Patent Publication Number: US-2022226926-A1

Title: Phase Change Assembly For A Linear Friction Welding System

Description:
This application is a divisional application of co-pending U.S. application Ser. No. 16/751,343, filed on Jan. 24, 2020 which is a divisional application of U.S. application Ser. No. 16/161,611, filed on Oct. 16, 2018 which issued as U.S. Pat. No. 10,569,355 on Feb. 25, 2020, which is a divisional application of U.S. application Ser. No. 14/820,806, filed on Aug. 7, 2015, which issued as U.S. Pat. No. 10,099,313 on Oct. 16, 2018, the entirety of which are each incorporated by reference herein. 
    
    
     FIELD 
     The present disclosure relates to linear friction welding. 
     BACKGROUND 
     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 
     The present disclosure in one embodiment provides a phase change assembly for a linear friction welding system which includes a single input shaft and a single output shaft with respective first and second gears, and a carriage rotatably supporting a third gear operably connected to the first and second gear and one of a roller and a fourth gear operably connected to the first and second gear. A linear actuator is operably connected to the carriage. A first stop is configured to stop movement of the carriage by the linear actuator in a first direction to provide a first predetermined phase relationship between the input shaft and the output shaft, and a second stop is configured to stop movement of the carriage by the linear actuator in a second direction opposite the first direction to provide a second predetermined phase relationship between the input shaft and the output shaft. 
     In some embodiments, a linear friction welding system includes a ram configured to vibrate along a welding axis, a cam follower operably connected to the ram, an eccentric including an eccentric outer periphery operably engaged with the cam follower, and an inner periphery, a first power shaft slidingly engaged with the eccentric, a second power shaft eccentrically engaged with the inner periphery, a timing component operably connected to the first power shaft and the second power shaft, a motor configured to drive the timing component, and a phase change mechanism engaged with the timing component and movable between a first position defining a first phase relationship between the first power shaft and the second power shaft, and a second position defining a second phase relationship between the first power shaft and the second power shaft. 
     In some embodiments, the timing component includes a timing component load segment between the first power shaft and the second power shaft, the phase change mechanism defines a first timing component load segment length when the phase change mechanism is in the first position, the phase change mechanism defines a second timing component load segment length when the phase change mechanism is in the second position, and the first timing component load segment length is greater than the second timing component load segment length. 
     In other embodiments, the timing component is operably connected to the first power shaft through a first gear, the timing component is operably connected to the second power shaft through a second gear, and the phase change mechanism includes a third gear operably engaged with the timing component. 
     In further embodiments, the third gear is operably engaged with the timing component load segment, and the phase change mechanism includes a fourth gear operably engaged with a feed segment of the timing component. 
     In certain embodiments, the timing component is a timing belt. 
     In yet another embodiment, the phase change mechanism further includes a carriage rotatably supporting the third gear and the fourth gear, and the carriage is movable by a linear actuator between the first position and the second position. 
     In another embodiment of the system, the carriage is movable between the first position and the second position along a phase change axis, the phase change mechanism includes a transfer plate fixedly connected to the carriage and to an actuator piston, the transfer plate is arranged to contact a first stop when the carriage is in the first position, and the transfer plate is arranged to contact a second stop when the carriage is in the second position. 
     In additional embodiments of the system, the first stop is selectably positionable at any one of a first plurality of locations so as to modify the location of the first position along the phase change axis. 
     In other embodiments of the system, the second stop is selectably positionable at any one of a second plurality of locations so as to modify the location of the second position along the phase change axis. 
     In yet other embodiments, the first stop comprises a first threaded bolt configured such that rotation of the first threaded bolt moves the first stop from a first of the first plurality locations to a second of the first plurality locations, and the second stop comprises a second threaded bolt configured such that rotation of the second threaded bolt moves the second stop from a first of the second plurality of locations to a second of the second plurality of locations 
     Another embodiment is directed to a method of operating a linear friction welding system that includes (i) a ram configured to vibrate along a welding axis, (ii) a cam follower operably connected to the ram, (iii) an eccentric including an eccentric outer periphery operably engaged with the cam follower, and an inner periphery, (iv) a first power shaft slidingly engaged with the eccentric, (v) a second power shaft eccentrically engaged with the inner periphery, (vi) a first timing component configured to drive both the second power shaft and a phase change assembly drive shaft, (vii) a motor configured to drive the first timing component, and (viii) a phase change assembly driven by the phase change assembly drive shaft. 
     The method includes positioning the phase change assembly in a first configuration thereby establishing a phase relationship between the first power shaft and the second power shaft whereat the ram does not vibrate when the first power shaft and the second power shaft rotate, and driving the timing component with the motor. Driving the motor results in driving the first power shaft and the phase change assembly with the timing component with the phase change assembly in the first configuration and driving the driving the second power shaft with the phase change assembly while the phase change assembly is in the first configuration. A establishing a scrub pressure is then established between two components to be welded with the phase change assembly in the first configuration while the first timing component is being driven. 
     When the scrub pressure is applied, a second phase relationship between the first power shaft and the second power shaft is established by moving the phase change assembly to a second configuration while the first power shaft and the second power shaft are being driven, thereby causing the ram to vibrate along the welding axis. 
     When the scrub is complete, the first phase relationship between the first power shaft and the second power shaft is reestablished by returning the phase change assembly from the second configuration to the first configuration resulting in stoppage of movement between the components. A forge pressure is then established between the two components with the phase change assembly returned to the first configuration. 
     In one or more embodiments, moving the phase change assembly to the second configuration includes lengthening a load segment of a second timing component of the phase change assembly. 
     In one or more embodiments, lengthening the load segment includes moving a carriage rotatably supporting a gear engaged with the second timing component load segment along a phase change axis. 
     In one or more embodiments moving the carriage includes moving the carriage from a first location associated with the first configuration toward a second location associated with the second configuration with a linear actuator. 
     In one or more embodiments moving the phase change assembly to the second configuration includes stopping movement of the carriage toward the second location with a first stop. 
     In one or more embodiments, a method includes determining a desired ram vibration amplitude and setting a position of the first stop based upon the desired ram vibration amplitude. 
     In one or more embodiments returning the phase change assembly includes moving the carriage toward the first location with the linear actuator, and stopping movement of the carriage toward the first location with a second stop. 
     In one or more embodiments positioning the phase change assembly at the first location includes positioning the second stop at a location whereat when the carriage contacts the second stop the ram does not vibrate when the first power shaft and the second power shaft rotate. 
     In one or more embodiments setting the position of the first stop includes changing the location of the first stop by rotating a first threaded bolt. 
     In one or more embodiments positioning the second stop includes changing the location of the second stop by rotating a second threaded bolt. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure may take form in various system and method components and arrangement of system and method components. The drawings are only for purposes of illustrating exemplary embodiments and are not to be construed as limiting the disclosure. 
         FIG. 1  depicts a partial side plan view of a linear friction welding system in accordance with principles of the disclosure; 
         FIG. 2  depicts a partial front cross-sectional view of the system of  FIG. 1 ; 
         FIG. 3  depicts a top cross-sectional view of the vibrating system of the linear friction welding system of  FIG. 1  depicting an eccentric portion of an inner power shaft positioned within an eccentric, with an eccentric outer surface and an outer power shaft engaged with the eccentric; 
         FIG. 4  depicts a front cross-sectional view of the vibrating system of  FIG. 3 ; 
         FIG. 5  depicts a rear plan view of the motor, vibrating system and phase change assembly of  FIG. 1 ; 
         FIG. 6  depicts a perspective view of the interior of the phase change assembly of  FIG. 5 ; 
         FIG. 7  depicts a plan view of the interior of the phase change assembly of  FIG. 6  with the phase change mechanism in a first position; 
         FIG. 8  depicts a perspective view of the phase change mechanism of the phase change assembly depicted in  FIG. 7 ; 
         FIG. 9  depicts partial perspective view of the phase change assembly of  FIG. 5  depicting the linear actuator and the phase change mechanism; 
         FIG. 10  depicts a schematic view of the control system of the linear friction welding system of  FIG. 1 ; 
         FIG. 11  depicts a simplified plan view of the phase change assembly of  FIG. 5  with the phase change mechanism in a first position; 
         FIG. 12  depicts a simplified plan view of the phase change assembly of  FIG. 5  with the phase change mechanism in a second position; and 
         FIG. 13  depicts a procedure that can be executed under the control of the control system of  FIG. 10  to form a welded unit with the linear friction welding system of  FIG. 1 ; 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a linear friction welding system  100  includes a pressing assembly  102  and a vibrating assembly  104  positioned within a frame  106 . The pressing assembly  102  includes an upper assembly  108  and a lower assembly  110 . The upper assembly includes a base  112 , and two rocker arm pairs  114  and  116  supporting a carriage  118  as further shown in  FIG. 2 . 
     Continuing with  FIG. 2 , the lower assembly  110  is generally aligned with the carriage  118  and includes a forge platen  120  supported above a main hydraulic press  122 . The main hydraulic press  122  defines a press axis  124 . An anti-rotation rod  126  extends from the forge platen  120  through a lower support plate  128 . A sensor  130  is associated with the anti-rotation rod  126 . In one embodiment, the sensor  130  is a linear voltage displacement transducer (LVDT). 
     Returning to  FIG. 1 , the vibrating assembly  104  includes a motor  140 , a phase change assembly  142 , a cam assembly  144 , and a ram  146 . The ram  146  is pivotably connected to the carriage  118  at a forward end and is pivotably connected to the cam assembly  144  at the opposite end through a connecting rod  148 . The ram  146  is configured for movement along a weld axis  150 . The motor  140  is connected to the cam assembly  144  and the phase change assembly  142  through a belt  152 . A belt tensioner  154  is provided for the belt  152  which is driven by a geared shaft  158  of the motor  140 . 
     The cam assembly  144 , shown in more detail in  FIGS. 3-4 , includes an inner power shaft  160 , an outer power shaft  162 , a coupler  164 , an eccentric  166 , and a cam follower  168 . The inner power shaft  160 , which in one embodiment is a “second power shaft”, is operably coupled with the motor  140  through the belt  152  and a gear  156  (see  FIG. 1 ) and rotates about an axis of rotation  170 . The inner power shaft  160  includes an eccentric portion  172  and a projection  174 . The outer power shaft  162 , which in one embodiment is a “first power shaft”, is operably coupled with the motor  140  through the belt  152  and the phase change assembly  142 , as discussed in further detail below, and also rotates about the axis of rotation  170 . The outer power shaft  162  includes a cavity  176  configured to rotatably receive the projection  174 . Rotatable engagement of the projection  174  within the cavity  176  keeps both the inner and outer power shafts  160 / 162  coaxial with the axis of rotation  170 . 
     The coupler  164  is a modified Oldham coupler including one bifurcated tongue  178  which mates with a groove  180  in the outer power shaft  162  (see  FIG. 3 ) and a second bifurcated tongue  182 , rotated ninety degrees with respect to the bifurcated tongue  178 , which mates with a groove  184  in the eccentric  166  (see  FIG. 4 ). The eccentric  166  further includes an outer eccentric periphery  186  and an inner periphery  188  defining a through-bore  190 . The bore  190  is sized to rotationally receive the eccentric portion  172  of the inner power shaft  160 . The outer eccentric periphery  186  defines a diameter that is closely fit within the inner diameter of the cam follower  168 . 
     The connecting rod  148  of the cam assembly  144  is pivotably connected to the ram  146  through a pivot  192  (see  FIG. 1 ). The ram  146  is in turn pivotably connected to the carriage  118  through a lower pivot pair  194  (only one is shown). The lower pivot pair  194  also pivotably connects the carriage  118  with a rearward rocker arm of each of the rocker arm pairs  114  and  116 . Another lower pivot pair  196  shown in  FIGS. 1 and 2  pivotably connects the carriage  118  with a forward rocker arm of each of the rocker arm pairs  114  and  116 . Four pivots  198  pivotably connect each of the rocker arms in the rocker arm pairs  114  and  116  to the base  112 . 
     As noted above, the outer power shaft  162  is operably coupled with the motor  140  through the phase change assembly  142 . The indirect coupling is described with initial reference to  FIG. 5  which shows the belt  152  configured to drive a phase change assembly shaft  210  through a gear  212 . The shaft  210  drives the outer power shaft  162  through the phase change assembly  142  which is depicted in  FIG. 6  with its front wall removed. 
     The phase change assembly  142  includes a gear  214 , which in one embodiment is a first gear, connected to the shaft  210 . A timing belt  216  (which in one embodiment is a “second timing component”) operably connects the gear  214  with a gear  218 , which in one embodiment is a second gear, which is operably connected to the shaft  162 . The belt  216  is engaged with four tensioners  220 ,  222 ,  224 , and  226 , and a phase change mechanism  228 . 
     The phase change mechanism  228  is further depicted in  FIGS. 7 and 8  and includes a carriage  230  which rotatably supports two gears  232  (which in one embodiment is a “fourth gear”) and  234  (which in one embodiment is a “third gear”), although in some embodiments a roller is used in place of one of the gears  232  and  234 . The carriage  230  is slidably supported within the phase change assembly  142  on one side by rail  236  which slides within guides  238  and  240  ( FIG. 7 ) and on the other side by rail  242  which slides within guides  244  and  246  ( FIG. 8 ). A transfer plate  248  is mounted to, or formed integrally with, the rear side of the carriage  230 . 
     As shown in  FIG. 9 , the transfer plate  248  is fixedly connected to a piston  260  of a linear actuator assembly  262 . The linear actuator assembly  262  is mounted to the phase change assembly  142  and oriented to move the carriage  230  along a linear actuator axis  264 . The linear actuator assembly  262  is controllable between a first condition which, in the depiction of  FIG. 9 , urges the piston  260  rightwardly until movement is terminated by a first stop  266 , and a second condition which, in the depiction of  FIG. 9 , urges the piston  260  leftwardly until movement is terminated by a second stop  268 . The second stop  268  in this embodiment is a bolt threadedly engaged with a stop mount  270  and the first stop  266  is a bolt threadedly engaged with the linear actuator assembly  262 . 
     The linear friction welding system  100  also includes a welding control system  280  depicted in  FIG. 10 . The control system  280  includes an I/O device  282 , a processing circuit  284  and a memory  286 . The control system  280  is operably connected to the main hydraulic press  122 , the motor  140 , the linear actuator assembly  262 , and a sensor suite  288 . In some embodiments, one or more of the components of the system  280  are provided as a separate device which may be remotely located from the other components of the system  280 . 
     The I/O device  282  in some embodiments includes 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 system  280 , and that allow internal information of the control system  280  to be communicated externally. 
     The processing circuit  284  may suitably be a general purpose computer processing circuit such as a microprocessor and its associated circuitry. The processing circuit  284  is operable to carry out the operations attributed to it herein. 
     Within the memory  286  are various program instructions  290 . The program instructions  290 , some of which are described more fully below, are executable by the processing circuit  284  and/or any other components of the control system  280  as appropriate. Parameter databases  292  are also located within the memory  286 . 
     Many components in the above described linear friction welding system  100  are similar to, and work in like manner as, components in the system described in detail in U.S. Pat. No. 8,376,210, incorporated herein by reference. By way of example, when the inner power shaft  160  has the same relative rotational position as the outer power shaft  162 , the relative phase of the inner power shaft  160  and the outer power shaft  162  are said to be matched, which may alternatively be referred to as being in phase, having the same relative phase, or having a system phase angle of zero. With a system phase angle of zero, and with the motor  140  operating, the ram  146  remains motionless. Movement of the ram  146  along the weld axis  150  is effected by controlling the shafts  160  and  162  to establish a non-zero phase angle. 
     The linear friction welding system  100  differs from the system disclosed in the &#39;210 patent, however, in the manner in which the system phase angle is established while using a single motor. This difference is realized by the incorporation of the phase change assembly  142 . Specifically, the belt  152  in one embodiment is a first timing component which rotates the gear  154  and the gear  212  at a fixed phase relationship. While there is a fixed relationship between the gear  154  and the inner power shaft  160 , the relationship between the gear  212  and the outer power shaft  162  is variable because of the phase change assembly  142  as discussed with further reference to  FIGS. 11 and 12 . 
     In  FIG. 11 , the linear actuator assembly  262  has been controlled to drive the transfer plate  248  against the stop  266  ( FIG. 9 ), and the position of the stop  266  has been adjusted by selective threading of the stop  266  into the linear actuator assembly  262  to provide a zero system phase angle. In the condition of  FIG. 11 , the timing belt  216  is defined by a feed segment  300  and a timing component load segment  302 . The feed segment  300  is defined as the portion of the timing belt  216  between the gears  214  and  218  from point  304  at the top of the gear  214  extending along the gear  232  to point  306  at the bottom of the gear  218 . The load segment  302  is defined as the portion of the timing belt  216  between the gears  214  and  218  from point  304  at the top of the gear  214  extending along the gear  234  to point  306  at the bottom of the gear  218 . 
     By controlling the phase change mechanism  228  to drive the transfer plate  248  against the stop  268  ( FIG. 9 ), the carriage  230  is driven in the direction of the arrow  308  in  FIG. 11  to the position depicted in  FIG. 12 . In  FIG. 12 , the length of the load segment  302 ′ of the timing belt  216  is greater than the length of the load segment  300  in  FIG. 11 . Because both of the gears  214  and  218  are engaged with the belt  216 , the belt  216  cannot simply slide past the gears  214  and  218 . Rather, at least one of the gears  214 / 218  must rotate in order to allow for some of the belt  216  on the feed segment  300  to move over to the load segment  302 ′. 
     Rotation of the gear  214 , however, is effected by the motor  140  through the belt  152  (see  FIG. 1 ). Accordingly, movement of the carriage  230  forces the gear  218  to rotate to allow a portion of the belt  216  to transfer from the feed side  300  to the load side  302 ′. This is indicated in  FIGS. 11 and 12  by schematic marks  310  and  312 . As evidenced by comparing the mark  310  in  FIG. 11  with the mark  310 ′ in  FIG. 12 , the rotational position of the gear  214  does not change as the carriage  230  moves. The mark  312 ′ in  FIG. 12 , however, indicates that the gear  218  has rotated from the location of the gear  218  in  FIG. 11  as indicated by the mark  312 . 
     Accordingly, since the shafts  160  and  162  were in phase when the phase change mechanism  228  was in the condition of  FIG. 11 , the shafts  160  and  162  are out of phase when the phase change mechanism  228  is in the condition of  FIG. 12 . While the gear  214  was not rotating in the foregoing explanation, those of skill in the art will recognize that the same discussion applies when the gear  214  is rotating. Thus, it is the relative speed of the gear  218  which is momentarily modified by movement of the carriage  230 . Consequently, with the motor  140  running, the ram  146  will vibrate along the welding axis  150  as discussed in more detail in the &#39;210 patent once the carriage moves away from the location of  FIG. 11 . 
     In order to stop vibration of the ram  146 , the carriage is simply controlled back to the position of  FIG. 11 , resulting in a momentary slowing of the rotation of the gear  214  forcing the shaft  162  back into phase with the shaft  160 . In one embodiment, the linear actuator assembly  262  is configured to selectively direct hydraulic fluid to one side or the other of a disk connected to the piston  260  and within the cylinder of the linear actuator assembly. Accordingly, the carriage is rapidly forced between the positions of  FIGS. 11 and 12 , and maintained at the desired position with continued hydraulic pressure against the disk to ensure the phasing of the shafts  160 / 162  does not inadvertently shift. 
     Additional details of the linear friction welding system  100  are provided with reference to a method  320  in  FIG. 13 , portions of which are performed under the control the control system  280 . At block  322 , the system phase angle is set to zero with the transfer plate  248  controlled against the stop  266 . While a zero system phase angle can be established with the motor  140  de-energized, in one embodiment the motor  140  is energized, and the bolt  266  is rotated until there is no movement of the ram  146 . 
     At block  324  the amplitude for movement of the ram  146  is set. Because there is a fixed relationship between the phasing of the shafts  160 / 162  and the amplitude of vibration of the ram  146 , the distance between the transfer plate  248  and the stop  268  establishes the amplitude of vibration. In one embodiment, a chart is provided which identifies the spatial relationship needed for a desired amplitude. The amplitude is then established by rotation of the stop  268  to the distance associated with the desired amplitude. 
     One of the components to be welded is then mounted to the forge platen  120  and the other component is mounted to the carriage  118  (block  326 ). Control of the method  320  is then passed to the control system  280 . At block  328  the processing circuit  284  executes program instructions  290  to establish a scrub pressure between the components to be welded. The processing circuit then controls motor  140  to the desired speed associated with the scrub (in some systems only a single speed is available) and controls the linear actuator assembly  262  to drive the transfer plate  248  against the stop  266  to initiate oscillation of the ram  146  and perform a scrub (block  330 ). The scrub pressure and scrub frequency in some embodiments are parameters stored in the parameter databases  292 . 
     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 system  100  as discussed more fully in the &#39;210 patent. 
     When the desired scrub has been performed at block  330 , burn parameters are established in the linear friction welding system  100  at block  332 . Specifically, the processing circuit  284  controls the main hydraulic press  122  to achieve a desired burn pressure based upon a value stored in the parameters database  292 . The processing circuit  284  further obtains a burn frequency from the parameters database  292  and controls the speed of the motor  140  to a speed corresponding to the desired burn frequency. 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 and burn frequency, have been established, a burn timer is started and counted down using a system clock or other appropriate clock. During the burn, the processing circuit  284  obtains input from the sensor suite  288  and modifies the speed of the motor  140  as needed to maintain the desired burn frequency and controls the main hydraulic press  122  to maintain the desired burn pressure. 
     When the burn timer has expired, movement of the ram  146  is terminated at block  334 . Movement can be terminated under the control of the processing circuit  284  by controlling the linear actuator  262  to move the phase change mechanism  228  from the second position ( FIG. 12 ) back to the first position ( FIG. 11 ) whereby the relative phase of the inner and outer shafts  160 / 162  are again matched. The transfer plate  248  is thus forced into contact with the stop  266 . 
     While the motor  140  rotates with no movement of the ram  146 , the processing circuit  284  controls the main hydraulic press  122  to establish a forge pressure at block  336  between the two weld components based upon data stored in the parameters database  292 . 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 is removed (block  338 ) and the weld verified (block  340 ). If desired, the processing circuit  284  may be used to determine the weld quality. Specifically, the initial position of the forge platen  120  as the two weld components came into contact can be stored and compared to the position of the forge platen  120  after 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 suite  288  and/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 procedure  320  provide precise information about the amount of energy placed into the components during the procedure  320 . 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 system  100  thus provides precise and independent control of pressure applied as well as the frequency and amplitude of oscillation during the procedure  320 . The use of a phase change assembly  142  reduces the number of motors required for operation from other methods. In addition, the phase change assembly  142  allows for the motor to remain on in between welds without movement of the ram. 
     While the present disclosure 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 disclosure 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&#39;s general inventive concept.