0235-摩托车前减震器的设计【全套13张CAD图】
0235-摩托车前减震器的设计【全套13张CAD图】,全套13张CAD图,摩托,车前,减震器,设计,全套,13,cad
摩托车前减震器的设计摘要:减震器又称缓冲器,是安装在摩托车悬挂装置上的一个重要零件。摩托车悬挂装置不仅决定了乘坐的舒适度,而且还是决定其运动性能的重要部件。而减震器的功能就是缓和由于路面不平引起的冲击,衰减摩托车的振动;提高乘坐舒适性,保护货载;减低车体各部分的运应力,增加零件的寿命;加强轮胎的附着性,有助于摩托车的操纵性、稳定性。 本文所设计的摩托车前减震器采用液力式减震方式,其工作行程为50 mm。通过弹簧减震为主。设计时减震弹簧采用组合式弹簧,由两段节距不同的等节距圆柱弹簧组成。在通常振动范围内,弹簧柔软,当车辆受到冲击时,弹簧变硬,有足够的能力吸收这种冲击能量。减震器的机能是利用流体通过减震杆上的孔、隙产生的粘性阻力。和固体摩托减震相比,利用液体紊流阻力的减震器,在一定阻尼力和吸收能量的条件下,质量小,尺寸小,并在相当的范围内具有能任意规定阻尼力对工作速度的关系等优点。在设计过程中对前减震器的工作原理进行了说明,并确定了工作部分主要零件的相关参数,在已知条件的前提下分别对减震弹簧直径和自由高度,阻尼孔的数量和直径等进行设计计算。 关键词:前减震器 弹簧 阻尼 设计 The design of motorcycle before the shock absorber Abstract : Dampers also known as buffer , is the installation of the hoisting device an important component . Motorcycle hoisting device will not only decide the ride comfort, but also to determine their performance movement of important parts . And the function of a shock absorber is easing due to the road surface uneven, the effect of vibration attenuation motorcycle; improveing ride comfort, Protection of cargo; reduceing the stress of the body operation, increaseing the life expectancy of components; strengthen tire adhesion. helping manipulation and stability of Motorcycle. In this paper , motorcycle before shock absorber and the overall program analysis and design is the main content. Useing hydraulic shock absorber, its itinerary to 50 mm . Mainly through the spring damping, supplemented dampers. Damping spring design using modular spring,the combination of spring two such different pitchs pitch cylindrical spring,. In the normal range of vibration, soft spring, when the vehicles to be shocked, springs stiffen and have sufficient capacity to absorb the impact energy . Damper function use the fluid through the Absorption of shock pole on the hole, the gap viscous resistance . And compared to solid motorized damping, the use of liquid turbulent resistance dampers, to a certain damping force and absorb energy conditions, Quality small, size small, and the lack of scale with arbitrary requirements damping force on the relationship between the pace of work and so on. In the process of designing,there are a note On the before shock absorber working principle , and to identify the major components of the work of the relevant parameters, Respectively damping springs, which includes determination and free height of the damping spring, Damping hole quantity and determination for the design and rehabilitation of resistanceKeywords :before the shock absorber damping spring damper design .毕业设计(论文)开题报告题目 摩托车前减震器的设计一、 选题的依据及意义:在我们常用的二轮摩托车中为了缓和冲击和震动,保证行车平顺性的要求,除了采用具有弹性的充气轮胎外,在悬挂装置(连接车架和车轮的零部件的总称)中应设计有必要的弹性元件和衰减振动的元件。当车轮受到的冲击和振动传给弹性元件后,弹性元件将它们变为缓和的振动,即振幅较大、频率较低(每分钟80次),使人们能适应其振动频率,再加上阻尼器将迅速衰减振幅、吸收其能量、防止共振,并控制车身振动加速不得高于0.50.6g。同样,为了满足行驶稳定性、乘坐舒适性两方面的要求,于是开始采用减震系统。前减震器用于摩托车前悬挂装置,它的作用主要是减轻前轮遇到障碍受到冲击时传至车架的冲击负荷和震动。通过对液力减震器的分析,它的液压平衡环节多,故障频繁,易污染,故决定选择弹簧液力阻尼式减震器。弹簧液力阻尼式减震器的减震效果好,制造成本较低,目前国内外摩托车减震器广泛采用这种形式的减震器。二、国内外研究概况及发展趋势(含文献综述):1885年,德国工程师戴姆勒将其改进的汽油机安装在车身和车轮均用木材制成上的三轮车上发明了世界上第一辆摩托车。但由于木制车身及车轮不耐颠簸,限制了车速(仅12km/h),所以戴姆勒的摩托车并无实用价值。1910年开始在前轮采用金属弹簧张力的双向、平行连接装置,30年代便发明了利用管内粘性机油的液压减震器。1955年以后前轮悬挂装置就采用了伸缩管式和底部杠杆式两类前叉。在伸缩桶式前叉、望远镜式的二个桶内由于有螺旋弹簧和油缸,加工精度要求高,生产效率低,阻碍了发展和应用。1960年二轮摩托车的大量生产,底部杠杆式前叉处于全盛时期,该系统具有结构简单、价格低廉等优点。后来伸缩式前叉又重新上市,用于当时盛行一时的两轮的赛车上,伸缩式前叉优秀的行驶性能方被证明。因此,大批量生产的摩托车也竟相采用伸缩式前叉,而且由于加工技术的提高,伸缩桶式前叉也得到了保证。所以,至今为止,各种型式的两轮摩托车都采用伸缩筒式前叉。同时,后轮悬挂装置的要求也迫切了,由于全链条传递驱动力,后轮必须采用长距离的固定方式。所以车体的缓冲仅只在坐垫下面安装有一金属弹簧。1950年才开始有正式的后悬挂装置。最初称滑栓式,并尝试采用摇臂式。50年代后半期才确立了摇臂式后悬挂装置,既是现代两轮摩托车的后悬挂装置的基础。进入70年代又开发了装有单减震器的单减震系统,特别是1973年开始用于越野车之后,公路赛车、大型运动车均很快的采用了这种单减震器后悬挂系统。我国自1957年7月洪都机械厂成功仿制M72型边三轮摩托车,揭开了我国生产摩托车的历史以来,到1987年摩托车生产量为1.2万辆。改革开放以来,我国摩托车产量得到了飞速增长,品种不断增多。目前在我国已形成了自己的摩托车生产体系,到1995年的产量超过700万辆,已成为世界上第一摩托车生产国。与摩托车生产相适应的减震器产量已达到1500万支,能生产9大系列50余种型号,基本满足了我国摩托车生产的发展需要,部分产品已达到国际同类产品水平,为我国摩托车工业的技术水平提高和发展打下了基础。三、研究内容及实验方案: 1.研究内容1)减震器整体方案分析与设计2) 摩托车减震器系统的弹簧特性摩托车悬挂装置的挠度 摩托车悬挂装置的理想弹簧特性 摩托车悬挂装特性置的实际弹簧3) 弹簧的材料及工艺弹簧材料的选用弹簧的制造工艺4) 减震器的速度特性及阻尼力节流阀的压力特性减震器的速度特性减震器阻尼力产生原理阻尼调节装置2.实验方案前减震器有很多种,常见的有弹簧空气阻尼式前叉、弹簧液力阻尼式减震器、油气伸缩式减震器等。其中弹簧空气阻尼式前叉虽然结构简单、造价低,但是它是以活塞管之间的间隙为空气阻尼的双向用途减震器,所以起减震效果不及其他结构的理想。然而油气伸缩式减震器的减震效果都很佳,甚至达到理想的减震效果,增加了舒适性和安全性。但其结构复杂,造价昂贵,大都用在大型或高级二轮车上,如雅马哈XJ750型、XJ750E,铃木GS750型赛车等。而弹簧液力阻尼式减震器不但结构简单,造价低,而且减震效果好,所以我将采用弹簧液力阻尼式前减震器作为我的实验方案。四、目标、主要特色及工作进度1. 目 标:1) 通过这次毕业设计将大学所学的基础知识综合运用起来,以此提高自己的综合素质以更好更快的适应社会发展的需求,并且学会在以后的工作中能独立完成设计工作。2) 用AUTO/CAD画出相关的零件图及装配图3) 写出设计的相关原理及计算过程2.主要特色:采用装有根据载荷状态调节衰减力的装置并在相当的范围内具有能任意规定阻尼力对工作速度的关系的减震系统,在高速行驶时调至较高的衰减力,很容易得到高速行驶稳定性;在平常行驶时,调至较低的衰减力,即可得到较好的乘坐舒适性。工作进度:1 收集、查阅、分析有关资料,外文资料翻译(6000字符),撰写开题报告; 第1周第4周 2减震器整体方案分析与设计; 第5周第6周 3计算确定工作部分主要零件的相关参数; 第7周第8周 4设计减震器部件装配图,拆绘主要零件图(折合A1图4张); 第9周第12周 5设计部件检验基准书; 第13周 6撰写毕业论文、毕业设计审查、毕业答辩。 第14周第17周 五、参考文献1庄志等编著. 摩托车理论与机构设计. 武汉:武汉测绘科技大学出版社,1991.12成大先主编. 机械设计手册. 单行本. 北京:化学工业出版社,2004.13 张龙全. 摩托车减震器弹簧的设计计算及工作图的绘制.摩托车技术2004年第5期4天之. 浅谈摩托车用减震器. 摩托车2003年第5期5. 刘爱红.纯阀片阻尼结构在摩托车后减震器的研究及应用.摩托车技术2006年第7 期6. 刘爱红. 后减震器阻尼阀系的研究与分析. 摩托车技术2004年第1期7Soon Kil Hong. Advancement of Aerospace Education and collabovative Recersh in the 21th century. HanKVK:Aviation Vniversity.8. 廖念钊等. 互换性与技术测量. 北京:中国计量出版社,2011.2第5版 图 纸 清 单序号图号图纸名称图幅1QJZQ-000减震器装配图A12QJZQ-001检验基准书A23QJZQ-000-01贮油筒零件图A24QJZQ-000-02减震弹簧零件图A25QJZQ-000-03工作缸装配图A26QJZQ-000-04减震杆零件图A27QJZQ-000-05导向套零件图A38QJZQ-000-06活塞环零件图A49QJZQ-000-07端盖零件图A410QJZQ-000-08压缩弹簧零件图A411QJZQ-000-09油封零件图A412QJZQ-000-10中间套零件图A4外语文献翻译摘自: 制造工程与技术(机加工)(英文版) Manufacturing Engineering and TechnologyMachining 机械工业出版社 2004年3月第1版 美 s. 卡尔帕基安(Serope kalpakjian) s.r 施密德(Steven R.Schmid) 著原文:20.9 MACHINABILITYThe machinability of a material usually defined in terms of four factors:1、 Surface finish and integrity of the machined part;2、 Tool life obtained;3、 Force and power requirements;4、 Chip control. Thus, good machinability good surface finish and integrity, long tool life, and low force And power requirements. As for chip control, long and thin (stringy) cured chips, if not broken up, can severely interfere with the cutting operation by becoming entangled in the cutting zone.Because of the complex nature of cutting operations, it is difficult to establish relationships that quantitatively define the machinability of a material. In manufacturing plants, tool life and surface roughness are generally considered to be the most important factors in machinability. Although not used much any more, approximate machinability ratings are available in the example below.20.9.1 Machinability Of SteelsBecause steels are among the most important engineering materials (as noted in Chapter 5), their machinability has been studied extensively. The machinability of steels has been mainly improved by adding lead and sulfur to obtain so-called free-machining steels.Resulfurized and Rephosphorized steels. Sulfur in steels forms manganese sulfide inclusions (second-phase particles), which act as stress raisers in the primary shear zone. As a result, the chips produced break up easily and are small; this improves machinability. The size, shape, distribution, and concentration of these inclusions significantly influence machinability. Elements such as tellurium and selenium, which are both chemically similar to sulfur, act as inclusion modifiers in resulfurized steels.Phosphorus in steels has two major effects. It strengthens the ferrite, causing increased hardness. Harder steels result in better chip formation and surface finish. Note that soft steels can be difficult to machine, with built-up edge formation and poor surface finish. The second effect is that increased hardness causes the formation of short chips instead of continuous stringy ones, thereby improving machinability.Leaded Steels. A high percentage of lead in steels solidifies at the tip of manganese sulfide inclusions. In non-resulfurized grades of steel, lead takes the form of dispersed fine particles. Lead is insoluble in iron, copper, and aluminum and their alloys. Because of its low shear strength, therefore, lead acts as a solid lubricant (Section 32.11) and is smeared over the tool-chip interface during cutting. This behavior has been verified by the presence of high concentrations of lead on the tool-side face of chips when machining leaded steels.When the temperature is sufficiently high-for instance, at high cutting speeds and feeds (Section 20.6)the lead melts directly in front of the tool, acting as a liquid lubricant. In addition to this effect, lead lowers the shear stress in the primary shear zone, reducing cutting forces and power consumption. Lead can be used in every grade of steel, such as 10xx, 11xx, 12xx, 41xx, etc. Leaded steels are identified by the letter L between the second and third numerals (for example, 10L45). (Note that in stainless steels, similar use of the letter L means “low carbon,” a condition that improves their corrosion resistance.)However, because lead is a well-known toxin and a pollutant, there are serious environmental concerns about its use in steels (estimated at 4500 tons of lead consumption every year in the production of steels). Consequently, there is a continuing trend toward eliminating the use of lead in steels (lead-free steels). Bismuth and tin are now being investigated as possible substitutes for lead in steels.Calcium-Deoxidized Steels. An important development is calcium-deoxidized steels, in which oxide flakes of calcium silicates (CaSo) are formed. These flakes, in turn, reduce the strength of the secondary shear zone, decreasing tool-chip interface and wear. Temperature is correspondingly reduced. Consequently, these steels produce less crater wear, especially at high cutting speeds.Stainless Steels. Austenitic (300 series) steels are generally difficult to machine. Chatter can be s problem, necessitating machine tools with high stiffness. However, ferritic stainless steels (also 300 series) have good machinability. Martensitic (400 series) steels are abrasive, tend to form a built-up edge, and require tool materials with high hot hardness and crater-wear resistance. Precipitation-hardening stainless steels are strong and abrasive, requiring hard and abrasion-resistant tool materials.The Effects of Other Elements in Steels on Machinability. The presence of aluminum and silicon in steels is always harmful because these elements combine with oxygen to form aluminum oxide and silicates, which are hard and abrasive. These compounds increase tool wear and reduce machinability. It is essential to produce and use clean steels.Carbon and manganese have various effects on the machinability of steels, depending on their composition. Plain low-carbon steels (less than 0.15% C) can produce poor surface finish by forming a built-up edge. Cast steels are more abrasive, although their machinability is similar to that of wrought steels. Tool and die steels are very difficult to machine and usually require annealing prior to machining. Machinability of most steels is improved by cold working, which hardens the material and reduces the tendency for built-up edge formation.Other alloying elements, such as nickel, chromium, molybdenum, and vanadium, which improve the properties of steels, generally reduce machinability. The effect of boron is negligible. Gaseous elements such as hydrogen and nitrogen can have particularly detrimental effects on the properties of steel. Oxygen has been shown to have a strong effect on the aspect ratio of the manganese sulfide inclusions; the higher the oxygen content, the lower the aspect ratio and the higher the machinability.In selecting various elements to improve machinability, we should consider the possible detrimental effects of these elements on the properties and strength of the machined part in service. At elevated temperatures, for example, lead causes embrittlement of steels (liquid-metal embrittlement, hot shortness; see Section 1.4.3), although at room temperature it has no effect on mechanical properties.Sulfur can severely reduce the hot workability of steels, because of the formation of iron sulfide, unless sufficient manganese is present to prevent such formation. At room temperature, the mechanical properties of resulfurized steels depend on the orientation of the deformed manganese sulfide inclusions (anisotropy). Rephosphorized steels are significantly less ductile, and are produced solely to improve machinability.20.9.2 Machinability of Various Other Metals Aluminum is generally very easy to machine, although the softer grades tend to form a built-up edge, resulting in poor surface finish. High cutting speeds, high rake angles, and high relief angles are recommended. Wrought aluminum alloys with high silicon content and cast aluminum alloys may be abrasive; they require harder tool materials. Dimensional tolerance control may be a problem in machining aluminum, since it has a high thermal coefficient of expansion and a relatively low elastic modulus.Beryllium is similar to cast irons. Because it is more abrasive and toxic, though, it requires machining in a controlled environment.Cast gray irons are generally machinable but are. Free carbides in castings reduce their machinability and cause tool chipping or fracture, necessitating tools with high toughness. Nodular and malleable irons are machinable with hard tool materials.Cobalt-based alloys are abrasive and highly work-hardening. They require sharp, abrasion-resistant tool materials and low feeds and speeds.Wrought copper can be difficult to machine because of built-up edge formation, although cast copper alloys are easy to machine. Brasses are easy to machine, especially with the addition pf lead (leaded free-machining brass). Bronzes are more difficult to machine than brass.Magnesium is very easy to machine, with good surface finish and prolonged tool life. However care should be exercised because of its high rate of oxidation and the danger of fire (the element is pyrophoric).Molybdenum is ductile and work-hardening, so it can produce poor surface finish. Sharp tools are necessary.Nickel-based alloys are work-hardening, abrasive, and strong at high temperatures. Their machinability is similar to that of stainless steels.Tantalum is very work-hardening, ductile, and soft. It produces a poor surface finish; tool wear is high.Titanium and its alloys have poor thermal conductivity (indeed, the lowest of all metals), causing significant temperature rise and built-up edge; they can be difficult to machine.Tungsten is brittle, strong, and very abrasive, so its machinability is low, although it greatly improves at elevated temperatures.Zirconium has good machinability. It requires a coolant-type cutting fluid, however, because of the explosion and fire.20.9.3 Machinability of Various MaterialsGraphite is abrasive; it requires hard, abrasion-resistant, sharp tools.Thermoplastics generally have low thermal conductivity, low elastic modulus, and low softening temperature. Consequently, machining them requires tools with positive rake angles (to reduce cutting forces), large relief angles, small depths of cut and feed, relatively high speeds, and proper support of the workpiece. Tools should be sharp.External cooling of the cutting zone may be necessary to keep the chips from becoming “gummy” and sticking to the tools. Cooling can usually be achieved with a jet of air, vapor mist, or water-soluble oils. Residual stresses may develop during machining. To relieve these stresses, machined parts can be annealed for a period of time at temperatures ranging from to (to), and then cooled slowly and uniformly to room temperature.Thermosetting plastics are brittle and sensitive to thermal gradients during cutting. Their machinability is generally similar to that of thermoplastics.Because of the fibers present, reinforced plastics are very abrasive and are difficult to machine. Fiber tearing, pulling, and edge delamination are significant problems; they can lead to severe reduction in the load-carrying capacity of the component. Furthermore, machining of these materials requires careful removal of machining debris to avoid contact with and inhaling of the fibers.The machinability of ceramics has improved steadily with the development of nanoceramics (Section 8.2.5) and with the selection of appropriate processing parameters, such as ductile-regime cutting (Section 22.4.2).Metal-matrix and ceramic-matrix composites can be difficult to machine, depending on the properties of the individual components, i.e., reinforcing or whiskers, as well as the matrix material.20.9.4 Thermally Assisted MachiningMetals and alloys that are difficult to machine at room temperature can be machined more easily at elevated temperatures. In thermally assisted machining (hot machining), the source of heata torch, induction coil, high-energy beam (such as laser or electron beam), or plasma arcis forces, (b) increased tool life, (c) use of inexpensive cutting-tool materials, (d) higher material-removal rates, and (e) reduced tendency for vibration and chatter.It may be difficult to heat and maintain a uniform temperature distribution within the workpiece. Also, the original microstructure of the workpiece may be adversely affected by elevated temperatures. Most applications of hot machining are in the turning of high-strength metals and alloys, although experiments are in progress to machine ceramics such as silicon nitride. SUMMARYMachinability is usually defined in terms of surface finish, tool life, force and power requirements, and chip control. Machinability of materials depends not only on their intrinsic properties and microstructure, but also on proper selection and control of process variables.译文:20.9 可机加工性一种材料的可机加工性通常以四种因素的方式定义:1、 分的表面光洁性和表面完整性。2、刀具的寿命。3、切削力和功率的需求。4、切屑控制。以这种方式,好的可机加工性指的是好的表面光洁性和完整性,长的刀具寿命,低的切削力和功率需求。关于切屑控制,细长的卷曲切屑,如果没有被切割成小片,以在切屑区变的混乱,缠在一起的方式能够严重的介入剪切工序。因为剪切工序的复杂属性,所以很难建立定量地释义材料的可机加工性的关系。在制造厂里,刀具寿命和表面粗糙度通常被认为是可机加工性中最重要的因素。尽管已不再大量的被使用,近乎准确的机加工率在以下的例子中能够被看到。20.9.1 钢的可机加工性因为钢是最重要的工程材料之一(正如第5章所示),所以他们的可机加工性已经被广泛地研究过。通过宗教铅和硫磺,钢的可机加工性已经大大地提高了。从而得到了所谓的易切削钢。二次硫化钢和二次磷化钢 硫在钢中形成硫化锰夹杂物(第二相粒子),这些夹杂物在第一剪切区引起应力。其结果是使切屑容易断开而变小,从而改善了可加工性。这些夹杂物的大小、形状、分布和集中程度显著的影响可加工性。化学元素如碲和硒,其化学性质与硫类似,在二次硫化钢中起夹杂物改性作用。钢中的磷有两个主要的影响。它加强铁素体,增加硬度。越硬的钢,形成更好的切屑形成和表面光洁性。需要注意的是软钢不适合用于有积屑瘤形成和很差的表面光洁性的机器。第二个影响是增加的硬度引起短切屑而不是不断的细长的切屑的形成,因此提高可加工性。含铅的钢 钢中高含量的铅在硫化锰夹杂物尖端析出。在非二次硫化钢中,铅呈细小而分散的颗粒。铅在铁、铜、铝和它们的合金中是不能溶解的。因为它的低抗剪强度。因此,铅充当固体润滑剂并且在切削时,被涂在刀具和切屑的接口处。这一特性已经被在机加工铅钢时,在切屑的刀具面表面有高浓度的铅的存在所证实。当温度足够高时例如,在高的切削速度和进刀速度下铅在刀具前直接熔化,并且充当液体润滑剂。除了这个作用,铅降低第一剪切区中的剪应力,减小切削力和功率消耗。铅能用于各种钢号,例如10XX,11XX,12XX,41XX等等。铅钢被第二和第三数码中的字母L所识别(例如,10L45)。(需要注意的是在不锈钢中,字母L的相同用法指的是低碳,提高它们的耐蚀性的条件)。然而,因为铅是有名的毒素和污染物,因此在钢的使用中存在着严重的环境隐患(在钢产品中每年大约有4500吨的铅消耗)。结果,对于估算钢中含铅量的使用存在一个持续的趋势。铋和锡现正作为钢中的铅最可能的替代物而被人们所研究。脱氧钙钢 一个重要的发展是脱氧钙钢,在脱氧钙钢中矽酸钙盐中的氧化物片的形成。这些片状,依次减小第二剪切区中的力量,降低刀具和切屑接口处的摩擦和磨损。温度也相应地降低。结果,这些钢产生更小的月牙洼磨损,特别是在高切削速度时更是如此。不锈钢 奥氏体钢通常很难机加工。振动能成为一个问题,需要有高硬度的机床。然而,铁素体不锈钢有很好的可机加工性。马氏体钢易磨蚀,易于形成积屑瘤,并且要求刀具材料有高的热硬度和耐月牙洼磨损性。经沉淀硬化的不锈钢强度高、磨蚀性强,因此要求刀具材料硬而耐磨。钢中其它元素在可机加工性方面的影响 钢中铝和矽的存在总是有害的,因为这些元素结合氧会生成氧化铝和矽酸盐,而氧化铝和矽酸盐硬且具有磨蚀性。这些化合物增加刀具磨损,降低可机加工性。因此生产和使用净化钢非常必要。根据它们的构成,碳和锰钢在钢的可机加工性方面有不同的影响。低碳素钢(少于0.15%的碳)通过形成一个积屑瘤能生成很差的表面光洁性。尽管铸钢的可机加工性和锻钢的大致相同,但铸钢具有更大的磨蚀性。刀具和模具钢很难用于机加工,他们通常再煅烧后再机加工。大多数钢的可机加工性在冷加工后都有所提高,冷加工能使材料变硬并且减少积屑瘤的形成。其它合金元素,例如镍、铬、钳和钒,能提高钢的特性,减小可机加工性。硼的影响可以忽视。气态元素比如氢和氮在钢的特性方面能有特别的有害影响。氧已经被证明了在硫化锰夹杂物的纵横比方面有很强的影响。越高的含氧量,就产生越低的纵横比和越高的可机加工性。选择各种元素以改善可加工性,我们应该考虑到这些元素对已加工零件在使用中的性能和强度的不利影响。例如,当温度升高时,铝会使钢变脆(液体金属脆化,热脆化,见1.4.3节),尽管其在室温下对力学性能没有影响。因为硫化铁的构成,硫能严重的减少钢的热加工性,除非有足够的锰来防止这种结构的形成。在室温下,二次磷化钢的机械性能依赖于变形的硫化锰夹杂物的定位(各向异性)。二次磷化钢具有更小的延展性,被单独生成来提高机加工性。20.9.2 其它不同金属的机加工性尽管越软的品种易于生成积屑瘤,但铝通常很容易被机加工,导致了很差的表面光洁性。高的切削速度,高的前角和高的后角都被推荐了。有高含量的矽的锻铝合金铸铝合金也许具有磨蚀性,它们要求更硬的刀具材料。尺寸公差控制也许在机加工铝时会成为一个问题,因为它有膨胀的高导热系数和相对低的弹性模数。铍和铸铁相同。因为它更具磨蚀性和毒性,尽管它要求在可控人工环境下进行机加工。灰铸铁普遍地可加工,但也有磨蚀性。铸造无中的游离碳化物降低它们的可机加工性,引起刀具切屑或裂口。它需要具有强韧性的工具。具有坚硬的刀具材料的球墨铸铁和韧性铁是可加工的。钴基合金有磨蚀性且高度加工硬化的。它们要求尖的且具有耐蚀性的刀具材料并且有低的走刀和速度。尽管铸铜合金很容易机加工,但因为锻铜的积屑瘤形成因而锻铜很难机加工。黄铜很容易机加工,特别是有添加的铅更容易。青铜比黄铜更难机加工。镁很容易机加工,镁既有很好的表面光洁性和长久的刀具寿命。然而,因为高的氧化速度和火种的危险(这种元素易燃),因此我们应该特别小心使用它。钳易拉长且加工硬化,因此它生成很差的表面光洁性。尖的刀具是很必要的。镍基合金加工硬化,具有磨蚀性,且在高温下非常坚硬。它的可机加工性和不锈钢相同。钽非常的加工硬化,具有可延性且柔软。它生成很差的表面光洁性且刀具磨损非常大。钛和它的合金导热性(的确,是所有金属中最低的),因此引起明显的温度升高和积屑瘤。它们是难机加工的。钨易脆,坚硬,且具有磨蚀性,因此尽管它的性能在高温下能大大提高,但它的机加工性仍很低。锆有很好的机加工性。然而,因为有爆炸和火种的危险性,它要求有一个冷却性质好的切削液。20.9.3 各种材料的机加工性石墨具有磨蚀性。它要求硬的、尖的,具有耐蚀性的刀具。塑性塑料通常有低的导热性,低的弹性模数和低的软化温度。因此,机加工热塑性塑料要求有正前角的刀具(以此降低切削力),还要求有大的后角,小的切削和走刀深的,相对高的速度和工件的正确支承。刀具应该很尖。切削区的外部冷却也许很必要,以此来防止切屑变的有黏性且粘在刀具上。有了空气流,汽雾或水溶性油,通常就能实现冷却。在机加工时,残余应力也许能生成并发展。为了解除这些力,已机加工的部分要在()的温度范围内冷却一段时间,然而慢慢地无变化地冷却到室温。热固性塑料易脆,并且在切削时对热梯度很敏感。它的机加工性和热塑性塑料的相同。因为纤维的存在,加强塑料具有磨蚀性,且很难机加工。纤维的撕裂、拉出和边界分层是非常严重的问题。它们能导致构成要素的承载能力大大下降。而且,这些材料的机加工要求对加工残片仔细切除,以此来避免接触和吸进纤维。随着纳米陶瓷(见8.2.5节)的发展和适当的参数处理的选择,例如塑性切削(见22.4.2节),陶瓷器的可机加工性已大大地提高了。金属基复合材料和陶瓷基复合材料很能机加工,它们依赖于单独的成分的特性,比如说增强纤维或金属须和基体材料。20.9.4 热辅助加工在室温下很难机加工的金属和合金在高温下能更容易地机加工。在热辅助加工时(高温切削),热源一个火把,感应线圈,高能束流(例如雷射或电子束),或等离子弧被集中在切削刀具前的一块区域内。好处是:(a)低的切削力。(b)增加的刀具寿命。(c)便宜的切削刀具材料的使用。(d)更高的材料切除率。(e)减少振动。也许很难在工件内加热和保持一个不变的温度分布。而且,工件的最初微观结构也许被高温影响,且这种影响是相当有害的。尽管实验在进行中,以此来机加工陶瓷器如氮化矽,但高温切削仍大多数应用在高强度金属和高温度合金的车削中。小结通常,零件的可机加工性能是根据以下因素来定义的:表面粗糙度,刀具的寿命,切削力和功率的需求以及切屑的控制。材料的可机加工性能不仅取决于起内在特性和微观结构,而且也依赖于工艺参数的适当选择与控制。
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