me
the welder had the idea of putting threads
onto the electrode and stud welding
was born.
During the 1940s, the immediate ap-
plication of stud welding was for the Navy
to help install wood decking onto naval
vessels. During WWII, this helped to
vastly speed up production of ships for the
U.S. Navy. The method was crude with
the operators controlling the arc timing
with their thumbs, but it was vastly supe-
rior to welding the deck retention fasten-
ers by hand.
Since this initial application of stud
welding, it has continued to evolve.
The Stud Welding Process
In the stud welding process, a metal
stud is joined to a metal workpiece by
heating both parts with an arc. Unlike
other fastening processes, stud welding
attaches the fastener to the workpiece
without marring or requiring access to the
other side. The benefits to this type of
welding include the following:
A strong weld that will not break,
loosen, or weaken
Faster, easier assembly with greater
productivity
Single-sided fastening
Increased cosmetic appeal without
marring the other side
Fewer manufacturing steps saves
time and money
Greater design freedom.
Going Digital
D
uring the 1990s, a major stud
welding company, based in north-
western Chicago, designed and
developed the first digital welding equip-
ment, significantly changing the industry.
With the introduction of digital stud
welding equipment into the marketplace,
the industry has seen increases in pro-
ductivity and reliability. Why is this? First
of all, digital stud welding equipment
uses microprocessors and/or digital sig-
nal processing to monitor and control the
weld profile in narrow time increments
(miliseconds). In traditional analog
power controllers, electrical component
tolerance is such that typical systems
need wider control limits to make the sys-
tem economical. Much of the equipment
delivers power to ±20% of the desired
output.
W
ith digital back-end control, ana-
log functions have been con-
verted into software; therefore,
component tolerance is not a significant
factor, and power is typically controlled
to ±2% or better. This makes the weld-
ing process more consistent, repeatable,
and predictable over time. Additionally,
it is more economical to outfit digital con-
trols with advanced features such as weld
setup memory, weld counters, automatic
profile adjustments, and multiple weld
outputs.
The Drawn Arc Stud
Welding Process
All of the above technological ad-
vances serve the unique needs of drawn
arc stud welding. Drawn arc stud welding
provides welding success under a broad
range of conditions. Producing one-sided,
full cross-sectional welds, the process
Impact of Digital
Technology on
Stud Welding
Information provided by Image Industries, Inc. (www.imageindustries.com), Huntley, Ill.
Stud welding advances from the analog world to the digital
29
WELDING JOURNAL DECEMBER 2006
30
forms a weld that is stronger than the sur-
rounding metal. Drawn arc welds offer
structural integrity, productivity, and leak
and corrosion resistance. They will not
break, loosen, or weaken over time.
Drawn arc stud welding can produce
welds in as little as 0.06 seconds for base
metals of 0.048 in. (1.2 mm) or thicker.
The process has good penetration, and it
welds almost any size or configuration of
metal stud to a workpiece.
The drawn arc process utilizes a DC
power supply to create the arc, a stud
welding tool, and metal fasteners. There
are three common processes within drawn
arc stud welding: flux and ferrule, short
cycle arc, and gas arc.
Flux and Ferrule
I
n drawn arc stud welding, the stud is
loaded into the stud gun chuck, and a
ferrule (ceramic shield that encases
the molten metal) is placed over the end.
The gun is placed against the work posi-
tion, and the trigger is pressed. The DC
power supply sends a signal that energizes
the weld tools internal lift mechanism,
lifting the stud and drawing a pilot arc. As
the stud and base metal are joined, the
metal begins to solidify and the weld is
created. The gun is lifted and the ferrule
is easily discarded.
Flux, embedded in the stud, cleanses
the atmosphere during the weld. During
arcing, the flux is vaporized and combines
with the contaminating elements in the air
to keep the weld zone clean at all times.
A graphic representation of the drawn arc
process is shown in Fig. 1.
Additional assembly steps in the
process such as punching, drilling, tapping,
and riveting are eliminated, making drawn
arc stud welding even more efficient.
Short Cycle Arc Stud
Welding
Short cycle arc stud welding uses no
flux load or ferrule and offers the short-
est welding times of all the drawn arc stud
welding methods. While its suitable for
high-volume, lower-strength applications,
it can produce porous welds and should
be selected when speed and cost are a pri-
ority over strength.
Gas Arc Stud Welding
The gas arc method uses inert shield-
ing gas with no flux or ferrule, making it
easier to automate, but it provides less fil-
let control and less depth of penetration
in comparison with the flux and ferrule
process. In gas arc welding, a spark shield
delivers the gas. The stud is loaded, and
the gun is positioned for welding. When
the user pulls the trigger, shielding gas
(preflow) floods the welding zone. The
stud is lifted, and the arc is generated.
While the stud remains lifted, the arc
melts the stud and base metal. Once the
arc time is complete, the stud is plunged
into the molten pool. The gas continues
to flow until the molten metal cools. The
gun can then be removed. Since no fer-
rule is used, this process lends itself well
to automation and robotics.
Drawn Arc Stud Welding
Applications
T
oday, the drawn arc stud welding
process has found extensive use in
a wide variety of applications
across an array of industries including the
following:
Automotive heat shields, power
steering, insulation, exhaust systems,
lighting systems, hydraulic/brake/fluid
lines, electrical wire routing, and trim
Construction bridges, buildings,
conduit, and piping
Farm equipment fenders, brack-
ets, cabs, spreaders, shrouding, thresher
teeth, and wiring and hose management
Highway equipment cover plates,
nonskid
devices,
wiring,
and
hose
management
Metal products barbecue equip-
ment, enclosures, heating/plumbing ap-
paratus, insulation enclosures, HVAC
units, and water storage systems
Industrial inspection cover plate at-
tachments, enclosures, flow indicators, ma-
terial handling equipment, and controls
Power generation and distribution
power transformer tanks and transducers
Shipbuilding insulation, wire man-
agement, and hatch covers
Electrical/electronic electrical en-
closures and hydraulic lines.
As valuable as digital innovations are
to techniques like drawn arc stud welding,
theyve proven essential to processes that
demand a high level of precision, such as
capacitor discharge (CD) stud welding.
The Impact of Digital CD
Stud Welding
A
pplying digital technology to CD
welding has yielded several bene-
fits. First, the voltage control is
more precise. In other words, the
Fig. 1 Main steps in drawn arc stud
welding. 31
WELDING JOURNAL
charge/discharge hysteresis window is
smaller with digital controls. This means
that the actual weld voltage is more accu-
rate and repeatable.
Digital electronics control the charge
profile more precisely via exacting phase
control. This means that a larger capacity
welding machine can be used with lower
amperage building line supplies without
tripping any circuit breakers.
Furthermore, in some applications, mi-
croprocessor control has allowed the
heavy bulky transformer to be eliminated
to achieve CD welding power supplies that
weigh as little as 10.5 lb with ¼-in. fas-
tener capability.
Most importantly, digital controls have
enabled advanced operator safety. In ana-
log systems with a shorted weld SCR, ca-
pacitor voltage can be present within the
weld tool at any time, endangering the op-
erator. The microprocessor in digital
power supplies is able to actively monitor
component health and deactivate the
power supply completely in the event of
critical component failures.
Capacitor Discharge
Process Advances
A
s with drawn arc stud welding,
technological advances in the ca-
pacitor discharge equipment have
basically reinvented the process for light-
weight applications. Capacitor discharge,
or CD stud welding, is a popular option
when appearance is a critical product fea-
ture. Using very short weld times, it per-
mits the welding of small-diameter studs
to thin, lightweight materials with very lit-
tle distortion, discoloration, or burning.
The weld cycle can be completed in 0.004
to 0.01 s on material as thin as 0.020 in.
(0.5 mm). The fast weld times of CD help
to minimize heat buildup. Additionally, it
allows the welding of dissimilar metals be-
cause the weld penetration is so slight that
it avoids metallurgical conflicts. Metals
typically used in this process include mild
steel, stainless steel, and aluminum, as
well as brass, tungsten, and copper.
A CD welding system, using a capaci-
tor storage system, delivers a rapid elec-
trical discharge, stud welding tools, and
fasteners. Ferrules and flux are not
needed.
Two techniques used in the CD method
are contact and gap. Both use a specially
designed stud with a projection, or igni-
tion tip, on its weld end. The stud tip pro-
vides accurate welding time control with
repeatable precision.
The qualit