單繩纏繞式提升機(jī)設(shè)計(jì)

購(gòu)買設(shè)計(jì)請(qǐng)充值后下載，資源目錄下的文件所見即所得，都可以點(diǎn)開預(yù)覽，資料完整，充值下載可得到資源目錄里的所有文件?！咀ⅰ浚篸wg后綴為CAD圖紙，doc,docx為WORD文檔，原稿無水印，可編輯。具體請(qǐng)見文件預(yù)覽，有不明白之處，可咨詢QQ:12401814 中原工學(xué)院畢業(yè)設(shè)計(jì)翻譯 刀具磨損為了避免金屬切削刀具失效，第三章講述了它的最低性能要求，即機(jī)械性能和耐熱性。刀具失效是指過量的磨損會(huì)導(dǎo)致刀具失去切削材料的能力。在本章中，文章主要講述了降低刀具磨損的累積使用特點(diǎn)和機(jī)制，它們是最終導(dǎo)致刀具被替代的因素。在現(xiàn)實(shí)生產(chǎn)實(shí)踐中，有一中表示嚴(yán)重磨損程度的連續(xù)譜，在這里沒有什么要考慮的和可能在實(shí)踐中北描述為立即失效的兩者之間沒有明顯的邊界.在本章和上一章節(jié)中有重復(fù)的內(nèi)容。 第二章和第三種的內(nèi)容表明，金屬切削刀具比普通機(jī)床軸承表面承受更大的摩擦力、正應(yīng)力、高溫。在大部分情況下，沒有辦法避免刀具磨損，但是可以研究如何避免加速刀具磨損的方法。刀具磨損的主要因素刀具表面應(yīng)力和溫度（主要取決于金屬切削模式車削、銑削、轉(zhuǎn)削）、刀具和工件材料、切削速度、進(jìn)給量、切削深度和切削液的類型等。在第二章中，主要講述了影響刀具磨損的因素的微小變化都會(huì)導(dǎo)致磨損的變化。機(jī)械加工中，刀具磨損方式和磨損率對(duì)金屬切削操作和切削條件的變化同樣敏感。雖然刀具磨損無法避免，但是通常情況下可以控制磨損方式來減少刀具磨損。4.1節(jié)中介紹了刀具磨損的主要方式。主要介紹了機(jī)械加工的經(jīng)濟(jì)型。為了盡量減少制造成本，不僅需要尋找最合適的刀具和工件材料，而且還要考慮切削刀具壽命。在刀具壽命結(jié)束時(shí)，刀具必須能夠替換或者維修以保證加工工件的精度、表面粗造度或者完整性。4.2節(jié)主要介紹了刀具壽命的標(biāo)準(zhǔn)和估算。4.1刀具磨損及其分類4.1.1 刀具磨損的形式根據(jù)刀具磨損的程度和磨損進(jìn)程，刀具磨損可分為兩類，即磨損和斷裂。磨損（如第二章討論）是一種粗糙材質(zhì)表面損失或者微接觸，或者磨粒較小，最小至分子或者原子的去除機(jī)理。它通常會(huì)持續(xù)進(jìn)行直到斷裂。另一方面，斷裂是比磨損更嚴(yán)重的損害，它的發(fā)生具有突然性。正如上面所說，從微磨損到嚴(yán)重?cái)嗔咽且环N連續(xù)的損害。圖4.1顯示了一個(gè)典型的磨損模式，在這種情況下的磨損一把硬質(zhì)合金刀具切割處于高速旋轉(zhuǎn)下的金屬工件。月牙洼前刀面磨損，前刀面?zhèn)纫韨?cè)邊磨損和在切削深度末端的凹口磨損，它們是磨損的典型方式。磨損量可以用在4.2節(jié)中介紹的VB、KT表示。然而磨損量隨著切削材料、切削方式和切削條件的變化而變化，如圖4.2。如圖4.2(a)顯示月牙洼和后刀面磨損存在可疑忽略的溝槽磨損，在開機(jī)后用硬質(zhì)合 金刀具切削高速旋轉(zhuǎn)的45鋼的條件下。如果改為銑削，一個(gè)有裂縫的大幅度月牙洼磨損將成為磨損的顯著特點(diǎn)（圖4.2（b）。當(dāng)陶瓷刀具車削鎳基超級(jí)合金時(shí)（圖4.2（c）項(xiàng)）在美國(guó)商務(wù)部線溝槽磨損是主要的磨損模式，而月牙洼和后刀面磨損幾乎可以忽略不計(jì)。圖4.2（d）給出了一個(gè)氮化硅陶瓷車削工具切削碳鋼的結(jié)果。月牙洼和后刀面磨損會(huì)在很短的時(shí)間內(nèi)磨損更大。在切削工件材料變?yōu)閎相態(tài)的情況下，大量的切削材料粘附于鈦鋁合金的K級(jí)硬質(zhì)合金刀具的側(cè)邊部分，這樣導(dǎo)致刀具磨損斷裂或者破碎。 圖4.1典型的硬質(zhì)合金刀具磨損形式（a）車削45碳鋼 （b）端面銑削45碳鋼（c）車削鉻鎳鐵718 （d）車削45碳鋼（e）車削鈦合金典型的工具損傷觀察磨損和斷裂： (a)刀具：燒結(jié)碳化物P10， v = 150 m min1,d = 1.0 mm,f = 0.19 mm rev1，t = 5分鐘; (b)刀具：燒結(jié)碳化物P10， v = 400 m min1， d = 1.0 mm， f = 0.19mm tooth1，t = 5min; (c)刀具： Al2O3/TiC陶瓷刀具，v = 100 m min1，d = 0.5 mm，f = 0.19 mm rev1，t = 0.5分鐘;(d)刀具：Si3N4陶瓷刀具，v = 300 m min1，d = 1.0 mm，f = 0.19 mm rev1，t = 1分鐘; (e)刀具：燒結(jié)碳化物P10，v = 150 m min1 d = 0.5 mm，f = 0.1 mm rev1，t = 2 min。 4.1.2 刀具磨損的原因第2.4章概述了導(dǎo)致磨料，膠粘劑和化學(xué)磨損機(jī)理的一般條件。在刀具的磨損，這些機(jī)理的重要性和發(fā)生的條件，可以按切削溫度來劃分，如圖4.3所示。再圖上有三個(gè)刀具磨損的因素被確定，分別為機(jī)械磨損、熱磨損和化學(xué)磨損。機(jī)械磨損包括腐蝕、剝落、早期斷裂和疲勞，它基本上與溫度無關(guān)。熱磨損包括塑性變形、熱擴(kuò)散和作為其典型形式的化學(xué)反應(yīng)，它隨著溫度的急劇增加。 （應(yīng)當(dāng)指出，熱擴(kuò)散和化學(xué)反應(yīng)是不是損害的直接原因。相反，它們會(huì)導(dǎo)致刀具表面被削弱，使磨損，抗機(jī)械沖擊或粘連可以更容易造成材料去除。）基于粘附的磨損被觀察到有一個(gè)在一定溫度范圍內(nèi)的局部最大值。 圖4.3刀具磨損和切削溫度的關(guān)系圖4.4機(jī)械磨損的分類(1)機(jī)械磨損根據(jù)刀具磨損的程度和磨損進(jìn)程，刀具磨損可分為兩類，即磨損和斷裂。磨損（如第二章討論）是一種粗糙材質(zhì)表面損失或者微接觸，或者磨粒較小，最小至分子或者原子的去除機(jī)理。它通常會(huì)持續(xù)進(jìn)行直到斷裂。另一方面，斷裂是比磨損更嚴(yán)重的損害，它的發(fā)生具有突然性。正如上面所說，從微磨損到嚴(yán)重?cái)嗔咽且环N連續(xù)的損害。無論機(jī)械磨損被列為磨損或斷裂，它都視磨粒的大小而定。如圖4.4所示的幾種不同的磨粒大小模式，它們從小于0.1微米達(dá)到約100微米（遠(yuǎn)大于100微米被視為失效）。磨料磨損（如圖2.29示意圖）通常是由滑動(dòng)對(duì)刀具硬質(zhì)顆粒的磨損造成的。硬質(zhì)顆粒無論是來自工作材料的微觀結(jié)構(gòu)，還是從切削邊緣破碎的顆粒。磨料磨損減少了刀具相對(duì)于粒子和一般取決于距離的切削困難（參見4.2.2節(jié)）。摩擦磨損發(fā)生在磨料顆粒比磨料磨損比較大的情況下。在刀具與工件之間相互滑動(dòng)運(yùn)動(dòng)，并且刀具材料的顆?；蛘呔Я１荒p破壞前，刀具材料的顆粒或者晶粒的機(jī)械性能被微細(xì)裂縫消弱。接下來主要依據(jù)破碎片的大?。ㄓ袝r(shí)候它由于它的大小限制被稱為細(xì)微碎片）。這是由機(jī)械沖擊載荷的規(guī)模導(dǎo)致切削力波動(dòng)大，而不是固有的波動(dòng)，導(dǎo)致局部應(yīng)力磨損。最后斷裂顆粒比破碎顆粒大，并分為三類：早期階段、難以預(yù)測(cè)階段和最后階段。削減如果刀具形狀或切割的條件是不適當(dāng)?shù)?，或者如果刀具?nèi)部存在一些缺陷，或在其邊緣有缺陷，這樣刀具磨損會(huì)立即發(fā)生在開始切削工件后。不可預(yù)知的斷裂可以發(fā)生在任何時(shí)間段，如果在切削過程中刀具或者工件尖端的壓力突然發(fā)生變化，例如抖動(dòng)或不規(guī)則的工件表面硬度不均勻所引起。最后階段斷裂可經(jīng)常被觀察到，特別是在銑削過程中并且刀具壽命末端的時(shí)候；這些主要是有機(jī)械疲勞或者熱應(yīng)力發(fā)生在工作部件凸出部分引起的磨損。(2)熱磨損塑性變形當(dāng)?shù)毒咛幱诟邷厍邢鳡顟B(tài)下時(shí)，刀具尖端部分不能承受氣條件下正應(yīng)力，此時(shí)熱磨損的塑性變形將被觀察到，如圖4.3所示。因此，發(fā)生于刀具處于高溫狀態(tài)下的硬度將作為塑性變形的顯著特點(diǎn)。所以例如一般情況下，高速鋼刀具及鈷含量高的硬質(zhì)合金刀具或金屬陶瓷刀具用于切削條件苛刻的條件下，特別是在高進(jìn)給速度的情況下。因此，邊緣變形將導(dǎo)致生成一個(gè)不正確的形狀尺寸的工件和快速去除工件材料的情況。(3)熱磨損擴(kuò)散磨損熱擴(kuò)散磨損的結(jié)果發(fā)生在高溫切削條件下，如果刀具和工件材料的元素會(huì)擴(kuò)散到彼此對(duì)方的結(jié)構(gòu)中。這是眾所周知的硬質(zhì)合金刀具，并已被研究了多年。例如Dawihl（1941）、特倫特（1952）、Trigger和Chao（1956年）、武山和村田（1963年）、格雷戈里（1965），庫(kù)克（1973）、上原（1976）、Narutaki和山根（1976年）、Usui et al（1978）和其他科學(xué)家。由擴(kuò)散控制的速率與絕對(duì)溫度以指數(shù)冪的形式成正比。在磨損的情況下，不同的研究者提出了不同的指前因子的因素：庫(kù)克研究提出了擴(kuò)散深度h與相應(yīng)的時(shí)間t之間的關(guān)系（公式4.1（a）；更早以前，竹山和村田（1963）也研究提出了這些觀點(diǎn)，并且更進(jìn)一步提出滑動(dòng)距離可能是一個(gè)更基本的變量（方程4.1（b）；隨后Usui et al. (1978)根據(jù)接觸力學(xué)和被2.4節(jié)提及的磨損提出了磨損會(huì)隨著正接觸應(yīng)力的增加而加?。ü?.1（c）。在以上所有例子中可知，磨損率的對(duì)數(shù)與1/將繪制出一條直線，直線的斜率就是C2。 圖示4.5火山口與側(cè)面磨損率深度碳素鋼轉(zhuǎn)由P20硬質(zhì)合金,來自Kitagawa(1988) 的研究圖4.5顯示了月牙洼和兩個(gè)側(cè)翼的深度為0.25碳含量處的磨損率和0.46碳含量鋼，用P20的硬質(zhì)合金刀具驚醒切削的結(jié)果，此實(shí)驗(yàn)為了驗(yàn)證方程的方式（4.1c）。圖4.5中出現(xiàn)兩個(gè)線性區(qū)域，并且當(dāng)1/8.510(-4) K(-1)(或1175K)時(shí)是一個(gè)臨界點(diǎn)。在較高溫度斜率（1175K）是鋼材和水泥之間的碳化物（庫(kù)克，1973年）擴(kuò)散過程的典型。在較低溫度下斜率是一個(gè)隨溫度變化的機(jī)械磨損過程的典型，例如摩擦磨損。擴(kuò)散可直接顯示在靜態(tài)條件下的高溫。如圖4.6顯示了一個(gè)典型靜態(tài)的擴(kuò)散試驗(yàn)結(jié)果，其中一個(gè)P-級(jí)硬質(zhì)合金刀具在1200攝氏度溫度下對(duì)一個(gè)0.15碳鋼持續(xù)加載30分鐘之間通過硬質(zhì)合金刀具和鋼界面在4Nital（一磺酸的合成酒精）蝕刻下，金相部分顯示鋼珠光體已經(jīng)從原來的水平增加。這意味著，硬質(zhì)合金中的碳已擴(kuò)散到剛里面。此外，電子探針顯微分析儀（EPMA）表明，鈷和鎢已從工具材料也擴(kuò)散到鋼鐵中，并且是鐵鐵擴(kuò)散到鋼刀具材料。許多研究者都認(rèn)為相互擴(kuò)散是硬質(zhì)合金刀具擴(kuò)（b） 到界面的距離（um）圖示4.6 典型的靜態(tài)擴(kuò)散試驗(yàn)結(jié)果,因?yàn)镻10耦合至0.15% C鋼(Narutaki和Yamane,1976年) （a）通過Nital蝕刻的接口部分;（b）通過電子探針分析元素的擴(kuò)散 散磨損的原因，但是沒有詳細(xì)的說明，關(guān)于這種現(xiàn)象將導(dǎo)致工件材料的去除效果。Naerheim和遄達(dá)（1977）提出，對(duì)雙方碳化鎢鈷（金級(jí)）和WC的磨損率，（鈦，鉭，鎢）的C -鈷（P級(jí)）硬質(zhì)合金是由擴(kuò)散速率控制鎢（和Ti和Ta）和碳原子組合成的工作的材料，如圖4.7所示。這種觀點(diǎn)是基于透射電子顯微鏡（TEM）對(duì)月牙洼磨損的觀察，顯示在該工具的碳化物顆粒內(nèi)無一0.01的工具芯片接口毫米的距離的結(jié)構(gòu)變化。對(duì)與于P級(jí)比K級(jí)材料磨損較慢，這是緩慢擴(kuò)散，它解釋了前者比后者的情況。Naerheim和遄達(dá)指出，在他們的切削試驗(yàn)中，被拉伸碳化物顆粒并沒有在粘附物的底部被觀察到。這不是上原的（1976年）的經(jīng)驗(yàn)。用K級(jí)或者P級(jí)含碳量為百分之47的刀具進(jìn)行切削，他收集切屑，并將它溶解在酸性溶液中提取粘結(jié)的碳化物，最后讓它通過一個(gè)0.1mm過濾嘴，通過這種方案進(jìn)行分類碳化物尺寸。用K -級(jí)刀具，他只觀察碳化物小于0.1毫米的大小，這與Trent研究結(jié)果相一致。然而，用P-級(jí)刀具，他觀察到碳化物大于0.1毫米大小。這表明K和P型材料不同的磨損機(jī)理。擴(kuò)散磨損的另一個(gè)例子是金剛石切割刀具、硅氮化硅陶瓷刀具和SiC晶須增韌氧化鋁陶瓷刀具在加工鋼時(shí)的嚴(yán)重磨損。碳、硅和氮在高溫下它們都極容易擴(kuò)散到鐵中，并且氮化硅和碳化硅很容易溶解于鐵水。如果一個(gè)層作為擴(kuò)散屏障沉積在刀具上，這樣就可以減少硬質(zhì)合金刀具的擴(kuò)散磨損熱。在實(shí)際生產(chǎn)中有兩種這樣類型沉積層：一個(gè)是由涂層刀具提供;另一種是保護(hù)性氧化層沉積在切割過程中的磨損表面，用于還原特殊鋼（如鈣脫氧鋼），即通常有belag之稱的層。注：文章來源Metal_Machining。8中原工學(xué)院畢業(yè)設(shè)計(jì)英文翻譯原文 Tool damageChapter 3 considered cutting tool minimum property requirements (both mechanical and thermal) to avoid immediate failure. By failure is meant damage so large that the tool has no useful ability to remove work material. Attention is turned, in this chapter, to the mech- anisms and characteristics of lesser damages that accumulate with use, and which eventu- ally cause a tool to be replaced. In reality, there is a continuous spectrum of damage severities, such that there is no sharp boundary between what is to be considered here and what might in practice be described as immediate failure. There is some overlap between this chapter and the previous one.Chapters 2 and 3 have demonstrated that cutting tools must withstand much higher fric- tion and normal stresses and usually higher temperatures too than normal machine tool bearing surfaces. There is, in most cases, no question of avoiding tool damage, but only of asking how rapidly it occurs. The damages of a cutting tool are influenced by the stress and temperature at the tool surface, which in turn depend on the cutting mode for exam- ple turning, milling or drilling; and the cutting conditions of tool and work material, cutting speed, feed rate, depth of cut and the presence or not of cutting fluid and its type. In Chapter 2, it was described in general that wear is very sensitive to small changes in sliding conditions. In machining, the tool damage mode and the rate of damage are simi- larly very sensitive to changes in the cutting operation and the cutting conditions. While tool damage cannot be avoided, it can often be reduced if its mode and what controls it is understood. Section 4.1 describes the main modes of tool damage.The economics of machining were introduced in Chapter 1. To minimize machining cost, it is necessary not only to find the most suitable tool and work materials for an oper- ation, but also to have a prediction of tool life. At the end of a tools life, the tool must be replaced or reground, to maintain workpiece accuracy, surface roughness or integrity. Section 4.2 considers tool life criteria and life prediction.4.1 Tool damage and its classification4.1.1 Types of tool damageTool damage can be classified into two groups, wear and fracture, by means of its scale and how it progresses. Wear (as discussed in Chapter 2) is loss of material on an asperity or micro-contact, or smaller scale, down to molecular or atomic removal mechanisms. It usually progresses continuously. Fracture, on the other hand, is damage at a larger scale than wear; and it occurs suddenly. As written above, there is a continuous spectrum of damage scales from micro-wear to gross fracture.Figure 4.1 shows a typical damage pattern in this case wear of a carbide tool, cutting steel at a relatively high speed. Crater wear on the rake face, flank wear on the flank faces and notch wear at the depth of cut (DOC) extremities are the typical wear modes. Wear measures, such as VB, KT are returned to in Section 4.2.Damage changes, however, with change of materials, cutting mode and cutting condi- tions, as shown in Figure 4.2. Figure 4.2(a) shows crater and flank wear, with negligible notch wear, after turning a medium carbon steel with a carbide tool at high cutting speed. If the process is changed to milling, a large crater wear with a number of cracks becomes the distinctive feature of damage (Figure 4.2(b). When turning Ni-based super alloys with ceramic tools (Figure 4.2(c) notch wear at the DOC line is the dominant damage mode while crater and flank wear are almost negligible. Figure 4.2(d) shows the result of turning a carbon steel with a silicon nitride ceramic tool (not to be recommended!). Large crater and flank wear develop in a very short time. In the case of turning b-phase Ti-alloys with a K-grade carbide tool, large amounts of work material are observed adhered to the tool, and part of the cutting edge is damaged by fracture or chipping (Figure 4.2(e).4.1.2 Causes of tool damageChapter 2.4 outlined the general conditions leading to abrasive, adhesive and chemical wear mechanisms. In the context of cutting tool damage, the importance and occurrence of these mechanisms can be classified by cutting temperature, as shown in Figure 4.3. Three causes of damage are qualitatively identified in the figure: mechanical, thermal and adhesive. Mechanical damage, which includes abrasion, chipping, early fracture and fatigue, is basi- cally independent of temperature. Thermal damage, with plastic deformation, thermal diffu- sion and chemical reaction as its typical forms, increases drastically with increasing temperature. (It should be noted that thermal diffusion and chemical reaction are not the direct cause of damage. Rather, they cause the tool surface to be weakened so that abrasion, mechanical shock or adhesion can then more easily cause material removal.) Damage based on adhesion is observed to have a local maximum in a certain temperature range.Mechanical damage Whether mechanical damage is classified as wear or fracture depends on its scale. Figure 4.4 illustrates the different modes, from a scale of less than 0.1 mm to around 100 mm (much greater than 100 mm becomes failure).Abrasive wear (illustrated schematically in Figure 2.29) is typically caused by sliding hard particles against the cutting tool. The hard particles come from either the work mater- ials microstructure, or are broken away from the cutting edge. Abrasive wear reduces the harder is the tool relative to the particles and generally depends on the distance cut (see Section 4.2.2).Attrition wear occurs on a scale larger than abrasion. Particles or grains of the tool material are mechanically weakened by micro-fracture as a result of sliding interaction with the work, before being removed by wear.Next in size comes chipping (sometimes called micro-chipping at its small-scale limit). This is caused by mechanical shock loading on a scale that leads to large fluctuations in cutting force, as opposed to the inherent local stress fluctuations that cause attrition.Finally, fracture is larger than chipping, and is classified into three types: early stage, unpredictable and final stage. The early stage occurs immediately after beginning a cut if the tool shape or cutting condition is improper; or if there is some kind of defect in the cutting tool or in its edge preparation. Unpredictable fracture can occur at any time if the stress on the cutting edge changes suddenly, for example caused by chattering or an irreg- ularity in the workpiece hardness. Final stage fracture can be observed frequently at the end of a tools life in milling: then fatigue due to mechanical or thermal stresses on the cutting edge is the main cause of damage.Thermal damage plastic deformationThe plastic deformation type of thermal damage referred to in Figure 4.3 is observed when a cutting tool at high cutting temperature cannot withstand the compressive stress on its cutting edge. It therefore occurs with tools having a high temperature sensitivity of their hardness as their weakest characteristic. Examples are high speed steel tools in general; and high cobalt content cemented carbide tools, or cermet tools, used in severe conditions, particularly at a high feed rate. Deformation of the edge leads to generation of an improper shape and rapid material removal.Thermal damage diffusionWear as a result of thermal diffusion occurs at high cutting temperatures if cutting tool and work material elements diffuse mutually into each others structure. This is well known with cemented carbide tools and has been studied over many years, by Dawihl (1941), Trent (1952), Trigger and Chao (1956), Takeyama and Murata (1963), Gregory (1965), Cook (1973), Uehara (1976), Narutaki and Yamane (1976), Usui et al. (1978) and others. The rates of processes controlled by diffusion are exponentially proportional to the inverse of the absolute temperature q. In the case of wear, different researchers have proposed different pre-exponential factors: Cook (1973) suggested depth wear h should increase with time t (equation 4.1(a); earlier, Takeyama and Murata (1963) also suggested this and the further possibility of sliding distance s being a more fundamental variable (equation 4.1(b); later Usui et al. (1978), following the ideas of contact mechanics and wear considered in Chapter 2.4, proposed wear should also increase with normal contact stress sn (equation 4.1(c). In all these cases, a plot of ln(wear rate) against 1/q gives a straight line, the slope of which is C2 igure 4.5 shows experimental results for both the crater and flank depth wear rates of a 0.25%C and a 0.46%C steel turned by a P20 grade carbide tool, plotted after the manner of equation (4.1c). Two linear regions are seen: in this case the boundary is at 1/q 8.5 104 K1 (or q 1175 K). The slope of the higher temperature data (q 1175 K) is typi- cal of diffusion processes between steels and cemented carbides (Cook, 1973). The smaller slope at lower temperatures is typical of a temperature dependent mechanical wear process, for example abrasion. Diffusion can be directly demonstrated at high temperatures in static conditions. Figure 4.6 shows a typical result of a static diffusion test in which a P-grade cemented carbide tool was loaded against a 0.15% carbon steel for 30 min at 1200C. A metallographic section through the interface between the carbide tool and the steel, etched in 4% Nital (nitric acid and alcohol) shows that the pearlite in the steel has increased from its original level. This means that carbon from the cemented carbide has diffused into the steel. Furthermore, elec- tron probe micro-analysis (EPMA) shows that Co and W from the tool material also diffuse into the steel; and iron from the steel diffuses into the tool material. Many researchers agree that mutual diffusion is the cause of carbide tool diffusion wear, but there is not agreement in detail as to the mechanism that then results in material removal.Naerheim and Trent (1977) have proposed that the wear rates of both WC-Co (K-grade) and WC-(Ti,Ta,W)C-Co (P-grade) cemented carbides are controlled by the rate of diffusion of tungsten (and Ti and Ta) and carbon atoms together into the work material, as indicated in Figure 4.7. This view is based on transmission electron microscope (TEM) observations on crater wear that show no structural changes in the tools carbide grains within a distance of 0.01 mm of the toolchip interface. The slower wear of P-grade than K-grade materials is explained by slower diffusion in the former than the latter case. Naerheim and Trent state that, in their cutting tests, pulled-out carbide grains were not observed adhering to the underside of chips. This was not Ueharas (1976) experience. He collected chips after turn- ing a 0.47% C steel with a K-grade or a P-grade tool, dissolved the chips in acid to extract adhered carbides and finally passed the solution through a 0.1m filter, to classify the carbide sizes. With K-grade tools, he only observed carbides less than 0.1 mm in size, in accord with Trent. However, with P-grade tools he observed carbides greater than 0.1 mm in size. This suggests a different wear mechanism for K- and P-type materials.Other examples of diffusion wear are the severe wear of diamond cutting tools, silicon nitride ceramic tools and SiC whisker reinforced alumina ceramic tools when machining steel. Carbon, silicon and nitrogen all diffuse easily in iron at elevated temperatures; and silicon nitride and silicon carbide dissolve readily in hot iron.Thermal diffusion wear of carbide tools can be decreased if a layer acting as a barrier to diffusion is deposited on the tool. There are two types of layer in practice: one is as provided by coated tools; the other is a protective oxide layer deposited on the wear surfaces during cutting special deoxidized steels (for example Ca-deoxidized steels), commonly known as a belag layer.10