Joining Processes

Metal joining is a controlled process used to fuse metals. Joining is an all-inclusive

term covering processes such as:

Welding
Brazing
Soldering
Adhesive Bonding
Mechanical Fastening
Riveting

Welding
In the welding process, two or more parts are heated and melted or forced
together, causing the joined parts to function as one. In some welding methods a
filler material is added to make the merging of the materials easier. There are many
different types of welding operations, such as the various arc welding, resistance
welding and oxyfuel gas welding methods. Welding is the most economical and
efficient way to join metals permanently. It is the only way of joining two or more
pieces of metal to make them act as a single piece. There are many ways to make
a weld and many different kinds of welds. Some processes cause sparks and
others do not even require extra heat. Welding can be done anywhere outdoors
or indoors, underwater and in outer space. Nearly everything we use in our daily
life is welded or made by equipment that is welded. Welders help build metal
products from coffeepots to skyscrapers. They help build space vehicles and
millions of other products ranging from oil drilling rigs to automobiles. In
construction, welders are virtually rebuilding the world, extending subways, building
bridges, and helping to improve the environment by building pollution control
devices. The use of welding is practically unlimited. There is no lack of variety of
the type of work that is done.

Brazing
Brazing is the joining of two dissimilar materials using a third material. During the
brazing process a filler metal is melted and distributed in between multiple solid
metal components after they have been heated to the proper temperature. The
filler metal must have a melting point that is above 840 degrees Fahrenheit but
below the melting point of the base metals and the metal must also have high
fluidity and wettability. No melting of the base metals occurs during brazing.
Brazing differs from welding in that brazing does not melt the base metals,
therefore brazing temperatures are lower than the melting points of the base
metals. For the same reason, brazing is a superior choice in joining dissimilar
metals. Brazed joints are strong. A properly-made joint (like a welded joint) will in
many cases be as strong as or stronger than the based metals being joined.
Soldering
Soldering is similar to brazing; the only real difference being that in soldering the
melting point of the filler metal is below 840 degrees Fahrenheit. Again, no melting
of the base metals occurs, but the filler metal wets and combines with the base
metals to form a metallurgical bond. Soldering is the process of joining two metals
by the use of a solder alloy, and it is one of the oldest known joining techniques.
Faulty solder joints remain one of the major causes of equipment failure and thus
the importance of high standards of workmanship in soldering cannot be
overemphasized.

Adhesive Bonding
In adhesive bonding a filler material, called an adhesive, is used to hold multiple
closely spaced parts together through surface attachment. The adhesive is a
nonmetallic substance; often it is a polymer. Adhesive bonding is used to fasten
two surfaces together, usually producing a smooth bond. This joining technique
involves glues, epoxies, or various plastic agents that bond by evaporation of a
solvent or by curing a bonding agent with heat, pressure, or time. Historically, glues
have produced relatively weak bonds. However, the recent use of plastic-based
agents such as the new super-glues that self-cure with heat has allowed
adhesion with a strength approaching that of the bonded materials themselves. As
a result, gluing has replaced other joining methods in many applications
especially where the bond is not exposed to prolonged heat or weathering.

Mechanical Fastening
Various fastening methods are used in mechanical assembly to mechanically
attach two or more parts together. Usually fasteners are used, being added on
during the assembly operation. Sometimes, however, fastening involves the
shaping of one of the components being assembled without the need of separate
fasteners. Mechanical fastening can be divided into methods that allow for easy
disassembly, threaded fasteners, and those that do not, rivets. Mechanical joining
falls into two distinct groups: fasteners and integral joints. Examples of fasteners
include: nuts and bolts, screws, pins and rivets; examples of integral joints
include: seams, crimps,snap-fits and shrink-fits.

The most common mechanical fastening methods include:

Integral fasteners
Threaded fasteners

Integral fasteners: are formed areas designed into sheet metal products. Integral
fasteners function by interlocking or interfering one component with other
components during assembly.

Threaded fasteners are a low-cost means of mechanically joining and holding

parts together. They are used where subsequent disassembly and reassembly may
be required. Threaded fasteners include machine screws, nuts and bolts, and
range in size from the miniscule to large diameters and lengths used in bridge and
building construction. Threaded fasteners are available in both standard and metric
sizes as well as a variety of thread types, thread pitch, tolerances, and
classifications. Threaded fasteners may be installed by hand with common hand
tools or by automated machinery. In such cases, the screws often have special
shaped ends, such as the cone-shaped point, to facilitate automated insertion in
mating components. Some form of mechanical joining needs to be used where
products need to be taken apart during their normal life

Riveting
Riveting is a forging process that may be used to join parts together by way of a
metal part called a rivet. The rivet acts to join the parts through adjacent surfaces.
A straight metal piece is connected through the parts. Then both ends are formed
over the connection, joining the parts securely. The metal work piece used to form
the connection may be hollow or it may be solid. Rivets have many uses, such as
in the construction and sheet metal industries. Riveting is one of the most ancient
metalwork joining processes.