Linear friction welder with helical groove

A linear friction welding system includes a power shaft defining a power shaft axis and including a first eccentric portion and a first power transfer portion, a power transfer rod engaged with the first power transfer portion, an actuator assembly operably coupled with the power transfer rod and configured to move the power transfer rod axially along the power shaft axis, a crank including a second eccentric portion operably coupled with the first eccentric portion, and a second power transfer portion engaged with the power transfer rod, the linear friction welding system configured such that axial movement of the power transfer rod causes rotational movement of the crank with respect to the power shaft about the power shaft axis, a cam follower operably connected to an outer surface of the second eccentric portion, and a ram operably connected to the cam follower and configured to vibrate along a welding axis.

FIELD OF THE INVENTION

The present invention relates to linear friction welding.

BACKGROUND OF THE INVENTION

Friction welding (FW) is a process of joining two components which may be made from the same or different materials. The FW process typically involves pressing one of the two components against the other component with a large amount of force and rapidly moving one of the two components with respect to the other component to generate friction at the interface of the two components. The pressure and movement generate sufficient heat to cause the components to begin to plasticize. Once the two components are plasticized at the contact interface, the relative movement of the two components is terminated and an increased force is applied. As the components cool in this static condition, a weld is formed at the contact interface.

The weld obtained using FW is a solid state bond which is highly repeatable and easily verifiable. For example, the amount of material donated by each component to the formation of the weld, which is referred to as “upset”, is well defined. Therefore, by carefully controlling the energy input into the FW system in the form of friction and forging pressure, the measured upset of a welded assembly provides verification as to the nature of the weld obtained.

As discussed above, relative movement of the two components is a critical facet of FW. Different approaches have been developed to provide the required relative movement. One widely used approach is rotational friction welding (RFW). RFW involves rotation of one component about a weld axis. RFW provides many benefits and is thus a favored welding approach in various industries including aerospace and energy industries.

RFW, however, does have some limitations. For example, in forming a weld, the interface between the two components must be evenly heated to generate a uniform plasticity within each of the components throughout the weld interface. If one area becomes hotter than another area, the material in that hotter area will be softer, resulting in an incongruity in the formed weld. To provide consistent heat generation throughout the component interface, the rotated component is necessarily uniformly shaped about the axis of rotation, i.e., circular. Moreover, since the heat generated is a function of the relative speed between the two materials, more heat will be generated toward the periphery of the rotated component since the relative speed at the periphery is higher than the relative speed at the rotational axis.

In response to the limitations of RFW, linear friction welding (LFW) was developed. In LFW, the relative movement is modified from a rotational movement to a vibratory movement along a welding axis. By controlling the amplitude and the frequency of the linear movement, the heat generated at the component interface can be controlled.

LFW thus allows for welding of a component that exhibits substantially uniform width. LFW, like RFW, is subject to various limitations. One such limitation is that LFW exhibits non-uniform heating along the welding axis due to the linear movement of the vibrated component. For example, when welding two components of identical length along the welding axis, the two components are aligned in the desired as-welded position. Due to the nature of previous LFW systems, this location corresponds to the rearmost position of the component which is moved. The leading edge of the vibrated component is then moved beyond the corresponding edge of the stationary component by a distance equal to the amplitude of the vibration. Moreover, the trailing edge of the vibrated component exposes a portion of the stationary component as the leading edge of the vibrated component moves beyond the corresponding edge of the stationary component. Accordingly, the portion of the vibrating component that moves beyond the corresponding edge of the stationary component and the exposed portion of the stationary component will not be heated at the same rate as the remaining surfaces at the component interface. Therefore, manufacturing process must take the incongruity of the welds into account such as by machining off a portion of the welded components at the leading edge and the trailing edge of the formed weld.

Moreover, in order to achieve the frequency and amplitude necessary to realize a weld, a LFW device must provide for rapid acceleration from a dead stop. The moving component must then be completely stopped and reaccelerated in a reverse direction. As the size of the vibrated component increases, the momentum that must be controlled becomes problematic. Thus, traditional LFW devices incorporate massive components which are very expensive.

A related limitation of LFW processes is that the relative motion between the two components must be terminated in order for the weld to form properly. Merely removing the motive force does not remove the momentum of the vibrated component. Additionally, any “rebound” or damped vibrations of the moving component as it is immobilized weakens the final weld since the plasticized metals begin to cool as soon as the vibrating movement is reduced.

One approach to solving the need to rapidly immobilize the moving component is to jam the motion-inducing system such as by forcibly inserting a device into the motion inducing system. Freezing the system in this fashion can provide the desired stopping time. This approach, however, results in significant forces being transmitted through the system, necessitating oversized components to be able to withstand the shock. Moreover, the exact position of the vibrated component with respect to the stationary component is not known. Therefore, manufacturing processes must account for a possible position error potentially equal to the amplitude of vibration.

Therefore, a LFW system and method which provides consistent welds is beneficial. A LFW system and method which allows for smaller components within the system would be beneficial. A LFW system and method which reduce the errors associated with the LFW process would be further beneficial.

SUMMARY OF THE INVENTION

The present invention in one embodiment is directed to a linear friction welding system includes a power shaft defining a power shaft axis and including a first eccentric portion and a first power transfer portion, a power transfer rod engaged with the first power transfer portion, an actuator assembly operably coupled with the power transfer rod and configured to move the power transfer rod axially along the power shaft axis, a crank including a second eccentric portion operably coupled with the first eccentric portion, and a second power transfer portion engaged with the power transfer rod, the linear friction welding system configured such that axial movement of the power transfer rod causes rotational movement of the crank with respect to the power shaft about the power shaft axis, a cam follower operably connected to an outer surface of the second eccentric portion, and a ram operably connected to the cam follower and configured to vibrate along a welding axis.

In another embodiment, a system includes a power shaft defining a power shaft axis and including a first eccentric portion, a crank including a second eccentric portion coupled with the first eccentric portion, a ram operably coupled with the second eccentric portion and defining a welding axis, a memory including program instructions, and a controller operably connected to the memory, and configured to execute the program instructions to control the phased relationship between the first eccentric portion and the second eccentric portion such that the ram does not vibrate along the welding axis while the power shaft is rotating by axially positioning a power transfer rod coupled to the power shaft and the crank along the power shaft axis, establish a first pressure between two components to be welded after controlling the phased relationship such that the ram does not vibrate, and modify the phased relationship such that the ram vibrates along the welding axis after the first pressure has been established.

DESCRIPTION

Referring toFIG. 1, a linear friction welding system100includes a pressing assembly102, a vibrating assembly104, and a stiffening assembly108, each of which are supported by a frame106. The pressing assembly102includes an upper assembly110and a lower assembly112. The upper assembly110includes a base114and two rocker arm pairs116and118(see alsoFIG. 2) supporting a carriage120.

Continuing withFIG. 2, the lower assembly112is generally aligned with the carriage120and includes a forge platen122supported above a main hydraulic press124. The main hydraulic press124defines a press axis126. An anti-rotation rod128extends from the forge platen122through a lower support plate130. A sensor132is associated with the anti-rotation rod128. In one embodiment, the sensor132is a linear voltage displacement transducer (LVDT).

Returning toFIG. 1, the vibrating assembly104includes a motor140, a cam assembly144, and a ram146. The ram146is rigidly connected to the carriage120at a forward end and is pivotally connected to the cam assembly144at the opposite end through a connecting rod148. The ram146is configured for movement along a weld axis150. The motor140is connected to the cam assembly144through a belt152.

The cam assembly144, shown in additional detail inFIG. 3, includes a power shaft160, an actuator assembly162, a crank164, a retaining sleeve166, and a cam follower168. The cam follower168is pivotably connected to the connecting rod148(this pivoting connection is not shown in the drawings).

The power shaft160, shown in further detail inFIGS. 4-6, includes a coupling portion170, an eccentric portion172, and a power transfer portion174. The power transfer portion174is in the form of a planar trench which extends completely through the power shaft160. An actuator bore176extends from a coupling portion178completely through the power transfer portion174along a power shaft axis of rotation180. The power transfer portion174generally defines a plane which includes the power shaft axis of rotation180.

The coupling portion170is configured to be operably coupled with the motor140through the belt152(FIG. 1) such that the power shaft160can be rotated about the axis of rotation180. Returning toFIG. 6, the coupling portion170has an origin182which is located on the axis of rotation180when the system100is assembled. The eccentric portion172has an origin184that is located directly below the origin182when the shaft160is in a “zero” position as depicted inFIG. 6. Accordingly, the outer periphery of the eccentric portion172is closer to the axis of rotation180at locations above a horizontal centerline186of the eccentric portion172than at corresponding locations below the horizontal centerline186.

With reference toFIGS. 7-10, the crank164includes an eccentric portion200. A bore202extends completely through the crank164and two grooves204/206extend outwardly from the bore202completely through the eccentric portion200. The grooves204/206extend generally helically about a groove axis208. The grooves204/206are “generally” helical in that the angular positions of the grooves204/206at locations closer to a first end portion210of the crank164change more quickly than at locations closer to a second end portion212. The generally helical nature of the grooves204/206is explained with further reference toFIG. 9.

InFIG. 9, the line214represents the location of the center of one of the grooves204/206from a location close to the end portion210(the top of the line214as depicted inFIG. 9) to a location close to the end portion212. Each location on the groove axis208is associated with a corresponding groove location that lies on a line orthogonal to the groove axis208at the intersection of the orthogonal line with the line214. For example, a line216is orthogonal to the groove axis208at groove axis location218and intersects the groove centerline214at a groove location220.

The grooves204and206are generally helical in that as the axial location along the groove axis208changes between the groove axis locations located close to the end portion210(e.g., groove axis locations222and224), the angular difference (i.e., the rotation of an associated orthogonal line, e.g., line216, about the axis208) between the associated groove locations (e.g., groove locations226and228) is much greater than the angular difference between the groove locations (e.g., groove axis locations230and232) associated with groove axis locations (e.g., groove locations234and236), even though the axial distance between the upper groove axis locations is the same as the axial distance between the lower groove axis locations.

Returning toFIG. 8, the bore202has an origin240while the eccentric portion200has an origin242that is located directly above the origin240when the crank164is in a “zero” degree position with the grooves204and206aligned with a vertical centerline244of the bore202as depicted inFIG. 8. Accordingly, while the grooves204and206are mirror images of each other (i.e., spaced 180 degrees apart at each location along the groove axis208), the groove204is deeper than the groove206in the view depicted inFIG. 8since the groove204extends through the thickest portion of the eccentric portion200. In this embodiment,FIG. 8depicts the grooves204and206at the groove axis location closest to the end portion210.FIG. 10depicts the grooves204and206at the groove axis location closest to the end portion212, also referred to herein as the “90 degree” location with the grooves204and206aligned with the vertical centerline244. InFIG. 10, the grooves204and206have about the same depth.

With reference toFIG. 3, the actuator assembly162includes an actuator rod assembly250fixedly mounted to a ball and screw assembly252. The actuator rod assembly250, also shown inFIGS. 11 and 12, includes an actuator rod254and an actuator rod holder256. The actuator rod254includes a bore258at one end while the opposite end is configured to be rotatably received within a coupling portion260of the actuator rod holder256. The coupling portion260is configured to allow the actuator rod254to rotate freely therein while maintaining a fixed axial relationship between the actuator rod holder256and the actuator rod254.

The actuator rod holder256further includes a coupling portion262which is press fit within a coupling portion264of the ball and screw assembly252(seeFIG. 3). The ball and screw assembly252may include a ball and screw Model No. R-44 commercially available from Rockford Ball Screw Company of Rockford Ill.

Assembly of the cam assembly144is described with initial reference toFIG. 13. The cam assembly144is assembled by insertion of the actuator rod254within the actuator bore176(seeFIG. 5) of the power shaft160through the coupling portion178. The actuator rod254and power shaft160are then inserted into the bore202of the crank164and the grooves204/206, the power transfer portion174, and the bore258are aligned. A power transfer rod270is then inserted into the aligned grooves204/206, power transfer portion174, and bore258to form an eccentric subassembly272. The power transfer rod270is sized to provide a close fit with each of the grooves204/206, power transfer portion174, and bore258. In this embodiment, the power transfer rod270includes a bore274extending lengthwise through the entire length of the power transfer rod270.

The eccentric subassembly272(shown inFIG. 14with bearing assemblies276and278) is then positioned within the retaining sleeve166. The retaining sleeve166is sized to fit tightly over the eccentric portion200of the crank164so as to retain the power transfer rod270within the grooves204/206, power transfer portion174, and bore258. The combined eccentric subassembly272and retaining sleeve166are then inserted within the cam follower168which is positioned in a cam assembly casing280. Once within the cam assembly casing280, the axial location of the power shaft160, the crank164, the retaining sleeve166, and the cam follower168along the axis of rotation180is fixedly established by bearing assemblies276and278.

With reference toFIGS. 1,15, and16, the stiffening assembly108includes two stiffening arms290and292which are pivotably connected to the frame106. Each of the stiffening arms290/292includes a respective turnbuckle assembly294/296which can be used to adjust the length of the stiffening arms290/292. The stiffening arms290/292pivotably support a base298.

The base298supports two linear bearings300/302. The base298is further connected to two hydraulic presses or cylinders304/306. The hydraulic cylinders304/306may be model 4HHFHF14K hydraulic cylinders available from The Sheffer Corporation of Cincinnati Ohio. The hydraulic cylinders304/306are pivotably mounted to the frame106through respective pivot assemblies308/310. The stiffening assembly108further includes two linear bearings312and314which are mounted to the frame106at a location between the hydraulic cylinders304/306. The linear bearings300/302/304/306may be, for example, TYCHOWAY model R987144745 linear bearings available from Bosch Rexroth Corporation of Hoffman Estates, Ill.

The linear friction welding system100is operated under the control of a welding control system320depicted inFIG. 17. The control system320includes an I/O device322, a processing circuit324and a memory326. The control system320is operably connected to a hydraulic pump328, the motor140, an actuator motor330, and a sensor suite332. If desired, one or more of the components of the system320may be provided as a separate device which may be remotely located from the other components of the system320.

The I/O device322may include a user interface, graphical user interface, keyboards, pointing devices, remote and/or local communication links, displays, and other devices that allow externally generated information to be provided to the control system320, and that allow internal information of the control system320to be communicated externally.

The processing circuit324may suitably be a general purpose computer processing circuit such as a microprocessor and its associated circuitry. The processing circuit324is operable to carry out the operations attributed to it herein.

Within the memory326are various program instructions334. The program instructions334, some of which are described more fully below, are executable by the processing circuit324and/or any other components of the control system320as appropriate. Parameter databases336are also located within the memory326.

Further details regarding the control system320and the linear friction welding system100are provided with reference to the procedure340ofFIG. 18. The processing circuit324executes the program instructions334to execute at least some of the procedure340ofFIG. 18. In different embodiments, the procedure340may be modified to include more or fewer steps depending upon the specific criterion.

At block342ofFIG. 18, the components which are to be welded are loaded into the linear friction welding system100. One of the components is fixedly positioned on the forge platen122while the other component is fixedly attached to the carriage120. The control parameters are loaded into the parameter databases336at block344. Parameters which may be loaded include scrub parameters, burn parameters, and forging parameters, each of which is further described below.

At block346, the stiffening assembly108is engaged with the component positioned on the forge platen122and at block348the system phase angle of the linear friction welding system100is established at a “0” system phase angle. A system phase angle of zero may be established using stored position information of the power shaft160and the axial location of the actuator rod254. The system phase angle is then verified by rotating the power shaft160at a low speed. Once the power shaft160is rotating, the processing circuit324, using one or more sensors from the sensor suite332, monitors the ram146for movement. In one embodiment, the sensor suite332includes an LVDT positioned to monitor movement of the ram146. When the system phase angle is zero, the ram146is motionless as explained with initial reference toFIG. 19.

FIG. 19depicts the power shaft160at its zero position with the origin184of the eccentric portion172located directly beneath the origin182of the coupling portion170(not shown inFIG. 19), with the origin182coincident with the axis of rotation180of the power shaft160.FIG. 19further depicts the crank164at its zero position with the origin242of the eccentric portion200located directly above the origin240of the bore202. The offset between the origin182and the origin184is selected to be the same as the offset between the origin240and the origin242. Accordingly, when the crank164and the power shaft160are in the arrangement ofFIG. 19, the eccentricity of the power shaft160is exactly offset by the eccentricity of the crank164.

Consequently, the origin242of the outer perimeter of the eccentric portion200is coincident with the axis of rotation180. Thus, the outer surface of the eccentric portion200is exactly centered on the axis of rotation180. Accordingly, as the eccentric portion200rotates about the axis of rotation180, every portion of the outer periphery of the eccentric portion200is located equidistant from the axis of rotation180. Therefore, the eccentric portion200simply spins within the cam follower168and the ram146does not move.

If there is any movement of the ram146, then the origin242of the eccentric portion200, the origin184of the eccentric portion172, and the origin182of the coupling portion170are not aligned as inFIG. 19. By way of example,FIG. 20depicts the power shaft160at its zero position with the origin184of the eccentric portion172located directly beneath the origin182of the coupling portion170as inFIG. 19. The eccentric portion200, however, has been rotated 90 degrees from the zero degree position (also shown inFIG. 8) to the ninety degree position (also shown inFIG. 10). Accordingly, while the origin240of the bore202is still aligned with the origin184of the eccentric portion172, the origin242of the eccentric portion200has been rotated in a counterclockwise direction by ninety degrees with respect to the orientation ofFIG. 19. This configuration is referred to herein as a “ninety degree system phase angle”. The offset between the origin242and the axis of rotation180results in movement of the ram146.

Specifically, as the power shaft160is rotated by the motor140, rotational force is transferred from the power transfer portion174of the shaft160to the power transfer rod270. Rotational force is further transferred from the power transfer rod270to the crank164by contact of the power transfer rod270with both the sidewall of the groove204and the side wall of the groove206. Accordingly, the origin242of the eccentric portion200is forced to rotate about the axis of rotation180along a circle350(seeFIG. 20). The periphery of the eccentric portion200thus sweeps an outermost area bounded by the circle352ofFIG. 20. For a given location of the eccentric portion200, the point of the eccentric portion200directly opposite to the point of the eccentric portion200farthest from the axis of rotation180lies on a circle354which defines the innermost location of the outer periphery of the eccentric portion200. For any axis passing through the axis of rotation and both the innermost circle354and the outermost circle352such as the axis356, the difference between the intersection358with the innermost circle354and the intersection360with the outermost circle352is the vibration amplitude of the system100. This difference is at a maximum when the cam assembly144is at a 90 degree system phase angle in this embodiment.

Modification of the system phase angle from a non-zero degree phase angle to the zero degree system phase angle ofFIG. 19is accomplished by using the actuator rod254to force the power transfer rod270to move axially within the grooves204and206. Specifically, both the crank164and the power shaft160are constrained from axial movement. Accordingly, axial movement of the actuator rod254forces the power transfer rod270to move axially within the power transfer portion174. Because the power transfer portion174extends axially along the axis of rotation180, axial movement of the power transfer rod270within the power transfer portion174is not impeded.

Axial movement of the power transfer rod270is somewhat impeded, however, by the generally helical grooves204and206. Specifically, the grooves204/206are not aligned with the axis180. Rather, the grooves204/206extend generally helically about the groove axis208which is aligned with the axis of rotation180. Accordingly, axial movement of the power transfer rod270forces the power transfer rod270against the sidewalls of the grooves204/206. Because the crank164is axially constrained, the force applied to the sidewalls of the grooves204/206because of the axial movement of the actuator rod254causes the crank164to rotate on the eccentric portion172of the power shaft160.

The axial position of the actuator rod254thus controls the orientation of the crank164with respect to the power shaft160. Accordingly, the phase between the eccentric portion172of the shaft160and the eccentric portion200of the crank164can be controlled by axially positioning the actuator rod254. The location of the actuator rod254is controlled by the processing circuit324which controls the actuator motor330which is connected to the ball and screw assembly252(seeFIG. 3). Sensors within the sensor suite332may be used to provide axial position data of the actuator rod254when controlling the motor330.

Returning to the procedure340ofFIG. 18, once a zero system phase angle has been established at block348, scrub parameters are established at block370. Scrub parameters are established under the control of the processing circuit324which controls the main hydraulic press124to raise the weld component mounted on the forge platen122into contact with the weld component mounted on the carriage120. By monitoring the pressure of the hydraulic press124, and/or using other sensory inputs, the processing circuit324determines when the two weld components are brought into contact. If the contact happens at a travel location of the forge platen122that is not expected, a user warning may be issued.

Once the components to be welded are in contact, the initial positions of the two weld components are stored, such as by storing the output of the sensor132, and the processing circuit324controls the main hydraulic press124to achieve a desired scrub pressure based upon a value stored in the parameters database336. The processing circuit324further obtains a scrub frequency from the parameters database336and controls the speed of the motor140to a speed corresponding to the desired scrub frequency. In embodiments wherein frequency is modified before modification of the system phase angle, the motor140at this point in the procedure will be rotating at a speed associated with the scrub frequency while the ram146remains motionless. The processing circuit324then controls motor330to axially position the actuator rod254at a location associated with a system phase angle that provides the desired scrub amplitude of the ram146in accordance with a scrub amplitude parameter stored in the parameter database336.

As discussed above with respect toFIGS. 19-20, modification of the system phase results in displacement of the origin242of the eccentric portion200resulting in oscillation of the eccentric portion200. This oscillation is transferred to the cam follower168(seeFIG. 3). Accordingly, the cam follower168is forced to rotate. The end of the connecting rod148which is coupled to the cam follower168is thus forced to follow the movement of the cam follower168. The coupler rod148translates the movement of the coupler receiving end to a linear vibratory movement along the weld axis150at the end of the connecting rod148coupled with the ram146.

Once the scrub pressure, scrub frequency, and scrub amplitude have been established, a scrub timer is started and counted down using a system clock or other appropriate clock. As the scrub is performed, a “wiping action” is generated by the linear friction welding system100. The wiping action is a result of the incorporation in the linear friction welding system100of the rocker arm pairs116and118. As the ram146vibrates along the weld axis150, the carriage120“swings” on the rocker arm pairs116and118as indicated by the arrow360ofFIG. 1. The vertical position of the carriage120thus varies as a function of the length of the rocker arm pairs116and118and the amplitude of the scrub vibration.

The cyclical variation in the height of the carriage120generates a cyclical variation in the pressure between the welding components. For example, when the ram146is at the middle location of the stroke, the carriage120is at its lowest vertical position. As the ram146oscillates, the carriage120swings along the arc defined by the rocker arm pairs116and118. Accordingly, the carriage120moves upwardly from the lowest vertical position, thereby relieving some of the pressure between the weld components as the ram146moves forwardly or backwardly from the mid-stroke position. Of course, this pressure variation could be removed by increasing the reaction speed of the main hydraulic press and/or increasing the sensitivity of the pressure control associated with positioning of the main hydraulic press122. Maintaining some amount of wiping action, however, is desired in order to increase the efficiency of the system.

Specifically, as two weld components are scrubbed, relative linear movement of the weld components is used to generate heat in the weld components because of friction between the weld components. As the temperature of the weld components increases, one or both of the components begins to plasticize at the weld interface. The plasticized material acts like a liquid, allowing the opposing surface to hydroplane on the plasticized surface. The reduced friction which results when the two surfaces are hydroplaning reduces the conversion of linear movement into heat.

Accordingly, for a given amount of linear movement, the resulting heat energy transferred to the two weld components is reduced when hydroplaning is occurring. The cyclical variation in pressure resulting from the wiping action of the linear friction welding system100, however, disrupts the plasticized layer between the weld components, reducing the hydroplaning effect and increasing the conversion of linear movement into heat. Depending upon the particular dimensions of the linear friction welding system100and the materials being welded, 10-25 percent less energy may be used to perform a particular scrub when wiping action as described herein is provided. Moreover, the uniformity of the energy transfer is increased along the weld component interface, resulting in a more consistent weld.

As will be recognized by those of skill in the art, the movement of the ram146is not purely along the axis150. Specifically, at the connection with the connecting rod148, the ram146moves substantially completely along the axis150while the end of the ram146that is rigidly connected to the carriage120is deflected away from and toward the axis150because of the rocker arm pairs116and118which force the carriage120to oscillate. Similarly, while the carriage120is described herein as oscillating because of the rocker arm pairs116and118, the amount of cross-axis movement may be significantly reduced by lengthening the rocker arm pairs116and118resulting in substantially pure axial movement.

When the desired scrub has been performed at block372, burn parameters are established in the linear friction welding system100at block374. Specifically, the processing circuit324controls the main hydraulic press124to achieve a desired burn pressure based upon a value stored in the parameters database336. The processing circuit324further obtains a burn frequency from the parameters database336and controls the motor140to a speed corresponding to the desired burn frequency. The processing circuit324then controls the motor330to an axial location corresponding to the desired burn amplitude based upon burn amplitude data stored in the parameters database336. In one embodiment, all of the changes from the scrub parameters to the burn parameters are controlled to occur substantially simultaneously.

Once the burn pressure, burn frequency, and burn amplitude have been established, a burn timer is started and counted down using a system clock or other appropriate clock, and a burn is performed at block376. During the burn, the processing circuit324obtains input from the sensor suite332and modifies the speed of the motor140as needed to maintain the desired burn frequency, modifies the axial location of the actuator rod254to maintain the desired amplitude, and controls the main hydraulic press124to maintain the desired burn pressure.

When the burn timer has expired, movement of the ram146is terminated at block378. Movement can be terminated under the control of the processing circuit324by adjusting the axial location of the actuator rod254using the motor330to obtain a system phase angle of zero. Then, while the motor140rotates with no movement of the ram146, the processing circuit324controls the main hydraulic press124to establish a forge pressure at block380between the two weld components based upon data stored in the parameters database336. The forge pressure applied to properly burned components which are not moving with respect to one another welds the two components together into a welded unit.

Once the components have been welded, the welded unit can be removed (block382) and the weld verified (block384). If desired, the processing circuit324may be used to determine the weld quality. Specifically, at block370, the initial position of the forge platen122as the two weld components came into contact was stored. At the completion of the welding of the two components into a welded unit, the processing circuit324may obtain position data from the sensor132indicative of the position of the forge platen122after a weld has been formed. The difference between the two locations indicates a loss of material from the two components at the contact point of the two components.

Additionally, the temperature of the two components can be established, either by sensory input from the sensor suite332and/or by historic knowledge of the effects of the scrub and burn processes on the materials of the two components. Furthermore, the actual pressure, frequency, and amplitude of the procedure340provide precise information about the amount of energy placed into the components during the procedure340. Consequently, the foregoing data may be used to calculate the amount of material lost due to flash and the nature of the weld formed.

The linear welding system100thus provides precise and independent control of pressure applied as well as the frequency and amplitude of oscillation during the procedure340. Accordingly, in addition to modifying the pressure between two components during scrubbing, burning, and forging of two components, the frequency and amplitude of oscillation may also be independently modified between the scrubbing and burning procedures.

By way of example,FIG. 21depicts a chart400depicting scrubbing, burning, and forging parameters during an exemplary welding process. At T=0, scrub pressure402, scrub frequency404, and scrub amplitude406are established. For titanium components, the scrub pressure402may be about 5,000 pounds per square inch (“psi”), the scrub frequency may be about 20 hertz (“Hz”), and the scrub amplitude406may be about 6 millimeters (“mm”). At T=1, which in this example may be after about 2 seconds, the scrub pressure402is changed to a burn pressure408of about 7,500 psi, the scrub frequency404is changed to a burn frequency410of about 40 Hz, and the scrub amplitude406is changed to a burn amplitude412about 4 mm. When the desired conditions have been established at the interface between the two components, then at T=2 the frequency414and amplitude of oscillation416is established at zero while a forge pressure418of about 15,000 psi is established. The two components then form a weld under the forge pressure418.

Moreover, in addition to the ability to independently control pressure and oscillation frequency and amplitude, the linear friction welding system100provides the ability to rapidly and precisely vary the various parameters. In one embodiment wherein the motor140is a servo motor nominally rated at 75 horsepower and 6,000 RPM with 2.0 service factor, the movement of the ram146following a burning process can be completely stopped within 0.25 seconds and more preferably within 0.1 sec.

In one embodiment, the actuator motor330is a model SGMGV-13D3A61 Sigma-5 servo motor manufactured by Yaskawa America, Inc. of Waukegan, Ill., coupled with a model SGDV-5R4D11A controller also manufactured by Yaskawa America, Inc. of Waukegan, Ill., both of which are commercially available from Applied Machine & Motion Control, Inc. of Cincinnati, Ohio.

Precision of amplitude control throughout the available range of amplitude is enhanced by the incorporation of the generally helical grooves204/206. Specifically, incorporation of the generally helical grooves204/206results, in the present embodiment, in a linear relationship between axial position of the actuator rod254and the system phase angle. The relationship between axial position of the actuator rod254and system phase angle is maintained in accordance with the parameters set forth in Table 1 below:

Table 1 shows the amplitude (in millimeters and inches) of vibration of the ram146that is achieved for different travel distances (Actuator Travel) of the actuator rod254. Table 1 further shows the system phase angle related to the axial location of the actuator rod254in both degrees and radians, as well as the movement of the shaft of the actuator motor330(in revolutions) that is needed to move the actuator rod254to the associated axial location. The precise orientation of the shaft of the actuator motor330is provided by incorporation of 24 Bit encoders which generate 16,777,215 encoder counts per revolution when controlling the actuator motor330.

The encoder on the actuator motor330and another encoder on the motor140are controlled by a model number DMC-4010-C012-I000 1-axis Ethernet/RS232 controller commercially available from Galil Motion Control, Inc. of Rocklin, Calif. The output of the encoder on the shaft of the motor140and the encoder on the actuator motor330, which may be included within the sensor suite332, are provided to the processing circuit324which uses the sensed position of the shaft of the motor140and the shaft of the actuator motor330as part of a control loop to finely control servo drivers which control the rotation of the motor140and of the actuator motor330. The control loop may be executed by the processing circuit324up to 1,000 times per second or faster. Accordingly, vibration of the ram146can be modified within 1/1,000 of a second of the determination that ram oscillation is to be modified.

The ability to rapidly stop all relative movement of the weld components provides for better welds and contributes to the increased efficiency of the linear friction welding system100discussed above. Moreover, the weld components can be placed under forge pressure without any axial loads (i.e., loads orthogonal to the forge axis) on the components or the associated tooling. In contrast, prior art systems terminate oscillation by application of a large axial force on the weld components resulting in the forge pressure being applied in the presence of a large axial load. The absence of an axial load on the weld components increases the quality of the final weld.

Rapid termination of movement of the ram146is also enhanced because the motor140and the associated power shaft160, actuator162, and crank164continue to rotate at a high rate. Accordingly, the stopping of movement of the ram146is not dependent upon countering inertia of the motor140and the associated power shaft160, actuator162, and crank164. In addition to increased stopping speed, this results in reduced shock to the motor140.

Moreover, the stiffening assembly108may be used to reduce undesired movement of the weld component positioned on the forge platen122, thereby increasing efficiency of the welding system100as well as providing increased weld quality. The stiffening assemblies are adjusted once a weld component is positioned on the platen122by adjusting the length of the stiffening arms282/294using the turnbuckle assemblies296/298. The stiffening arms282/294are adjusted so that the linear bearings300/302are substantially aligned with the linear bearings312/314with the weld component positioned therebetween. In some instances, temporary fixtures may be attached to the weld component with one or more of the linear bearings300/302/312/314abutting the temporary fixture.

Once the weld component and stiffening arms292/294are positioned, the processing circuit324may be used to control flow of hydraulic fluid to the hydraulic cylinders306/308. If desired, the same hydraulic system used for the main hydraulic press may be used. The hydraulic cylinders306/308then pull the linear bearings300/302toward the linear bearings312/314against the weld component positioned on the platen122. By clamping the weld component in this manner, movement of the weld component because of movement of the ram146is substantially reduced. Moreover, because the weld component is clamped between opposed linear bearings, the ability to finely control the pressure applied to the two weld component in the welding system100with the main hydraulic press is not unacceptably hindered.

The ability to modify the amplitude of the ram146and frequency of the motor140enables the linear friction welding system100to be used to form welds using different types of materials without requiring retooling of or physical modifications of the linear friction welding system100. The precise control further enables unique capabilities including modified starting and stopping locations and varied scrub profiles. If desired, various modifications to the linear friction welding system100may be made to optimize the system100for particular welding operations.

While the present invention has been illustrated by the description of exemplary processes and system components, and while the various processes and components have been described in considerable detail, the applicant does not intend to restrict or in any limit the scope of the appended claims to such detail. Additional advantages and modifications will also readily appear to those skilled in the art. The invention in its broadest aspects is therefore not limited to the specific details, implementations, or illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.