US20040043704A1

US20040043704A1 - Method and apparatus for high speed cutting

Info

Publication number: US20040043704A1
Application number: US10/233,268
Authority: US
Inventors: Mark Saberton
Original assignee: Individual
Current assignee: Flow International Corp
Priority date: 2002-08-30
Filing date: 2002-08-30
Publication date: 2004-03-04

Abstract

A workpiece is cut by being selectively moved along a first axis under a cutting device, the cutting device being selectively moved along a second axis that is perpendicular to the first axis. Motion of the workpiece and the cutting device is controlled to cut a workpiece. In one embodiment of the invention, the workpiece is selectively moved along the first axis by actuation of a first linear motor, and the cutting device is selectively moved along the second axis by actuation of a second linear motor. The cutting device may be a high-pressure fluid jet system.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved method and apparatus for high-speed cutting of an object.

2. Description of the Related Art

High-pressure fluid jets, including high-pressure abrasive water jets, are used to cut a wide variety of materials in many different industries. Systems for generating high-pressure abrasive water jets are currently available, for example the Paser 3 system manufactured by Flow International Corporation, the assignee of the present invention. An abrasive jet cutting system of this type is shown and described in Flow's U.S. Pat. No. 5,643,058, which patent is incorporated herein by reference. In such systems, high-pressure fluid, typically water, flows through an orifice in a cutting head to form a high-pressure jet, into which abrasive particles are entrained as the jet flows through a mixing tube. The high-pressure abrasive water jet is discharged from the mixing tube and directed toward an object or workpiece to cut the workpiece along a selected path. After the jet passes through the object being cut, the fluid and waste associated with the cutting are collected in a catcher tank.

Various systems are currently available to move a high-pressure fluid jet along a selected path. (The terms “high-pressure fluid jet” and “fluid jet” used throughout should be understood to incorporate all types of high-pressure fluid jets, including but not limited to, high-pressure water jets and high-pressure abrasive water jets.) Such systems are commonly referred to as two-axis, three-axis and five-axis machines. Conventional three-axis machines mount the cutting head assembly on a ram that imparts vertical motion along a Z-axis, namely toward and away from the workpiece to be cut. The ram, in turn, is mounted to a bridge via a carriage, the carriage being free to move parallel to a longitudinal axis of the bridge in a horizontal plane. The bridge is slideably mounted on one or more rails to move in a direction perpendicular to the longitudinal axis of the bridge. In this manner, the high-pressure fluid jet generated by the cutting head assembly is moved along a desired path in an X-Y plane, and is raised and lowered relative to the workpiece, as may be desired. Conventional five-axis machines work in a similar manner but provide for movement about two additional rotary axes, typically about one horizontal axis and one vertical axis. Similar machines are also available to manipulate other types of cutting devices.

Other types of machining equipment, for example metal punch press machines, move the workpiece to be cut along two axes in an X-Y plane. Regardless of whether prior art systems maintain the workpiece stationary and move the cutting device, or hold the cutting device stationary while moving the workpiece, these systems all use relatively complex mechanical drive assemblies, for example ball screw drives or rack-and-pinion assemblies.

Applicant believes it is desirable and possible to provide an improved system for cutting a workpiece. The present invention provides such a system.

BRIEF SUMMARY OF THE INVENTION

Briefly, the present invention provides an improved method and apparatus for cutting a workpiece, for example with a high-pressure fluid jet. (The terms “cutting” and “cut” used throughout should be understood to cover all types of cutting, including, but not limited to, engraving, scribing, etching, etc., in addition to cutting through a workpiece.)

More particularly, a workpiece to be cut is held and selectively moved across a top surface of a table along a first axis by a part gripper mounted to the table. In one embodiment, the part gripper and associated workpiece are selectively moved along the first axis by a linear motor mounted to a longitudinal beam of the table. A cutting device is mounted to a boom for selective movement along a second axis that is perpendicular to the first axis. In one embodiment, the cutting device is a cutting head assembly that selectively produces an ultrahigh-pressure fluid jet. Alternatively, it may be any type of cutting device, including but not limited to, a laser, plasma cutter, or scriber, etc.

In one embodiment, the boom is coupled to the table, such that forces generated by movement of the cutting device along the second axis are dissipated through the framework of the table. In one embodiment, the cutting device is selectively moved along the second axis by actuation of a second linear motor coupled to the boom. In this manner, the workpiece is cut using, in combination, the movement of the workpiece along one axis, and movement of the cutting device along a second axis, perpendicular to the first. An appropriate controller, including software, is used to control motion of the workpiece and of the cutting device, as will be understood by one of ordinary skill in the art.

Because all cutting takes places in a narrow area along the second axis, any waste generated by the cutting, including water and abrasives if used, may be collected by placing a single-axis container underneath the table, along the second axis. This is in contrast to prior art systems where cutting occurs substantially over the entire length and width of a cutting table, requiring a catcher tank to extend substantially the full length and width of the workpiece.

In accordance with another aspect of the present invention, a shoe is coupled to a distal end of the cutting device, the shoe being made of a material having a sufficient hardness to displace the workpiece as needed to substantially maintain a standoff distance between the cutting device and the workpiece within a desired tolerance. For example, if the workpiece is sheet metal, it will be understood by one of ordinary skill in the art that such a workpiece is not perfectly flat, and that it may distort as it is cut. By providing a shoe around a distal end of the cutting device, being formed of a material that is harder than the material being cut, the shoe will push against the workpiece and displace it as necessary to maintain a desired standoff distance. In one embodiment, the shoe surrounds the distal end of a high-pressure fluid jet cutting head, and an outlet end of the mixing tube of the cutting head assembly is inset from an end surface of the shoe.

By moving the workpiece along one axis while moving the cutting device along a second perpendicular axis, maximum speed of cutting and acceleration are increased. Furthermore, by using two linear motors in accordance with the present invention, in contrast to more complex mechanical drive systems of the prior art, manufacturing costs are reduced, and speed of cutting, accuracy, and reliability are increased. For example, while prior art systems allow cutting in the range of 400-3,500 inches per minute, cutting may be done in accordance with the present invention at the rate of 5,000 inches per minute. In addition, the present invention eliminates the problems associated with large, prior art catcher tanks, and handling of waste is simplified, given the relatively small container that may be used to catch the discharged jet and waste along the second axis of the machine.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a front isometric view of an assembly provided in accordance with the present invention. [0014]
FIG. 2 is a front isometric view of a table and boom subassembly of the cutting assembly shown in FIG. 1. [0015]
FIG. 3 is a rear isometric view of the subassembly show in FIG. 2. [0016]
FIG. 4 is an isometric view of a portion of the assembly of FIG. 1, with elements removed for clarity. [0017]
FIG. 5 is a schematic illustration of a side view of the assembly shown in FIG. 1. [0018]
FIG. 6 is a cross-sectional elevational view of a shoe provided in accordance with the present invention, shown mounted on a high-pressure fluid jet cutting head.[0019]

DETAILED DESCRIPTION OF THE INVENTION

There are many systems currently available for engraving a workpiece or cutting one or more parts of any desired shape from a workpiece. For example, as discussed previously, ultrahigh-pressure abrasive water jet systems such as those manufactured by Flow International Corporation, move a cutting head along a selected path in an X-Y plane, over a fixed workpiece. Other systems, for example metal punch press machines, maintain the punch or cutting device in a stationary position, while the workpiece is moved in two directions in an X-Y plane. These conventional systems use relatively complex mechanical drive systems, that entail numerous moving parts, and the associated cost and reliability problems associated with such mechanisms. Also, the upper speed at which conventional systems may cut is restricted, given limitations of the mechanical drives. For example, currently available water jet systems allow cutting at rates of 400-1,000 inches per minute. The present invention provides an apparatus and method for cutting a workpiece that overcomes many of these limitations. [0020]
More particularly, as illustrated in FIG. 1, a [0021] workpiece 10 to be cut is held and selectively moved by a part gripper 11 that is coupled to a table 12. In one embodiment, the part gripper 11 and associated workpiece 10 are selectively moved along a first axis 24 by actuating a first linear motor 17. A cutting device, such as a cutting head assembly 13, is coupled to a boom 14 for selective movement along a second axis 25 that is perpendicular to the first axis 24. Boom 14 is cantilevered over the table 12 and is rigidly mounted to mast 15, which in turn is rigidly mounted to the base frame 19 of table 12. In one embodiment, the cutting device 13 is selectively moved along the second axis 25 by actuation of a second linear motor 18. A container 16 is removably positioned underneath table 12, and is aligned along the second axis 25 defined by boom 14, to catch any waste material resulting from cutting of the workpiece.
A controller incorporating appropriate software, controls motion of the [0022] workpiece 10 along the first axis 24 and motion of the cutting device 13 along the second axis 25, to move the high-pressure fluid jet along a desired path. It will be understood that cutting a workpiece in accordance with the present invention may result in scribing a selected design into a workpiece or the cutting of a part having a desired shape, or any desired combination thereof. In one embodiment of the present invention, motion of the workpiece and cutting device are controlled to cut a part in the workpiece that is connected to the workpiece by small tabs. Once one or multiple parts are cut into a workpiece in this manner, the tabs are broken and the parts are removed from the workpiece. The formation and location of the tabs may be dictated by the control system, as will be understood by one of ordinary skill in the art.
Although the apparatus of the present invention may take many forms, one exemplary embodiment is illustrated in FIGS. 2 and 3. As seen in these two figures, the table [0023] 12 may be formed of a base frame 19, including a longitudinal beam 33. The boom 14 is either rigidly coupled to or integrally formed with mast 15, that in turn is rigidly fixed to or integrally formed with the table 12, for example through longitudinal beam 33. As further seen in FIGS. 2 and 3, in one embodiment, the mast 15 is further coupled to a secondary longitudinal beam 20. Given the coupling of the boom 14 to table 12, forces generated by motion of the cutting device 13 along the boom 14 are transmitted and dissipated through the longitudinal beams and diagonal braces 46 of the table. A slot 23 is defined in the table 12, the high-pressure fluid jet or other cutting device being allowed to pass through slot 23 as it cuts the workpiece, if such cutting extends through the entire depth of the workpiece.
As best seen in FIGS. 4 and 5, a first set of [0024] rails 34 is mounted on an upper surface of the longitudinal beam 33 defining a first trough 36 therebetween. A plurality of magnets 38 are positioned within the first trough 36. Gripper plate 28 is coupled to both bearing boxes 39 provided on rails 34, and to motor coil 40 of first linear motor 17. As motor coil 40 selectively moves along magnets 38, the part gripper 11 and workpiece 10 held thereby, selectively move along the rails 34, defining the first axis 24. By bolting the gripper plate to the motor coil, the gripper plate not only moves with the motor coil, but also acts as a heat sink for the motor. Part gripper 11 may be of conventional design, such as those sold by Alternative Parts, Inc. Clamps 47 are selectively raised and lowered via a pneumatic cylinder to allow a workpiece to be inserted and grasped by the part gripper 11.
In one embodiment, a second set of [0025] rails 35 is mounted on a side surface of the boom 14, defining a second trough 37 therebetween to receive a second linear motor 18 having the same structure defined above for the first linear motor 17 provided on the longitudinal beam 33. Conventional boots 51 may be placed over the motors and their respective paths of motion.
Although the upper region of table [0026] 12 may be formed in a variety of ways, in one embodiment, a metal plate 26 having a slot provided therein is laid on top of the frame 19, such that the slot in the metal plate is aligned with the slot defined in the table. Alternatively, the plate may be integral to the frame, or it may be eliminated. It is desirable for an upper support surface 30 of the table to have a low coefficient of friction. In one embodiment of the present invention, this is achieved by positioning strips of polymer brushes 27 having a low coefficient of friction across the top surface of the table 12. An insert made of high-molecular weight plastic may be placed into the slot 23 to improve the wear of this region as the cutting device passes along the length of the slot.
In some applications, for example when cutting sheet metal, it may be desirable to provide a [0027] shoe 21 in accordance with the present invention, as illustrated in FIG. 6. Shoe 21 is positioned around a distal end of the cutting device, and preferably is of sufficient hardness to displace the workpiece being cut as needed to substantially maintain a standoff distance 31 between the cutting device and the workpiece. For example, if the cutting device is a cutting head of a high-pressure fluid jet system, as illustrated in FIG. 6, the standoff 31 is the distance between an exit orifice 32 of the mixing tube 45 and an upper surface of the workpiece 10. A first end 48 of shoe 21 may be coupled to the cutting device in any appropriate manner, for example via a threaded connection. A second end 49 of shoe 21 is positioned on or adjacent the workpiece 10 when in use. The body 50 of shoe 21 is formed of a material selected to be harder than the material being cut. For example, if the workpiece is sheet metal, the shoe 21 may be formed of hardened steel. In one embodiment, a distal end of the cutting head, for example the end of mixing tube 45, is inset from the end surface of shoe 21, such that the shoe also acts as a pierce shield.
As will be understood by one of ordinary skill in the art, an ultrahigh-pressure fluid jet, including an abrasive fluid jet if desired, is generated by the cutting [0028] head assembly 13 shown in FIG. 6 by allowing a quantity of pressurized fluid to flow through inlet 41. The pressurized fluid flows through orifice 42 secured in orifice mount 43, to generate a high-pressure fluid jet 29. If desired, a quantity of abrasive is introduced into the assembly via abrasive inlet port 44, where the abrasive is entrained in the fluid jet and discharged through mixing tube 45 to impinge against the workpiece 10. Although the present invention has been described herein in the context of the cutting being performed by a high-pressure fluid jet, it will be understood that other types of cutting devices may be used, for example a laser, a plasma cutter, a scriber, etc.
Many advantages are achieved in accordance with the present invention. By moving the workpiece along one axis while moving the cutting device along a second perpendicular axis, maximum speed of cutting and acceleration are increased. By using direct drive linear motors, for example those manufactured by Yaskawa, high accelerations and speed of cutting are achieved, with improved accuracy. For example, while conventional water jet systems allow cutting at a rate of 400-1,000 inches per minute, the present invention allows cutting at a maximum travel velocity of at least 5,000 inches per minute, providing significant cost benefits and advantages. [0029]
By eliminating the more complex mechanical drives of conventional systems, the cost of the assembly is reduced, and reliability is improved. Furthermore, limitations such as “backlash” associated with conventional mechanical drive systems are eliminated by use of direct drive linear motors. Because all pieces of the assembly are integrally formed and prealigned at the time of assembly, the apparatus may be simply plugged in and used, rather than being leveled or lagged to the floor, as required in conventional systems. [0030]
An additional advantage is the elimination of a need for a catcher tank extending substantially the same length and width as the workpiece. More particularly, in conventional systems where the cutting occurs over almost the entire X-Y plane defined by the workpiece, it is necessary to be able to catch debris along the entire area. It has therefore been necessary to provide a large catcher tank having dimensions approximately equal to those of the workpiece. When using large catcher tanks, systems are required to maintain the abrasives in suspension, and eliminate waste from the catcher tank. In contrast, cutting in accordance with the present invention occurs over a small region along the second axis, such that a relatively [0031] small container 16 may be removably positioned under the table along this second axis, to catch debris. Given the small area of the container, the contents may be directly pumped out, thereby simplifying waste disposal. Although this may be achieved in a variety of ways, in one embodiment, the container 16 is simply provided with locking casters that allows the container to be removably positioned under the table, and provided with a drain line 22 allowing fluid communication between an interior region and exterior of the container. A slot catcher 52 extends from an underside of the table 12 along the length of slot 23 into the interior of container. In one embodiment, slot catcher 52 is coupled to container 16 such that it is removably positioned under the table 12.
It will be understood that a variety of workpieces may be cut in accordance with the present invention, and that the size and weight of the workpiece that can be handled may be increased by simply increasing the size of the linear motors. By way of example only, the present invention may be used to cut a six foot by ten foot piece of 10 gauge sheet metal. [0032]
From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims. [0033]

Claims

1. A method of cutting a workpiece comprising:

selectively moving the workpiece to be cut along a first axis under a fluid jet produced by a cutting head; and

selectively moving the cutting head along a second axis that is perpendicular to the first axis.

2. The method according to claim 1 further comprising:

gripping the workpiece to be cut by a member mounted to a first linear motor; and

actuating the first linear motor to selectively move the workpiece to be cut along the first axis.

3. The method according to claims 1 or 2 further comprising:

actuating a second linear motor coupled to the cutting head to selectively move the cutting head along the second axis.

4. The method according to claim 1 further comprising:

controlling motion of the workpiece and the cutting head to cut a part in the workpiece that is connected to the workpiece by tabs; and

breaking the tabs to remove the part from the workpiece.

5. The method according to claim 1 further comprising:

positioning a container underneath the workpiece along the second axis to collect the fluid jet and waste resulting from the cutting of the workpiece.

6. The method according to claim 1 further comprising:

cutting the workpiece at a rate of up to 5,000 inches per minute.

7. A method for cutting a workpiece comprising:

gripping a workpiece to be cut by a member mounted to a first linear motor;

actuating the first linear motor to selectively move the workpiece along a first axis under a fluid jet produced by a cutting head;

actuating a second linear motor coupled to the cutting head to selectively move the cutting head along a second axis that is perpendicular to the first axis; and

cutting the workpiece at a rate of up to 5,000 inches per minute.

8. A method of cutting a workpiece comprising:

selectively moving a workpiece to be cut along a first axis under a means for cutting; and

selectively moving the means for cutting along a second axis that is perpendicular to the first axis.

9. A method according to claim 8 further comprising:

10. The method according to claims 8 or 9 further comprising:

actuating a second linear motor coupled to the means for cutting to selectively move the means for cutting along the second axis.

11. An apparatus for cutting a workpiece comprising:

a table;

a gripper assembly mounted to the table, the gripper assembly selectively holding the workpiece to be cut and being selectively moveable along a first axis;

a boom coupled to the table; and

a cutting device coupled to the boom, the cutting device being selectively moveable along a second axis that is perpendicular to the first axis.

12. The apparatus according to claim 11 further comprising:

a first linear motor coupled to the table and to the gripper assembly; and

a second linear motor coupled to the boom and to the cutting device.

13. The apparatus according to claims 11 or 12 wherein the cutting device further comprises a cutting head that selectively produces a high-pressure fluid jet.

14. The apparatus according to claims 11 or 12 wherein the cutting device further comprises a laser.

15. The apparatus according to claims 11 or 12 wherein the cutting device further comprises a plasma cutter.

16. The apparatus according to claims 11 or 12 wherein the cutting device further comprises a scriber.

17. The apparatus according to claim 11 further comprising a container that is removably positioned beneath the table aligned along the second axis.

18. The apparatus according to claim 11 wherein the table is provided with an upper support surface having a low coefficient of friction.

19. The apparatus according to claim 13 further comprising:

a shoe coupled to a distal end of the cutting head, the shoe being made of a material having a sufficient hardness to displace the workpiece being cut as needed to substantially maintain a standoff distance between an exit orifice of the cutting head and the workpiece within a desired tolerance.

20. An apparatus for cutting a workpiece comprising:

a frame having a longitudinal beam that defines a first axis;

a first set of rails coupled to the longitudinal beam and configured to receive a first linear motor;

a boom coupled to the frame and extending perpendicular to the first axis to define a second axis; and

a second set of rails coupled to the boom and configured to receive a second linear motor.

21. The apparatus according to claim 20 further comprising:

a slot provided in the frame aligned with and positioned beneath the boom.

22. The apparatus according to claim 20 further comprising:

a first linear motor coupled to the first set of rails and to a gripping device; and

a second linear motor coupled to the second set of rails and to a cutting device.

23. The apparatus according to claim 22 wherein the cutting device is an assembly for generating a high-pressure fluid jet.

24. The apparatus according to claim 22 wherein the cutting device further comprises a laser.

25. The apparatus according to claim 22 wherein the cutting device further comprises a plasma cutter.

26. The apparatus according to claim 22 wherein the cutting device further comprises a scriber.

27. The apparatus according to claim 20 further comprising:

a support surface coupled to the frame, the support surface having a low coefficient of friction.

28. The apparatus according to claim 20 further comprising:

a container removably positioned beneath the slot in the frame.

29. The apparatus according to claim 23 further comprising:

30. An apparatus for maintaining a standoff distance, comprising:

a body having a first end that is selectively coupled to a cutting device and a second end that is positioned on or adjacent a workpiece to be cut when in use, the body being formed of a material having a sufficient hardness to displace the workpiece being cut as needed to substantially maintain a standoff distance between the cutting device and the workpiece within a desired tolerance.