Experimental study and evaluation methodology on hard surface integrity

Funded by the Ministry of Education of China- “985” of international cooperation project “Clean Manufacturing Technology”. X. P. Zhang (*) . Z. Q. Yao Mechanical Engineering School of Shanghai Jiao Tong University, Shanghai 200030, People’s Republic of China e-mail: zhangxp@sjtu.edu.cn C. R. Liu Industrial Engineering School of Purdue University, West Lafayette, IN 47907-1287, USA e-mail: liuch@ecn.purdue.edu
Int J Adv Manuf Technol (2007) 34: 141–148 DOI 10.1007/s00170-006-0575-6
ORIGINA L ARTI CLE
XuePing Zhang . C. Richard Liu . Zhenqiang Yao
Experimental study and evaluation methodology on hard surface integrity
research is to analyze the conflict in turning parameter selection and then establish a harmonious approach to resolve it.
2 Experiment procedure
2.1 Samples preparation Samples are the inner rings of a certain type of rolling bearings. Their heat treatment is the same as that of the actual rolling bearings. All the samples were austenitized at a temperature of 850°C for 2 h, quenched in oil at 70∼90°C for 30 min, then tempered at 170∼190°C for 3 h. The measured hardness for each sample is 62∼63 HRC. The chemical composition of the work material as specified by the manufacturer is listed in Table 1. The inner diameter of the ring is 45 mm, the outer is 65 mm, and the width is 25 mm. The end surface of samples is the right part to be super-finish hard turned by CBN insert. 2.2 Testing system A cutting tool (CBN insert) constructed of cubic boron nitride manufactured by Sandvik Coroman was selected for the experiment. The insert’s γ, α, r" are −30°, 0 and 0.4 mm, respectively. The tool holder used in the experiments is PCLNL 1616 H 09 matched up to the CBN insert. Before each cut, a new insert with the same specification is applied in order to eliminate the effect of tool wear occurred in the foregoing process. The cutting tool is fixed in the numerical control machine tool of INDEX G200 and a three-jaw chuck is used for chucking the workpiece, all of which construct an enough rigid machine tool system to guarantee the components a favorable surface finish. 2.3 Hard turning process The cutting tool is fed linearly in a direction perpendicular to the axis of rotation. Turning is carried out on the numerical machine tool of INDEX G200 that provides the
142 Table 1 Nominal chemical composition (wt%) of hardened bearing steel Fe Balanced C 1.05 Cr 1.54 Mn 0.44 Si 0.30 P 0.012 S 0.002 1 2 3 4 5 6 7 8 9 Table 3 Experimental layout using an (L9(34)) orthogonal array Cutting parameter level Experiment no. s Cutting speed 1 1 1 2 2 2 3 3 3 ap Depth of cut 1 2 3 1 2 3 1 2 3 f Feed rate 1 2 3 3 1 2 2 3 1
1 Introduction
For more than a decade, hard turning, which cuts hardmachined material (HRC45∼65) by polycrystalline cubic boron nitride (PCBN/CBN), has been recognized as a potential substitute for abrasive-based processes due to its clear economic benefit, flexibility, and superior surface integrity [1–3]. It is an inevitable but important consequence of hard turning to produce surface structural change in component introduced by a material removal process, which results in intense, localized and rapid thermal mechanical working. The machined surface therefore shows an extremely different structure from the bulk [4, 5]. Surface integrity, defined as all aspects of surfaces such as surface finish, metallurgical change and residual stresses, is the most important concern for the component and has attracted substantial effort around the world [6–8]. The majority of published research has focused on the surface finish, residual stress, micro-hardness, and white layer (micro-structural alterations) of the hard turned components in a given turning parameters, or optimizing one of them to achieve an optimal combination of turning parameters [9–11]. Few efforts have systemically investigated the best turning parameter combination to achieve superior surface integrity. In other words, the problem of evaluating the best turning parameter has not been completely solved when a conflict occurs in selecting the most favorable surface finish, residual stresses, or thermal damage layer. In fact, an evaluation methodology is urgently demanded when hard turning is widely applied in manufacturing industry. This paper focuses on the optimization combination and effect sequence of hard turning parameters designedly to achieve a superior surface finish, residual stresses, and white layer respectively. The Taguchi method, a powerful tool to design optimization for quality, will be used in the experiment to predict the turning parameter optimization on superior surface integrity. The eventual objective of this
Received: 20 November 2004 / Accepted: 24 February 2006 / Published online: 14 April 2006 # Springer-Verlag London Limited 2006
Βιβλιοθήκη Baidu
Abstract The Taguchi method is adopted experimentally to investigate the surface integrity (surface roughness, residual stress, and thermal damage layer) of hardened bearing steel in hard dry turning, and the validation experiments are consequently performed. It was revealed that the value and effect sequence of optimal hard turning parameter varies with different objectives of surface integrity. However, it is quite difficult to select or determine the optimal combination of hard turning parameters. A hard-turned component performance, which reflects an integrated impact of surface integrity, should be fully recognized to resolve the inherent conflict in the selection process. Based on it, an evaluation methodology composed of four steps is proposed that surface integrity should be evaluated by the service/fatigue life of hard-turned components and therefore turning parameters. It bears significance for super-finish hard turning further application in respect that it provides an integrated approach for hard turning parameter optimization to achieve a superior surface integrity. Keywords Hard dry turning . Surface integrity . Turning parameter . Optimization methodology