Metal fusion bonding – Process – Using dynamic frictional energy
Reexamination Certificate
2002-12-13
2004-08-24
Stoner, Kiley (Department: 1725)
Metal fusion bonding
Process
Using dynamic frictional energy
C228S002100
Reexamination Certificate
active
06779709
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
This invention pertains to friction welding and more particularly to a portable inertia friction-welding machine.
2. Background of the Invention
Friction welding is a solid-state process in which workpieces are placed under compressive force with each other. The contact surfaces (joint or faying surfaces) are moved with respect to each other, typically by rotation, to produce sufficient heating to weld the workpieces together. Various types of friction welding are detailed in the AWS Welding Handbook, 8th Ed., Vol. 2, American Welding Society, 1991.
Two types of friction welding are in common use: 1) direct-drive friction welding and 2) inertia friction welding. In direct-drive friction welding, one of the workpieces is loaded into a rotating spindle and brought into contact with a second workpiece under a low compressive force referred to as a first friction force or preheat force. In some cases, the first friction force may not be used. Frictional heating is continued for a preset time or displacement distance, i.e., the distance the two workpieces move toward each other due to the first compressive force. Typically a higher compressive force, termed the second friction force or welding force is then applied causing plasticized metal to be extruded from the joint (contacting surfaces of the two workpieces). Again the second compressive force may be applied for a preset time or distance. The rotating spindle is then brought to a stop by means of a braking system such as a caliper and/or by means of an electric brake in the spindle drive motor. A third compression force, typically referred to as the upset force, is applied to consolidate the joint. The upset force may be applied while the spindle is braking or after it stops. If the upset force is applied while braking, the microstructure of the joint reflects a rotational-type of forging. If the upset force is applied after the spindle has stopped, the microstructure of the joint reflects an axial-type of forging.
In inertia friction welding, the frictional heating is provided by stored rotational kinetic energy in the form of one or more flywheels mounted on the rotating spindle. The inertia of the system is changed by either adding or removing flywheels from the spindle or changing the spindle rotational speed or both. To begin the welding process, the two workpieces are loaded into the welding machine, typically one workpiece is secured to the spindle and the other workpiece secured to the tailstock of the machine. The spindle is then accelerated to a predetermined velocity, i.e., rotational speed typically expressed in revolutions per minute (rpm)), and the spindle drive means is disengaged allowing the spindle, with attached flywheel(s), and the workpiece mounted in the spindle to coast. The rotating workpiece is then brought into contact with the stationary workpiece with an applied compressive force to begin the frictional heating of the two workpieces. The flywheel comes to a stop as its kinetic energy is transitioned into thermal energy (frictional heating) at the interface of the two workpieces. In some cases, as the flywheel slows down or after it has stopped, the compressive force is increased so as to apply an upset force to complete the joint. Additional details as to inertia and direct-drive friction welding can be found in T. Stotler, “Procedure Development and Practice Considerations for Inertia and Direct-Drive Friction Welding” in ASM Handbook, Volume 6, ASM International, United States, 1993, pp. 888-891.
As noted above, friction welding has largely focused on direct-drive and inertia welders. Both of these welders have been extremely large units securely mounted to the shop floor and often weigh a ton or more. U.S. Pat. Application Pub No. US 2002/0036225 Al illustrates a friction-welding machine while U.S. Pat. Nos. 3,235,162; 3,234,644; 3,571,905; 3,591,068; and 4,030,658 illustrate inertia welding machines. In both the direct-drive and inertia machines, the tailstock-mounted workpiece has been used to apply the compressive forces by axially moving the tailstock-mounted workpiece toward the rotating second workpiece mounted in a rotating chuck. That is, the rotating chuck (and a first workpiece) was mounted to be axially stationary; the second workpiece was secured in the tailstock piece to be rotationally stationary but moveable in an axial direction in order to apply the requisite compressive force. Typically both the rotating chuck and the tailstock were mounted on a base with the tailstock drawn toward the rotating chuck by mechanical means. Some machines use a fixed tailstock in which compressive forces are achieved by moving the rotating unit by means of a carriage and piston assembly.
One of the first attempts at producing a portable machine is found in U.S. Pat. No. 3,185,368. Although various improvements were made to make the machine as light as possible, it remained a massive machine that was truck mounted for use in the field. Although there are some portable friction welders on the market, these machines have difficulty welding large diameter parts (i.e., greater than about ¾-in.) or welding materials that need short welding times such as aluminum, due to the high torque requirements. These machines are direct-drive friction welders to avoid the need for large and heavy flywheels although, occasionally a small amount of additional weight is occasionally used to overcome the initial torque peak and motor stalling that occurs when the workpieces first touch. Even in these cases, the only way to overcome the low-torque capabilities is to reduce the initial compressive forces significantly. However, this dramatically increases the weld time and, unfortunately, such long weld times often have a detrimental affect on the mechanical properties of the resulting weld of the workpiece materials. At best, these machines can only friction weld small studs or appurtenances (less than about ½ inch in diameter) to plates or pipe with a resulting low pull-off strength, typically less than 30,000 lbs.
To achieve the required torque and spindle speed for a direct-drive unit for large appurtenances with a 30,000 lb pull off strength would require at least a ten horsepower electric motor in combination with a large gear box. This results in a machine that is either too large and heavy to carry and position, i.e., is no longer portable, or too large to obtain access to the welding area, e.g., the inside of a vehicle. To even consider the use of inertia welders with their large and heavy flywheels for welding appurtenances greater than ½ or ¾ inch diameter flies in the very face of portability.
In addition to the inability of current portable direct-drive friction welders to weld large diameter appurtenances, i.e., appurtenances having a minimum pull-off strength of 30,000 lb, there are additional problems in using such units, especially when attempting to weld internally threaded, large diameter appurtenances. First of all, plasticized metal formed during the welding process extrudes into the internal threads at the base of the appurtenance and blocks the effective use (maximum engagement) of the internal threads. Second, the plasticized metal also extrudes on the external surface of the appurtenance and can interfere with the attachment of parts to the plate using the appurtenance. That is, the part cannot be screwed into the appurtenance and brought flush with the plate to which the appurtenance is joined. The extruded metal (flash) can also promote crevice corrosion when the resulting assembly is exposed to hostile environments such as seawater or corrosive chemicals. Third, it is difficult to grasp an internally threaded appurtenance in the welder to effectively produce both rotational and compressive axial forces. This can result in rotational slippage and, as a result, there may be insufficient heating to produce a satisfactory weld. It can also result in axial slippage that can result in both insufficient heating and compressi
Stotler Timothy
Trapp Timothy J.
Dawsey David J.
Edison Welding Institute, Inc.
Gallagher Michael J.
Gallagher & Dawsey Co. LPA
LandOfFree
Portable inertia welder does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Portable inertia welder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Portable inertia welder will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3274083