Structural Changes of Surface Layers of Hard Turned Parts by Wiper and Conventional Geometry

Aims: The aim of this paper is to achieve information about surface and sub-surface layers after hard turning by mixed ceramic tool with different geometry – Wiper and conventional and to compare achieved results to find out advantages of its use. Second aim is to obtain graphs of the influence of the tool wear on the surface structural changes.
Study Design: The experiment on hard turning was carried out with differently shaped mixed ceramic tools.
Place and Duration of Study: Slovak University of Technology in Bratislava, Faculty of Materials Science and Technology, Institute of Production Technologies and Institute of Materials Science, between November 2013 and May 2014.
Methodology: In the case of cutting tool wear and structural changes measurement this experiment was carried out on two different workpiece sizes – 1. 125 mm long cylinder to achieve cutting tool wear, 2. 10 mm long rings for structural changes. Microscopy for cutting tool wear measurement and X – ray diffraction for structural changes measurement was used. Cutting tool wear was represented by VB parameter and structural changes were represented by structural phase content, crystallites and lattice.
Results: Information about structural phase contents was achieved. There are some differences between surface and sub-surface layers after hard turning by mixed ceramic tool. Surface layer consists of more austenite phase than sub-surface layers. But there were not very big differences between used cutting tool geometry and its influence on the cutting tool wear. Both geometries were used more than 40 minutes till the flank wear parameter VB reached to 0.25 mm. The thickness of the surface heat influenced layer depends on the cutting tool wear and it is influenced by the cutting tool geometry – application of the Wiper geometry leads to thinner “white layer”.
Conclusion: It is very important to take into consideration cutting tool geometry when dealing with surface integrity after hard turning. But all achieved results depend on the used cutting parameters, cutting tool material, workpiece material, cutting force components, machine stiffness in specific experiments.