Tweco 500SP PowerMaster Automation - Manual (Page 65)

POWERMASTER 400SP, 500SP AUTOMATION
March 16, 2007 6-5
6.04 Pulsed Arc Welding Parameters
A. Pulse period t
P
The pulse period for separating the droplet is between
1.5 and 3.0 ms depending on wire diameter and the
pulse current setting I
P
.
If the pulse period is too long, material transfer only
takes place during the pulse phase.
Arc formation and drop rate can be affected by
additional pulse stages.
B. Pulse voltage U
P
and pulse current I
P
Since welding with pulsed arc is based on the
temporary utilization of the pinch effect, the drop-
separating pulse current must always be large enough
to exceed critical current intensity depending on wire
diameter, wire material and shielding gas composition,
etc. If this value is not achieved, material transfer takes
place completely or partially in the short circuit with
possible spatter.
C. Wire feed speed v
D
and pulse frequency
f
P
The main condition for a controlled material transfer
with one drop per pulse is to set a defined drop
volume. The volume of the melted drop must then be
identical with the volume of the wire electrode fed in
each pulse period. The necessary wire feed speed v
D
results from the product of pulse frequency fP and
the wire length “L” melted in each pulse period. From
this relationship you see that a change in wire feed
speed requires a linear change in pulse frequency. A
rise in electrode melt rate by increasing wire feed
speed needs a higher pulse frequency. The objective
drop diameter should be about .045" (1.2mm) with a
wire diameter of .045" (1.2mm).
D. Primary current
Arc length ionization must be maintained during the
primary current phase, whose period results from the
selected frequency and pulse period. This requires
currents ranging between 25 and 80 A depending on
wire diameter, material and material thickness. The
primary current can also be used to affect the arc and
material transfer. At a constant ratio of wire feed speed
and pulse frequency, the arc length can be changed
by varying the primary current and the associated
voltage. Reducing the primary current causes a
shorter arc. This can be used to counteract arc
deflection with fillet welds or at high welding rates.
The time of drop separation can be affected by varying
the ratio of primary current to pulse current. Normally
the objective is to separate the drop just after the
current pulse in the primary current phase (in the third
pulse current phase). This can be achieved by
increasing the primary current and reducing the pulse
current at the same time. Remember that excessively
high primary current will melt the free wire end too
quickly. This will form very large drops which can
lead to spatter during the transition to the welding
pool.
E. Pulse MIG applications
The main application for pulse MIG is for precision
MIG welding of aluminium, stainless steel, steel and
other weldable materials.
• Spray transfer welding permitted at lower-than-
normal average weld currents.
• No spatter or undercut in the majority of welding
applications.
• Precise control of welding power, to assure bead
shape and root penetration rivalling TIG welding.
• High energy arc produced, that virtually
eliminates the risk of lack of fusion.
• Improved arc control for out-of-position welding
and more effective welding of thin materials,
with all the advantages of spray transfer.
• Optimized pulse programs for gas/wire
combinations
• TwinPulse® capabilities.
• Exceptional out-of-position welding for non-
ferrous materials, including aluminium.
• Effortless TIG-like weld appearance on
aluminium and stainless steel
• Deeper weld penetration
• Accurate penetration on sheet metal
• Superior welding characteristics on hard-facing
and high alloy steels
• The ability to use larger-than-normal diameter
wires on thin base material, providing a cost
saving on wire
• Spray arc welding vertical up, giving smoother
welds, better control and deeper penetration
• Improved edge wetting in Pulse GMAW process
At the lower end of the performance range the pulsed
arc cannot fully replace the dip transfer. The reason
is the continuous arc that occurs in the primary
current phase. This phenomenon does not exist with
the short-circuiting arc. An exception to this is when
welding aluminium and aluminium alloys. Normally,
these materials can only be reliably welded using a
pulsed arc. In the upper performance range, the
pulsed arc is preferable to the sprayer arc, in particular
for welding aluminium materials and high-alloy steels.