WO2013085955A1

WO2013085955A1 - Linear friction welding method

Info

Publication number: WO2013085955A1
Application number: PCT/US2012/067873
Authority: WO
Inventors: Stephen A. Johnson
Original assignee: Apci, Llc
Priority date: 2011-12-05
Filing date: 2012-12-05
Publication date: 2013-06-13

Abstract

A method for bonding materials using friction welding, particularly linear friction welding, that involves forming and machining the weld surfaces of the two work pieces to provide a three dimensional contour so that certain areas of the weld surface are heated more than other areas. Selectively contouring the weld surfaces allows thermal energy to be generated in selected areas before other areas so as to control the conduction of thermal energy evenly or selectively across the entire weld surface.

Description

LINEAR FRICTION WELDING METHOD

This application claims the benefit of U.S. Provisional Patent Application, Serial No. 61/630,132 filed December 5, 2011, and U.S. Provisional Patent Application, Serial No.

61/630,146 filed December 5, 2011, the entirety of which are both incorporated by reference herein.

This invention relates to a method for bonding materials using friction welding, particularly linear friction welding, that reduces the effects of first "flash" on the welding process and flash buildup around the weld interface.

Background and Summary of the Invention

Linear Friction welding (LFW) is a process of joining two components which may be made from the same or different materials. The LFW process typically involves pressing the two components together under a large amount of force and rapidly vibrating the components with respect to one another to generate friction at the interface between the two components. The pressure and movement generate sufficient heat to cause the material at the interface to plasticize. Once the material at the interface begins to plasticize, the vibration is stopped and an increased force is applied. As the plasticized material of both components cools in this static condition, the components are bonded together and a weld is formed.

A persistent problem with linear friction welding (LFW) is the problem of "first flash." During the linear friction welding process, the "first" flash occurs when the friction begins and starts generating heat. The thermal energy quickly plasticizes the material at the weld surface. However, because the conduction of thermal energy is time based, there is a delay in the thermal energy conducting away from the weld surface. Consequently, when the vibration begins, the friction quickly plasticizes a shallow region of the weld surface, but as the thermal energy conducts away from the weld surface, the weld surface cools creating a premature bond. This premature bond is referred to as the first fiash and can cause the LFW machine to lock up placing stress on the work pieces, the weld interface and machine fixtures. The "first flash" problem is an inherent problem because it is almost impossible to create a 100% perfect interface between two components. Heretofore, the "first flash" problem was addressed simply by building LFW machines with enough power and rigidity to shear thru the premature bond of the first flash. This approach is undesirable and unpractical because the size and the expense of the LFW machines are typically over 10 times the size needed to make the weld.

Another problem inherent in friction welding, particularly, linear friction welding (LFW) is the extrusion of plasticized material laterally from the weld interface. This extruded material is commonly referred to as "flash." While flash around the weld is normally ground or machined from the joined work piece, in many applications flash cannot be easily removed. Consequently, it is highly desirable to produce welds using friction welding that reduces or eliminates flash around the weld interface.

The present invention is a friction welding method, particularly a linear friction welding method that diminishes the effects of first flash and that can be used to reduce or eliminate the extrusion of flash from selected areas of the weld interface. The LFW method of this invention involves forming and machining the weld surfaces of the two work pieces to provide a three dimensional contour and cavities so that certain areas of the weld surface are heated more than other areas. Selectively contouring the weld surfaces allows thermal energy to generate in selected areas before other areas so as to control the conduction of thermal energy selectively and evenly across the entire weld surface.

To reduce of prevent flash, the weld surface is formed, cut or machined to have elongated troughs or cavities in weld surfaces and notches in the side of one of the components. The trough or cavities form flash traps, where flash collects during the weld process. The flash traps are inset from the edge of the work piece along the sides of the component where flash is undesirable. The flash trap divides the weld surface into a larger main weld surface area and a smaller peripheral weld surface area. The notches are formed, cut or machined in the side of the work piece where flash is undesirable and extends under the peripheral surface area adjacent and below the bottom of the flash traps. The depth and shape of notches are calculated and configured so that the structural integrity of the material above the notches will begin to yield at a load just under the load of the weld pressure used in the weld formation. When the weld interface is formed, the friction generated by the weld pressure and vibration plasticizes the material of the main weld surface area and produces flash, which migrates toward and collects in the flash trap. The notches in the sides of the component, however, act as mechanical load limiters over the small peripheral weld surface area. The notches allow the material to start to deform under the weld pressure, which prevents the material of the peripheral weld surface area from plasticizing and producing flash. Since the material of the peripheral surface area never plastisizes and the flash from the main weld surface area is collected in the flash trap, no flash is extruded from the non-flash sides of the weld interface.

The method of the present invention may take form in various systems and components, as well as in the arrangement of those systems and components. The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. The drawings are only for purposes of illustrating exemplary embodiments and are not to be construed as limiting the invention.

Brief Description of the Drawings

The drawings illustrate the present invention, in which:

Fig. 1 is a simplified perspective of two work pieces to be joined illustrating a step of an embodiment of the linear friction welding (LFW) process of this invention;

Fig. 2 is a simplified perspective of the two work pieces to be joined illustrating another step of said embodiment of the LFW process of this invention which involves contouring the weld surface of one of the work pieces;

Fig. 3 is a simplified perspective of the two work pieces to be joined illustrating another step of said embodiment of the LFW process of this invention which involves pressing the two work pieces together under a weld pressure;

Fig. 4 is a simplified perspective of the two work pieces to be joined illustrating another step of said embodiment of the LFW process of this invention which involves pressing the two work pieces together under a weld pressure and rapidly vibrating the work pieces; and

Fig. 5 is a simplified perspective of the two work pieces to be joined illustrating another step of said embodiment of the LFW process of this invention which involves pressing the two work pieces together under a forge pressure to form the weld interface;

Fig. 6 is a simplified perspective of two work pieces being joined using a linear friction welding process illustrating the flash being expelled from the weld interface of two work pieces;

Fig. 7 is a simplified perspective of two work pieces to be joined illustrating a step of another embodiment of the linear friction welding (LFW) process of this invention;

Fig. 8 is a simplified perspective of the two work pieces to be joined illustrating another step of said other embodiment of the LFW process of this invention which involves

forming a cavity in one of the work pieces;

Fig. 9 is a simplified perspective of the two work pieces to be joined illustrating another step of said other embodiment of the LFW process of this invention which involves

forming a notch in the work piece;

Fig. 10 is a simplified perspective of the two work pieces to be joined illustrating another step of said other embodiment of the LFW process of this invention which involves

pressing the two work pieces together under a weld pressure;

Fig. 11 is a simplified perspective of the two work pieces to be joined illustrating another step of said other embodiment of the LFW process of this invention which involves

pressing the two work pieces together under a weld pressure and rapidly vibrating the work pieces, thereby producing flash that collects in the flash trap;

Fig. 12 is a simplified perspective of the two work pieces to be joined illustrating another step of said other embodiment of the LFW process of this invention which involves

pressing the two work pieces together under a forge pressure to form the weld interface; and

Fig. 13 is a simplified perspective of the two work pieces to be joined illustrating another step of said other embodiment of the LFW process of this invention which involves

pressing the two work pieces together under a weld pressure and rapidly vibrating the work pieces, thereby producing flash that collects in the flash trap.

Description of the Preferred Embodiment Referring now to the drawings, Figs. 1-5 illustrate the method for bonding materials using linear friction welding (LFW) that reduces the "first flash" affects and Figs. 6-13 illustrate a method for bonding materials using linear friction welding that reduces or eliminates the extrusion of flash around the weld interface.

Both methods of this invention may employ the use of any linear friction welding (LFW) equipment, machine or apparatus; however, the methods are best employed using the linear friction welding (LFW) apparatus, such as the ones developed by APCI, Inc. in South Bend, Indiana and described in U.S. Patent Number 8,070,039 on December 6, 2011. The teachings of U.S. Patent Number 8,070,039 are incorporated herein by reference. The LFW apparatus from APCI are ideal for the repair process of this invention because of their ability to control the amplitude, frequency and termination of the weld oscillation, as well as the weld and force pressures during the weld process. The teachings of U.S. Patent Number 8,070039 are incorporated herein by reference. The LFW Machine generally includes a press assembly and a vibration assembly supported at opposite ends of a frame. The frame also supports the various electrical and hydraulic controls. The press assembly includes a hydraulic press for providing the forge pressure for the welding process and a fixture operatively connected to the ram for securely holding one of the work pieces to be joined. The vibration assembly includes an oscillator mechanism and a carriage shiftably supported by a pair of rocker arms and operably connected to the oscillator. The carriage supports a second fixture holding the other work piece to be joined. The oscillator mechanism includes various motors, cam assemblies and a ram. The ram is rigidly connected to the carriage and is configured for movement along a weld axis that is perpendicular to the longitudinal axis of both work pieces. In addition, the linear friction welding (LFW) methods of this invention can be used to bond ferrous work pieces regardless of configuration or metal composition. In addition, the method can be employed when bonding dissimilar materials. Both LFW methods of this invention involve several calculations based on the yield strength of the materials being bonded. A material's yield strength is defined generally in engineering and material science as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible.

Referring now specifically to Figs. 1-5, one embodiment of the LFW method of this invention begins with preparing one or more of the work pieces 10. Typically, both component work pieces 10 to be joined initially have relatively flat facing weld surfaces 12, which will be bonded together in the weld process to from the weld interface 16 using a linear friction welding machine (Fig. 1). Weld surface 12 of one work piece is selectively ground or machined to form a three dimensionally contoured weld surface 12A. Instead of a roughly flat weld surface, the work piece is machined to have a raised ridge 14 and recessed area 13. For any particular weld interface to be formed, weld surface 12A is contoured and configured so that various peaks and ridges are formed in areas where additional thermal energy is desired and that the recessed areas correspond to areas where less thermal energy is desired. During the weld process, friction generates thermal energy first at these elevated peaks and ridge.

In other applications, the weld surface of either or both work pieces may be ground or machined to be sloped. The weld surface may be angled to slope from one end or side to the other, or angled to slope toward or away from the middle and periphery of the work pieces. In certain applications, multiple slopes may be used to create elevations and depressions across the weld surface as desired.

Once the contoured weld surface 12 A is formed in one or both of work pieces 10, both work pieces are mounted into the fixture of a linear friction welding machine (not shown). Once both work pieces 10 are properly seated and secured to the LFW machine, the LFW machine vibrates one or both of the work pieces while pressing them together under an initial load or "weld pressure" (Figs. 4, 5 and 7). Because the raised peaks and ridges of the weld surface are first in contact, the friction caused by the vibration and the weld pressure causes the material of the raised ridge 14 to plasticize before the recessed area 13 of weld surface 12 A. As ridge 14 plasticizes, material is lost from the weld surface 12A in the form of "flash." Because of the relative small area of ridge 14, the initial thermal energy generated by the friction at the ridge is quickly conducted downward toward recessed area 13 and across the rest of weld surface 12 A.

It should be noted that for each particular weld application, the three dimensional contour of the weld surface is calculated and machined to generate the desired amount of thermal energy at the desired areas across the entire weld surface. The weld surface can be selectively contoured to concentrate thermal energy in certain areas by machining the weld surface to elevate those areas. In addition, the weld surface can be selectively contoured to control the timing of the application of the thermal energy across the weld surface to be controlled. During the weld process, because the raised peaks and ridges of the weld surface experience friction before the recessed areas, the elevated peaks and ridges receive more thermal energy and plasticize quicker than the recessed areas. Consequently, selectively contouring the weld surface also allows certain areas to be heated before others due to the relative height between the elevations and the depression in the weld surfaces. The contouring of the weld surface into peaks, ridges and corresponding depressions reduces the surface area so that any premature bonding that takes place atop the peaks and ridges due to "first flash" is easily overcome by the mechanical force of the LFW machine's vibration, thereby preventing any mechanical seizures.

Once the friction has plasticized the material across the entire weld surface 12 A, the vibration is stopped and the work pieces are pressed together under a final load or forging pressure, which forms the weld interface 16 (Fig. 6). It should be noted that the LFW method of this invention uses weld and forge pressures calculated based on the yield strength of the materials being joined. Ideally, the final forge pressure is approximately 86-94% of the material yield strength of the given work piece. The initial weld pressure is approximately fifty percent (50%)) of the final forge pressure, but may range between 30-60%) of the forge pressure.

Referring now specifically to Figs. 6-13, a second embodiment of the LFW method of this invention begins with preparing one or more of the work pieces 10. An elongated trough or cavity (referred hereinafter as a "flash trap") 21 is cut or machined into weld surface 12 of the bottom work piece 10, which provides a void into which the flash collects during the weld process (Fig. 8). In most linear friction welding machines, the work pieces are oriented vertically; consequently, the flash trap 21 is formed into the bottom work piece (as shown). The shape, depth, and size of flash trap 21 is configured to receive the volume of flash produced during the weld process, which is generally a product of the material being bonded, the weld time and the area of weld interface. As shown, flash trap 21 is formed along one edge of the work piece on the side of work piece 10 where flash is undesirable, i.e. the non-flash side 18 of the work piece. In other applications, multiple flash traps may be formed, cut or machined in the weld surface along edges of other work piece sides where flash is also undesirable or around the entire periphery of the bottom work piece. It should be noted that the figures illustrate a single flash trap formed along one side of the bottom work piece 10 for simplicity of explanation only. In addition, flash trap 21 is inset from the edge of the non-flash side of the work piece, which divides the weld surface into a larger main weld surface area 12A and a smaller side or peripheral weld surface area 12B.

Next, a notch 23 is formed, cut or machined in the non- flash side 18 of bottom work piece 10 (Fig. 9). As shown, notch 23 is located below the bottom of flash trap 21 and generally extends under peripheral weld surface area 12B. The depth and shape of notch 23 is calculated and configured so that the structural integrity of the material above the notch will begin to yield at a load just under the weld pressure of the LFW process.

Once flash trap 21 and notch 23 are formed in bottom work pieces 10, both work pieces are mounted into the fixture of a linear friction welding machine (not shown). Once both work pieces 10 are properly seated and secured to the LFW machine, the LFW machine vibrates one or both of the work pieces while pressing them together under an initial load or "weld pressure" (Figs. 10, 11 and 12). Friction caused by the vibration and the weld pressure causes the material of main weld surface area 12A to plasticize and produce flash 20. The flash produced from plasticized material of main weld surface area 12A migrates toward and collects in flash trap 21. While the flash is produced over the main weld surface area 12 A, notch 23 acts as a mechanical load limiter over the small peripheral weld surface area 12B. Under the load of the weld pressure, the material under the peripheral surface area 12B starts to yield around notch 23. Because the weld pressure over the surface area is mechanically diminished because of structural integrity of the material around notch 23, not enough friction is generated to plasticize the material of peripheral surface area 12B, thereby preventing the production of flash in this area. Once the friction has plasticized the material of main weld surface area 12 A, the vibration is stopped and the work pieces are pressed together under a final load or forging pressure, which forms the weld interface 16 (Fig. 12). It should be noted that notch 23 is not large enough to affect over-all the structural integrity of the bottom work piece or significantly weaken the weld interface of the joined work pieces. In addition, the LFW method of this invention uses weld and forge pressures calculated based on the yield strength of the materials being joined. Ideally, the final forge pressure is approximately 86-94% of the material yield strength of the given work piece. The initial weld pressure is approximately fifty percent (50%) of the final forge pressure, but may range between 30-60%) of the forge pressure.

The embodiment of the present invention herein described and illustrated is not intended to be exhaustive or to limit the invention to the precise form disclosed. It is presented to explain the invention so that others skilled in the art might utilize its teachings. The embodiment of the present invention may be modified within the scope of the following claims.

Claims

I claim:

Claim 1 : A method of bonding together two work pieces having facing weld surfaces, the method comprising:

a. Contouring the weld surface of one of the work pieces such that the weld surface has raised peaks and ridges,

b. Pressing the weld surfaces of the work pieces together under a first load; c. Vibrating the work pieces relative to one another whereby the friction between the weld surface of the work pieces plasticizes the material of the weld surface of work pieces; and

d. Pressing the weld surfaces of the work pieces under a second load to form a weld interface between the work pieces.

Claim 2: The method of Claim 1 wherein the second load is approximately 86-94% of the yield strength of the second work piece.

Claim 3 : The method of Claim 1 wherein the first load is approximately fifty percent of the second load.

Claim 4: The method of Claim 1 wherein the raised peaks and ridges correspond to areas of the weld surface to receive more thermal energy.

Claim 5. A method of bonding together a first work piece and a second work piece using linear friction welding, where each of the first work piece and the second work piece has a flat weld surface and the second work piece also has a sidewall adjacent the weld surface thereof, the method comprising:

a. Forming a cavity in the weld surface of the second work piece inset from a terminal edge thereof,

b. Forming a notch in the sidewall of the second work piece below the cavity thereof,

c. Pressing the weld surfaces of each of the first work piece and the second piece together under a first load;

d. Vibrating one of the first work piece and the second work piece against the other of the first work piece and the second work piece whereby the friction between the first work piece and the second work piece plasticizes the weld surface of the first work piece and a portion of the weld surface of the second work piece that is not over the notch whereby flash produced from the oscillation of the plasticized weld surface of each of the first work piece and the second work piece collects within the cavity; and

e. Pressing the weld surfaces of each of the first work piece and the second work piece together under a second load to form a weld interface between the first work piece and the second work piece.

Claim 6: The method of Claim 5 wherein the second load is approximately 86-94% of the yield strength of the second work piece. The method of Claim 5 wherein the first load is approximately fifty percent of the