US RE39019 E1
A method of friction welding first and second parts together at an angular orientation relative to each other includes the steps of mounting the first part in a spindle for axial rotation and the second part in a non-rotatable holder. The spindle is then rotated and the angular orientation of the first part relative to the second part is determined at any specific time. The holder is moved toward the spindle to bring the second part into frictional contact with the first part at a selected one of the specific times that the angular orientation is determined. Accordingly, due to frictional contact, the respective contacting surface of the parts are melted. The speed of the rotation of the spindle is then decreased and the holder is moved toward the spindle to forcibly urge the first and second parts together at the contacting surface. Rotation of the spindle is stopped at a specific determined angular orientation of the first part relative to the second part while continuing to forcibly urge the parts together to allow cooling and fused solidification of the contacting surfaces.
1. A method of friction welding first and second parts together having a specific axial orientation relative to each other in which said first part is mounted to a spindle for axial rotation said second part is mounted to a non-rotatable holder moveable toward said spindle along the axis of rotation of said first part, comprising the steps:
a. causing said spindle and mounted first part to be rotated at a desirable speed while determining the angular axial orientation of said first part relative to said second part at any specific time,
b. moving said holder toward said spindle to bring said second part into frictional contact with said first part at a selected one said specific time to cause heating of said first and second parts and the melting of the respective contacting surfaces thereof,
c. then decreasing the speed of rotation of said spindle and mounted first part and simultaneously moving said holder towards said spindle to forcibly urge said first and second parts together at said contacting surfaces, and
d. stopping rotation of said spindle and mounted first part at a specific determined angular axial orientation of said first part relative to said second part while still forcibly urging said first and second parts together to allow cooling and fused solidification of said contacting surfaces.
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9. A method of using a friction welding machine to weld a pair of workpieces together at a desired final angular orientation relative to each other, the friction welding machine including a rotatable spindle and a non-rotatable tailstock, the method comprising the steps of:
calculating a set of weld parameters used to control the friction welding machine, the set of welding parameters including a desired spindle speed and a desired spindle position;
mounting a first one of the pair of workpieces to the rotatable spindle and a second one of the pair of workpieces to the non-rotatable tailstock;
rotating the rotatable spindle;
monitoring at least one of an actual spindle speed and an actual spindle position to produce a measurement;
comparing the measurement with at least one of the desired spindle speed and desired spindle position;
adjusting at least one of the actual spindle speed or the actual spindle position so that the actual spindle position is substantially similar to the desired spindle position; and
bringing the pair of workpieces into frictional contact with each other to generate a weld such that the workpieces are welded together in the desired final angular orientation relative to each other.
10. The method according to
repeating the monitoring, comparing, and adjusting steps until the actual spindle speed equals the desired spindle speed.
11. The method according to
entering a set of input parameters into the computing device, the input parameters including the desired final angular orientation between the pair of workpieces and the physical characteristics of the pair of workpieces.
12. The method according to
13. The method according to
14. The method according to
positioning the rotatable spindle in a desired initial angular position; and
rotating the rotatable spindle so that the actual spindle speed for a current one of the phases is substantially equal to the desired spindle speed for the current phase.
15. The method according to
wherein each of the phases, adjusting the actual spindle speed of the rotatable spindle so that the desired spindle speed for each of the phases is substantially equal the desired spindle speed of each of the phases.
16. The method according to
17. The method according to
monitoring either the actual spindle position of the rotatable spindle or the actual spindle speed periodically.
18. The method according to
calculating a difference between the actual spindle position and the desired spindle position;
communicating the difference to the controller; and
adjusting the actual spindle position to minimize the difference.
19. The method according to
utilizing the comparison between the actual spindle position and the desired spindle position at a particular time point to determine the required adjustment to the actual spindle speed.
20. The method according to
moving the non-rotatable tailstock towards the rotatable spindle according to the set of weld parameters.
21. The method according to
contacting the first one of the pair of workpieces to a second one of the pair of workpieces; and
generating heat at a contact surface formed between the pair of workpieces.
22. An apparatus for controlling a friction welding machine, comprising:
a motion controller;
a position sensor; and
a computing device for accepting the entry of input parameters, the computing device operatively coupled to the motion controller and the position sensor; wherein
the computing device being programmed to (i) calculate a set of weld parameters from input parameters, wherein the weld parameters include a desired spindle speed and desired spindle position, (ii) cause the motion controller to produce a command signal indicative of a desired spindle speed calculated from a set of input parameters, (iii) receive a status signal from the position sensor indicative of an actual spindle position at a specific time point, (iv) compare the actual spindle position to the desired spindle position calculated from the set of input parameters at the specific time point, and (v) cause the motion controller to deliver a difference signal to make any necessary corrections to the rotational speed.
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This is a continuation of application Ser. No. 60/038,332 filed Feb. 27, 1997.
The present invention relates generally to a control system for use on friction welding machines for controlling the final angular orientation of two workpieces relative to each other that have been welded together using the friction welding process.
A software computer program forming an appendix consisting of 5 pages is included as part of the specification.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the public Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
Friction welding machines are generally well known in the art. In a friction weld, heat is generated by rubbing two workpieces together until the material at the interface between the two pieces reaches a plastic state. The two workpieces are then forged together under pressure to finalize the weld and expel gases, thus forming a single component having an integral bond. A friction weld can typically be formed in a very short period of time compared to more conventional are welding methods, and thus friction welds are less labor intensive, more uniform and more cost effective than conventional methods. Friction welders are especially well suited for welding round bars or tubes to each other, or for welding round workpieces to flat plates, disks or gears. The friction welding process is frequently used to produce automotive drive shafts, automotive air bag canisters, gear shafts and engine valves, as well as other applications in which a high quality weld is required.
On a friction welder, one of the workpieces is mounted to a rotating chuck assembly while the other workpiece is fixed in a stationary chuck or tailstock. A drive motor accelerates the rotating chuck to a predetermined speed, and the parts are then forced together with the friction induced heat producing a material flux. The pieces are then forged together under pressure, which expels gas and produces a fine grain weld.
Friction welders are generally divided into two categories, inertia friction welders and the more conventional direct drive friction welders. The rotating chuck on inertia friction welders is drivingly connected to a flywheel. A drive motor accelerates the flywheel to speed, the drive motor is then disconnected, and the kinetic energy stored in the flywheel is converted to heat energy as the two workpieces are forced together under extremely high pressure. The rotating chuck rapidly decelerates to a stop and the weld is formed at the interface between the two workpieces. Inertia friction welding has a number of inherent drawbacks which makes it unsuitable for many applications. First, the flywheel bearings gradually heat up, which depletes the available kinetic energy because energy is lost through increased friction. Second, due to the very high forge pressure required, inertia welding is unsuitable for thin walled tubes and many soft metals, such as aluminum. In general, the quality and uniformity of inertia friction welds are hard to control.
On direct drive friction welders, the drive motor used to rotate one of the workpieces remains engaged until the weld is complete and the rotating workpiece comes to a halt. Unfortunately, the final orientation of the rotating workpiece relative to the stationary workpiece is not easily controlled. In many applications, it is critical that the two workpieces be welded together in a predetermined angular orientation relative to one another. For example, the yoke at one end of an automotive drive shaft must be perpendicular to the yoke at the other end of the drive shaft; otherwise, the drive line components will be prone to premature failure. Similarly, on many gear shafts and other components the gear at one end of the shaft must be precisely located relative to another gear or cam lobe on the shaft.
In order to achieve precise angular orientation a number of approaches have been attempted. For example, one prior art approach uses a defined braking mechanism which applies a braking force as the rotating spindle decelerates and approaches the desired final orientation which in turn is conveyed to the rotating spindle via an electronic signal or mark. Usually however, due to variations in the braking mechanism and other variables, the deceleration of the spindle is not uniform. Frequently, the brake must be released and the drive motor must be temporarily re-engaged in order to force the spindle to the desired location. Thus the rate of deceleration, as well as the final angular position of the rotating workpiece, is relatively uncontrolled. In many instances as the spindle approaches the desired stopping point, it becomes clear that the spindle has or will stop short of the desired alignment mark, while at other times the spindle will completely pass the mark. If the spindle stops short, the drive motor is re-engaged and the spindle is accelerated and driven to the mark. If the spindle overshoots the mark, the drive motor is re-engaged and the spindle is turned an extra rotation in order to reach the mark again. Unfortunately, in each instance the spindle has slowed significantly and the weld has already begun to cool and the material has begun to harden. Any subsequent accelerations and rotations of the spindle cause microfractures in the crystal structure of the material, resulting in a lower quality, high risk weld. Furthermore, the defined braking method is not accurate enough for many applications. In general, the defined braking method is unsuitable for applications in which the final angular orientation is critical and is also unsuitable for many aluminum welds, aircraft quality welds, air bag welds and other safety related welds.
Accordingly, there exists a need for a control system for friction welders that can control the final orientation of one workpiece relative to the other, and that consistently produces a uniform high quality weld suitable for use on aircraft and safety related applications and on a wide variety of material types.
The control system according to the present invention allows two workpieces to be welded together at a desired angular orientation. The control system of the present invention allows two pieces to be welded together with greater precision and accuracy than is possible with any of the prior art control methods. The control system constantly monitors the angular orientation of the spindle at any given point in time, and compares the present spindle orientation with a predetermined desired spindle orientation that has been calculated by a host computer. The computer calculates the desired orientation of the rotating spindle at any given moment during the weld process, including during the acceleration phase, the burn-off and weld phases, and through the deceleration phase until the spindle stops at the predetermined desired final angular orientation. The programmable host computer determines and calculates all of the critical weld parameters, depending on the material properties, weld characteristics, thickness, and rotating mass of the pieces to be welded together. Based upon this information, the computer generates a desired spindle profile curve which becomes a reference point for the desired speed and the desired angular position of the rotating spindle at every point during the weld process. Using the profile curve, a motion controller connected to and controlled by the central computer constantly compares the actual spindle orientation to the desired spindle orientation throughout the process, and makes the necessary corrections to ensure that the actual orientation conforms to the desired orientation.
A motion controller is operatively connected to the host computer, and generates a motion command or speed signal, which is communicated to a drive motor that drives the spindle. A position sensor is connected to the rotatable spindle, and a tachometer is connected to the drive motor. The position sensor and the drive motor communicate constant feedback to the motion controller regarding the present position of the rotatable spindle and the present speed of the drive motor. The present orientation is compared to the desired orientation for that particular moment in the weld cycle, and the motion controller constantly makes adjustments to the spindle speed, either by increasing or decreasing the speed, in order to conform the actual spindle orientation to the desired spindle orientation.
The control system employs a proportional-integral-derivative controller (“PID controller”), which enables the control system to respond very quickly to differences between the actual and the desired spindle orientation. The control system can thus respond very quickly to increases or decreases in friction between the two workpieces as the materials heat up and as the weld is being formed. At any given moment, parameters indicative of the present spindle orientation and the present spindle speed are sent to the motion controller, which compares the actual orientation to the desired orientation. The motion controller then makes any necessary corrections and varies the speed of the drive motor accordingly. Thus, by making the system more responsive, the angular orientation of the rotatable spindle at any given moment can be precisely controlled as can the rotational speed of the spindle. Each of these variables are constantly measured and compared to target values calculated and communicated by the host computer to the PID controller.
Accordingly, it is an object of this invention to provide an improved control system for friction welders.
It is another object of this invention to provide a control system for friction welders that allows two workpieces to be welded together in a precise angular orientation.
A further object of this invention is to provide a control system for friction welders that enables two workpieces to be welded together with much more precision than is possible in known existing friction welding methods.
These and other objects to the invention will become readily apparent to those skilled in the art upon a reading of the following description.
The embodiment herein described is not intended to be exhaustive or to limit the invention to the precise form disclosed. It is chosen and described to explain the principles of the invention and its application and practical use to best enable others skilled in the art to follow its teachings.
Referring now to the drawings, a control system for a friction welder according to the present invention is generally indicated by the reference numeral 10. Control system 10 is operatively connected to and controls the operation of a friction welding device 12. Friction welder 12 includes a rotating spindle 14, having a chuck assembly 16 for securing a first workpiece 18, and a non-rotating chuck assembly or tailstock 20 for holding a second workpiece 22. Typically, tailstock 20 is slidably mounted to a track or slide 24. An actuator 25 enables tailstock 20 holding second workpiece 22 to move towards spindle 14 holding first workpiece 18 in a direction parallel to the axis 27 of rotating spindle 14, thus enabling first and second workpiece's 18, 22 to be brought into contact with each other.
As shown in
Tachometer 34 generates a signal which indicates the actual speed 35 (see
Referring now to
When the operator initiates the start command 82, the computer 26 performs the pre-weld calculations 93 and creates the output register 70, which contains values for each of the variables 39, 44, 46, 48, 49, 50, 53, 61, 63, 65, 67, 69, 71, 72, 74, 79, 81 and 83 as shown in FIG. 7. Computer 26 generates the spindle profile curve 120 shown in
As shown in
Upon completion of subroutine 92A, a signal is sent to computer 26 which indicates that the second phase 96 is about to commence. Phase 96, which commences at a time indicated by time T1 in
Phase 96 is followed by a forge phase 100 which commences at time T2, and which terminates when the desired forge rotations 50 have been completed and the spindle rotation has stopped, which occurs at time T3. During forge phase 100, spindle 14 decelerates in accordance with profile curve 120. Forge phase 100 is in turn followed by a dwell phase 102 in which the two workpieces are maintained under pressure as the material at workpiece interface 19 cools, with phase 102 terminating at time T4. At the initiation of the forge phase 100, motion controller 28 begins decelerating the spindle 14, and subroutine 101 via control loop 40 constantly compares the desired forge rotations 50, in increments of 1/1000th of a revolution, to the actual forge rotations 51 as dictated by the spindle profile 120 for that particular moment during phase 100, and motion controller 28 makes the necessary speed adjustments via speed signal 54. The comparison by subroutine 101 continues until the forge phase 100 is complete at time T3, at which point the spindle 14 has stopped at the desired final position 42. Also during the forge phase 100, as the spindle 14 begins to slow down, computer 26 sends a signal to actuator 25, which causes an increase in pressure between first workpiece 18 and second workpiece 22 up to the forge force level 83.
When spindle 14 stops, computer 26 measures the actual travel of actuator 25 and compares the actual upset length 104 to the desired upset length 74 and determines if the actual upset 104 is within bounds. Subroutine 110 monitors the time under forge pressure, and sends a signal to computer 26 when the dwell time is complete, which occurs at time T4. At time T4, the forge pressure is released and the weld cycle is complete. Finally, motion controller 28 reports any final positional errors to computer 26, which can be communicated to the operator.
The invention is not to be limited to the following claims but it may be modified within the scope of the claims.