ES2960556T3 - Wire drawing die with associated bit holder - Google Patents

Abstract

The invention relates to a drawing die and the associated bit holder. The tip holder is constructed so that at least 20% of the tip mantle surface remains exposed to the coolant during drawing in a limited number, for example two, three up to twelve separate areas. This ensures sufficient cooling of the tip. The bit holder comprises a base plate with protruding clamps that hold the bit. The pen holder is made from a single piece of material. An associated method of inserting the tip into the bit holder is also described. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Wire drawing die with associated bit holder

Technical field

The invention relates to the field of drawing dies used for drawing metal wires. The drawing die according to claim 1 is particularly suitable for drawing metal wire in liquid lubricants, also called "wet drawing". The tip of the drawing die is held in a tip holder according to a second aspect which is not part of the claimed invention. A method for inserting the tip into the bit holder is also described, which represents a third aspect that is part of the invention.

Background of the technique

In the production of metal wires such as steel wires, copper alloys or aluminum alloys, for example, the wire is drawn through subsequently smaller holes in drawing dies, resulting in a gradual reduction of the wire diameter . The drawing dies are kept on a drawing bench which is provided with multiple winches between the drawing dies that pull the wire through the holes. A lubricant is applied to the wire to reduce friction between the drawing die and the passing wire.

Since the plastic deformation of the wire and the friction between the wire and the drawing die generate a lot of heat, the drawing die must be cooled to prevent premature failure of the drawing die. In dry drawing, that is, when dry powder is used as a lubricant, the drawing dies are individually provided with a coolant supply. In wet drawing, the drawing dies and wire are immersed in a liquid emulsion that acts as a lubricant and coolant. In the rest of the application there will be constant use of the word "coolant", although the expert will understand that this "coolant" also has other functions such as lubrication.

This application focuses on drawing dies for use in wet drawing machines and processes, "wet drawing dies" or simply referred to as "drawing dies" hereinafter. A typical wet drawing bench can fit between ten and fifty drawing dies. A typical wire mill uses hundreds to millions of drawing dies each year.

Known wet drawing dies consist of a cylindrical tip which is held in a cylindrical metal housing. The tip is made of a very hard material in which a funnel-shaped axial hole is machined and polished. The housing is made of machined steel. A problem with known wet drawing dies is that thermal heat transport is not always optimal since the heat has to leave the tip and must be absorbed by the casing which in turn is in contact with the coolant. To overcome this cooling problem different suggestions have been made in the prior art:

GB 872 225 (D4) describes a tip holder (called "die holder" in D1) in which the tip 17 (called "pellet" in D1) is held in the holder which is provided with a "chamber" with " "radial ports" that run from the perimeter of the chamber to supply coolant medium immediately around the tip. The holder is complex to manufacture and coolant must be injected into the radial ports to cool the tip.

DE596506 (D5) describes an "F" bit holder for a dry drawing die in which cooling channels are provided in the bit holder. The bracket is difficult to manufacture and the coolant must be supplied separately.

GB298821 describes a housing for a drawing die wherein the housing consists of a hollow member enclosing the die, the hollow member being provided with inlet openings at the front of the housing and outlet openings at the rear of the housing. , the inlet and outlet openings communicating with an annular space between the tip and the housing for the passage of a cooling liquid to the matrix. The support is complex to manufacture and a forced passage of coolant through the drawing die is necessary to achieve good cooling.

Document CN201324454U describes a bit holder provided with external circumferential cooling grooves. According to the experience of the inventors, the cooling slots easily accumulate dirt, thus reducing the cooling capacity of the dies.

Document GB896478 (D1), which forms the basis of the preamble of claim 1, describes a gas-cooled die housing which at one end is provided with an annular recess with a curved section surrounding the die insert. The annular recess connects with spaced radial holes to circumferentially spaced horizontal longitudinal passages that extend from end to end of the die housing and are in direct contact with the outer surface of the insert. This design is complex and the insert is not open for direct and unobstructed access with coolant.

US 2924329 (D2) discloses a die retainer for vertically holding a finishing die by two laterally spaced arcuate members. This is a die retainer and not a drawing die comprising a tip and a tip holder.

DE 25 38 177 (D3) shows a disc for holding a drawing die. The disc is provided with channels to cool the drawing die and the drawn wire with a jet of cooling water.

To overcome the drawbacks of the prior art, the inventors have devised a completely new design of a drawing die which will now be described in detail.

Disclosure of the invention

A main object of the inventors is to provide a drawing die whose tip can be well cooled. Another object of the inventors is to provide a drawing die and an associated bit holder that is easy to manufacture and has a low cost both in terms of material and manufacturing cost. Another object of the invention is to provide a method of mounting the bit in the bit holder. Yet another object which is not part of the invention is to provide a method of producing the bit holder.

According to a first aspect of the invention, a drawing die is presented with the characteristics of claim 1. The drawing die comprises a tip and a tip holder, the tip having a through hole. The through hole will generally be funnel or trumpet shaped. The wire enters through the widest entrance of the funnel, called the "entry cone," and exits through the narrowest spout. After the spout, the through hole opens again forming an "exit cone". The through hole defines a tip shaft.

The tip has a frustoconical and/or cylindrical coating that is coaxial to the tip axis. In this way, the tip liner can be completely cylindrical along the entire axial length of the tip. Or the tip coating may be that of a single truncated cone along the entire axial length of the tip. A truncated cone is the frustum of a cone. The liner may also be a combination of a cylindrical surface over a portion of the axial length and a truncated cone over the remaining portion of the axial length. The alternative and equivalent wording is that the tip has a "substantially cylindrical coating."

The tip holder leaves at least 20% of the tip coating surface uncovered and this in a limited number of uncovered areas. "Uncovered area" means that the bit holder does not contact the bit in that area. Possibly the areas are separated, meaning that a line can be drawn between the areas on the tip coating, without entering the areas. The total surface area of uncovered areas is at least 20% of the coating surface. For clarity: Liner surface means the circumferential frustoconical and/or cylindrical liner surface of the tip, thus excluding the axial end areas (upper and lower) of the tip. The number of uncovered, possibly separate, areas is two, three, four, five, six, seven or eight, up to and including twelve.

When the number of uncovered areas is less than two, the bit holder will not be able to hold the bit sufficiently. When there are more than twelve bare areas, the bit holder is difficult to produce.

In an alternative and equivalent way of describing the invention, at least 20% of the surface of the coating is visible, that is, it is in the line of sight when viewing the bit held in the bit holder in all directions perpendicular to the axis of tip.

As the coolant completely surrounds the drawing die when it is immersed in coolant during drawing, the coolant can reach the tip coating unhindered and immediately. Since the coolant has free access to the tip coating, the tip cools very well. There is no need to cool the supply channels as the tip is directly exposed to the coolant due to the open structure of the tip holder. Due to the open structure of the bit holder, there is no risk of the cooling channels becoming clogged (e.g. due to dirt in the coolant), which would prevent the cooling of the die.

According to the invention, the clamps are provided with a protuberance, a projection, a projection on the radial inner side of the clamp at the end opposite the base plate. This protuberance prevents the tip from coming out of the bit holder when the machine stops and the wire recoils during drawing.

In a reduced form of the invention, the drawing die consists only of the tip and the bit holder and no other parts.

In other preferred embodiments at least 30%, 40%, 50%, 60%, 70% or even 80% of the coating surface remains uncovered by the bit holder. Although cooling will be further improved by increasing the surface exposure of the tip coating, it is becoming increasingly difficult to hold the tip in the die holder. The purpose of the inventive drawing die is to expose as much of the tip coating as possible while the tip is held in the tip holder to improve tip cooling.

In another alternative and equivalent way of describing the invention, the bit holder covers a maximum of 80% of the surface of the tip coating in a number of areas covered by the bit holder, said number of covered areas being one, two, three, four , five, six, seven or eight up to and including twelve. Mutatis mutandis, the cooling capacity of the tip will increase when the coverage of the tip coating by the tip holder is reduced to at most 70, 60; 50, 40, 30 or even 20% of the tip coating surface area.

The tip is made of a hard material such as cermet, carbide, cemented carbide, polycrystalline diamond (PCD) compacts or monocrystalline diamonds of natural or synthetic origin. Mainly cemented carbides such as tungsten carbides are used with, for example, a cobalt-containing binder. PCD compacts are also preferred for use in the invention.

In an alternative definition of the invention, the bit holder comprises a base plate from which clamps protrude. The clamps serve to hold the tip firmly. The clamps are unitary to the base plate, meaning that the base plate and clamps are made from a single, unitary piece of material - there are no welds or mechanical connections between the base plate and the clamps. The base plate has at least one through hole that is coaxial to the tip shaft through which, during use, the wire is drawn. The wire is pulled in the direction from the clamps towards the base plate.

According to the invention, the clamps are provided with a protuberance, a projection, a projection on the radial inner side of the clamp at the end opposite the base plate. This protuberance prevents the tip from coming out of the bit holder when the machine stops and the wire recoils during drawing.

The clamps cover a maximum of 80% of the tip liner surface. Less coverage, such as less than 70, 60, 50, 40, 30, or even 20%, will further increase tip cooling, but at the expense of it not holding as well in the die holder. It is preferred that at least 20% of the liner surface be in the line of sight when viewing the tip held in the tip holder in all directions perpendicular to the tip axis. The amount of visible surface can also be more than 30, 40, 50, 60, 70 or even 80% of the coating surface.

The base plate may have any shape but more preferably the base plate has a polygonal shape, for example a regular polygonal shape or a Reuleaux polygon shape. Preferably, the number of vertices is equal to the number of clamps.

In another highly preferred embodiment, the base plate is in the shape of a ring.

In another preferred embodiment, the clamps protruding from the base plate are evenly distributed angularly. If, for example, the number of clamps is three, the angle between clamps is 120° viewed from the tip axis. In case the number of clamps is "N", the angle between the clamps, seen from the tip axis, is 360° / N.

In another preferred embodiment, a recess is provided around the through hole in the base plate of the bit holder. The recess serves to receive the base of the tip. The "base of the tip" is one of the surfaces that axially delimit the tip on the side of the tip exit cone.

The number of clamps is at least two, since at least two clamps are needed to hold something, or any greater number, such as two, three, four, five, six, seven or eight up to and including twelve. Increasing the number of clamps complicates manufacturing. Preferably the number of clamps is three, four, five or six. Depending on the manufacturing method, an even or odd number of clamps may be preferred. When manufacturing the bit holder by machining, an even number of clamps is more preferred, while an odd number of clamps may be more preferred when casting the die holder.

In a highly preferred embodiment, the transition between the base plate and the clamps protruding from said base plate is rounded. More specifically, the transition from the base plate to the clamps is rounded between the clamps. By rounded we mean that the transition does not have sharp angles where dirt can accumulate. The minimum radius of curvature is at least half a millimeter. One, two or more millimeters is better.

In another preferred embodiment, the protruding clamps for the base plate extend at least two-thirds of the axial length of said tip outside the base plate. Less extension of the clamps results in too low clamping force for the tip. Most preferred, the clamps protrude about the axial length of the tip out of the base plate. No more is necessary, as this results in superfluous material.

According to a second aspect that is not part of the claimed invention, a bit holder is presented. The bit holder has a base plate with clamps that protrude from the base plate. The clamps and the base plate are a whole, that is, unitary. The clamps and base plate are made from the same uninterrupted piece of material. The base plate has a through hole in the center of the base plate to allow the wire to pass through. The bit holder is specifically designed for use in the drawing die as described in the first aspect of the invention because the radial inner top of the clamps is provided with a protuberance, a projection, a projection on the radial inner side of the clamp. on the end opposite the base plate to hold the top of the tip.

According to a preferred example, the bit holder has an axis of symmetry passing through said through hole and which is perpendicular to the base plate. In a preferred embodiment, the protruding clamps are uniformly angularly distributed around the axis of symmetry.

In another preferred example, the base plate of the bit holder is a ring. The number of protruding clamps is two, three, four, five, six, seven or eight or up to and including twelve.

Preferably, at the transition where the clamps extend and exit the base plate, the transition is rounded. Preferably, the radius of curvature at the transition is greater than half a millimeter, for example one, two or more millimeters. This is to prevent dirt buildup during use of the drawing die in the wet drawing machine.

Other preferred examples of the bit holder may display the following additional features:

• The circumferential thickness (relative to the tip axis) of the protruding clamps decreases radially toward the center of the bit holder. In this way, sufficient surface area of the tip coating is exposed while the clamps are still strong enough to hold the tip.

• The clamps are held mechanically by a retaining ring that connects all the clamps. The retaining ring fits into notches made circumferentially in the top of the clamps. The retaining ring serves to give additional strength to the clamps.

According to a third aspect of the invention, a method is provided for gripping a tip in a bit holder, thereby forming a drawing die according to the invention. The method begins by providing a bit holder according to the second aspect of the invention. A tip is provided next to it. The tip has a cylindrical or truncated conical circumferential coating or a concatenation of both. In an additional step a force is applied to the center of the base plate while holding the outer edge of the base plate. The force is exerted from the side opposite the side of the base plate where the clamps protrude. This force opens the clamps very slightly, but enough to allow a temporary grip on the tip. This allows the tip to be inserted between the protruding clamps. In a final step, the tip is pressed completely into the bit holder. Possibly the base of the tip is housed in the recess of the base plate.

In an alternative implementation of the method, the method can be combined with heating the bit holder, for example when purely cylindrical tips are used. However, care must be taken that the combination of the force applied at the center of the base plate with the heat applied does not lead to plastic deformation of the die holder.

According to a fourth aspect that is not part of the claimed invention, a method of producing the bit holder according to the above by metal injection molding is described. The method includes the steps of:

• Provide a mixture of a binder comprising a metal powder;

• Injection mold the mixture in a mold whose internal cavity has the shape of the bit holder, thus forming a new bit holder;

• Remove the new tip holder from the mold;

• Peel off the binder from the new tip holder, thus forming an annealed tip holder;

• Sinter the annealed bit holder until maximum densification is achieved;

• Cool the sintered bit holder, resulting in a finished bit holder.

Brief description of the figures in the drawings

Figure 1 shows a prior art wire drawing die;

Figure 2 shows a first wire drawing die which does not form part of the invention;

Figure 3 shows a second wire drawing die which does not form part of the invention;

Figure 4 shows a third wire drawing die according to the invention.

Figure 5 shows a fourth wire drawing die which does not form part of the invention;

Figure 6 illustrates the method of inserting the tip into the bit holder;

Similar elements in different figures carry the same unit number and tens, the hundred indicates the number of the figure.

Mode or modes to carry out the invention

Figure 1 shows a prior art drawing die 100 comprising a tip holder 102, also called a "housing", and a tip 104. The tip has a through hole 110 through which the wire is guided. The wire enters through the wide entry cone 106 and exits through the smaller exit cone 108. The through hole is therefore funnel-shaped.

The tip is made of cemented tungsten carbide and cobalt is used as a binder. The size and finish of the tips are standardized in international standards such as ISO 1684 and ISO 2804. The tip size is indicated by DxH, where "D" is the outer diameter of the tip (usually in mm) and "H" is the axial height of the tip (also usually expressed in mm). A typical tip size is, for example, 12x10 or 16x13. The shape of the outer casing of the tip is generally cylindrical (when the tip is inserted into the casing by a "hot casing") or is a combination of a cylindrical surface with a frustoconical chamfer on the side of the exit cone (when the tip It is inserted into the casing by means of a “cold casing”). Tips are commercially available from suppliers such as Ceratizit, Hyperion and many others.

In prior art drawing dies, the tip holder is a steel cylinder with a central hole into which the tip fits firmly (by means of a "hot" or "cold" housing). As the tip coating is in close contact with the steel casing, there is a general belief that the heat generated at the tip will easily pass through the barrier between the tip and the steel. However, due to dirt or lubricants remaining on the tip or housing, a microgap can occur between the tip and the housing, creating a thermal barrier, thereby reducing heat extraction and increasing the temperature of the tip during the wire drawing.

Figure 2 shows a drawing die 200 not according to the invention. It consists of a tip 204 which is a conventional tip that is held in the bit holder 202. The bit holder has an open design so that approximately 50% of the outer coating of the tip 204 is not covered in three separate areas. The sum of the uncovered areas amounts to approximately 50% of the coating surface. Put another way: the bit holder only covers approximately 50% of the tip surface, leaving the remaining part directly visible.

The relationship between the surface area that is not covered and the total surface area of the coating can be verified by various means, for example:

• Using spray paint (a “line of sight” coating technique), wire drawing the entire die, removing the tip, measuring the painted surface and comparing it to the tip coating surface;

• Using computer-assisted visual techniques based on images of the drawing die. The surface of the exposed coating of the tip is calculated taking into account the cylindrical shape of the tip.

Constructing a drawing die in this manner leaves, during use of the drawing die, the tip directly exposed to the coolant in which the drawing die is immersed. In this way a strong tip cooling effect is obtained, better than having the tip cover completely enclosed in the cylindrical housing of the prior art. It is important here that the coolant can have direct, unobstructed and unimpeded contact with the tip without the need for additional coolant feed (through, for example, channels) to the tip.

In the shape of the bit holder 202, a base plate 212 can be distinguished from which three clamps 214, 214', 214'' protrude from the plane of the base plate 212. The clamps 214, 214', 214'' are distributed along of the tip axis under an angle of 120°, that is, they are distributed angularly uniformly around said axis. Since the bit holder 202 is machined from a single piece of material, the clamps and base plate are unitary. The base plate 212 is in this case a ring provided with a central through hole to allow the wire to pass through.

A second drawing die 300 not according to the invention is shown in Figure 3. The drawing die 300 is similarly made of a single piece of material in which the clamps 314 protrude from a base plate 312 that forms the bit holder 302. The difference with the first drawing die is that the transition 316 from the plate base to the protruding clamps is rounded. The rounding prevents dirt from collecting in the corner between the base plate and the clamp. Also on the base plate 312, a circular recess is provided to receive the base of the tip (not visible in Figure 3).

Note that in both the first and second practical drawing dies the clamps narrow and gradually become thinner radially towards the tip axis, that is, the circumferential thickness of the clamps decreases towards the tip axis. This way, the tip liner surface remains uncovered without compromising the strength of the clamps.

A practical embodiment of a drawing die 400 according to the invention is shown in Figure 4. The tip 404 is held in the die holder 402 by means of six clamps 414 evenly distributed angularly. The transition from the base plate 412 to the clamp is rounded with a radius of curvature of approximately 1.5 mm. Note that in this case the width of the clamps 414 remains constant. Furthermore, protuberances 422 are provided on the top of the clamps, on the radially inner side. The protuberances 422 serve to prevent the wire from coming out of the tip 404 of the tip holder 402 when the drawing machine is suddenly stopped and the wire recoils and rebounds.

A third drawing die 500 not according to the invention is shown in Figure 5. The six clamps 514 are connected with a retaining ring 520. The retaining ring fits into circumferential notches 524 made in the top of the clamps. Retaining ring adds extra strength to 514 clamps.

The material the bit holder is made of is tool steel or machine steel. Some examples are EN 11 SMnPb30 and EN C45E or similar.

The following methods can be used to produce the bit holders: First is the method of machining the bit holder. In this method, material is removed from a round steel rod corresponding to the outside dimensions of the die holder. For example, the gaps between the protruding clamps are milled with chisels or drills at the end of the rod. The procedure ends with turning the end of the rod. With current numerical control machines the procedure can be easily automated.

Second is the casting method. A mold can be made using the lost wax technique that represents the bit holder. Pouring molten metal into the mold and opening the mold after solidification results in a mold. Additionally, the mold needs to be finished to obtain the desired tolerances, making this method somewhat less preferred.

Thirdly, the metal injection molding technique is used. The technique includes the steps of:

• Completely mix a binder with a metal powder to obtain a homogeneous mixture of raw material or

obtain a raw material prepared and commercially available;

• Injection mold the mixture in a mold thus forming a "green" bit holder. The mold cavity is shaped like the bit holder;

• Remove the green tip holder from the mold;

• Remove the binder from the green bit holder, thus forming a "brown" bit holder;

• Sinter the brown bit holder until maximum densification is achieved. During sintering, the original dimensions of the brown bit holder will be reduced. This shrinkage must be taken into account in the design of the tip holder mold.

The colors "green" and "brown" are commonly used in metal injection molding, but have no relation to the actual color of the part. They are only indicative of the condition of the casing: “green” can be replaced by “fresh” and “brown” can be replaced by “annealed”. The technique allows matrix supports to be manufactured in large quantities and at low cost. Bit holders made with this technique show some small bubbles of gases trapped within the metal. Small bubbles are an indication that this metal injection molding technique has been used.

Figures 6, “a” to “d” illustrate the method of how to insert the bit into the bit holder according to the invention. In Figure 6 a of the bit holder 602. A seal 632 is pressed against the center of the base plate. Figure 6 “b”.

Exerting force 634 through seal 632 opens clamps 614 protruding from the bit holder. By actuating the tip 604 by a force 636, the tip is fully inserted into the bit holder. See Figure 6 “c”.

After all forces are released, the tip is held firmly between the clamps 614 as illustrated in Figure 6 “d”.

Claims (9)

1. A drawing die (200, 300, 400, 500) comprising a tip (204, 304, 404, 504) and a tip holder (202, 302, 402, 502) for holding said tip, said tip having a hole through that defines a tip axis, said tip also having a frustoconical and/or cylindrical coating coaxial to said tip axis, wherein said bit holder has a base plate (212, 312, 412, 512) with clamps (214, 314, 414, 514) that protrude from the plane of said base plate to hold said tip, said clamps are unitary to said base plate, said base plate having a through hole coaxial to said tip axis in which at least 20% of the surface of said coating is in the line of sight when the tip held in the bit holder is viewed in all directions perpendicular to the tip axis, characterized by said clamps (414) are provided with a protuberance, a projection, a projection (422) on the radial inner side of said clamps at the end opposite said base plate. 2. The drawing die (200, 300, 400, 500) according to claim 1, wherein the number of protruding clamps are two, three, four, five, six, seven, eight up to and including twelve. 3. The drawing die (200, 300, 400, 500) according to claim 1 or 2, wherein said clamps cover at most 80% of the surface of said coating. 4. The drawing die (200, 300, 400, 500) according to any one of claims 1 to 3, wherein said protruding clamps are uniformly angularly distributed around said tip axis. 5. The drawing die (300) according to any one of claims 1 to 4, wherein said base plate is provided with an annular recess to receive the base of said tip. 6. The drawing die (300, 400) according to any one of claims 1 to 5, wherein the transition from the base plate to the clamps projecting from the base plate (316, 416) is rounded. 7. The drawing die (200, 300, 400, 500) according to any one of claims 1 to 6, wherein said clamps projecting from the base plate extend at least two-thirds of the axial length of said tip outside said base plate. 8. The drawing die (200, 300) according to any one of claims 1 to 7, wherein the circumferential thickness of said protruding clamps (214, 314) decreases radially towards said tip axis. 9. A method of holding a tip (604) in a bit holder (602), thereby forming a drawing die (600) according to any one of claims 1 to 8, comprising the steps of: - Providing a bit holder, said bit holder having a base plate (212, 312, 412, 512) with clamps projecting from said base plate (214, 314, 414, 514), said clamps and said base plate being unitary, said base plate having a through hole in the center of said base plate; - Provide a tip; - Apply a force (634) to the center of the base plate (632) while holding the outer edge of the base plate (630); - partially insert said tip between the protruding clamps; - Press (636) said tip completely inside said bit holder.