WELDING AND FABRICATION

Welding
Welding is a process of joining metal-based materials together. The technique is called fusion.
This is a complex function that involves using heat and pressure. There are many specialized
tools and individual processes used in the welding field.
Although welding is as a single part of the metal fabrication process, it’s a highly skilled trade
requiring a lot of training and practice to master.

Welding
With welding, two or more pieces of metal are joined together, through a combination of heat
and pressure. This is a popular process because the pieces of metal can be any shape or size.

The common welding methods are

1. Gas welding
2. Arc welding
3. Soldering

1. Gas welding (oxyacetylene welding)

Gas welding uses the heat from a concentrated flame to melt metals and then join them. Gas
welding is possible with or without filler metal.

The flame is controlled using a welding torch. An oxygen gas canister and a fuel gas canister is
connected to the welding torch. The welder can control the flame by controlling the number of
gases fed to the torch using a pressure regulator.
 Most commonly, we see a gas combination of oxygen and acetylene, which is capable of
producing 3200°C (5792 oF). Other fuel gases that are also seen in gas welding are hydrogen,
butane, and propane.

Some of the popular applications of gas welding are:

 Fabrication of sheet metal

 Automobile and aircraft industries

 Joining ferrous and non-ferrous meta

Advantages of gas welding:

 Easily portable equipment

 Superior flame control

 Low cost and maintenance

 Can also be used for Gas Cutting

 Cheaper equipment cost

Disadvantages of gas welding:

 Not suitable for very thin sections

 Lower temperatures than arc welding

 Harder to flux shield

 No suitable for reactive metals

2. Arc welding

This is a very widespread form of welding

As the name suggests, arc welding uses an electric arc to melt materials before joining them
together. A power supply is used to create an electric arc is between an electrode (which can be
either consumable or non-consumable) and the base metal to melt the metals at the point of
contact.

The welding area is usually protected by some type of shielding gas, vapor, or slag. This is
because the atmospheric air can interact with the weld pool and cause oxidation.

This electric arc can create temperatures upwards of 6300°F (3500°C), which is high enough to
melt metals like carbon steel.

There are different types of arc welding, such as shielded metal arc welding (SMAW), flux-cored
arc welding (FCAW), submerged arc welding (SAW), plasma arc welding (PAW) to exemplify.

Applications of arc welding:

 Shipbuilding
 Automotive industries

 Construction industries

 Mechanical industries

Advantages of Arc welding:

 Suitable for high-speed welds

 Simple welding apparatus

 Portability as a result of the simple equipment

 Can work on AC or DC

 Superior temperatures

Disadvantages of arc welding:

 Not suitable for welding thin metals

 Requires skilled welders

 Cannot be used for reactive metals like Aluminum or Titanium

3. Soldering

What is Soldering?

Soldering is one of the oldest and most popular techniques used for joining similar or dissimilar
metals. It uses a filler material to join parent materials that remain solid. It is a low-temperature
analog to brazing which uses filler alloys with melting temperatures below 450 °C (840 °F). This
process may or may not require a fluxing agent. The filler metals melt at low temperatures so
there is minimum part distortion and heat damage to sensitive parts. The filler metal is called
solder which when solidifies, is then bonded to the metal parts to join them. The most commonly
used solder is tin alloy and lead. Soldering is extensively used in the electronics industry for
joining wires, capacitor, resistor, etc. with the joining plate.
Soldering and brazing jointly represent one of several methods used for joining two or more
pieces of metal. In essence, a joint is made in metal using an alloy of two or more metals to hot-
glue the parts together. The word “glue” here does not mean just sticking something together as
the items to be joined are to be bonded at a molecular level to the alloy, which imparts
considerable strength to the joint. Soldering and brazing are the only metal joining methods that
can produce smooth and rounded fillets at the periphery of the joints. Both the operations involve
heating the filler metal and joint surfaces above ambient temperature. Both are essentially the
same metal joining technique, the difference being the temperature at which each method is
performed. Brazing filler metals melt above 450 °C whereas solder filler metals melt below 450
°C.

What is Brazing?

Brazing is yet another metal joining process in which two or metals are joined together by
heating and melting a filler metal, which then bind the two pieces together and join them. It can
be applied to a wide variety of materials, including metals, ceramics, glasses, plastic, and
composite materials. Although it is not as strong as fusion welding, it is the strongest form of
metal bonding without melting the parent metal of the components being joined together. So this
process requires more heat input than other soldering operations such as mechanical fastening,
adhesive bonding, solid state joining, welding and so on. This process can also be used to join
dissimilar metals such as silver, gold, copper, aluminum, etc. Brazing is necessarily done
at temperature above 450 °C but below the critical temperature of metal.
 FABRICATION
Metal fabrication is the creation of metal structures by cutting, bending and assembling
processes. It is a value-added process involving the creation of machines, parts, and structures
from various raw materials.
Metal fabrication is a broad term referring to any process that cuts, shapes, or molds metal
material into a final product. Instead of an end product being assembled from ready-made
components, fabrication creates an end product from raw or semi-finished materials. There are
many different fabrication manufacturing processes. Metal fabrication is used for both custom
and stock products.

Materials used in Fabrication

i) sheet metal
 ii) plates
iii) rods
iv) sections

Types of Metal Fabrications

Choosing a metal fabrication method suited to a given project depends on part geometry, the
product’s intended purpose, and the materials used in crafting it. Common metal fabrication
processes are as follows:

Casting , Cutting , Drawing , Folding

Forging Extrusion Machining Punching
Shearing Stamping Welding

Casting
Casting is when molten metal is poured a mold or die and allowed to cool and harden into the
desired shape. The metal fabrication process is ideal for mass-production of parts with the reuse
of the same mold to create identical products. There are several different types of casting. Die-
casting is when liquid metal is forced into a die instead of a mold, and there the applied pressure
keeps it in place until it hardens. This process is known for the high-speed applications it
supports. Permanent mold casting involves pouring the molten metal into a mold.

There are a variety of types of casting processes. In some cases, a vacuum is also used in this
process. Permanent mold casting can create stronger castings than die casting, but they can be
difficult to remove from the final product. For this reason, semi-permanent mold castings are
also available. These molds have expendable cores, making them more manageable and less
costly to remove. The final casting process is sand casting. With sand casting, castings are made
by pressing a pattern into a fine mixture of sand. This forms a mold for the molten metal to be
poured into. This process is slow but is generally more economical than the other forms of
casting. It is also good to use when intricate designs are needed, or for large metal fabrication.

Cutting

This very common type of metal fabrication is the cutting of a workpiece to split it into smaller
sections. While sawing is the oldest method of cutting, modern methods include laser cutting,
waterjet cutting, power scissors, and plasma arc cutting. There are many different methods of
cutting, from manual and power tools to computer numerical computer (CNC) cutters. Cutting
may be the first stage in a longer fabrication process or the only process used.

Die cutting is another cutting process that uses a die to slice metal. Rotary die cutting uses a
spinning cylindrical die to cut the material that is fed through a press. Flatbed die cutting is used
on thicker metal materials and uses a dies on a press to cut out shapes when the die stamps down
on the metal.

Drawing

Drawing uses tensile force to pull metal into and through a tapered die. The die stretches the
metal into a thinner shape. Usually drawing is performed at room temperature, and is called cold
drawing, but the metal workpiece can be heated in order to reduce the required force.

This process is considered deep drawing when the end product has a depth that is equal to or
greater than its radius. It is usually used with sheet metal fabrication to turn sheets into hollow
cylindrical or box-shaped vessels.

Folding

This metal fabrication process works by manipulating metal to bend at an angle. The most
common means is with a brake press that creates creases in the metal by pinching it. The
workpiece is held between a punch and a die and forced to crease with pressure from the punch.
This process is usually used to shape sheet metal. Folding can also be done by hammering the
workpiece until it bends, or by using a folding machine, also known as a folder. The machine has
a flat surface where the flat sheet metal is placed, a clamping bar that holds the workpiece in
place, and a front panel that lifts upwards and forces the metal extended over it to bend.
Fabricating knives using the forging process.

Image credit: Francesco de Marco/Shutterstock.com

Forging

Forging uses compressive force to shape metal. A hammer or die strikes the workpiece until the
desired shape is formed. This manufacturing process can be done with the metal at room
temperature and is called cold forging. Forging can also be performed with the metal heated to a
range of above room temperature to below the recrystallization temperature and is then called
warm forging. When the metal is heated to its recrystallization temperature, which varies by
metal, the process is called hot forging. Forging is one of the oldest types of metal fabrication,
with blacksmiths using forging centuries ago.

Examples of stainless steel forgings

Extrusion

In the extrusion manufacturing process, the workpiece is forced through or around an open or
closed die. When forced through an open or closed die, the diameter of the workpiece is reduced
to the cross-section of the die. When pressed around a die, a cavity is formed within the
workpiece. Both of these processes generally use a metal slug or cylinder (a billet) as the
workpiece, and a ram to perform the impact operation. The resulting cylindrical item product is
often wiring or piping. The die cross-section can have different shapes to produce differently
shaped parts. Extrusion can be continuous to create very long pieces, or semi-continuous in order
to create many shorter pieces.
Also called cold extrusion, impact extrusion is performed at room temperature and increases the
strength of the part, making it stronger than the original material. When enough force is applied
to the appropriate metal, it starts to flow into the available shape, much like the movement of
viscous liquid. Cold extrusion is commonly used for steel metal fabrication.

Hot extrusion is performed at an increased temperature, to keep the metal from hardening and to
make it easier to push through the die. It’s usually used for copper fabrication, as well to
create custom aluminum parts.

Machining

The metal fabrication method called machining refers to the process of shaping metal by
removing the unwanted material from it. This process can be performed in a variety of ways.
There are many different machining processes, including drilling, turning, and milling.

Drilling uses a rotary cutting tool, the drill bit, to cut a hole in the material. The drill bit presses
against the metal while being rotated very quickly in order to create a circular hole.

Turning uses a lathe to rotate the metal while a cutting tool moves in a linear motion to remove
metal along the diameter, creating a cylindrical shape. The cutting tool can be angled differently
to create different shapes. It can be done manually or with a CNC turning machine. CNC
machining is generally used when part measurements must be extremely precise.

Milling uses rotating multi-point cutting tools to progressively remove material from the
workpiece until the desired shape is achieved. The metal is slowly fed into the rotating cutting
tool, or the tool is moved across the stationary metal, or both the workpiece and the tool are
moved in relation to each other. This process can be done manually or with a CNC milling
machine. Milling is often a secondary or finishing process, but it can be used as the sole method
of metal fabrication from start to finish. The different types of milling include face milling, plain
milling, angular milling, climb milling, and form milling.
A CNC punching machine fabricates holes in sheet metal.

CNC -It is a computerized manufacturing process in which pre-programmed software and

code controls the movement of production equipment. CNC machining controls a range of
complex machinery, such as grinders, lathes, and turning mills, all of which are used to cut,
shape, and create different parts and prototypes.
Punching

Uniquely shaped turrets on a punch press hit the metal through or into a die to create holes. The
end product can either be the piece of metal with holes for fastening purposes, or it can be the
now removed, and shaped metal pieces called the blanking. Most punch presses are mechanical
but smaller and simpler punches can be hand-powered. CNC punch presses are also now
common and are used for both heavy and light metal work in metal fabrication.
Shearing

This type of metal fabrication is where one long, straight cut is achieved by combining two tools,
with one of the tools above the metal and the other one located below for applying pressure. The
upper blade forces the metal down onto the stationary lower blade and fractures it. The fracture
then spreads inward for complete separation. The sheared edges are usually burred. It is ideal for
cutting smaller lengths and differently shaped materials since the blades can be mounted at
angles to reduce the required force.

Stamping

This metal fabrication process is similar to punching, except the press doesn’t create a hole in the
metal, but an indentation. The turret doesn’t completely force the metal through the die, but only
raises it. Stamping is used to form shapes, letters, or images in a metal panel or sheet.
Mechanical and hydraulic are the two types of stamping presses. Metal stamping machines cast,
punch, cut and shape metal sheets. Sheets of up to 1/4 inch thickness are molded into specified
shapes and sizes. The presses used for metal stampings can create a wide range of products, and
they can perform a series of operations including blanking, metal coining, and four slide
forming. Coining (as the title implies) can be used to create coins, but it has other uses as well,
such as parts for electronics. Four slide forming incorporates a variety of stamping and forming
processes to create more complex products, and it is particularly effective for smaller parts.

Safety

i) personal safety
ii) workplace safety
 Need for Protective Equipment and Proper Maintenance
 Protection Against Burns and Harmful X-rays
 Fire and Health Safety Precautions
 Clear Working Environment
 Regular Inspection for Gas Leaks
 Proper Storage of Flammable Products
 Proper Checking and Maintenance of Electrical Nodes