Undergraduate engineering educational experiences can be greatly
enhanced when students get to "see and do" things that compliment
the traditional classroom lecture. Using funding provided by the National
Science Foundation, the Gateway Materials Group is developing education
modules that demonstrate fundamentals in materials science and engineering
at the introductory and intermediate levels. These modules contain hands-on
laboratory and instrumentation procedures, multi-media instruction modules
and video demonstrations. Educators will ultimately be able to pick and
choose from these tools based on their particular university's curricula.
In welding, two or more metal parts are joined to form a single
piece. Both similar and very dissimilar metals may be welded. The bond
joining these two pieces is metallurgical and requires considerable
diffusion. It is not simply mechanical, as in riveting and bolting. Welding
frequently involves a metal weld rod that serves to provide additional
material to help form the weld. A variety of welding methods exist,
including arc and gas welding.
In brazing, the
braze metal melts, but the parts being joined may not. The bond is more
often formed by limited solid-state diffusion of braze metal into the
joined parts. In soldering, neither melting nor solid-state diffusion of
the joined surfaces takes place. The joint is usually produced by the
adhesion of melted solder to each metal surface.
One of the most characteristic displays associated with welding
processes is the generation of sparks. This is the typical layman's
exposure to welding and welding processes sometimes encountered at the site
of a construction project.
These displays often consist of small molten metal drops being
generated and flung away from the weld zone at high speeds.
To generate molten metal in the ambient environment, the welding
process requires the interaction of an intense heat source with the
materials to be joined. Here, welding takes place as such a heat source moves
down the length of the interface between a bar and the surface to which it
is being welded.
A typical source of such intense heat is the welding arc. A large
voltage potential is created between a cathode and an anode (usually the
weld zone). At a specific cathode-anode separation a region of hot ionized
gas (plasma) is created and conducts electrons from the cathode to the
anode. This gas is at an extremely high temperature. Both the weld zone and
external sources of metal can be liquified by exposure to this gas.
In joining two or more objects through welding, additional metal is
often needed to form a continuous weld. This is supplied by the use of
welding rods. Dissolution of the parent materials may or may not be
significant in forming or maintaining joint strength.
The molten electrodeand
base metal must be shielded against the ambient atmosphere. Oxygen and
nitrogen may interact with the molten metal in the weld 'pool' to decrease
the ductility of the final weld. The electrode shown in the diagram has a
covering of material (flux) that quickly forms a protective 'slag' during
welding. This slag covers the molten metal.
generation of the slag also produces a reducing gas shield which further
decreases exposure to oxygen. The entire process is very rapid and exists
well outside of equilibrium.
Here the electric arc exists between the flux-covered metal
electrode and the metal being welded. Heat from the electric arc melts both
the end of the electrode and the base metal to be joined. As the electrode
moves down the length of the weld it is consumed.
Gas Tungsten Arc Weldingalso uses the heat of an electric arc between a tungsten electrode
and the base metal. A separate welding filler rod is fed into the molten base
metal, if needed. A shielding gas flows around the arc to minimize
The tungsten electrode is visible at the top of these images as a
cone-shaped object. The shining liquid bridging the separate pieces of base
metal is the weld pool. The filler rod is visible in the foreground as a
solid rod being fed into the weld pool. The bright arc operates at many
1,000's of degrees centigrade and is easily able to melt the incoming rod.
This process differs from slag-shielded welding in that a shielding
gas flows over and protects the weld zone. No slag/flux is required and no
significant chemical interactions occur between the weld pool and the argon
or helium shielding gas typically used.
Gas Metal Arc Weldingis a
special variation on arc welding in which the electrode filler metal is fed
directly through the torch tip. As arcing occurs the electrode instantly
melts, forming molten droplets that fall into the weld pool. Shielding gas
is supplied through the torch tip to prevent chemical interactions with the
The Oxyacetylene Weldingprocess does not use an arc. Instead it combusts oxygen and
acetylene gases to provide a high temperature flame for welding. At
approximately 3,100°C, this flame provides enough heat to melt most metals.
During industrial welding processes (for example, automotive
production) the use of robotics is common. This is desirable for several
reasons among which are:
1) Safety --- these
high temperature operations can generate both flying molten droplets and
hazardous ultraviolet radiation. Removing human interaction completely is
the surest way to avoid injury.
--- robotics can, when properly implemented, produce nearly identical welds
in a large number of parts. No human operator, however skilled, can produce
the same weld each and every time.
Brazing is a process similar to welding in that a liquid metal flows
between two or more metal surfaces to be joined and solidifies to form a
continuous solid. However, brazing occurs at lower temperatures generally
involving direct melting of the braze. This liquid must then 'wet' (spread
out over) the surfaces of the metals involved.
process depends upon surface roughness, the nature of the metal surfaces
involved, temperature (generally > 500 degrees C) and the presence or
absence of a flux. In general, a braze will wet a metal surface if it:
1) forms an intermetallic compound with the solid or
2) is taken into solid-solid solution by the metal.
The ability of a molten metal to flow and cover a surface is
critical to the suitability of a particular alloy as a braze material. Key
to this ability is the parameter called the "contact angle." The
condition for the liquid to completely wet a solid surface is that this
contact angle must be zero.
therefore, liquid will wet and run over the surface of a solid if the
surface energy of the solid is high relative to the sum of the liquid (g L/V)
and solid/liquid (g S/L) interface surface energies.
These images show the change in the contact angle of a molten
droplet on a surface at temperature. At the beginning of the experiment
(the left-hand image) the contact angle is larger than at the end (the right-hand
image) of the experiment.
Soldering is similar to brazing but takes place at temperatures <
500 degrees C. The majority of soldered joints are used to interconnect
electronic components. There the surfaces to be joined are copper-based.
The solder itself is usually a Sn-Pb alloy having a melting point below
In the operation
show here, solder wire containing a flux core is melted in contact with a
heated soldering 'pencil.' A high melting point organic acid (R3COOH) is
usually the main component of the flux. This acid is important in the
process as it reacts with the cupric oxide found on the surface of the
copper. This cleans the metal surface and allows for efficient wetting by
the molten alloy.
Welding Engineering at Ohio State has been recognized throughout
industry as a leader in education and research. More than 1,000 students
have graduated from this unique, world-renowned program since 1947. We
continue to attract bright, cross-disciplinary students to our department.
Our program is the
only American Board of Engineering Technology accredited welding
engineering program in the United States. We offer a comprehensive
education in welding engineering with bachelor's, master's, and doctorate
degrees. Our students experience hands-on application of the scientific
principles inherent to welding processes.
engineering program provides the engineering training needed to function
effectively in manufacturing industries. Coursework combines several
engineering fields. Four academic areas are treated:
including engineering mechanics, stress analysis, structures, machine and
• the materials used in manufacture, with course work in physical
metallurgy, metallography, and physical chemistry;
• manufacturing processes including electrical equipment and
• fitness for service including nondestructive testing.
The Department of
Welding Engineering provides in-depth training in welding materials,
design, processes, and evaluation. This prepares the student for complex research,
production, and applications work in modern industry.
124 Welding Engineering Laboratories, 190
West 19th Avenue
EWI is the largest nonprofit,
industrially-driven engineering organization in the U.S. dedicated to
advancing and applying materials joining technology to benefit industry.
Established in 1984 as part of Ohio's Thomas Edison Program, this resource
center links industry, government and academic organizations to promote
industrial competitiveness through technology development.
Dedicated to uniting people and technology,
EWI's industrially-experienced engineers can quickly isolate and solve
urgent manufacturing problems or investigate failed components. The EWI
staff works hand-in-hand with members to assess critical problems, optimize
designs, develop solutions and achieve results.