INFLUENCE OF TILT ANGLE AND FEED DIRECTION ON SURFACE ROUGHNESS, CUTTING FORCES AND TOOL LIFE IN HIGH SPEED MILLING OF HARDENED TOOL STEEL

Isabela da Costa Castanhera¹; Anselmo Eduardo Diniz¹

¹ Faculdade de Engenharia Mecânica /UNICAMP

doi:10.20906/CPS/COB-2015-0334

Resumo

In this work surface roughness, tool wear and cutting forces are analyzed in high speed milling process of hardened tool steel AISI D6 utilized in moulds and dies manufacturing. High speed milling enables the increase of productivity and decrease of costs and production time as other processes, EDM and polishing, can be substituted successfully by finishing in one machine and one workpiece fixation. However, it requires appropriate cutting strategies. The vicinity of the center of a ball nose end mill (typical tool used in this kind of process) has a low cutting speed which leads the workpiece allowances to plastic deformation, situation avoided by the use of tilt angle and lead angle (the tool axis is not perpendicular to the workpiece). The tool path strategy, ascendant cut or descendent cut (which influence the tilt and lead angle variation along the cutting), is very important for a good surface finish and tight geometric tolerances. This work analyses a four axis milling having as input variables the tilt angle (with small values of tilt angle in such a way to avoid the contact of the tool tip with the AISI D6 steel workpiece and without tilt angle) and feed direction (in order to have ascendant and descendant cutting in the milling of a circular surface). A 12 mm diameter ball nose end mill with ultra-fine grain size and TiAlN coating was used in the milling experiments. Roughness values evolution, tool life and flank wear evolution and cutting forces were investigated according each tool path strategy. The main conclusion is that the chosen strategy (ascendant or descendant cutting) is, among the tested variables, the main variable of influence on tool life and surface finish, improving or worsening them.

Palavras-chave: high speed milling; tilt angle; hardened steel; surface roughness; cutting forces; tool path strategy