MIL-W-8939A (MI)
3.2.1 Electronic component lead materials. Electronic components to be
resistance welded shall contain lead materials conforming to MIL-STD-1276
wherever possible.
Other types of leads shall be used only if they have been
found suitable for the purpose, and if weld schedules can be developed which
conform to applicable quality assurance provisions of this specification.
3.3 Fabrication and procedure. Welded electronic circuit modules and
assemblies shall be fabricated in accordance with the applicable drawings or
documents.
3.4
Equipment.
3.4.1 Welding machine. The welding machine shall consist of a suitable
source of electrical energy, suitable electrodes, and a means of reliably
controlling and indicating the magnitude of the current and welding force.
The force and current controls shall operate so that no current flows until
the welding force is applied at the welding electrodes.
The current shall be
cut off before the force is removed.
3.4.2 Electrodes.
Suitable electrode material, identified by
Resistance Welder Manufacturers Association (RWMA) class (see RWMA Bull 34),
shall be used to perform welding in conformance with this specification.
Electrodes with insulated shanks shall be used where required.
3.4.3 Shear testing machines. Weld shear testing machines shall be
provided as required.
All shear testing machines snail be accurate within
percent of the indicated reading.
Shear test machines shall be checked for
accuracy at intervals not greater than three months, whenever any significant
operational changes are made thereto, or when relocated.
3.5 Jigs and fixtures. All tooling that is required to position welds
or assist in the assembly of welded parts that must pass through the magnetic
field during the welding operation in a manner that would cause magnetic
disturbances to the welding cycle shall be made of nonmagnetic materials
insofar as practical.
Jigs and fixtures shall be so designed that no welding
current shunts through the locating devices rather than the workplaces.
3.6 Maintenance of equipment.
Unless otherwise specified, each item of
equipment shall be inspected periodically as recommended by the manufacturer.
Adequate maintenance shall be furnished, and defective parts affecting machine
operation shall be replaced before production welding is resumed.
3.7 Weld standards.
3.7.1 External appearance of welds.
3.7.1.1 Defects.
The surface of all welds shall be free from cracks
and voids when examined at a minimum magnification of 10 diameters.
The
contractor shall establish limits for other external appearance criteria, such
as excessive expulsion, bulging, and the like.
Such limits for electrode
indentation, embedment, and set-down shall be not greater than either 50
percent of the thickness of the member most. affected or 35 percent of the
total thickness of both materials.
Check the source to verify 3
that this is the current version before use.
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