This paper presents an analysis of noise occurrence at a diesel engine, and a design to prevent the noise which occurred unperiodically with frequency over 5kHz. The mechanism of noise occurrence was assumed to be as follows. The noise occurred when the following conditions were combined: (1) cavitation appeared in the oil film at the main bearing, (2) main journal vibration in the radial direction induced further appearance and collapse of the cavitation. The mechanism was verified by the following items derived from numerical analyses and experimental results, (a) the existence of cavitation at the time of noise occurrence, (b) the instability of the main journal-oil film, (c) the simultaneous fluctuation of the combustion pressure.

Finally, the observation of excited oil film and the measurement of noise were conducted simultaneously by making a test rig based on the mechanism in order to investigate the relation between the cavitation and noise. The noise occurred when the cavitation reached the atmosphere at the end of oil film. The reaching of cavitation was prevented by cutting a ring groove at the end of a circular piece, and the noise was reduced. The noise reduction was confirmed on an actual engine by using a main bearing with grooves cut at both ends.

Toshiaki Tanaka, Koukichi Nakanishi, Yasuhiro Yogo,
Sayuri Kondo, Yoshinari Tsuchiya, Toshiyuki Suzuki,
Atsuo Watanabe

Hot forging is a manufacturing method that is applied to a wide variety of high-strength automotive components. To satisfy demands for lower costs and shorter production preparation times, it is vital that we be able to predict the die life. Around 70 % of the die failures that occur in hot forging processes result from the wear that occurs as the temperature of the die increases.

　In this paper, we describe a newly developed technology that can be used to predict the temperature and wear of the dies used in hot forging. Through an examination of axisymmetric dies, we found that the amount of wear in the dies can be forecast using a model composed of the cumulative friction work of the metal flow on the surfaces of the dies and the yield strengths of the die materials at elevated temperatures. We also found that the die temperature can be predicted by applying a cooling model that considers the relationship between the heat transfer coefficient and the Reynolds number of the lubricant jets that are generally used in hot forging. Using the cooling and die load models, we were able to determine the hot forging die life with sufficient accuracy at the process design stage. We have also developed a process design CAE system, based on our wear and cooling models, which is capable of predicting the die wear life and temperature.

Masatoshi Sawamura, Yasuhiro Yogo, Sayuri Kondo,
Toshiaki Tanaka, Koukichi Nakanishi,
Toshiyuki Suzuki, Atsuo Watanabe

We have been developing a process design CAE system to predict die wear life in the process design stage for the hot forging of steel. Our goal is to reduce production costs by shortening the development period, while maximizing the life of the die. In our system, we use an expression that defines the relationship between die wear, die strength, and friction factors, such as die pressure, sliding speed, and the coefficient of friction. To predict the die wear life with high precision, it is important to obtain the actual coefficient of friction and the heat transfer coefficient for use in a die temperature analysis that considers both heat and deformation. It is also important to clarify the effect of these friction factors on the die softening and wear. For this study, we considered the use of a hot forging die with a forging machine that is typically used for the production of connecting rods and so on. We determined the lubricant adhesion and the heat transfer coefficient variation that results from spraying lubricant, by performing a lubricant spray model test. Moreover, we devised a new hot ironing test to obtain the relationship between the coefficient of friction and the lubricant conditions, as well as the relationship between the friction factors and die temperature.