Pioneer Zephyr Budd shotweld stainless steel souvenir

Shot welding is a type of electric resistance welding which, like spot welding, is used to join two pieces of

metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

together. The distinguishing feature is that in shot welding, strips and sheets of metal (usually stainless steel) are "sewed" together with rows of uniform spot welds. The weld is achieved by clamping the two pieces together then passing a large

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

through them for a short period of time. Shot welding was patented by Earl J. Ragsdale, a

mechanical engineer Mechanical may refer to: Machine * Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement * Mechanical calculator, a device used to perform the basic operations o ...

at the Edward G. Budd Manufacturing Company in 1932 to weld

stainless steel Stainless steel, also known as inox, corrosion-resistant steel (CRES), or rustless steel, is an iron-based alloy that contains chromium, making it resistant to rust and corrosion. Stainless steel's resistance to corrosion comes from its chromi ...

. This welding method was used to construct the first stainless steel train, ''

Pioneer Zephyr The ''Pioneer Zephyr'' is a diesel engine, diesel-powered trainset built by the Budd Company in 1934 for the Chicago, Burlington & Quincy Railroad (CB&Q), commonly known as the Burlington Route. The trainset was the second internal combustion-po ...

'', in 1934, and became the standard construction technology for railroad passenger cars thereafter.

Method

In the early 20th century, the Edward G. Budd Manufacturing Company had been innovative in the field of sheet metal fabrication, and had revolutionized the construction of automotive bodies in steel during the 1920s. Edward Budd and his employees, notably Earl Ragsdale, recognized the important

metallurgical Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys. Metallurgy encompasses both the ...

characteristics of 18/8 stainless steel (known today as SAE 304 austenitic stainless steel) and further developed a spot welding process to take advantage of the oxidized layer on the surface of stainless steel. Heat treating the 18-8 stainless steel leaves the metal with non-magnetic and

ductile Ductility refers to the ability of a material to sustain significant plastic deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic deformation, which is reversi ...

properties. Repeatedly reheating the metal to 1000–1100°C impairs the mechanical and chemical properties of the metal. The metal becomes susceptible to

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

due to carbide precipitation, and loses fatigue resistance. The important factor in controlling the metal's properties is the dwell time at those temperatures. Using a controlled time element and recorder, a power supply with smooth current, and very brief high currents, a satisfactory spot weld may be produced. The corona of the shot weld should not exist on the metal, and the equipment used produces satisfactory welds with a smaller than normal diameter. Sufficient electrode force is applied to hold the two sheets of metal together and the peak current rapidly creates a forge weld at the interface between the two sheets, producing a small nugget of weld metal, which when cooled results in a shear-resistant metal interface. Good shotwelds have twice the

shear strength In engineering, shear strength is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a mater ...

of a

rivet A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylinder (geometry), cylindrical shaft with a head on one end. The end opposite the head is called the ''tail''. On installation, the deformed e ...

of similar diameter and can be placed 50% closer together. When done properly,

distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...

, which is a problem in fusion welding processes, is eliminated.

References

{{Reflist Welding Budd Company