Effect of workpiece structure on burr formation in micro-drilling

The effect of workpiece structure and drill diameter on burr formation in drilling was investigated. The characteristic results are that burr formation is reduced when the grain size of the workpiece increases, and this effect of grain size becomes especially important when the drill diameter is very small and its tool edge is dull or worn. These facts are explained as follows: since the number of crystal grains covered by drilling a part is small when the workpiece structure grain size is large and drill diameter is small, the effect of crystal anisotropy on working stresses becomes smaller and the effect of the crystal boundaries on drilling work per revolution becomes smaller for micro-drill feed. Therefore, chips are easily separated from the workpiece during plastic deformation, and only small burrs will be produced in micro-drilling