An investigation of bell mouthing in precision hole machining with self-piloting tools

The bell mouth is the tapered hole entrance and it is unavoidable disadvantage of the machining with self-piloting tools. A comprehensive theoretical and experimental study of bell mounting in precision hole machining with self-piloting tools is carried out. The prime concern of the theoretical part is the mechanism of the bell mouth formation. The main factors affecting bell mouth have been revealed by analyzing mechanics of tool entrancing into the workpiece. Three working methods with self-piloting tools are considered and the recommendations made relevant to the tool and machine tool design. Experimental part of the study involved Boring and Trepanning Association self-piloting drilling on special designed deep-hole drilling machine. The main objective of this part was to obtain the quantitative relationships between the bell mouth parameters and the cutting regime. The technique of the statistical design of experiments along with a special procedure for the data acquisition and analysis provided to cover the whole range of the process parameters and to get the mathematical model accounted the parameters interaction.