A prototype robot shoulder casting has been poured into a furanic resin bonded mold in a foundry laboratory environment. The 4 kg finished part was poured at 715 ± 5 °C from 8 kg of primary A356 alloy. The solidification times varied between 2 and 6 minutes inside the casting up to 9 minutes in the risers. A complete metallurgical study was performed in different sections of the casting; they included: 1. measurement of the microporosity levels at 6 locations inside the casting; 2. determination of the structure fineness (secondary dendrite arm spacing, DAS) at 6 locations; 3. assessment of radiographic quality in the whole casting per ASTM E-155 reference radiographs; 4. measurement of the tensile properties of 6 specimens excised from the casting. The predicted microporosity and DAS in the whole casting were obtained via solidification modeling. The validity of the prediction could be assessed by comparison with the measured values in selected sections of the casting. The Quality Index, based on the tensile properties, was used to relate the metallurgical quality of the casting to the requirements of ASTM B686-02 standard applying to premium quality aluminum castings. The prediction of the Quality Index Q by solidification modeling was confirmed to be a useful practical tool when evaluating the capacity of given casting conditions to deliver the expected level of "Quality" such as Class 1, 2, 3 or Class 10,11,12 as defined by ASTM B686. When compared with experimental results, it was found that the predictions of the DAS and Quality Index were satisfactory, while the prediction of microporosity was only indicative. Since current standards are based on minimum values of the Quality Index, it was possible to rate the robot shoulder casting in term of "Class number" per ASTM B686.
展开▼
