JOINING PROCESSES AND EQUIPMENT
Fusion Welding Processes
Oxyfuel gas, arc and high-energy beam welding are among
the most commonly used joining operations. Gas welding uses chemical energy, whereas arc
and high-energy beam welding use electrical energy to supply the necessary heat for
welding. In all these processes, heat is used to bring the joint being welded to a liquid
state. Shielding gases are used to protect the molten weld pool and weld area against
oxidation. Filler rods may or may not be used in oxyfuel gas and arc welding to fill the
weld area.
The selection of a welding process for a particular operation
depends on a workpiece material, its thickness and size, shape complexity, type of joint,
strength required, and changes in product appearance cause by welding. A variety of
equipment is available, much of which is now computer controlled with programmable
features.
Cutting metals is also done with processes whose principles are
based on oxyfuel gas and arc welding. Cutting steel occurs mainly by oxidation and
burning. The highest temperatures for cutting are obtained by plasma-arc-cutting.
Solid-State Welding Processes
In additional to the traditional joining processes of oxyfuel gas
and arc welding, a number of other joining processes that are based on producing a strong
joining pressure and/or heat are available. Surface preparation and cleanliness are
important in some of these processes. Pressure is applied mechanically or by explosives.
Heat may be supplied externally, as in friction welding. Among important developments is
the combining of the diffusion bonding and superplastic forming processes. Productivity is
improved, as in the capability to make complex parts economically
As in all manufacturing operations, certain hazards are inherent in
welding operations, some relate to the machinery and equipment used and others to the
nature of the process. Proper safety precautions must always be taken in work areas where
welding is done.
The Metallurgy of Welding: Welding
Design and Process Selection
The metallurgy of the welded joint is an important aspect of all
welding processes because it determines the strength and toughness of the joint. The
welded joints consist of solidified metal and a heat-effected zone, with a wide variation
in microstructure and properties, depending on the metals joined and the filler metals.
Because of severe thermal gradients in the weld zone, distortion, residual stresses, and
cracking can be a significant problem.
Metals and alloys can be welded and joined by variety processes.
Their weldability depends greatly on their composition, the type of welding operation
involved, and the control of welding parameters. Important consideration includes joint
design, surface preparation, protective atmospheres, the appearance and quality of the
welded joints for safety and reliability. General guidelines are available to help in the
initial selection of suitable and economical welding processes for particular application.
Brazing, Soldering Adhesive
Bonding, and Mechanical Fastening Processes
Joining processes that do not only rely on fusion or pressure at the
interfaces include brazing and soldering. Instead, these processes utilize filler material
that requires some temperature rise in the joint. They can be used to join dissimilar
metals of intricate shapes and various thicknesses.
Adhesive bonding has gained increased acceptance in major
industries, such as aerospace and automotive. In addition to good bond strength, adhesive
have other favorable characteristics, such as sealing, insulating, preventing
electrochemical corrosion between dissimilar metal, and reducing vibration and noise
through internal dumping in the bond. Surface preparation and joint are important factors
in adhesive bonding.
Mechanical fastening is one of the oldest and most commons joining
methods. Bolts, screws, and nuts are common fasteners for machine component and
structures, which are likely to be taken apart for maintenance, ease of transportation,
and various other reasons. Rivets are semipermanent or permanent fasteners used in
buildings, bridges, and transportation equipment. A wide variety of other fasteners and
fastening techniques are available for numerous permanent or semipermanent applications.
Thermoplastics can be joined by fusion-welding techniques, adhesive
bonding. And mechanical fastening. Thermosets are usually joined mechanical means, such as
molded-in inserts and fasteners, as well as solvent bonding.
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