LAPORAN PRAKTIKUM PROSES MANUFAKTUR

MODUL 2 WELDING

OLEH : KELOMPOK : 28 ANGGOTA : 1. Astrid Parama Ningrum (13406026) 2. Bona Mangkirap (13406043) 3. Irma Sofiani (13406049) 4. Nadia Fadhilah Riza (13406069) 5. Prila Sista Lilly Jane (13406080) 6. Ira Wulandari (13406094)

LABORATORIUM TEKNIK PRODUKSI PROGRAM STUDI MESIN

INSTITUT TEKNOLOGI BANDUNG 2007

PURPOSE

1. Participants understand the variety of welding process

2. Participants understand the standard working process of Spot

Welding, Oxyacetylene Welding and Metal Arc Welding

3. Participants understand the parameter and sequences of

operations from each welding processes

BASIC THEORY

Welding Processes are divided into two major categories:

Fusion Welding : in which coalescence is accomplished by melting two

parts to be joined, in some cases adding filler metal to the joint

Solid State Welding : in which heat and/or pressure are used to

achieve coalescence, but no melting of the base metal occurs and no

filler metal is added

Fusion Welding is by far the more important category. It includes arc welding,

resistance welding, oxy-fuel gas welding and other fusion welding process

which cannot be classified as any of three types.

Arc Welding

A process in which coalescence of the metals is achieved by the heat from

electric arc between an electrode and the work. An electric arc is

discharge of electric current across a gap in a circuit. It is sustained by the

presence of a thermally ionized column of gas through which current

flows. To initiate the arc, the electrode is brought into contact with the work

and is then quickly separated from it by a short distance. A pool of molten

metal, consisting of base metal and filler metal is form in near the tip of

electrode. In most arc-welding process, filler metal is added during the

operation to increase the volume and strength of the weld joint. As the

electrode is moved along the joint, the molten weld pool solidifies in its

wake. Electric current was generated at current source. Current source

can produce the Alternating Current (AC) or Direct Current (DC).

Below is the figure of arc welding process:

Types of metal transfer in metal arc welding:

1. Surface tension: the melted drops of the electrode makes contact

with the puddle and is pulled in due to the surface tension of the

work piece

2. Spray arc: the melted drops of metal are sprayed from the drops of

the melted electrode, and carried by the electric arc towards the

work piece

3. Short circuit: metal is transferred from the wire to the weld pool only

when contact between the two is made, or at each short circuit

Spot Welding

It is widely used in mass production of automobiles appliances, metal

furniture and other products made of sheet metal. Resistance spot welding

is a resistance welding process in which fusion of the faying surfaces of a

lap joint is achieved a one location by opposing electrodes. The process is

used to joint sheet metal parts of thickness 3 mm or less using a series of

spot welds, in situation where an airtight assembly is not required. The

size and shape of the weld spot is determined by the electrode tip, the

most common electrode shape being round, but hexagonal, square, and

other shapes are also used. The resulting weld nugget is typically 5 to 10

mm in diameter, with an HAZ extending slightly beyond the nugget into the

base metal. If the weld is made properly, its strength will be comparable to

that of the surrounding metal. The steps in a spot welding cycle are shown

in the figure below

Oxyacetylene Welding

This type of welding process uses flame, which comes from the mixture of

oxygen and acetylenes, in order to heat the work pieces to its melting

temperature, with or without the use of filler.

The flame in this process is caused by two chemical reactions:

i. C2H2 + O2 2 CO + H2 + heat

ii. 2CO + H2 + 1.5 O2 2 CO2 + H2 + heat

Reaction (i) produces about a third of the produced heat. The product of

the reaction is capable of conducting chemical reactions, so that a second

reaction occurs.

Reaction (ii) produces about two thirds of the produced heat.

Types of flame:

The reactions above produce a flame with a temperature of around

3200 C. The proportion of oxygen and acetylene determines the

type of flame which is created, which are:

1. Neutral flame: the mixture of oxygen and acetylene is on

equal proportion, which results an equal combination

proportion of blue and white flame.

2. Reducing/carburizing flame: acetylene is of a higher

proportion than oxygen, which results in a flame “whiter” than

the neutral flame, which makes this flame has a lower

temperature than the neutral flame.

3. Oxidizing flame: oxygen is of a higher proportion than

acetylenes. Its results the color of flame “bluer” than the

neutral flame, which makes this flame the hottest possible

one to be produced by an oxyacetylene weld.

The proportion between oxygen and acetylene must be determined

through the gas regulators.

ANALISYS

1. Spot welding

This type of welding falls in the category of solid state welding,

because the work pieces never goes through the melting phase.

Instead, the work pieces are able to be forged together, due to the

softening of the material and the pressure applied towards them,

thus causing the two work pieces to be forged be one.

The highest temperature is between the work pieces, because in

this area, the resistance comes from the air (between the work

pieces), and the two work pieces (which naturally have higher

resistance levels than the electrodes).

2. Oxyacetylene welding

The proportion between oxygen and acetylene must be determined

on gas regulators

The proportions between those two gasses produce a different type

of flame, which affects the temperature of the flame. The benefits of

the different types of flames are also different, as following:

Neutral flame: this type of flame is mostly use in the industy,

because of its adequate heat for welding most materials, and

has minimal corrosive characteristics.

Oxidizing flame: this type of flame has the highest

temperature, but has a tendency to cause corrosion due to

its high oxygen concentration, thus it is only used to weld

materials with high melting temperature (i.e. cast iron).

Carburizing flame: this type of flame has the lowest

temperature, produced by an oxyacetylene weld, thus it is

only used for materials with low melting temperatures (i.e.

aluminum).

3. Metal arc welding

There are 2 methods of contacts between the work piece and electrode,

which are:

a. The work piece is connected to the negative pole, and the electrode

is connected to the positive pole. This way, the width of the bond

created by the welding process, is wider with shorter penetration,

due to the force of the movement of the electrons from the negative

pole (work piece) to the positive pole (electrode), so that the

electrons would be drawn towards the electrode, and would tend to

spread on the surface of the work pieces, causing the bond to be

wider. This method is more suitable when welding thin work pieces,

in order to ensure that the bond does not exceed the depth of the

work pieces.

b. The work piece is connected to the positive pole, and the electrode

is connected to the negative pole. This way, the bond created by

the welding process, is narrower with deeper penetration, due to

the force of the movement of the electrons from the negative pole

(electrode) to the positive pole (work piece), so that the electrons

move towards the work piece, causing them to force their way in to

a deeper level in the work piece. This causes the deep penetration.

This method is more suitable when welding thicker work pieces, in

order to ensure a stronger bond.

c. During the welding process, the position of the electrode towards

the work piece may not be 90 degrees, because it would cause the

inability of the flame to be turned on. Ideally, the angle between the

electrode and the work piece is about 70 degrees.

d. The electrode in arc welding is made of the filler material covered

with a certain coating made of clay. When the electrode burned and

melted, this coating also undergoes by those processes, so that the

gas from the coating protects the flame from turning off, and

protects the work piece from infiltration of oxygen, which may

reduce the quality of the welding material.

e. While welding, the tip of the electrode may not be attached to the

work piece. Between the two, there must be a certain distance. If

the distance is too close, electrode will stuck to the work piece, and

won’t be able to be moved. If the distance is too far, the flame will

enlarge and eventually die out. During the process, the distance

between the electrode and the work piece must be maintained by

constantly drawing the electrode nearer to the work piece, in line

with the reduction of the electrode.

f. Before welding, the work pieces should be placed in a fixed

position, so that the welding process can occur with a good result in

terms of positioning.

g. During the welding process, the ideal movement of the electrode is

in a zigzag motion, so that the filler which is produced covers the

whole area of contact between the work pieces.

Post Observation Task

Spot welding

1. Draw the work piece of welding process (put the dimension and description which compatible with mechanical drawing), write the material of the work piece!

*Spot welding was not completed in the observation*

: 2. Describe the procedure that has been done in the spot welding

process! a. Check the machine condition

b. Set the electrode, copper for example

c. Nip the plate that will be joint between a pair of electrode

d. Flow a huge electric current in a short

e. Stop the electric current

f. Leave for a while until the molten spot between the two plate to

persist and it’s temperature become normal

g. The work piece will be joined after the spot freeze.

3. Write the full name and function of the component of spot welding

machine which used in the practicum!

a. Upper horn

b. Rocker arm

c. Air cylinder

d. Tap switch

e. Secondary flexible conductor

f. Electrode holder : to hold the electrode in static position

g. Lower horn

h. Transformer secondary

i. Foot control

j. Air valve

k. Electrodes (to flow the electric current)

Oxyacetylene welding

1. Draw the work piece of oxyacetylene process (put the dimension and

description which compatible with mechanical drawing), write the

material of the work piece!

Material of the work piece: ST 37

2. Describe the procedure that has been done in the oxyacetylene

welding process!

a. Check the appliances’ condition

b. Connect the torch with the oxygen’s and acetylene’s tube

c. Set the flow of gas

d. Set the composition of oxygen and acetylene to get a proper

flame

e. Use the safety goggle

f. Prepare the work piece that will be weld

g. Light the torch by using the lighter

h. Hold the well controller in right hand and filler in the left hand

i. Light the filler until it is melted then direct it to the gaps between

the work pieces.

j. Do the process until both of the work pieces are joined

3. Write the full name and function of the component of oxyacetylene

welding machine which used in the practicum

Controller lid: The lid of the gas tube to control the flow of the

gas

Flammable gas: So that the gas could quickly produced flame

Oxygen : To accommodate oxidation

Rubber-tube: where the gas flow

Manual controller lid: manually adjustable lid to control the flow

of the gas running from the rubber-tube.

Welding flame and fusion unit: where the gases are fused and

produces flame

Burner edge: the boundary part of the welding tool that is

pointed directly to the work piece

Flame: produced from the blend of the gases used to be

contacted directly to weld the work piece.

Metal Arc Welding

1. Describe the operation procedure of electric welding with electrodes

(give the scheme of the tools)!

Electric arc welding procedure:

Turn on the transformation

Place the work piece on the work table

Connect the negative pole to the work piece and the positive

pole to the electrode

Check the electric arc flame before welding

Do the welding process concerning the capability of the

electrode to fill the welding part

Use safety goggle and gloves if needed.

Electric arc welding process scheme :

AC or DC

power

source

arc

electroda

electroda

holder

solidified

weld metal

2. Describe the form of metal transferring at electric welding (globular,

spray, and short-circuit), how the metal transfer occurs in this

experiment?

Globular

Material transfer forms bigger lumps

Spray

The form of material transfer looks like the globular ones but

smaller

Short Circuit

The material transfer is like flowing because of the small gap

between materials.

From the experiment, the material transfer occurs was the short-circuit

transfer because of the small gap between electrode and the work

piece

3. What is the effect of discontinued welding to the welding result, what is

the cause and how to overcome the problem?

The holder must be set by keeping the consistent distance to

overcome the irregular gap between electrode and the work piece

so that the arc does not scatter

The effect of the dazzling flame could be overcame by using safety

goggle

Common Welding Process

Which one is the best welding process in this practicum and how do you

compare the other types of welding process (not practiced in this practicum)

that you have learned?

The best process is the oxyacetylene welding because it is easier to do and

the flame is not too dazzling to your eyes so that you can directly see the

result on your work piece and control the movement of the filler.

CONCLUSION

The Welding Process consists of spot welding, oxyacetylene welding, and

metal arc welding.

The operation principle of each welding process is:

1. Spot Welding, without filler metal and the work piece will be forged

because of centered heat

2. Oxyacetylene Welding, using filler metal with combustions reaction

between oxygen and acetylene for heating the work piece

3. Metal Arc Welding, using filler metal which is combined with electrode.

Electrode is given by electric current and welding is starting

The process procedures:

In spot welding, first of all, we have to check the machine condition. Fit

the welding parameter, and then welding process is starting (squeeze

time, weld time, hold time, off time).

In oxyacetylene welding, oxygen and acetylene gas are flowing to the

torch by hoses. In torch, each gas composition is regulated with gas

control valve. Both of the gas will be mixed and producing the fire in

welding tip, then work pieces are closed and heated until reach the

melting point of filler metal. While the work piece is becoming hot, the

filler metal is put in filling gap until the filler metal is melted.

In metal arc welding, the transformation is turned on and then the

electrode is forged in the electrode clamp. Do the welding process with

make the electrode closer with work pieces so that the filler metal in

the electrode will be melted and finally will be forged with other work

piece.

Daily applications of three welding process are vary. But in real life, metal arc

welding is commonly used because it is more effective and efficient than

others.

Spot welding is less efficient because the work piece have to be moved

continuously so it’s need more power and longer time.

In oxyacetylene welding, filler metal is melted with the work piece which is

heated before (left hand grasp the filler metal, right hand grasp the welding

torch). While the metal arc welding is only putting the electrode to work pieces

so the filler metal can immediately fill the gap.

The make the welding process optimal, it can be done with several ways. For

the example, in metal arc welding, the welding is started with the end of the

work piece so that the work pieces cannot move. Other example is clamping

the work pieces in the edge so that it cannot be moved.

ENCLOSURE

Welding Simulation Oxygen and Acetylene tubes

Electrode Classification

The electrode classification