外文翻譯--機(jī)械加工件表面層物理學(xué)性能改變的主要成因及處理措施

畢業(yè)設(shè)計(jì) （ 論文 ）譯文 題目名稱 ： 機(jī)械加工件表面物理學(xué)性能 改變的主要成因及處理措施 院系名稱 ： 班 級 ： 學(xué) 號 ： 學(xué)生姓名 ： 指導(dǎo)教師 ： 中原工學(xué)院畢業(yè)設(shè)計(jì)譯文 1 Appendix 5 The main causes and treatment of the changes of the physical properties in machining 1. The main reasons A metals machinability is its ease of achieving a required production of machined components relative to the cost. It has ma ny 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 face 1) Hardening of the three main factors. (1) The geometry 中原工學(xué)院畢業(yè)設(shè)計(jì)譯文 2 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 中原工學(xué)院畢業(yè)設(shè)計(jì)譯文 3 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 microstructure is different from leaving would inevitably lead to changes in the volume of surface residual stress. 3) the factors that affect the residual stress (1) In the cutting process, where the impact of hardening, hot forging and metallurgical structure changes in the factors that will cause the surface residual stress.Factors influenced the workpiece material, cutting speed, rake angle, and a factor in the different cutting conditions, the impact is not the same.For example, the Turning with positive rake angle of 45 steel, regardless of changes in cutting speed, workpiece surface always produces the residual tensile stress, mainly due to poor performance of 45 hardened steel, cutting the heat factor plays a leading role, there is no residual pressurestress conditions. (2) In the grinding process, severe plastic deformation, the surface temperature is high, thus, thermal factors and surface plastic deformation on the workpiece residual stress effects are great.First, the grinding depth of the surface residual stress on the nature of the workpiece, the size greatly.When it is small, the grinding temperature is low, plastic deformation plays a dominant role, the workpiece surface residual compressive stress； when it increases, the grinding heat increased, although the increased plastic deformation in the workpiece surface residual tensile stress, whenit increases to a certain extent, the plastic deformation will gradually dominate the residual stress is gradually increasing.Second, the workpiece material and heat treatment on the nature of residual stress, grinding cracks have a great relationship, in general, depends on the nature of the surface residual stress the strength of the workpiece material, thermal conductivity, plastic and other factors.The higher strength of the material, the worse the thermal conductivity, lower plasticity, grinding metal surface residual tensile stress the greater the tendency to produce greater the possibility of grinding cracks. 4) Changes in metal microstructure and surface grinding burn (1) the surface microstructure changes and the reasons for grinding burn machining 中原工學(xué)院畢業(yè)設(shè)計(jì)譯文 4 process, when the role of cutting heat to the workpiece surface layer temperature exceeds the critical temperature of phase change materials, the microstructure of the workpiece surface will change,In general the cutting process, because the chip can take most of the cutting heat, cutting heat has little effect on the workpiece.In the grinding process, due to the high speed grinding (typically 35 80m / s range), the grinding pressure than large, flat area on the cutting grinding heat generated by the cutting process than the general several times larger, and the grinding chip is very small, very little heat away (less than 20% of total calories), most of the heat is passed to the workpiece surface so that the workpiece surface with a high temperature.Often cause severe surface changes in the microstructure of metal, the metal surface hardness and strength decrease, resulting in residual stress and even lead to micro cracks, which is the phenomenon of grinding burn, it will seriously affect the use of performance parts. (2) measures to improve the process of grinding burn a) The reasonable choice of grinding parameters.Cylindrical grinding mill as an example to the amount of the impact of burns.Radial feed increases, different depths below the surface and the surface temperature will rise, burns increased. At this point, such as increasing the grinding speed, it will increase the degree of surface burns.Increased vertical feed the workpiece, grinding wheel and workpiece contact time shortened, reduced thermal effect, grinding burn relief.To compensate for the increase of the feed leaving the vertical surface roughness increases the defect, can be wide grinding wheel.Circular workpiece feed speed increases, the surface of the grinding zone temperature increased, the heat of the reaction time shortened, so that burns to reduce, but will increase the surface roughness.Commonly used to improve the grinding wheel speed to compensate.Therefore, in order to reduce the grinding burn can have a smaller surface roughness, can improve grinding speed and feed rate of workpiece circumference. b) the workpiece material.Workpiece material hardness and strength of the higher, the greater the toughness, the smaller the thermal conductivity, the grinding heat when grinding the more relevant the higher the temperature of the grinding zone.However, the hardness of workpiece material is too low, easy to plug the wheel, the grinding effect is not good. c) The correct choice of wheel.Wheel hardness is too high, not falling after blunt abrasive, easy to cause burns.Therefore, the choice of particle size large, soft grinding wheel grinding wheel can improve the performance, but also easy to plug debris will help 中原工學(xué)院畢業(yè)設(shè)計(jì)譯文 5 prevent burns. 2. Treatment measures Analysis of the surface layer of the physical and mechanical properties, the use of machined parts has great influence on performance and service life, enhance and improve the processing of the surface layer of the physical and mechanical properties, mainly adopt the following measures: 1) the final process to select the appropriate processing method Residual stress on the surface of the workpiece or machine parts have a direct impact on work performance, and the nature of the surface residual stress depends on the final machining process the workpiece processing methods.Therefore, the final workpiece machining method selection process should consider the specific working conditions of the workpiece and the possible failure modes.By the alternating stress of the workpiece, starting from the improved fatigue strength of the workpiece, the workpiece should be selected to avoid residual stress residual stresses in the final processing methods. For the relative sliding of two parts, the sliding surface will gradually produce wear and tear.There are many reasons caused by sliding wear, both the mechanical effect of sliding wear, but also bonding, diffusion and oxidation wear the role of physical and chemical factors.When the work surface compression stress suffered more than the material allowable stress, the metal surface will wear.To enhance the capacity of the workpiece to resist sliding friction, the final processing procedures should be chosen in the surface residual tensile stress of the processing methods. For the two parts relative to rolling, the relative motion there mechanical or rolling surface friction, there is also bonding, diffusion, oxidation and other physical and chemical aspects of the combined effects, rolling will gradually wear the same face.but the decisive factor causing rolling wear is the subsurface depth h at the maximum tensile stress. 2) Rolling Process Processing is the use of a rolling wheel or ball high hardness at room temperature, under the squeeze on the surface, to produce plastic deformation, after rolling, so that the convex surface on the original peak to the adjacent concave valley fillto, reduce the surface roughness, and surface of the metal lattice distortion as a result chilled layer and the residual stress and improve the carrying capacity of the workpiece and fatigue strength. 中原工學(xué)院畢業(yè)設(shè)計(jì)譯文 6 3. Conclusion Understand the physical properties of surface machining causes, and control, treatment measures, according to the role of the workpiece using different processing methods, resulting in better surface quality, and improve product performance. 中原工學(xué)院畢業(yè)設(shè)計(jì)譯文 7 附錄 5.1 機(jī)械加工件表面層物理學(xué)性能改變的主要成因及處理措施 1.主要原因 一種金屬材料的可加工性是能夠簡單實(shí)現(xiàn)所需要求的加工工件的相對成本。它包括許多方面，例如能源（或動(dòng)力）的消耗。磨屑的形成，表面的完整性，和刀具的壽命。低的能量消耗，短的（或斷的磨屑），光潔度和具有較長壽命的刀具通常表現(xiàn)出良好的切削性能的方面。這些方面的一部分直接關(guān)系到機(jī)械的連續(xù)運(yùn)行和加工過程的熱學(xué)條件。原則上，這些方面可通過機(jī)械的力學(xué)性能和熱分析進(jìn)行預(yù)測 (但目前有些是超出預(yù)測的 )。還有其他方面，主要是刀具的壽命，不僅取決于 表面的應(yīng)力和連續(xù)變化的溫度，而且也取決于切削和刀具之間的微觀結(jié)構(gòu)、機(jī)械和化學(xué)性能。 在 1954 年，希爾提出一個(gè)方法，可以避免如圖 3.19 所示從而得到所需的工具的硬度。按照 原來的說法，工具不會(huì)在其屈服點(diǎn)達(dá)到力平衡，工具表面的接觸應(yīng)力和間隙上的零點(diǎn)應(yīng)力之間的差異是有限制的，前刀面上所允許的最大受力值為表面接觸應(yīng)力。 如下圖所示圓柱極坐標(biāo)系，其中，坐標(biāo)原點(diǎn)在工具的頂端，在前刀面的表面上，角變量的變化可以從 0 到 b。 1） .影響加工硬化的因素主要有三方面。 ( 1) 具幾何形狀的影響 刃口半 徑增大 ,切屑變形增大 , 徑向切削分力增大 ,后刀面對工件的擠壓、 摩擦作用加劇 , 工件塑性變形增大 ,硬化程度增大 , 硬化層深度也增大。因此 ,增大刀具前角與減小刃口半徑都能減小切屑變形 ,減小硬化程度。 中原工學(xué)院畢業(yè)設(shè)計(jì)譯文 8 ( 2) 切削用量的影響 切削用量中 ,對加工硬化影響最大的是切削速度和進(jìn)給量。在中、 低速階段 , 增大切削速度 , 后刀面與工件的作用時(shí)間縮短 , 使塑性變形的擴(kuò)展深度減小 , 且切削速度增大使工件材料的屈服極限提高 , 塑性降低。此外 , 在此范圍中切削速度增大還會(huì)使切削溫度升高 , 加強(qiáng)硬化的回復(fù)作用 ,硬化層深度減小。當(dāng) 切削速度大于 90m/ min 時(shí) , 切削熱在工件表面層上的作用時(shí)間也縮短了 , 回復(fù)作用減弱 , 硬化程度增加。隨著進(jìn)給量增大 , 切削力也增大 , 表面層金屬的塑性變形增大 ,硬化程度加劇。但當(dāng)進(jìn)給量過小時(shí) ( 如 f: 0. 050. 08mm) ,可能使切削厚度小于刀具刃口半徑 ,此時(shí)刀具與工件摩擦力加劇 ,使加工硬化現(xiàn)象反而增大。 ( 3) 被加工材料的影響 工件材料硬度越低 ,塑性越大 , 切削后硬化程度越嚴(yán)重。根據(jù)不同的工件材料和加工條件 ,采用合適的切削液 ,有助于減輕加工硬化現(xiàn)象。 2) 表層殘余應(yīng)力的產(chǎn)生有以 下幾方面原因 : (1) 冷態(tài)塑性變形引起的殘余應(yīng)力。切削過程中在切削力作用下 ,金屬切削層產(chǎn)生劇烈的塑性變形 , 使金屬表層的比容積增大 ,體積增大 , 但其變化受到與之相連的里層金屬的阻礙而在表面層產(chǎn)生殘余壓應(yīng)力。 (2) 熱態(tài)塑性變形引起的殘余應(yīng)力。切削過程中 , 在切削熱的作用下 ,加工表面的表面層產(chǎn)生熱膨脹 ,但金屬基體溫度較低 , 阻礙表層金屬的熱塑變形而使表層產(chǎn)生壓應(yīng)力。切削結(jié)束后 , 表面層溫度降低 ,其收縮又受到基體的阻礙而產(chǎn)生拉應(yīng)力。所以磨削溫度越高 ,熱塑變形就越大 , 殘余拉應(yīng)力也越大 , 甚至?xí)?dǎo)致磨削表面產(chǎn) 生裂紋。 (3) 金相組織變化引起的殘余應(yīng)力。切削時(shí) ,當(dāng)工件表面溫度高于金屬相變溫度 ,會(huì)引起金屬表層金相組織變化。不同深度處溫度不同 ,其相變也不相同。由于不同的金相組織的密度不同 , 必然引起體積的變化而使表層產(chǎn)生殘余應(yīng)力。 3) 影響殘余應(yīng)力的因素 (1) 在切削加工中 , 凡影響加工硬化、 熱塑性變形及金相組織變化的因素 ,都會(huì)引起表面殘余應(yīng)力。影響較大的因素有工件材料、切削速度、 刀具前角等 ,且一種因素在不同的切削條件下 ,其影響是不相同的。例如用正前角車刀車削 45 鋼時(shí) ,無論切削速度如何變化 ,工件表層始終 產(chǎn)生的是殘余拉應(yīng)力 , 主要原因是 45 鋼淬火性能差 ,切削中熱因素起了主導(dǎo)作用 ,沒有產(chǎn)生殘余壓應(yīng)力的條件。 (2) 在磨削加工中 ,塑性變形嚴(yán)重 ,工件表面溫度高 , 因而 , 熱因素與塑性變形對工件表層殘余應(yīng)力的影響都很大。首先 , 磨削深度對工件表層殘余應(yīng)力的性質(zhì)、 大小有很大影響。當(dāng)其較小時(shí) , 磨削溫度較低 ,塑性變形起主導(dǎo)作用 , 工件表層產(chǎn)生殘中原工學(xué)院畢業(yè)設(shè)計(jì)譯文 9 余壓應(yīng)力 ； 當(dāng)其增大 ,磨削熱隨之增加 ,雖塑性變形加劇 , 在工件表層產(chǎn)生殘余拉應(yīng)力 ,當(dāng)其增大到一定程度后 , 塑性變形又會(huì)逐漸占據(jù)主導(dǎo)地位 ,殘余壓應(yīng)力逐漸增大。其次 , 工件材 料及其熱處理狀態(tài)對殘余應(yīng)力的性質(zhì)、 磨削裂紋產(chǎn)生也有很大關(guān)系 , 一般而言表層殘余應(yīng)力的性質(zhì)取決于工件材料的強(qiáng)度、 導(dǎo)熱性、 塑性等因素。材料的強(qiáng)度越高 ,導(dǎo)熱性越差 , 塑性越低 , 磨削時(shí)金屬表層產(chǎn)生殘余拉應(yīng)力的傾向就越大 ,產(chǎn)生磨削裂紋的