Measurement uncertainty assessment of Coordinate Measuring Machines by simulation and planned experimentation Francesco Aggogeri a , Giulio Barbato b , Emanuele Modesto Barini b , Gianfranco Genta b , Raffaello Levi b, * a DIMI – Universita ` di Brescia, via Branze 38, 25123 Brescia, Italy b DISPEA – Politecnico di Torino, corso Duca degli Abruzzi 24, 10129 Torino, Italy 1. Introduction The challenges of globalization, product life-cycle time reduc- tion and matching customer demands mandate reliable control of production systems. Enhancement of product quality standards implies delving into control and inspection methods. In this scenario quality control demands require tight standards of product inspection. A current industrial problem is addressed in this paper, namely how to develop a reliable approach to measurement of industrial pieces on a Coordinate Measuring Machine in order to obtain dependable measurements. CMMs are versatile instruments used for precision inspection in industry, and their unique properties more than justify substantial investment; nevertheless uncertainties associated with them are to be reckoned with [1–3]. A correct statement of measurement uncertainty is nowadays a must for companies wishing to comply with ISO 9000 standards [4–6], which requires an effective measurement management and measurement process control [7]. Only a dependable, cost effective inspection system can ensure quality products, reducing to an acceptable level the risk of accepting substandard parts and/or discarding conforming ones. Such considerations have pushed companies to invest resources on these issues. Estimation of measurement uncertainty entails taking into account the multipurpose characteristics of coordinate measuring systems. A substantial number of sources of uncertainty is to be reckoned with, including machine components, fixtures and probes, strategy for data acquisition and/or sampling, data processing and measurement environment [8]. In the light of these considerations, an assessment of measurement variability was undertaken, exploiting a comparison between a simulative method, developed at Politecnico di Torino, and results of a recent national round robin test. Evaluation of measurement uncertainty using a simulative method was shown to yield substantial advantages in terms of cost savings, lead time reduction and management integration. 2. Background on CMM measurement uncertainty estimation Uncertainty evaluation of CMM measurements is made awkward by the sheer complexity of such machines. Substantial efforts were carried out by academia, national and international institutes and organizations, leading to a number of different approaches. These methods cover e.g. empirically approximated methodologies, counseling from measurement experts, and numerical simulations, the latter made possible by the dramatic CIRP Journal of Manufacturing Science and Technology 4 (2011) 51–56 A R T I C L E I N F O Article history: Available online 16 February 2011 Keywords: Bootstrap Coordinate Measuring Machines (CMM) Measurement uncertainty Round robin test Simulation A B S T R A C T Current standard procedures for the evaluation of measurement uncertainty of Coordinate Measuring Machines (CMM) being not fully satisfactory, other methods are considered. Conformity to geometric and dimensional tolerances, specified for an industrial workpiece previously involved in a comprehensive round robin test, was checked with CMM. Measurement uncertainty was also assessed exploiting a simulation method, developed at Politecnico di Torino, offering several advantages in terms of CMM operability and substantial cost savings. Estimates of measurement variability due to single and combined effects of factors considered, obtained from testing in a representative verification, are discussed in the light of results of simulation. ß 2011 CIRP. * Corresponding author. Tel.: +39 011 564 7260; fax: +39 011 564 7299. E-mail addresses: francesco.aggogeri@ing.unibs.it (F. Aggogeri), raffaello.levi@polito.it (R. Levi). Contents lists available at ScienceDirect CIRP Journal of Manufacturing Science and Technology jou r nal h o mep age: w ww.els evier .co m/lo c ate/c irp j 1755-5817/$ – see front matter ß 2011 CIRP. doi:10.1016/j.cirpj.2011.01.007