In machining, different machining steps have different requirements for the use of cutting fluid. When the rough and finish machining of the workpiece are carried out separately, the appropriate cutting fluid can be selected according to the respective characteristics of the rough and finish machining.
Rough machining: cooling is the most important
During rough machining, the back feed and feed of cutting are usually larger than those of finishing machining, so it will encounter greater cutting resistance and generate more cutting heat, which will aggravate tool wear and workpiece thermal deformation. Therefore, the cutting fluid selected in the rough machining process should mainly focus on its cooling function, and the concentration of cutting fluid is generally lower than that of finish machining. Water based cutting fluid, which is mainly used for cooling and has certain lubrication, cleaning and rust prevention functions, is a good choice.
When the milling object is a workpiece with irregular shape and uneven allowance, or the intermittent machining method is adopted, because the cutting speed is lower than continuous uniform machining, the influence of cutting heat is relatively small, and the lubrication and cooling effects can be considered more evenly. Internal liquid supply and spray liquid supply can have a good effect.
When rough machining difficult to machine materials and non-ferrous metals, water-based extreme pressure emulsion can be used as machining fluid because of the low requirements for surface roughness and certain machining allowance.
Generally, cutting fluid is not used for rough machining of cast iron and brittle non-ferrous metals. Because this material will produce fine chip fragments, which will flow under the impact of cutting fluid. During the flow process, due to deposition, some small cutting fluid transmission pipes will be blocked or adhered to the moving parts of the machine tool. In addition, the chips will also react with cast iron, causing the cutting fluid to deteriorate and reduce the performance of the cutting fluid. Cutting fluid is not used, but the influence of chips and cutting heat cannot be ignored. Dust extraction device can be used to remove chips and heat.
Finishing: high speed and low speed are different
The most remarkable characteristics of finish machining are high cutting speed and small cutting force. The cutting heat generated by chip deformation is lower than that generated by tool flank friction, and the thermal deformation of workpiece is not very significant. Cutting fluid mainly acts on the flank of the tool. When using cutting fluid for finish machining, sufficient pressure should be provided, because if it cannot penetrate into the cutting area, it will not play its due role. In that way, the tool is prone to wear on the flank, which affects the roughness of the machined surface.
Finish machining is divided into high-speed finish machining and low-speed finish machining, which is divided according to the cutting speed of the tool. If oil-based cutting fluid is used in high-speed finishing, oil smoke, oil mist and oil vapor will be produced due to low viscosity and flash point, and some toxic volatiles will be secreted, affecting the health of workers. Therefore, high-speed machining is suitable for using emulsion or microemulsion containing extreme pressure additives in water-based cutting fluid, and the concentration is slightly higher than that of rough machining. When high-speed finish machining non-ferrous metals, emulsions of inactive extreme pressure additives should be selected.
In low-speed finishing, because of the low degree of friction and the low heat generated, it is not easy to have the problem of toxic and harmful substances in high-speed finishing. Therefore, it is more important to maintain better lubricity and machining accuracy of the workpiece, and it is more appropriate to use oil-based cutting fluid. When finishing ferrous materials at low speed, active extreme pressure cutting oil should be selected; Inactive extreme pressure cutting oil should be selected when finishing nonferrous metals at low speed
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