ch 9 joining of metals [read-only] - kau 9 joining of... · 2015-05-11 · advantages and...

5/11/2015

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Dr. Abdel-Wahab El-Morsy Faculty of Engineering - Rabigh

Basic WorkshopBasic Workshop

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Joining of Metals

Welding

RivetingClamping

Adhesive Bonding

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Welding Process

Welding is the process of joining together two pieces of metals through

heat alone (fusion welding) with/without filler material or through heat

and pressure (Forging) without filler material.

Welding

Pressure Welding

Friction Welding

Resistance Welding

Forge Welding

Fusion Welding

Thermit Welding

Arc Welding

Gas Welding


Five basic types of weld joint designs

Types of Joints and Welding Positions

Welding Process

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Four Welding Positions

Welding Process


Fusion Welding

Fusion welding is a process in which metals are welded together by brining

them to the molten state at the surface to be joined with or without the

addition of filler metal without pressure.

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1. Gas welding:Oxyacetylene welding (OAW)

2. Arc welding:Shielded metal arc welding (SMAW)

Gas–tungsten arc welding (GTAW)

Plasma arc welding (PAW)

Gas–metal arc welding (GMAW)

Flux-cored arc welding (FCAW)

Submerged arc welding (SAW)

Electroslag welding (ESW)

3. High-energy beam welding:

Electron beam welding (EBW)

Laser beam welding (LBW)

Three major types of fusion welding are as follows:

Fusion Welding


Variation of heat input to the workpiece with power density of the heat source

Fusion Welding

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Gas WeldingOxy – Acetylene Welding

Gas welding is a process that melts and

joins metals by heating them with a flame

caused by the reaction between a fuel gas

and oxygen

Fusion Welding


Temperature distribution in a neutral

oxyacetylene flame


Fusion Welding

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Three Types of Flames

Neutral Flame: This refers to case where oxygen and acetylene

are mixed in equal amounts and burned at the tip of the torch

Reducing Flame: When excess acetylene is used, the resulting

flame is called a reducing flame. The combustion of acetylene is

incomplete

Oxidizing Flame When excess oxygen is used, flame becomes

oxidizing because of the presence of unconsumed oxygen


Fusion Welding


Welding Movements

Forward weldingBackward welding


Fusion Welding

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Advantages and Disadvantages

The main advantage of the oxyacetylene welding process is that

• The equipment is simple,

• Portable, and

• Inexpensive.

It is convenient for maintenance and repair applications.

However, due to its limited power density,

• The welding speed is very low, and

• The total heat input per unit length of the weld is rather high,

resulting in large heat-affected zones and severe distortion.

The oxyacetylene welding is not recommended for welding reactive metals such

as titanium and zirconium because of its limited protection power


Fusion Welding


Flame cutting of a steel plate with an oxyacetylene

torch, and a cross section of the torch nozzle.

Cross section of a flame-cut

plate, showing drag lines


Fusion Welding

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� Thermit material is a mixture of Al and processed iron oxide.

� A wax pattern is then made around the joint .

� A mold made of refractory sand is built around the wax pattern and

joint to hold the molten metal after it is poured.

� The sand mold is then heated to melt out the wax and dry the mold.

� The mold should be properly vented to permit the escape of gases

and to allow the proper distribution of the metal at the joint.

Thermit Welding

Fusion Welding


Thermit Welding

Fusion Welding

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Electric arc welding is a fusion welding where high temperature is obtained from

the electrical energy, filler material is needed, which is molten to the gab between

the two parts to be joined.

The electric are circuit consists of:� The power supply,

� An electrode cable,

� A ground cable,

� An electrode holder, and

� The electrode rod.

Electrod

e

Electrode

holder

Base Metal

Power

supply

Filler

materialGround

Power supply

Fusion Welding

Electric Arc Welding


Shielded arc welding is a process that

melts and joins metals by heating

them with an arc established between

a covered electrode and the metals

Fusion Welding


Shielded Metal Arc Welding

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Functions of Electrode CoveringCovering of the electrode contains various chemicals and metal powder in order

to perform one or more of the functions:

1. Protection2. Deoxidation3. Arc stabilization4. Metal Addition

Advantages and DisadvantagesThe welding equipment is:

• Relatively simple, and

• Inexpensive as compared to other arc welding processes.

Gas shield is not clean enough for reactive metals such as Al and Ti.

The limited length of the electrode (about 35cm) requires electrode changing,

and this further reduces the overall production rate

Fusion Welding


Shielded Metal Arc Welding


Gas–tungsten welding is a process that melts and

joins metals by heating them with an arc between

a nonconsumable tungsten electrode and metals

The gas goes through the torch body and is directed

by a nozzle toward weld pool to protect it from air.

Protection from air is much better than in Shielded

arc welding.

Fusion Welding


Gas Tungsten Arc Welding

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Advantages of Gas-Tungsten Arc Welding

� Suitable for joining thin sections because of its limited heat inputs.

� It can be used to weld butt joints of thin sheets by fusion without the addition of

filler metals

� Gas–tungsten arc is a very clean process, it can be used to weld reactive metals,

such as Ti and zr, Al, and Mg.

Disadvantages of Gas-Tungsten Arc Welding

� The deposition rate is low.

� Excessive welding currents can cause melting of electrode and results in brittle

tungsten inclusions in the weld metal.

Fusion Welding


Gas Tungsten Arc Welding


Gas–metal arc is a process that melts and joins

by heating them with an arc established between

a continuously fed filler wire electrode and the

metals.

Shielding arc and the molten weld pool is often

obtained by using inert gases such as argon and

helium

Fusion Welding


Gas Metal Arc Welding

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Advantages

� Gas–metal arc welding can be very clean when using an inert shielding gas.

� The main advantage of Gas–metal arc over Gas–tungsten arc is the much

higher deposition rate, which allows thicker workpiece to be welded at

higher welding speeds.

Disadvantages

� Gas–metal arc welding guns can be bulky and difficult to reach small areas

or corners.

Fusion Welding


Gas Metal Arc Welding


Pressure Welding

Pressure welding is a process in which metals are welded together by

bringing them to the plastic state (without melting) at the surfaces to

be joined while pressing them together.

Pressure Welding

Friction Welding

Resistance Welding

Forge Welding

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Resistance Welding

� Resistance welding uses the electric current and mechanical pressure

to create a weld between two pieces of metal.

� Weld electrodes conduct the electric current to the two pieces of metal

as they are forged together

Resistance welding types:

• Resistance Spot Welding,

• Resistance Seam Welding,

• Projection Welding

Pressure Welding


Resistance Welding Benefits

• High speed welding

• Easily automated

• Suitable for high rate production

• Economical

Resistance Welding Limitations

• Initial equipment costs

• Lower tensile and fatigue strengths

• Lap joints add weight and material

Resistance Welding

Pressure Welding

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Spot Welding

Seam Welding

Projection Welding

Resistance Welding

Pressure Welding


� Friction Stir Welding is a solid state joining (the metal is not melted during

the process), in which a cylindrical shouldered tool (pin) is inserted into the

joint line between two work pieces.

� Frictional heat is created between the wear resistant pin and the two pieces,

which are butted together and clamped onto a backing bar

Friction Stir Welding

Pressure Welding

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Pressure Welding



Pressure Welding

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� Good mechanical properties in the as welded condition

� No consumables and no filler or gas shield is required.

� Easily automated on milling machines - lower set-up costs.

� Can operate in all positions (horizontal, vertical, ….etc).

� Generally good weld appearance and minimal thickness

� Low environmental impact.

� Exit hole left when tool is withdrawn.

� Large forces required with heavy clamping necessary.

� Less flexible than arc processes.

� Slower traverse rate.

Disadvantages of the process

Advantages of the process


Pressure Welding


Clamping

Temporary ConnectionsThese clamps are used to position or hold

components temporarily for various tasks

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A rivet is a permanent mechanical fastener. Before being installed a

rivet consists of a smooth cylindrical shaft with a head on one end.

The end opposite the head is called the buck-tail.

Riveting


� The rivet is placed in a punched or pre-drilled hole, and the tail is upset so that it

expands to about 1.5 times the original shaft diameter, holding the rivet in place.

� To distinguish between the two ends of the rivet, the original head is called the

factory head and the deformed end is called the shop head or buck-tail

Riveting

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Riveting


1

2

3 4

5

6

Riveting

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Adhesive bonding

• Adhesive bonding describes a wafer bonding technique with applying

an intermediate layer to connect substrates of different materials.

• These produced connections can be soluble or insoluble.

• The commercially available adhesive can be organic or inorganic and

is deposited on one or both substrate surfaces.

The most important process parameters for achieving a high bonding

strength are:

� adhesive material

� coating thickness

� bonding temperature

� processing time

� chamber pressure


Materials that soften by heating and then cooling it becomes hardened again and

this material Polyamide, vinyl polymers and cellulose derivatives in addition to

natural materials (i.e. resins and waxes)

Thermo Plastic Adhesive

Thermo Setting Adhesive

A material that becomes hardened as a result of chemical reactions and can not

therefore be re-relaxation again by heating after hardened

Adhesive materials can be divided depending on the nature of the hardening of two types

Adhesive bonding

ch 9 joining of metals [read-only] - kau 9 joining of... · 2015-05-11 · advantages and...

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