Determination of tool nose radii of cutting inserts using machine vision

Purpose - The nose radii of cutting inserts are normally measured using a profile projector or toolmaker's microscope. Since only a sector of a circle is available for the measurement using such instruments, the radii determined from these methods are inaccurate. The purpose of this paper is to present an alternative method of determining the nose radii more accurately using machine vision. Design/methodology/approach - The 2D images of the cutting inserts were captured using a CCD camera with the aid of back lighting. The tool nose center in each digitized image was located based on the tool geometry. The curved nose profile was transformed into a linear profile using polar-radius transformation. The nose radius was then varied within ten pixels of the nominal radius and the average deviation from a straight line profile in the nose region in the polar-radius plot was evaluated. The radius corresponding to the minimum average deviation is identified as the most accurate radius value. Findings - For the 15 simulated images of cutting inserts tested, the error in radii determine by the proposed method varied from -4.9 to 3.7 percent. But, the radii were about 9 to 22 percent higher than those measured using the profile projector on commercially available inserts. The radii measured using the profile projector was closer to the nominal radii with an average deviation of -3.2 percent compared to those measured using the proposed method. Research limitations/implications - The cutting inserts must be clean and free from dust particles when capturing the images; and the insert must be aligned accurately so that the plane of the nose profile is perpendicular to the optical axis of the CCD camera. Practical implications - The proposed method can be used to determine the nose radii accurately. If the exact nose radius of an insert is known, the tool path can be programmed precisely to obtain high-dimensional accuracy in the finished product. Originality/value - The paper shows how a new method of determining the tool nose radii of cutting inserts more accurately compared to the conventional methods, based on a sector of the nose profile, has been developed.