机械专业毕业设计（论文）外文翻译-外圆磨削中磨削强化效果的试验研究

机械专业毕业 设计 领导形象设计圆作业设计ao工艺污水处理厂设计附属工程施工组织设计清扫机器人结构设计 （论文）外文翻译-外圆磨削中磨削强化效果的试验研究 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 外圆磨削中磨削强化效果的试验研究 *CorrespondingV. S. K. Venkatachalapathy *Corresponding B. Rajmohan V. S. K. Venkatachalapathy *Send correspondence to: rajmohan51@mitindia.edu Department of Mechanical Engineering V.R.S. College of Engineering & Technology Arasur Villupuram (Dt.) Tamil Nadu India B. Rajmohan *Send correspondence to: rajmohan51@mitindia.edu Department of Production Technology MIT, Anna University Chromepet Chennai Tamil Nadu India 摘要:最近高强度和高熔点合金被广泛应用于结构和另外的场合。这些高性能的材料都比较难以加工，也难以保证高的尺寸和形状精度。磨削是应用于精加工的最普遍和常见的方法之一，和其他机械加工方法如车削、铣削相比，磨削时产生的热量是非常高的。在散热条件不佳的情况下，磨削产生的热量会使工件温度迅速上升，这可能会导致工件被烧伤。由磨削过程产生的烧伤以被很好的证明而且可以按颜色对其进行分类，这些损伤在周期性载荷的作用下会降低产品寿命，甚至可能会导致灾难性的问题发生。在磨削工艺中，一种新的叫做磨削强化的热处理方法和其数学模型被提出，在这一工序中要解决的问题是如何有效利用磨削产生的热量来改进表面强度和表面金相组织，并且要防止工件破坏。为此进行了一个用氧化铝砂轮加工AISI6150和AISI5200的实验，并且结论被进行了探讨。 关键词:外圆磨削、磨削热、传热比、表面织构、表面强化。 1( 引言 磨削是具有尺寸公差、几何精度和表面光洁度要求的零件的通用而且最后的精加工过程。磨削是机械加工中精度最高的加工方法，它是主要的机械加工方法，占加工费用的25%。几乎所有的产品都或多或少的应用了磨削，而且他们都把精度归因于磨削。 磨削是应用砂轮在工件上以细小微粒的形式不断地去除材料。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离所需尺寸很近然后再用磨削完成加工工序。随着磨床的出现，磨 1 削已成为高档材料的主要加工方法。它是能得到所需尺寸同时进行抛光的最经济的一种加工方法，而且能在同一机床上不换砂轮进行粗精加工。 之前，很多科学家对磨削时产生热量的浪费和及其对表面质量的影响进行了研究。根据磨削环境，热量主要通过工件散失，从而导致工件表面热量大量积累。热量的大量积累使工件表面温度升高。高温在工件表面造成一些如裂缝、回火层或白色腐蚀的破坏。如果工件表层温度超过910?，表面晶相将发生变化。Shaw和Vyas已经对磨削产生的表面破坏进行了深刻的理论阐述。在磨削时，造成表面损伤的热影响层能被观察到。零件表面损伤，不能达到质量要求将给制造商带来严重的浪费。 大多数研究的目的是想预知在磨削强化过程中不希望得到的改变从而避免之。无论如何，在磨削过程中热量的生成量是被限制的。 通过对当今热处理和磨削经验的概括，三个被重点限制的因素是: i. 表面强化的热处理方法很多，例如电磁感应淬火等，但他们很难进行集成化。 ii. 这些表面强化方法不能对不规则产品进行完全表面强化。 iii. 继热处理之后，由于磨削强化强化材料数量的上升，结构成为磨削应主要关心的问题。 以上所述的问题促使研究人员去研究在回转磨削过程中怎样有效利用产生的热量来改进产品质量。 2(工件材料的选择 钢的性能是利用在不同的温度下α与γ混合晶相对碳有不同的溶解能力来调节的。硬化过程是根据奥氏体在特定的临界冷却速度下向马氏体转变从而阻止奥氏体的转变。 Konig和Menser强调指出用工件材料的性能参数来描述磨削过程中工件性能是不可能的。他们同时指出硬度的增加是因为马氏体，它以碳化物的形式保持不变的硬度。马氏体的硬度取决于材料中碳和其他合金元素的含量。在这一工艺中AISI6150和AISI52100被选为工件材料。 3(工艺参数的影响 回转磨削具有很多可变参数，但是只有三个重要参数:1)切削深度，2)进给量，3)磨削来回次数。 在相互联系的区域切削时，热量的产生与切削深度成正比。大的切削深度导致持续长时间的热作用，所以增加切削深度使进入工件的热量增加，这将在工件表面造成烧伤，甚至造成工件表面破坏及影响工件精度。 增加进给量将会增加发热量。进给量的两个主要影响因素是: i. 小的进给量，传递能量高，但是切削功率较低进而使硬化层深度小。 2 ii. 大的进给量，磨削力大，但是导致接触时间短、传递能量减少，进而硬化层深度小。 因此，一个适中的进给量才能在工件表面得到最大的硬化层。 增加磨削来回次数只能在工件表面的某一深度增加硬度，超出这一深度硬度将下降。因为增加切削时间和切削力将产生过多的热量，所以在很短的时间里磨削产生的热量将会接近于工件材料的熔点。因而在超过一定的切削速度后工件硬度将下降。这些过多的热量将影响成形表面的晶相或造成零件变形。 4(温度模型 有效温度的观点已经被通过对很多相互联系的理论和实验结果的估计分析所证实。在这一实例中，磨削强化的程度受进入工件的热量的影响。 工件表面的有效温度主要受工艺参数的影响，而且Shaw已经把材料的热电性能和可磨削性能描述出来。许多观测者建议在机械和冶金行业特有的研磨工业中，工件表面可以通过控制表面温度来加工。 Rowe et al通过对氧化铝和硅碳化合物砂轮的一系列实验测定出热容量。联系层模型认为在整个磨削层中存在能量分隔区，而砂轮体积模型假设工件和砂轮是可变的热源。Shaw用一个比例系数把微粒性能和这一模型联系起来。 Rowe et al提出了粒子模型，在其理论中的进入工件的热量比率认为大多数热量不是通过切屑和冷却液散失的。 Rowe et al已经研究过砂轮热容量对工件表面晶相的重要性，其方法是测温和分析磨削部位。 5(有关术语 进入工件的传热比:进入工件的传热比是进入工件的热量与总热量之比。 QwR, Qt 在这里: — 进入工件的热量(J) Qw — 产生的总热量(J) Qt 如果用根式的形式表示，分割率则为: R,0.83,b,(kpc),V,l,,Q wwemt 3 在这里: -2-0.5-1— 工件的热系数(J m s K) (kpc)w 砂轮宽度(m) b — — 切削速度(m/sec)V w — 纹理长度(m) le — 环境温度(?C) , m — 产生的总热量(J) Qt 分割率的根式表达式是在假定热量分布均匀而且热量只在工艺内部流动时成立。 6(理论模型 理论模型要求预知分割率和工件温度。首先，应用Rowe et al提出的微粒联系区域模型而且认为在整 个磨削过程中的能量是联系的，则很多材料的分割率被表述为: '121R,1，{VV,[(kpc)(kpc)]} swsw 在这里: -2-0.5-1(kpc)— 砂轮的热容量系数(J m s K) s — 砂轮旋转速度(m/s) VS — 工件运动速度(m/s) V w 氧化铝砂轮的热容量系数: ,2,0.5(kpc),0.2kJmsK,1 s 利用材料物理性能得到的各种工件的热容量系数: (kpc),AISI52100 w 4 ,2,0.5,1 ,10.5kJmsK (kpc),AISI6150w ,2,0.5,1 ,12.8kJmsK各种工件材料的分割率如下: 对于AISI52100: 工件速度()=1.099m/sec Vw 砂轮转速()=30m/sec Vs '12 1R,1，{(VV),[(kpc)(kpc)]}swsw '解得: R,0.90948,0.91对于AISI6150: '近似解得: R,0.9246,0.925如果考虑切屑()和冷却液(e)上流失的热量，那么预知的分割率将下降: ecfcc 'R,R[1,{(e，e)e}] cccfc 式中: — 切屑所含能量(J) ec 3ee根据Howe et al的经典评价为6 J/mm,在沸腾的液体中趋向于无穷小(=0)。于是，考虑ecfcfcc 这些因素则原先的分割率变为: 'R,R[1,(6e)] c 在能量很小时，切屑所含能量的影响显地越来越重要，根据粒子联系模型，切屑所含能量被假定为 3e,30Jmm c 于是，工件材料的分割率被表述为: 5 '' R,R,{1,(630)},R,[0.8] '因此， R,R,[0.8] 利用Rowe et al发展的粒子联系模型解决砂轮和工件间的热量分割: , R,1{1，(kr,V),[1(kpc)]}wsgeosw在这里: -1-1 — 砂轮的热传导率(Wm K) kge -1-1= 35 W m K(对于氧化铝砂轮) kge — 径向切削深度() r,mo 对于AISI5210: R,1{1，(kr,V),[1(kpc)]}wsgeosw 3R,R,0.73,1{1，(35r,30),1，(10.5，10)} wso ,6解得，r,2.71，10,2.71,m. o 最佳的纹理长度() le l,r,d. eoe 已知: , d,[d,d(d，d)]eswsw 式中:—等效直径(m);—砂轮直径 (m);—工件直径 (m) dddesw ,6-3l,(2.71，10),(0.0318)解得，。因此， =0.2935×10 m=0.29 mm.切削持续时间d,0.0318mee (t), ,解得，t,9.66,sec。 t,lVes 6 7(进入工件热量的计算 从根式表达式得: . R,QQ,0.83b(kpc),V,l,Qwtwwemt因此， . Q,0.83b(kpc)V,l,,wwwem 对于AISI52100 进入工件的总热量: 312,312 Q,0.83[0.06][10.5，10][1.099][0.2935，10],32w 解得， =300 J.可知， QW Q,kA,tdx {dx=1(unit length)}, ,T,QkA, 这里， -1-1-1-1 K — 热传导率(W m K) 43.3 W m K 2-32A = 面积(m)=6.597×10 m -3?T = 300/(6.597×10)(43.3) 解得，T = 1050?C T1 = 1083? 对于AISI6150 R,1{1，(kr,V),[1(kpc)]}, wsgeosw 3R,R,0.74,1{1，(35r,30),1(12.8，10)}, wso ,6r,2.0118，10,2.0,m解得，. o 最佳粒子接触长度() le 7 l,r,deoe ,6,3l,(2.0，10)(0.0318),0.25，10m,0.25mm e 粒子接触时间(t) ,3 t,lV,0.25，1030,8.43,seces 对于AISI6150 进入工件的总热量， 312,312 Q,0.83(0.06)(12.8，10)(1.099)[0.25，10],32w -1-1-32Q,kA,Tdx解得，.可知(dx=1)，这里k=53.6 W m K， A=6.599×10 m.Q,338J w 解得，T=955?C, T=987?C 1 奥氏体向马氏体转变是由于接触面积上产生的温度导致的。 8(试验 通过改变切削深度、进给量和磨削来回次数来进行实验研究。为了得到磨削强化层，一个 标准 excel标准偏差excel标准偏差函数exl标准差函数国标检验抽样标准表免费下载红头文件格式标准下载 的氧化 铝砂轮被选定，并且初步确定了磨削环境。这些意味着为引导马氏体晶相的改变，高的材料去除率是有必 要的。在这个实验中，切削速度是根据表面粗糙度和加工精度要求来改变的。磨削环境在下面给出: 表1 磨削条件 工艺: 回转磨削 砂轮: 氧化铝A46L5V 材料: AISI6150&AISI52100 切削速度: 30m/s 冷却液: 乳浊液 R各种粗糙度参数如轮廓算术平均偏差，轮廓最大高度，微观不平度十点高度被测量出来。表RRzat面裂缝被用电磁裂缝探测器进行探测，并且结果被进行了分析。、 8 9(试验结果和探讨 从微观结构上看这是明显的，在磨削过程中产生的大多数切屑已被腐蚀变暗，但也有白色腐蚀带的存在。这意味着炭化物微粒几乎完全被从铁素体基体中分离出来。(晶粒细小的马氏体结构产生了) a. 经过磨削的AISI6150样本的显微结构。b. 经过磨削的AISI52100样本的显微结构。 这些被腐蚀的晶相显示当温度到810?时有大量的碎屑产生,而到950?或更高时白色腐蚀带将产生,这正如Doye和Dean所提出的一样。但是在大的磨削深度时，工件表面温度将对切削有更大的影响，尽管表面热量的产生和冷却是迅速的。在这一工艺中得到的理论模型也被在相关领域中得到。以下指出磨削材料在表层以下各深度的硬度。 c(磨削来回次数决定硬化程度(AISI6150)。 d. 磨削来回次数决定硬化程度(AISI52100)。 从磨削样本和切削样本的比较中可以得出磨削强化可以得到较大的硬度。在这实验中应用了冷却液，尽管它对磨削强化没有太大的影响。 9 e. 比较车削样本和磨削样本的硬度(AISI6150)。 f. 比较车削样本和磨削样本的硬度(AISI52100)。 采用大的切削深度且增加磨削来回次数，散热面积和接触时间将随着切削能量的增加而增加。继续增加切削深度，硬度将下降。这是因为切削深度超过一定的限度后，切削能力将下降。磨削强化的零件被用电磁探测器进行检测，要求无缺陷。 g(磨削来回次数的影响(AISI6150)。 h(磨削来回次数的影响(AISI52100)。 10(表面织构的控制 表面晶相组织是在环境条件改变或不变的情况下，工件表面进行的机械或其他表面成形工艺决定的。材料的自然表面对材料的机械性能有很大的影响。在有些材料的机械工艺下这些关系被进一步显现。 Nam et al已经阐明，精加工是机械制造的关键。以前，对表面特征和功能要求的关系关注的很少。缺 10 乏对摩擦和磨损现象的认识已成为一个有关表面特征和摩擦表面设计制造的循环问题。因而，尽管设计的重点是要求工件表面摩擦小、磨损少和经济利益，但是迄今为止仍不能设计和制造出最佳的光滑表面。 在结构实用性上，表面的自然斜槽是最重要的。对于承载，则表面的自然峰的数量更为重要。因而工件样本的表面不平度被测量出来，而且测量结果被进行了划分。 i(磨削样本的表面粗糙度值(AISI6150)。 j(磨削样本的表面粗糙度值(AISI52100)。 根据国际标准，这一结果是可以被接受的(磨削的表面粗糙度在0.1到0.16的范围内是可以被,mRa 接受的)。 11(结论 实验证明外圆磨削中产生的热量可以被作为新的热处理方法来有效利用。 根据现有的回转磨削知识和实验结果，得出以下结论: , 磨削硬化部分是细小微粒的马氏体，它是通过表面奥氏体层的短时自淬得到的。 , 冷却液可以避免烧伤和改进表面质量，但是它对淬硬的影响是微不足道的。 , 磨削强化的零件上很少出现裂缝，但仍须用电磁探测器进行检查。实验证明，机械加工部分在垂直 装夹时容易淬硬。 , 磨削强化的加工方法可以被用主轴、凸轮轴、轴承侧面、导轨和另外的功能面等普遍应用磨削的工 艺中。 , 可以推断对于AISI6150 10时(最大切削深度为0.9mm)，硬度是增加的，硬化层为1mm。对于 AISI52100磨削来回次数为14，(最大切削深度为1.3mm)时，硬化层为1.6mm。磨削来回次数超过 11 14，则硬度下降。由此可认为，AISI52100可增加的碳含量和磨削来回次数比AISI6150多。 , 理论温度模型是用微粒接触模型找出切屑和工件分界面的温度，看哪一温度与Doyle和Dean提出 的比较符合。实际上，联系区域产生的热量是奥氏体向马氏体转变的主要热源。 这是可以肯定的，采用这种新方法进行表面强化具有很大的经济利益，这是因为它可以提高集成化程度，而且它也可以实现向另外表面强化工艺的技术转变。磨削强化工艺的应用导致工艺路线的缩短和工序时间的减少，当然也降低了生产成本。 参考文献 1 Des Ruisseaux N.R., Zerkle R.D., Thermal analysis of the grinding process, Trans. ASME J. Eng. Ind., 92 (1970) 428–432. 2 Shaw M.C., Vyas A., Heat affected zones in grinding of steels, Ann. CIRP, 43/1 (1994) 571–581. 3 Shaw M.C. Fundamentals of grinding, New Developments in Grinding, Shaw M.C. Carnegic Press, 1972. 4 Guo C., Malkin S., Heat transfer in grinding, J. Mater. Process. Manuf. Sci., 1 (1992) 16–27. 5 Doyle E.D., Dean S.K., An insight into grinding from materials viewpoint, Ann. CIRP, 29 (2) , (1980) 571–575. 6 Konig W., Menser J., Influence of the composition and structure of steels on the grinding process, Ann. CIRP, 30 (2) , (1981) 541–553. 7 Shaw, M.C. Grinding temperatures. In 12th North American Manufacturing Research Conference Proceedings, SME, 1984, pp. 304–308. 8owe W.B., Pettit J.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. 9 Rowe W.B., Black S.C., Mills B., Ql H.S., Morgan M.N., Experimental investigation of heat transfer in grinding, Ann. CIRP, 44 (1995) 329–332. 10 Rowe W.B., Black S.C.E., Morgan M.N., Validation of thermal properties in grinding, Ann. CIRP, 47 (1) , (1998) 275–279. 11 Howes T.D., Neailey K., Honsun A.J., Fluid film boiling in shallow-cut grinding, Ann. CIRP, 36 (1) , (1987) 223–226. 12 Nam P., Sub, Nannaji, Surface engineering, Ann. CIRP, 36 (1) , (1987) 403–408. 12 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 Experimental Studies on the Grind-Hardening Effect in Cylindrical Grinding *CorrespondingV. S. K. Venkatachalapathy *Corresponding B. Rajmohan V. S. K. Venkatachalapathy *Send correspondence to: rajmohan51@mitindia.edu Department of Mechanical Engineering V.R.S. College of Engineering & Technology Arasur Villupuram (Dt.) Tamil Nadu India Search ALL works by V. S. K. Venkatachalapathy B. Rajmohan *Send correspondence to: rajmohan51@mitindia.edu Department of Production Technology MIT, Anna University Chromepet Chennai Tamil Nadu India Search ALL works by B. Rajmohan Abstract In recent 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 higher 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., the specific energy developed during grinding is very high. At a critical level of specific grinding (1) experienced by the workpiece may be such that thermal damage is induced. Heat energy, the temperature rise damage induced by the grinding process is well documented and may be categorized by temper colors that are at least unsightly and probably indicative of more serious damage, including thermal cracks, tempered zone, etc., (2) which can lead to catastrophic failure of critical machine parts that shortens the life of products subject to cyclic loading. In this work, a new heat treatment process called ―grind hardening‖ and a mathematical model are introduced, and this work deals with how the in-process energy in grinding can be effectively utilized to improve the surface hardness and surface texture, and also to prevent damages. An experimental study has also been carried out in grinding AISI 6150 and AISI 52100 steels with an alumina wheel, and the results are discussed. Keywords Cylindrical grinding, Grinding heat, Partition ratio, Surface texture, Surface hardening 13 1 Introduction Grinding is a versatile and also final machining process in the production of components requiring close dimensional tolerances, geometrical accuracies, and a smooth 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 in industrialized countries. Almost all products have either been machined by grinding at some stage of their production or have been processed by machines, which owe their precision to abrasive operations. Grinding removes metal from the workpiece in the form of small chips by the mechanical 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 work 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 economically by this process to the size and finish that is not possible by any other method. Grinding often permits heavy stock removal and good finish on the same machine, even without changing wheels. (3) 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 via 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 alterations in the surface layer like cracks, tempered zones, or white etching areas (WEA). If the material in the surface layer is heated above the upper critical temperature (910?C) during grinding, diffusion and phase transformation take place. Shaw and Vyas gave an impressive theoretical description of metallurgical damages in ground surfaces. (2) Under abusive grinding conditions, the formation of a heat affected zone (HAZ), which damages the ground surface, was observed. (4) A thermally damaged component may, therefore, incur a significant cost to the manufacturer in failing a quality standard. The aim of most investigations was the prediction of undesired alterations in order to avoid thermal damages when grinding hardened steels. In any case, the quantities of generated heat in grinding are considered as a restricting factor. By summarizing today's experience in heat treatment and grinding, three important limitations can be identified: i There are many heat-treatment processes for surface hardening, like induction hardening, case hardening process, etc., but they are very difficult to integrate into the production line, ii These surface-hardening processes cannot be done perfectly as in the case of irregular- and contour-shaped objects and iii Subsequent to heat treatment, structural parts are subjected to grinding, in the course of which impairment of hardened materials can arise because of the thermomechanical influences of the grinding processes. 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. 14 2. Selection of the workpiece material 3 Influence Of The Process Parameters Cylindrical grinding has many parameters that can be varied, but only three are very important: i) depth of cut; ii) feed speed; and iii) number of passes. The heat generated is proportional to the depth of the cut at the contact zone, because higher depths of cut result in longer 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 causing surface damage, grinding heat can also affect the precision of the workpiece. Increasing the feed speed is generally connected with increasing process forces. The two main effects of feed speed are i At very low feed speed, the traveling energy is high, due to lower cutting power, the extent of hardened layer is reduced. ii At very high feed speed, the cutting power increases, but due to the decreased contact time and lower traveling energy, the extent of the hardened layer is once again reduced. Thus, a moderate or medium feed speed is always preferable to produce maximum hardness in the surface. Increasing the number of passes increases the hardness at the surface 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 close 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 thermal expansion and distortion of the workpiece. 4 Temperature Modeling 15 Usually the validity of a thermal approach is substantiated by means of evaluating the various thermal properties using various correlation theories and experimental results. In this case, the grind-hardening effect is being quantified by means of heat entering into the workpiece. The effective work surface temperature is principally influenced by the process 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 machined surfaces can be produced by controlling the effective work surface temperature. Rowe et al. (8) determined the thermal properties by steady-state experiments for alumina and silicon carbide wheels. 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. Shaw used an area ratio factor to correlate grain properties with such a model. Rowe et al. (9) proposed a grain model in which the partition ratios (partition ratio is defined as the proportion of heat entering into workpiece to the total heat developed) were considered without considering the energy convected away by the chips and coolant. Rowe et al. (10) have investigated the significance of the grinding-wheel thermal properties on the surface texture of the workpiece. The approach was to measure temperature and analyze the proportion of grinding 5. Terminology Involved Partition ratio (R): The partition ratio is the proportion of the heat entering the workpiece to the total heat. where , Q—Amount of heat entering the workpiece (J) w , Q—Total heat produced (J) t For a square law distribution, the partition ratio is given by where -2-0.5-1, (c)—Thermal contact coefficient for workpiece (J m s K) w , b—Grinding width (m) , V—Work speed (m/sec), w , l—Grain contact length (m) e , —Background temperature (?C), m 16 , Q—Total heat produced (J) t Justification for using the square law distribution is based on the assumption that the heat distribution is uniform along the contact area and that the flow is radially inward to the work. energy entering the workpiece. 6 Theoretical Model Theoretical models are required to predict the partition ratio and workpiece temperature. First, using a grain contact 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. where -2-0.5-1, (c)—Wheel bulk thermal coefficient (J m s K) s , V—Speed of the grinding wheel (m/s), s , V—Speed of the workpiece (m/s) w The bulk thermal coefficient for alumina wheel The bulk thermal coefficient for each workpiece material is found by using their physical properties The partition ratios for various workpiece materials are as follows. 17 For AISI 52100 On solving, R=0.909480.91. For AISI 6150 Similarly, on solving, R=0.92460.925. If the allowance for the energy convected away by the chips (e) and coolant (e) is considered, then the cccf predicted partition ratio is reduced, i.e., 3where e—Specific chip energy (J/mm). c 3According to Howes et al., (11) a typical value of e is 6 J/mm and e tends to be very small where fluid cccf boiling occurs (e=0). cf Thus, considering the allowance, the original partition ratio can be given by The effect of the chip energy becomes increasingly significant at lower specific energies. According to the grain contact model, the specific energy of the chip is assumed to be Thus, the partition ratios for the workpiece material were found as 18 Therefore, R=R[0.8]: Using the grain contact model developed by Rowe et al., (9) the solution for partitioning of heat between the wheel and the workpiece is where -1-1, k—Thermal conductivity of the grinding wheel (Wm K) ge -1-1, k=35 W m K (for alumina wheel) ge , r—Radial depth of cut (m) o For AISI 52100 -6On solving, r=2.71×10=2.71 m. o Optimal grain contact length (l), e It is known that where , d—Equivalent diameter (m) e , d—Diameter of wheel (m), s , d—Diameter of workpiece (m) w -6-3On solving, d=0.0318 m. Therefore, l=(2.71×10)(0.0318) =0.2935×10 m=0.29 mm. Grain contact ee time (t), t=l/V, on solving, t=9.66 sec. es 19 7 Calibration Of Total Heat Entering Into The Workpiece From the square law distribution, Therefore, For AISI 52100 Total heat entering into workpiece On solving, Q=300 J. It is known that w where -1-1-1-1, k—Thermal conductivity (W m K)43.3 W m K 2-32, A=Area (m)=6.597×10 m -3, T=300/(6.597×10)(43.3) On solving, T=1050?C For AISI 6150 20 -6on solving, r=2.0188×10=2.0 m. o Optimal grain contact length (l) e Grain contact time(t) For AISI 6150 The total heat entering into the workpiece -1-1-32On solving Q=338 J. It is known that Q=kAT/d(d=1), where k=53.6 W m K and A=6.599×10 m. On wxx solving, T=955?C, T=987?C 1 This temperature developed at the contact area is the real cause for the phase transformation, i.e., austenite into fine martensite. 8 Experimentation 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 conditions 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 grinding. The grinding conditions are given in Table 1 . Table 1. Grinding conditions : Cylindrical grinding Process Grinding wheel : Alumina A46L5V 21 Materials : AISI 6150 & AISI 52100 Cutting speed : 30 m/s Coolant : Emulsion The various roughness parameters like centerline average R, peak to valley height R, and average peak to at valley height R were measured. The surface cracks were analyzed with the use of electromagnetic crack z detector. The results are discussed. 9 Results And Discussions It is evident from the microstructures (shown in Figs. 1 2) that the bulk of chip produced during machining has etched darkly, but white etching bands are also present. This means that the carbide atoms are almost fully segregated all along the ferritic matrix. (i.e., a fine martensitic structure is generated). Figure 1. Microstructure of ground specimen AISI 6150. Figure 2. Microstructure of ground specimen AISI 52100. This etching response suggests that a temperature of about 810?C has been reached in the bulk of chip and about 950?C or more in the white etching bands, which may be expected as reported by Doyle and Dean. (5) Thus, the temperature at the workpiece surface could have an important influence on metal removal at a large wheel depth of cut. However, heating and cooling of the surface would occur rapidly, and this may have the influence of producing phase changes in the surface. The theoretical model developed in this present work also gives the same temperature that developed at the contact area. The following graphs (shown in Figs. 3 4) show the coarse hardness of the ground material at various depths beneath the surface. 22 Figure 3. Hardening results depending on number of passes (AISI 6150). Figure 4. Hardening results depending on number of passes (AISI 52100). The higher hardness obtained during this grind hardening effect when comparing ground specimen with turned specimen is shown in Figs. 5 6 (number of passes 10 in Fig. 3 and number of passes 14 in Fig. 4 ). The experiments were carried out with the application of a coolant, however the coolant does not have much impact in the grind-hardening effect. Figure 5. Comparison of hardness of turned and ground specimen (AISI 6150). Figure 6. Comparison of hardness of turned and ground specimen (AISI 52100). With the higher depth of cut and increased number of passes (shown in Figs. 7 8), the area and the time for heat transfer is increased due to the increase (to certain depth of cut only) in traveling energy. A further increase in the total depth of the cut (increase in number of passes) decreases the hardness. This is because 23 the increase in the total depth of the cut after a certain period decreases the specific cutting energy. The grind-hardened components were also inspected using an electromagnetic crack detector, and no flaws were found. Figure 7. Influence of number of passes (AISI 6150). Figure 8. Influence of number of passes (AISI 52100). 10 Control Of Surface Texture Surface texture is defined as the inherent or enhanced condition of a surface produced in a machining or other surface-generating operations. The nature of the surface layer may have a strong influence on the mechanical properties of the material. This association is more pronounced in some materials and under certain machining operations. Nam et al., (12) have stated that the surface finish is a major concern in manufacturing. Yet very little attention has been given to elucidate the relationship between the characteristics and the functional requirements of surfaces. A recurring problem in the specification of surface characteristics, and the design and manufacture of tribological surfaces has been the lack of a clear understanding of the friction and wear phenomena. Consequently, despite the engineering importance of low-friction and low-wear surfaces and the resulting economic benefits, so far it has been impossible to design and manufacture sliding surfaces optimally. On structural applications, the nature of declivity troughs of the surface is the most important, while on bearing applications, the nature and number of crests on the surface is more significant. Therefore, the surface roughness of the ground specimen was also measured and the results were plotted (Figs. 9 10). 24 Figure 9. Surface roughness values of a ground specimen (AISI 6150). Figure 10. Surface roughness values of a ground specimen (AISI 52100). The results are at acceptable levels according to Japanese International Standard. (The acceptable range of finish R in grinding is 0.1 to 0.16 m). a 11 Conclusion Experimental investigations have shown that the generated heat in cylindrical grinding could be effectively utilized as a new heat treatment process. With the existing knowledge in grind hardening and based on the test results, the following findings are presented: , The grind hardened parts are characterized by fine grained martensitic layers, which were obtained by short-time austenisation of surface layers with self-quenching. , The application of coolant may avoid thermal damage and improve surface finish, but it has a negligible effect in quenching. , Surface cracks are not found in the grind hardened component. It was also checked by using an electromagnetic crack detector. Machine parts that are used under normal loading conditions can be easily grind hardened. , Possible industrial applications for surface hardening by the grinding lie in the production of running faces for rotary shaft seals, camshaft, lateral faces of the bearings, guide ways, and many other functional surfaces that are frequently ground (Fig. 11 ). , It is also inferred that there is a considerable increase in hardness up to 10 passes (total depth of cut 0.9 mm), and a depth of hardness penetration is 1 mm for AISI 6150 (Figs. 3 7). The depth of hardness penetration is 1.6 mm for AISI 52100 (Figs. 4 8) at 14 passes (total depth of cut 1.3 mm), after that the hardness decreases. This may be attributed to the increase in the carbon percentage and the number of passes in AISI 52100 than in AISI 6150. , The theoretical temperature model is developed by using a grain contact model to find out the temperature at the interface between the cutting grain and the workpiece, which gives the best 25 agreement with the suggestions given by Doyle and Dean. (5) Actually, the temperature developed at the contact area is the main source for the phase transformation, i.e., austenite to fine martensite. It is promising to note that the adoption of this new surface-strengthening method may have a great economical benefit due to its increased integration level, and it is also a technological alternative to the other surface hardening processes. This leads to shorter production sequences and reduced throughout time, as well as decreased cost. Figure 11. Industrial parts for grind hardening. reference 1 Des Ruisseaux N.R., Zerkle R.D., Thermal analysis of the grinding process, Trans. ASME J. Eng. Ind., 92 (1970) 428–432. 2 Shaw M.C., Vyas A., Heat affected zones in grinding of steels, Ann. CIRP, 43/1 (1994) 571–581. 3 Shaw M.C. Fundamentals of grinding, New Developments in Grinding, Shaw M.C. Carnegic Press, 1972. 4 Guo C., Malkin S., Heat transfer in grinding, J. Mater. Process. Manuf. Sci., 1 (1992) 16–27. 5 Doyle E.D., Dean S.K., An insight into grinding from materials viewpoint, Ann. CIRP, 29 (2) , (1980) 571–575. 6 Konig W., Menser J., Influence of the composition and structure of steels on the grinding process, Ann. CIRP, 30 (2) , (1981) 541–553. 7 Shaw, M.C. Grinding temperatures. In 12th North American Manufacturing Research Conference Proceedings, SME, 1984, pp. 304–308. 8 Rowe W.B., Pettit J.A., Boyle A., Moruzzi J.L., Avoidance of thermal damage in grinding and prediction of the damage threshold, Ann. 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