0235-摩托車前減震器的設計【全套13張CAD圖】

0235-摩托車前減震器的設計【全套13張CAD圖】,全套13張CAD圖,摩托,車前,減震器,設計,全套,13,cad 摩托車前減震器的設計 摘要：減震器又稱緩沖器，是安裝在摩托車懸掛裝置上的一個重要零件。摩托車懸掛裝置不僅決定了乘坐的舒適度，而且還是決定其運動性能的重要部件。而減震器的功能就是緩和由于路面不平引起的沖擊，衰減摩托車的振動；提高乘坐舒適性，保護貨載；減低車體各部分的運應力，增加零件的壽命；加強輪胎的附著性，有助于摩托車的操縱性、穩(wěn)定性。 本文所設計的摩托車前減震器采用液力式減震方式，其工作行程為50 mm。通過彈簧減震為主。設計時減震彈簧采用組合式彈簧，由兩段節(jié)距不同的等節(jié)距圓柱彈簧組成。在通常振動范圍內(nèi)，彈簧柔軟，當車輛受到?jīng)_擊時，彈簧變硬，有足夠的能力吸收這種沖擊能量。減震器的機能是利用流體通過減震桿上的孔、隙產(chǎn)生的粘性阻力。和固體摩托減震相比，利用液體紊流阻力的減震器，在一定阻尼力和吸收能量的條件下，質量小，尺寸小，并在相當?shù)姆秶鷥?nèi)具有能任意規(guī)定阻尼力對工作速度的關系等優(yōu)點。 在設計過程中對前減震器的工作原理進行了說明，并確定了工作部分主要零件的相關參數(shù)，在已知條件的前提下分別對減震彈簧直徑和自由高度，阻尼孔的數(shù)量和直徑等進行設計計算。 關鍵詞：前減震器 彈簧 阻尼 設計 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 resistance Keywords ：before the shock absorber damping spring damper design . 畢業(yè)設計（論文）開題報告 題目 摩托車前減震器的設計 一、 選題的依據(jù)及意義： 在我們常用的二輪摩托車中為了緩和沖擊和震動，保證行車平順性的要求，除了采用具有彈性的充氣輪胎外，在懸掛裝置（連接車架和車輪的零部件的總稱）中應設計有必要的彈性元件和衰減振動的元件。當車輪受到的沖擊和振動傳給彈性元件后，彈性元件將它們變?yōu)榫徍偷恼駝?，即振幅較大、頻率較低（＜每分鐘80次），使人們能適應其振動頻率，再加上阻尼器將迅速衰減振幅、吸收其能量、防止共振，并控制車身振動加速不得高于0.5～0.6g。同樣，為了滿足行駛穩(wěn)定性、乘坐舒適性兩方面的要求，于是開始采用減震系統(tǒng)。 前減震器用于摩托車前懸掛裝置，它的作用主要是減輕前輪遇到障礙受到?jīng)_擊時傳至車架的沖擊負荷和震動。通過對液力減震器的分析，它的液壓平衡環(huán)節(jié)多，故障頻繁，易污染，故決定選擇彈簧液力阻尼式減震器。彈簧液力阻尼式減震器的減震效果好，制造成本較低，目前國內(nèi)外摩托車減震器廣泛采用這種形式的減震器。 二、國內(nèi)外研究概況及發(fā)展趨勢（含文獻綜述）： 1885年，德國工程師戴姆勒將其改進的汽油機安裝在車身和車輪均用木材制成上的三輪車上發(fā)明了世界上第一輛摩托車。但由于木制車身及車輪不耐顛簸，限制了車速（僅12km/h），所以戴姆勒的摩托車并無實用價值。 1910年開始在前輪采用金屬彈簧張力的雙向、平行連接裝置，30年代便發(fā)明了利用管內(nèi)粘性機油的液壓減震器。1955年以后前輪懸掛裝置就采用了伸縮管式和底部杠桿式兩類前叉。在伸縮桶式前叉、望遠鏡式的二個桶內(nèi)由于有螺旋彈簧和油缸，加工精度要求高，生產(chǎn)效率低，阻礙了發(fā)展和應用。1960年二輪摩托車的大量生產(chǎn)，底部杠桿式前叉處于全盛時期，該系統(tǒng)具有結構簡單、價格低廉等優(yōu)點。后來伸縮式前叉又重新上市，用于當時盛行一時的兩輪的賽車上，伸縮式前叉優(yōu)秀的行駛性能方被證明。因此，大批量生產(chǎn)的摩托車也竟相采用伸縮式前叉，而且由于加工技術的提高，伸縮桶式前叉也得到了保證。所以，至今為止，各種型式的兩輪摩托車都采用伸縮筒式前叉。同時，后輪懸掛裝置的要求也迫切了，由于全鏈條傳遞驅動力，后輪必須采用長距離的固定方式。所以車體的緩沖僅只在坐墊下面安裝有一金屬彈簧。1950年才開始有正式的后懸掛裝置。最初稱滑栓式，并嘗試采用搖臂式。50年代后半期才確立了搖臂式后懸掛裝置，既是現(xiàn)代兩輪摩托車的后懸掛裝置的基礎。 進入70年代又開發(fā)了裝有單減震器的單減震系統(tǒng)，特別是1973年開始用于越野車之后，公路賽車、大型運動車均很快的采用了這種單減震器后懸掛系統(tǒng)。 我國自1957年7月洪都機械廠成功仿制M72型邊三輪摩托車，揭開了我國生產(chǎn)摩托車的歷史以來，到1987年摩托車生產(chǎn)量為1.2萬輛。改革開放以來，我國摩托車產(chǎn)量得到了飛速增長，品種不斷增多。目前在我國已形成了自己的摩托車生產(chǎn)體系，到1995年的產(chǎn)量超過700萬輛，已成為世界上第一摩托車生產(chǎn)國。與摩托車生產(chǎn)相適應的減震器產(chǎn)量已達到1500萬支，能生產(chǎn)9大系列50余種型號，基本滿足了我國摩托車生產(chǎn)的發(fā)展需要，部分產(chǎn)品已達到國際同類產(chǎn)品水平，為我國摩托車工業(yè)的技術水平提高和發(fā)展打下了基礎。 三、研究內(nèi)容及實驗方案： 1.研究內(nèi)容 1）減震器整體方案分析與設計 2) 摩托車減震器系統(tǒng)的彈簧特性 ①摩托車懸掛裝置的撓度 ②摩托車懸掛裝置的理想彈簧特性 ③摩托車懸掛裝特性置的實際彈簧 3) 彈簧的材料及工藝 ①彈簧材料的選用 ②彈簧的制造工藝 4) 減震器的速度特性及阻尼力 ①節(jié)流閥的壓力特性 ②減震器的速度特性 ③減震器阻尼力產(chǎn)生原理 ④阻尼調節(jié)裝置 2.實驗方案 前減震器有很多種，常見的有彈簧空氣阻尼式前叉、彈簧液力阻尼式減震器、油—氣伸縮式減震器等。 其中彈簧空氣阻尼式前叉雖然結構簡單、造價低，但是它是以活塞管之間的間隙為空氣阻尼的雙向用途減震器，所以起減震效果不及其他結構的理想。然而油—氣伸縮式減震器的減震效果都很佳，甚至達到理想的減震效果，增加了舒適性和安全性。但其結構復雜，造價昂貴，大都用在大型或高級二輪車上，如雅馬哈XJ750型、XJ750EⅡ，鈴木GS750型賽車等。 而彈簧液力阻尼式減震器不但結構簡單，造價低，而且減震效果好，所以我將采用彈簧液力阻尼式前減震器作為我的實驗方案。 四、目標、主要特色及工作進度 1. 目 標： 1) 通過這次畢業(yè)設計將大學所學的基礎知識綜合運用起來，以此提高自己的綜合素質以更好更快的適應社會發(fā)展的需求，并且學會在以后的工作中能獨立完成設計工作。 2) 用AUTO/CAD畫出相關的零件圖及裝配圖 3) 寫出設計的相關原理及計算過程 2.主要特色： 采用裝有根據(jù)載荷狀態(tài)調節(jié)衰減力的裝置并在相當?shù)姆秶鷥?nèi)具有能任意規(guī)定阻尼力對工作速度的關系的減震系統(tǒng)，在高速行駛時調至較高的衰減力，很容易得到高速行駛穩(wěn)定性；在平常行駛時，調至較低的衰減力，即可得到較好的乘坐舒適性。 ⒊工作進度： 1． 收集、查閱、分析有關資料，外文資料翻譯(6000字符)，撰寫開題報告； 第1周—第4周 2．減震器整體方案分析與設計； 第5周—第6周 3．計算確定工作部分主要零件的相關參數(shù)； 第7周—第8周 4．設計減震器部件裝配圖，拆繪主要零件圖（折合A1圖4張）； 第9周—第12周 5．設計部件檢驗基準書； 第13周 6．撰寫畢業(yè)論文、畢業(yè)設計審查、畢業(yè)答辯。 第14周—第17周 五、參考文獻 [1]．莊志等編著. 摩托車理論與機構設計. 武漢：武漢測繪科技大學出版社，1991.1 [2]．成大先主編. 機械設計手冊. 單行本. 北京：化學工業(yè)出版社,2004.1 [3]． 張龍全. 摩托車減震器彈簧的設計計算及工作圖的繪制.摩托車技術2004年第5期 [4]．天之. 淺談摩托車用減震器. 摩托車2003年第5期 [5]. 劉愛紅.純閥片阻尼結構在摩托車后減震器的研究及應用.摩托車技術2006年第7 期 [6]. 劉愛紅. 后減震器阻尼閥系的研究與分析. 摩托車技術2004年第1期 [7]．Soon Kil Hong. Advancement of Aerospace Education and collabovative Recersh in the 21th century. HanKVK:Aviation Vniversity. [8]. 廖念釗等. 互換性與技術測量. 北京：中國計量出版社，2011.2·第5版 圖 紙 清 單 序號 圖號 圖紙名稱 圖幅 1 QJZQ-000 減震器裝配圖 A1 2 QJZQ-001 檢驗基準書 A2 3 QJZQ-000-01 貯油筒零件圖 A2 4 QJZQ-000-02 減震彈簧零件圖 A2 5 QJZQ-000-03 工作缸裝配圖 A2 6 QJZQ-000-04 減震桿零件圖 A2 7 QJZQ-000-05 導向套零件圖 A3 8 QJZQ-000-06 活塞環(huán)零件圖 A4 9 QJZQ-000-07 端蓋零件圖 A4 10 QJZQ-000-08 壓縮彈簧零件圖 A4 11 QJZQ-000-09 油封零件圖 A4 12 QJZQ-000-10 中間套零件圖 A4 外語文獻翻譯 摘自: 《制造工程與技術（機加工）》（英文版） 《Manufacturing Engineering and Technology—Machining》 機械工業(yè)出版社 2004年3月第1版 美 s. 卡爾帕基安(Serope kalpakjian) s.r 施密德(Steven R.Schmid) 著 原文： 20.9 MACHINABILITY The 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 Steels Because 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 “l(fā)ow 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 Materials Graphite 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 Machining Metals 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 heat—a torch, induction coil, high-energy beam (such as laser or electron beam), or plasma arc—is 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. SUMMARY Machinability 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. 譯文： 20.9 可機加工性 一種材料的可機加工性通常以四種因素的方式定義： 1、 分的表面光潔性和表面完整性。 2、刀具的壽命。 3、切削力和功率的需求。 4、切屑控制。 以這種方式，好的可機加工性指的是好的表面光潔性和完整性，長的刀具壽命，低的切削力和功率需求。關于切屑控制，細長的卷曲切屑，如果沒有被切割成小片，以在切屑區(qū)變的混亂，纏在一起的方式能夠嚴重的介入剪切工序。 因為剪切工序的復雜屬性，所以很難建立定量地釋義材料的可機加工性的關系。在制造廠里，刀具壽命和表面粗糙度通常被認為是可機加工性中最重要的因素。盡管已不再大量的被使用，近乎準確的機加工率在以下的例子中能夠被看到。 20.9.1 鋼的可機加工性 因為鋼是最重要的工程材料之一（正如第5章所示），所以他們的可機加工性已經(jīng)被廣泛地研究過。通過宗教鉛和硫磺，鋼的可機加工性已經(jīng)大大地提高了。從而得到了所謂的易切削鋼。 二次硫化鋼和二次磷化鋼 硫在鋼中形成硫化錳夾雜物（第二相粒子），這些夾雜物在第一剪切區(qū)引起應力。其結果是使切屑容易斷開而變小，從而改善了可加工性。這些夾雜物的大小、形狀、分布和集中程度顯著的影響可加工性?；瘜W元素如碲和硒，其化學性質與硫類似，在二次硫化鋼中起夾雜物改性作用。 鋼中的磷有兩個主要的影響。它加強鐵素體，增加硬度。越硬的鋼，形成更好的切屑形成和表面光潔性。需要注意的是軟鋼不適合用于有積屑瘤形成和很差的表面光潔性的機器。第二個影響是增加的硬度引起短切屑而不是不斷的細長的切屑的形成，因此提高可加工性。 含鉛的鋼 鋼中高含量的鉛在硫化錳夾雜物尖端析出。在非二次硫化鋼中，鉛呈細小而分散的顆粒。鉛在鐵、銅、鋁和它們的合金中是不能溶解的。因為它的低抗剪強度。因此，鉛充當固體潤滑劑并且在切削時，被涂在刀具和切屑的接口處。這一特性已經(jīng)被在機加工鉛鋼時，在切屑的刀具面表面有高濃度的鉛的存在所證實。 當溫度足夠高時—例如，在高的切削速度和進刀速度下—鉛在刀具前直接熔化，并且充當液體潤滑劑。除了這個作用，鉛降低第一剪切區(qū)中的剪應力，減小切削力和功率消耗。鉛能用于各種鋼號，例如10XX，11XX，12XX，41XX等等。鉛鋼被第二和第三數(shù)碼中的字母L所識別（例如，10L45）。（需要注意的是在不銹鋼中，字母L的相同用法指的是低碳，提高它們的耐蝕性的條件）。 然而，因為鉛是有名的毒素和污染物，因此在鋼的使用中存在著嚴重的環(huán)境隱患（在鋼產(chǎn)品中每年大約有4500噸的鉛消耗）。結果，對于估算鋼中含鉛量的使用存在一個持續(xù)的趨勢。鉍和錫現(xiàn)正作為鋼中的鉛最可能的替代物而被人們所研究。 脫氧鈣鋼 一個重要的發(fā)展是脫氧鈣鋼，在脫氧鈣鋼中矽酸鈣鹽中的氧化物片的形成。這些片狀，依次減小第二剪切區(qū)中的力量，降低刀具和切屑接口處的摩擦和磨損。溫度也相應地降低。結果，這些鋼產(chǎn)生更小的月牙洼磨損，特別是在高切削速度時更是如此。 不銹鋼 奧氏體鋼通常很難機加工。振動能成為一個問題，需要有高硬度的機床。然而，鐵素體不銹鋼有很好的可機加工性。馬氏體鋼易磨蝕，易于形成積屑瘤，并且要求刀具材料有高的熱硬度和耐月牙洼磨損性。經(jīng)沉淀硬化的不銹鋼強度高、磨蝕性強，因此要求刀具材料硬而耐磨。 鋼中其它元素在可機加工性方面的影響 鋼中鋁和矽的存在總是有害的，因為這些元素結合氧會生成氧化鋁和矽酸鹽，而氧化鋁和矽酸鹽硬且具有磨蝕性。這些化合物增加刀具磨損，降低可機加工性。因此生產(chǎn)和使用凈化鋼非常必要。 根據(jù)它們的構成，碳和錳鋼在鋼的可機加工性方面有不同的影響。低碳素鋼（少于0.15%的碳）通過形成一個積屑瘤能生成很差的表面光潔性。盡管鑄鋼的可機加工性和鍛鋼的大致相同，但鑄鋼具有更大的磨蝕性。刀具和模具鋼很難用于機加工，他們通常再煅燒后再機加工。大多數(shù)鋼的可機加工性在冷加工后都有所提高，冷加工能使材料變硬并且減少積屑瘤的形成。 其它合金元素，例如鎳、鉻、鉗和釩，能提高鋼的特性，減小可機加工性。硼的影響可以忽視。氣態(tài)元素比如氫和氮在鋼的特性方面能有特別的有害影響。氧已經(jīng)被證明了在硫化錳夾雜物的縱橫比方面有很強的影響。越高的含氧量，就產(chǎn)生越低的縱橫比和越高的可機加工性。 選擇各種元素以改善可加工性，我們應該考慮到這些元素對已加工零件在使用中的性能和強度的不利影響。例如，當溫度升高時，鋁會使鋼變脆（液體—金屬脆化，熱脆化，見1.4.3節(jié)），盡管其在室溫下對力學性能沒有影響。 因為硫化鐵的構成，硫能嚴重的減少鋼的熱加工性，除非有足夠的錳來防止這種結構的形成。在室溫下，二次磷化鋼的機械性能依賴于變形的硫化錳夾雜物的定位（各向異性）。二次磷化鋼具有更小的延展性，被單獨生成來提高機加工性。 20.9.2 其它不同金屬的機加工性 盡管越軟的品種易于生成積屑瘤，但鋁通常很容易被機加工，導致了很差的表面光潔性。高的切削速度，高的前角和高的后角都被推薦了。有高含量的矽的鍛鋁合金鑄鋁合金也許具有磨蝕性，它們要求更硬的刀具材料。尺寸公差控制也許在機加工鋁時會成為一個問題，因為它有膨脹的高導熱系數(shù)和相對低的彈性模數(shù)。 鈹和鑄鐵相同。因為它更具磨蝕性和毒性，盡管它要求在可控人工環(huán)境下進行機加工。 灰鑄鐵普遍地可加工，但也有磨蝕性。鑄造無中的游離碳化物降低它們的可機加工性，引起刀具切屑或裂口。它需要具有強韌性的工具。具有堅硬的刀具材料的球墨鑄鐵和韌性鐵是可加工的。 鈷基合金有磨蝕性且高度加工硬化的。它們要求尖的且具有耐蝕性的刀具材料并且有低的走刀和速度。 盡管鑄銅合金很容易機加工，但因為鍛銅的積屑瘤形成因而鍛銅很難機加工。黃銅很容易機加工，特別是有添加的鉛更容易。青銅比黃銅更難機加工。 鎂很容易機加工，鎂既有很好的表面光潔性和長久的刀具壽命。然而，因為高的氧化速度和火種的危險（這種元素易燃），因此我們應該特別小心使用它。 鉗易拉長且加工硬化，因此它生成很差的表面光潔性。尖的刀具是很必要的。 鎳基合金加工硬化，具有磨蝕性，且在高溫下非常堅硬。它的可機加工性和不銹鋼相同。 鉭非常的加工硬化，具有可延性且柔軟。它生成很差的表面光潔性且刀具磨損非常大。 鈦和它的合金導熱性(的確，是所有金屬中最低的)，因此引起明顯的溫度升高和積屑瘤。它們是難機加工的。 鎢易脆，堅硬，且具有磨蝕性，因此盡管它的性能在高溫下能大大提高，但它的機加工性仍很低。 鋯有很好的機加工性。然而，因為有爆炸和火種的危險性，它要求有一個冷卻性質好的切削液。 20.9.3 各種材料的機加工性 石墨具有磨蝕性。它要求硬的、尖的，具有耐蝕性的刀具。 塑性塑料通常有低的導熱性，低的彈性模數(shù)和低的軟化溫度。因此，機加工熱塑性塑料要求有正前角的刀具（以此降低切削力），還要求有大的后角，小的切削和走刀深的，相對高的速度和工件的正確支承。刀具應該很尖。 切削區(qū)的外部冷卻也許很必要，以此來防止切屑變的有黏性且粘在刀具上。有了空氣流，汽霧或水溶性油，通常就能實現(xiàn)冷卻。在機加工時，殘余應力也許能生成并發(fā)展。為了解除這些力，已機加工的部分要在（）的溫度范圍內(nèi)冷卻一段時間，然而慢慢地無變化地冷卻到室溫。 熱固性塑料易脆，并且在切削時對熱梯度很敏感。它的機加工性和熱塑性塑料的相同。 因為纖維的存在，加強塑料具有磨蝕性，且很難機加工。纖維的撕裂、拉出和邊界分層是非常嚴重的問題。它們能導致構成要素的承載能力大大下降。而且，這些材料的機加工要求對加工殘片仔細切除，以此來避免接觸和吸進纖維。 隨著納米陶瓷（見8.2.5節(jié)）的發(fā)展和適當?shù)膮?shù)處理的選擇，例如塑性切削（見22.4.2節(jié)），陶瓷器的可機加工性已大大地提高了。 金屬基復合材料和陶瓷基復合材料很能機加工，它們依賴于單獨的成分的特性，比如說增強纖維或金屬須和基體材料。 20.9.4 熱輔助加工 在室溫下很難機加工的金屬和合金在高溫下能更容易地機加工。在熱輔助加工時（高溫切削），熱源—一個火把，感應線圈，高能束流（例如雷射或電子束），或等離子弧—被集中在切削刀具前的一塊區(qū)域內(nèi)。好處是：（a）低的切削力。（b）增加的刀具壽命。（c）便宜的切削刀具材料的使用。（d）更高的材料切除率。（e）減少振動。 也許很難在工件內(nèi)加熱和保持一個不變的溫度分布。而且，工件的最初微觀結構也許被高溫影響，且這種影響是相當有害的。盡管實驗在進行中，以此來機加工陶瓷器如氮化矽，但高溫切削仍大多數(shù)應用在高強度金屬和高溫度合金的車削中。 小結 通常，零件的可機加工性能是根據(jù)以下因素來定義的：表面粗糙度，刀具的壽命，切削力和功率的需求以及切屑的控制。材料的可機加工性能不僅取決于起內(nèi)在特性和微觀結構，而且也依賴于工藝參數(shù)的適當選擇與控制。