Abstract: A method is provided for producing a piston for an internal-combustion engine of the structure in which a piston body which is composed of a crown having a groove for fitting a piston ring into an outer circumference surface and a skirt in connection with the bottom of the crown is provided with an annular cavity for flowing cooling liquid on an inside of the groove, the method comprising the steps of: forming the crown and the skirt individually; forming an annular groove for the annular cavity in the inner bottom of the crown and an annular rib in connection with the open edge of the annular groove before the crown and the skirt are joined together; bending the rib toward the opening of the annular groove by application of pressure to close the opening of the annular groove to thereby form the annular cavity; and joining the crown and the skirt together.

Abstract: A method is provided for producing a piston for an internal-combustion engine of the structure in which a piston body which is composed of a crown having a groove for fitting a piston ring into an outer circumference surface and a skirt in connection with the bottom of the crown is provided with an annular cavity for flowing cooling liquid on an inside of the groove, the method comprising the steps of: forming the crown and the skirt individually; forming an annular groove for the annular cavity in the inner bottom of the crown and an annular rib in connection with the open edge of the annular groove before the crown and the skirt are joined together; bending the rib toward the opening of the annular groove by application of pressure to close the opening of the annular groove to thereby form the annular cavity; and joining the crown and the skirt together.

Abstract: A method is provided for efficiently manufacturing a high quality internal combustion engine piston having an annular cavity allowing for good circulation of cooling fluid. An annular groove is formed at the circumferential edge of the top face of a piston crown, or at the top of the exterior circumferential face of the crown, and an annular protruding strip is formed as a continuation of an edge of the opening of the annular groove. The protruding strip is bent in the direction of the opening of the annular groove by bringing to bear a pressure roller 11, while rotating the main piston body. Consequently, the opening of the annular groove is closed, whereby an annular cavity for circulating cooling fluid is formed so as to surround a pressure receiving recess.