1. INCREASED PRODUCTIVITY AND SPEED WITH DIGITALLY CONTROLLED
SOFTWARE BASED MIG WELDING EQUIPMENT
Mr. Aarno Laine
M/S KEMPI OY., Finland
Introduction
The MIG/MAG/Pulsed MIG welding process has been developed to increase
productivity. The starting point has been to develop the welding characteristics so that
TIG and MMA welding can be replaced with a more economical and productive method.
New characteristic curves have been added to the welding range of stainless steels so that
even rarer steel qualities can be welded with standard programs.
Digitally Controlled-welding machine has been developed for demanding welding of
stainless steels. This is made possible by digital control technology both in the power
source and in the wire feeder. This makes it possible to update the equipment with new
programs and characteristics whenever necessary.
Synergic 1 – Knob welding:
As is well known, the welding process involves a large number of welding parameters. In
digitally controlled, software based machines the welding parameters change with the
wire-feed speed. This makes it easier to set the correct values in different welding
situations and it makes simple to repeat the correct settings.
The type of equipment can be used to weld all stainless solid and flux cored wires. The
share of flux cored wires in the welding of stainless steel has been increasing for years
already. Because, MIG welding is widely accepted for the welding of demanding
stainless targets in the industrial countries, the use of solid wire is becoming the
established method in the welding of ordinary stainless steels.
With solid wires the shielding gas is usually Ar+2%CO2 and with flux cored wires Ar+8-
25%CO2.
There is some machine, which has 13 pre-programmed synergic MAG curves for
stainless steels. Each curve consists of 14 parameters affecting the arc and the weld.

2. One of the most important parameters affecting the burning of the arc is the behaviour of
the short-circuit current, i.e., the arc-force in the short–arc and mixed-arc ranges. In the
traditional welding machines with step-wise adjustment, the inductance is selected by
setting the output of the earth cable from the choker. In some machine microprocessor
calculates and adjusts the set rate of change of the current of the arc in the short circuit
and keeps the arc at the desired length.
Example: welding parameters with the most common wire/gas combination 1.0mm /
316L / Ar+2%CO2
Arc force and inductance:
Depending on the circumstances, such as tolerances (composition of the wire, purity of
the gas, etc.), the digitally controlled software based welding machine gives the welder
the possibility to change the shape of the pulse to fit the circumstances. In addition the
welder can then change the behavior of the arc as he likes.
The coarseness or softness of the arc can be increased from the standard setting in the
short-arc and mixed-arc ranges.
A soft arc does not cause as much spatter as a coarse arc, but, on the other hand, it is
sensitive (more unstable) to movements of the hand and it uses a higher temperature.

3. A coarse arc is stable to weld (it allows the welder to push melt for example against the
root backing), but it easily causes spatter. The arc is also colder so that thin-sheet welding
succeeds even with high values and welding is faster.
Pulsed MIG welding:
Pulsed MIG welding is best suited for welding stainless steel with a solid wire.
The shield gas Ar+2%CO2 is the most common with solid wire, and in special cases an
addition of helium is necessary to increase weldability. Also other gas mixtures can be
used.
Some digitally controlled, software based machine has 16 pre-programmed synergic
pulsed MIG curves for stainless steels. Each curve consists of 16 parameters affecting the
arc and the welding.
In pulsed MIG welding the timing and shape of the current pulse is important so that the
filler material melts into the weld pool evenly and without spatters.
Increased productivity and speed:
Example : welding parameters with the most common wire/gas combination 1.0 mm
/ 316L / Ar+2%CO2 :

4. Adjustment of pulse height:
Because the circumstances involve several parameters (composition of the wire, purity of
the gas, etc.), digitally controlled machine also makes it possible to change the form of
the pulse to suit the circumstances.
High pulse is needed when the drops do not separate easily as with high-nickel filler
wires or if an easily targeted arc is desired. Too high a pulse will disperse the drops and
cause Micronics spatter.
A lower pulse is used when the drops separate easily, for example with a lower CO2
addition in the shield gas. The targeting of the arc is not as good as with a higher pulse.
Too low a pulse cannot separate the filler drop, so that it is transferred to the weld pool
through the short circuit or in the form of coarse spatter.
Cable compensation :
The length of the cables affects the length of the arc, which means that it has to be
taken into account. When cable length increases, so does the voltage drop to the
cables, which is compensated for by correspondingly increasing the voltage of the
power source. Automatic calibration makes it easier to adjust the voltage increase.
Use of the memory :
The memory channels makes it possible to find the settings again quickly and exactly. In
addition, when using the gun / remote control, they make it possible to find 5 different
welding values even during welding.
The display of the synergic panel shows the set welding values, and values used during
the welding can be recalled by means of the “weld data” – button so that the values can
be transferred for example to the WPS.

5. The sheet thickness table gives the preliminary welding values for the butt weld.
The selection windows of the synergic curve specify the filler material being used, the
gas, the diameter and the detailed curve number.
Customer specific programs:
The welding parameter can be changed when needed. The synergic curves are changed
through a PC by using the window based MIG Prog. Programme and a DLI interface.
This makes it possible for example to change the texts in the menu displays so that they
are more suitable to the customer’s needs and they even make it possible to create a
synergic curve for a new wire. They can be stored in the user function menu reserved for
the customer.
Any necessary new curves can also be added from the curve bank.
Welding characteristics:
The welding characteristics of digitally controlled software based machine sometime
tailored specifically for stainless steel. The ignition of the arc is one of the most important
stages in welding, because poor ignition creates a lot of spatter and even defective joins at
the start of the weld. In this type of machine ignition is extremely good because of the
high slope-up of the start current and the sufficient heat input.
Attention has also been paid to the burning of the arc as well as to the pointing of the arc
and to its tolerance to disturbances, which is seen well in position welding and specially
in pulse welding.
In the user mode it is possible to change the standard settings, for example the start and
end function, such as the creep start, the hot start function, the crater filling time and the
end level. It is easy to return to the standard settings.
Double pulse and aluminium welding
Difference between the ordinary pulse and double pulse:
Pulse MIG welding in simplest terms is achieved by varying the welding current
between background and peak current within a desired frequency range. To
achieve arc stabilization for any given filler wire and the shielding gas
combination, there are close to 20 parameters that optimize the current waveform,
which include dedicated parameters for controlling the peak and background

6. current. During the peak time one droplet of filler material is detached and
transferred across the open arc into the weld pool.
The background current is kept to a level at which the arc does not extinguish and
no filler material is detached. The pulsed frequency normally varies between 50
and 250 Hz and equalizes the burn off rate of the filler wire to give a constant arc
length without short-circuits. To simplify the use of the welding machine, there are
ready-made programs commonly known as synergic curves, saved in its memory
for different materials, materials thickness, wire diameter and the shielding gases.
To the user this means the setting of the correct welding parameters to achieve the
desired heat input is defined with just one main wire-feed speed control with fine-
adjustment of the arc-length. Commonly known as “one knob control”. Pulse
welding has been used to join the materials, as it welds at cooler temperatures. In
other words, it has lower energy input. This prevents burning through and the
excess heating of the background of the sheet. Distortions in welding are minor
and the welding does not cause spatter as the filler metal is transferred without
short-circuits. Managing the molten metal is made easier, especially in position
welding. In double pulse welding, the welding current and the wire feed speed are
pulsed. In addition, the pulsing of the current moves within the frequency defined
as a set value, at the minimum and the minimum and maximum current level of
normal pulsing, to a higher level, as can be seen in Figure 2. The frequency, the
number of times per second the pulsing moves to the higher level, can be selected
in the Set Up function on the function panel between 0.1-3 Hz. In figure 2, this
change happened twice. At the same time, the voltage rises. The energy of the arc
thus grows during the double pulse period compared to the basic pulse level. As
the energy changes, the melting power also changes. In normal pulse welding, the
wire feed is set to the desired value and the welding begins. When welding with
double pulse, in addition to the wire feed speed (for example 10 m/min), the
amplitude for the wire feed is also defined. This amplitude defines the minimum
and maximum value of the wire feed speed during the double pulse period. In case
of figure 2, the set values of the wire feed was 10 m/min and the amplitude 2.0,

7. and thus the wire feed varied between 8 m/min and 12 m/min during welding. In
other words, the wire feed pumps during welding. The result is visible as a weld
surface that resembles TIG welding, as presented in figure 3.
Using double pulse in aluminium welding
The main purpose of the double pulse machine is to refine and extend the benefits
brought by conventional synergic pulse thus simplifying welding, with greatly
improved welding quality. When welding aluminium, this means the weld is
faultless with an appearance resembling that of TIG welding, so often desired
when welding thin materials, such as those in bicycles and furniture. When
production-welding aluminium, the most common welding defects are porosity,
poor fusion, undercuts and cracks at the end of the weld. Poor fusion is often
caused by poor working technique, resulting in insufficient arc energy to melt the
base metal and remove an oxide layer whose melting points is 2,052 degree C.
Moreover, the deficiency in arc energy is emphasized by the rapid heat
conductivity of the base metal. On the other hand, the low melting point of
aluminium is visible as excessive melting of the base material, resulting in an
under-cut or burn through next to the weld. Cracking phenomena in welds are
mainly related to the choice of filler metal and to the performance of the welding.
The correct choice of the filler metal according to the base metal can be made with
help of various aluminium standers or tables from filler metal suppliers. The
porosity of the weld is mainly due to hydrogen that has entered the weld for a
variety of reasons. Dominant factors include cleanliness, the welding process,
groove preparation, the performing of the welding and the composition of the base
filler metals. For example, AIMg4, 5Mn is easier to weld in terms of porosity than
AIMgSi1, which is often used in extrusions.
Double pulse welding of the thin materials (1 - 5 mm)
The greatest benefits of double pulse with thin materials include good weldability
and the appearance of the weld. These benefits are emphasized in position
welding. Straight-line moving is used in welding. Quick oscillation, normally used

8. with aluminium, is not needed. These facilitates control of the weld pool in the
fillet corner.
As a result of the pumping of the arc, typical to double pulse, the appearance of
the weld resembles TIG welding. The pumping of the arc also affects the practical
performance of the welding. During the double pulse period, the arc energy and
the wire feed speed grow and enable sufficient penetration of the base metal.
When returning to the basic pulse, what we might call a deceleration phase, the
length of the arc shortens and the welding becomes slower and steadier. This is an
advantage when the root opening in the groove varies, as the risk of burning
through is reduced. In practice, welders feel they get more time to control the
molten metal. As it is a case of pulse welding, the material moves in drops without
short-circuits or splattering. Table 1 presents the double pulse welding parameters
for different aluminum thickness, the wire feed speed and its amplitude, and the
frequency of the double pulse. As basic instruction for welding thin materials, it
can be stated that the frequency of the double pulse to be used it increased and
amplitude of the wire feed-in reduced as the material thickness decreases.
Double Pulse Welding of Thicker Materials
Good weldability and appearance are also important in welding thicker materials.
In structures in which the material thickness is more than 5mm, the benefits of the
methods also very much include the evaluation both of penetration and formation
of gas pores. With double pulse welding, the depth of penetration can be changed
using amplitude and frequency. This is also visible in macrograph in figure 4. In
case presented in figure 4b, 15 mm Al 6082-T6 material has been welded using
double pulse. The size of the fillet is 5 mm. With the current selection of the
parameter, the energy of the arc reaches the level at which welding and control of
molten metal is easy and energy of the arc is sufficient to melt the fillet corner
without preheating. As end-result similar to figure 4a, achieved with the basic
pulse, appear to be good, but the energy has been insufficient to melt the base

9. metal enough. It is also possible to use double pulse in end welding. When
welding on one side against a ceramic backing in a root opening of 4 mm, double
pulsing and moving the gun in a straight line facilitate the welding. Particularly in
horizontal welding, the controlling of the top of the groove becomes easier. The
same regularity applies to the formation of the gas pores as with other current
forms. In the test that aimed at comparing the occurrences of gas pores in welds, 6
mm of aluminium AIMgSi1 (A16082-T6) was welded in a horizontal position
against a ceramic backing in a root opening of 4mm. In X-ray taken of the welds,
the gas pores were smaller and more evenly distributed in the weld than with the
normal pulse.