When using a cutting fluid primarily 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. On the contrary, if the cutting fluid used is mainly cooling (such as water-based cutting fluid), it should be kept 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, 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 cause thermal cycling, which can lead to cracks and edge breakage in hard and brittle tool materials (such as hard alloy tools). Intermittent use of cutting fluid not only shortens tool life, but also causes uneven roughness of the working surface.

Another benefit of using cutting fluid correctly is the effective removal of chips, which also helps to extend tool life. If the cutting fluid nozzle is properly placed, it can prevent the chip discharge groove of the milling cutter and drill bit from being blocked or blocked by chips. For the processing of some large workpieces, or for strong cutting and grinding with large feed rates, two or more rows of coolant nozzles are used to fully cool them, which is beneficial for improving machining efficiency and ensuring machining quality.

1、 Cutting fluid cooling and manual refueling method

Solid or paste lubricants can be applied or dropped onto cutting tools or workpieces using a brush or brush (mainly when tapping threads or threading dies). Recently, a handheld liquid supply device has been developed, which atomizes lubricants through pressure and sprays them onto cutting tools and workpieces. On machine tools without a dosing cooling system, manual oiling is an effective method if the quantity of drilling or threading is not large. When two different processes need 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 overflow method

The most common method of using cutting fluid is the overflow method. Use a low-pressure pump to inject cutting fluid into the pipeline and flow out from the nozzle through a valve. The nozzle is installed near the cutting area. The cutting fluid flows through the cutting area and then flows to different parts of the machine tool, and then gathers in the oil collection pan. From the oil collection pan, it flows back into the cutting fluid tank for recycling. Therefore, the cutting fluid tank should have sufficient capacity to allow time for the cutting fluid to cool and settle fine chips and abrasive particles. Depending on the type of processing, the volume of the cutting fluid tank is about 20-200L, and for individual processing, it is even larger, such as drilling deep holes and strong grinding. The cutting fluid tank can reach 500-1000L or larger. A coarse filter should be installed inside the oil collection tray to prevent large cutting 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 processed workpiece, finer grinding debris, grinding wheel particles, and cutting particles must be removed. For gun drilling deep hole processing, a 10um filter paper must be used for filtering. The use of filtering equipment can avoid excessive pollutants or metal particles in the cutting fluid, which helps to maintain the cleanliness of the cutting fluid and extend its service life. Modern automated machine tools are generally equipped with cutting fluid filtration, separation, and purification devices. The overflow method can make the cutting fluid continuously flow to the cutting area and wash away the chips. The flow rate of cutting fluid needs to be higher in order to submerge the tool and workpiece with the cutting fluid.

In addition to providing appropriate cutting fluid to the cutting area, there should also be sufficient 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 ℃, cutting cannot continue. Therefore, deep hole drilling machines are generally equipped with larger cooling oil tanks.

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 best to use two or more nozzles, one to deliver cutting fluid to the cutting area, while the others are used to assist in cooling and flushing away chips. When turning and boring, it is required to directly deliver the cutting fluid to the cutting area, so that the cutting fluid covers the cutting edge and workpiece, providing good cooling effect.

Practical experience has shown that the inner diameter of the cutting fluid nozzle 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 delivered between the tool and the workpiece without cutting obstacles, which helps to provide lubrication at low speeds.

When drilling and reaming horizontally, it is best to deliver the cutting fluid to the cutting area through the inner hole of the hollow tool, ensuring that there is sufficient cutting fluid at the edge and flushing the chips out of the hole. Due to the fact that the spiral groove of the drill bit (to discharge chips) plays a role in discharging cutting fluid from the cutting area outward, even for vertical drills, there is very little cutting fluid entering the cutting area. Only hollow drill bits can solve this problem.

3、 Cutting fluid cooling and high-pressure method

For certain machining processes, such as deep hole drilling and sleeve drilling, high-pressure (pressure ranging from 0.69 to 13.79 MPa) cutting fluid systems are commonly used for oil supply. Deep hole drilling uses a single blade drill bit, similar to boring, except that there is a passage for cutting fluid inside the drill bit. Hole drilling is a drilling method of drilling a cylindrical hole on a workpiece but leaving a solid cylinder behind.

When the tool enters the workpiece, the drilled solid cylinder passes through the hollow cylindrical cutting head and uses a pressure pump to deliver cutting fluid around the tool, forcing chips to flow out from the center of the tool. The cutting fluid used for drilling holes must have good extreme pressure and anti sintering properties, low viscosity to flow freely around the tool, and good oiliness to reduce the friction coefficient between the tool and the workpiece, as well as between the tool and chips. 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 drilling chip groove as the passage for cutting fluid, with a cutting fluid pressure of 0.35-0.69MPa. The rotating sealing sleeve flows into the drill bit and then directly enters the cutting area. The cutting fluid flowing out of the hole helps to remove chips. Compared with the overflow method, using oil hole drilling is a significant improvement in deep hole drilling, with a significant increase in drill life and productivity. The high-pressure method is beneficial for the cutting fluid to reach the cutting area and is sometimes used on other machine tools. Grinding makes the high-pressure nozzle beneficial for cleaning the grinding wheel.