積層造形砂型の曲げ強度に及ぼすかさ密度及び接触点数の影響

抄録

  It is generally said that the strength of sand molds becomes higher with increasing mold density. In the case of green sand, models on the correlation between the bulk density and strength have been proposed, but there are only a fewe studies on the relationship between the bulk density and strength of self-hardening sand molds. In the compaction model of green sand, the plastic deformation of the bentonite layer affects the high densification of sand molds. Therefore, attempts have been made to build a model on the strength of molds assuming that sand particles do not contact each other. This green sand model should not be applied to self-hardening molds in which sand particles contact each other and the resin forms necking. In this study, we investigated the relationship between bulk density and strength of furan self-hardening sand mold, utilizing the difference in the bulk density of sand molds prepared with additive manufacturing equipment. As a result, the following was clarified.

  In an organic self-hardening mold that forms necking, the strength of the mold is proportional to the number of contact points between the sand particles. The number of contact points increases with the increase in the bulk density or packing fraction. The estimated strength of one contact point in this study was about 0.042N. The two-dimensional contact point number of the sand mold related to bending strength was only about 3.5% of the three-dimensional contact point number. The strength of the sand mold is expressed with a quadratic function of packing fraction or bulk density. The results of this study clearly reveal the relationship between the number of contact points and strength in organic self-hardening molds.