It is necessary to minimize thermal deformation of machinery in order to carry out high-precise processing. For this reason, use of low thermal expansion material is effective, and wide applications of low thermal cast iron to mechanical structures are anticipated. To apply to machine structure components, fatigue strength must be evaluated.
  In this study, rotating bending fatigue tests and fatigue crack propagation tests were carried out in low thermal expansion cast irons subject to two kinds of heat treatments, normalizing and solution treatment. The grain size decreased by solution treatment, and static strength improved slightly. The fatigue limit ratio of low thermal expansion cast iron is 0.27 to 0.31, and is smaller than 0.57 in FCD450. The fatigue strength improved by solution treatment, because the fracture origin was slip from crystal grain in materials subject to normalizing and solution treatment. The decrease in grain size by solution treatment seemed to improve fatigue strength. The improvement in fatigue strength by the solution heat treatment also drastically increased the threshold stress intensity factor range ΔK_th because crack propagates in curvature and bifurcation in two materials. Threshold stress intensity factor range, ΔK_th, was drastically increased by the solution treatment due to the roughness induced crack closure seen markably in this material.

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  In precision casting where production is of comparatively small scale, the use of photo-solidified polymer models in place of conventional lost-wax models can be recommended. Precision casting products using photo-solidified polymer models have the tendency for unstable product size compared with precision casting products using conventional lost-wax models. Dimensional changes in honeycomb structure models made by SL5170 epoxy photo-solidified polymer was measured during and after building, and experiments were conducted to investigate the cause of dimensional changes. As a results, it was confirmed that during building, there exists a swelling phenomenon due to liquid polymer although the rate of dimensional change is extremely small. It was found that after building, there exists a swelling phenomenon due to moisture in the atmosphere. The rate was comparatively large, that it had a bad influence on the quality of precision casting products.

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  It is confirmed that there exists dimensional changes due to swelling both in photo-solidified polymer models currently being built and after building due to swelling. In order to decrease this dimensional changes, it is effective to heighten molecule joint force by reinforcing the hardening of photo-solidified polymer models. In case of rapid prototyping, the hardening depth based on the setup of the laser currently being built mainly determines the degree of hardening. Depending on the kind of polymer, ultraviolet ray irradiation may be required after building. Experiments were conducted on the hardening depth of models made by SL5170 epoxy photo-solidified polymer and the effects of post-curing processing. The results confirmed that increasing the degree of hardening by setting the hardening depth deeply during building and performing post-curing processing after building is effective against dimensional changes.

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