The mechanics of power hacksawing and the cutting action of blunt tools

The work presented in this thesis is part of and continuation of the work carried out by the author on the Mechanics of Power Hacksawing, on behalf of a hacksaw blade manufacturer. Process parameters which influence the metal. removal rate during power hacksawing have been identified and thus a detailed explanation of the basic sawing mechanism-suggested. Power hacksaw machine characteristics have also been investigated. The problem of blade testing is discussed. A method for assessing the blade performance is proposed which is based on metal removal rate but is independent of the machine characteristics. This could be 'used as a quality index for power hacksaw blades. This performance index is found to vary with workpiece breadth and tooth pitch. A theoretical model is used to give some explanation of this variation. iiowever, there is evidence that the gullet size and goemetry arc, more significant factors influencing the variation in blade performance with changes in the breadth of the workpiece and pitch of the blade teeth. Examinations of saw blade teeth have revealed that they have large cutting edge radii compared to the layer of metal removed, indicating that saw blades are basically blunt tools. The cutting action of tools with large cutting edge radii has been investigated and extensive simulation tests have been undertaken. From the observations of the chip formation mechanism and measurements of the relative position of the tool and machined surface during cutting, some new light is thrown upon the ploughing process. A slip-line field is proposed which qualitatively represents the assumed chip formation mechanism under steady state cutting conditions. The application of an empirical relationship between the chip tool contact length and the undeformed chip thickness in conjunction with the slipline field, provides quantitative correlation with the test results of a single point tool and qualitative correlation with a hacksaw blade.