Shrinkage Investigation of Ductile Iron Castings

It has been a challenging mission to assure that ductile iron castings meet customer internal soundness specifications with acceptable process capabilities to get approval in new automotive model launch processes. Shrinkage conditions were investigated in the new program launch stage. Several factors were investigated including carbon equivalent, carbon levels, silicon levels, molten iron preconditioners and other additives. This study investigated shrinkage size by taking digital photos and measuring each shrinkage indication size using software comparing to the size limits from the customer Internal Soundness Specification. Thermal analysis was utilized to evaluate iron conditions to correlate shrinkage tendency. Statistical tools were applied to determine whether the factors in this investigation truly affected casting shrinkage characteristics. High process capability (Ppk) values were achieved by adopting optimal process parameters and using proper additives, and the program was launched successfully. Additional studies were conducted to confirm that the ductile iron meets customer specification including mechanical properties, microstructure, impact property, and casting hardnessunder all conditions.