Usually we can choose according to the recommendation of the machine tool supplier; Secondly, it can also be selected according to conventional experience. For example, when using high-speed steel tools for low-speed cutting, pure oily metal cutting fluid is usually used, and when using cemented carbide tools for high-speed cutting, water-soluble metal cutting fluid can usually be used; When the liquid supply is difficult or the cutting fluid is not easy to reach the cutting area, pure oily metal cutting fluid (such as tapping, inner hole broaching, etc.) can be used. In other cases, water-soluble metal cutting fluid can usually be used.
In short, the specific type of cutting fluid should be selected according to the specific cutting conditions and requirements, the different characteristics of pure oily metal cutting fluid and water-soluble metal cutting fluid, and the different actual conditions of each factory, such as the ventilation conditions of the workshop, the waste liquid treatment capacity and the use of cutting fluid in the previous and subsequent processes.
Secondly, after selecting the type of cutting fluid, the type of cutting fluid should be preliminarily selected according to the cutting process, the material of the workpiece to be machined and the requirements for the machining accuracy and roughness of the workpiece. For example, when selecting grinding cutting fluid, we should consider not only the conditions of ordinary cutting, but also the characteristics of the grinding process itself: we all know that grinding is actually a process of simultaneous cutting with multiple tools. The feed rate of grinding is small, and the cutting force is usually small, but the grinding speed is high (30-80m/s), so the temperature of the grinding area is usually high, which can be as high as 800-1000 ℃, It is easy to cause local burns on the surface of the workpiece, and the grinding thermal stress will deform the workpiece, and even cause cracks on the surface of the workpiece.
At the same time, because the grinding process will produce a large number of metal debris and grinding wheel grit, which will affect the surface roughness of the workpiece; Therefore, when selecting the water-soluble metal cutting fluid for grinding, we need the cutting fluid to have good cooling, lubrication and cleaning washability. According to the different materials of the workpiece, when selecting water-soluble metal cutting fluid, we should also select different cutting fluid products from the different characteristics of different materials. For example, when cutting high hardness stainless steel, we should select extreme pressure water-soluble metal cutting fluid with good extreme pressure performance according to its characteristics of high hardness, high strength and difficult cutting, so as to meet the requirements of extreme pressure lubrication of cutting fluid in the cutting process; For materials such as aluminum alloy and copper alloy, due to the characteristics of high toughness and activity of the material itself, when selecting water-soluble metal cutting fluid, the lubricity and cleaning of the cutting fluid are more required, and the workpiece cannot be corroded at the same time.