毕业设计（论文）译文题目名称：机械加工件表面物理学性能 改变的主要成因及处理措施 院系名称： 班 级： 学 号： 学生姓名： 指导教师： 中原工学院毕业设计译文Appendix 5The main causes and treatment of the changes of the physical properties in machining1. The main reasonsA metals machinability is its ease of achieving a required production of machined components relative to the cost. It has many aspects, such as energy (or power) consumption, chip form, surface integrity and finish, and tool life. Low energy consumption, short (broken) chips, smooth finish and long tool life are usually aspects of good machinability. Some of these aspects are directly related to the continuum mechanical and thermal conditions of the machining process. In principle, they may be predicted by mechanical and thermal analy- sis (but at the current time some are beyond prediction). Other aspects, principally tool life, depend not only on the continuum surface stresses and temperatures that are generated but also on microstructural, mechanical and chemical interactions between the chip and the tool.The required tool hardnesses to avoid the yielding shown in Figure 3.19 have been obtained by a method due to Hill (1954).The requirement that the tool does not yield at its apex, together with force equilibrium in the tool, limits the difference between the rakeface contact stress and the zero stress on the clearance face and hence places a maximum value on the allowable rake face contact stress With the cylindrical polar coordinate system shown in Figure A5.1(a), in which the origin is at the tool apex and the angular variable q varies from 0 on the rake face to b on the clearance face1) Hardening of the three main factors. (1) The geometry Cutting edge radius increases, the chip deformation increases, the radial cutting force increases, the face of the workpiece after the extrusion tool, increasing friction, plastic deformation of the workpiece increases, the hardening increases, increasing the depth of hardened layer.Therefore, increasing the rake angle and cutting edge radius can reduce the chip deformation decreases, reducing the degree of hardening. (2) the impact of cutting Cutting the greatest impact on the work hardening is the cutting speed and feed.In the middle and low-speed stage, increasing the cutting speed, flank and shorten the role of the workpiece, so that the expansion of the depth of plastic deformation decreases, and the cutting speed increases to improve the workpiece material yield limit, plasticity decreases.In addition, the cutting speed in this range so that the cutting temperature will increase and strengthen the role of hardening response, hardening depth decreases.When the cutting speed is greater than 90m / min, the cutting heat in the surface layer on the role of time has been shortened, weakened back, hardening increased.As the feed rate increases, cutting force also increases, plastic deformation of the surface layer of the metal increases, the hardening worse.But when the feed rate is too small (eg, f: 0. 05 0. 08mm), may be less than the thickness of the cutting tool edge radius, tool and workpiece friction time increased, so that instead of hardening increases. (3) of the processed material The lower hardness of workpiece material, the greater plasticity, hardening after cutting more serious.Depending on the workpiece material and processing conditions, the use of appropriate cutting fluid to help reduce the hardening phenomenon.2）Surface residual stress generation are the following reasons:(1) Cold plastic deformation caused by residual stress.Role in the cuttingforce in cutting process, the metal layer of a sharp cutting plastic deformation than the volume of the metal surface increases, volume increases, but the changes are connected to the inner layer of metal barriers and residual in the surface layerstress.(2) The plastic deformation caused by thermal residual stress.cutting process,the role of heat in the cutting, processing, production of surface layer ofthermal expansion, but the low temperature metal matrix and hinder thethermoplastic deformation of the metal surface leaving the surface compressive stresses.After cutting, the surface layer temperature decreases,the contraction and obstruction by the matrix tensile stress.Therefore, thehigher the grinding temperature, the greater the thermoplastic deformation, thegreater the residual tensile stress, and even lead to grinding surface cracks.(3) The microstructure of the residual stress caused by the change.Cutting, when the surface temperature is higher than the metal phase transition temperature, can cause changes in microstructure of the metal surface.Different temperatures at different depths, the phase transition is not the same.Because the density of the different microstruc