| 摘要 |
PURPOSE:To secure the highly accurate machining of a top ring as well as to keep off any ring stick attributable to unevenness of the machined surface, by forming a piston's top ring groove, which is cast in with heterogeneous materials, into a stepped form. CONSTITUTION:A heterogeneous material 5 such as refractory work or the like is cast in a top ring groove part 2 of a piston 1. Each of stepped parts 6 and 7 is formed in a position nearby a bottom surface 2c of side faces 2a and 2b of the top ring groove 2. With this constitution, in time of finishing the groove 2, the groove bottom surface 2c is no longer required for machining, and a cutting tool cuts only these groove side faces 2a and 2b so that a tip of the cutting tool is in no case touched to the groove bottom surface 2c at all, thus machining accuracy is improvable. |
