Download - Modification of Welding Die
MODIFICATION OF WELDING DIE
ABSTRACT
The recent development in the field of automobile has
made the production of automobiles very easier but at the same
time, due to technological advances, the industry has become very
competitive. While manufacturing a car, it is a hard task to
manufacture it with the required standards at initial stages of
production. In order to improve the productivity, we should
optimize the parameters of the production.
In this project our main objective is to Modify the Shape
of the welding die. The study was conducted on Santro car’s Body.
The study was performed in the body shop of HMIL. The
parameters of the welding die are noted and compared with the
implementation made in this project.
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1 INTRODUCTION:
1.1 HYUNDAI PLANT:
Hyundai Motors India was established in the year 1996 in
Irrungattukottai near Chennai. It is known as Hyundai Motors India Limited
(HMIL). This is the only manufacturing unit in India. However, they are
planning to open a second manufacturing unit as well. Hyundai Motors Co
was established in 1967 and now the largest car manufacturer of South
Korea. The different models of cars that Hyundai Motors India Limited
(HMIL) has launched in the Indian market are
Hyundai Santro Xing
Hyundai Getz
Hyundai Accent
Hyundai Sonata
Hyundai Elantra
Hyundai Sonata Embera
Hyundai Tucson
Hyundai Terracan
Hyundai i10
HMIL plant is equipped with
The Press Shop
The Body Shop
The Paint Shop
Assembly Shop
The Aluminum Foundry
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The Engine & Transmission Shop
The Plastic Extrusion Unit
The Plastic Paint Shop
The Test Track
HMIL certified with ISO 14001 certification for high quality
environmental standards. They have also installed the Environment
Management System (EMS) in their Chennai manufacturing unit. Hyundai
Motors India Limited is a fully owned subsidiary of Hyundai Motor Co.
1.2 HYUNDAI PLANT DESCRIPTION:
Hyundai’s fully integrated manufacturing capabilities include:
a) Press Shop
b) Body Shop
c) Paint Shop
d) Engine Shop
e) Transmission Shop
f) Plastic Shop
g) Assembly Shop
h) Aluminum Cast Shop
a) PRESS SHOP
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In Press Shop all the sheet Metal Panels, like, the floor, doors, roof,
fenders, hood and tailgate of a car are produced using equipment like
Blanking Line, Tandem press line etc. These panels are stored in pallet and
sent to Body Shop for welding.
b) BODY SHOP
In Body Shop all the sheet metal panels and parts, which are
supplied from press shop and vendors respectively are converted in to
final shape of the car body. Body manufacturing is divided into Floor,
Side, Body Build, Moving and Body Complete. The major process of an
automotive body is electric resistant welding. After welding the complete
body (Body in White) is sent to paint shop through conveyor skid for
painting.
c) PAINT SHOP
The car bodies which arrive here from the body shop are painted in
conveyors and controlled painting process. The purpose of painting is to
give corrosion resistance property and appearance value to the car body.
The coat of paint must give to the surface the desired color gloss, the
abrasion and the corrosion resistance.
When the appearance is beautiful, it raises the car’s value. Paint is
applied on to the car body by air assisted spraying. The spraying is done
with all spray guns and accessories.
There are 14 shades of paint can be applied with one single booth
and 122 sets of spray accessories are available to achieve the better
quality application.
d) ENGINE SHOP
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In machine shop components like, cylinder blocks, cylinder head,
cam shaft, crank shaft and connecting rod, which need precision
dimensional accuracy, are machined using special purpose machines.
Machine shop is getting raw material from MIP and from vendors. Then
these components are supplied to Engine and Transmission Shop for assembly of
engine.
e) TRANSMISSION SHOP
Transmission shop consists of Transmission assembly, Heat
treatment, and clutch housing, Sleeve, Speed gears, Shaft & gear lines &
Gears development. Fully computerized Numerical controlled machines,
Fully automated gear – testing machines to check critical dimensions and
detect defects like Nick, Burr and Run out etc., Sophisticated
Transmission dynamo tester with built in high sensitive sensors for
measuring vibration and software to analyze performance.
f) PLASTIC SHOP
This shop consists of injection moulding line and Bumpers, painting
line. In Injection moulding line, crash pad, front and rear bumper,
luggage room side trims left and right, and all door trims are produced in
the injection moulding machine and then supplied to the assembly shop
for assembling and Transmission Shop for assembly of engine.
g) ASSEMBLY SHOP
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The assembly shop is the largest shop at HMIL, and has recently
been expanded to create a separate assembly line EFI sonata. The car
bodies, which came from special PBS conveyor after painting are fitted
with plastic, like mechanical and electrical parts from various shops and
vendors. Here assembly cars are checked and rechecked for major
assembly defects by QC inspectors.
The inspection is divided into interior and exterior inspection and
the defects are being recorded in the inspection card. The defects, if any
are corrected simultaneously on the conveyor line itself.
After inspection, the car goes to the chassis line for wheel alignment
and head lamp aiming, roll and brake test, pit inspection for defects in the
chassis and the air conditioning and the emission tests. On passing these
tests, the car next goes to road test or proving ground. In road test cars
are tested for smoothness of operation, pick up, rattling, wind and
abnormal noises. Braking and steering and a host of other functions. The
cars then returns to assembly shop for undergo to shower test, to check
the water leakage. After the shower test, the vehicles enter the final line,
where they are again re-inspected for touch up defects like scratch, dent
and paint problems. The car is then signed off and parked outside the
Assembly Shop were the PDI drivers again check and drive away to yard
for custom delivery.
h) ALUMINIUM CAST SHOP
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In Al-Cast shop, a critical component of the engine i.e., cylinder
head is made by die casting process in aluminum foundry. Basic
requirement of the Hi-Tech engine is to manufacturing defect free casting
for cylinder head.
1.3 BODY SHOP LAYOUT
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FIG -1.1 – BODY SHOP LAYOUT
1.4 BODY PARTS DETAILS
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FIG-1.4- BODY PARTS DEATILS
1.5 BODY SHOP OPERATIONS:
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HOOD
LH
ROOF
LH
REAR
In Body Shop all the sheet metal panels and parts, which are supplied from
press shop and vendors respectively are welded in to final shape of the car
body. Body manufacturing is divided into floor line, side line, body build
line, and body complete line. The major process of an automotive body is
resistance welding and applying sealers. After welding the complete body
(Body in white) is sent to paint shop through conveyor skid for painting.
Major process in body shop:
Welding
o Spot welding
o Mig welding(inert gas)
o Mig brazing
Sealer application
1.5.1 Welding:
Welding is a fabrication process that joins materials, usually metals or
thermoplastics, by causing coalescence. This is often done by melting the
work pieces and adding a filler material to form a pool of molten material
(the weld puddle) that cools to become a strong joint, pressure is sometimes
used in conjunction with heat, to produce the weld. This is in contrast with
soldering and brazing, which involve melting a lower-melting-point material
between the work pieces to form a bond between them, without melting the
work pieces. In body shop two welding operations are carried out. They are:
Spot welding
Mig welding
Mig brazing
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Spot welding is the most common welding application found in the
manufacturing field. Also referred to as resistance welding, it is used
to join thin metals together.
While it is commonly used in the automotive industry to join sheet metal
frames together, the spot welding application has a variety of project uses.
Automated spot welding is quick, effective, and precise. Spot welding is an
economic solution.
Spot welding is a type of resistance welding used to weld various sheet
metals. The process uses two shaped copper alloy electrodes to concentrate
welding current into a small "spot" and to simultaneously clamp the sheets
together. Forcing a large current through the spot will melt the metal and
form the weld. The attractive feature of spot welding is a lot of energy can
be delivered to the spot in a very short time that permits the welding to occur
without excessive heating to the rest of the sheet.
FIG -1.5.1(a) – SPOT WELDING
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Typical components of an integrated robotic spot welding cell:
Spot welding robot
Spot welding gun
Weld timer
Electrode tip dresser
MIG welding is the process of using electricity to melt and join pieces of
metal together. MIG welding is sometimes referred to as the "hot glue gun"
of the welding world and is generally regarded as one of the easiest type of
welding.
FIG -1.5.1(b) – MIG WELDING
An arc is struck between a consumable electrode and the sheet metal to be
welded. The consumable electrode is in the form of continuous filler metal.
An inert gas surrounds the arc and shields it from the ambient to prevent
oxidation.
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Carbon steels, low alloy steels, stainless steels, most aluminum alloys, zinc
based copper alloys can be welded using this process.
Brazing is a method of joining two pieces of metal in which a solder with a
melting point below that of the base metal is heated to its melting point in a
reducing atmosphere so that it fuses and then infiltrates the gaps between the
two pieces through capillary action.
FIG – 1.5.1(c) MIG BRAZING
This method works well, especially when joining pieces of different
materials, as well as for thin-wall structures or complicated shapes, etc. The
solder is spread in a narrow gap with a high degree of joining accuracy, in
order to ensure high air tightness. With an appropriate overlap, the joint
becomes even stronger than the base metal, allowing this technique to be
used in products that require high strength.
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1.6:Electric Resistance Welding
Welding Many thin sheet metal parts, especially stainless steel parts, are
joined by one of the forms of electric resistance welding, either spot welding
or seam welding.
Spot Welding: Two copper electrodes are held in the jaws of the spot
welding machine, and the material to be welded is clamped between them.
Pressure is applied to hold the electrodes tightly together, and electrical
current flows through the electrodes and the material. The resistance of the
material being welded is so much higher than that of the copper electrodes
that enough heat is generated to melt the metal. The pressure on the
electrodes forces the molten spots in the two pieces of metal to unite, and
this pressure is held after the current stops flowing long enough for the metal
to solidify. The amount of current, pressure, and dwell time are all carefully
controlled and matched to the type of material and the thickness to produce
the correct spot welds.
In spot welding, heat is produced by electrical resistance between copper
electrodes. Pressure is simultaneously applied to electrode tips to force metal
together to complete fusing process. Spot or weldnugget size is directly
related to tip size.
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Seam Welding: Rather than having to release the electrodes and move the
material to form a series of overlapping spot welds, a seam-welding machine
is used to manufacture fuel tanks, enclosures and other components where a
continuous weld is needed. Two copper wheels replace the bar-shaped
electrodes. The metal to be welded is moved between them, and electric
pulses create spots of molten metal that overlap to form the continuous
seam.
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2. LITERATURE REVIEW:
2.1 INITIAL STUDY:
OBJECTIVE: To modify the shape of the welding die.
STUDY SAMPLE: Santro MXI.
2.1.1 INITIAL STUDY DATA:
To find out the formation of dent and their conditions at body shop and
paint shop, over 50 bodies were studied and rechecked in body shop.
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ROOF
2.2 DATA COLLECTION
2.2.1 DESCRIPTION
Spot welding is one of a group of resistance welding processes
that involve the joining of two or more metal parts together in a localised
area by the application of heat and pressure. The heat is generated within the
material being joined by the resistance to the passage of a high current
through the metal parts, which are held under a pre-set pressure.
The process is used for joining sheet materials and uses shaped copper alloy
electrodes to apply pressure and convey the electrical current through the
workpieces. Heat is developed mainly at the interface between two sheets,
eventually causing the material being welded to melt, forming a molten
pool, the weld nugget. The molten pool is contained by the pressure applied
by the electrode tip and the surrounding solid metal.
Fig.1. Resistance spot weld section
Weld quality is controlled mainly by good process control together
with periodic testing of samples. While a number of monitors have been
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developed, there is still a desire to produce a low cost, reliable and robust in-
process weld quality monitor, in order to reduce or eliminate periodic
destructive tests. Some controllers now incorporate feedback control systems
that monitor current and voltage (resistance) on the welding machine and,
with limited setting up, allow automatic, in-process adaption of the welding
procedure (time and current) to maintain weld quality for different thickness
and material stack-up combinations, for example. While not necessarily
guaranteeing weld quality completely, these controllers can also provide
some correction for variation in other process factors, such as contamination,
current shunting and part fit-up.
Ultrasonic non-destructive testing has been proved and widely applied
at vehicle manufacturers. Despite improvements in automatic signal analysis
for ease of operation and weld quality indication, the technique still requires
skill and training to achieve high accuracy.
Other recent equipment developments have included improved medium frequency power supplies, servo operated guns and automatic electrode dressing and changing tools.
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2.2.2.FACTORS AFFECTING SPOT WELDING
2.2.2.1. HEAT FACTOR:
A modification of Ohm’s Law may be made when watts and heat are
considered synonymous. When current is passed through a conductor the
electrical resistance of the conductor to current flow will cause heat to be
generated. The basic formula for heat generation may be stated:
H = I2R where H = Heat
I2 = Welding Current
Squared
R = Resistance
The secondary portion of a resistance spot welding circuit, including the
parts to be welded, is actually a series of resistances. The total additive value
of this electrical resistance affects the current output of the resistance spot
welding machine and the heat generation of the circuit.
The key fact is, although current value is the same in all parts of the
electrical circuit, the resistance values may vary considerably at different
points in the circuit.
The heat generated is directly proportional to the resistance at any point in
the circuit.
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SQUEEZE TIME − Time between pressure application and weld.
HEAT OR WELD TIME − Weld time is cycles.
HOLD TIME − Time that pressure is maintained after weld is made.
OFF TIME − Electrodes separated to permit moving of material for next
spot.
The resistance spot welding machines are constructed so minimum
resistance will be apparent in the transformer, flexible cables, tongs, and
electrode tips. The resistance spot welding machines are designed to bring .
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It is at the the welding current to the weldment in the most efficient
mannerweldment that the greatest relative resistance is required. The term
“relative” means with relation to the rest of the actual welding circuit.
There are six major points of resistance in the work area. They are as
follows:
1. The contact point between the electrode and top workpiece.
2. The top workpiece.
3. The interface of the top and bottom workpieces.
4. The bottom workpiece.
5. The contact point between the bottom workpiece and the electrode.
6. Resistance of electrode tips.
The resistances are in series, and each point of resistance will retard current
flow. The amount of resistance at point 3, the interface of the workpieces,
will depend on the heat transfer capabilities of the material, its electrical
resistance, and the combined thickness of the materials at the weld joint. It is
at this part of the circuit that the nugget of the weld is formed
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2.2.2.2.TIME FACTOR:
Resistance spot welding depends on the resistance of the base metal and the
amount of current flowing to produce the heat necessary to make the spot
weld.
Another important factor is time. In most cases several thousands of amperes
are used in making the spot weld. Such amperage values, flowing through a
relatively high resistance, will create a lot of heat in a short time. To make
good resistance spot welds, it is necessary to have close control of the time
the current is flowing. Actually, time is the only controllable variable in
most single impulse resistance spot welding applications. Current is very
often economically impractical to control. It is also unpredictable in many
cases.
Most resistance spot welds are made in very short time periods. Since
alternating current is normally used for the welding process, procedures may
be based on a 60 cycle time (sixty cycles = 1 second). Previously, the
formula for heat generation was used.
With the addition of the time element, the formula is completed as follows:
H = I2RTK
where H = Heat
I2 = Current Squared
R = Resistance
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T = Time
K = Heat Losses
Control of time is important. If the time element is too long, the base metal
in the joint may exceed the melting (and possibly the boiling) point of the
material.
This could cause faulty welds due to gas porosity.There is also the
possibility of expulsion of molten metal from the weld joint, which could
decrease the cross section of the joint weakening the weld. Shorter weld
times also decrease the possibility of excessive heat transfer in the base
metal. Distortion of the welded parts is minimized, and the heat affected
zone around the weld nugget is substantially smaller.
2.2.2.3.PRESSURE
The effect of pressure on the resistance spot weld should be carefully
considered. The primary purpose of pressure is to hold the parts to be
welded in intimate contact at the joint interface. This action assures
consistent electrical resistance and conductivity at the point of weld. The
tongs and electrode tips should NOT be used to pull the workpieces
together. The resistance spot welding machine is not designed as an
electrical “C” clamp! The parts to be welded should be in intimate contact
BEFORE pressure is applied. Investigations have shown that high pressures
exerted on the weld joint decrease the resistance at the point of contact
between the electrode tip and the workpiece surface. The greater the
pressure the lower the resistance factor.
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Proper pressures, with intimate contact of the electrode tip and the base
metal, will tend to conduct heat away from the weld. Higher currents are
necessary with greater pressures and, conversely, lower pressures require
less amperage from the resistance spot welding machine. This fact should be
carefully noted particularly when using a heat control with the various
resistance spot welding machines.
2.2.2.4.ELECTRODE TIPS:
Copper is the base metal normally used for resistance spot welding tongs
and tips. The purpose of the electrode tips is to conduct the welding current
to the workpiece, to be the focal point of the pressure applied to the weld
joint, to conduct heat from the work surface, and to maintain their integrity
of shape and characteristics of thermal and electrical conductivity under
working conditions.
Electrode tips are made of copper alloys and other materials. The Resistance
Welders Manufacturing Association (RWMA) has classified electrode tips
into two groups:
Group A − Copper based alloys
Group B − Refractory metal tips
The groups are further classified by number.
Group A, Class I, II, III, IV, and V are made of copper alloys.
Group B, Class 10, 11, 12, 13, and 14 are the refractory alloys.
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Group A, Class I electrode tips are the closest in composition to pure copper.
As the Class Number goes higher, the hardness and annealing temperature
values increase, while the thermal and electrical conductivity decreases.
Group B compositions are sintered mixtures of copper and tungsten, etc.,
designed for wear resistance and compressive strength at high temperatures.
Group B, Class 10 alloys have about 40 percent the conductivity of copper
with conductivity decreasing as the number value increases. Group B
electrode tips are not normally used for applications in which resistance spot
welding machines would be employed.
2.2.2.5. ELECTRODE TIP SIZE:
When you consider that it is through the electrode that the welding current is
permitted to flow into the workpiece, it is logical that the size of the
electrode tip point controls the size of the resistance spot weld. Actually, the
weld nugget diameter should be slightly less than the diameter of the
electrode tip point.
If the electrode tip diameter is too small for the application. the weld nugget
will be small and weak. If, however, the electrode tip diameter is too large,
there is danger of overheating the base metal and developing voids and gas
pockets. In either instance, the appearance and quality of the finished weld
would not be acceptable.
To determine electrode tip diameter will require some decisions on the part
of the weldment designer.
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The resistance factors involved for different materials will certainly have
some bearing on electrode tip diameter determination. A general formula has
been developed for low carbon steel. It will provide electrode tip diameter
values that are usable for most applications.
The formula generally used for low carbon steel is as follows:
Electrode tip diameter = 0.100” + 2t
where “t” is the thickness in inches of one thickness of the metal to be
welded. This formula is applicable to the welding of metals of dissimilar
thicknesses. The formula is applied to each thickness individually, and the
proper electrode tip diameter selected for each size of the joint.
For example, if two pieces of 0.062” sheet metal are to be joined, the
electrode tip diameter would be the same for both sides of the joint. The
calculation would be as follows:
Electrode tip dia. = 0.100 + 2t
= 0.100 + 2 x 0.062”
= 0.100 + 0.124”
Electrode tip dia. = 0.224”
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2.2.2.6.PRESSURE OR WELDING FORCE:
The pressure exerted by the tongs and the electrode tips on the workpiece
have a great effect on the amount of weld current that flows through the
joint. The greater the pressure, the higher the welding current value will be,
within the capacity of the resistance spot welding machine. Setting pressure
is relatively easy. Normally, samples of material to be welded are placed
between the electrode tips and checked for adequate pressure to make the
weld. If more or less pressure is required, the operating manual for the
resistance spot welding machine will give explicit directions for making the
correct setting. As part of the setting up operation, the tong and electrode tip
travel should be adjusted to the minimum required amount to prevent
“hammering” the electrode tips and tip holders.
2.2.2.7.HEAT BALANCE:
There is no particular problem of heat balance when the materials to be
welded are of equal type and thickness. The heat balance, in such cases, is
automatically correct if the electrode tips are of equal diameter, type, etc.
Heat balance may be defined as the conditions of welding in which the
fusion zone of the pieces to be joined are subjected to equal heat and
pressure
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2.2.3.
ELECTRODES USED IN SPOT WELDING :
In most of the automobile industries , spot welding is considered as a
main operation ,because it is the intial process where the frame of the entire
body is being worked upon . The main part of a welding machine is the
electrodes used in them , here in spot welding two electrodes are used, which
are being placed in such a way that one electrode at the top and the other at
the bottom of the weld .
The electrode used here is copper .Since spot welding is done because of
current supplied ,the electrode used should possess good conductivity ,hence
copper is considered to be one of the best conductors of
electricity ,Moreover it can withstand large amount of heat produced . The
following properties will clearly show its characteristics.
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PROPERTIES :
Properties Value
Specific Weight ,N/cc .0896
Melting Point, celcius 1083
Modulus of elasticity E,N/ mm2 1.230*105
Modulus of Rigidity G,N/ mm2 0.390*105
Thermal Conductivity k,cal/s cm
celcius
0.940
Coefficient of linear expansion 16.2
Poisson’s ratio v 0.26
Store stability 3 months (at room temperature)
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2.2.3.1.COOLING SYSTEM IN ELECTRODE:
Cooling system is every important concept, because this is where the
heat produced will get decipated and in most of the spot welding cases
Water cooling is employed . Here also water cooling is used . The main
function of the water is to take the heat produced during welding process
else the electrode may get damaged at a particular point ,this will reduce the
overall efficiency of the machine
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The cooling is mainly done to keep the electrode from reaching
its melting point and here the coolant used is water . The figure given above
clearly depicts the flow of water . Here its a one way flow of water ,the
water flows from the tank in the respective station and it flows through a
tube touches the inside tip of the electrode and floes out through the same
tube. This is how the water cooling takes place.
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2.2.3.2ADVANTAGES:
Water is easily available source .
Maintenance is simple when compared with other coolants.
Water has got good specific het capacity and thermal conductivity.
It can transmit heat with comparatively less volumentric flow.
The water jacket can also reduce the noise produced to some extent.
2.2.4.ROBOT USED FOR SPOT WELDING :
Robot welding is the use of mechanized programmable tools (robots),
which completely automate a welding process by both performing the weld
and handling the part. Processes such as gas metal arc welding, while often
automated, are not necessarily equivalent to robot welding, since a human
operator sometimes prepares the materials to be welded. Robot welding is
commonly used for spot welding and arc welding in high production
applications, such as the automotive industry.
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Robot welding is a relatively new application of robotics, even though
robots were first introduced into US industry during the 1960s. The use of
robots in welding did not take off until the 1980s, when the automotive
industry began using robots extensively for spot welding. Since then, both
the number of robots used in industry and the number of their applications
has grown greatly.
Cary and Helzer suggest that, as of 2005, more than 120,000 robots are used
in North American industry, about half of them pertaining to welding.
Growth is primarily limited by high equipment costs, and the resulting
restriction to high-production applicationsRobot arc welding has begun
growing quickly just recently, and already it commands about 20% of
industrial robot applications. The major components of arc welding robots
are the manipulator or the mechanical unit and the controller, which acts as
the robot's "brain". The manipulator is what makes the robot move, and the
design of these systems can be categorized into several common types, such
as the scara robot and cartesian coordinate robot, which use different
coordinate systems to direct the arms of the machine.The technology of
signature of image processing has been developed since the late 1990s for
analyzing electrical data in real time collected from automated, robotic
welding, thus enabling the optimization of welds.
Here in Hyundai SIX DEGREES OF FREEDOM robots are used and they
are learning robots . They are made to work with the help of the programmes
, these make them do their work with atmost precision , The robot has
electromagnet at its arm and this is used to hold the tool . Since same robots
are used to make different models ,and for different models different tool
heads are used to weld and hence this electromagnet is used . They are more
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than 300 stations are there in the company and each station has got
minimum of 2 and maximum of 10 robots according to the wotk on the
particular robot .
2. 3.DESCRIPTION OF PROBLEM :
The problem occurs when the scara robot welds the roof part of the model
Mxi (santro) at a particular station #302 . In this station there are two scara
robots working on two models santroMXI and i20 models . When the frame
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of the model Mxi comes to the station both the robots does about 17 welds
to fix the roof of car .
When these robots takes the welding tool on the top of the car to weld, the
upper holder and the lower bottom clashes with the roof of the frame and
hence it creates a dent formation on the roof , due to this dent many body is
being rejected at the inspection time and also when the body goes to the
paint shop . In order to ensure quality to the coustomers this problem should
solved .This is due to the shape of the holder and the bottom part of the
welding die, also the problem should be solved with out affecting the weld
done in any means.
2. 3.1.PRECAUTIONS:
The modification should not affect the weld at any circumstances . The
factors discussed above should always be taken care of , Because this
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problem deals with the quality of the car as a whole and also it shouldn’t
reduce the number of the cars produced.
The water line for the cooling system shouldn’t be affected.
The heat produced should not be affected by modification.
The pressure applied on the sheet metal should not be affected.
The stresses produced during welding should not increase due to this
modification.
Also the time taken for welding should not increase.
Every aspect should be the same and the dent formation should be
eliminated.
There shouldn’t be increase in heat produced at the electrode tip.
Also care should be taken, so that no major change occurs in the
parameters of the weld .The quality shouldn’t depreciate at any chance
and hence this is a crucial problem .
2. 4.SOLUTION:
The solution has to be made keeping all the precaution in mind .There
are two possible solutions which can be made to solve the problem. One is
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that the whole robot has to reprogrammed to do the job without clashing ,
this was tried but the clash still took place. The other solution is that the
contour of the welding tool has to be redesigned in such a way that ,the
clash shouldn’t takes place, so that the dent should be eliminated .
This can be implemented only if it is proved to be effcient , means that it
shouldn’t affect the weld produced .So first when the welding tool was to
be modified , first the cooling system should not be affected . And the heat
distribution on the welding die should be the same. The stresses produced
on the weld namely the shear stresses , tear stresses and the comparative
stress should be the same no major difference should be seen. This solution
is possible only when the welding die is clearly designed and analyzed .
If the analysis is same then further calculations can prove them to be worth
of being implemented.
2. 4.1.STEPS TO BE TAKEN:
Implementation can be made only be made if the modification is
proved that it wont affect the weld at any circumstance .To prove three
major steps are necessary . After completing these three steps calculations
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has to be done to completely prove it that its wont affect the weld . The three
steps are
Developing the model of the welding die in any design package
and here PRO E has been used for model generation
The generated model should be analysed in any analysis
package and here ansys has been used to do analysis part.
After completing the model generation and analysis
calculations have to be made for stresses.
These three steps has to prove that the modification made doesn’t affect the
cooling system, heat distribution and stresses doesn’t increase
respectively.Then modification made can be implemented.
2. 5.MODEL GENERATION :
The model generation is an important part because this where the model is
created for analysis . Many modeling packages are available . Here PRO E is
used to generate the model . The steps taken to draw the model are
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STEP I :
The existing model of the welding die both holder and the bottom part is
being generated in PRO E
STEP II :
Necessary modification to be made in the models to prevent the clashing is
decided, here care is taken to prevent the modification affecting the water
line .
STEP III :
The modification decided to be made is done on the model
And its generated without affecting the waterline.These steps are being taken
during the model generation part .
2. 5.1.MODEL OF EXISTING UPPER DIE:
39
The arrow clearly shows the fouling part , so this particular part has to be
eliminated to prevent the fouling .
2. 5.2.MODEL OF EXISTING LOWER DIE:
40
This particular part fouls with the roof of the car
The arrow shows the part of bottom which fouls with the roof
of the frame , if this particular part is eliminated then the clashing can be
avoided .
2.6.MODIFICATION OF THE EXISTING MODELS :
41
This particular part of bottom fouls with the roof.
The above generated models of both the holder and the bottom part
shows clearly part of them which fouls with the roof of the car , If these
parts are eliminated then the clashing can be eliminated.
Keeping the water line in mind the following modification was decided to be
done on the holder and the bottom part of the welding die . In the holder part
when the water line inside was studied , it showed that the water line runs at
an angle of 60 to the axis of the electrode . So the holder was being
machined at angle of 50 to the axis of the electrode This eliminates the
fouling area and also doesn’t affect the water line. Hence this modification
was done .
Similarly for the bottom part, when the water line inside is studied,it showed
that the water line runs at an angle of 50 inside them .So the bottom was
modified by machining it angle of 30 to the axis of the electrode . This
seems to eliminate the clashing part without affecting the water line inside .
So this modification was carried on.
2.6.1.MODEL OF MODIFIED UPPER DIE :
42
The fouling part was eliminated by machining the excess part at an angle of
50 degrees to the axis of the electrode .This doesn’t affect the cooling
system of the welding die.
2.6.2.MODEL OF MODIFIED LOWER DIE:
43
MODIFICATION MADE
The fouling part was eliminated by machining the excess part at an angle of
30 to the axis of the electrode . This doesn’t affect the cooling system inside
the bottom part .
2.7.ANALYSIS:
44
MODIFICATION MADE
The analysis part is very important . The modified parts are now to be
analysed and compared with the analysis of existing parts and it should be
the same . If they are same,then the modifications made has not affected the
structure or the heat distribution at the welding .
If the analysis is not the same then the model has to be designed again . Two
types of analysis has to be done .
Structural analysis due to the load .
Theraml analysis , for heat distribution at the Welding die .
Many analysis packages are available , here ansys has been used to do the
analysis of the existing and the modified bottom and holder.
2.7.1.STRUCTURAL ANALYSIS FOR EXISTING UPPER DIE:
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Structural analysis is done because in spot welding certain force is applied
on the electrode to keep the welding sheets together however the electrodes
shouldn’t be used for holding purposes,but this force is applied to prevent
the sheets from slipping . Here a load of 50 N is applied on the holder part
to hold the sheets .
2.7. 2 . STRUCTURAL ANALYSIS FOR MODIFIED UPPER DIE:
46
Structural analysis is also done to modified holder . The same load
of 50 N was applied and then the analysis was done to prove ,that
the analysis done doesn’t affect the structure of the welding die.
2.7. 3 . STRUCTURAL ANALYSIS FOR EXISTING LOWER DIE:
47
Structural analysis for the bottom part of the welding die is also done . Here
a load of 50 N is given and analysed .This analysis was also done in ansys .
2.7.4. STRUCTURAL ANALYSIS FOR MODIFIED LOWER DIE:
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Same load of 50 N is applied on the modified bottom of the welding die too .
2.8.CALCULATIONS:
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Given data:
1.Thickness of the weld,t : 0.7mm
2.Current supplied,I : 110*100A
3. Weld nugget diameter, d : 6mm
4. External load applied, p : 5kgf
5. Squeeze time : 30 cycles
6.Heat/weld time : 12 cycles 7.Hold time : 10 cycles
8. Off time : 20 cycles
9. Number of robots : 2
10. Number of welds : 17
FORMULAES USED :
50
1. 1 = 4 F
N/mm2
i . . d2
2. 2 = F
N/mm2
i . . d . s
3. s = { 1/ , 2/ } N/mm2
4. D = 0.100 + 2t mm
5. H = I2RT J
1, Shear stress
2, Tear stress
s Comparative stress Coefficient of weld joint
2.8.1. CALCULATION FOR EXISTING WELDING DIE :
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D = 0.100 + 2t “
= 0.100 + 2(0.28)” = 0.66” . = 16 mm
Diameter of electrode tip = 16 mm
1 = 4 * 5 * 9.81
N/mm2
17 . . 62
= 0.1024 N/mm2
Shear stress 1 = 0.1024 N/mm2
2 = 5 * 9.81
N/mm2
17 . . 6 . 0.7
= 0.2186 N/mm2
Tear stress 2 = 0.2186 N/mm2
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s = { 0.1024/0.65 , 0.2186/0.5 } N/mm2
= { 0.1575 , 0.4372 } N/mm2
Comparative stress s = { 0.1575 , 0.4372 } N/mm2
H = I2RT J
T = squeeze time + heat/weld time + hold time + off time
= 1.041 + 0.416 + 0.3472 + 0.6944
= 2.49~ 2.5 secs .
R = V / I
= 440/ ( 110 * 100)
= 0. 04
H = (110*100)2 * 0.04 * 2.5
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= 121*10 6 J
Heat generated H = 121*10 6 J
2.8.2.CALCULATION FOR MODIFIED WELDING DIE :
54
D = 0.100 + 2t “
= 0.100 + 2(0.28)” = 0.66” . = 16 mm
Diameter of electrode tip = 16 mm
1 = 4 * 5 * 9.81
N/mm2
17 . . 62
= 0.1024 N/mm2
Shear stress 1 = 0.1024 N/mm2
2 = 5 * 9.81
N/mm2
17 . . 6 . 0.7
= 0.2186 N/mm2
Tear stress 2 = 0.2186 N/mm2
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s = { 0.1024/0.65 , 0.2186/0.5 } N/mm2
= { 0.1575 , 0.4372 } N/mm2
Comparative stress s = { 0.1575 , 0.4372 } N/mm2
H = I2RT J
T = squeeze time + heat/weld time + hold time + off time
= 1.041 + 0.416 + 0.3472 + 0.6944
= 2.49~ 2.5 secs .
R = V / I
= 440/ ( 110 * 100)
= 0. 04
H = (110*100)2 * 0.04 * 2.5
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= 121*10 6 J
Heat generated H = 121*10 6 J
3. CONCLUSION:
57
As an outcome of this project, the WELDING DIE which causes dent
formation in the roof panel is now prevented by this implementation. It is
found that in body shop, due to the improper shape of the welding die dent is
being formed on the car body. After implementing this solution the welding
die shape is found to be satisfactory, thus fouling has been prevented
completely.
In this project we have changed the shape of the welding die, where the
fouling part has been eliminated. Due to this elimination both the pressure
applied and cooling has not been affected at any circumstance and because
of this the roof pattern formation is now according to the specification.
After the implementation of the new design of welding die, it is found that
the error occurred at the final output stage has been reduced to a great extent.
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