his paper is the first to optimize the friction stir welding
process of pipes (FSWoP) considering the tool pin diameter
effect using the multi criteria decision making (MCDM)
techniques. Significant parameters of the FSWoP process
have been considered in many optimization studies,
however, the effect of the tool pin diameter has been never
studied. Experimental work was performed using a new
modified fixture to eliminate the post-process problems.
Experiments were performed at three levels of three
parameters: tool pin diameter tool, rotational speed and
travel speed. For optimization, the MCDM methods were
applied as an approach for selecting the optimal values of
the parameters. Using MCDM in optimizing the FSWoP
process is rare and has a limited number of publications. The
MCDM techniques used are the Grey Relational Analysis
(GRA) and Technique for Order of Preference by Similarity
to Ideal Solution (TOPSIS) to find the optimum process
parameters which maximize the values of responses: the
tensile strength and the hardness of the welded joint. The
same results were obtained through both techniques and the
optimum values for the used parameter ranges were 5 mm,
1800 RPM and 10 mm/min for the pin diameter, rotational
speed and travel speed respectively.