【正文】 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 builtup 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 nonresulfurized 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 and is smeared over the toolchip interface during cutting. This behavior has been verified by the presence of high concentrations of lead on the toolside face of chips when machining leaded steels.When the temperature is sufficiently highfor instance, at high cutting speeds and feeds —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 wellknown 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 (leadfree steels). Bismuth and tin are now being investigated as possible substitutes for lead in steels.CalciumDeoxidized Steels. An important development is calciumdeoxidized steels, in which oxide flakes of calcium silicates (CaSo) are formed. These flakes, in turn, reduce the strength of the secondary shear zone, decreasing toolchip 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 builtup edge, and require tool materials with high hot hardness and craterwear resistance. Precipitationhardening stainless steels are strong and abrasive, requiring hard and abrasionresistant 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 bine with oxygen to form aluminum oxide and silicates, which are hard and abrasive. These pounds 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 position. Plain lowcarbon steels (less than % C) can produce poor surface finish by forming a builtup 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 builtup 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。謝謝大家！　　 附錄 1The machinability of materialThe machinability of a material usually defined in terms of four factors:（1）Surface finish and integrity of the machined part。我在設計過程中出現(xiàn)了很多錯誤，也給老師帶來很多麻煩，但老師一直很細心的幫我指正出來，感謝歐老師的細心指導以及這段時間來對我的教育?？偟膩碚f，這次設計，使我們在基本理論的綜合運用及正確解決實際問題等方面得到了一次較好的訓練。本次課程設計主要經(jīng)歷了兩個階段：第一階段是機械加工工藝規(guī)程設計，第二階段是專用夾具設計。夾具的主要定位元件為 V 形塊與定位塊，因為該定位元件的定位基準為孔的軸線，所以基準重合△B=0，由于存在間隙，定位基準會發(fā)生相對位置的變化即存在基準位移誤差。①鉆孔切削力：查《機床夾具設計手冊》P70 表 36，得鉆削力計算公式： ??式中 P───鉆削力t───鉆削深度, 80mmS───每轉(zhuǎn)進給量, D───麻花鉆直徑, Φ23mmHB───布氏硬度，140HBS 所以 ??=800（N）鉆孔的扭矩： .???式中 S───每轉(zhuǎn)進給量, D───麻花鉆直徑, Φ23mmHB───布氏硬度，140HBS .???= 32 5.1.=1580(N設計時要在滿足精度的前提下提高勞動生產(chǎn)效率，降低勞動強度。 （5）力求結(jié)構(gòu)簡單，裝卸方便。 （3）夾具體應具有良好的加工精度和尺寸穩(wěn)定性。夾具在生產(chǎn)中投入使用時要承受多種力度的作用，所以工裝夾具應具備足夠的強度和剛度。（3）設計的夾具怎樣排削；此次加工利用麻花鉆和擴刀、鉸刀，排削通過鉆模板與工件之間的間隙排削。 （3）能擴大機床的使用范圍 （4）能降低成本 在批量生產(chǎn)后使用夾具后，由于勞動生產(chǎn)率的提高，使用技術(shù)等級較低的工人以及廢品率下降等原因，明顯的降低了成本夾具制造成本分攤在一批工件上，沒個工件制造的成本是極少的，遠遠小于由于提高勞動生產(chǎn)率而降低的成本，元件批量越大使用夾具所取得的經(jīng)濟效應就越大。，一般鉸鏈壓板、螺釘、夾緊裝置等。（2）導向 如銑床夾具中的鉆模板與鉆套，能迅速的確定鉆頭的位置，并引導其進行鉆削，導向元件制成模板形成故鉆床夾具長稱為鉆模、鏜床夾具（鏜模）也是具有導向的功能的。（2）夾緊 工件定位后將其固定，使其在加工過程中保持定位位置不錯的操作。同時也擴大各種機床使用范圍必不可少重要手段。在成批、大量生產(chǎn)中，工件的裝夾是通過機床夾具來實現(xiàn)的。當工件定位后，為了避免在加工中受到切削力、重力等的作用而破壞定位，還應該用一定的機構(gòu)或裝置將工件加以固定。在加工中除了需要機床、刀具、量具之外，成批生產(chǎn)時還要用機床夾具。故校驗合格。由于是對稱銑，選較小量 f= mm/z。（6）計算基本工時tm＝L/ Vf=(32+80)/475=。查《切削手冊》表 ，壽命 T=180min（4）計算切削速度 查得 Vc＝98mm/s，則 n=439r/min,Vf=490mm/s據(jù) XA6132 銑床參數(shù)，選擇