Metal working – Method of mechanical manufacture – Magnetically shaping
Patent
1998-03-19
1999-11-16
Bryant, David P.
Metal working
Method of mechanical manufacture
Magnetically shaping
29511, 29516, 72 56, B21D 2614, B21D 3904, B23P 1100, B23P 1700
Patent
active
059834781
DESCRIPTION:
BRIEF SUMMARY
This invention relates to end fittings for torque tubes that are mechanically connected at the ends of the tubes to the end fittings by forming the material of the tube ends around the end fittings, and to an apparatus for forming a portion of a tube onto an insert. More particularly, this invention relates to an end fitting onto which the ends of the torque tubes may be electromagnetically formed using tubing material as purchased without preliminary heat treating and storage at cold temperatures and to a tube forming apparatus for electromagnetically deforming the end of a tube onto an insert to form a torque transmitting mechanical joint between the tube and the insert that is as strong or stronger than the tube itself and is very fatigue resistant.
BACKGROUND OF THE INVENTION
There are many uses of an elongated metal tube having end fittings connected to the tube with a rigid mechanical joint. Push rods and torque tubes are two very common uses of this type of device. Torque tubes are used for mechanically transmitting torque from a driver to a driven device through a torque tube. These applications often require that the torque tube be light and inexpensive, have high fatigue strength and an ultimate yield strength at the end fitting equal to or exceeding that of the tube itself. Drive shafts for vehicles such as cars and trucks are examples of a type of torque tube requiring such characteristics. Presently, vehicle drive shafts are made of steel tubing attached at their ends to torque coupling fittings such as U-joint components or the like. The use of aluminum tubing in a vehicle drive shaft would have an attractive weight saving benefit, but the difficulties of forming high strength aluminum tubing onto the end fittings without expensive preliminary heat treating has deterred the use of aluminum tubing in this application.
In aviation applications, the requirements for light weight mechanical systems have dictated use of aluminum tubing for torque tubes for many years. However, the apparatus and methods for attachment of the end fittings on these torque tubes have some unsatisfactory properties that manufacturers and operators of commercial transport airplanes would prefer to eliminate. Riveting the end fitting onto the tube is costly because it is labor intensive. The rivets can loosen after extensive service, resulting in lost motion and possibly resulting eventually in failure after many years unless the torque tube is inspected and repaired or replaced when the rivets begin to loosen.
Welding or brazing the tubing to the end fitting presents the difficulties of a heat affected zone adjacent the fused joint, and low tolerance fit-up requirements for the fitting and the tube. Crack propagation in the fused joint can also be a problem; it may be difficult to detect by ordinary inspection procedures, and failures that do occur may be catastrophic and result in failure of flight critical control surfaces. Therefore, welding or brazing is rarely used in load-bearing flight critical hardware.
Mechanically forming the tubing onto the end fitting is a promising technique because it does not require fasteners nor produce the heat affected zone of a fused joint. Some potentially usable techniques for exerting pressure on the aluminum tubing to deform it around the end fitting for this purpose are swaging, hydroforming, rubber press forming, electromagnetically forming, explosive forming. Electromagnetic forming is especially appealing because of the potential for efficient, high volume, precisely repeatable production processes, but existing apparatus and techniques to deform aluminum tubing materials possessing the required properties of high strength and corrosion cracking resistance have resulted in formation of cracks in the tubing during forming onto the end fitting. The resulting cracks are unacceptable because of the shortening of the fatigue life of the torque tube.
Electromagnetically pulse forming 2024 aluminum tubing in the T-3 condition onto end fittings shown in U.S. Pat. No. 4,523,872 usi
REFERENCES:
patent: 3132290 (1964-05-01), Kumpf
patent: 3360972 (1968-01-01), Schwinghamer et al.
patent: 4148091 (1979-04-01), Hansen et al.
patent: 4561799 (1985-12-01), Arena
Dolan Larry E.
Eickelberg John L.
Reed Blake E.
Scarborough Ron N.
Bryant David P.
Neary J. Michael
The Boeing Company
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