Carsten 205 GTI 1,9 T skrev:
ae86 skrev:
mig & mag er da det samme..
Nej, gassen afgører, hvad der er hvad.
Det er rigtigt .. Det er det samme svejseværk men hvis der er Carbondioxide (Co2), Oxygen (O2) eller Hydrogen (H2) i flasken (aktiv gas) så er det MAG og hvis der er Argon (Ar) eller Helium (He) i flasken er det MIG ...
Shielding Gases
Argon and helium are the two inert shielding gases used for
protecting the molten weld pool. The inert classification indicates
that neither argon nor helium will react chemically with the
molten weld pool. However, in order to become a conductive
gas, that is, a plasma, the gas must be ionized. Different gases
require different amounts of energy to ionize, and this is
measured in terms of the ionization energy. For argon, the
ionization energy is 15.7 eV. Helium, on the other hand, has an
ionization energy of 24.5 eV. Thus, it is easier to ionize argon
than helium. For this reason argon facilitates better arc starting
than helium.
The thermal conductivity, or the ability of the gas to transfer
thermal energy, is the most important consideration for selecting
a shielding gas. High thermal conductivity levels result in more
conduction of the thermal energy into the workpiece. The
thermal conductivity also affects the shape of the arc and the
temperature distribution within the region. Argon has a lower
thermal conductivity rate — about 10% of the level for both
helium and hydrogen. The high thermal conductivity of helium
will provide a broader penetration pattern and will reduce the
depth of penetration. Gas mixtures with high percentages of
argon will result in a penetration profile with a finger-like
projection into the base material,
and this is due to the lower thermal conductivity of argon.
Inert Shielding Gases
Argon is the most commonly used inert gas. Compared to
helium its thermal conductivity is low. Its energy required to
give up an electron, ionization energy, is low, and this results in
the finger-like penetration profile associated with its use. Argon
supports axial spray transfer. Nickel, copper, aluminum, titanium,
and magnesium alloyed base materials use 100% argon
shielding. Argon, because of its lower ionization energy, assists
with arc starting. It is the main component gas used in binary
(two-part) or ternary (three-part) mixes for GMAW welding. It
also increases the molten droplet transfer rate.
Helium is commonly added to the gas mix for stainless and
aluminum applications. Its thermal conductivity is very high,
resulting in the broad but less deep penetration profile.
When in use, arc stability will require additions of arc voltage.
Helium additions to argon are effective in reducing the dilution of
base material in corrosion resistant applications. Helium/argon
blends are commonly used for welding aluminum greater than 1”
(25 mm) thick.
Reactive Shielding Gases
Oxygen, hydrogen, nitrogen, and carbon dioxide (CO2) are
reactive gases. Reactive gases combine chemically with the
weld pool to produce a desirable effect.
Carbon Dioxide (CO2) is inert at room temperature. In the
presence of the arc plasma and the molten weld puddle it is
reactive. In the high energy of the arc plasma the CO2 molecule
breaks apart in a process known as dissociation. In this
process, free carbon, carbon monoxide, and oxygen release
from the CO2 molecule. This occurs at the DC+ anode region
of the arc. At the DC- cathode region, which is invariably the
work piece for GMAW, the released elements of the CO2
molecule undergo the process of recombination. During recombination
higher energy levels exist and are responsible for the
deep and broad penetration profile that characterizes the use of
carbon dioxide.
Dissociation and Recombination
During the process of dissociation, the free elements of the CO2
molecule (carbon, carbon monoxide, and oxygen) mix with the
molten weld pool or recombine at the colder cathode region of
the arc to form, once again, carbon dioxide. The free oxygen
combines chemically with the silicon, manganese, and iron to
form oxides of silicon, manganese and iron. Formed oxides,
commonly referred to as silica islands, float to the surface of the
weld pool, then solidify into islands on the surface of the finished
weld or collect at the toes of a weld. Higher levels of carbon
dioxide (higher oxidation potential) increases the amount of slag
formed on the surface of the weld. Lower levels of carbon
dioxide (lower oxidation potential) increase the amount of alloy,
silicon and manganese retained in the weld. As a result, lower
carbon dioxide levels, in a binary or ternary shielding gas blend,
increase the yield and ultimate tensile strength of a finished weld
Oxygen (O2) is an oxidizer that reacts with components in the
molten puddle to form oxides. In small additions (1-5%), with a
balance of argon, it provides good arc stability and excellent
weld bead appearance. The use of deoxidizers within the
chemistry of filler alloys compensates for the oxidizing effect of
oxygen. Silicon and manganese combine with oxygen to form
oxides. The oxides float to the surface of the weld bead to form
small islands, and are more abundant under CO2 shielding than
with blends of argon and oxygen gas.
Hydrogen (H2) in small percentages (1-5%), is added to argon
for shielding stainless steel and nickel alloys. Its higher thermal
conductivity produces a fluid puddle, which promotes improved
toe wetting and permits the use of faster travel speeds.
Binary Shielding Gas Blends
Two-part shielding gas blends are the most common and they
are typically made up of either argon + helium, argon + CO2, or
argon + oxygen.
Argon + Helium
Argon/helium binary blends are useful for welding nickel based
alloys and aluminum. The mode of metal transfer used is either
axial spray transfer or pulsed spray transfer. The addition of
helium provides more puddle fluidity and flatter bead shape.
Helium promotes higher travel speeds. For aluminum GMAW,
helium reduces the finger-like projection found with pure argon.
Helium is also linked to reducing the appearance of hydrogen
pores in welds that are made using aluminum magnesium fillers
with 5XXX series base alloys. The argon component provides
excellent arc starting and promotes cleaning action on
aluminum.
Common Argon + Helium Blends
75% Argon + 25% Helium — this binary blend is frequently
applied to improve the penetration profile for aluminum, copper,
and nickel applications. The puddle is more fluid than with 100%
argon.
75% Helium + 25% Argon — the higher helium content increases
the thermal conductivity and puddle fluidity. The penetration
profile is broad, and it exhibits excellent sidewall penetration.
Argon + CO2
The most commonly found binary gas blends are those used for
carbon steel GMAW welding. All four traditional modes of
GMAW metal transfer are used with argon/CO2 binary blends.
They have also enjoyed success in pulsed GMAW applications
on stainless steel where the CO2 does not exceed 4%.
Axial spray transfer requires CO2 contents less than 18%.
Argon/CO2 combinations are preferred where millscale is an
unavoidable welding condition. As the CO2 percentage increases,
so does the tendency to increase heat input and risk burnthrough.
Argon/CO2 blends up to 18% CO2 support pulsed
spray transfer.
Short-circuiting transfer is a low heat input mode of metal
transfer that can use argon/CO2 combinations. Optimally, these
modes benefit from CO2 levels greater than or equal to 20%.
Use caution with higher levels of argon with short-circuit metal
transfer.
Common Short-Circuiting Transfer Shielding Gas Blends
75% Argon + 25% CO2 — reduces spatter and improves weld
bead appearance on carbon steel applications.
80% Argon + 20% CO2 — another popular blend, which further
reduces spatter and enhances weld bead appearance on carbon
steel applications.
Common Axial Spray Transfer shielding gas blends
98% Argon + 2% CO2 — for axial or pulsed spray with stainless
steel electrodes and carbon steel electrodes. This blend has
seen repeated success on high-speed sheet metal applications.
There is excellent puddle fluidity and fast travel speeds associated
with this shielding gas blend.
95% Argon + 5% CO2 — for pulsed spray with carbon steel
electrodes. The addition of 5% CO2 provides for additional
puddle fluidity, and it lends itself to heavier fabrication than
blends with 2% CO2.
92% Argon + 8% CO2 — for both axial and pulsed spray
applications on carbon steel. Higher energy in axial spray
transfer increases puddle fluidity.
90% Argon + 10% CO2 — for either axial spray or GMAW-P
applications on carbon steel. The penetration is broader and it
reduces the depth of the finger-like penetration exhibited by
argon + oxygen mixes.
85% Argon + 15% CO2 — the higher CO2 level in axial or
pulsed spray transfer increases sidewall fusion on sheet metal or
plate thickness material. Generally produces improved toe
wetting on carbon steel with low levels of millscale. In GMAW-S,
short circuiting transfer, the lower CO2 level translates to less
heat for welding parts with less risk of burnthrough.
82% Argon + 18% CO2 — the effective limit for axial spray with
CO2. Popular European blend used for a wide range of welding
thicknesses. Broad arc enhances penetration profile along the
weld interface. Also lends itself well for use in short-circuiting
transfer or STT applications.
Argon + Oxygen
Argon/oxygen blends attain axial spray transfer at lower currents
than argon/CO2 blends. The droplet sizes are smaller, and the
weld pool is more fluid. The use of argon + oxygen has
historically been associated with high travel speed welding on
thin materials. Both stainless steel and carbon steel benefit from
the use of argon/oxygen blends.
99% Argon + 1% Oxygen — used for stainless steel applications.
The use of oxygen as an arc stabilizer enhances the fine droplet
transfer and maintains the puddle fluidity for this gas blend.
Stainless steel welds will appear gray because of the oxidizing
effect on the weld pool.
98% Argon + 2% Oxygen — used as a shielding gas for either
carbon or stainless steel applications. The earliest use of
argon/oxygen blends for axial spray transfer on carbon steel
employed 2% oxygen level. It is typically applied to applications
that require high travel speed on sheet metal. Applied with
either axial spray or pulsed spray transfer modes. Stainless
deposits are dull gray in appearance. This blend is often used
when superior mechanical properties are required from low alloy
carbon steel electrodes.
95% Argon + 5% Oxygen — general purpose axial spray or
pulsed spray transfer shielding gas applied to heavier sections of
carbon steel. The base material is usually required to be free of
contaminants with a low level of millscale.
Ternary Gas Shielding Blends
Three-part shielding gas blends continue to be popular for
carbon steel, stainless steel, and, in restricted cases, nickel
alloys. For short-circuiting transfer on carbon steel the addition
of 40% helium, to argon and CO2, as a third component to the
shielding gas blend, provides a broader penetration profile.
Helium provides greater thermal conductivity for short-circuiting
transfer applications on carbon steel and stainless steel base
materials. The broader penetration profile and increased
sidewall fusion reduces the tendency for incomplete fusion.
For stainless steel applications, three-part mixes are quite
common. Helium additions of 55% to 90% are added to argon
and 2.5% CO2 for short-circuiting transfer. They are favored for
reducing spatter, improving puddle fluidity, and for providing a
flatter weld bead shape.
Common Ternary Gas Shielding Blends
90% Helium + 7.5% Argon + 2.5% CO2 — is the most popular
of the short-circuiting blends for stainless steel applications. The
high thermal conductivity of helium provides a flat bead shape
and excellent fusion. This blend has also been adapted for use
in pulsed spray transfer applications, but it is limited to stainless
or nickel base materials greater than .062" (1.6 mm) thick. It is
associated with high travel speeds on stainless steel applications.
55% Helium + 42.5% Argon + 2.5% CO2 — although less
popular than the 90% helium mix discussed above, this blend
features a cooler arc for pulsed spray transfer. It also lends itself
very well to the short-circuiting mode of metal transfer for
stainless and nickel alloy applications. The lower helium
concentration permits its use with axial spray transfer.
38% Helium + 65% Argon + 7% CO2 — this ternary blend is for
use with short-circuiting transfer on mild and low alloy steel
applications. It can also be used on pipe for open root welding.
The high thermal conductivity broadens the penetration profile
and reduces the tendency to cold lap.
90% Argon + 8% CO2 + 2% Oxygen — this ternary mix is
applied to short-circuiting, pulsed spray, and axial spray modes
of metal transfer on carbon steel applications. The high inert
gas component reduces spatter.
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