Investigation of tool deflection during milling of thread in Cr-Co dental implant

Milling is a good option for manufacturing internal threads in hard-to-cut dental components due to lower cutting forces. In the case of a very small drilled diameter, the tool cannot be large enough to reduce tool deflection nor sufficiently small to avoid the influence of the tool penetration. As a consequence, both situations need to be considered and no other research study dealt with this aspect for the modeling of thread milling forces. This article deals with the analysis of forces, deflection, and undercutting during machining of one typical internal thread geometry used for implants in a chrome-cobalt dental alloy. The geometry is analyzed considering the influence of tool penetration and it is presented new equations to identify the regions where it occurs. Machining experiments are conducted acquiring cutting forces and tool axis position in order to calculate the tool radial forces and estimate tool deflection. Manufactured threads geometry is measured to evaluate dimension quality. It can be claimed that the tool trajectory should consider one extra revolution around the drilled hole in order to machine the undercut material due to tool deflection for this small tool diameter.