SMAW & FCAW
These two are highly acceptable process of welding in industries as per foundry is concern
we will discuss more about these two types in details and i will give you some references for more details
1. SMAW- It stand for shielded metal arc welding , an arc welding process in which joining takes place between the tip of covered electrode and the surface of the base metal
Advantages and applications
Shielded Metal Arc Welding (SMAW) or
Stick welding is a process which melts and joins metals by heating them with an
arc between a coated metal electrode and the work piece. The electrode outer
coating, called flux, assists in creating the arc and provides the shielding
gas and slag covering to protect the weld from contamination. The electrode core
provides most of the weld filler metal.
When the electrode is moved along
the work piece at the correct speed the metal deposits in a uniform layer called
a bead
The
Stick welding power source provides constant current (CC) and may be either
alternating current (AC) or direct current (DC), depending on the electrode
being used. The best welding characteristics are usually obtained using DC power
sources
The power in a welding circuit is
measured in voltage and current. The voltage (Volts) is governed by the arc
length between the electrode and the work piece and is influenced by electrode
diameter. Current is a more practical measure of the power in a weld circuit
and is measured in amperes (Amps).
The amperage needed to weld depends on
electrode diameter, the size and thickness of the pieces to be welded, and the
position of the welding. Thin metals require less current than thick metals,
and a small electrode requires less amperage than a large one.
It is preferable to
weld on work in the flat or horizontal position. However, when forced to weld
in vertical or overhead positions it is helpful to reduce the amperage from
that used when welding horizontally. Best welding results are achieved by
maintaining a short arc, moving the electrode at a uniform speed, and feeding
the electrode downward at a constant speed as it melts
SHIELDED METAL ARC
WELDING (SMAW)
PROCEDURE
1. Work piece
Make sure work piece is clean before welding.
2. Work Clamp
Place as close to the
weld as possible
3. Electrode
Before striking an arc, insert an
electrode in the electrode holder. A small diameter
electrode requires less current than a
large one. Follow recommendations of the electrode manufacturer when setting weld
amperage or just follow according to your WPS/PQR.
4. Arc Length
Arc length is the distance from the
electrode to the work piece. A short arc with correct amperage will give a sharp,
crackling sound. Correct arc length is related to electrode diameter. Examine
the weld bead to determine if the arc length
is correct.
Arc length for 1/16
and 3/32 in. diameter electrodes should be about 1/16 in. (1.6mm); arc length for
1/8 and 5/32 in. electrodes should be about 1/8 in. (3 mm)
5. Slag
Use a chipping hammer and wire brush
to remove slag. Remove slag and check
weld bead before
making another weld pass
Striking An Arc −
Scratch Start Technique
Drag electrode across work piece like
striking a match; immediately lift electrode slightly after touching work. If
arc goes out, electrode was lifted too high. If electrode sticks to work piece,
use a quick twist to free it.
Striking An Arc −
Tapping Technique
Bring electrode straight down to work
piece; then lift slightly to start arc. If arc goes out, electrode was lifted too
high. If electrode sticks to work piece, use a quick twist to free it
Positioning Electrode
Holder
Hold the electrode nearly
perpendicular to the work, although tilting it ahead (in the direction of
travel) will be helpful
Electrode Movement During
Welding
1. Stringer Bead − Steady Movement along
Seam
2. Weave Bead − Side
To Side Movement along Seam
Conditions That
Affect Weld Bead Shape
Electrode
Angle
Arc Length
Travel Speed
Poor Weld Bead
Characteristics
1. Large Spatter Deposits
2. Rough, Uneven Bead
3. Slight Crater During Welding
4. Bad Overlap
5. Poor Penetration
Good Weld Bead Characteristics
1. Fine Spatter
2. Uniform Beads
3. Moderate Crater During Welding
4. No Overlap
5. Good Penetration Into Base Metal
Typical Weld Joints
Types of Groove
(Butt) Joint Welds
1. Tack Welds
Prevent butt joint distortion by tack
welding the materials in position before final weld. Work piece distortion
occurs when heat is applied locally to a joint. One side of a metal plate will
“curl” up toward the weld. Distortion will also cause the edges of a butt joint
to pull together ahead of the electrode as the weld cools
2. Square Groove Weld
3. Single V-Groove Weld
4. Double V-Groove Weld
Materials up to 3/16 in.
(5 mm) thick can often be welded without special preparation
using the square groove
weld. However, when welding thicker materials it may
be necessary to prepare
the edges (Vgroove) of butt joints to ensure good welds.
The single or double
V-groove weld is good for materials 3/16 − 3/4 in. (5-19 mm) thick. Generally,
the single V-groove is used on materials up to 3/4 in. (19 mm) thick and when,
regardless of thickness, you can weld from one side only. Create
a 30 degree bevel with oxyacetylene or plasma cutting equipment. Remove scale
from material after cutting. A
grinder can also be used to prepare bevels.
Groove (Butt) Joint
Training Procedure
Practice welding butt joints on 1/8
in. (4mm) or thicker material. (Avoid thinner materials since they require
greater skill.) Separate the squared edges of the material about 1/16 in. (1.6
mm) and make a butt weld all the way through with a 1/8 in. electrode. (You may
need to adjust the weld current and travel speed to obtain the desired weld.)
Perform a similar exercise on 1/4 in. (6 mm) material, depositing a bead on
each side of the joint and fusing one to the another (no bevel needed).
Practice making a single V-groove weld
on 1/4 in. (6 mm) plate beveled 30°. Start with a 1/8 in. electrode for
the first bead and finish with a 5/32 in. (4 mm) electrode. Be sure to penetrate
about 1/32 in. (1 mm) beyond the bottom of the “V” or root. Perform a similar
exercise on thicker materials. Generally, deposit a bead for each 1/8 in. (3mm)
of material thickness, cleaning the joint between layers. On heavier plates, it
may be necessary to weave the top layers to fill the groove.
Weld
defects and its troubleshooting
Possible cause
|
Corrective action
|
Arc length too long.
|
Reduce arc length.
|
Work piece dirty.
|
Remove all grease,
oil, moisture, rust, paint, coatings, slag, and dirt from work surface before
welding
|
Damp electrode.
|
Use dry electrode.
|
2. Excessive Spatter
Scattering of molten metal particles
that cool to solid form near weld bead.
Possible cause
|
Corrective action
|
Amperage too high
for
electrode.
|
Decrease amperage
or select larger electrode
|
Arc length too long
or voltage
too high
|
Reduce arc length
or voltage.
|
3.
Incomplete fusion
Failure of weld metal to fuse
completely with base metal or a preceding weld bead
Possible Cause
|
Corrective action
|
Insufficient heat
input.
|
Increase amperage.
Select larger electrode and increase amperage.
|
Improper welding
technique
|
Place stringer bead
in proper location(s) at joint during welding.
Adjust work angle
or widen groove to access bottom during welding.
Momentarily hold
arc on groove side walls when using weaving technique.
Keep arc on leading
edge of weld puddle.
|
Work piece dirty.
|
Remove all grease,
oil, moisture, rust, paint, coatings, slag, and dirt from work surface before
welding.
|
4 . Excessive
Penetration
Weld metal melting through base metal
and hanging underneath weld.
Possible cause
|
Corrective action
|
Excessive heat
input.
|
Select lower
amperage. Use smaller electrode
|
Improper weld
technique.
|
Adjust travel
speed.
|
FCAW-FLUX
CORED ARC WELDING
Flux Cored Arc Welding (FCAW) is a
welding process by fusion which is widely used on ferrous metal. The consumable
electrode can have an interior flux or a mix of flux and metal powder and has a
tubular form . It is as semi-automatic or automatic arc welding process
Advantages and applications
·
FCAW may be an
"all-position" process with the right filler metals (the consumable
electrode)
·
No shielding gas
needed with some wires making it suitable for outdoor welding and/or windy
conditions
·
A high-deposition rate
process (speed at which the filler metal is applied) in the 1G/1F/2F
·
Some
"high-speed" (e.g., automotive) applications
·
As compared to SMAW
and GTAW, there is less skill required for operators.
·
Less precleaning of
metal required
·
Metallurgical benefits
from the flux such as the weld metal being protected initially from external
factors until the slag is chipped away
Used on the following alloys:
·
Mild and low alloy
steels
·
Stainless steels
·
Some high nickel
alloys
·
Some
wearfacing/surfacing alloys
·
Porosity chances very
low
Disadvantages
Of course, all of the usual issues that occur in welding can
occur in FCAW such as incomplete fusion between base metals, slag inclusion (non-metallic inclusions), and cracks in
the welds. But there are a few concerns that come up with FCAW that are worth
taking special note of:
·
Melted Contact Tip –
happens when the contact tip actually contacts the base metal, thereby fusing
the two and melting the hole on the end
·
Irregular wire feed –
typically a mechanical problem
·
Porosity – the gases
(specifically those from the flux-core) don’t escape the welded area before the
metal hardens, leaving holes in the welded metal
·
More costly filler
material/wire as compared to GMAW
·
The equipment is less
mobile and more costly as compared to SMAW or GTAW.
·
The amount of smoke
generated can far exceed that of SMAW, GMAW, or GTAW.
·
Changing filler metals
requires changing an entire spool. This can be slow and difficult as compared
to changing filler metal for SMAW or GTAW.
·
Creates more fumes
than stick welding.[1]
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