Weld gun arm casting

Details Weld gun arm casting Weld gun arm casting

2000-12-21

2001-10-23

Elve, M. Alexandra (Department: 1725)

Electric heating

Metal heating

For bonding with pressure

C219S086100, C219S078010, C420S494000

Reexamination Certificate

active

06307173

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to weld gun arm castings useful in robotic welding.
2. Background
Robotic welding is widely used in modem automotive assembly lines for joining a variety of different parts. In a typical robotic welder, heat for welding is generated by a resistance electrode mounted in a weld gun arm. Since electricity is supplied to the electrode directly through the weld gun arm, the weld gun arm must be designed to carry a high electrical load. In addition, it must be strong and shock resistant. In addition, it must exhibit these properties over a long useful life, as most weld gun arms are designed for making as many as 1 million or more welds.
Accordingly, current industrial specifications call for the best weld gun arms in use today, known as “Class III RWMA” weld gun castings (“RWMA refers to the Resistance Welding Manufacturers' Association), to be made from materials having a minimum Rockwell Hardness of 90B and a minimum electrical conductivity of 45% IACS.
Because of these demanding requirements, and because of their complex shape, most weld gun arms used in the North America automotive industry are made from cast, precipitation hardened copper alloys of the following composition:
Alloy
Be wt. %
Co wt. %
Ni wt. %
Balance
Class III
.35-.80
none
1.80-2.0 
Cu
(GM/Ford)
Class III
.35-.50
none
1.30-1.60
Cu
(Daim/Crys)
See, in particular, Harkness et al., Beryllium-Copper and Other Beryllium-Containing Alloys,
Metals Handbook
, Vol. 2, 10th Edition, ©1993 ASM International, which indicates that alloys having high electrical conductivities as well as excellent strength and hardness can be made by adding small amounts of beryllium and nickel to copper metal and then precipitation hardening the alloy so obtained.
Weld gun arms are supplied industrially by fabricators who design different gun arms for different applications. In normal practice, these fabricators also manufacture their own weld gun arms from molten alloys prepared by them. That is, the fabricators prepare one of the above alloys, usually from pure copper metal, pure nickel and a BeCu master alloy containing 4% Be obtained from a beryllium supplier. The fabricator then casts the alloy into a near net shape article—i.e., a casting whose shape is very close to the final shape of the ultimate product desired. The near net shape casting is then worked such as by drilling, cutting or bending to produce the product weld gun arm casting. Precipitation hardening is usually done after fabrication is complete, although it can be done before final shaping if desired.
A significant problem facing the robotic welding industry is premature weld gun arm failure. Most weld gun arm castings are designed for a predetermined useful life such as 1 million or more welds. Many achieve this goal. However, many crack or break long before their useful lives have expired. This often requires shut down of production lines as well as expensive replacement of parts.
Accordingly, it is an object of the present invention to provide new technology for reliably and consistently making weld gun arm castings which not only exhibit the strength, hardness and electrical conductivity of currently available product but also avoid premature failure.
In addition, it is a further object of the present invention to provide new weld gun castings which exhibit the strength, hardness and electrical conductivity of currently available product and, in addition, superior fatigue resistance as compared to currently available product.
SUMMARY OF THE INVENTION
These and other objects are accomplished by the present invention which is based on the discovery that premature failure of BeNiCu weld gun arm castings can be substantially avoided, without sacrificing strength, hardness or electrical conductivity, by including cobalt in the casting and further by controlling the (Ni+Co)/Be ratio in the casting to be about 4 or greater.
Thus, the present invention provides a new BeCu alloy for making weld gun arm castings comprising about 0.5 to 0.6 wt. % Be, about 0.4 to 0.6 wt. % Co and about 1.8 to 2.0 wt. % Ni, with the balance being Cu and incidental impurities, the (Ni+Co)/Be ratio in the alloy being at least about 4.
In addition, the present invention provides a new weld gun arm casting comprising an unwrought body of complex shape having a distal end for mounting a resistance electrode and a proximal end for attaching to the robotic assembly of a robotic welder, the casting being made from a BeNiCu alloy comprising about 0.5 to 0.6 wt. % Be, about 0.4 to 0.6 wt. % Co and about 1.8 to 2.0 wt. % Ni, with the balance being Cu and incidental impurities, the (Ni+Co)/Be ratio in the alloy being at least about 4.
In addition, the present invention provides a new process for reliably and consistently producing weld gun arm castings exhibiting excellent fatigue resistance and long useful lives, the process comprising forming the castings from a BeNiCu alloy comprising about 0.5 to 0.6 wt. % Be, about 0.4 to 0.6 wt. % Co and about 1.8 to 2.0 wt. % Ni, with the balance being Cu and incidental impurities, the (Ni+Co)/Be ratio in the alloy being about 4.


REFERENCES:
patent: 1957214 (1934-05-01), Horstkotte
patent: 2038390 (1936-04-01), Silliman
patent: 2094784 (1937-10-01), Bremer
patent: 3811611 (1974-05-01), Tholander et al.
patent: 4594116 (1986-06-01), Inagaki
patent: 6011237 (2000-01-01), Yang
Woldman's Engineering Alloys, ASM International 1994 8th edition p. 1354.*
John C. Harkness et al., “Beryllium-Copper and Other Beryllium-Containing Alloys,”Metals Handbook, vol. 2, 10 Ed, ©1993 ASM International.

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