The dynamical cutting edge number results from the process kinematics and can be obtained with a thermo-element inside the machined workpiece. Each impulse during grinding should indicate a grit-workpiece contact [PEKL57, DAUD60]. The smaller the contact area of the thermo-element is, the more reliably the temperature peaks can be related to grits.
Luminescence offers another approach. Known luminescence of diamonds for X-rays allows to measure number and size of free-standing diamond grits in a resin bonded diamond wheel after it has been irradiated with focussed X-rays [TOML78a].
6.2.2.3 Replica Methods
The grinding wheel topography itself exhibits some challenges to most measurement methods, such as reflectivity, transparency of grits, or abrasiveness. Therefore, the abrasive layer topography is replicated, but the reproduction quality has to be considered. A simple method is to press a plain paper and a carbon paper onto the wheel surface [GOED36, LORT75]. Every blackened area can be interpreted as cutting edge.
Another method by Nakayama and Shaw works with grinding in an inclined polished plate [NAKA66, KONI70]. Through plate inclination, the grit density in different depths can be obtained. Grinding wheel topography can also be copied onto a workpiece, if workpiece rotations and grinding wheel rotations are coupled with an integer value [PAHL68].
6.2.2.Б Modeling
Several researchers have been working on describing the cutting edge shape because this knowledge is crucial for modeling of wheel and workpiece topography [DOMA06]. Cubes, spheres, ellipses, or octahedrons are common approximations for grit shapes.
Much research has been done on kinematical-geometrical models, where the grinding wheel topography engages with the workpiece. Heinzel, Brinksmeier et al. [HEIN09b, BRIN06] give a broad overview on the state-of-the-art. Kassen [KASS69] did 2D computer simulation. Today 3D simulations help to understand generated surfaces [KOSH03]. New research uses randomly shaped and distributed polyhedrons as grits, which is particularly suited for porous wheels [ZHAG11].