Choice of casting process.

In order to determine the best process for the fabrication of the rivets, some important points were taken into account with regard to the molding step. This is due to the fact that the mold must meet a number of requirements. Among these requirements are: To support the weight of the liquid metal, to withstand the erosive action of the liquid metal at the time of the leak, to generate as little gas as possible, in order to avoid mold erosion and contamination of the metal, to facilitate the escape of gases generated to the atmosphere and the costs associated with the manufacturing process. Therefore, these factors were decisive in defining the rivet manufacturing project.

After comparing the processes (Table 1), it was concluded that the sand moulding process is the best suited for the fabrication of the rivets. In addition, the specimen used to perform the tensile test was fabricated by the sand moulding process. Therefore, it has a maximum tensile stress value different from the value that would correspond if it were manufactured by other casting processes. Since this value is so important in order to design the rivets to sustain the request of 35kN. This difference is due to the fact that the parts manufactured by the sand moulding process are more resistant than if it were manufactured by a metallic mold, for example, because the sand allows greater escape of the hydrogen during the solidification.

Table 1 - Comparison of the analyzed processes

Processes	Fatores analisados
	ustaining of the molten metal weight	Sustaining of the molten metal erosion	Gas release	Cost
Sand	ACCEPTABLE	ACCEPTABLE	GOOD	LOW
Investiment process	ACCEPTABLE	ACCEPTABLE	BAD	HIGH
Permanent mould	ACCEPTABLE	ACCEPTABLE	BAD	HIGH

Source: Own