WO1997027962A1

WO1997027962A1 - Multi-penetration computerized thread rolling system

Info

Publication number: WO1997027962A1
Application number: PCT/US1997/001326
Authority: WO
Inventors: James F. Nowicke
Original assignee: Central Rolled Thread Die Co., Inc.
Priority date: 1996-01-31
Filing date: 1997-01-30
Publication date: 1997-08-07
Also published as: AU2247697A

Abstract

A thread rolling attachment includes a pair of opposed pivoting arms (4) each having a threading roll (2) attached to one end thereof. A wedge (12) is located between the other ends of the arms (4), and is linearly movable for controlling movement of the dies (2). A computer controller controls the rotation of a stepper motor which drives a ball nut and which causes axial movement of a ball screw. The ball screw is attached by a clevis. The computer controller is programmable for performing multi-penetration and for returning to a predetermined starting position close to the blank for reducing the threading cycle time. This device may be retro-fit on an existing pneumatic threading system by removing the pneumatic drive and attaching the stepper motor and ball screw and clevis and controller to the already existing system. The system also counts revolutions of one of the dies and if the number differs from an expected number then an alarm is sounded.

Description

MULTI-PENETRATION COMPUTERIZED THREAD ROLLING SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The present invention relates to thread rolling attachments of the type in which a wedge is' driven between rollers to actuate thread rolling dies, and more particularly to a thread rolling system in which a stepper motor drives a ball screw/nut that is connected to the wedge to permit improved control of movement of the dies, including multi-penetration. The invention also relates to a method of and apparatus for retro-fitting existing pneumatically and/or hydraulically controlled thread rolling attachments to permit improved control thereof .

2. Description of the Related Art.

Radial infeed thread rolling attachments are well-known in the art and are shown, for example, in U.S. Patent Nos. 4,426,869; 4,617,816; and 4,766,750, the content of each of which is incorporated herein by reference. Such radial infeed thread rolling attachments are also sold, for example, by CJ. WINTER MACHINE WORKS, INC._TM, of Rochester, New York. A typical thread rolling attachment of this type is shown in Fig. 1. Threading rolls or dies 2 are carried on the operating ends of a pair pivot arms 4 which are mounted on pivot pins 6. The opposite ends of the pivot pins are spring loaded inwardly, i.e., in a direction to normally maintain the threading rolls disengaged from the blank or work-piece 14 that is to be threaded, and include rollers 10 mounted thereto. A piston (not shown) is contained within a cylinder 8 and is movable into and out of the cylinder by means of hydraulic or pneumatic pressure within the cylinder. The piston moves a wedge-shaped operating member 12 between spring-loaded rollers 10 to pivot threading rolls 2 into engagement with blank 14.

This type of thread rolling attachment has several shortcomings. Movement of wedge 12 is controlled by a hydraulic or pneumatic cylinder, the pressurized flow to which is controlled by a flow control valve. Using such a flow control valve, there is no method to accurately control the penetration rate into the blank. Moreover, there is no method by which the penetration rate into the blank may be controlled so as to allow penetration at different rates during the thread rolling cycle. For example, during initial contact between the rollers and the blank, it is desirable to have a slower penetration rate to allow the rollers to track with the blank, i.e., to come up to the same speed as the rotating blank. It may also be desirable to slow the penetration rate of the rollers near the end of the rolling cycle to reduce the load on, and thereby increase the life of, the threading dies. Because there is no way to accurately control the movement of the pneumatic cylinder, multi-penetration at varying penetration rates is not possible using the conventional pneumatically controlled thread rolling attachment.

Accordingly, it would be desirable to have a thread rolling system that enables improved control of movement of the thread rolling dies. More specifically, it would be desirable to have a thread rolling attachment in which multi-penetration at varying penetration rates is possible.

Because there are many existing thread rolling attachments in use, such as those sold by CJ. WINTER MACHINE WORKS, INC_TM, it would also be desirable to have a method of and apparatus for retro-fitting existing thread rolling attachments to enable the improved control and multi-penetration features of the present invention to be used with existing thread rolling attachments.

SUMMARY OF THE INVENTION The present invention is a thread rolling apparatus which includes a pair of opposed pivoting arms, each arm having an operating end and a second end, a threading roll attached to the operating end of each pivot arm, and a wedge located between the second ends of the pivoting arms. The wedge is linearly movable for moving the dies toward each other and into contact with a blank, and away from each other. A computer controller controls the rotation of a stepper motor. Drive means is attached between the output shaft of the stepper motor and the wedge for converting the rotational motion of the output shaft to linear movement of the wedge so that movement of the wedge may be computer controlled.

The drive means preferably includes a ball nut, pulleys or other means for attaching the output shaft of the stepper motor to the ball nut for rotating the ball nut, a ball screw mounted within the ball nut so that rotation of the ball nut causes axial movement of the ball screw, and a clevis attaching the output end of the ball screw to the wedge.

The computer controller is programmable so that the user may input feed per revolution data and depth of feed data for one or more penetrations by the thread rolling attachment. The controller generates the necessary commands to the stepper motor for conducting the one or more penetrations on a blank.

The computer controller may also be programmed with a starting position for the dies at a position in close proximity to the blank. The computer controller maintains the dies in the starting position until a penetration cycle is initiated.

Compressed air or a compressed air/oil mixture may be used to pressurize the system to prevent contamination and to lubricate the ball nut and ball screw.

In a method of retro-fitting an existing thread rolling attachment the pneumatic cylinder from the existing thread rolling attachment is removed and replaced by a replacement drive having a stepper motor, a computer controller for controlling rotation of the stepper motor, and drive means comprising a ball nut, means for attaching the output shaft of the stepper motor to the ball nut for rotating the ball nut, and a ball screw mounted within the ball nut. The output end of the ball screw is then attached to the wedge.

A method of controlling the penetration of a thread rolling attachment includes the steps of: providing a stepper motor for controlling linear movement of a wedge of the thread rolling attachment; inputting feed per revolution data for one or more penetrations of the thread rolling attachment; inputting depth of feed data for the one or more penetrations of the thread rolling attachment; and controlling the stepper motor for conducting the one or more penetrations on a blank.

Finally, an improved thread rolling attachment includes a computer controller and an encoder for determining the number of rotations of a die during penetration of the die into a blank. The computer controller compares the number of rotations of the die to an expected number of rotations of the die and generates an alarm when the number of rotations of the die differs from the expected number of rotations of the die.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross-sectional side view of a conventional thread rolling attachment.

Fig. 2 is a cross-sectional side view of the stepper motor and drive mechanisms of the improved thread rolling system of the present invention.

Fig. 3 is a flow diagram showing operation of the control software of the invention. Fig. 4 is a perspective view of an operator interface in accordance with the invention.

Fig. 5 is a cross-sectional side view of a thread rolling attachment including a die rotational velocity encoder.

DETAILED DESCRIPTION OF THE INVENTION

As shown in Fig. 2, the present invention is an apparatus for attachment to a radial infeed thread roll attachment such as those shown and described above with respect to Fig. 1, in the aforementioned U.S. Patent Nos. 4,426,869; 4,617,816; and 4,766,750, and those sold by CJ. WINTER MACHINE WORKS, INC_TM The apparatus comprises a motor assembly 100 and a drive assembly 102. Motor assembly 100 consists of a stepper motor 106 having an output shaft 108. Mounted on output shaft 108 is a pulley 110. An angular contact bearing assembly 112 supports drive pulley 110.

Drive assembly 102 includes a ball screw 120 and a ball nut 122 mounted within a cylindrical housing 124. An exposed end of ball screw 120 includes a clevis 126 which is adapted to be attached to the wedge of a radial infeed thread rolling attachment, such as those described above, by a pin or other attachment means. Ball screw 120 extends through a retainer plate 128. Attachment of the drive assembly 102 to the thread rolling attachment is preferably by means of bolts (not shown) which extend through shafts 180 and retainer plate 128, and which are attached to the thread rolling attachment. Ball screw 120 and ball nut 122 are preferably a conventional 4-pitch ball screw/nut assembly, such as those which may be purchased from ROTON PRODUCTS™, St. Louis, Missouri.

Ball nut 122 is rotatable within housing 124 so that rotation of ball nut 122 causes axial movement of ball screw 120. Ball nut 124 is threaded into a ball nut retainer 128 which is secured within a pulley 130 by means of a keyway, bolts, or other attachment mechanism, and which is open at the pulley end. Rotation of pulley 130 causes rotation of ball nut retainer 128 and ball nut 122, thereby resulting in axial movement of ball screw 120. Ball nut retainer 128 includes lips 132 by means of which angular contact bearings 134 support ball nut retainer 128, ball nut 122 and ball screw 120. Angular contact bearings 112 and 134 are preferably conventional cup and cone bearings such as those available from TIMKEN C0._TM, Canton, Ohio.

An electrical contact switch 140 is mounted near the open end of ball nut retainer 128 by means of a non-electrically conducting bracket 142, which is preferably constructed of a plastic material. A shut-off plug 144, which is constructed of an electrically conducting material, is mounted over the pulley end of ball screw 120 and has an outer diameter closely toleranced to the inner diameter of ball nut retainer 128 but with sufficient clearance to permit axial movement of ball screw 120. As discussed in more detail below, as ball screw 120 moves axially toward the pulley end, shut-off plug 142 will eventually make contact with switch 140, thereby grounding the switch.

A supply of pressurized air with an oil mist is attached to connector 152 to force the air/oil mist into cylinder 124 by means of a pneumatic conduit 150. This maintains a positive pressure within cylindrical housing 124 to prevent dirt and other foreign matter from entering the drive assembly, and also keeps the ball screw, ball nut and angular contact bearings lubricated. A conduit 154 provides a supply of pressurized air/oil mist to bearings 112 of motor assembly 100.

Pulley 130 on the drive assembly and pulley 110 on the motor assembly are connected via a conventional drive belt (not shown) , which is preferably cogged, and each of the pulleys include corresponding teeth. These types of pulleys and belts are available from T.B. WOOD'S SONS CO._TM, Chambersburg, PA. The pulleys and belt are preferably contained under a cover (not shown) , with conduit 154 also pressurizing the interior of the pulley cover to prevent foreign matter from affecting the pulleys and belt.

In certain types of thread rolling attachments, the wedge is mounted so that movement of the wedge toward the dies causes the dies to close, and movement of the wedge away from the dies causes the dies to open. Other types of thread rolling attachments operate the opposite, i.e., movement of the wedge toward the dies causes the dies to open, and movement of the wedge away from the dies causes the dies to close. The present invention is applicable to either type of thread rolling attachment, but will be described hereinafter with respect to the former type. Those skilled in the art will appreciate the modifications necessary to apply the present invention to the latter type of attachment.

In operation, rotation of stepper motor 106 rotates stepper motor pulley 110, which in turn rotates drive assembly 130. Rotation of drive assembly pulley 130 rotates ball nut 122, which causes axial movement ball screw 120. Since ball screw 120 is connected to the wedge of the thread rolling attachment by means of clevis 126, outward movement of ball screw 120 causes the dies on the thread rolling attachment to close, and inward movement of ball screw 120 causes the thread rolling attachment dies to open.

The stepper motor is preferably an SX83-135 microstepping motor from PARKER HANNIFIN CORPORATION_TM. This stepper motor produces approximately 400 oz-in of torque and has a resolution up to 50,800 steps per revolution. It is foreseen that any appropriate stepper motor may be used in the present invention.

The stepper motor operates in conjunction with a computer controller 500, such as those of the SX or SXF Series Packaged Microstepping Systems, also from PARKER HANNIFIN_TM. This type of controller include a programming language by which operation of the stepper motor may be controlled. The controller 500 is programmed so as to allow control over movement of the wedge into the thread rolling attachment to an extent not possible in conventional thread-rolling attachments that are pneumatically controlled. The controller 500 drives an operator interface 502, such as the RP240 Operator Interface from PARKER HANNIFIN_TM (Fig. 4) . This type of interface includes a two-line, 40 character per-line LCD display, and various data entry keys and LED status indicators.

Fig. 3 shows a flow diagram of the software that is programmed into controller 500 that operates to control the thread rolling attachment. When the system is turned on, a user is prompted to enter a password (200) . If the password is correct (202) , operation of the software continues. Otherwise, the user is prompted to re-enter their password (204) .

As previously mentioned, an electrical switch 140 is included on drive assembly 102. This switch is also referred to as the "home" switch. At this point during operation of the software, the controller actuates stepper motor 106 to retract ball screw 120 until shut-off plug 144 in the end of ball screw 120 contacts the home switch. Shut-off plug 144 and ball screw 120 are grounded, and home switch 140 is connected to a connector on the controller that detects a ground condition. When shut-off plug 144 contacts home switch 140 (206) thereby grounding the connector, this signals the controller that ball screw 120 is fully retracted, and stops the stepper motor from retracting the ball screw further. The fully retracted position is set as the "home" or "zero" position (208) . From the home position, the ball screw has a pre-determined allowable range of travel, which is preferably one step of the stepper motor in the negative direction, i.e. toward the home switch, and a pre-determined number of steps in the positive direction sufficient to prevent the ball screw from bottoming out in the ball nut or to prevent the rollers or wedge of the thread rolling attachment from contacting each other in a manner that would damage the attachment. Thus, the controller is set with travel limits that prevent the ball screw from retracting past the home position and from extending beyond a pre-determined limit.

Once the limits of travel are set (208) , a menu is displayed which permits the user to enter (i) a jog mode (210); (ii) a teach mode (212); or (iii) an auto-run mode (214) . The jog mode (210) enables the user to manually control the stepper motor to retract or extend ball screw 120, and to thereby open and close the dies of the thread rolling attachment. Once the jog mode has been initiated, the clockwise- movement (218) , counter-clockwise-movement (220) , and stop (222) keys are depressed to rotate the ball screw in opposite directions to retract and extend the ball screw. The controller will not allow movement of the ball screw in the jog mode, or in any mode, beyond the allowable travel limits. A typical cycle in which the thread rolling attachment is used to place threads on a blank involves other pieces of machinery that perform different functions as well. When the thread rolling attachment is to be used, a cross-slide moves the thread rolling attachment into position adjacent to the blank work-piece and a micro-switch is actuated by the cross-slide to notify the thread rolling attachment that the blank is in position. In a conventional thread rolling attachment system, the wedge is fully withdrawn when the thread rolling attachment is not in use, and then fully extended when air is supplied to the pneumatic cylinder. The time that it takes the wedge to move from the fully retracted position to a position in which it makes contact with the work-piece is time wasted in the overall cycle. In the present invention, in the teach mode (212) , a "starting position" is programmed into the system so that the wedge retracts only enough that the thread rolling dies just clear the work-piece so that the thread rolling attachment may be moved into and out of position adjacent to the work-piece. In the teach mode, a blank is positioned between the dies of the thread rolling attachment and the stepper motor is manually operated to move the dies just into contact with the blank. This is achieved by means of control buttons which move the dies 0.0100 (224), 0.0010 (226), and 0.0001 (228) inches respectively. A change direction key (230) allows movement of the dies in the opposite direction. Once the user has set the dies just in contact with the blank, a teach key (232) is depressed which causes the dies to back up by a pre¬ determined amount, preferably 0.005 inches (234), so that clearance is provided between the dies and the blank. This position is stored as the starting position (236) . Thus, once the starting position has been set, the dies will retract to 0.005 inches from the blank when not in use. This reduces wasted time in the thread rolling cycle. Obviously, the system may be modified so that the dies are positioned at any pre-determined distance from the blank.

The auto-run mode (214) is initiated when it is desired to perform thread rolling. Once the auto-run mode is operated, the system first determines whether the teach cycle has been completed (238), i.e., whether a starting position has been stored. If no starting position has been stored (240) , the teach mode is automatically started. If a starting position has been stored (242) , the user is prompted to enter the specific parameters for the thread rolling cycle (244-270) . The user first enters the spindle rpm of the blank (244) , the feed depth per revolution for a first penetration (248) , and the depth of feed for the first penetration (252) . After entering each value, the user is prompted to ensure that the correct value has been entered. If multiple penetrations are to be performed, the user may enter feed per revolution and depth of feed for additional penetrations in the cycle (256-270) . While a maximum of three penetrations per cycle are indicated in Fig. 3, it is foreseen that additional penetrations may be provided if desired.

As discussed above, the system preferably includes a predetermined travel limit so as to prevent the ball screw from bottoming out in the ball nut. Prior to beginning the auto-cycle, the system determines whether the total feed depth from the starting position will result in an over-travel condition. If an over-travel condition would occur, the system preferably notifies the user of the over- travel condition, prevents initiation of the auto- cycle, and displays the menu which permits the user to enter the jog mode (210) , the teach mode, or the auto-run mode (214) .

Once all of the feed information has been entered, the system displays the total depth of feed (272) . If the total depth of feed is correct, an auto-cycle is initiated (274) in which the thread rolling attachment is placed in a mode to perform thread rolling. The system converts the depth of feed data entered by the user to steps of the stepper motor to achieve the selected depth, and the feed per revolution data into steps per second data (276) . When the cross-slide comes into position, it actuates a micro-switch to indicate that the input cycle has begun. When the controller receives the input signal (278) , it operates the stepper motor to move the ball screw in accordance with the desired depth of feed and feed per revolution for each penetration (280) . Once threading is complete, the controller operates the stepper motor to retract the dies by twice the total depth of feed plus .005 inches (282), which is ordinarily sufficient for the dies to clear the newly rolled threads. If moving the dies to this position will require the ball screw to retract beyond the home position, the ball screw is retracted only to the home position. Once the threaded blank has been removed from between the dies, the micro-switch input to the controller is set to zero, which causes the controller to move the dies back to the teach position to wait for the next input cycle. In a preferred embodiment of the invention, the spindle rpm is limited to a range of from 0.00 to 10,000 rpm, the feed per revolution range is limited to the range of from 0.0005 to 0.0100 inches, and the depth of feed is limited to a range of from 0.00 to 0.100 inches. It will be appreciated that these ranges are not intended to limit the scope of the invention, and that other ranges may be used, if desired. Also in the preferred embodiment, the default stepper motor configuration operates at 25,000 steps per revolution. Using pulleys having a 2:1 ratio of the stepper motor pulley to the drive assembly pulley, and a 4-pitch ball screw, the controller may control movement of the ball nut at 200,000 steps per revolution, which far surpasses the available control for pneumatically controlled thread roll attachments. Control at a greater resolution is possible as well.

The present invention may be used to retrofit existing thread rolling attachments, such as those sold by CJ. WINTER MACHINE WORKS, INC._TM In order to retrofit such existing thread rolling attachments, the pneumatic cylinder is unbolted from the thread rolling attachment, and any attachment between the pneumatic cylinder and the wedge, which is usually a clevis and pin, is detached, thereby releasing the pneumatic cylinder from the thread rolling attachment body. Any air/oil mist and electrical connections to the pneumatic cylinder are also disconnected. To attach drive means 102 of the present invention to the existing thread rolling attachment, clevis 126 is attached to the wedge by means of a pin or bolt. The drive means 102 includes bolt holes extending therethrough which match the bolt pattern of the existing thread rolling attachment, so that the drive means 102 may be bolted directly to the thread rolling attachment in lieu of the pneumatic cylinder. Because the "home" and starting" positions are set interactively when the thread rolling attachment is to be used, no adjustment of the ball screw extension is necessary during the retrofit. The existing pressurized air/oil mist lines from the CJ. WINTER device are attached to drive means 102 and stepper motor 100, and the controller is connected to the micro-switch which is actuated when the cross-slide comes into position adjacent to the thread rolling attachment. Drive means 102 and stepper motor 100 are preferably attached to the existing thread roll attachment as an assembly.

An additional feature of the invention enables the controller to measure the rotation of dies 2 on the thread rolling attachment to ensure that the dies are tracking properly on blank 14. If the dies are not tracking properly, the resultant threaded blank may be defective and the user may wish to discard the blank. As shown in Fig. 5, a position or number of rotations encoder is attached to one of the dies to measure the number of rotations of the die. The output of the encoder is transmitted to the controller which determines the number of rotations of the die and compares this number to the known spindle rpm of the blank. If the difference between these values exceeds a pre-determined threshold, an LED on the controller, or any other appropriate alarm means is actuated to indicate to the user that the blank being threaded should be discarded. In one embodiment, a shaft 300 extends from encoder 302, and frictionally rides against the die. Encoder 302 generates an output representative of the number of rotations of the shaft. Alternatively, the encoder may be a rotational disc attached to the die which has registrations thereon that may be read by an optical or magnetic reader (not shown) to determine the number of rotations of the die. Absolute and incremental encoders that are suitable for use in the invention are sold, for example, by PARKER HANNIFIN_TM. An absolute encoder is a position verification device that provides unique position information for each shaft location. An incremental encoder is capable of indicating rotary motion and direction of movement. The output of the incremental or rotary encoder is directed to the controller, which determines the number of rotations of the die. It is foreseen that any appropriate encoder may be used in lieu of the incremental encoders and absolute rotary encoders described herein.

During set-up, the operator of the system would be prompted to enter the number of starts on the thread roll, e.g., a thread roll with 4 individual threads running off its end is a four start roll an is approximately 4 times as large as the work-piece blank. The controller has already calculated the number of work-piece revolutions required to roll the thread, and the number of expected thread roll revolutions is the ratio of (work-piece revolutions/number of starts on the thread roll) . The encoder counter is reset to zero at the start of each auto-cycle. At the end of the auto-cycle, the controller compares the number of encoder pulses, i.e., the number of thread roll revolutions, to the number of anticipated encoder pulses. If the difference between these numbers exceed a predetermined limit, an alarm condition would occur.

Although the present invention has been described in detail with respect to certain embodiments and examples, variations and modifications exist which are within the scope of the present invention as defined in the following claims.

Claims

1. A thread rolling apparatus which comprises: a thread rolling attachment comprising a pair of opposed pivoting arms, each having an operating end and a second end, a threading roll attached to the operating end of each pivot arm, and a wedge located between the second ends of the pivoting arms, the wedge being movable in a first linear direction for moving the dies toward each other and into contact with a blank, and an opposite direction for moving the dies away from each other; a stepper motor comprising a rotational output shaft; a computer controller for controlling rotation of the stepper motor; and drive means for attaching the output shaft of the stepper motor to the wedge for converting the rotational motion of the output shaft to linear movement of the wedge; whereby linear movement of the wedge may be accurately controlled by the computer controller.

2. The thread rolling apparatus according to claim 1 wherein the drive means comprises: a ball nut; means for attaching the output shaft of the stepper motor to the ball nut for rotating the ball nut; a ball screw mounted within the ball nut, whereby rotation of the ball nut causes axial movement of the ball screw, the ball screw having an output end; and means for attaching the output end of the ball screw to the wedge.

3. The thread rolling apparatus according to claim 2 wherein the means for attaching the output shaft of the stepper motor to the ball screw comprises: a pulley on the output shaft of the motor; a pulley attached to the ball nut; and belt means extending around the pulley on the output shaft of the motor and the pulley attached to the ball nut.

4. The thread rolling apparatus according to claim 2 wherein the means for attaching the output end of the ball screw to the wedge comprises a clevis.

5. The thread rolling apparatus according to claim 1 wherein the computer controller comprises: means for inputting feed per revolution data for at least one penetration of the thread rolling attachment; means for inputting depth of feed data for the at least one penetration of the thread rolling attachment; and means for controlling the stepper motor for conducting the at least one penetration on a blank.

6. The thread rolling apparatus according to claim 1 wherein the computer controller comprises: means for inputting feed per revolution data for at least two penetrations of the thread rolling attachment; means for inputting depth of feed data for the at least two penetrations of the thread rolling attachment; and means for controlling the stepper motor for conducting the at least two penetrations on a blank.

7. The thread rolling apparatus according to claim 2 wherein the computer controller comprises: means for inputting feed per revolution data for one or more penetrations of the thread rolling attachment; means for inputting depth of feed data for the one or more penetrations of the thread rolling attachment; and means for controlling the stepper motor for conducting the one ore more penetrations on a blank.

8. The thread rolling apparatus according to claim 2 wherein the computer controller comprises means for inputting a starting position for the dies at a position in close proximity to the blank, the computer controller maintaining the dies in the starting position until a penetration cycle of a blank is initiated.

9. The thread rolling apparatus according to claim 1 further comprising: means for determining the number of rotations of at least one die during a penetration of the dies into a blank, the computer controller comprising means for comparing the number of rotations of the at least one die to an expected number of rotations of the die and for generating an alarm when the number of rotations of the at least one die differs from the expected number of rotations of the die by a predetermined amount.

10. The thread rolling apparatus according to claim 7 further comprising: means for determining the number of rotations of at least one die during a penetration of the dies into a blank, the computer controller comprising means for comparing the number of rotations of the at least one die to an expected number of rotations of the die and for generating an alarm when the number of rotations of the at least one die differs from the expected number of rotations of the die by a predetermined amount.

11. The thread rolling apparatus according to claim 10 wherein the means for determining the number of rotations of at least one die comprises an absolute encoder or an incremental encoder.

12. The thread rolling apparatus according to claim 2 further comprising: a cylinder, wherein the ball screw and ball nut are positioned within the cylinder; and means for supplying compressed air or a compressed air and oil mixture to the interior of the cylinder for pressuring the interior of the cylinder and for lubricating the ball nut and ball screw.

13. An apparatus for retro-fitting a thread rolling attachment having a pair of opposed pivoting arms, each arm having an operating end and a second end, a threading roll attached to the operating end of each pivot arm, a wedge located between the second ends of the pivoting arms, and a pneumatic cylinder for moving the wedge in a first linear direction for moving the dies toward each other and an opposite direction for moving the dies away from each other, the apparatus comprising: a stepper motor comprising a rotational output shaft; a computer controller for controlling rotation of the stepper motor; drive means comprising a ball nut, means for attaching the output shaft of the stepper motor to the ball nut for rotating the ball nut, and a ball screw, having an output end, mounted within the ball nut, whereby rotation of the ball nut causes axial movement of the ball screw; and means for attaching the output end of the ball screw to the wedge.

14. The thread rolling apparatus according to claim 13 wherein the means for attaching the output shaft of the stepper motor to the ball screw comprises: a pulley on the output shaft of the motor; a pulley attached to the ball nut; and belt means extending around the pulley on the output shaft of the motor and the pulley attached to the ball nut.

15. The thread rolling apparatus according to claim 13 wherein the means for attaching the output end of the ball screw to the wedge comprises a clevis.

16. The thread rolling apparatus according to claim 13 wherein the computer controller comprises: means for inputting feed per revolution data for at least one penetration of the thread rolling attachment; means for inputting depth of feed data for the at least one penetration of the thread rolling attachment; and means for controlling the stepper motor for conducting the at least one penetration on a blank.

17. The thread rolling apparatus according to claim 13 wherein the computer controller comprises means for inputting a starting position for the dies at a position in close proximity to a blank, the computer controller maintaining the dies in the starting position until a penetration cycle of a blank is initiated.

18. The thread rolling apparatus according to claim 13 further comprising: a cylinder, wherein the ball screw and ball nut are positioned within the cylinder; and means for supplying compressed air or a compressed air and oil mixture to the interior of the cylinder for pressuring the interior of the cylinder and for lubricating the ball nut and ball screw.

19. A thread rolling attachment comprising: a pair of opposed pivoting arm, each having an operating end and a second end; a threading roll attached to the operating end of each pivot arm; a wedge located between the second ends of the pivoting arms, the wedge being linearly movable for moving the dies toward and away from each other; a computer controller; and means for determining the number of rotations of at least one die during a penetration of the dies into a blank, the computer controller comprising means for comparing the number of rotations of the at least one die to an expected number of rotations of the die and for generating an alarm when the number of rotations of the at least one die differs from the expected number of rotations of the die by a predetermined amount.

20. The thread rolling apparatus according to claim 19 wherein the means for determining the number of rotations of at least one die comprises an absolute encoder or an incremental encoder.

21. A method of retro-fitting a thread rolling attachment having a pair of opposed pivoting arms, each arm having an operating end and a second end, a threading roll attached to the operating end of each pivot arm, a wedge located between the second ends of the pivoting arms, and a pneumatic cylinder for moving the wedge in a first linear direction for moving the dies toward each other and an opposite direction for moving the dies away from each other, the method comprising the steps of: removing the pneumatic cylinder from the thread rolling attachment; providing a replacement drive comprising: a stepper motor comprising a rotational output shaft, a computer controller for controlling rotation of the stepper motor, and drive means comprising a ball nut, means for attaching the output shaft of the stepper motor and the ball nut for rotating the ball nut, a ball screw mounted within the ball nut, whereby rotation of the ball nut causes axial movement of the ball screw, the ball screw comprising an output end; and attaching the output end of the ball screw to the wedge.

22. A method of controlling a thread rolling system comprising a stepper motor for controllably moving a wedge between a pair of pivoting arm having thread rolling dies attached thereto, the method comprising the steps of: inputting feed per revolution data for one or more penetrations of the thread rolling attachment; inputting depth of feed data for the one or more penetrations of the thread rolling attachment; and controlling the stepper motor for conducting the one or more penetrations on a blank.

23. The method according to claim 22 further comprising the steps of inputting a starting position for the dies at a position in close proximity to the blank, maintaining the dies in the starting position until a penetration cycle of a blank is initiated; and returning the dies to the starting position after removal of a threaded blank.