アルミニウム合金ダイカスト金型内の溶湯圧力変化と鋳造欠陥

抄録

  Surface defects of die castings, such as surface folds, cold shut and misrun etc., are thought to occur due to the solidification of molten metal during mold filling. However, die casting is a process in which mold filling and solidification are completed under high pressure, thus varying the casting pressure may also have some effects on surface defects.
  In this study, we investigated the effects of solidification on mold filling and pressure transmission and elucidated the influences of casting pressure on the quality of die castings.
  In the mold filling process of JIS AC4C alloy, flow resistance was found to increase with the increase of solid phases, thus decreasing the velocity of molten metal flow. Cold shut occurred due to the rapid drop of molten metal temperature as a result of the decrease in the flow velocity. A similar phenomenon was also observed for JIS AD12.1 alloy, although this alloy shows a skin-formation type solidification. The pressure transmission of molten metal was found to weaken gradually with the increase of solid phases and eventually completely stop and give rise to casting defects. In addition, resistance to molten metal flow due to back-pressure, shape resistance of the mold cavities, etc. were seen. These results indicate that a comparatively higher plunger pressure is necessary to obtain die castings without defects.