Roll Formed Flexible Die Plate For Rotary Cutting Tool

Abstract

A method of making a rotary cutting tool for cutting a web of material comprises the steps of roll forming a first flexible die plate into a cylindrical shape, mounting the cylindrically shaped die plate onto a cylindrically shaped fixture, and machining cutting elements onto the roll formed die plate. The roll formed die plate may then be removed from the fixture and attached to a cylinder. The first die plate can cooperate with a second die plate attached to a second cylinder to cut the thin web of material.

Description

RELATED APPLICATION

This application is a 35 U.S.C. §371 national phase application of PCT/US2007/060262, filed Jan. 9, 2007, which claims priority benefit of U.S. provisional patent application No. 60/757,799 filed on Jan. 10, 2006.

FIELD OF THE INVENTION

This invention relates to improvements in rotary cutting tools and more particularly to improvements in flexible die plates for rotary cutting tools.

BACKGROUND OF THE INVENTION

Rotary cutting tools are useful for manufacture of carton blanks and other workpieces from sheets or webs of material. In particular, rotary die cutting tools are used in high speed cutting of a moving sheet or web of paper, paperboard, plastics or composite materials. As one example, rotary die cutting machines are used for the high speed mass production of paperboard carton blanks that are subsequently folded into the shape of cartons or boxes such as cereal and cracker boxes, etc. Rotary cutting tools include solid rotary dies, where the cutting surface is made part of the cylinders, and flexible rotary dies, where a die plate is wrapped around a cylinder.

It is important that the die plates of flexible dies be properly affixed to the cylinder and aligned, both with respect to the cylinder and with respect to each other. This is especially important given the speed of rotation of the die cylinders associated with high volume production. Known techniques for affixing and aligning the die plates include forming the die plate out of a magnetic material and inserting magnets into the die cylinders so that they are magnetically attracted to one another. However, such a design greatly increases the costs of the die cylinders for several reasons, including the cost of the magnets, the cost of machining holes into the cylinders to receive the magnets, and the difficulty in assembly.

In addition, known flexible die plates are formed by a chemical etching process where an acid or base is applied to metal to dissolve away unwanted material. In practice, a chemical is applied to a flat sheet of metal to produce the desired cutting elements on a flexible die plate. The flat flexible die plate is then bent around a cylinder and attached by one of several methods such as use of strong magnet or welding. There are numerous limitations in the chemical etching process, both in terms of limitations in the properties of the die pates made by the process and difficulties in the process for assembling the die plates to the cylinders. For example, tool steels (steels with large amounts of non-ferrite alloys) are more difficult to chemically etch. Chemical etching works better with carbon steels, but carbon steels are relatively brittle and not ideal for forming, bending and other operations. Also, some geometries such as undercuts are difficult to make. Further, known chemically etched die plates are relatively thin in part to make them easier to assemble to cylinders. However, thicker die plates are more desirable as they can be longer lasting and more resistant to position change.

With regards to the process, use of magnets requires extensive machining of cylinders, thereby making such cylinders quite expensive. Further, both magnets and welding die plates to the cylinder require extensive changeover time when switching die plates, undesirably increasing downtime for printing. Known chemically etched flexible die plates are awkward to assemble with the cylinder. The thin flexible die plates are shipped to the customer as flat plates that are spring-like and resist bending around the cylinder. It would be desirable to provide an enhanced flexible die plate that is long lasting and robust, which is easy to install with reduced downtime.

SUMMARY OF THE INVENTION

In accordance with a first aspect, a method of making a rotary cutting tool for cutting a web of material comprises the steps of roll forming a first flexible die plate into a cylindrical shape, mounting the cylindrically shaped die plate onto a cylindrically shaped fixture, and machining cutting elements onto the roll formed die plate. The roll formed die plate may then be removed from the fixture and attached to a cylinder. The first die plate can cooperate with a second die plate attached to a second cylinder to cut the thin web of material. Optionally the die plate may be roll formed a second time with a radius generally equal to a radius of the cylinder to which the die plate is to be attached.

From the foregoing disclosure and the following more detailed description of various preferred embodiments it will be apparent to those skilled in the art that the present invention provides a significant advance in the technology of rotary cutting tools. Particularly significant in this regard is the potential the invention affords for providing a high quality, low cost method of making a flexible die plate for a rotary cutting tool. Additional features and advantages of various preferred embodiments will be better understood in view of the detailed description provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a rotary cutting tool in accordance with a preferred embodiment.

FIGS. 2A-2c are a series of schematic views of a flexible die plate of the rotary cutting tool of FIG. 1, showing the introduction of a radius to the flexible die plate, and ending in a die plate having a radius.

FIG. 3 is a top side view of the cylinder with the die plate removed, showing the position adjustment devices.

FIG. 4 is an isolated perspective view of a die cylinder adapted to receive a flexible die plate in accordance with a preferred embodiment.

FIG. 5 is a perspective view of a die cylinder with a flexible die plate pulled away to reveal an attachment and alignment device for the die plates.

FIG. 6 is a close up perspective view of the attachment and alignment device for the die plate.

FIG. 7 is an exploded perspective view of the position adjustment device.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the rotary cutting tool as disclosed here, including, for example, the specific dimensions of the cutting elements of the flexible die plates, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to improve visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity of illustration. All references to direction and position, unless otherwise indicated, refer to the orientation illustrated in the drawings.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

It will be apparent to those skilled in the art, that is, to those who have knowledge or experience in this area of technology, that many uses and design variations are possible for the rotary cutting tool disclosed here. The following detailed discussion of various alternative and preferred features and embodiments will illustrate the general principles of the invention with reference to a rotary cutting tool suitable for use in industrial applications where flat paperboard-like materials are to be cut. Other embodiments suitable for other applications will be apparent to those skilled in the art given the benefit of this disclosure.

Referring now to the drawings, FIG. 1 shows a rotary cutting tool 10 in accordance with a preferred embodiment having an upper die cutting assembly 96 and a lower die cutting assembly 98. The upper die cutting assembly has a cylinder 14 and die plate 18 wrapped around the cylinder, and the lower die cutting assembly 98 has a cylinder 16 and a die plate 20 wrapped around the cylinder. Each of the assemblies 96, 98 are mounted on a stand 12 so that the cylinders 14, 16 come into close proximity with one another. The upper cylinder 96 is rotatable about axis 97 and the lower cylinder is rotatable about axis 99, with the axes 97 and 99 generally parallel with one another. Each die plate's position is preferably adjustable with respect to the die cylinder at one or more mounting locations near pins 24, 25.

Each die plate has cutting blades or elements 26, 27, preferably formed as unitary extensions of the corresponding die plate. Cutting elements are understood here to include broadly any machined changes to the die plate, including raises, recesses and markings. The cylinders 14, 16 are in registry with one another so that they rotate together. When a thin web of material (for example, paperboard used to make cereal boxes) is fed between the rotating die plates 18, 20, the cutting elements or blades 26, 27 cooperate to cut the thin web of material into carton blanks.

In accordance with a highly advantageous feature, the flexible die plates disclosed herein may advantageously be roll formed prior to machining cutting elements and prior to installation on the corresponding cylinder. A curve may be introduced to the flexible die plate so that the die plate forms a generally cylindrical shape, and a radius of the die plate so produced generally corresponds to the radius of a cylinder which the die plate is designed to wrap around. FIGS. 2A-2C show schematically a flexible die plate gradually rolled into a generally cylindrical shape which is formed to fit around a cylinder 18. The generally cylindrical shape makes die plates disclosed herein much easier to install around a cylinder than known chemically etched flexible dies. Holes 120 may be formed near corners of the generally rectangular die plate prior to roll forming, to be used for attaching the die plate to the fixture and to the die cylinder.

In accordance with a highly advantageous method of manufacture, the die plates may be roll formed to a cylindrical shape which corresponds to the cylindrical shape of a fixture. That is, the die plate has about the same radius as the fixture, and fits snugly on the fixture. Next, the curved die plate may be mounted on the fixture and machined. In addition to roll forming the flexible die plates, preferably the die plates are heat treated, particularly at the cutting elements. Rockwell hardness of the cutting elements of at least 55, and most preferably about 58-60 may be achieved by heat treating. Moreover, roll-forming the flexible die plate introduces stress. Application of heat to the cutting elements relieves the stress prior to hardening, thereby advantageously increasing the useful life of the die plates.

If the fixture and the cylinder happen to have about the same diameter, the die plate may be removed from the fixture and installed on the cylinder. If not, the machined, generally cylindrical flexible die plate may be roll formed a second time into a generally cylindrical shape formed to fit around the cylinder used for making carton blanks. The radius of the flexible die plate so formed is approximately the same radius as that of the cylinder 18, and most preferably a radius slightly larger than the radius of the cylinder 18 to allow for snug assembly. Thus, the order of manufacture can comprise first roll forming the unmachined die plate to fit on a fixture cylinder, machining cutting elements onto the die plate, heat treating the cutting elements, optionally roll forming the die plate a second time to create a die plate having a radius about the same as a cylinder it will be attached to, and then assembling the position adjustment devices, magnets and die plates to the cylinder. After attaching each die plates to its corresponding cylinder, fine position adjustment can then occur. In final assembly, the die plates and cylinders can cut paperboard because they are positioned in close proximity to one another as shown in FIG. 1. Because of the speed of installation and the speed of disassembly, it is easy to switch products being manufactured. Thus, this method of manufacture of flexible die plates allows for greater use of low volume or limited edition production runs.

FIG. 3 shows a preferred embodiment of a cylinder 14 with the flexible die plate removed, having a position adjustment device on either side, with each position adjustment device comprising yoke 90 and y-slide 30, discussed in greater detail below. Positioned between the position adjustment devices are one or more magnets 60. The magnets are used to help hold the flexible die plate in place until the fasteners 24, 25 are attached. Bearer surfaces 75 may be provided, extending radially around the axis of rotation a little beyond the cylindrical surface. The bearer surfaces can engage bearer surfaces on an adjacent cylinder and thereby act as protection for the cutting surfaces of the die plates.

FIG. 4 shows the die cylinder 14 of FIG. 3, having a cylindrical surface 19 with a constant radius about an axis of rotation 97. Two sides 17 extend from either end of the cylindrical surface 19 (only one side is visible in the perspective view of FIG. 3) generally perpendicular to the axis of rotation and to the cylindrical surface. A large space comprises pocket 62 for the magnets and pockets 64 for the fine position adjustment devices. When the pockets 62, 64 are combined, they result in a large groove cutaway in the cylindrical surface of the cylinder 14. A first opening 39 and a second opening 34 are positioned on each side 17, and connect to the corresponding pocket 64. In certain preferred embodiments the openings 39 and 34 may be formed as a single opening. Openings 79 in pockets 64 of the die cylinder 14 are sized to receive pins for securing the corresponding yokes 90 to the cylinder.

FIG. 5 shows a die plate 18 with the cutting surfaces removed for simplicity of illustration, leaving only the thick die corners 29 and the alignment surfaces 111. Alignment surfaces 111 can be used for guidance of the die plate in a second roll forming operation to change the radius of the die plate to correspond with the radius of the cylinder to which it will be attached as discussed above. The die plate is partially unwrapped around a die cylinder 14, and when installed ends of the die plate meet at the dotted line shown in FIG. 5. Partially unwrapping the die reveals a pair of position adjustment devices. Each position adjustment device preferably comprises a yoke 90, adjustable slide 30 and various other elements as described in greater detail below. The adjustable slides 30 are positioned in yokes 90 which are in turn connected to the die plates remote from the cutting surfaces of the die plates. More specifically, as shown in the Figs., the adjustable slides 30 are positioned on the underside of the die plate 18, the side opposite the side of the die plate with the cutting surfaces. In the embodiment shown in the drawings, pair of fixed pins or bolts 73 secure the yoke 90 to the cylinder. Alternatively, one of the fixed pins may be replaced with an adjustable slide assembly slidable along the X-axis, if needed.

FIG. 6 is a close-up view of one of the position adjustment devices. Preferably the die plates are adjustably captivated to the die cylinder. Adjustably captivated as used herein means that the motion of one part with respect to another part is partially restricted. For example, the adjustable slide 30 is free to slide back and forth with respect to the die cylinder around the axis of rotation of the die cylinder (along the Y-axis labeled in FIG. 6). However, the adjustable slide is captivated so that it is held in a pocket in the yoke, and cannot leave the pocket along the Z-axis. In a similar manner the outer eccentric 40 is adjustably captivated to the slide 30, and the inner eccentric 50 is adjustably captivated to the outer eccentric 40.

The pocket in the yoke is preferably oversized, in the sense that the adjustable slide 30 in inserted into the pocket and leaves a gap 55 for adjustment along the Y-axis, and a gap along the X-axis. The top surfaces of the yoke, slide, first eccentric and second eccentric, respectively, are preferably flush with the outer cylindrical surface of the cylinder. That is, these surfaces may be machined down to share a common radius with the die cylinder 14. An eccentric adjustment screw 38 extends through first opening 39 on the side wall to urge the outer eccentric 40 to rotate with respect to the adjustable slide. A wedge adjustment screw 32 extends through second opening 34 and engages a wedge 70 to urge the adjustable slide along the Y-axis. First opening 39 and second opening 34 may alternatively be formed as a single opening. An adjustable clamp 80 fills up the gap along the x-axis, urging the slide 30 against one wall of the pocket in the yoke.

Yoke 90 has an opening 66 sized to receive pin 24 securing the die plate 18 to the yoke. In a similar manner bolt 73 extends through opening 69 to secure the yoke to the cylinder. In this manner the flexible die plate is secured to the cylinder. Other attachment mechanisms may also be used.

FIG. 7 is an exploded perspective view of the adjustable slide assembly. Wedge 70 and clamp 80 cooperate to secure the position of the adjustable slide 30. The outer eccentric sits in a cavity in the adjustable slide. The eccentric engagement screw (shown in FIG. 6) engages the outer eccentric 40. The outer eccentric engages the adjustable slide. Similarly, the smaller eccentric 50 engages the larger eccentric 40. Opening 67 in the small eccentric 50 receives screw 25, at an opening in the die plate. The die plate 18 is captivated between the screw 25 and the slide 30 so that the die plate is adjusted by adjustment of the adjustable slide assembly.

It will be apparent to those skilled in the art, that is, to those who have knowledge or experience in this area of technology, that many uses and design variations are possible for the flexible die plates disclosed here. The following detailed discussion of various alternative and preferred features and embodiments will illustrate the general principles of the invention with reference to a rotary cutting tool suitable for use in industrial applications where flat paper-like materials are to be cut. Other embodiments suitable for other applications will be apparent to those skilled in the art given the benefit of this disclosure.

Claims

1. A method of making a rotary cutting tool comprising, in combination, the steps of:

roll forming a first flexible die plate into a cylindrical shape;

mounting the cylindrically shaped die plate onto a cylindrically shaped fixture; and

machining cutting elements onto the roll formed die plate.

2. The method of making a rotary cutting tool further comprising the step of attaching the die plate to a corresponding cylinder.

3. The method of claim 1 wherein the fixture has a cylindrical, curved surface and the curve of the die plate generally corresponds to the curved surface of the fixture.

4. The method of claim 1 further comprising the step of:

removing the die plate from the fixture and roll forming the die plate a second time, forming the die plate into a generally cylindrical shape.

5. The method of claim 4 further comprising a cylinder having a radius, wherein the generally cylindrical shape of the flexible die plate is has a radius which is about the same size as the radius of the cylinder.

6. The method of claim 4 further comprising a cylinder having a radius, wherein the generally cylindrical shape of the flexible die plate is has a radius which is slightly larger than the radius of the cylinder.

7. The method of claim 1 further comprising the step of heat treating the cutting elements formed on the flexible die plate.

8. The method of claim 1 further comprising the step of assembling the flexible die plate and a position adjustment device to a cylinder, wherein the position adjustment device provides for position adjustment of the flexible die plate on the cylinder.

9. The method of claim 8 wherein the position adjustment device comprises a yoke which receives a y-slide and at least one eccentric.

10. The method of claim 8 further comprising the steps of:

roll forming a second flexible die plate into a cylindrical shape;

mounting the second die plate onto the cylindrically shaped fixture;

machining cutting elements onto the roll formed die plate;

assembling the second die plate and a second position adjustment device to a second cylinder; and

positioning cylinders with attached die plates in close proximity to one another, allowing the die plates to cooperate to cut a thin web of material.