Influence of pre-drilling hole and feed rate on welded surface strength of pine-itauba joints

Rotary friction welding technique is a promising alternative of joining dowel-laminated timber (DLT) and dowelled cross-laminated timber (DCLT), without any adhesive. Studies on the welding of Brazilian woods are few and recent, mainly when determining the optimal welding parameters. Therefore, an exploratory study was carried out to evaluate the influence of pre-drilling hole and dowel feed rate on the welded surface strength of pine (Pinus taeda) and itauba (Mezilaurus itauba) joints, determining optimal welding parameters for these woods. The study was complemented with a macrostructural analysis of welded specimens and the determination of the taper rate of itauba dowels, to comprehend the mechanical performance of these welded joints. The specimens comprised itauba dowels, 10 mm in diameter, welded at a rotation of 1000 rpm and feed rates of 100, 300, 400 and 500 mm/min, into single-stage (8 mm in diameter) and two-stage (8 and 7 mm in diameter) pre-drilled holes, made in pine substrates. They were subjected to tensile tests and to macrostructure analysis. The results revealed that two-stage pre-drilled holes contributed to improving the mechanical strength of these welded joints. Feed rates higher than 100 mm/min avoid excessive wear and charring of the dowels, while feed rates lower than 500 mm/min prevent dowel splintering. The optimal welding parameters for pine joints welded with itauba dowels are two-stage pre-drilled holes and a feed rate of 400 mm/min.