Holding Things Together

Article excerpt

Cars, bridges, skyscrapers, natural gas pipelines, and even computers would be much more expensive, or perhaps nonexistent, were it not for the unheralded technology of welding.

Metals are the biggest component of automobiles, and the manner in which they are joined together determines a vehicle's overall strength and durability. Today's cars and trucks are far stronger and safer, require less maintenance, and are more economical to operate than their predecessors of 50 years ago. And one of the main reasons is the thousands of strong, reliable welds that hold them together.

Despite its importance in automobile assembly and countless other manufacturing processes, welding is a largely unsung technology. It's even something of an enigma. The term welding has become a popular metaphor for strength and durability, and even for unity among individuals. Many of us speak of stuck drawers that seem "welded shut" and stubborn bolts that appear to be "welded on." Yet consumers rarely inquire about or inspect welds in the products they buy. In fact, to much of the general public, mention of the term welding conjures only images of cluttered shops, black helmets, and showers of sparks.

In reality, however, modern welding is a booming, high-tech subscience of metallurgy. Most of today's welders are no longer the body-shop variety. Instead, they are welding engineers trained in metallurgy as well as in chemistry, computer automation, thermodynamics, stress analysis, and heat transfer. Although modern welding dates back to only the 1930s, it has revolutionized most types of manufacturing, assembly, and construction. Strong, reliable welds have increased the quality and lowered the cost of countless products. They have furthered the advancement of science and even created a few new industries along the way. From computer circuit microwelds to the massive welded joints of bridges and skyscrapers, welding is literally holding together more and more of our world.

Welding refers to the various techniques of joining metals by fusion (thermal) or solid-state (pressure) processes, but modern welding techniques are almost exclusively of the fusion type. Welds are continuous metal joints that, when properly applied, are as strong as--or even stronger than--the metal itself. Held together by nothing more than atomic or molecular bonding, welds eliminate the need for adhesives and mechanical joining devices such as bolts and rivets.

Welding is possible because of the inherent attraction that similar metals have for each other. In a theoretical model, metals that are properly cleaned and smoothed to maximize surface contact will automatically join by atomic bonding. But cost-effective technologies to achieve this ideal type of contact weld do not yet exist. In the current state of the art, heat generated by electrical arcs and resistance, oxyacetylene flames, lasers, and/or electron beams is necessary to bond metals together.

The first welders

When the art of joining metals together originated in the Bronze Age, it was initially limited to the use of nails and staples, crude adhesives, and to hammering folded seams of bronze sheets. In hammer-forge welding, the first true welding process, metalworkers heated folded seams of bronze sheets nearly to their melting point, then hammered them together. Repetitive cycles of heating and hammering fused the bronze together in strong welds.

Pre-Columbian Amerindian gold workers in South America developed the first welding fluxes, substances used to help metals fuse together. They heated the edges of adjoining gold sheets almost to the melting point, then added powdered copper acetate, a flux obtained by dissolving native copper in vinegar. Without the use of pressure, the flux created an actual atomic fusion of the gold sheets. Strong and nearly undetectable, these joints were identical to the fusion welds achieved by modern jewelers. …