In recent years, one of the most important issues in the automotive industry is the improvement of fuel economy started from the environmental problem. Making cars lighter and reducing the coefficient of friction are two ways to improve fuel economy. Reducing the weight of a cylinder, an engine component, is a typical example. The traditional, mainstream method to reduce cylinder weight has been to convert cast iron cylinder blocks into aluminum cylinder blocks by using cast iron sleeves. To further make engines lighter and more compact, however, it is desirable that cast iron sleeves be abolished, or, in other words, making cylinder blocks sleeveless.
A typical technology to make cylinder blocks sleeveless is applying anti- wear coating on a bore wall. Electroplating is currently the mainstream method used for this technology. It must be noted, however, electroplating is used primarily for low-pressure cast cylinders. It is not applied to die-cast cylinders because of the porosity in the bore walls in the die-cast cylinders. Application of this technique to die-cast cylinders, therefore, is extremely important for the purpose of increasing casting productivity and realizing lightweight and compact designs through reduction of the wall thickness.
We chose to look into the plasma-spraying technology as a candidate for solving this problem. Since this technique allows high-speed formation of coatings as thick as several hundred microns regardless of the work material, the plasma-spraying technology sheds light to sealing of the porosity. The abundance of the raw material for making the coating also leads to easy formation of cheap, composite coating by combining various raw material powders.
This paper reports the process of developing low-cost, sleeveless spray- coated cylinders by the plasma-spraying technology taking advantage of the above-mentioned properties. Use of the technique with die-cast material is also reported.