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

38

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:

45

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:

48

Same load of 50 N is applied on the modified bottom of the welding die too .

2.8.CALCULATIONS:

49

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 :

51

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

52

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

53

= 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

55

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

56

= 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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