Stir-friction hot working control system
A stir-friction hot-working or welding arrangement uses a pin tool having a ligament 22 and a shoulder 224. The force required for incremental penetration increases markedly when the shoulder is reached. A control system for maintaining a set penetration depth includes a load cell for measuring force or pressure applied to the pin tool. The control system compares a reference signal representing the desired force with the actual force from the load cell, to produce an error signal which controls the penetration force, thereby tending to maintain a desired penetration depth. In a particular embodiment, the reference signal ramps up from a low or zero value at turn-on, to reduce forces applied upon initial penetration. In another embodiment, position signals are used to control a modulator or multiplier, which changes the error signal applied at certain positions of penetration, or at certain velocities of penetration.
This invention relates to control arrangements for stir-friction welders, and more particularly to automatic positioning systems for stir-friction welders.
BACKGROUND OF THE INVENTION
In order to make appropriate welds, the pin tool or ligament 22 of
The roller arrangement 26 for controlling the depth of penetration of the pin tool during stir-friction welding or hot working is effective, but the roller apparatus makes it inconvenient to change the penetration depth from one workpiece to another, and it is not possible to make small adjustments in the depth of penetration during a weld or hot-working procedure.
Another prior-art method which can be used to control the depth of penetration of a stir-friction pin tool into a workpiece is by the use of distance measuring devices or sensors (not illustrated) which measure the distance between the upper surface of the workpiece, corresponding to surface 14us in
Improved control arrangements are desired for stir friction welding.
SUMMARY OF THE INVENTIONA method according to the invention for stir-friction welding a planar workpiece uses a rotating pin tool which includes a pin or ligament. The pin or ligament defines a diameter at locations closer to the tip of the pin tool than a particular location along its length, and also includes or defines a shoulder at the location. The shoulder has a larger diameter than the pin. The method includes the steps of rotating the tool, and applying force to the pin tool with the pin tool plunged into one side of the workpiece, and with the shoulder essentially coincident with the surface of the one side of the workpiece, so that the rotating pin creates a friction-stirred region. According to an aspect of a method according to the invention, the workpiece and the rotating tool are moved laterally (in a direction orthogonal to the axis of rotation) relative to each other, so that the friction-stirred region progresses along the workpiece. During the moving step, a signal is generated which is representative of the force applied to the pin tool. A reference signal is generated which is representative of that force which is sufficient to maintain the shoulder against the one surface of the workpiece. The signal representative of the force applied to the pin tool is compared with the reference signal, for generating an error signal representative of the difference between the force applied to the pin tool and the reference signal. The error signal is used to control the step of applying force in a manner tending to maintain the shoulder in contact with, or essentially coplanar with, the one surface of the workpiece, as a result of which, or whereby, the pin maintains substantially constant plunge depth.
In a particularly advantageous mode of practicing a method according to the invention, the step of applying force includes the steps of coupling a lead screw to the pin tool and to a fixed reference point, so that rotation of the lead screw applies pressure or force to the pin tool. The shaft of a force motor is coupled to the lead screw, for rotating the lead screw in response to rotation of the force motor, as a result of which, or whereby, the force applied to the pin tool is responsive to the rotational position of the shaft of the force motor. The shaft of the force motor is rotated in response to at least the magnitude of the error signal, and preferably in opposite rotational directions in response to the variation of the error signal relative to a particular value of the error signal, which is preferably a zero value. In a most preferred embodiment of the invention, the maximum force which can be applied to the pin tool is limited.
The method according to the invention may further include initial steps which cause the pin tool to plunge into the workpiece. These steps include positioning the tip of the pin tool adjacent the one surface of the workpiece, and generating a signal representing the plunge of the pin tool relative to the one surface of the workpiece. Other steps include generating a monotonically changing signal which represents a profile of the desired depth of plunge as a function of time, generating a difference signal representing the difference between the actual plunge of the pin tool and the desired depth of plunge, rotating the pin tool, and controlling the force in response to the difference signal in such a manner that the force increases when the actual plunge is less than the desired plunge, and decreases when the actual plunge is more than the desired plunge. The step of moving the workpiece and the rotating tool laterally relative to each other begins when the actual plunge equals the desired plunge.
BRIEF DESCRIPTION OF THE DRAWING
It should be noted that pressure divided by area equals force, so they are not identical measures. However, with a constant-area system, force and pressure are proportional, and they are often used interchangeably.
Head 440 of
As illustrated in
It should be understood that in the plot 500 of
Considering the characteristics of plot 500 of
The feedback arrangement as described in conjunction with
The arrangement of
Other embodiments of the invention will be apparent to those skilled in the art. For example, while a general-purpose computer processor has been described as controlling the feedback, a dedicated processor could also be used, and might even be advantageous, by virtue of simplicity and reliability. While the term “motor” has been used to describe a transducer from electricity to mechanical energy, other devices than a conventional rotary motor may be used, as for example piezoelectric or magnetic devices, or linear motors. While the feedback loops have shown simple feedback schemes, but many types of feedback control may be used, including proportional-integral-derivative (PID) control.
Thus, a method according to an aspect of the invention for stir-friction hot-working or welding a planar workpiece (14) uses a rotating pin tool (22) which includes a pin or ligament defining a diameter at locations closer to the tip of the pin tool (22) than at a particular location along its length, and also including or defining a shoulder (224) at the location. The shoulder (224) has a larger diameter (D) than the pin diameter (d). The method includes the steps of rotating the tool, and applying pressure or force to the pin tool (22) with the pin tool (22) plunged into one side (14us) of the workpiece (14), and with at least a portion (524) of the shoulder (224) essentially coincident with the surface (14us) of the one side of the workpiece (14), so that the rotating pin creates a friction-stirred region. According to an aspect of a method according to the invention, the workpiece (14) and the rotating tool (22) are moved laterally (in a direction orthogonal to the axis of rotation) relative to each other (by motor 470, rack 472 and gear 474), so that the friction-stirred region (14b) progresses along the workpiece (14). During the moving step, a signal is generated, which is representative of the pressure or force applied to the pin tool (22). A reference signal is generated (block 610) which is representative of that force (B) which is sufficient to maintain the shoulder (224) against the one surface (14us) of the workpiece (14). The signal representative of the force applied to the pin tool (22) is compared (in error signal generator 612) with the reference signal, for generating an error signal representative of the difference between the force applied to the pin tool (22) and the force represented by the reference signal. The error signal is used to control the step of applying force in a manner tending to maintain the shoulder (224) in contact with, or essentially coplanar with, the one surface of the workpiece (14), as a result of which, or whereby, the pin maintains substantially constant plunge depth.
In a particularly advantageous mode of practicing a method according to the invention, the step of applying force includes the steps of coupling a lead screw (430) to the pin tool (22) and to a fixed reference point (410), so that rotation of the lead screw (430) applies pressure or force to the pin tool (22). The shaft of a force or lead-screw motor (450) is coupled (by gear 451) to the lead screw (430), for rotating the lead screw (430) in response to rotation of the force or lead-screw motor (450), as a result of which, or whereby, the pressure or force applied to the pin tool (22) is responsive to the rotational position of the force motor (450) shaft (450s). The shaft (450s) of the force motor (450) is rotated in response to at least the magnitude of the error signal (generated by error signal generator 612), and preferably in opposite rotational directions in response to the variation of the error signal relative to a particular value of the error signal, which is preferably a zero value. In a most preferred embodiment of the invention, the maximum pressure or force which can be applied to the pin tool (22) is limited.
The method according to the invention may further include initial steps which cause the pin tool (22) to plunge into the workpiece (14). These steps include positioning the tip of the pin tool (22) adjacent the one surface of the workpiece (14), and generating a signal representing the plunge of the pin tool (22) relative to the one surface of the workpiece (14). Other steps include generating a monotonically changing signal which represents a profile of the desired depth of plunge as a function of time, generating a difference signal representing the difference between the actual plunge of the pin tool (22) and the desired depth of plunge, rotating the pin tool (22), and controlling the force in response to the difference signal in such a manner that the force increases when the actual plunge is less than the desired plunge, and decreases when the actual plunge is more than the desired plunge. The step of moving the workpiece (14) and the rotating tool laterally relative to each other begins when the actual plunge equals the desired plunge.
Claims
1-8. (Canceled)
9. A stir-friction welder, comprising:
- a frame;
- a lead screw rotatably interconnected with said frame;
- a first drive interconnected with said lead screw;
- a first sensor located between said frame and said lead screw;
- a controller interconnected with said first sensor and said first drive;
- a head mounted on said lead screw; and
- a pin tool interconnected with said head, wherein rotation of said lead screw by said first drive, responsive to an input by said first sensor to said controller, changes a position of said head along said lead screw, and thereby a plunge depth of said pin tool relative to a workpiece.
10. A stir-friction welder, as claimed in claim 9, wherein:
- said first sensor is a load cell.
11. A stir-friction welder, as claimed in claim 9, further comprising:
- a bearing holder and a bearing mounted in said bearing holder, wherein said lead screw is rotatably supported by said bearing, wherein said first sensor interfaces with said bearing holder.
12. A stir-friction welder, as claimed in claim 9, wherein:
- said head comprises a second drive interconnected with pin tool, wherein said second drive rotates said pin tool relative to the workpiece.
13. A stir-friction welder, comprising:
- a frame;
- a lead screw rotatably interconnected with said frame;
- a first drive interconnected with said lead screw;
- a first sensor that is stationary;
- a controller interconnected with said first sensor and said first drive;
- a head mounted on said lead screw; and
- a pin tool interconnected with said head, wherein rotation of said lead screw by said first drive, responsive to an input by said first sensor to said controller, changes a position of said head along said lead screw, and thereby a plunge depth of said pin tool relative to a workpiece.
14. A stir-friction welder, as claimed in claim 13, wherein:
- said first sensor is located between said frame and said lead screw.
15. A stir-friction welder, as claimed in claim 13, wherein:
- said first sensor is a load cell.
16. A stir-friction welder, as claimed in claim 13, further comprising:
- a bearing holder and a bearing mounted in said bearing holder, wherein said lead screw is rotatably supported by said bearing, wherein said first sensor interfaces with said bearing holder.
17. A stir-friction welder, as claimed in claim 13, wherein:
- said head comprises a second drive interconnected with pin tool, wherein said second drive rotates said pin tool relative to the workpiece.
Type: Application
Filed: Feb 5, 2004
Publication Date: Jan 13, 2005
Inventors: Glynn Adams (Slidell, LA), Zachary Loftus (New Orleans, LA), Joseph McCormac (Huntsville, AL), Richard Venable (Grant, AL)
Application Number: 10/773,045