Civil Engineering Reference
In-Depth Information
11.3 Electrically Assisted Friction Stir Welding
The process of friction stir welding involves high tool forces and requires robust
machinery; hence, the forces involved make tool wear a predominant problem. As
a result, many alternatives have been proposed in decreasing tool forces, such as
laser-assisted friction stir welding and ultra-sound-assisted friction stir welding.
However, these alternatives are not commercially successful on a large scale due
to scalability and capital/maintenance costs.
In an attempt to reduce forces in a cost-effective manner, electrically assisted fric-
tion stir welding (EAFSW) is studied in this work. EAFSW is a result of applying
the concept of electrically assisted manufacturing (i.e., passing high direct electri-
cal current through a workpiece during processing) to the conventional friction stir
welding process. The concept of EAFSW is a relatively new adaptation of conven-
tional frictional stir welding, which is well established. The expected benefits are
reduction in the feed force and torque, which allow for improved processing produc-
tivity as well as the possibility for deeper weld penetration.
The effect of passing direct electric current through Aluminum 6061 during the
welding process is studied in this section with respect to the feed force and torque.
From this study, it is shown that the feed forces are reduced by 58 % on average
in the EAFSW process compared to a conventional frictional stir welding process.
Also, a decrease in torque at the start of the feed is present in the EAFSW process
as compared to conventional friction stir welding.
11.3.1 Electrically Assisted Friction Stir Welding
Background
Electrically assisted friction stir welding (EAFSW) is a variant of traditional FSW,
in which the EAM processing methodology is integrated into the FSW process
by passing electricity through the workpiece during the welding process [
12
]. As
a result of the high forces associated with conventional friction stir welding, the
process of EAFSW could elevate these excessive forces and reduce the required
machine size and stiffness. Additionally, as most heat is generated by the tool
flange, this limits the processing depth of the traditional FSW process. With the
incorporation of EAFSW, this limited penetration depth can be eliminated as the
flow of electrical current creates both a temperature rise and direct material soften-
ing. The implementation of this process will require additional safety and insula-
tion measures; however, the cost is expected to be lower than that for comparable
technologies such as laser-assisted friction stir welding.
The application of EAM to FSW has only started very recently. In 2005, Long
et al. performed finite element modeling of an electrically enhanced FSW process
and concluded that plunge force can be considerably decreased by passing electric
current and also stated that the temperature profile can be achieved in half the time
