外文翻譯--外圓磨削中磨削強(qiáng)化效果的試驗(yàn)研究

1、<p>　　Journal Article | Print Published: 04/01/2003 | Online Published: 03/20/2003 Pages: 245 - 259 DOI: 10.1081/AMP-120018908 Materials and Manufacturing Processes , Volume 18 , Issue 2 </p><p>　　外圓

2、磨削中磨削強(qiáng)化效果的試驗(yàn)研究</p><p>　　V. S. K. Venkatachalapathy *Corresponding </p><p>　　B. Rajmohan *Corresponding</p><p>　　V. S. K. Venkatachalapathy*Send correspondence to: </p><p

3、>　　rajmohan51@mitindia.edu Department of Mechanical EngineeringV.R.S. College of Engineering & TechnologyArasur Villupuram (Dt.) Tamil Nadu India </p><p>　　B. Rajmohan*Send correspondence to: &

4、lt;/p><p>　　rajmohan51@mitindia.edu Department of Production Technology MIT, Anna UniversityChromepet Chennai Tamil Nadu India </p><p>　　摘要：最近高強(qiáng)度和高熔點(diǎn)合金被廣泛應(yīng)用于結(jié)構(gòu)和另外的場(chǎng)合。這些高性能的材料都比較難以加工，也難以保證高的尺

5、寸和形狀精度。磨削是應(yīng)用于精加工的最普遍和常見(jiàn)的方法之一，和其他機(jī)械加工方法如車(chē)削、銑削相比，磨削時(shí)產(chǎn)生的熱量是非常高的。在散熱條件不佳的情況下，磨削產(chǎn)生的熱量會(huì)使工件溫度迅速上升，這可能會(huì)導(dǎo)致工件被燒傷。由磨削過(guò)程產(chǎn)生的燒傷以被很好的證明而且可以按顏色對(duì)其進(jìn)行分類(lèi)，這些損傷在周期性載荷的作用下會(huì)降低產(chǎn)品壽命，甚至可能會(huì)導(dǎo)致災(zāi)難性的問(wèn)題發(fā)生。在磨削工藝中，一種新的叫做磨削強(qiáng)化的熱處理方法和其數(shù)學(xué)模型被提出，在這一工序中要解決的問(wèn)題是如何

6、有效利用磨削產(chǎn)生的熱量來(lái)改進(jìn)表面強(qiáng)度和表面金相組織，并且要防止工件破壞。為此進(jìn)行了一個(gè)用氧化鋁砂輪加工AISI6150和AISI5200的實(shí)驗(yàn)，并且結(jié)論被進(jìn)行了探討。</p><p>　　關(guān)鍵詞：外圓磨削、磨削熱、傳熱比、表面織構(gòu)、表面強(qiáng)化。</p><p><b>　　引言</b></p><p>　　磨削是具有尺寸公差、幾何精度和表面光潔度

7、要求的零件的通用而且最后的精加工過(guò)程。磨削是機(jī)械加工中精度最高的加工方法，它是主要的機(jī)械加工方法，占加工費(fèi)用的25%。幾乎所有的產(chǎn)品都或多或少的應(yīng)用了磨削，而且他們都把精度歸因于磨削。</p><p>　　磨削是應(yīng)用砂輪在工件上以細(xì)小微粒的形式不斷地去除材料。磨削去除材料很慢，所以在磨削之前一般都要用其他的加工方法把工件加工到離所需尺寸很近然后再用磨削完成加工工序。隨著磨床的出現(xiàn)，磨削已成為高檔材料的主要加工方法

8、。它是能得到所需尺寸同時(shí)進(jìn)行拋光的最經(jīng)濟(jì)的一種加工方法，而且能在同一機(jī)床上不換砂輪進(jìn)行粗精加工。</p><p>　　之前，很多科學(xué)家對(duì)磨削時(shí)產(chǎn)生熱量的浪費(fèi)和及其對(duì)表面質(zhì)量的影響進(jìn)行了研究。根據(jù)磨削環(huán)境，熱量主要通過(guò)工件散失，從而導(dǎo)致工件表面熱量大量積累。熱量的大量積累使工件表面溫度升高。高溫在工件表面造成一些如裂縫、回火層或白色腐蝕的破壞。如果工件表層溫度超過(guò)910℃，表面晶相將發(fā)生變化。Shaw和Vyas已經(jīng)

9、對(duì)磨削產(chǎn)生的表面破壞進(jìn)行了深刻的理論闡述。在磨削時(shí)，造成表面損傷的熱影響層能被觀察到。零件表面損傷，不能達(dá)到質(zhì)量要求將給制造商帶來(lái)嚴(yán)重的浪費(fèi)。</p><p>　　大多數(shù)研究的目的是想預(yù)知在磨削強(qiáng)化過(guò)程中不希望得到的改變從而避免之。無(wú)論如何，在磨削過(guò)程中熱量的生成量是被限制的。</p><p>　　通過(guò)對(duì)當(dāng)今熱處理和磨削經(jīng)驗(yàn)的概括，三個(gè)被重點(diǎn)限制的因素是：</p><p

10、>　　表面強(qiáng)化的熱處理方法很多，例如電磁感應(yīng)淬火等，但他們很難進(jìn)行集成化。</p><p>　　這些表面強(qiáng)化方法不能對(duì)不規(guī)則產(chǎn)品進(jìn)行完全表面強(qiáng)化。</p><p>　　繼熱處理之后，由于磨削強(qiáng)化強(qiáng)化材料數(shù)量的上升，結(jié)構(gòu)成為磨削應(yīng)主要關(guān)心的問(wèn)題。</p><p>　　以上所述的問(wèn)題促使研究人員去研究在回轉(zhuǎn)磨削過(guò)程中怎樣有效利用產(chǎn)生的熱量來(lái)改進(jìn)產(chǎn)品質(zhì)量。</

11、p><p><b>　　2．工件材料的選擇</b></p><p>　　鋼的性能是利用在不同的溫度下α與γ混合晶相對(duì)碳有不同的溶解能力來(lái)調(diào)節(jié)的。硬化過(guò)程是根據(jù)奧氏體在特定的臨界冷卻速度下向馬氏體轉(zhuǎn)變從而阻止奧氏體的轉(zhuǎn)變。</p><p>　　Konig和Menser強(qiáng)調(diào)指出用工件材料的性能參數(shù)來(lái)描述磨削過(guò)程中工件性能是不可能的。他們同時(shí)指出硬度的增

12、加是因?yàn)轳R氏體，它以碳化物的形式保持不變的硬度。馬氏體的硬度取決于材料中碳和其他合金元素的含量。在這一工藝中AISI6150和AISI52100被選為工件材料。</p><p><b>　　3．工藝參數(shù)的影響</b></p><p>　　回轉(zhuǎn)磨削具有很多可變參數(shù)，但是只有三個(gè)重要參數(shù)：1）切削深度，2）進(jìn)給量，3）磨削來(lái)回次數(shù)。</p><p>

13、;　　在相互聯(lián)系的區(qū)域切削時(shí)，熱量的產(chǎn)生與切削深度成正比。大的切削深度導(dǎo)致持續(xù)長(zhǎng)時(shí)間的熱作用，所以增加切削深度使進(jìn)入工件的熱量增加，這將在工件表面造成燒傷，甚至造成工件表面破壞及影響工件精度。</p><p>　　增加進(jìn)給量將會(huì)增加發(fā)熱量。進(jìn)給量的兩個(gè)主要影響因素是：</p><p>　　小的進(jìn)給量，傳遞能量高，但是切削功率較低進(jìn)而使硬化層深度小。</p><p>

14、　　大的進(jìn)給量，磨削力大，但是導(dǎo)致接觸時(shí)間短、傳遞能量減少，進(jìn)而硬化層深度小。</p><p>　　因此，一個(gè)適中的進(jìn)給量才能在工件表面得到最大的硬化層。</p><p>　　增加磨削來(lái)回次數(shù)只能在工件表面的某一深度增加硬度，超出這一深度硬度將下降。因?yàn)樵黾忧邢鲿r(shí)間和切削力將產(chǎn)生過(guò)多的熱量，所以在很短的時(shí)間里磨削產(chǎn)生的熱量將會(huì)接近于工件材料的熔點(diǎn)。因而在超過(guò)一定的切削速度后工件硬度將下降。

15、這些過(guò)多的熱量將影響成形表面的晶相或造成零件變形。</p><p><b>　　4．溫度模型</b></p><p>　　有效溫度的觀點(diǎn)已經(jīng)被通過(guò)對(duì)很多相互聯(lián)系的理論和實(shí)驗(yàn)結(jié)果的估計(jì)分析所證實(shí)。在這一實(shí)例中，磨削強(qiáng)化的程度受進(jìn)入工件的熱量的影響。</p><p>　　工件表面的有效溫度主要受工藝參數(shù)的影響，而且Shaw已經(jīng)把材料的熱電性能和可磨

16、削性能描述出來(lái)。許多觀測(cè)者建議在機(jī)械和冶金行業(yè)特有的研磨工業(yè)中，工件表面可以通過(guò)控制表面溫度來(lái)加工。</p><p>　　Rowe et al通過(guò)對(duì)氧化鋁和硅碳化合物砂輪的一系列實(shí)驗(yàn)測(cè)定出熱容量。聯(lián)系層模型認(rèn)為在整個(gè)磨削層中存在能量分隔區(qū)，而砂輪體積模型假設(shè)工件和砂輪是可變的熱源。Shaw用一個(gè)比例系數(shù)把微粒性能和這一模型聯(lián)系起來(lái)。</p><p>　　Rowe et al提出了粒子模型，

17、在其理論中的進(jìn)入工件的熱量比率認(rèn)為大多數(shù)熱量不是通過(guò)切屑和冷卻液散失的。</p><p>　　Rowe et al已經(jīng)研究過(guò)砂輪熱容量對(duì)工件表面晶相的重要性，其方法是測(cè)溫和分析磨削部位。</p><p><b>　　5．有關(guān)術(shù)語(yǔ)</b></p><p>　　進(jìn)入工件的傳熱比：進(jìn)入工件的傳熱比是進(jìn)入工件的熱量與總熱量之比。</p>

18、<p><b>　　在這里：</b></p><p>　　— 進(jìn)入工件的熱量（J）</p><p>　　— 產(chǎn)生的總熱量（J）</p><p>　　如果用根式的形式表示，分割率則為：</p><p><b>　　在這里：</b></p><p>　　— 工件的熱系數(shù)

19、（J m-2 s-0.5 K-1）</p><p>　　b — 砂輪寬度（m）</p><p>　　— 切削速度（m/sec）</p><p><b>　　— 紋理長(zhǎng)度（m）</b></p><p>　　— 環(huán)境溫度（°C） </p><p>　　— 產(chǎn)生的

20、總熱量（J）</p><p>　　分割率的根式表達(dá)式是在假定熱量分布均勻而且熱量只在工藝內(nèi)部流動(dòng)時(shí)成立。</p><p><b>　　6．理論模型</b></p><p>　　理論模型要求預(yù)知分割率和工件溫度。首先，應(yīng)用Rowe et al提出的微粒聯(lián)系區(qū)域模型而且認(rèn)為在整個(gè)磨削過(guò)程中的能量是聯(lián)系的，則很多材料的分割率被表述為：</p&g

21、t;<p><b>　　在這里：</b></p><p>　　— 砂輪的熱容量系數(shù)（J m-2 s-0.5 K-1）</p><p>　　— 砂輪旋轉(zhuǎn)速度（m/s）</p><p>　　— 工件運(yùn)動(dòng)速度（m/s）</p><p>　　氧化鋁砂輪的熱容量系數(shù)：</p>

22、<p>　　利用材料物理性能得到的各種工件的熱容量系數(shù)：</p><p>　　各種工件材料的分割率如下：</p><p>　　對(duì)于AISI52100：</p><p>　　工件速度（）=1.099m/sec</p><p>　　砂輪轉(zhuǎn)速（）=30m/sec</p><p><b>　　解得：&l

23、t;/b></p><p>　　對(duì)于AISI6150： </p><p><b>　　近似解得: </b></p><p>　　如果考慮切屑（）和冷卻液（）上流失的熱量，那么預(yù)知的分割率將下降：</p><p>　　式中： — 切屑所含能量（J）</p><p>　　根據(jù)H

24、owe et al的經(jīng)典評(píng)價(jià)為6 J/mm3,在沸騰的液體中趨向于無(wú)窮?。?0）。于是，考慮這些因素則原先的分割率變?yōu)椋?lt;/p><p>　　在能量很小時(shí)，切屑所含能量的影響顯地越來(lái)越重要，根據(jù)粒子聯(lián)系模型，切屑所含能量被假定為 </p><p>　　于是，工件材料的分割率被表述為:</p><p><b>　　因此，</b></p>

25、;<p>　　利用Rowe et al發(fā)展的粒子聯(lián)系模型解決砂輪和工件間的熱量分割：</p><p><b>　　,</b></p><p><b>　　在這里：</b></p><p>　　— 砂輪的熱傳導(dǎo)率(Wm-1 K-1)</p><p>　　= 35 W&

26、#160;m-1 K-1（對(duì)于氧化鋁砂輪）</p><p>　　— 徑向切削深度（） </p><p>　　對(duì)于AISI5210：</p><p><b>　　解得，.</b></p><p><b>　　最佳的紋理長(zhǎng)度(）</b></p><p><b>

27、;　　.</b></p><p><b>　　已知：</b></p><p><b>　　,</b></p><p>　　式中：—等效直徑（m）；—砂輪直徑 (m)；—工件直徑 (m)</p><p>　　解得，。因此， =0.2935×10-3 m=0.29

28、0;mm.切削持續(xù)時(shí)間（t）, ,解得，。</p><p>　　7．進(jìn)入工件熱量的計(jì)算</p><p><b>　　從根式表達(dá)式得：</b></p><p><b>　　.</b></p><p><b>　　因此，</b></p><p><b&

29、gt;　　.</b></p><p>　　對(duì)于AISI52100</p><p><b>　　進(jìn)入工件的總熱量：</b></p><p>　　解得， =300 J.可知，</p><p>　　{dx=1(unit length)},</p><p><b>　　,&

30、lt;/b></p><p><b>　　這里，</b></p><p>　　K — 熱傳導(dǎo)率(W m-1 K-1) 43.3 W m-1 K-1</p><p>　　A = 面積(m2)=6.597×10-3 m2</p><p>　　△T

31、= 300/(6.597×10-3)(43.3)</p><p>　　解得，T = 1050°C T1 = 1083℃</p><p>　　對(duì)于AISI6150 </p><p><b>　　,</b></p><p><b>　　,</b></p>&

32、lt;p><b>　　解得，.</b></p><p>　　最佳粒子接觸長(zhǎng)度()</p><p><b>　　粒子接觸時(shí)間(t)</b></p><p>　　對(duì)于AISI6150</p><p><b>　　進(jìn)入工件的總熱量，</b></p><p&g

33、t;　　解得，.可知 (dx=1)，這里k=53.6 W m-1 K-1， A=6.599×10-3 m2.解得，T=955°C, T1=987°C</p><p>　　奧氏體向馬氏體轉(zhuǎn)變是由于接觸面積上產(chǎn)生的溫度導(dǎo)致的。</p><p><b>　　8．試驗(yàn)</b></p><

34、p>　　通過(guò)改變切削深度、進(jìn)給量和磨削來(lái)回次數(shù)來(lái)進(jìn)行實(shí)驗(yàn)研究。為了得到磨削強(qiáng)化層，一個(gè)標(biāo)準(zhǔn)的氧化鋁砂輪被選定，并且初步確定了磨削環(huán)境。這些意味著為引導(dǎo)馬氏體晶相的改變，高的材料去除率是有必要的。在這個(gè)實(shí)驗(yàn)中，切削速度是根據(jù)表面粗糙度和加工精度要求來(lái)改變的。磨削環(huán)境在下面給出：</p><p><b>　　表1 磨削條件</b></p><p>　　各種粗糙度參

35、數(shù)如輪廓算術(shù)平均偏差，輪廓最大高度，微觀不平度十點(diǎn)高度被測(cè)量出來(lái)。表面裂縫被用電磁裂縫探測(cè)器進(jìn)行探測(cè)，并且結(jié)果被進(jìn)行了分析。、</p><p><b>　　9．試驗(yàn)結(jié)果和探討</b></p><p>　　從微觀結(jié)構(gòu)上看這是明顯的，在磨削過(guò)程中產(chǎn)生的大多數(shù)切屑已被腐蝕變暗，但也有白色腐蝕帶的存在。這意味著炭化物微粒幾乎完全被從鐵素體基體中分離出來(lái)。（晶粒細(xì)小的馬氏體結(jié)構(gòu)

36、產(chǎn)生了）</p><p>　　a. 經(jīng)過(guò)磨削的AISI6150樣本的顯微結(jié)構(gòu)。b. 經(jīng)過(guò)磨削的AISI52100樣本的顯微結(jié)構(gòu)。</p><p>　　這些被腐蝕的晶相顯示當(dāng)溫度到810℃時(shí)有大量的碎屑產(chǎn)生,而到950℃或更高時(shí)白色腐蝕帶將產(chǎn)生,這正如Doye和Dean所提出的一樣。但是在大的磨削深度時(shí)，工件表面溫度將對(duì)切削有更大的影響，盡管表面熱量的產(chǎn)生和冷卻是迅速的。在這一工藝中得到的理

37、論模型也被在相關(guān)領(lǐng)域中得到。以下指出磨削材料在表層以下各深度的硬度。</p><p>　　c．磨削來(lái)回次數(shù)決定硬化程度（AISI6150）。 </p><p>　　d. 磨削來(lái)回次數(shù)決定硬化程度（AISI52100）。</p><p>　　從磨削樣本和切削樣本的比較中可以得出磨削強(qiáng)化可以得到較大的硬度。在這實(shí)驗(yàn)中應(yīng)用了冷卻液，盡管它對(duì)磨削強(qiáng)化沒(méi)有太大的影響。<

38、;/p><p>　　e. 比較車(chē)削樣本和磨削樣本的硬度（AISI6150）。</p><p>　　f. 比較車(chē)削樣本和磨削樣本的硬度（AISI52100）。</p><p>　　采用大的切削深度且增加磨削來(lái)回次數(shù)，散熱面積和接觸時(shí)間將隨著切削能量的增加而增加。繼續(xù)增加切削深度，硬度將下降。這是因?yàn)榍邢魃疃瘸^(guò)一定的限度后，切削能力將下降。磨削強(qiáng)化的零件被用電磁探測(cè)器進(jìn)行

39、檢測(cè)，要求無(wú)缺陷。</p><p>　　g．磨削來(lái)回次數(shù)的影響（AISI6150）。</p><p>　　h．磨削來(lái)回次數(shù)的影響（AISI52100）。</p><p>　　10．表面織構(gòu)的控制</p><p>　　表面晶相組織是在環(huán)境條件改變或不變的情況下，工件表面進(jìn)行的機(jī)械或其他表面成形工藝決定的。材料的自然表面對(duì)材料的機(jī)械性能有很大的影

40、響。在有些材料的機(jī)械工藝下這些關(guān)系被進(jìn)一步顯現(xiàn)。</p><p>　　Nam et al已經(jīng)闡明，精加工是機(jī)械制造的關(guān)鍵。以前，對(duì)表面特征和功能要求的關(guān)系關(guān)注的很少。缺乏對(duì)摩擦和磨損現(xiàn)象的認(rèn)識(shí)已成為一個(gè)有關(guān)表面特征和摩擦表面設(shè)計(jì)制造的循環(huán)問(wèn)題。因而，盡管設(shè)計(jì)的重點(diǎn)是要求工件表面摩擦小、磨損少和經(jīng)濟(jì)利益，但是迄今為止仍不能設(shè)計(jì)和制造出最佳的光滑表面。</p><p>　　在結(jié)構(gòu)實(shí)用性上，表面

41、的自然斜槽是最重要的。對(duì)于承載，則表面的自然峰的數(shù)量更為重要。因而工件樣本的表面不平度被測(cè)量出來(lái)，而且測(cè)量結(jié)果被進(jìn)行了劃分。</p><p>　　i．磨削樣本的表面粗糙度值（AISI6150）。</p><p>　　j．磨削樣本的表面粗糙度值（AISI52100）。</p><p>　　根據(jù)國(guó)際標(biāo)準(zhǔn)，這一結(jié)果是可以被接受的（磨削的表面粗糙度在0.1到0.16的范圍內(nèi)

42、是可以被接受的）。</p><p><b>　　11．結(jié)論</b></p><p>　　實(shí)驗(yàn)證明外圓磨削中產(chǎn)生的熱量可以被作為新的熱處理方法來(lái)有效利用。</p><p>　　根據(jù)現(xiàn)有的回轉(zhuǎn)磨削知識(shí)和實(shí)驗(yàn)結(jié)果，得出以下結(jié)論：</p><p>　　磨削硬化部分是細(xì)小微粒的馬氏體，它是通過(guò)表面奧氏體層的短時(shí)自淬得到的。<

43、/p><p>　　冷卻液可以避免燒傷和改進(jìn)表面質(zhì)量，但是它對(duì)淬硬的影響是微不足道的。</p><p>　　磨削強(qiáng)化的零件上很少出現(xiàn)裂縫，但仍須用電磁探測(cè)器進(jìn)行檢查。實(shí)驗(yàn)證明，機(jī)械加工部分在垂直裝夾時(shí)容易淬硬。</p><p>　　磨削強(qiáng)化的加工方法可以被用主軸、凸輪軸、軸承側(cè)面、導(dǎo)軌和另外的功能面等普遍應(yīng)用磨削的工藝中。</p><p>　　可以

44、推斷對(duì)于AISI6150 10時(shí)（最大切削深度為0.9mm），硬度是增加的，硬化層為1mm。對(duì)于AISI52100磨削來(lái)回次數(shù)為14，（最大切削深度為1.3mm）時(shí)，硬化層為1.6mm。磨削來(lái)回次數(shù)超過(guò)14，則硬度下降。由此可認(rèn)為，AISI52100可增加的碳含量和磨削來(lái)回次數(shù)比AISI6150多。</p><p>　　理論溫度模型是用微粒接觸模型找出切屑和工件分界面的溫度，看哪一溫度與Doyle和Dean提出的

45、比較符合。實(shí)際上，聯(lián)系區(qū)域產(chǎn)生的熱量是奧氏體向馬氏體轉(zhuǎn)變的主要熱源。</p><p>　　這是可以肯定的，采用這種新方法進(jìn)行表面強(qiáng)化具有很大的經(jīng)濟(jì)利益，這是因?yàn)樗梢蕴岣呒苫潭?，而且它也可以?shí)現(xiàn)向另外表面強(qiáng)化工藝的技術(shù)轉(zhuǎn)變。磨削強(qiáng)化工藝的應(yīng)用導(dǎo)致工藝路線(xiàn)的縮短和工序時(shí)間的減少，當(dāng)然也降低了生產(chǎn)成本。</p><p><b>　　參考文獻(xiàn)</b></p>

46、<p>　　1 Des Ruisseaux N.R., Zerkle R.D., Thermal analysis of the grinding process, Trans. ASME J. Eng. Ind., 92 (1970) 428–432. </p><p>　　2  Shaw M.C., Vyas A., Heat affected

47、 zones in grinding of steels, Ann. CIRP, 43/1 (1994) 571–581. </p><p>　　3  Shaw M.C. Fundamentals of grinding, New Developments in Grinding, Shaw M.C. Carnegic Press, 1972. </p>&l

48、t;p>　　4  Guo C., Malkin S., Heat transfer in grinding, J. Mater. Process. Manuf. Sci., 1 (1992) 16–27. </p><p>　　5  Doyle E.D., Dean S.K., An insight into grinding from mater

49、ials viewpoint, Ann. CIRP, 29 (2) , (1980) 571–575. </p><p>　　6  Konig W., Menser J., Influence of the composition and structure of steels on the grinding process, Ann. CIRP, 30 (2) , (1981) 5

50、41–553. </p><p>　　7  Shaw, M.C. Grinding temperatures. In 12th North American Manufacturing Research Conference Proceedings, SME, 1984, pp. 304–308.</p><p>　　8 owe W.B., Pettit J

51、.A., Boyle A., Moruzzi J.L., Avoidance of thermal damage in grinding and prediction of the damage threshold, Ann. CIRP, 37 (1) , (1988) 327–330. </p><p>　　9  Rowe W.B., Black S.C., M

52、ills B., Ql H.S., Morgan M.N., Experimental investigation of heat transfer in grinding, Ann. CIRP, 44 (1995) 329–332. </p><p>　　10  Rowe W.B., Black S.C.E., Morgan M.N., Va

53、lidation of thermal properties in grinding, Ann. CIRP, 47 (1) , (1998) 275–279. </p><p>　　11  Howes T.D., Neailey K., Honsun A.J., Fluid film boiling in shallow-cut grinding, Ann. CIRP, 3

54、6 (1) , (1987) 223–226. </p><p>　　12  Nam P., Sub, Nannaji, Surface engineering, Ann. CIRP, 36 (1) , (1987) 403–408.</p><p>　　Journal Article | Print Published: 04/01/2003 | Online Pub

55、lished: 03/20/2003 Pages: 245 - 259 DOI: 10.1081/AMP-120018908 </p><p>　　Materials and Manufacturing Processes , Volume 18 , Issue 2 </p><p>　　Experimental Studies on the Grind-Hardening Effe

56、ct in Cylindrical Grinding</p><p>　　V. S. K. Venkatachalapathy *Corresponding </p><p>　　B. Rajmohan *Corresponding</p><p><b>　　Abstract</b></p><p>　　In rece

57、nt years high-strength and high-temperature alloys are used for structural and other applications. These newer high-performance materials are inherently “more difficult to machine” and also necessitate the need for highe

58、r dimensional and geometrical accuracy. Grinding is one of the most familiar and common abrasive machining processes used for the finishing operation. Compared to other machining processes such as turning, milling, etc.,

59、 the specific energy developed during grinding is ver</p><p><b>　　Keywords </b></p><p>　　Cylindrical grinding, Grinding heat, Partition ratio, Surface texture, Surface hardening</

60、p><p>　　1 Introduction </p><p>　　Grinding is a versatile and also final machining process in the production of components requiring close dimensional tolerances, geometrical accuracies, and a smoot

61、h surface finish. There are no processes that can compete with grinding for precision machining operations. It is a major manufacturing process that accounts for about 25% of the total expenditure on machining operations

62、 in industrialized countries. Almost all products have either been machined by grinding at some stage of their produ</p><p>　　Grinding removes metal from the workpiece in the form of small chips by the mecha

63、nical action of abrasive particles bonded together in a grinding wheel. However, it is a slow way to remove the stock, thus other methods are used to bring the work quite close to its required dimensions and then the wor

64、k is ground to achieve the desired finish. With the advent of abrasive machining, grinding is also accepted as a dependable process for higher material removal rates. Parts can now be produced more e</p><p>

65、　　In the past, many scientists investigated the dissipation of heat in grinding and the resulting influence on the surface finish of the workpiece. Depending on the grinding conditions, the heat flux mainly takes part vi

66、a the workpiece and leads to a large thermal loading in the surface. This thermal load is superimposed by a mechanical load, causing a high temperature in the surface. This thermomechanical load may cause some undesired

67、alterations in the surface layer like cracks, tempered zones, </p><p>　　The aim of most investigations was the prediction of undesired alterations in order to avoid thermal damages when grinding hardened ste

68、els. In any case, the quantities of generated heat in grinding are considered as a restricting factor.</p><p>　　By summarizing today's experience in heat treatment and grinding, three important limitatio

69、ns can be identified:</p><p>　　The above said problems caused the authors to investigate how this process-generated heat energy can be effectively utilized for quality improvement in cylindrical grinding.<

70、;/p><p>　　2. Selection of the workpiece material</p><p>　　3 Influence Of The Process Parameters</p><p>　　Cylindrical grinding has many parameters that can be varied, but only three are

71、 very important: i) depth of cut; ii) feed speed; and iii) number of passes.</p><p>　　The heat generated is proportional to the depth of the cut at the contact zone, because higher depths of cut result in lo

72、nger heat treatment duration. Increasing depths of cut lead to higher quantities of energy entering into the workpiece. This will lead to a large amount of thermal damage on the surface of the workpiece. In addition to c

73、ausing surface damage, grinding heat can also affect the precision of the workpiece.</p><p>　　Increasing the feed speed is generally connected with increasing process forces. The two main effects of feed spe

74、ed are</p><p>　　Thus, a moderate or medium feed speed is always preferable to produce maximum hardness in the surface.</p><p>　　Increasing the number of passes increases the hardness at the surf

75、ace only to a certain depth of cut, after that, it decreases. Because of an increase in contact time and traveling energy, excessive heat transfer takes place. Due to this, the specific energy in grinding reaches very cl

76、ose to the melting energy of the workpiece material in a short period. So the hardness decreases after a certain number of passes. This excessive heat transfer affects the surface finish of the component due to the</p

77、><p>　　4 Temperature Modeling</p><p>　　Usually the validity of a thermal approach is substantiated by means of evaluating the various thermal properties using various correlation theories and exper

78、imental results. In this case, the grind-hardening effect is being quantified by means of heat entering into the workpiece.</p><p>　　The effective work surface temperature is principally influenced by the pr

79、ocess parameters, and the thermophysical properties of the work and abrasive materials were described by Shaw. (7) Most of the observations suggest that the mechanical and metallurgical characteristics of abrasively mach

80、ined surfaces can be produced by controlling the effective work surface temperature.</p><p>　　Rowe et al. (8) determined the thermal properties by steady-state experiments for alumina and silicon carbide whe

81、els. The contact zone models consider the partitioning of energy over the whole grinding contact zone. The wheel-bulk-property model assumes the workpiece and the grinding wheel are subjected to a sliding heat source. Sh

82、aw used an area ratio factor to correlate grain properties with such a model.</p><p>　　Rowe et al. (9) proposed a grain model in which the partition ratios (partition ratio is defined as the proportion of he

83、at entering into workpiece to the total heat developed) were considered without considering the energy convected away by the chips and coolant.</p><p>　　Rowe et al. (10) have investigated the significance of

84、 the grinding-wheel thermal properties on the surface texture of the workpiece. The approach was to measure temperature and analyze the proportion of grinding </p><p>　　5. Terminology Involved</p><

85、;p>　　energy entering the workpiece.</p><p>　　6 Theoretical Model</p><p>　　Theoretical models are required to predict the partition ratio and workpiece temperature. First, using a grain contac

86、t zone model proposed by Rowe et al. (9) and by considering the partitioning of energy over the whole grinding contact, the partition ratio for various materials was found. </p><p><b>　　where </b>

87、;</p><p>　　(c)s—Wheel bulk thermal coefficient (J m-2 s-0.5 K-1)</p><p>　　Vs—Speed of the grinding wheel (m/s),</p><p>　　Vw—Speed of the workpiece (m/s)</p>&l

88、t;p>　　The bulk thermal coefficient for alumina wheel </p><p>　　The bulk thermal coefficient for each workpiece material is found by using their physical properties </p><p>　　The partition rat

89、ios for various workpiece materials are as follows. </p><p>　　For AISI 52100 </p><p>　　On solving, R=0.909480.91.</p><p>　　For AISI 6150 </p><p>　　Similarly, on solving

90、, R=0.92460.925.</p><p>　　If the allowance for the energy convected away by the chips (ecc) and coolant (ecf) is considered, then the predicted partition ratio is reduced, i.e., </p><p>　　where

91、ec—Specific chip energy (J/mm3). </p><p>　　According to Howes et al., (11) a typical value of ecc is 6 J/mm3 and ecf tends to be very small where fluid boiling occurs (ecf=0).</p><p>　　Thus

92、, considering the allowance, the original partition ratio can be given by </p><p>　　The effect of the chip energy becomes increasingly significant at lower specific energies. According to the grain contact m

93、odel, the specific energy of the chip is assumed to be </p><p>　　Thus, the partition ratios for the workpiece material were found as </p><p>　　Therefore, R=R[0.8]: </p><p>　　Using t

94、he grain contact model developed by Rowe et al., (9) the solution for partitioning of heat between the wheel and the workpiece is </p><p><b>　　where </b></p><p>　　kge—Thermal conduct

95、ivity of the grinding wheel (Wm-1 K-1)</p><p>　　kge=35 W m-1 K-1 (for alumina wheel)</p><p>　　ro—Radial depth of cut (m)</p><p>　　For AISI 52100 </p><

96、p>　　On solving, ro=2.71×10-6=2.71 m.</p><p>　　Optimal grain contact length (le), </p><p>　　It is known that</p><p><b>　　where</b></p><p>　　de—E

97、quivalent diameter (m)</p><p>　　ds—Diameter of wheel (m),</p><p>　　dw—Diameter of workpiece (m)</p><p>　　On solving, de=0.0318 m. Therefore, le=(2.71×10-6)(0.0318) =0.2935

98、×10-3 m=0.29 mm. Grain contact time (t), t=le/Vs, on solving, t=9.66 sec.</p><p>　　7 Calibration Of Total Heat Entering Into The Workpiece</p><p>　　8 Experimentation</p>

99、;<p>　　Investigations were carried out experimentally with varying depths of cut, feed, and number of passes. For the attainment of grind hardening, a standard alumina wheel was employed, and rough grinding condit

100、ions were selected. This means that a high-specific-metal removal rate was necessary to induce martensitic phase transformation. In this experiment, the number of passes were varied according to the rough and finish grin

101、ding. The grinding conditions are given in Table 1 .</p><p>　　The various roughness parameters like centerline average Ra, peak to valley height Rt, and average peak to valley height Rz were measured. The su