Experimental Investigation of Process Parameters on

Experimental Investigation of Process Parameters on
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
Experimental Investigation of Process
Parameters on Strength of Welding Joint in
GMAW
Sandip Deshmukh1, Yogesh Lande2, Prof. Milind Mhaske3 Prof. S B Belkar4
1
Department of Mechanical Engineering, PRECOE Loni, Pune University, India
2
Department of Mechanical Engineering, AV Polytechnic Sangamner, India
3
Department of Mechanical Engineering, PRECOE Loni, Pune University, India
4Department of Mechanical Engineering, PRECOE Loni, Pune University, India
Abstract
The strength value most desired in any welding process is an excellent Ultimate Tensile Strength (UTS) of the weld,
compared with the parent metal. Process parameters applied during the welding process ought to be subjected to
continuous scrutiny and assessment because of the ever increasing demand for structural and industrial materials
with weld joints possessing higher strength values. This study is intended to investigate the inadequacies of existing
GMAW welding process parameters utilized by the investigated industrial firm in its signature welding protocol, by
suggesting alternative, uniquely crafted, and improved process parameters to replace its existing signature welding
protocol, thereby improving the weld results by attaining higher UTS. These suggested process parameters were
thereafter subjected to reported literature, following which optimization was achieved by employing the Taguchi
Method. Then in future work we will study the strength on universal testing machine and calculating the results.
Keywords— GMAW Welding, GMAW, Taguchi method, ANNOVA
•
Introduction
Metal Inert Gas welding as the name suggests, is a process in which the source of heat is an arc formed between a
consumable metal electrode and the work piece, and the arc and the molten puddle are protected from contamination
by the atmosphere (i.e. oxygen and nitrogen) with an externally supplied gaseous shield of inert gas such as argon,
helium or an argon-helium mixture. No external filler metal is necessary, because the metallic electrode provides the
arc as well as the filler metal. It is often referred to in abbreviated form as MIG welding. MIG is an arc welding
process where in coalescence is obtained by heating the job with an electric arc produced between work piece and
metal electrode feed continuously. A metal inert gas (MIG) welding process consists of heating, melting and
solidification of parent metals and a filler material in localized fusion zone by a transient heat source to form a joint
between the parent metals. Gas metal arc welding is a gas shielded process that can be effectively used in all
positions.
•
•
•
•
•
GMAW can be done in three different ways
Semiautomatic Welding - equipment controls only the electrode wire feeding. Movement of welding gun is
controlled by hand. This may be called hand-held welding.
Machine Welding - uses a gun that is connected to a manipulator of some kind (not hand-held). An operator has
to constantly set and adjust controls that move the manipulator.
Automatic Welding - uses equipment which welds without the constant adjusting of controls by a welder or
operator. On some equipment, automatic sensing devices control the correct gun alignment in a weld joint.
Working Principle of MIG Welding
• As shown in fig. the electrode in this process is in the form of coil and continuously fed towards the work
during the process. At the same time inert gas (e.g. argon, helium, or CCCC) is passed around electrode from the
same torch. Inert gas usually argon, helium, or a suitable mixture of these is used to prevent the atmosphere from
contacting the molten metal and HAZ. When gas is supplied, it gets ionized and an arc is initiated in between
3774
www.ijariie.com
892
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
electrode and work piece. Heat is therefore produced. Electrode melts due to the heat and molten filler metal
falls on the heated joint.
• The arc may be produced between a continuously fed wire and the work. Continuous welding with coiled
wire helps high metal depositions rate and high welding speed. The filler wire is generally connected to the
positive polarity of DC source forming one of the electrodes. The work piece is connected to the negative
polarity. The power source could be constant voltage DC power source, with electrode positive and it yields a
stable arc and smooth metal transfer with least spatter for the entire current range.
Fig.1 Basic working principle
Fig.2 Schematic of GMAW
The gas shield around it does not ionized, which prevents weld against atmospheric co contamination and
surface oxidation. Some torch has water cooling systems.MIG welding is also called Gas Metal Arc Welding. The
filler metal is transmitted from electrode to joint by different methods. It is dependent on the current passing through
the electrode and voltage.
•
GMAW / MIG welding applications
MIG may be operated in semiautomatic, machine, or automatic modes. All commercially important applicable
metals such as carbon steel, high-strength, low-alloy steel, and stainless steel, aluminum, copper, titanium, and
nickel alloys can be welded in all positions with this process by choosing the appropriate shielding gas, electrode,
and welding variables.
•
MIG Welding Effecting parameters
Weld quality and weld deposition rate both are influenced very much by the various welding parameters and
joint geometry. Essentially a welded joint can be produced by various combinations of welding parameters as well
as joint geometries. These parameters are the process variables which control the weld deposition rate and weld
3774
www.ijariie.com
893
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
quality. The weld bead geometry, depth of penetration and overall weld quality depends on the following operating
variables.
• Electrode size, Welding current, Arc voltage
• Arc travel speed, Welding position
• Gas Flow rate, Shielding Gas composition
• Electrode extension (length of stick out)
•
Electrode Size: The electrode diameter influences the weld bead configuration (such as the size), the depth
of penetration, bead width and has a consequent effect on the travel speed of welding. As a general rule, for the
same welding current (wire feed speed setting) the arc becomes more penetrating as the electrode diameter
decreases. To get the maximum deposition rate at a given current, one should have the smallest wire possible that
provides the necessary penetration of the weld. The larger electrode diameters create weld with less penetration but
welder in width. The choice of the wire electrode diameter depends on the thickness of the work piece to be welded,
the required weld penetration, the desired weld profile and deposition rate, the position of welding and the cost of
electrode wire. Commonly used electrode sizes are (mm): 0.8, 1.0, 1.2, 1.6 and 2.4. Each size has a usable current
range depending on wire composition and spray- type arc or short- circuiting arc is used. [7]
•
Welding Current: The value of welding current used in MIG has the greatest effect on the deposition rate,
the weld bead size, shape and penetration. In MIG welding, metals are generally welded with direct current polarity
electrode positive (DCEP, opposite to TIG welding), because it provides the maximum heat input to the work and
therefore a relatively deep penetration can be obtained. When all the other welding parameters are held constant,
increasing the current will increase the depth and the width of the weld penetration and the size of the weld bead.
•
Welding Voltage: The arc length (arc voltage) is one of the most important variables in MIG that must be
held under control. When all the variables such as the electrode composition and sizes, the type of shielding gas and
the welding technique are held constant, the arc length is directly related to the arc voltage. High and low voltages
cause an unstable arc. Excessive voltage causes the formation of excessive spatter and porosity, in fillet welds it
increases undercut and produces narrower beads with greater convexity, but an excessive low voltage may cause
porosity and overlapping at the edges of the weld bead. And with constant voltage power source, the welding current
increase when the electrode feeding rate is increased and decreased as the electrode speed is decreased, other factors
remaining constant. This is a very important variable in MIG welding, mainly because it determines the type o metal
transfer by influencing the rate of droplet transfer across the arc. The arc voltage to be used depends on base metal
thickness, type of joint, electrode composition and size, shielding gas composition, welding position, type of weld
and other factors.
•
Shielding Gas: The primary function of shielding gas is to protect the arc and molten weld, pool from
atmosphere oxygen and nitrogen. If not properly protected it forms oxides and nitrites and result in weld deficiencies
such as porosity, slag inclusion and weld embrittlement. Thus the shielding gas and its flow rate have a substantial
effect on the following: Arc characteristics, Mode of metal transfer, penetration and weld bead profile, speed of
welding, cleaning of action, weld metal mechanical properties. Argon, helium and argon-helium mixtures are used
in many applications for welding non-ferrous metals and alloys. Argon and Carbon dioxide are used in Carbon steel.
[7]
•
Arc Travel Speed: The travel speed is the rate at which the arc travels along the work- piece. It is controlled
by the welder in semiautomatic welding and by the machine in automatic welding. The effects of the travel speed
are just about similar to the effects of the arc voltage. The penetration is maximum at a certain value and decreases
as the arc speed is varied. For a constant given current, slower travel speeds proportionally provide larger bead and
higher heat input to the base metal because of the longer heating time. The high input increases the weld penetration
and the weld metal deposit per unit length and consequently results in a wider bead contour. If the travel speed is too
slow, unusual weld build-up occurs, which causes poor fusion, lower penetration, porosity, slag inclusions and a
rough uneven bead. The travel speed, which is an important variable in MIG, just like the wire speed (current) and
the arc voltage, is chosen by the operator according to the thickness of the metal being welded, the joint fit-up and
welding position.
•
•
Literature Review
UgurEsme etal, studied an investigation of the effect andoptimization of welding parameters on the tensileshear
strength in the resistance spot welding (RSW)process. The experimental studies were conductedunder varying
electrode forces, welding currents,electrode diameters, and welding times.[2]
3774
www.ijariie.com
894
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
•
Anoop C A, Pawan Kumar etal, studied use of taguchi method to design process parameters that optimize
mechanical properties of weld specimen Aluminium alloy 7039 used in aircraft, automobiles, infantry combat
vehicles and high speed trains. Process parameters of Pulsed GTAW setup considered are Pulse Current, Base
current and Pulse Frequency Assigning process parameters to L-9 orthogonal array, experiments were conducted
and optimization condition was obtained along with the identification of most influencing parameters using S/N
analysis, mean response analysis and ANOVA[3]
•
Chang etal, studied that the Taguchimethod as a powerful optimization tool for designing high quality systems
that is based on orthogonal arrayexperiments with an optimum setting of process controlparameters.[4]
•
T. KURS¸UN etal, studied medium-carbon steel (AISI 1030) plates of 10 mm thickness, were welded by using
the synergic controlledpulsed (GMAW-P) and manual gas metal arc (GMAW) welding techniques. Constant
wire feed speed, voltage, welding speedand gas flow rates and ASP316L austenitic stainless steel filler metal
were used in thesetechniques. The interface appearances of the welded samples were examined by optical
microscopy (OM), scanning electronmicroscopy (SEM), energy dispersive spectrometry (EDS) and X-Ray
diffraction (X-RD). In order to determine mechanicalproperties of samples, the tensile, impact and
microhardness tests were conducted. The GMAW-P joints of AISI 1030 steel couples showed superior tensile
strength, less grain growth and narrower heat affected zone (HAZ) when compared withGMAW joints, and this
was mainly due to lower heat input, fine fusion zone grain and higher fusion hardness.[5]
•
P. V. Gopal Krishna, K. Veladri and Syed Qasim Ali Research on welding of materials like steel isstill critical
and ongoing. K. Kishore, P. V. GopalKrishna, K. Veladri and Syed QasimAli[5] Researchon welding of
materials like steel is still critical andongoing. [6]
•
SouravDatta, Ajay Biswas, Gautam Majumdar Sensitivity Analysis has been carried out to check the case
sensitiveness of relationimportance of different bead geometry parameters imposing predominant effect on the
optimalparametric combination. [7]
•
P K Palani, Dr N Murugan, The DOE using Taguchi approach cansignificantly reduce time required for
experimentalinvestigations6-8. In this investigation, in the firststage, Taguchi's orthogonal arrays were
usedtoconduct the experiments to find the contributions ofeach factor and to optimize the parameter
settings.[8]AISI D2 and D3 tool steel materials are select for studying effect of process sequence on behavior of
cryotreated cold work tool steel at different process cycles. The chemical composition of specimen (dia.10mm,
Height 35mm) was analyzed in optical emission spectroscope (OES). The machine used for the analysis of raw
material chemical composition was named as Spectrophoto Analyzer [AS 200(Switzerland)].
• OBJECTIVE
By selecting optimized welding parameter , improving the tensile strength of pipe joints welded by using Gas
metal arc welding
To reduce the cracking
To reduce the porosity due to improper welding parameter
To improve welding fusion
To avoid oxidation
To improve appearance
To improve welding quality
•
•
•
•
•
•
•
• GMAW Defects
Common weld defects include:
•
Lack of fusion
•
Lack of penetration or excess penetration
•
Porosity
•
Inclusions
•
Cracking
•
Undercut
•
Lamellar tearing
Any of these defects are potentially disastorous as they can all give rise to high stress intensities which may
result in sudden unexpected failure below the design load or in the case of cyclic loading, failure after fewer load
cycles than predicted.
3774
www.ijariie.com
895
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
•
Types of Defects
•
Fusion and penetration: To achieve a good quality join it is essential that the fusion zone extends the full
thickness of the sheets being joined. Thin sheet material can be joined with a single pass and a clean square edge
will be a satisfactory basis for a join. However thicker material will normally need edges cut at a V angle and may
need several passes to fill the V with weld metal. Where both sides are accessible one or more passes may be made
along the reverse side to ensure the joint extends the full thickness of the metal.
Lack of fusion results from too little heat input and / or too rapid traverse of the welding torch (gas or electric).
Excess penetrations arises from to high a heat input and / or too slow transverse of the welding torch (gas or
electric). Excess penetration - burning through - is more of a problem with thin sheet as a higher level of skill is
needed to balance heat input and torch traverse when welding thin metal.
•
Porosity: This occurs when gases are trapped in the solidifying weld metal. These may arise from damp
consumables or metal or, from dirt, particularly oil or grease, on the metal in the vicinity of the weld. This can be
avoided by ensuring all consumables are stored in dry conditions and work is carefully cleaned and degreased prior
to welding.
•
Inclusions: These can occur when several runs are made along a V join when joining thick plate using flux
cored or flux coated rods and the slag covering a run is not totally removed after every run before the following run.
•
Cracking: This can occur due just to thermal shrinkage or due to a combination of strain accompanying
phase change and thermal shrinkage. In the case of welded stiff frames, a combination of poor design and
inappropriate procedure may result in high residual stresses and cracking. Where alloy steels or steels with carbon
content greater than about 0.2% are being welded, self cooling may be rapid enough to cause some (brittle)
martensite to form. This will easily develop cracks. To prevent these problems a process of pre-heating in stages
may be needed and after welding a slow controlled post cooling in stages will be required. This can greatly increase
the cost of welded joins, but for high strength steels, such as those used in petrochemical plant and piping, there may
well be no alternative.
Solidification Cracking: This is also called centreline or hot cracking. They are called hot cracks because they
occur immediately after welds are completed and sometimes while the welds are being made. These defects, which
are often caused by sulphur and phosphorus, are more likely to occur in higher carbon steels. Solidification cracks
are normally distinguishable from other types of cracks by the following features:
• They occur only in the weld metal - although the parent metal is almost always the source of the low melting
point contaminants associated with the cracking
• They normally appear in straight lines along the centreline of the weld bead, but may occasionally appear as
transverse cracking
• Solidification cracks in the final crater may have a branching appearance
• As the cracks are 'open' they are visible to the naked eye
Fig.3 Centreline crack
A schematic diagram of a centreline crack is shown above on breaking open the weld the crack surface may
have a blue appearance, showing the cracks formed while the metal was still hot. The cracks form at the
solidification boundaries and are characteristically inter dendritic. There may be evidence of segregation associated
with
the
solidification
boundary.
The main cause of solidification cracking is that the weld bead in the final stage of solidification has insufficient
strength to withstand the contraction stresses generated as the weld pool solidifies. Factors which increase the risk
include:
• insufficient weld bead size or inappropriate shape
•
welding under excessive restraint
•
material properties - such as a high impurity content or a relatively large shrinkage on solidification
3774
www.ijariie.com
896
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
Joint design can have an influence on the level of residual stresses. Large gaps between conponents will increase
the strain on the solidifying weld metal, especially if the depth of penetration is small. Hence weld beads with a
small depth to width ratio, such as is formed when bridging a large wide gap with a thin bead, will be more
susceptible to solidification cracking.
In steels, cracking is associated with impurities, particularly sulphur and phosphorus and is promoted by carbon,
whereas manganese and sulphur can help to reduce the risk. To minimise the risk of cracking, fillers with low
carbon and impurity levels and a relatively high manganese content are preferred. As a general rule, for carbon
manganese steels, the total sulphur and phosphorus content should be no greater than 0.06%. However when
welding a highly restrained joint using high strength steels, a combined level below 0.03% might be needed.
Weld metal composition is dominated by the filler and as this is usually cleaner than the metal being welded,
cracking is less likely with low dilution processes such as MMA and MIG. Parent metal composition becomes more
important with autogenous welding techniques, such as TIG with no filler.
Hydrogen induced cracking (HIC) - also referred to as hydrogen cracking or hydrogen assisted cracking, can occur
in steels during manufacture, during fabrication or during service. When HIC occurs as a result of welding, the
cracks are in the heat affected zone (HAZ) or in the weld metal itself.
Four requirements for HIC to occur are:
• Hydrogen be present, this may come from moisture in any flux or from other sources. It is absorbed by the
weld pool and diffuses int o the HAZ.
• A HAZ microstructure susceptible to hydrogen cracking.
• Tensile stresses act on the weld
• The assembly has cooled to close to ambient - less than 150oC
HIC in the HAZ is often at the weld toe, but can be under the weld bead or at the weld root. In fillet welds cracks
are normally parallel to the weld run but in butt welds cracks can be transverse to the welding direction.
•
Undercutting: In this case the thickness of one (or both) of the sheets is reduced at the toe of the weld. This
is due to incorrect settings / procedure. There is already a stress concentration at the toe of the weld and any
undercut will reduce the strength of the join.
•
Lamellar tearing: This is mainly a problem with low quality steels. It occurs in plate that has a low
ductility in the through thickness direction, which is caused by non metallic inclusions, such as suphides and oxides
that have been elongated during the rolling process. These inclusions mean that the plate can not tolerate the
contraction stresses in the short transverse direction. Lamellar tearing can occur in both fillet and butt welds, but the
most vulnerable joints are 'T' and corner joints, where the fusion boundary is parallel to the rolling plane. These
problem can be overcome by using better quality steel, 'buttering' the weld area with a ductile material and possibly
by redesigning the joint.
•
Inspection
•
Detection Visual Inspection: Prior to any welding, the materials should be visually inspected to see that
they
are
clean,
aligned
correctly,
machine
settings,
filler
selection
checked,
etc.
As a first stage of inspection of all completed welds, visual inspected under good lighting should be carried out. A
magnifying glass and straight edge may be used as a part of this process.
Undercutting can be detected with the naked eye and (provided there is access to the reverse side) excess penetration
can often be visually detected.
•
Liquid Penetrant Inspection: Serious cases of surface cracking can be detected by the naked eye but for
most cases some type of aid is needed and the use of dye penetrant methods are quite efficient when used by a
trained
operator.
This procedure is as follows:
• Clean the surface of the weld and the weld vicinity
• Spray the surface with a liquid dye that has good penetrating properties
• Carefully wipe all the die off the surface
• Spray the surface with a white powder
• Any cracks will have trapped some die which will weep out and discolour the white coating and be clearly
visible
•
X - Ray Inspection: Sub-surface cracks and inclusions can be detected 'X' ray examination. This is
expensive, but for safety critical joints - eg in submarines and nuclear power plants - 100% 'X' ray examination of
welded joints will normally be carried out.
3774
www.ijariie.com
897
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
•
Ultrasonic Inspection: Surface and sub-surface defects can also be detected by ultrasonic inspection. This
involves directing a high frequency sound beam through the base metal and weld on a predictable path. When the
beam strikes a discontinuity some of it is reflected beck. This reflected beam is received and amplified and
processed
and
from
the
time
delay,
the
location
of
a
flaw
estimated.
Porosity, however, in the form of numerous gas bubbles causes a lot of low amplitude reflections which are difficult
to
separate
from
the
background
noise.
Results from any ultrasonic inspection require skilled interpretation.
•
Magnetic Particle Inspection: This process can be used to detect surface and slightly sub-surface cracks in
Ferro-magnetic materials (it cannot therefore be used with austenitic stainless steels). The process involves placing a
probe on each side of the area to be inspected and passing a high current between them. This produces a magnetic
flux at right angles to the flow of the current. When these lines of force meet a discontinuity, such as a longitudinal
crack, they are diverted and leak through the surface, creating magnetic poles or points of attraction. A magnetic
powder dusted onto the surface will cling to the leakage area more than elsewhere, indicating the location of any
discontinuities. This process may be carried out wet or dry, the wet process is more sensitive as finer particles may
be used which can detect very small defects. Fluorescent powders can also be used to enhance sensitivity when used
in conjunction with ultra violet illumination.
• Welding Problems
In much the same way that the automatic transmission has simplified the process of driving, Gas Metal Arc Welding
(GMAW) has simplified the process of welding. Of all welding methods, GMAW is said to be one of the easiest to
learn and perform. The main reason is because the power source does virtually all the work as it adjusts welding
parameters to handle differing conditions; much like the sophisticated electronics of an automatic transmission.
Because less skill is required, many operators are able to GMA weld at an acceptable level with limited training.
These same operators run into trouble, however, when they begin creating inferior welds and are unable to diagnose
and correct their own problems. The guidelines listed below will help even inexperienced operators create high
quality welds as well as offering tips for those who have been using the GMAW process for a number of years.
Most common welding problems fall into four categories:
• Weld porosity
• Improper weld bead profile
• Lack of fusion
• Faulty wire delivery related to equipment set-up and maintenance.
•
Weld Metal Porosity:
Porosity
Problem
#1:
Improper
Surface
Conditions
The most common cause of weld porosity is an improper surface condition of the metal. For example, oil, rust, paint
or grease on the base metal may prevent proper weld penetration and hence lead to porosity. Welding processes that
generate a slag such as Shielded Metal Arc Welding (SMAW) or Flux-Cored Arc Welding (FCAW) tend to tolerate
surface contaminates better than GMAW since components found within the slag help to clean the metal’s surface.
In GMAW, the only contamination protection is provided by the elements which are alloyed into the wire.
Porosity Problem #2: Gas Coverage The second leading cause of porosity in welds is a problem with the shielding
gas coverage. The GMAW process relies on the shielding gas to physically protect the weld puddle from the air and
to act as an arc stabilizer. If the shielding gas is disturbed, there is a potential that air could
Porosity Problem#3: Base Metal Properties Another cause of weld porosity may be attributed simply to the
chemistry of the base metal. For instance, the base metal may be extremely high in sulfur content.
•
Improper Weld Bead Profile: If operators are experiencing a convex-shaped or concave-shaped bead, this
may indicate a problem with heat input or technique.
Improper
Bead
Problem
#1:
Insufficient
Heat
Input
A convex or ―ropy‖ bead indicates that the settings being used are too cold for the thickness of the material being
welded. In other words, there is insufficient heat in the weld to enable it to penetrate into the base metal.
Improper Bead Problem #2: Technique A concave or convex-shaped bead may also be caused by using an
improper welding technique. For example, a push or forehand technique tends to create a flatter bead shape than a
pull or backhand technique.
Improper
Bead
Problem
#3:
Inadequate
Work
Cable
Problems with the work cable can result in inadequate voltage available at the arc. Evidence of a work cable
problem would be improper bead shape or a hot work cable.
3774
www.ijariie.com
898
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
•
Lack of Fusion: If the consumable has improperly adhered to the base metal, a lack of fusion may occur.
Improper fusion creates a weak, low quality weld and may ultimately lead to structural problems in the finished
product.
Lack of Fusion Problem: Cold Lapping in the Short Arc Transfer Process: In short arc transfer, the wire
directly touches the weld pool and a short circuit in the system causes the end of the wire to melt and detach a
droplet. This shorting happens 40 to 200 times per second. Fusion problems may occur when the metal in the weld
pool is melted, but there is not enough energy left to fuse it to the base plate. In these cases, the weld will have a
good appearance, but none of the metal has actually been joined together. Since lack of fusion is difficult to detect
visually, it must be checked by dye-penetrant, ultrasonic or bend testing.
•
Faulty Wire Delivery: If the wire is not feeding smoothly or if the operator is experiencing a chattering
sound within the gun cable, there may be a problem with the wire delivery system. Most of the problems related to
wire delivery are attributed to equipment set-up and maintenance.
Faulty Wire Delivery Problem #1: Contact Tip There is a tendency among operators to use oversized tips, which
can lead to contact problems, inconsistencies in the arc, porosity and poor bead shape.
Faulty Wire Delivery Problem #2: Gun Liner A gun liner, like the contact tip, must be sized to the wire being fed
through it. It also needs to be cleaned or replaced when wire is not being fed smoothly.
Faulty Wire Delivery Problem #3: Worn Out Gun Inside the gun are very fine strands of copper wire that will
eventually break and wear out with time.
•
Remedy
If the gun becomes extremely hot during use in one particular area, that is an indication that there is internal
damage and it will need to be replaced. In addition, be certain that the gun is large enough for the application.
Operators like to use small guns since they are easy on the hand, but if the gun is too small for the application, it will
overheat.
Faulty Wire Delivery Problem #4: Drive Roll Drive rolls on the wire feeder periodically wear out and need to be
replaced.
Faulty Wire Delivery Problem #5: Wire Coming off Reel and Tangling some wire feeding problems occur
because the inertia from the wire reel causes it to coast after the gun trigger is released.
• Troubleshooting of GMAW
Today’s MIG welders have become so easy to use that when a weld doesn’t turn out as expected or the
equipment starts acting differently, it can confuse the operator and leave him searching for an answer. This article
will look at some of the most common equipment and technique issues that crop up and how to solve them. Consult
your manual for your specific machine’s set up and operation. Many companies post their manuals on-line. Miller
manuals as well as additional troubleshooting tips can be found at MillerWelds.com.
Equipment Issues: Often, the complaint is heard that a welder was working perfectly and then suddenly the
operator started experiencing problems with arc stability, burnbacks or porosity in the weld. If this happens, after
changing wire or gas, the new spool of wire or cylinder of gas should be checked first.
Shielding Gas: Make sure you’re using the right shielding gas. When welding steel, a 75% Ar – 25% CO2 mixture
is usually recommended. If you were to inadvertently use 100% argon on steel, the weld will have low penetration
and produce excessive spatter. Similarly, if instead of using the 100% argon usually recommended for aluminum,
you use a 75/25 mix, the weld will turn black, and you will observe tiny aluminum ―BB’s‖ on the weld surface.
Turning up the amperage to compensate will only cause melt-thru.
If you were achieving satisfactory welds before changing gas, use a cylinder you know to be good and see if that
corrects the problem.
Electrode Wire: Exposed to moisture in the air or environment, welding wire not used for a period of time can
develop an oxide layer. If feeding or arc instability problems occur after changing wire, examine the spool to make
sure the wire is in good condition. If you’re not planning on using a spool of wire immediately, make sure to store it
in a plastic bag in a dry environment, preferably with small packages of desiccant.
Wire feeding issues can affect performance; good welds require a consistent wire feed supply. One way to test if
wire is feeding smoothly is to feed wire against a block of wood and watch for continuous smooth wire coil up,
which implies there is no obstruction to wire feed. If the wire does not coil smoothly, there is a problem somewhere
in the wire feed process.
Cable Liners: A kinked, worn, wrong size or partially plugged liner can easily lead to burnback or arc instability
issues. Removable liners can be blown out with compressed air if dirty or replaced if worn or kinked.
3774
www.ijariie.com
899
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
Wire Feeder Drive Rolls: The drive rolls are designed to feed the electrode wire smoothly from the wire spool into
the gun cable. However, if drive roll tension is set too tightly, the drive rolls not only can deform the wire (i.e., take
on shape of drive roll grooves) – causing it to wear down the liner and contact tube – but also cause rough wire
feeding, which can lead to arc instability or burnback. Too little tension can lead to wire slipping. Follow your
owner’s manual’s instructions.
Wire Feeder Spool Brake:The electrode wire spool is mounted on a support arm equipped with a hub brake that
prevents the spool from ―free-wheeling‖ when the arc stops. Operators should set the brake with just enough tension
to prevent freewheeling; too much tension will impede smooth wire feed through the drive rolls and gun cable,
leading to arc instability, inconsistent wire feeding or burnback.
MIG Gun: Welders may find that issues with liners and contact tips are the source of most problems (arc instability,
wire stubbing, burnback) related to the arc and electrode wire. Make sure that you match contact tip size with the
wire size you’re using. In addition, liners that are too small or too large can cause poor wire feeding. MIG guns are
never intended to be used as a pry bar or hammer; abuse can damage the MIG gun’s internal components and cause
wire feed and shielding gas malfunctions.
Shielding Gas: Shielding gas protects the molten weld pool from the surrounding atmosphere, which would
otherwise contaminate the weld. Figure 1 shows how the lack of shielding gas can cause porosity (pinholes) in the
weld bead are formed in the face and weld interior in the absence of shielding gas. Check that there are no gas flow
problems in the MIG gun (e.g., tear or hole in gas hose) and that the MIG gun o-rings are in good condition. Make
sure the valve is turned on and supplying gas at the specified flow rate. If all of these checkpoints are O.K.,
determine if a fan or breeze is blowing away the flow of shielding gas around the arc.
Fig.4 No Shielding Gas – A lack of or inadequate shielding gas is easily identified by the porosity and (pinholes) in
the face and interior of the weld.
Work Connection: Arc stumbling can occur if there is a poor connection between the workpiece or workbench and
the welding machine output stud. Make sure the clamp is in good working condition and the work lead’s cable lug is
making good contact. Grind off rust or paint and ensure that the work clamp is connected as close to the work area
as possible.
Voltage and Wire Feed Speed (WFS) Settings:Increasingly, welding equipment manufacturers are developing
MIG welders that simplify parameter settings with automatic features. Miller’s Auto-Set™, for example, enables
users to set wire diameter and material thickness only¾then Auto-Set automatically sets WFS and voltage to achieve
optimal welding results. In addition, most commercially available MIG welders today come with parameter charts
that specify the proper voltage and WFS (amperage) settings for optimum welding performance. Manual setting is
still available for broader applications, but the use of parameter charts is highly recommended and usually is
available for download from provider web sites.
When manually setting parameters, here’s what to look for:
3774
www.ijariie.com
900
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
Fig.5 Voltage Too High: Too much voltage is marked
by poor arc control, inconsistent penetration, and a turbulent weld pool that fails to consistently penetrate the base
material.
Fig.6 Voltage Too Low – Toolittle voltage results in poor arc starts, control and penetration. It also causes excessive
spatter, a convex bead profile, and poor tie-in at the toes of the weld.
Fig.7 Wire Feed Speed/Amperage Too High – Setting the wire feed speed or amperage too high (depending on
what type of machine you're using) can cause poor arc starts and lead to an excessively wide weld bead, burnthrough and distortion.
3774
www.ijariie.com
901
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
Fig.8 Wire Feed Speed/Amperage Too Low – Anarrow, oftentimes convex bead with poor tie-in at the toes of the
weld marks insufficient amperage.
Operator Issues
Operators are under complete control of travel speed and gun angle, so they can affect welding results with
variations in their individual techniques.
Travel Speed: Excessively fast travel speed can lead to insufficient penetration because the arc does not stay in one
place long enough to build up sufficient heat. This results in a narrow, convex bead with poor toe tie-in (Figure 7).
Too-slow travel speed may produce a large weld with excessive heat input resulting in heat distortion and possible
burnthrough (See Figure 8). In most cases, proper travel speed is when the arc is on the leading edge of the puddle.
Gun Travel Angle: If your welds tend to have more spatter and less penetration and there is general arc instability,
check your travel angle. Normal welding conditions in all positions specify a travel angle of 5 to 15 degrees for good
weld puddle control. Excessive torch angle can cause limited penetration and
•
Experimental Procedure
• Material
The material used for Gas metal arc welding (GMAW) is EN8 steel. The entire specimens were machined into the
dimensions of 200mm long x 75mm x 10 mm thick. The details composition (weight %) of specimens is shown in
TableI. This metal had very good welding characteristics and could be welded by all of the common welding
techniques.
TABLE I
Chemical Composition of Base and Filler Metal (Weight %) Alloy
Material
AISI1040(EN8)
ER 70S-6
C
0.40
Mn
0.75
Si
0.25
S(max)
0.05
P(max)
0.04
Cu(max)
-
0.19
1.63
0.98
0.025
0.025
0.025
Mechanical Properties
Tensile Strength -465 (N/mm2)
% Elongation-16% min
Hardness(HV) -201-255 BHN
3774
www.ijariie.com
902
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
• WeldingMachine
This sections provides the important specifications of the tool used in the welding process
Fig.9 Gas Metal Arc Welding M/C
• Welding Process Parameter Selection
Based on literature review following is the range selected for three process parameter
TABLEII
Process
parameter
Welding
Current(Amp)
Arc Voltage
(volts)
Wire
Feed
Rate (m/min)
•
•
Process
Designation
Level
1
Level
2
Level
3
A
180
210
240
B
24
27
30
C
2
3
4
EXPERIMENTAL WORK
Universal Testing Machine –Computerized
Fig.10 Universal Testing Machine
Application:
Mechatronic Control System is a prominent manufacturer of Universal Testing Machine which is available in
electronic and computerized functioning. This machine is used to test the tensile and compressive properties of
3774
www.ijariie.com
903
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
material. The reason Universal Testing machine is named so because it can perform all the tests right from
compression, bending to tension and examine the material in all mechanical properties. We offer these in grade of
10T, 20T, 40T, 60T and 100T.
Radiographic and ultrasonic weld inspection are the two most common methods of non-destructive testing
(NDT) used to detect discontinuities within the internal structure of welds. The obvious advantage of both these
methods of testing is their ability to help establish the weld’s internal integrity without destroying the welded
component. We shall briefly examine these two methods of non-destructive testing (NDT). We shall consider how
they are used and what types of welding discontinuities they can be expected to find. We shall examine their
advantages over other inspection methods and their limitations.
•
Radiographic Testing (RT)
This method of weld testing makes use of X-rays, produced by an X-ray tube, or gamma rays, produced by a
radioactive isotope. The basic principle of radiographic inspection of welds is the same as that for medical
radiography. Penetrating radiation is passed through a solid object, in this case a weld rather that part of the human
body, onto a photographic film, resulting in an image of the object's internal structure being deposited on the film.
The amount of energy absorbed by the object depends on its thickness and density. Energy not absorbed by the
object will cause exposure of the radiographic film. These areas will be dark when the film is developed. Areas of
the film exposed to less energy remain lighter. Therefore, areas of the object where the thickness has been changed
by discontinuities, such as porosity or cracks, will appear as dark outlines on the film. Inclusions of low density,
such as slag, will appear as dark areas on the film while inclusions of high density, such as tungsten, will appear as
light areas. All discontinuities are detected by viewing shape and variation in density of the processed film.
•
Ultrasonic Testing (UT)
This method of testing makes use of mechanical vibrations similar to sound waves but of higher frequency. A
beam of ultrasonic energy is directed into the object to be tested. This beam travels through the object with
insignificant loss, except when it is intercepted and reflected by a discontinuity. The ultrasonic contact pulse
reflection technique is used. This system uses a transducer that changes electrical energy into mechanical energy.
The transducer is excited by a high-frequency voltage, which causes a crystal to vibrate mechanically. The crystal
probe becomes the source of ultrasonic mechanical vibration. These vibrations are transmitted into the test piece
through a coupling fluid, usually a film of oil, called a couplant. When the pulse of ultrasonic waves strikes a
discontinuity in the test piece, it is reflected back to its point of origin. Thus the energy returns to the transducer. The
transducer now serves as a receiver for the reflected energy. The initial signal or main bang, the returned echoes
from the discontinuities, and the echo of the rear surface of the test piece are all displayed by a trace on the screen of
a cathode-ray oscilloscope. The detection, location, and evaluation of discontinuities become possible because the
velocity of sound through a given material is nearly constant, making distance measurement possible, and the
relative amplitude of a reflected pulse is more or less proportional to the size of the reflector.
•
Results And Discussion
Microscopic study
3774
www.ijariie.com
904
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
Fig.15 Microstructure of base metal
Fig.16 Microstructure of Heat Affected Zone
TABLE III
Experimental result for UTS and S/N ratio
welding
current
(amp)
180
180
180
210
210
210
240
240
arc
voltage
(voltage)
24
27
30
24
27
30
24
27
wire feed
rate
(M/min)
2
3
4
3
4
2
4
2
tensile
strength
(Mpa)
255.500
269.270
375.130
358.000
395.750
455.250
218.875
363.625
S/N
ratio
48.1478
48.6038
51.4836
51.0777
51.9484
53.1650
46.8039
51.2131
TABLE IV
S/N response table for UTS
Level
1
2
3
Delta
Rank
welding
current
(amp)
49.41
52.06
50.28
2.62
2
arc voltage
(voltage)
wire feed
rate
(M/min)
50.81
50.84
50.08
0.76
3
48.68
50.59
52.49
3.82
1
TABLE V
Result of annova for UTS
Symbol
Parameter
DOF
A
B
C
Error
Total
I
V
W
2
2
2
2
8
3774
Sum
of sq.
10.965
21.841
1.157
5.191
39.154
Mean
F
%
5.483
10.920
0.579
2.595
2.11
4.21
0.22
32.26
64.37
3.36
0.01
100
www.ijariie.com
905
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
Fig.17 Main effect plot for means.
Fig.18 Main effect plot for SN ratios
•
Conclusions
The following conclusions, from the experiential investigation can be made about the welding parameter and
their influence on strength of weld and its quality From results of present experimental investigation and by doing
Taguchi analysis the following conclusions are drawn
•
Optimal Parameter are- A2B3C2 that are as follows
Level 2 welding current 210 amp
Level 3 arc voltage 30 volt
3774
www.ijariie.com
906
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
Level 2 wire feed rate 3 m/min
•
From Annova analysis for UTS It is found that arc voltage has 64.37 % influence on tensile strength of
welded joint
•
Future scope
This study does not indicate for the other types of welding process as well as other types of welding process
parameter. However one can pay attention to different material, filler material and applications in different areas.
Acknowledgment
The author thanks Prof. Kharde R.R. (HOD, Mech. Dept.), Prof. Mhaske M.S. PG I/C, PRECOE Loni, all my
friends and all staff of mechanical department Amrutvahini Polytechnic, PRECOE Loni for their help during this
work.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
References
K.Y. Benyounis, A.G. Olabi; ―Optimization of different welding processes using statistical and numerical
approaches – A reference guide.‖ Advances in Engineering Software 39 (2008) 483–496.
Ugur r Esme; ―Application of Taguchi method for theoptimization of resistance spot welding process.‖
TheArabian Journal for Science and Engineering, Volume 34,Number 2B
Anoop C A, Pawan Kumar, " Application of Taguchi Methods and ANOVA in GTAW Process Parameters
Optimization for Aluminium Alloy 7039 ", International Journal of Engineering and Innovative Technology
(IJEIT) Volume 2, Issue 11, May 2013 M. Aagakhani, E. Mehardad, E. Hayati, ―Parameteric optimization of
GMAW process by Tagauchi Method on weld dilution‖, International Journal of Modeling and Optimization,
Vol. 1, No. 3, August’2011.
C. Chang, J. Yang, C. Ling and C. Chou ―Optimization of Heat Treatment Parameters with the Taguchi Method
for the A 7050 Aluminim Alloy‖. IACSIT International Journal of Engineering and Technology, vol.2, no. 3,
2010, pp. 269-272.
T. Kursun"Effect of the GMAW and GMAW-P welding processes on microstructure, hardness, tensile and
impact strength of AISI 1030 steel joints‖Archives of metallurgy and materials Volume 56 2011 Issue 4.
K. Kishore, P. V. Gopal Krishna, K. Veladri and SyedQasim Ali; ― Analysis of defects in gas shielded
arcwelding of AISI1040 steel using Taguchi method.‖ ARPNJournal of Engineering and Applied Sciences, Vol
5, No.1.
SouravDatta, Ajay Biswas, GautamMajumdar; ―Sensitivity analysis for relative importance of differentweld
quality indicator influencing optimal processcondition of Submerged Arc Welding using Gray basedTaguchi
Method‖ The International Journal forManufacturing science & production, Vol. 10 No. 2 2009
P K Palani, Dr N Murugan, ―Modeling of Heat Input inStainless Steel Cladding using Taguchi’s Design
ofExperiments‖ IE(I) Journal-MC, Vol. 87, January 2
John W. FISHER, Sougata ROY ―Improving Fatigue Strength of Welded Joints by Ultrasonic Impact
Treatment‖ International Journal of Fatigue, Vol. 25, 2003, pp. 1239-1247.
Bipin Kumar et. al.‖ A Review on effect on preheating and post weld heat treatment on mechanical behavior of
ferrous metals‖ International Journal of Engineering Science and Technology Vol. 2(4), 2010, 625-631
T. Senthil Kumar, V. Balasubramanian , M.Y.Sanavullah―Influences of pulsed current tungsten inert gas
welding parameters on the tensile properties of AA 6061 aluminum alloy‖, Journal of Materials and design,
Vol. 28 (2007)-Science Direct, pp 2080-2092.
J.P. Ganjigatti, Dilip Kumar Pratihar, A. Roy Chaudhary―Global versus cluster-wise regression analyses
forprediction of bead geometry in MIG welding process.Journal of Materials processing and technology, Vol.
189 (2007)-Science Direct pp 352-366.
.Sukhomay Pal, Surjya K. Pal ,Arun K. Samantaray―Artificial neural network modeling of weld jointstrength
prediction of a pulsed metal inert gas welding process using arc signals‖ Journal of Materials
processtechnology, Vol. 202 (2008)-Science Direct pp 464- 474.
A.M. Torbatia, R.M. Mirandab, L. Quintinoc, S. Williamsa, D.Yappa ―Optimization procedures for GMAW of
bimetal pipes‖Journal of Materials process technology, Vol. 211 (2011)-Science Direct pp 1112-1116.
3774
www.ijariie.com
907
Vol-3 Issue-1 2017
IJARIIE-ISSN(O)-2395-4396
15. D.S. Nagesh, G.L. Datta Prediction of weld bead geometry and penetration in shielded metal-arc welding using
artificial neural networks‖ Journal of Materials process technology, Vol. 123 (2002)-Science Direct pp 303-312.
16. Y. Ruan, X.M. Qiu,W.B. Gong, D.Q. Sun, Y.P. Li ―Mechanical properties and microstructures of 6082-T6joint
welded by twin wire metal inert gas arc welding with the SiO2 flux. Journal of Materials and design‖, Vol. 32
(2012)-Science Direct pp 20-24.
17. Satyaduttsinh P. Chavda, Jayesh Desai, Tushar Patel ―A Review on Optimization of MIG Welding Parameter
using Taguchis DOE Method‖ IJEMR journal, Volume-4(2014) , pp 16-21.
18. Anoop C A, Pawan Kumar, ― Application of Taguchi Methods and ANOVA in GTAW Process Parameters
Optimization for Aluminium Alloy 7039‖ International Journal of Engineering and Innovative Technology
(IJEIT) Volume 2, Issue 11, May 2013, pp 54-58.
19.
3774
www.ijariie.com
908
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement