On the quality and integrity of broached surfaces

Surface integrity or in other words surface quality is a general term that is widely used in academia and industry to describe the characteristics and attributes of the workpiece surface after being modified or altered by manufacturing processes. Quality and integrity of the workpiece surface is a key design factor particularly when the part is likely to sustain severe service conditions such as very high or very low temperatures, corrosive environments, and dynamic loading and unloading. Broaching, as the focal point of this paper, is a machining operation in which roughing, semi-finishing, and finishing of the desired profile is achieved simultaneously by only one stroke of the tool with no further finishing operation required. Hence, the quality and integrity of final part during service life is directly governed by the broaching regime. The present paper aims to study the effects of broaching on the integrity of machined surface. Several samples from two types of steels (AISI 12L14, AISI 1045) and one type of aluminum (Al 7075) were prepared. The samples were examined to study both surface and subsurface characteristics of the broached surface including surface roughness, subsurface microhardness, and subsurface plastic deformation. The results showed gradual effect of successive teeth on the integrity of workpiece surface. It was shown that the surface and, to some extent, subsurface of the machined part were affected by the combined effect of successive teeth; however, it was determined that the effect of last teeth (finishing teeth) was dominant. This can be clearly seen through microhardness and surface roughness readings.