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Cold welding or contact welding is a
solid
Solid is one of the State of matter#Four fundamental states, four fundamental states of matter (the others being liquid, gas, and Plasma (physics), plasma). The molecules in a solid are closely packed together and contain the least amount o ...
-state
welding
Welding is a fabrication (metal), fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing Fusion welding, fusion. Welding is distinct from lower ...
process in which joining takes place without
fusion
Fusion, or synthesis, is the process of combining two or more distinct entities into a new whole.
Fusion may also refer to:
Science and technology Physics
*Nuclear fusion, multiple atomic nuclei combining to form one or more different atomic nucl ...
or heating at the interface of the two parts to be welded. Unlike in
fusion welding
Fusion welding is a generic term for welding processes that rely on melting to join materials of similar compositions and melting points. Due to the high-temperature phase transitions inherent to these processes, a heat-affected zone is created i ...
, no
liquid
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...
or molten phase is present in the joint.
Cold welding was first recognized as a general materials phenomenon in the 1940s. It was then discovered that two clean, flat surfaces of similar
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
would strongly adhere if brought into contact while in a
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
(see
Van der Waals force
In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and th ...
). Newly discovered micro- and nano-scale cold welding
has shown potential in
nanofabrication
Nanolithography (NL) is a growing field of techniques within nanotechnology dealing with the engineering (patterning e.g. etching, depositing, writing, printing etc) of Nanometre, nanometer-scale structures on various materials.
The modern term re ...
processes.
Cold welding is common in jointing solid copper wires. Wire heads are put in claws and pressed together. This process is repeated until the joint is solid. Small wires can be jointed with hand-held manual welders while larger wires require hydraulic welders. The joint is firmer than basic wire.
Applications include wire stock and electrical connections (such as
insulation-displacement connector
An insulation-displacement contact (IDC), also known as insulation-piercing contact (IPC), is an electrical connector designed to be connected to the conductor(s) of an insulated cable by a connection process which forces a selectively sharpe ...
s and
wire wrap
Wire wrap is an electronic component assembly technique that was invented to wire telephone crossbar switches, and later adapted to construct electronic circuit boards. Electronic components mounted on an insulating board are interconnected by l ...
connections).
In space
Mechanical problems in early
satellites
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotop ...
were sometimes attributed to cold welding.
In 2009 the
European Space Agency
, owners =
, headquarters = Paris, Île-de-France, France
, coordinates =
, spaceport = Guiana Space Centre
, seal = File:ESA emblem seal.png
, seal_size = 130px
, image = Views in the Main Control Room (1205 ...
published a
peer reviewed
Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work (peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer review ...
paper detailing why cold welding is a significant issue that spacecraft designers need to carefully consider.
The paper also cites a documented example
from 1991 with the
Galileo spacecraft
''Galileo'' was an American robotic space probe that studied the planet Jupiter and its moons, as well as the asteroids Gaspra and Ida. Named after the Italian astronomer Galileo Galilei, it consisted of an orbiter and an entry probe. It was ...
high-gain antenna.
One source of difficulty is that cold welding does not exclude relative motion between the surfaces that are to be joined. This allows the broadly defined notions of
galling
Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together. Galling is cau ...
,
fretting
Fretting refers to wear and sometimes corrosion damage of loaded surfaces in contact while they encounter small oscillatory movements tangential to the surface. Fretting is caused by adhesion of contact surface asperities, which are subsequent ...
,
stiction
Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. The term is a portmanteau of the words ''static'' and ''friction'', and is perhaps also influenced by the verb '' to stick''.
Any ...
and
adhesion
Adhesion is the tendency of dissimilar particles or surfaces to cling to one another ( cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another).
The forces that cause adhesion and cohesion can be ...
to overlap in some instances. For example, it is possible for a joint to be the result of both cold (or "vacuum") welding and galling (or fretting or impact). Galling and cold welding, therefore, are not mutually exclusive.
Nanoscale
Unlike cold welding process at macro-scale which normally requires large applied pressures, scientists discovered that single-crystalline ultrathin gold
nanowire
A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre (10−9 metres). More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less ...
s (diameters less than 10 nm) can be cold-welded together within seconds by mechanical contact alone, and under remarkably low applied pressures.
High-resolution
transmission electron microscopy
Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a g ...
and in-situ measurements reveal that the welds are nearly perfect, with the same crystal orientation, strength and electrical conductivity as the rest of the nanowire. The high quality of the welds is attributed to the nanoscale sample dimensions, oriented-attachment mechanisms and mechanically assisted fast
surface diffusion
Surface diffusion is a general process involving the motion of adatoms, molecules, and atomic clusters ( adparticles) at solid material surfaces.Oura, Lifshits, Saranin, Zotov, and Katayama 2003, p. 325 The process can generally be thought of in t ...
. Nanoscale welds were also demonstrated between gold and silver, and silver and silver, indicating that the phenomenon may be generally applicable and therefore offer an atomistic view of the initial stages of macroscopic cold welding for either bulk metals or metallic
thin film
A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ap ...
.
See also
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References
Further reading
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External links
* {{Wikisource-inline, Advanced Automation for Space Missions/Appendix 4C
Welding