Estudo da usinagem de sedes de válvulas de admissão de motores de combustão interna

Abstract

The excessive vibrations are common during the chamfering of valve seats and induce operator to reduce cutting speed and feed rate, causing reduction of the productivity. The objective of this work was to study the chamfering of the intake valve seats of the cylinder head of an internal combustion engine. The valve seats are machined with PCBN blades from sintered steel rings with 370-410 HB hardness. This work was developed in a partnership with the companies Fiat Powertrain Technologies and Mapal Tools. The justification to do this work is that there was a need to know better the influence of cutting speed, feed rate and PCBN blade geometry in the vibrations and roundness deviations resulting from the machining of the valve seats. With this knowledge, modifications were proposed in order to obtain a stable cut, higher productivity, lower cost and a better sealing of the combustion chamber, resulting in smaller emission of gases from the engine. The analysis carried out showed that the vibrations and roundness deviations tend to reduce when applying cutting speed between 80 and 100 m/min, feed rate between 0.04 and 0.08 mm/rev, using PCBN blades with T-chamfer cutting edge honing around 60 μm.