Soldagem pontual por fricção (FSpW) de poliamida 6
Abstract
Friction Spot Welding (FSpW) is an innovative technique developed and
patented in 2005 by the Helmholtz Zentrum Geesthacht (HZG) research center
in Germany. FSpW uses the friction between a rotating tool and the workpieces
to generate heat enough to cause diffusion across the interface to consolidate
the weld. This new welding technology has been tested and optimized with the
objective of produce overlap weld joints between two polyamide 6 plates. Full
factorial design of experiments (24) and analysis of variance (ANOVA) allowed
to explain the effects of weld parameters as rotational speed (RS), welding time
(WT), plunge depth (PP), holding pressure time (HPT) and the interactions
between these main parameters on the microstructural characteristics and
mechanical strength of the joints. The rotational speed (RS) and welding time
(WT), within the limits studied, had greater influence on the mechanical single
lap shear strength of the joints that achieved up to 26 MPa. This behavior was
related to the higher heat generation during the weld, reaching temperatures of
up to 275°C, thereby increasing the welded area. The parameter holding
pressure time (HPT), designed in this study allowed the cooling and
solidification of the polymer under pressure, improving the weld surface
finishing and avoiding defects as voids in the weld area. The most common
failure for the joints with higher mechanical strength was the fracture of one of
the plates while the joints with lower mechanical strength showed interface
shear failure. The degree of crystallinity of PA6 in the welded area did not show
a significant difference as compared to the base material. The molecular weight
of PA6 in the welded area was reduced in the worst case 7% as compared to
the base material (Mv = 41.800 g/mol), and that reduction occurred linearly with
the increase of the temperature during the welding; however, that low degree of
degradation was not found to affect the mechanical strength of the joints. These
characteristics emphasize the potential of this FSpW as an alternative to the
current welding methods for polyamide 6.