Robotic grinding is among the least studied processes due to its complexity compared to conventional grinding and other machining processes. In robotic grinding with a light, flexible robot, low manipulator stiffness is a key factor affecting process behavior and causing impact phenomena. Force prediction and thermal damage are important aspects to consider in robotic grinding because of the vibrational nature of the process. The portable robot used in the process under study is a multi-purpose track-based manipulator developed by IREQ, Hydro-Quebec’s research institute. The main application of this light-weight robot, named “SCOMPI” (Super COMPact robot Ireq), is in situ maintenance of hydro turbine runners. It is observed that the grinding process by this robot is interrupted at each revolution of the wheel rather than having a continous cutting action. This impact cutting behavior appears due to the low stiffness of the flexible manupulator under high grinding forces. Special attention has thus been given to gain a better understanding of the material removal process in such robotic grinding. The objective is to establish appropriate relations among chip formation, operational cutting forces, temperature, material removal rate and consumed power in the process.
The purpose of this study is to use numerical and experimental methods to gain a better understanding of this flexible robotic grinding process. First, a finite element thermal analysis is carried out to evaluate thermal aspects of the process, such as the energy partition ratio and temperature distribution in the workpiece. A new representation of the heat source in line with the impacting effects of robotic grinding is considered in the model. Experimental measurements in conjunction with numerical analyses led to an energy partition model applicable to this study under varying operating conditions. In the second part, the topography of grinding wheels used in the process is characterized and related to depth of cut. The cutting edges of wheels have a significant effect in process efficiency and are essential in understanding material removal in the grinding process. The variation of wheel topography due to process conditions is demonstrated. Knowledge of the edges involved in cutting during the process are vital for micro-scale modeling of cutting interactions occuring in the wheel-workpiece contact zone. Ongoing work on micro-scale force modeling through FEM will benefit from this wheel topography study. The third part of this thesis is dedicated to enhancing the empirical basis for an existing force model of the process. An impact cutting regime is observed by means of high-speed camera recordings and measured process force signals. This regime is detected at different grinding power levels and used in identifying the empirical coefficients. The energy partition model from the first part of study is also incorporated to obtain a friction-chip energy ratio used to determine the force model constants
