Improving the surface morphology by adjusting the cutting parameters during cryogenic milling of Ti-6Al-4V

Abstract

The surface morphology of a component is characterized by its topography as well as the mechanical and metallurgical subsurface properties. These properties highly influence the application behavior of technical components, such as fatigue life and wear resistance. When milling the titanium alloy Ti-6Al-4V, cryogenic cooling, which leads to a better cooling effect, can improve the surface morphology. The resulting reduction of the thermal load promotes strain hardening as well as the introduction of compressive residual stresses in the subsurface, improving the application behavior. However, in order to manufacture workpieces with suitable subsurface properties, in-depth knowledge of the correlations between the cutting parameters, the thermo-mechanical load, and the resulting surface morphology is necessary.

In the investigations presented here, Ti-6Al-4V is machined via end milling while applying cryogenic CO2-cooling. The influence of the cutting parameters is investigated via a systematical variation of the cutting speed and the feed per tooth. By measuring the process forces as well as the occurring temperatures when milling, the thermo-mechanical load is characterized. Finally, the surface topography as well as the microhardness in the surface layer are measured to evaluate the surface morphology of the workpiece.

The results show that the cutting speed and the feed per tooth have a decisive impact on the thermo-mechanical load during cryogenic milling. Using cutting parameters that promote high forces and/or low temperatures during milling results in a significantly increased microhardness in the surface layer of the workpiece. The surface topography is also improved by adjusting the feed per tooth in terms of a favorable cutting strategy. As a result, a favorable combination of cutting parameters is found in order to optimize the surface morphology regarding the mechanical and metallurgical subsurface properties as well as the surface topography.

Keywords: Machining; Cryogenic milling; Ti-6Al-4V; Surface morpholog