Method of solid state welding and welded parts

Details Method of solid state welding and welded parts Method of solid state welding and welded parts

2001-08-13

2003-10-28

Dunn, Tom (Department: 1725)

Metal fusion bonding

Process

Using dynamic frictional energy

C219S601000, C428S615000

Reexamination Certificate

active

06637642

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an improved method of solid state welding metal parts particularly, but not exclusively, ferrous or titanium metal parts including pipes or tubes which are joined to form pipelines, and oil, gas and geothermal wells and the like, and the improved friction welded parts having improved properties and reduced flash made by the method of this invention. The rapid friction welding method of this invention utilizes high frequency induction preheating to the hot working temperature of the parts to be welded in a non-oxidizing atmosphere which results in improved efficiencies and welded product.
BACKGROUND OF THE INVENTION
Construction of pipelines for example has depended almost exclusively on arc welding processes for the past eighty years. These processes have delivered high quality welds but at considerable expense. The direct and indirect costs of welding generally represent a large proportion of the cost of building pipelines. In the case of offshore pipelines, where the substantial cost of the laybarge comes into play, it is vital that welding be as rapid as possible and yet the bigger the pipe is, the slower the welding becomes. This encourages the use of multiple welding stations so that up to a half dozen welds are executed simultaneously. For deepwater offshore pipelines, there is yet another problem; the bending stresses of the completed pipe hanging off the stern of the laybarge become unacceptably high for a given combination of pipe diameter, wall thickness and water depth. Therefore in these cases, it is necessary to weld the pipe in a near vertical orientation on the laybarge, which in turn dictates that only one or perhaps two weld stations may be accommodated, thus reducing the productivity by a factor of three or more.
Longfelt Need For The Invention
There has therefore been a longfelt need for a reliable, high quality rapid welding process for repetitious welds required for pipeline construction. Ideally, this should be a “one-shot” process where the entire circumference is welded simultaneously in one quick action.
Known Welding Processes
The ancient blacksmith process of forge welding involves heating of iron or steel members to their hot working temperature (or plastic state), bringing the two members into intimate contact and then applying joining pressure to the two members as by hammering, pressing or rolling to produce the weld.
Arc welding is an old welding process dating back over 100 years. The original process has not changed much since the introduction of stick electrodes in 1907. Shielded Metal Arc Welding (SMAW) is the most widely used welding method today but is only one method in the general category, arc welding, includes at least a dozen distinct processes. All of these processes share the common characteristic that a continuous supply of filler metal is heated by electric arc discharge to liquefaction in the immediate proximity of the faying surfaces allowing it to melt into the parent metal and then solidify.
Flash welding and the various forms of resistance welding produce welds with very little liquefaction. Large electric currents are used to resistively heat the faying surfaces up to the hot working temperature where the metal assumes plastic properties and then can be forged together under pressures much lower than the normal yield strength of the metal.
Induction welding is a type of forge welding where the faying surfaces are heated to hot working temperature by induction heating and then rapidly pressed together to produce the weld. In contrast to flash and resistance welding processes, induction welding is much less prone to causing local hot spots and therefore has no undesirable liquefaction effects.
Friction welding exists as several variations but all rely upon the same principle, that sliding friction is used to convert kinetic energy (usually rotational motion) into heat to raise the temperature of the two faying surfaces to the hot working temperature, at which point the mating workpieces are forcefully pressed together to complete the weld. At no time during the process is any of the metal melted and therefore this process falls into the category known as solid state welding, which also includes several uncommon processes such as diffusion welding, explosion welding and ultrasonic welding. Since no liquefaction occurs, these welding processes are immune to the below-stated list of fusion welding defects. Continuous friction welding is probably the first known type of friction welding and appears to have originated in the mid 1950s. Inertia friction welding is an innovation where the predominant prior method using a large motor to furnish continuous kinetic energy throughout the welding cycle was improved by the use of a direct coupled flywheel to store kinetic energy from a much smaller drive motor and release it in a concentrated burst in a shortened, self arresting welding cycle.
Radial friction welding is a more recent innovation with particular importance when both workpieces are large or cumbersome elements like pipelines where it is difficult or impossible to rotate either faying surface at the high speeds required by conventional friction welding. In this method, a third element is introduced. Instead of rotating either of the two workpieces, a center ring is rotated around the abutting ends of the workpieces and simultaneously subjected to powerful axial forces to reduce the diameter and increase the axial length. When sufficient frictional heating has been generated to heat the faying surfaces to the hot working temperature, the rotation is stopped and the radial pressure is increased.
Twist compression welding is a recently disclosed development in related welding technology. It was developed as modification of conventional diffusion welding of aluminum to overcome weld quality problems resulting from oxide films by introducing a small amount of sliding motion to physically disrupt and disperse the aluminum oxide film normally present on all aluminum surfaces. The geometry of joints addressed in the prior art are of the socket and pin type where a cylindrical weld interface is achieved by inserting the end of one tube into the enlarged and induction preheated end of a mating tube and simultaneously rotating one with respect to the other approximately 12&pgr; radians (6 revolutions).
In 1993, Ferte and Pierquin were granted U.S. Pat. No. 5,240,167 for “Friction Welding Method With Induction Heat Treating”. The process disclosed in the Ferte patent calls for augmentation of friction welding with induction heat treating for the purpose of preventing cracking in precipitation hardened nickel superalloys for aeronautical engine parts.
Problems with Prior Welding Processes
Forge welding usually depends upon heating the workpieces in a furnace or fire in which case it is a slow process invariably resulting in oxidation of the exposed surfaces. These metal oxides are all non-metallic in their mechanical properties and thus are inherently brittle at room temperature. When the heated workpieces are then brought together and forged, these oxides extrude along the weld interface producing a brittle lamination between the workpieces. When cooled below the hot working temperature, the weld joint is prone to fracture along the plane of this lamination. This type of welding is very dependent on operator skill and therefore erratic in quality.
Fusion welding processes (which includes all types of arc welding) all depend upon liquefaction of part of the base metal. Therefore fusion welding processes are all vulnerable to a class of defects not encountered in the aforementioned forge welding. So-called fusion welding defects include: porosity, slag inclusions, incomplete fusion, inadequate penetration, undercut, melt through, various weld metal cracks and many more irregularities. Although the automation of certain arc welding processes improves the consistency of weldirig, the probability of such defects can never be completely eliminated. Even when automated, arc welding is still a rel

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