【正文】 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。 tool wear is high.Titanium and its alloys。 see Section ), 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. Machinability of Various Other Metals Aluminum is generally very easy to machine, although the softer grades tend to form a builtup edge, resulting in poor surface finish. High cutting speeds, high rake angles, and high relief angles are remended. Wrought aluminum alloys with high silicon content and cast aluminum alloys may be abrasive。 Force and power requirements。這時(shí)，通過扇形齒輪、齒條、撥叉使軸4與孔盤5從右向左移到原位，則孔盤5推動(dòng)三組齒桿10連同撥叉撥動(dòng)三個(gè)滑移齒輪移動(dòng)，改變齒輪嚙合對，達(dá)到變速目的。在孔盤5不同直徑的圓周上，有大小不等的兩種孔眼，以供齒桿6,8,10右端階臺銷插入。圖51 操縱機(jī)構(gòu)示意圖變速時(shí)，將變速桿1扳向左邊，使固定在同軸上的扇形齒輪2順時(shí)針轉(zhuǎn)動(dòng)，帶動(dòng)與其嚙合的齒條右移，通過齒條右端的撥叉，撥動(dòng)軸4及固定在右端的變速孔盤5向右移動(dòng)，使變速孔盤的孔眼與相配合的齒桿全部脫離。集中式操縱機(jī)構(gòu)由一個(gè)或兩個(gè)操作件完成一個(gè)變速過程，操作方便，但結(jié)構(gòu)較復(fù)雜。查《機(jī)械設(shè)計(jì)課程設(shè)計(jì)手冊（第3版）》表66中知對于軸承7314C的基本額定靜載荷，基本額定動(dòng)載荷,軸承的預(yù)期壽命為。則：一對軸承的當(dāng)量動(dòng)載荷軸承壽命1 軸Ⅵ右端的滾動(dòng)軸承7014C的壽命計(jì)算查《機(jī)械設(shè)計(jì)課程設(shè)計(jì)手冊（第3版）》表66中知對于軸承7014C的基本額定靜載荷，基本額定動(dòng)載荷,軸承的預(yù)期壽命為。軸承壽命所以選用軸承N314E可以滿足要求。由于，故由《機(jī)械設(shè)計(jì)》表135知X=1，Y=0。則：當(dāng)量動(dòng)載荷軸承壽命所以選用7013C軸承不符合壽命要求，故改選軸承為軸承7313C，并重新計(jì)算軸承壽命。軸承壽命所以選用軸承N409E可以滿足要求。由于軸Ⅳ的軸向載荷很小，故由《機(jī)械設(shè)計(jì)》表135知X=1，Y=0。由于軸Ⅳ的軸向載荷很小，故由《機(jī)械設(shè)計(jì)》表135知X=1，Y=0。則：當(dāng)量動(dòng)載荷軸承壽命所以選用6007軸承不符合壽命要求，故改選軸承為軸承6307，并重新計(jì)算軸承壽命。軸承壽命所以選用軸承6208可以滿足要求。由于軸Ⅲ的軸向載荷很小，故由《機(jī)械設(shè)計(jì)》表135知X=1，Y=0。則：當(dāng)量動(dòng)載荷軸承壽命所以選用6005軸承不符合壽命要求，故改選軸承為圓柱滾子軸承N207E，并重新計(jì)算軸承壽命。軸承壽命所以選用6205軸承可以滿足要求。由于軸Ⅱ的軸向載荷很小，故由《機(jī)械設(shè)計(jì)》表135知X=1，Y=0。由于軸Ⅰ的軸向載荷很小，故由《機(jī)械設(shè)計(jì)》表135知X=1，Y=0。則：當(dāng)量動(dòng)載荷軸承壽命軸承6005不符合壽命要求，故改選軸承為滾動(dòng)軸承6405，并重新計(jì)算軸承壽命。(a)(b)(c)(d)(e)圖411 軸Ⅴ的載荷分析圖（1）求軸上載荷①軸的受力分析如圖49（a）所示：②水平面受力與彎矩如圖49（b）所示：③垂直面受力與彎矩如圖49（c）所示：④彎矩合成如圖49（d）所示：⑤扭矩如圖49（e）所示：（2）按彎扭合成強(qiáng)度條件校核軸的危險(xiǎn)面B由得軸的材料為45鋼調(diào)質(zhì)，()，故安全。其它兩個(gè)位置的載荷比中位小，故安全。為了考慮兩者循環(huán)特性的不同，引入折合系數(shù)?！稒C(jī)械設(shè)計(jì)課程設(shè)計(jì)手冊（第三版）》[M].北京：高等教育出版社，2007。由《機(jī)械設(shè)計(jì)》中式1012得：===696Mpa===675Mpa⑧ 計(jì)算：a、試算小齒輪分度圓直徑，代入與中較小的值：≥= =所以滿足滿足接觸疲勞強(qiáng)度要求。設(shè)計(jì)計(jì)算：m≥= mm=為了更好的滿足接觸強(qiáng)度要求。30） 由圖1020d查得大小齒輪的彎曲疲勞極限為，31） 計(jì)算應(yīng)力循環(huán)次數(shù)： 。26） 選用7級精度。 幾何尺寸的計(jì)算：⑦ 計(jì)算分度圓直徑：d= mZ=619=114mmd= mZ=671=426mm⑧ 計(jì)算中心距：a===270mm⑨ 計(jì)算齒輪寬度：b==114=為了防止齒輪因裝配誤差產(chǎn)生軸向錯(cuò)位導(dǎo)致嚙合齒寬減小而增大輪齒單位齒寬的工作載荷，所以將小齒輪齒寬在圓整的基礎(chǔ)上人為地加寬5mm，取B=91mm，B=96mm5第四級多聯(lián)齒輪的計(jì)算：由于多聯(lián)滑移齒輪需要滑移黏合，所以各齒輪對的中心距都相等。20） 計(jì)算大小齒輪的直徑計(jì)算圓周速度為V：V===21） 查圖108得動(dòng)載系數(shù)，由于是直齒輪，22） 由表102查得齒高 h==6 mm=， ，查表104插值得23） 由圖1013插值查得24） 載荷系數(shù)，載荷系數(shù)比小，能滿足彎曲強(qiáng)度要求，不需要校正。20） 由圖1018取彎曲疲勞壽命系數(shù)21） 計(jì)算彎曲疲勞許用應(yīng)力：去彎曲疲勞安全系數(shù)S=. ==360Mpa，==380Mpa。15） 大小齒輪的材料40Cr（調(diào)質(zhì)并表面淬火），硬度為48~55HRC。3）（）齒輪對的計(jì)算：d1= m=396=234mm，d2= m=266=156mm，中心距a==195mm. 齒寬 B1=48mm，B2=53mm。f、 由《機(jī)械設(shè)計(jì)》圖1021e中并按齒面硬度查得小齒輪的接觸疲勞強(qiáng)度極限=1100Mpa；大齒輪的接觸疲勞強(qiáng)度極限=1100Mpah、根據(jù)齒輪的材料、熱處理方法及應(yīng)力循環(huán)次數(shù)查《機(jī)械設(shè)計(jì)》中圖1019取小齒輪的接觸疲勞系數(shù)K=；大齒輪的接觸疲勞系數(shù)為K=載荷系數(shù)i、計(jì)算接觸疲勞許用應(yīng)力：取失效概率為1%，對接觸疲勞強(qiáng)度計(jì)算，由于點(diǎn)蝕破壞發(fā)生后只引起噪聲、振動(dòng)增大，并不立即導(dǎo)致不能繼續(xù)工作的后果，故安全系數(shù)S=。11） 12） 查取齒形系數(shù)，計(jì)算大小齒輪的計(jì)算大小齒輪的，并加以比較：====，小齒輪數(shù)值大。5） 取第二級傳動(dòng)比最大的傳動(dòng)比計(jì)算轉(zhuǎn)矩： 。4第三級傳動(dòng)齒輪對（）的計(jì)算：1） 按傳動(dòng)方案，選用直齒圓柱齒輪傳動(dòng)。小齒輪采用正變位mm；大齒輪采用負(fù)變位mm3第二級多聯(lián)齒輪的計(jì)算：1） 由于多聯(lián)滑移齒輪需要滑移黏合，所以各齒輪對的中心距都相等，因此第一個(gè)多聯(lián)齒輪的模數(shù)為6mm。 按齒面接觸疲勞強(qiáng)度校核：由設(shè)計(jì)計(jì)算公式109a進(jìn)行試算即：d≥（109a）① 確定公式中的各計(jì)算數(shù)值：a、 由設(shè)計(jì)對象知外嚙合時(shí)公式中的正負(fù)號取正號b、 根據(jù)配對齒輪的材料類型為鍛鋼鍛鋼，由《機(jī)械設(shè)計(jì)》表106查得的彈性影響系數(shù)Z= 。mm 其中=；n==698r/min；3） 由圖1021d查得大小齒輪的彎曲疲勞極限為4） 由《機(jī)械設(shè)計(jì)》式1013計(jì)算應(yīng)力循環(huán)次數(shù)得:(已知銑床為兩班制，工作壽命為15年)N=60 njL=6069812830015=310N==105） 由圖1018取彎曲疲勞系數(shù)6） 計(jì)算彎曲疲勞許用應(yīng)力，取彎曲疲勞安全系數(shù)S=，==328Mpa，==336Mpa。10） 計(jì)算齒輪寬度：B1=57mm，B2=52mm。6） 根據(jù)齒數(shù)與模數(shù)重新計(jì)算分度圓直徑=， =，中心距a=，圓整為a=103mm。2. 按齒面接觸強(qiáng)度設(shè)計(jì)按式（1021）試算，即d≥（1021）（1）確定公式內(nèi)的各計(jì)算數(shù)值1)試選Kt=.2)由圖1030選取區(qū)域系數(shù)Zh=.3)由圖1026查的a1=，a2=,則a=a1+a2=4)由表106查得材料