Fuel economy legislation is requiring further improvements to piston friction reduction as well as additional gains in thermal efficiency. A piston material change from aluminum to steel is enabling advancements in both demands. Furthermore, steel material properties lead to increased piston strength, robustness and durability. All this can be achieved at a lower compression height compared to an aluminum reference piston. Therefore, piston mass can be reduced despite the increase in material density. Since steel pistons require cooling of the combustion bowl region and the ring belt just like the aluminum counterpart, MAHLE implemented a new innovative metal joining technology by using laser welding to generate a cooling gallery. The TopWeld® concept offers design flexibility which cannot be matched by any other welding process. This is especially advantageous for complex combustion bowl geometries that are needed in modern diesel engines to meet fuel economy and emission requirements.