Joining of copper alloys on spheroidal graphite cast irons is important to enhance the wear resistance of sliding parts. Although the joining is attempted by brazing, inserting, or others, these method have many technical problems. Thus we try to join a spheroidal graphite cast iron and a copper alloy by using Ni/Al mixed compacts, as insert materials, which take place combusion synthesis reaction. As a result, we succeeded in joining a spheroidal graphite cast iron and a copper alloy at 1023K, and succeeded even at a lower temperature of 923K. Advantages inherent to the SHS process for joining include the lower temperature and the shorter time in joining, as compered with conventional diffusion joinings.

View full abstract

  This paper presents the results of the direct observation of the packing behavior of sand in the vacuum suction molding process for making sand cores and the investigation of the density distribution in produced cores. The packing mechanisms were studied based on these experimental results. The packing process can be divided into two stages : the first stage during which the sand flows rapidly and collides with cavity walls until the cavity is filled and the last stage when sand particles move slowly due to the air flow after the first stage. The final density depends on both the collision and D’Arcy effects in each stage. It was found that the following places tend to have lower density : corners where the sand is difficult to flow-in, places where the air flow is divided, places finally filled and places where a strong shear flow occurs.

View full abstract

  The effects of casting conditions on solidification structure and banded segregation of Al-4.4%Cu alloy produced by centrifugal casting were investigated. Addition of grain refiner caused three zones in the radial direction ; equiaxed, fine equiaxed, and coarse equiaxed zone. Banded segregation was formed in the fine equiaxed zone obtained by horizontal centrifugal casting with smaller centrifugal forces than 100G. Smaller centrifugal force resulted in more numbers of banded segregation. No banded segregation was observed in the ingot obtained by vertical centrifugal casting. The effects of superheat and vibration were small. The grain size in the banded segregation was 150μm which was double that in the neighboring phases. Cu concentration was low in the equiaxed zone, and high in the fine equiaxed zone. It was about 5.6% in the banded segregation, larger than that in the neighboring fine equiaxed zone (about 4.9%). It is believed that the flow in the solid-liquid coexisting region caused by gravity force resulted in the banded segregation.

View full abstract

  Despite the advancement of the numerical methods of solidification analysis, one-dimensional analytical solutions of pure metals present the merit of giving a wide perspective, because of their simple forms of equations. Past analytical solutions can be classified depending on the heat resistances considered in the model : that in solid, interface and/or mold. Two approximate analytical solutions for the problem considering all the three resistances are given ; the sensible heat in the solidified metal is neglected in one solution and considered in the other. The latter agrees well with numerical solutions. The former is less precise when Stefan number is large, but gives a wide perspective to the problem, since it involves only three dimensionless numbers. Each of the past solutions considering one or two resistances can be interpreted as an approximation to this solution, applicable only in a specific range of variables.

View full abstract

  The Cyclic Steady Heat Balance Method (CSM) is proposed to calculate temperature and heat of a die casting die in cyclic steady state without repeated numerical calculations. In this method the mean cavity side surface temperature during casting and that during spray cooling are studied, assuming that a stepwise temperature change takes place in the cavity. CSM is applied to a simple two-dimensional shaped die with a waterline type cooling channel. The cooling condition is given and mean surface temperature and heat are calculated. The results are used to judge whether the strength of cooling, the cooling time and the pitch of a cooling channel etc. are appropriate. The high accuracy of the proposed method was confirmed by comparing with cyclic numerical calculations. The CPU time of the former is one tenth or less of the latter.

View full abstract

  In cast-in insertions, the state of bonding largely depends on the solidification processes of the interface melt. In this report, steel bar insertion in spheroidal graphite cast iron was analyzed with a new simulation method taking into consideration the nucleation and growth of solidification cells. With this method, uncleous generation is taken as a function of undercooling from stable and metastable eutectic temperatures which are estimated from the Si concentration of the melt. The solid fraction is calculated from the number and diameter of the growing cells in a unit volume. The calculated results on volume ratios 6, 10, and 27 showed that the gross progress of the primary solidification and the following remelting is almost the same as the calculations by a simple method where the solid fraction is an approximated function of only the temperature. The new method gives faster re-solidifying progress, and results in earlier completion of the solidification melt than the approximated function method. Temperature measurements at the interface suggest that the new method is more accurate and explains the experimental results better.

View full abstract

  Recently, the green sand molding process by means of the air-flow + squeeze (flask type) is being used. In this study, the air-flow stage is investigated. It is essential to know how sand particles are moved by air pressure. Numerous experimental studies have been conducted, but none have clarified the behavior of sand particles, nor optimized the molding process. The purpose of this study is to develop a process model using the distinct element method (DEM). In this model, the individual particles are moved by three forces, namely, contact force, drag force and gravitational force. Numerical simulation was performed to predict the behavior of the sand particles during the air-flow stage, and laboratory experiments were carried out to examine the calculated results. From the simulation, contact force, drag force and inertia force of individual particles were obtained as the function of time. The inlet air velocity was seen to affect the phenomena of molding sand compaction. This study applying DEM, produced useful information such as the effective molding parameters for the optimization of the air-flow process.

View full abstract