When To Use Cutting Fluid

[Arlene Dematteo]

usage of metal cutting fluid

the usage of cutting fluid has a great impact on tool life and machining quality. Even the best cutting fluid cannot play its due role if it cannot be effectively transported to the cutting area. Therefore, when selecting cutting fluid based on lubrication (such as cutting oil), it should be transported to the part where 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 edge of the tool. Under this condition, 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 chip. Continuous application of cutting fluid is better than intermittent application of cutting fluid. Intermittent application of cutting fluid will produce thermal cycle, resulting in cracks and edge collapse of hard and brittle tool materials (such as cemented carbide tools). Intermittent use of cutting fluid can not only shorten the tool life, but also make the working surface rough and uneven

another advantage of the correct use of cutting fluid is the effective removal of chips, which also helps to prolong the tool life. If the nozzle of cutting fluid is properly placed, the chip removal groove of milling cutter and drill bit can be prevented from being blocked or blocked by chips. For the processing of some large workpieces, or strong cutting and grinding with large feed rate, two or more rows of coolant nozzles shall be used to fully cool them, which is conducive to improving the processing efficiency and ensuring the processing quality

1. Overflow method:

the most common method of using cutting fluid is overflow method. The cutting fluid is pumped into the pipeline with a low-pressure pump and flows out of the nozzle through the valve. The nozzle is installed close to the cutting area. After flowing through the cutting area, the cutting fluid flows to different parts of the machine tool, 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 sufficient volume to allow time for the cutting fluid to cool and settle the fine chips and abrasive particles. Depending on the type of processing, the volume of the cutting fluid tank is about 20-200l, and it is larger for individual processing, such as deep hole drilling and strong grinding. The cutting fluid tank can reach 500-1000l or more. A coarse filter shall be set in the oil collecting pan to prevent large cutting from entering the cutting fluid tank, and a fine filter shall be installed at the oil suction port of the pump. For grinding, diffractive grinding, deep hole drilling, deep hole boring and other machine tools, due to the high requirements for the surface quality of the processed workpiece, finer wear debris, grinding wheel particles and cutting particles must be removed. For example, for gun drilling deep hole processing, 10um filter paper shall be used for filtration. The use of filtration equipment can avoid excessive pollutants or excessive metal particles in the cutting fluid, which is helpful to keep the cutting fluid clean and prolong the service life of the cutting fluid. Modern automatic machine tools are generally equipped with cutting fluid filtration, separation and purification devices

the overflow method can make the cutting fluid flow continuously to the cutting area and wash away the chips. The flow of cutting fluid should be larger, so that the tool and workpiece can be submerged by cutting fluid. In addition to providing appropriate cutting fluid to milling operation the cutting area, there should also 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 rapidly. When the fluid temperature exceeds 60 ℃, the cutting cannot continue. Therefore, deep hole drilling machines are generally equipped with a large cooling oil tank

the distribution of cutting fluid flow directly affects the efficiency of cutting fluid. The nozzle should be positioned so that the cutting fluid will not be thrown away from the tool or workpiece due to centrifugal force. It is preferable to use two or more nozzles, one to send the cutting fluid to the cutting area, while the other is used to assist in cooling and washing away the chips

during turning and boring, it is required to send the cutting fluid directly to the cutting area, so that the cutting fluid can cover the edge of the tool and the workpiece and play a good cooling role. Practical experience has proved that the inner diameter of the nozzle of 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 lower side 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 there is enough cutting fluid at the edge and flush the chips out of the hole. Because the spiral groove of the drill bit (to discharge the chips) has to discharge the cutting fluid from the cutting area to the outside, even for the vertical drill, there is very little cutting fluid entering the cutting area. Only the hollow drill bit can solve this problem. At present, most drilling holes in China are made of fried dough twist drill. The cutting fluid is in the opposite direction of chip removal. Therefore, cutting fluid is difficult to enter the blade, which affects the cooling and lubricating effect of the cutting fluid, resulting in the drill being prone to burn, wear seriously and low durability. How to improve the supply method of cutting fluid is a problem worthy of study

during milling, it is better to have two nozzles to deliver the cutting fluid to the feed and discharge sides of the milling cutter. The cutting fluid from one nozzle is sent to the cutting area by the milling cutter teeth, and the cutting fluid from the other nozzle flushes the chips out of the cutter. The narrow milling cutter can use the standard circular nozzle, and the wide milling cutter should use the flat nozzle, whose width is at least 3 /4 of the tool width, so as to have a good coverage

for plane milling, the annular liquid ejector made of pipe with many small holes is better. In this way, the cutting fluid can be sent to each edge, so that the tool can be completely immersed in the cutting fluid and play a uniform cooling role. If a certain size of end milling cutter is often used, it is better to have a fan-shaped annular ejector, and the curve at its opening matches the radius of the cutter

generally, good results can be obtained by using low-pressure and large flow grinding fluid during grinding. However, when the flow is too large, unnecessary splashing will occur, especially for synthetic cutting fluid with poor defoaming performance, which is more likely to cause overflow of grinding fluid. The method of installing splash plate and adding defoaming agent can be adopted

2. High pressure method:

for some machining, 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 edge drill bit, which is similar to boring, but there is a path of cutting fluid in the drill bit. Casing drilling is a method of drilling a cylindrical hole in a workpiece but leaving a solid cylinder. When the tool enters the workpiece, the drilled solid cylinder passes through the hollow cylindrical cutter head and sends the cutting fluid around the tool with a pressure pump, forcing the chip to flow out of the tool center. The cutting fluid used for hole drilling must have good extreme pressure and sintering resistance, low viscosity to flow freely around the tool, and good oiliness to reduce the friction coefficient between the tool and the workpiece and between the tool and chip. The main problem of deep hole drilling is how to maintain sufficient cutting fluid flow in the cutting area. One way is to use the cuttings groove as the path of 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 cuttings. In deep hole drilling, oil hole drilling is a great progress compared with overflow method, and the service life and productivity of bit are greatly improved

high pressure method is helpful for cutting fluid to reach the cutting area, and sometimes it is also used on other machine tools. Grinding makes the high-pressure nozzle conducive to the cleaning of grinding wheel

3. Centralized supply method of cutting fluid

for large and medium-sized machining plants, if possible, the centralized circulation system should be considered to supply cutting fluid for multiple machine tools, but each machine tool must use the same cutting fluid. Several grinding machines can use a conveyor system connected together to deal with wear debris. Centralized treatment of fine chips and wear debris wetted by cutting fluid can reduce manual treatment and improve working conditions

the centralized cutting fluid supply system enables the factory to better maintain the cutting fluid. The cutting fluid is concentrated in a large pool. Through regular sampling inspection, the