Ballizing is a method of burnishing an internal diameter by forcing a precision ground steel or a
tungsten carbide ball through a slightly undersized pre-machined hole. This plastic deformation
process produces a smooth surface with favorable mechanical properties and negative residual
stresses. The objective of this investigation is to determine the optimal setting of the ballizing
parameters while ballizing 70/30 cu-zn brass alloy. The parameters considered are interference,
wall thickness of the hole, number of passes, ball speed and initial surface roughness of the hole,
whereas the responses are surface roughness, residual stresses and microhardness variation of the
ballized hole. The optimal setting of the parameters is determined through experimental planning,
conducted and analyzed using Taguchi method. It is found that the initial surface roughness of the
hole exerted the greatest effect on surface roughness of the ballized hole, followed by interference
and wall thickness of the hole. The No. of passes and ball speed were found to have only a slight
influence on the surface finish. A critical interference (300 µm) exists for maximum improvement
in roughness. Based on the experimental results, the optimal ballizing for compressive residual
stresses were obtained at 4 mm wall thickness, 400 µm interference and 2 mm/sec ball speed.The
initial surface roughness and No. of passes were found to have no significant effect on the residual
stresses. The optimum conditions for surface roughness and residual stresses are different. The
microhardness just below the ballized surface was improved up to 65%. The maximum depth of
the plastically deformed layer was observed at 300 µm below the ballized surface. Generally, it
was observed that the maximum value of the strain hardening increases with the increase in both
interference and wall thickness. The results of confirmation experiment agree will with the
predicted optimal settings.