Planejamento de experimentos aplicado no processo de fundição para entender a causa da variação indesejada na resistência à tração do ferro fundido cinzento

Abstract

The tensile strength is a mechanical property of cast iron, resulting from the combination of the casting process factors, which needs to be controlled because it defines the class of the material. The company, where the study was conducted, produces grey cast iron components for its products and this mechanical property is evaluated on standard specimen. It was verified that the cast iron of this company has an undesired variation in the result of tensile strength, of the four foundry processes analyzed, only one reaches the expected result. In the search for the identification of the cause of this variation, the main process factors that could directly affect the strength of the material were defined as: carbon equivalent, metal temperature in the casting, inoculation of the metal and cooling time of the part inside the mold. Then, DOE tool was applied, where the factors were combined in a matrix of experiments resulting in sixty-four specimens were produced in sixteen process conditions. After the conclusion of the experiment, it was evidenced that a single factor, the carbon equivalent, is responsible for 50% of the variation of the response generated by the experiment. It has been proposed to readjust this critical process factor to appropriate levels to ensure a stable result of tensile strength across all of the company's processes.