Precision Manufacturing Process Monitoring with Acoustic Emission - eScholarship

International Journal of Machine Tools & Manufacture 46 (2006) 176–188 www.elsevier.com/locate/ijmactool Precision manufacturing process monitoring with acoustic emission D.E. Lee a , I. Hwang a , C.M.O. Valente b , J.F.G. Oliveira b , D.A. Dornfeld a, * a Laboratory for Manufacturing Automation, Department of Mechanical Engineering, University of California, Berkeley, CA 94720-1740, USA b University of Sao Paulo, Nucleus of Advanced Manufacturing, Sao Carlos, Brazil Received 27 January 2005; accepted 7 April 2005 Available online 13 June 2005 Abstract Current demands in high-technology industries such as semiconductor, optics, MEMS, etc. have predicated the need for manufacturing processes that can fabricate increasingly smaller features reliably at very high tolerances. In situ monitoring systems that can be used to characterize, control, and improve the fabrication of these smaller features are therefore needed to meet increasing demands in precision and quality. This paper discusses the unique requirements of monitoring of precision manufacturing processes, and the suitability of acoustic emission (AE) as a monitoring technique at the precision scale. Details are then given on the use of AE sensor technology in the monitoring of precision manufacturing processes; grinding, chemical–mechanical planarization (CMP) and ultraprecision diamond turning in particular. q 2005 Elsevier Ltd. All rights reserved. Keywords: Acoustic emission; Precision; Process monitoring 1. Introduction Current demands in high-technology industries such as semiconductor, optics, MEMS, etc. have predicated the need for manufacturing processes that can fabricate increasingly smaller features reliably at very high toler- ances. This increasing demand for the ability to fabricate features at smaller length scales and at greater precision can be represented in the Taniguchi curve (Fig. 1), which demonstrates that the smallest achievable accuracy (and, as a consequence, smallest reproducible feature) decreases as a function of time [1]. In situ monitoring systems that can be used to characterize, control, and improve the fabrication of these smaller features are therefore needed to meet increasing demands in precision and quality. Sensor-based monitoring yields valuable information about the manufacturing process that can serve the dual purpose of process control and quality monitoring, and will ultimately be the part of any fully automated manufacturing environment. However, a high degree of confidence and reliability in characterizing * Corresponding author. Tel.: C1 510 642 0906; fax: C1 510 643 7492. E-mail addresses: cmov@sc.usp.br (C.M.O. Valente), dornfeld@me. berkeley.edu (D.A. Dornfeld). the manufacturing process is required for any sensor to be utilized as a monitoring tool. As demonstrated in a previous review paper by Dornfeld et al. [2], acoustic emission (AE) has demonstrated a high degree of confidence in character- izing various phenomena related to material removal, particularly at the microscale, hence lending credence to its suitability for precision manufacturing process monitor- ing. This work serves to demonstrate sensitivity of AE at the three different manufacturing regimes outlined in the Taniguchi curve; the normal/conventional, precision, and ultraprecision scales (Fig. 1). 2. Requirements for sensor technology at the precision scale In material removal processes at the precision scale, the undeformed chip thickness can be on the order of a few microns or less, and can approach the nanoscale in some cases. At these length scales, the surface, subsurface, and edge condition of machined features and the fundamental mechanism for chip formation are much more intimately affected by the material properties and microstructure of the workpiece material, such as ductile/brittle behavior, crystal- lographic orientation of the material at the tool/chip interface, and microtopographical features such as voids, secondary phases, and interstitial particulates [3,4]. 0890-6955/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmachtools.2005.04.001