Development of Engine Valve Seats Directly Deposited onto Aluminum Cylinder Head by Laser Cladding Process 920571

A new technologies for manufacturing of engine valve seats have been developed. This process, different from the conventional method that valve seats made of sintered alloy were press-fit into the cylinder head, is directly formed valve seats onto cylinder head by using the laser cladding technique.

In order to develope the cylinder head with laser cladding valve seats, the laser cladding technology by which copper based alloy is deposited onto aluminum alloy with little dilution and stable bead has been established. And the unique cladding alloy, which is two phases in the liquid stage and in which iron or molybdenum rich hard particles are dispersed in the solid state, has been developed.

Based on this technique, the practical process has been successfully completed. It was revealed that the cylinder head with laser cladding valve seats has many advantages that are improvement of the engine performance and temperature reduction of valves and their seats compared with conventional one.

At Le Mans 24 Hours Endurance Race, this technology was applied to Toyota's racing cars at first. Then “Celica GT Four”s with cylinder heads by using the laser cladding have been taken into service August in 1991.

THE CONVENTIONAL ENGINE VALVE SEATS have been formed into the cylinder heads by press-fitting, such a wear resistance alloy as sintered alloy. As at the present time there are more and more demands for a higher engine performance and efficiency, the conventional press-fit method has some limits for the degree of freedom in the design around the combustion chamber, which is vital for the enhancement of the engine cooling performance.

In this regard some persons ^(1,2,3) have done efforts to provide the seat functions directly into the cylinder head, by using the laser surface alloying or the MMC (Metal Matrix Composite) technique in stead of the conventional press-fit method. Those methods, however, have never been used in practice, because the valve seat durability becomes lower and the wear resistance tends to detriorate particularly at high temperatures.

The authors took notice of the laser cladding technique that has the possibility to provide a valve seat durability higher than the use of the laser surface alloying or the MMC method, and has also the possibility of such seats directly onto the cylinder head. In order to ensure the adequate seat durability into an aluminum (hereafter referred as “Al”) alloy substrate material, as we already know through the experiences in the past by using the laser surface alloying or the MMC, it was necessary to deposit different kinds of materials, which has higher melting point and better wear resistance against high temperature condition than Al-alloy. A proper technique to serve this purpose was completely absent in practice, but the authors, et al. initiated this study under such a circumstance.

As result, a new technique has been developed to deposit a copper based alloy with a higher melting point by 400K more than the Al-alloy with little dilution. The technique has been so enhanced that it is now applied to the engine valve seats. It has also been verified that the engine performance is improved and the cost can be made lower than that of the conventional sintered alloy press-fit technique.

In this paper, emphasis will be placed on the descriptions of the laser cladding technique, and materials for cladding, which constitutes to the basis of this develoment. The production system and the improvement of engine performance will also be reported.