In recent years, demands for increased output and low fuel consumption in automobile engines have been mounting. Light weight and high performance is demanded of the main operating parts, such as pistons.
In response to these demands, the crown thickness and pin boss unit thickness has been reduced by tremendous improvements in the fatigue strength, compared to strength obtained by conventional methods, by utilizing Squeeze Casting techniques. In addition, the thickness of the inside face of the pistons has been reduced by making use of a split core. Furthermore, by manufacturing a cooling gallery, the heat load has been reduced; by introduction of hollow regions, an extremely light weight and compact piston has been developed.
Three new techniques are indicated here. Firstly, the technique of attaining soundness in material and excellent fatigue strength by the Squeeze Casting technique, which is superior to those attained by conventional methods. Secondly, the technique of using a split core for forming an undercut part on the inside surface of the piston in the Squeeze Casting method, that is to say, the technique of preventing deformation and damage to the core due to the pressure of the molten metal and preventing the permeation of the molten metal in the split core. The third technique is the technique of manufacturing a pressure resistant and impermeable removable core for the compact cooling gallery, used in the Squeeze Casting method.