Hybrid Taguchi-Gray Relation Analysis Method for Design of Metal Powder Injection-Molded Artificial Knee Joints with Optimal Powder Concentration and Volume Shrinkage

Artificial knee joints play a critical role in improving the quality of life of the elderly and those with knee injuries. Such knee joints are fabricated using a composite material consisting of metal alloy particles and polymer resin and are generally produced using the metal powder injection molding (MIM) process. However, if the local powder concentration of the molded product is too low, the mechanical properties and aesthetic appearance of the joint are severely degraded. Similarly, if the product undergoes excessive shrinkage following removal from the mold, the dimensional accuracy will fail to meet the design specifications. Accordingly, the present study applies a hybrid approach based on the Taguchi robust design methodology and gray relation analysis (GRA) theory to determine the optimal MIM processing conditions that simultaneously maximize the powder concentration uniformity while minimizing the volume shrinkage. The feasibility of the proposed approach is demonstrated by means of CAE (Computer Aided Engineering) mold flow simulations. The results show that while the robust Taguchi design method enables the optimal processing parameters that maximize the powder concentration uniformity and minimize the volume shrinkage to be individually determined, the hybrid Taguchi-GRA method enables both quality measures to be optimized simultaneously.