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1、MechanicalManufacturingTechnologyCutting heat and cutting temperatureCutting heat is one of the important physical phenomena in the cutting process.The cutting heat and the cutting temperature produced by it affect the cutting process,tool wear and tool life,machining accuracy and surface quality.1.
2、Generation and transmission of cutting heatDuring the cutting process,elastic and plastic deformation occurs due to the metal being cut,and there is friction between the workpiece and the tool,and friction between the chip and the tool,so that a lot of heat is generated in the cutting area(contact r
3、ange of workpiece,chip and tool),which we call cutting heat.When cutting ductile materials,the deformation and friction are greater,so more heat is generated.When its cutting speed is increased,because the deformation of chips are smaller,so the percentage of heat generated by plastic deformation is
4、 reduced,but the percentage of friction generated heat is much higher.When cutting brittle materials,the percentage of heat generated by friction on the flank surface increases.Fig.1 Generation and transmission of cutting heatChipToolWorkpieceu(1)The source of cutting heat generationThere are three
5、main sources of cutting heat：The heat of work transformation of elastic and plastic deformation of processed material in unit time-Qb；The heat generated by friction between the rake face of the tool and the bottom of the chip in a unit of time-Qq；The heat generated by the friction between the flank
6、surface of the tool and the surface of the workpiece in a unit of time-Qh。If one ignores the work done in the feeder motion,the heat produced per unit of time equal to the work done in unit time in the main motion:Q=FccQ=Qb+Qq+QhWhere Fc is the cutting force；c is the cutting speed.u(2)Transmission o
7、f cutting heatThe cutting heat generated in the cutting area is transmitted out by chip,workpiece,cutter and surrounding medium in the cutting process.The main factors that affect the heat conduction are the thermal conductivity of workpiece and tool materials and the condition of surrounding medium
8、.2.Cutting temperature and its distributionu(1)The cutting temperature The cutting temperature,refers to the average temperature of the contact zone between the rake face and the chip.u(2)The measurement of cutting temperature The natural thermocouple method；The artificial thermocouple method；The in
9、frared temperature measurement method.u(3)Cutting temperature distributionIn the process of cutting,the temperature of each point on a certain instantaneous workpiece,chip and tool is usually different,and the distribution of temperature,that is the temperature field changes with time.In the shear z
10、one,the temperature of each point along the shear plane is almost the same,but the temperature gradient in the direction perpendicular to the shear plane is very large.Fig.2 Cutting temperature distributionToolWorkpieceChipWorkpiecematerial:Low carbon Free Cutting Steels,toolDepth of cutting layer D
11、ry cutting,preheat The highest temperature points on the rake face and flank surface are not on the cutting edge,but at a certain distance from the cutting edge.The temperature gradient of the bottom layer near the rake face is very large,which means that the friction heat on the rake face is concen
12、trated on the bottom layer of the chip,which has a great influence on the shear strength of the bottom metal of the chip.Therefore,the increase of cutting temperature will decrease the friction coefficient on the rake face。The contact length of the cutter face is narrow,so the temperature rise and f
13、all on the workpiece surface is completed in a very short time.When the tool passes,the machined surface is subjected to a thermal shock.3.Main factors affecting cutting temperatureu(1)The influence of cutting parametersEmpiricalformulaThe average temperature of the contact area of the rake face mea
14、sured by the natural thermocouple method,；Cutting temperature coefficient related to workpiece,tool material,etc；Index ofFig.3 InfluenceofcuttingspeedandworkpiecematerialoncuttingtemperatureTool material:Cutting tool geometry parameter:Steel(normalized)Machining variables:The experiments show that t
15、he cutting speed doubles the cutting speed and the cutting temperature increases by about 32%；The second one is the feedf,which doubles the feed and increases its cutting temperature by 18%；The cutting depth aP has the least effect，when aP doubles,the cutting temperature increases by about 7%.So,of
16、these three elements of machining variables,cutting speed c,which has the most significant effect on temperature,is the most significant.The main reason is that as the speed increases,the frictional heat increases;With the increase of f,the cutting deformation is reduced,and the heat taken away by t
17、he chip is also increased;with the increase of the cutting depth,the cutting width is increased,and the heat dissipation area is significantly increased.u(2)The influence of tool geometry parametersThe most important influence on cutting temperature is the rake angle and the leading cutting edgeangl
18、e.The cutting temperature decreases with the increase of rake angle 0.With the decrease of the main deflection angle,the nominal width and thickness of the cutting layer increase,and the cutting temperature decreases because of the increase of the heat dissipation volume of the cutter head.Fig.4 Inf
19、luence of the rake angle on cutting temperatureFig.5 Influence of the leading cutting edgeangle on cutting temperatureCutting temperatureCutting temperatureLeading cutting edgeangleRake angleu(3)The influence of workpiece materialThe higher the strength and hardness of the workpiece material,the mor
20、e cutting heat will be generated,so the higher the cutting temperature;the smaller the heat transfer coefficient of the workpiece material,the slower the heat transfer speed,and the higher the cutting temperature.u(4)The influence of tool wearThe cutting temperature increases with the tool wear.u(5)The influence of cutting fluidThe use of cutting fluid can reduce friction,reduce the generation of cutting heat,at the same time,with the flow of cutting fluid,it can also take away part of the heat,thus reducing the cutting temperature.Thanksforwatching