coolant nozzles are used to fully cool, which is conducive to improving processing efficiency and ensuring processing quality.
1.Cutting fluid cooling – Manual refueling
Solid or pasty lubricants can be applied or dripped onto the tool or work piece with a brush pen or brush (mainly tapping threads, die sleeve threads). Recently, a portable liquid dispenser has also been developed. The lubricant is atomized by pressurization and sprayed onto tools and work pieces.
On machines without a cooling system, manual refueling is an effective method if the number of holes or taps is not large.
When two different processes are to be performed on the same machine, manual refueling can be used in conjunction with the overflow cooling system on the machine.
2.Cutting fluid cooling – Overflow method
The most common method of using cutting fluid is the overflow method. The cutting fluid is driven into the pipeline with a low-pressure pump and flows out of the nozzle through the valve, which is installed near the cutting area.
After the cutting fluid flows through the cutting area, it flows to different parts of the machine tool, and then is collected in the oil collecting pan, after that, the cutting fluid flows back from the oil collecting pan to the cutting fluid tank for recycling.
Therefore, the cutting fluid tank should have a sufficient volume to allow the cutting fluid 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, and the volume of other individual processing is larger. Such as drilling deep holes and strong grinding, the cutting fluid tank can reach 500-1000L or larger.
A coarse filter should be provided in the oil collecting pan to prevent large cuttings from entering the cutting fluid tank, and a fine filter is installed at the suction port of the pump.
For grinding, refining and deep hole drilling, deep hole boring and other machine tools, due to the high quality of the surface of the work piece being processed, it is necessary to remove finer grinding debris, grinding wheel particles and cutting particles. Such as gun drilling deep hole processing, you need to use 10um filter paper for filtering.
The use of filtering equipment can avoid excessive contamination or excessive metal particles in the cutting fluid, which helps to keep the cutting fluid clean and prolong the life of the cutting fluid. Modern automatic 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 flush away the chips. The flow of cutting fluid needs to be larger so that the tool and the work piece are submerged by the cutting fluid.
In addition to supplying the 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, so deep-hole drilling machines are generally equipped with large cooling oil tanks.
The distribution of cutting fluid directly affects the efficiency of the cutting fluid. The nozzle should be placed in a position that the cutting fluid will not be thrown away from the tool or work piece due to centrifugal force.
It is best to use two or more nozzles, one to send the cutting fluid to the cutting area, and the other to assist in cooling and flushing the chips.
Turning and boring require cutting fluid to be sent directly to the cutting area, so that the cutting fluid covers the cutting edge of the tool and the work piece to play a good cooling role.
Practical experience has proven 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 transferred between the tool and the work piece without cutting obstacles, which helps to lubricate at low speeds.
When drilling horizontally and reaming holes, 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 sufficient cutting fluid and punch the chips out of the hole.
Because the spiral groove of the drill bit (to discharge chips) has to discharge the cutting fluid from the cutting area, even if it is a vertical drill, there is very little cutting fluid entering the cutting area, only hollow bits can solve this problem.
3.Cutting fluid cooling– High pressure
For some processing, such as deep hole drilling and sleeve 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, similar to boring, except that there is a path for cutting fluid inside the drill bit. Sleeve drilling is a method of drilling a cylindrical hole in a work piece but leaving a solid cylinder.
When the tool enters the work piece, the drilled solid cylinder passes through the hollow cylindrical cutter head and uses a pressure pump to send cutting fluid around the tool, forcing chips to flow out of the center of the tool.
The cutting fluid for sleeve drilling must have good extreme pressure and sintering resistance, and the viscosity should be very low in order to flow freely around the tool. It should also have good oiliness to reduce the friction coefficient between the tool and the work piece, as well as between the tool and the chip.
The main problem of deep hole drilling is how to maintain sufficient cutting fluid flow in the cutting area.
One method is to use the cuttings flute as a path for cutting fluid. The pressure of the cutting fluid is 0.35-0.69 MPa, which 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 drill bit service life and productivity have been greatly improved.
The high-pressure method facilitates the cutting fluid to reach the cutting area, and is sometimes used on other machine tools.
Grinding enables the high-pressure nozzle to facilitate the cleaning of the grinding wheel.
4.Cutting fluid cooling– Spraying
Cutting fluid can be sprayed on the tools and work pieces in the form of airborne oil mist. The cutting fluid passes through a small nozzle and uses compressed air with a pressure of 0.069-0.552 MPa to disperse the cutting fluid into small droplets and spray it 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).
The cutting fluid with good cooling performance is used, and the small droplets contact the hot cutting tool, work piece or chip, which can quickly evaporate and remove the heat.
Spray cooling does not require splash plates, oil pans and oil return pipes. It uses only a small ball, and the work piece is dry, even if there is a little oil, it is easy to dry.
The spraying has the following advantages
1) Tool life is longer than that of dry cutting;
2) When there is no or unsuitable overflow system, it can be used to provide cooling effect;
3) Cutting fluid can reach places that are not accessible by other methods;
4) The velocity of the cutting fluid between the work piece and the tool is higher than the overflow method. The cooling efficiency is calculated based on the same volume of cutting fluid, which is many times higher than the overflow method;
5) Costs can be reduced under certain conditions;
6) You can see the work piece being cut.
The disadvantages of the spraying are the limited cooling capacity and the need for ventilation.
Three types of spraying device
1) Attractive type:
The principle is the same as the household sprayer, which mainly uses the thin waist tube principle. The compressed air draws the cutting fluid out of the tank and mixes and atomizes it in the air stream. It has a tube for compressed air and another tube for siphoning cutting fluid, and is connected to the mixing joint. It is suitable for spraying low viscosity cutting oil and spray of emulsion.
2) Air pressure type (pressurization method):
The principle is that the cutting fluid is packed in a sealed liquid cylinder and pressurized with 0.2-0.4MPa compressed air. When the solenoid valve is opened, the cutting fluid is pressed out and mixed with the compressed air stream and atomized through the mixing valve. This device is suitable for spraying water-based synthetic liquids and emulsions, but the aqueous solution and emulsion must not contain fatty oils or suspended solids. The atomization mixing ratio can be adjusted by the mixing valve and the pressure regulating valve.
3) Spray type:
The principle is to use a gear pump to pressurize the cutting fluid and spray it directly into the compressed air stream 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 machine processing, CNC machine processing. The spray device with solenoid valve control is suitable for tapping threads and reaming holes on CNC machine tools.
5.Cutting fluid cooling– Cooling liquid method
There are many types of cooling liquid cooling methods, such as nitrogen, argon, carbon dioxide and other gases can be compressed into a liquid and placed in a cylinder. Freon gas can be compressed into a liquid by mechanical devices and released during use.
Through the regulating valve, the nozzle is directly injected into the cutting area, and the tools, work pieces and chips are cooled by gasification and heat absorption.
This method has a very good cooling effect and is suitable for 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.Cutting fluid cooling– Centralized supply system for cutting fluid
For large and medium-sized machinery processing plants, wherever possible, consideration should be given to using a centralized circulation system to supply cutting fluid to multiple machine tools, but each machine must use the same cutting fluid. Several grinders can handle abrasive debris with a linked conveyor system.
Centralized processing of fine chips and abrasives moistened by cutting fluid can reduce manual processing and improve working conditions.
The centralized cutting fluid supply system allows the factory to better maintain the cutting fluid.
The cutting fluid is concentrated in a large pool. Through regular sampling inspection, the original fluid or water is regularly replenished according to the inspection results, which is convenient for controlling the concentration of the cutting fluid.
You can also reduce the number of sampling inspections, so that more items can be checked to ensure the quality of cutting fluid during use.
Compared with many separate multi-cutting fluid supply systems that are separately provided, the maintenance cost of the cutting fluid is reduced, and the cost is relatively reduced.
The main advantage of the centralized supply system is that it can effectively remove the oil slick and metal particles in the cutting fluid by centrifugation.
At the same time, half of the bacteria in the cutting fluid are removed (because bacteria easily grow on the interface between the floating oil of the cutting fluid and the metal particles).
The continuous removal of these dirt, regular quality inspections, and the systematic use of additives or stock solutions based on these inspection results are all important factors that make a centralized system very effective in extending the life of the cutting fluid. This also reduces waste disposal of water-soluble cutting fluids.
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