Complex-shaped piston oil galleries with piston crowns made by cast metal or powder metal processes

Abstract

A steel piston with an oil gallery, and process for forming a steel piston oil gallery channel, which corresponds to the complex shape of the combustion bowl in the piston crown. The piston crown is made by a cast metal or powder metal forming process. The oil gallery channel is formed to the basic shape that corresponds to the shape of the walls of the combustion bowl. Machine-turning surfaces in the oil gallery channel can be machine finished as desired. Surfaces in the oil gallery which cannot be machined with conventional turning operations, such as recesses and protrusions into the channel, are left in the original as-formed condition.

What is claimed is: 
     
         1 . A method of manufacturing a piston, comprising the steps of:
 providing a lower member including sidewall portions and pin bores;   providing an upper crown member having a combustion bowl on an upper side thereof and a lower surface on a lower side thereof, wherein the combustion bowl includes a plurality of protrusions spaced from one another along its outer perimeter;   machining the lower surface of the upper crown member; and   joining the upper crown member to the lower crown member.   
     
     
         2 . The method of  claim 1 , wherein the joining step includes welding. 
     
     
         3 . The method of  claim 1 , wherein the machining step includes machining portions of the lower surface located opposite the protrusions. 
     
     
         4 . The method of  claim 1 , wherein the machining step includes machining the lower surface to a shape corresponding to a shape of the combustion bowl. 
     
     
         5 . The method of  claim 1  including providing the piston with an outer rim surrounding the combustion bowl, a ring belt depending from the outer rim, a cooling gallery disposed radially inwardly of the ring belt, and the machining step includes machining the lower surface until the upper crown member has a substantially uniform thickness along the cooling gallery. 
     
     
         6 . The piston of  claim 1 , wherein the machining step includes machining portions of the lower surface located opposite the protrusions and spaced from one another by as formed portions. 
     
     
         7 . The method of  claim 1 , wherein the machining step includes machine turning. 
     
     
         8 . The method of  claim 1  including the step of providing the piston with an outer rim surrounding the combustion bowl, a ring belt depending from the outer rim, and a closed cooling gallery disposed radially inwardly of the ring belt; and wherein
 the joining step includes welding; 
 the machining step includes machining portions of the lower surface located opposite the protrusions, machining the lower surface to a shape being the same as a shape of the combustion bowl, and machining the lower surface until the upper crown member has a substantially uniform thickness along the cooling gallery; and 
 the machining step includes machine turning.