Method to statistically secure field test results for rock drilling tools

Abstract: The aim of this project is to find a statistical method that describes survival and outcome of a prototype drilling tool from several references and determine how many references are needed for a statistically secure result. The project also answers which variables that affects the outcome. 60 drilling bits of two different types were studied and the variables that are investigated are penetration rate, rotation speed, rotation torque, flush flow, feed force and accumulated depth. Hypothesis test is used for determining how a prototype drills compared to the references and linear regression is used to determine how the references drills. Only accumulated depth affects the survival time with a correlation of 77.7% that was improved to 89.6 % by removing big time gaps that was not of interest for the result. The accuracy of the linear regression for 30 drill bits of one type for max depth related to survival time was 80.3 %. A minimum of 20 prototypes must be tested before determining the outcome of the prototypes in comparison to the references.