Before piston crowns are welded, the complete ring groove section, the outside diameter and the entire top of the crown will be removed. Also the inner sealing faces will be pre-machined. Piston crowns are heat treated in our oven to release welding stresses. Machining takes place on CNC controlled turning machines which can automatically machine the parabolic crown top. Machining of the ring grooves is programmed to ensure the ring groove heights according to the engine builders’ specification. The ring grooves are double chromium plated.