Applied Surface Science 288 (2014) 208–214 Contents lists available at ScienceDirect Applied Surface Science jou rn al h omepa g e: www.elsevier.com/locate/apsusc Correlation between contact surface and friction during the optical glass polishing N. Belkhir * , T. Aliouane, D. Bouzid Laboratory of Applied optics, Institute of Optics and Precision Mechanics, University Ferhat Abbas, Setif 1, Algeria a r t i c l e i n f o Article history: Received 22 February 2013 Received in revised form 21 September 2013 Accepted 1 October 2013 Available online 11 October 2013 Keywords: Optical glass Polishing Pressure distribution Surface contact Friction a b s t r a c t This study aims to determine the correlation between the contact surface, the polishing pressure and the friction coefficient during the optical glass polishing. For this purpose, BK7 optical glass samples were polished and the mentioned parameters were measured to find a correlation between them. Several methods of characterization have been used; the mechanical profilometer, the AFM, and in addition setups for measuring forces and the contact surface have been developed and adapted to the polishing machine. The found results have shown the existence of a close relationship between the three parameters and the influence of each other. This have allowed to deduce that during the polishing process it is very important to control the contact pressure and the polisher form according to the pressure distribution in order to guarantee a very high quality of the polished surface. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The reproducibility of optical surfaces with high accuracy is a major aim of the optical industry development. The free abrasives polishing process consists of a frictional contact between the sam- ple and the rotating polishing pad. In polishing, slurry of abrasive grain sizes below 1 m is supplied on a soft polisher generally used in this operation. The fine abrasive particles are retained on the pad surface resiliently and plastically, and the work surfaces are scratched microscopically. Polishing actions are by far smaller if compared with lapping, contributing to the successful applications to the brittle materials [1]. Several hypotheses were proposed to describe the material removal in the polishing process [1–5], but the most used is the combined hypothesis of two actions; a mechanical action gener- ated by the abrasive grains and a chemical one produced by the reaction between the suspension liquid and the polished material. During the polishing process, material removal is highly influ- enced by the local pressure and the relative speed between the tool and the workpiece. For a constant tool pressure, the shape change can be easily found. However, this is not possible in several cases because of the tool and the workpiece shapes that are not gener- ally the same, the roughness (overlap between the polisher and the * Corresponding author. Tel.: +213 36844653; fax: +213 36844653. E-mail addresses: belnab2002@yahoo.fr, belkhir nabil@univ-setif.dz (N. Belkhir). sample asperities), the presence of the forces and the accelerations simultaneously activating on the surface to be polished [6–11]. The material removal model proposed by Savio et al. [2] shows a sat- isfactory estimation of the material removal as a function of the process parameters. The polishing process can produced highly mirror surface. Mate- rial is removed at a very low rate. Consequently, the geometry of the surface needs to be very close to the correct shape before polishing. The polishing pressure is applied on the abrasive through the comfortable polishing pad. This allows the abrasive to follow the contours of the workpiece surface and limits the penetration of individual grains into the surface. The use of fine abrasive grains involves a moderate abrasive action between the grains and the workpiece. The polishing operation principal consists to the con- tact between the sample and the polishing pad with the presence of the abrasive grains. During the process, the friction of the sam- ple surface on the polisher allows the abrasive grains to remove the hydrated layer formed on the surface of the sample by the chemical reaction. It was reported that the effect due to friction is propor- tional to the compressive force [12]. The polishing rate is assumed to be proportional to the friction between the substrate and the pad [13]. In polishing, the removal material on the surface is closely related to the variation of the friction coefficient [14]. Bowden and Tabor [15] have stated that the true area of con- tact is a very small percentage of the apparent contact area. The true contact area is formed by asperities. When the normal force increases, more asperities come into contact and the average area of each asperity contact grows. The frictional force is dependent on 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.10.008