机械制造及自动化毕业设计外文翻译.doc

摩托车前减震器的设计【12张CAD图纸和说明书】

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目   录
1  绪论………………………………………………………………………………(1)
2  总体方案设计
2.1 研究内容及实验方案…………………………………………………………(3)
   2.2 工作原理………………………………………………………………………(3)
3  摩托车减震器的功能和结构形式
3.1 减震器的功能…………………………………………………………………(5)
3.2 摩托车前减震器的结构形式…………………………………………………(5)
3.2.1 弹簧空气式…………………………………………………………………(5)
3.2.2 单筒伸缩式…………………………………………………………………(5)
3.2.3 双筒伸缩式…………………………………………………………………(6)
3.2.4 油—汽伸缩式………………………………………………………………(6)
3.2.5 防下沉伸缩式前减震器……………………………………………………(7)
4  摩托车后减震器的主要特性
4.1 摩托车减震器的弹簧特性……………………………………………………(8)
4.1.1 摩托车悬挂装置的挠度……………………………………………………(8)
4.1.2 摩托车悬挂装置的理想弹簧特性…………………………………………(9)
   4.2 摩托车减震弹簧的材料及工艺………………………………………………(10)
   4.2.1 弹簧材料的种类……………………………………………………………(10)
 4.2.2弹簧制造工艺………………………………………………………………(11)
   4.3 摩托车减震器的阻尼特性……………………………………………………(11)
4.3.1 阻力——速度特性…………………………………………………………(11)
   4.3.2 阻力——位移特性…………………………………………………………(13)
   4.4 摩托车减震器的阻尼力………………………………………………………(14)
 4.4.1 复原行程阻尼力计算………………………………………………………(14)
4.4.2 压缩行程阻尼力计算………………………………………………………(16)
4.4.3 减震器额定阻力……………………………………………………………(17)
4.4.4 示功图………………………………………………………………………(17)
5  摩托车后减震器的结构设计
5.1 减震器的主要零件结构参数…………………………………………………(19)
5.1.1 工作缸径的确定……………………………………………………………(19)
 5.1.2 贮油筒径的确定……………………………………………………………(19)
 5.1.3 减震器基长的确定…………………………………………………………(20)
 5.1.4 工作行程……………………………………………………………………(20)   
5.2 摩托车后减震器主要零件的结构设计………………………………………(21)
 5.2.1 弹簧的结构尺寸设计和计算………………………………………………(21)
5.2.2 减震弹簧按实际工作状态绘图的优点……………………………………(24)
 5.2.3 减震器减震杆杆的设计……………………………………………………(24)
5.2.4 活塞环设计计算……………………………………………………………(26)
 5.2.5 贮 油 筒……………………………………………………………………(29)
5.2.6 导向套(衬套)……………………………………………………………(30)
 5.2.7 油封…………………………………………………………………………(31)
6  摩托车减震器主要零部件的组装工艺
   6.1 装配工艺原则…………………………………………………………………(34)
   6.2 装配工艺流程…………………………………………………………………(34)
6.2.1 活塞、活塞杆的装配………………………………………………………(34)
6.2.2 前减震器总成装配…………………………………………………………(35)
7  摩托车后减震器的检验与质量评定
7.1 出厂检验………………………………………………………………………(36)
 7.2 减震器型式检验………………………………………………………………(36)
 7.3 减震器质量等级评定方法……………………………………………………(37)
8  总结………………………………………………………………………………(38)
参考文献……………………………………………………………………………(39)
致    谢……………………………………………………………………………(40)
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

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 resistance
Keywords :before the shock absorber   damping spring    damper    design
1  绪论
世界上第一个有记载、比较简单的减震器是1897年由两个姓吉明的人发明的。他们把橡胶块与叶片弹簧的端部相连,当悬架被完全压缩时,橡胶减震块就碰到连接在汽车大梁上的一个螺栓,产生止动。这种减震器在很多现代汽车悬架上仍有使用,但其减震效果很小。
机动脚踏两用车实际上是内燃机技术与自行车技术相结合的产物,它开辟了摩托车的实用时代。随着摩托车的快速和适应野外行驶的需要,必须提高车辆对路面的缓冲能力。早在1899年,贝劳摩托车上开始用了弹性后悬挂装置,后来比利时型摩托车采用了前轮弹性悬挂,以及英吉安C摩托车采用的前、后轮弹性悬挂均可算作早期摩托车悬挂装置的杰出代表。
特别是二轮摩托车在操作性、稳定性、舒适性方面,与悬挂装置有着重要的关系。1990年就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。1995年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。在伸缩筒式前叉、望远镜式的二个筒内由于有螺旋弹簧和油缸,加工精度要求高,生产效率很低,阻碍了发展和应用。1960年二轮摩托车的大批量生产,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。后来伸缩筒式前叉又重新上市,用于当时盛行一时的两轮赛车上,伸缩筒式前叉优秀的行驶性能方被充分证明。因此,大批量生产的摩托车也竞相采用伸缩筒式前叉,而且由于加工技术的提高,伸缩筒式生产精度也得到了保证。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。
1910年开始对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。最初称为滑栓式,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,即是现代两轮摩托车的后悬挂装置的基础。
同样,为了提高行驶稳定性、乘坐舒适性,后轮行程逐年增大,减震器组件行程在结构上受到了限制。因此前倾后减震器、后减震器组件安装位置前移等,用以增大杠杆比的方法增大后抡幸臣。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年开始用与越野车之后,公路赛车,大型运动车均很快地采用了这种单减震器后悬挂系统。
   两轮摩托车,其发动机排量从50的家用车到1500的大型旅游车。对悬挂装置,根据不同排量、不同用途的车辆的要求,其设计的方法各有不同,但又存在有共同之处,即最近的悬挂装置将行驶稳定性、操终性、舒适性都放在主要位置上。
大部分两轮车还是采用液压式伸缩式前叉,除了要求完全吸收较大的冲击,提高结构刚度外,最后采用经四氟乙烯(teflon)处理的金属套筒用作滑动表面,大大的减小了伸缩筒运动时产生的摩擦。
两轮车增大车轮行程就具有良好的舒适性,最近前叉行程增大为140~180mm,越野车可达300mm左右,且具有降低弹簧刚度、阻尼力的倾向,向提高稳定性的方向发展。当然在不断增大车轮运动行程,两轮车在一人或二人乘坐的不同载荷条件下,车体下沉量是不同的。特别是制动时由于重心前移,车体姿势变化更大。采用空气调节式的油气悬挂装置或抗“点头”装置的悬挂装置,可以有效地防止紧急制动时的车体前倾变化。
自从20世纪60年代开始,几乎每年都有几十项减震器专利出现,表1是《汽车文摘》摘录的汽车悬架减震器专利技术的统计,其中在美国申请的专利技术尤为多,且专利申请人大多是日本的公司和个人。国内外减震器产品在许多方面存在着较大的差距:(1)产品的结构与性能方面(减震器的可拆性与速度特性间的差距);(2)制造技术与工艺设备方面(原材料、减震油、橡胶制品、连杆制造工艺、冲压工艺、粉末冶金制造工艺、贮油筒制造工艺等方面的差距);(3)测试手段方面;(4)总成装配方面,此外,由于轿车减震器是作为一个不可拆元件整体出厂销售的,一旦其中某个小零件发生失效,整个减震器也就报废了,因而减震器技术的发展和研究应该成为我国汽车行业发展和水平提高的一个重要课题。



我国自1957年7月洪都机械厂成功地仿制M72型边三轮摩托车,揭开了我
国生产摩托车的历史以来,到1978年摩托车生产量为1.2万辆。改革开放以来,
我国摩托车生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摩
托车工业生产体系,到1995年的生产量超过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,部分产品已达到了国际同类产品水平,为我国摩托车工业的技术水平提高和发展打下了基础。


2  总体方案设计
2.1研究内容及实验方案
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
①摩托车悬挂装置的挠度
      ②摩托车悬挂装置的理想弹簧特性
      ③摩托车悬挂装特性置的实际弹簧
(3) 弹簧的材料及工艺
①弹簧材料的选用
②弹簧的制造工艺
(4) 减震器的速度特性及阻尼力
①节流阀的压力特性
②减震器的速度特性
③减震器阻尼力产生原理
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、XJ750EⅡ,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。

内容简介:
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
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