A die or punch for a press tool.

FIELD OF INVENTION

This invention relates to a die or punch for use in a press tool. A preferred form of the invention relates to a die or punch with a replaceable shoulder portion for a power press.

BACKGROUND

Metal presses come in many and varied forms. At one end of the spectrum is the "garage press" which is a simple and low cost fabricated construction designed to be versatile for the many and varied one-off tasks that it might be needed for in an automotive workshop, i.e. removal of bearings from a wheel hub etc. At the other end of the spectrum is the high precision, high speed "minting press" designed to stamp out coinage with extreme accuracy by the millions. Other common presses within this spectrum include Press Brakes and power presses. Press Brakes are designed to manufacture long sheet metal components such as storage cabinets and building products like roof guttering etc. Power press is a generic term used for the most common type of press that is used to manufacture a myriad of metal components that are in everyday use, ranging from small automotive components to building bracketry, furniture, electrical goods, componentry and an endless list of other everyday widgets.

A Press Brake is typically a machine used to bend relatively thin pieces of sheet metal one simple fold at a time. Because the machine is used to bend thin pieces of sheet metal the forces exerted on the work piece are relatively small. The machine can be easily changed to varying speeds and stroke heights (the extent to which the punch travels down towards the work piece and die). The tools for a Press Brake are standard and can be fitted or removed quickly. Press Brake tools are typically relatively lightweight and can be lifted by hand. In a Press Brake operation, at the bottom of the stroke there is usually only contact on the work piece at three points; from the punch on the top middle and the two shoulders of the die on the bottom. A power press is used to bend or punch holes in relatively thick pieces of metal. The forces exerted by a power press are much greater than those exerted by a typical Press Brake. A power press is set up to very fine tolerances; for example the tools used in the power press are fitted onto slides to ensure that they are always in the same position relative to one another. Power press tools - comprising a die and a punch - are securely fitted to the machine; a process that can easily take an hour or more. The tools are made from solid steel and are very heavy, often requiring special equipment to lift them into position. At the bottom of the power press stroke the work piece is usually completely sandwiched between the punch and the die, i.e. there is no gap anywhere.

In a power press the radius of the shoulders of the tools is normally determined by the thickness of the work piece. The cosmetic appearance of the work piece is, generally speaking, not so important. A power press is normally used for repetitive press work - one machine might perform 10,000 identical operations a day, day in, day out. Power presses are not usually used to make one-off bends in sheet metal.

Tools used in power presses are often made from heat treated and hardened specialist tool steels. High carbon steel can be hardened by first heating the steel then rapidly cooling the steel. The steel is then reheated to a lower temperature and allowed to cool slowly. It is sometimes just possible to tap a threaded hole into a hardened steel tool. However it is extremely difficult and expensive to do so. It is usually more cost effective to replace a hardened steel tool than to tap a threaded hole into the tool.

It is a problem to constantly repair or maintain the hardest worked areas of a metal forming tool used in a power press. The hardest worked areas of a tool are usually the shoulders. Damage to the shoulders is caused by the work piece being drawn across the shoulder, or the shoulder being drawn across the work piece. Basically the damage is caused by the friction between the two faces generating enough heat at a microscopic level that some of the surface particles melt and then cause further damage to the surrounding face. Factors that determine the amount of damage sustained by the tool include:

• The properties of the work piece material

· The pressure exerted between the face of the tool shoulder and the work piece • The speed at which the work piece is drawn over the tool shoulder or the tool shoulder is drawn over the work piece

• The amount and quality of lubricant between the faces

• The quality of the tooling material

· The surface finish of both the work piece and the tooling material

• General cleanliness of the surfaces of the work piece and the tool shoulder

• Other minor factors such as room temperature

• Production rate (the more uses of the tool per hour the more frequently the tool may need replacing due to damage).

It is an object of a preferred embodiment of the present invention to go at least some way towards addressing the problem of damage to the shoulder or shoulders of the tool. While this object applies to the preferred embodiment, it should be understood that it is not intended to limit the scope of the claims. This is because the object of the invention perse is simply to provide the public with a useful choice.

The term "comprising" and derivatives thereof, e.g. "comprises", if and when used herein in relation to a combination of features should not be taken as excluding the possibility that the combination may have further unspecified features. For example, a statement that an arrangement "comprises" certain parts does not mean that it cannot also, optionally, have additional parts.

SUMMARY OF INVENTION According to one aspect of the invention there is provided a die or punch for a press tool comprising:

a body; and

a roller assembly having a holder and a roller;

the holder shaped to slidably engage with a complementary cavity in the body to facilitate secure installation of the holder in the body, the holder being able to be removably inserted into the body to present the roller as a forming edge to shape a work piece in a press tool, the roller being able to turn with respect to the holder when shaping the work piece to protect the roller against wear. Optionally the roller comprises a cylinder arranged to turn, and which is replaceable, with respect to the holder. Optionally the roller is releasably secured to the holder by way of a clip.

Optionally the roller has a groove to facilitate securement by the clip.

Optionally the holder comprises a slot to facilitate securement of the clip.

Optionally the clip is generally in a horseshoe shape. Optionally ends of the roller are held in end retaining plates and the roller is able to rotate with respect to the plates.

Optionally the holder has at least one channel adapted to enable the passage of lubricant from an aperture in the holder to the roller.

Optionally there are two channels which run from opposite ends of the holder.

Optionally the holder has at least one fastening groove in a side thereof adapted to engage with a complementary protrusion in the body to facilitate secure installation of the holder in the body.

Optionally there are two fastening grooves, each running substantially the length of opposite sides of the holder. Optionally the holder is shaped to retain the roller in place in the press tool.

Optionally the roller assembly bisects the internal angle of the shoulder of the body of the die or punch to which it is fitted. Optionally the press tool is a fitted to a power press.

Optionally the press tool is made from hardened steel.

Optionally the roller assembly is retrofitted to the punch or die. Optionally the holder has a wider portion at or towards the base of the holder when compared to the roller end of the holder.

BRIEF DESCRIPTION OF THE DRAWINGS

Some preferred forms of the invention will now be described by way of example and with reference to the accompanying drawings, of which:

Figure 1 is a schematic side view showing a press tool in 3 dispositions of use; Figure 2 is a schematic side view of parts of the press tool when in use;

Figure 3 is an isometric view of the press tool in more detail, after the work piece has been formed;

Figure 4 is an exploded isometric view illustrating a roller assembly;

Figure 4A is an exploded isometric view illustrating a second embodiment of roller assembly;

Figure 5 is an isometric view of the roller assembly of figure 4 when assembled; Figure 6 is an exploded end view of the roller assembly of figure 4;

Figure 7 is an exploded side view of the roller assembly of figure 4;

Figure 8 is a cross-section end view of the roller assembly when assembled, at the point where the clip holds the roller in place;

Figure 9 shows end views of a number of different holder shapes;

Figure 10A is a schematic side view of the press tool in use, particularly illustrating one of the roller assemblies;

Figure 10B is a schematic side view of a press tool in use, particularly illustrating another embodiment of roller assembly;

Figure 11 is an isometric view of a solid one piece insert without a roller assembly, prior to installation;

Figure 12 is an isometric view showing detail of a roller;

Figure 13 is an isometric exploded view of an alternative roller assembly;

Figure 14 is an isometric view of the alternative roller assembly when assembled;

Figure 15 is a schematic side view of an alternative press tool prior to operation; Figure 16 is a schematic side view of the alternative press tool at an initial stage of operation;

Figure 17 is a schematic side view of the alternative press tool at a further advanced stage of operation; and

Figure 18 shows a die and punch with a plurality of rollers and holders DETAILED DESCRIPTION

Figure 1 shows a power press tool 1 having a die 2 and a punch 3 in three stages of use. The left hand image shows the punch 3 ready to move down on a work piece 4 in the form of a piece of metallic material laid over the die 2. The centre image shows the punch 3 just after it has first made contact with the work piece 4. The right hand image shows the power press tool when the punch is fully in the die's cavity 5 and has caused the work piece 4 to assume the shape of the cavity. Referring to figure 2, the shoulder 6 of the die 2 is exposed to substantial wear inducing force via the work piece 4 as the punch 3 forces the work piece 4 across it. The work piece may also receive scuff marks from being forced across the shoulder

6 of the die 2. These scuff marks require linishing to remove. Linishing involves grinding or belt sanding the affected area to improve the flatness of the surface. Linishing may also include polishing the surface. However, the press tool 1 shown in Figure 3 has features (not shown in figures 1 and 2) to address this.

Referring to figure 3, each shoulder of the die 2 has an interference fitted releasable wear resistant roller assembly 7. The roller assembly 7 slides into the shoulder 6 of the die at an angle which bisects the internal angle of the die, and presents a rolling curved wear edge 8 for contacting the work piece 4. The angle of the roller assembly

7 with respect to the shoulder of the die is preferably one which bisects the included angle of the shoulder of the die. In this case the included angle of the shoulder of the die is 90° and the angle of the roller assembly is about 45°. To facilitate fitting of the roller assembly into the die, the roller assembly has longitudinal grooves 7a (see figures 4 and 5) formed to engage with complementary protrusions (not shown) in the main body of the die. In some embodiments the rollers extend to the edge of the die. The rolling edge 8 enables the work piece 4 to roll over it and avoid the type of point loading that would occur if the edge was static.

Alternatively the roller assembly may be any suitable shape to fit the complementary cavity in the punch and/or die 2. Figure 9 shows different embodiments of roller assembly 7 that can be used. While figures 4, 4A and 5 show roller assemblies 7 with grooves 7a to engage with complementary protrusions it should be appreciated that these are not essential to every embodiment of roller assembly 7. For example, roller assemblies 29 - 33 of figure 9 do not have grooves. It is possible for the roller assembly to be any suitable shape to engage the complementary cavity in the punch 3 and/or die 2. A suitable shape is one that has a uniform cross section in a plane from the roller to the base (for example, as shown in figure 9) and can be fitted to the punch and/or die by means of an interference fit. It is possible for roller assembly 7 to have protrusions and the punches and/or dies to have complementary grooves for example. As shown in figure 9 some embodiments of roller assemblies have bases wider than the roller portions. Others (for example 27 and 28) have grooves that fit complementary protrusions in the punch 3 and/or die 2. Each of the roller assemblies is arranged to form an interference fit into a complementary cavity in the punch 3 and/or die 2. As shown in figure 9 the shape of the roller assembly holder may vary. In preferred embodiments the roller assembly holder has as least three distinct faces that form an interference fit with three distinct sides of a cavity in the die 2 or punch 3. As shown in figure 9, some holders may have more than three distinct faces that form the interference fit with corresponding faces in the punch 3 or die 2.

The rolling edge 8 means that the work piece 4 is no longer scraped over the shoulder of the die 2. Due to the reduction in friction between the shoulder of the die 2 and the work piece 4 less force is required to form the work piece than when a static shoulder is present on die 2. The action of rolling edge 8 also reduces scuffing on the work piece meaning that the need to linish the work piece to repair shoulder damage is significantly reduced or eliminated.

The wear resistant roller assembly 7 is shown in more detail at figures 4-8. As particularly shown in figure 4A, it comprises a holder 9 with an upper edge in the form of a cradle 10. A roller 11 in the form of a metallic bar, which is circular in transverse cross section, sits in the cradle 10. The holder and roller are preferably made from bearing compatible materials. The materials used may be influenced by the particular work to be performed and the functionality required. A preferred combination would be a phosphor bronze holder and a hardened steel roller.

In preferred embodiments the rollers are manufactured from hardened steel. In these embodiments it may be possible to manufacture the remainder of the punch and/or die from less hard, less expensive materials that won't necessarily need to be hardened. If the punch and/or die can be manufactured from a less expensive material then there are potential savings to be made in costs, machining and lead time.

The roller is held in the holder by way of a clip 12. The clip 12 is releasably secured in a slot 13 of the holder and engages a groove 14 of the roller 11. The arrangement is such that the roller 11 can turn while sitting in the cradle, to reduce frictional wear as the work piece moves across it under pressure from the punch. The roller 11 may or may not have a hollow centre. In some embodiments there may be multiple of the clips, all installed the same way in spaced relationship, depending on the length of the roller 1 1. Figure 4A shows an embodiment with two clips, one at each end of the roller. The clips 12 help maintain the roller in position in the holder 9 and provide means for connecting the roller and holder to prevent the roller moving along its rotational axis with respect to the holder. Wear is also addressed by a lubricant system. Referring to figures 4A and 5, the holder 9 has a channel 15 at each end. As indicated in figure 7, the channels 15 lead to the cradle 10. Lubricant can be pumped into the channels so it reaches the cradle, provides lubrication to the roller 1 1 and further reduces wear and tear to the roller assembly 7.

Referring to figure 12, in some embodiments of the invention the roller 11 may have a grooved marker line 1 1a at one end, or on some other part of its surface, so that an operator can easily observe whether it is turning in use, as it should be. If it is not turning, then the operator can apply more lubricant via the channels 15 and/or disassemble to investigate the cause of the roller ceasing to rotate.

Figure 10A illustrates contact between the work piece 4 and the die 2 when a roller assembly 7 is in place (some of the features mentioned above are omitted, for ease of illustration). As can be seen in figure 10A the tool with holder and roller has the same overall dimensions as a tool without the holder and roller. No additional plates or fastenings are needed. The roller extends the length of the die 2. There are no protruding ends of the roller. The roller and holder can be dimensioned to stay within the ends of the tool. The work piece contact surface provided by the roller is similar to that of a conventional power press tool. Figure 10B shows another embodiment of work piece and die 2 where a second embodiment of roller assembly 7 is in place. If the roller 1 1 becomes worn over time it can be readily replaced without having to replace the punch 3 and/or die 2 as a whole, or even the roller assembly 7 as a whole, or to do substantial work on the punch and/or die 2 to recover its shape. For example, if necessary, the whole roller assembly 7 can be replaced without having to replace the punch and/or die 2 in its entirety. Alternatively, the holder 9 can be retained and just the roller 11 replaced.

Replacing the roller can involve removing the roller assembly 7 from the punch 3 and/or die 2. Removal of the roller assembly may be effected by sliding the roller assembly out of the cavity in punch 3 and/or die 2. Some force may need to be applied to slide the assembly 7 out of the punch 3 and/or die 2. Once removed from the punch or die, a new roller 11 can be fitted to the roller assembly 7 and the roller assembly 7 slid back into the punch 3 or die 2. In some cases the replacement can be effected without removing the punch or die from the power press. As the roller assembly 7 can be replaced by punching or sliding the parts out of the punch or die and then sliding new parts into the punch or die there is little skill involved in replacement. This reduces the cost of replacing parts as a skilled toolmaker is not required,

Additionally a punch and/or die can be altered to allow the roller and holder to be retrofitted to the punch or die. Although it is impractical to tap a threaded screw hole into a hardened steel punch or die, it is possible to cut a cavity or slot for the roller and holder using a wire erosion machine. Wire erosion machines were developed in the 1960s and can be used to cut hardened steel tools. A wire erosion machine can be used to cut a cavity in a hardened steel tool - including one damaged in the shoulder area - to allow a roller assembly to be retrofitted to the tool. The precision available with a wire erosion machine means that the cavity can be cut to produce an interference fit with the roller assembly. As the roller or combination of roller and holder can be replaced when they wear, retrofitting holders and rollers provides a clear advantage over replacing the tools themselves. Cavities for rollers assemblies can also be formed when the tool is first created. While cutting a cavity in the punch 3 or die 2 may slightly reduce the strength of the power press tool, a similar maximum force per square inch can still be applied. In general, the force required to form the work piece when the roller assembly is in place will be less than the force required without the roller as the roller reduces the amount of friction created between the work piece 4 and the punch 3 and/or die 2 as the work piece is formed.

Referring again to figure 3, in some embodiments the punch 3 may have friction fitted releasable wear resistant inserts 16 at its lower contact shoulders. These have radius shaped edges to reduce wear from contact with the work piece 4. The punch's inserts 16 can be removed and replaced when worn, without having to replace the rest of the punch. The inserts 16 can be made from hardened or coated steel meaning that the body of the punch can be made from less hard, less expensive material that does not need to be hardened. The inserts 16 differ from the roller assemblies 7 in that they do not have a roller 11. However in some alternative embodiments the punch inserts may be formed and function the same as the die roller assemblies 7. In other embodiments, where wear is not such an issue, but slippage of a work piece is, the punch inserts 16 may be serrated to better grip the work piece when acting on it.

In some aspects of the invention there may be a selection of the roller assemblies 7 and inserts 16, each made of different materials, or with work piece contacting parts made of different material, for different jobs.

Referring to figure 11 , an alternative embodiment of the invention may have solid one-piece inserts 17 - i.e. without a roller 11. These can be formed of materials of different characteristics, e.g. co-efficient of friction, depending on the needs of a particular job, and can be readily replaced when worn.

Figures 13 and 14 illustrate a roller assembly for a die or punch according to a further embodiment. In this case the roller 18 is retained in the cradle 19 of the holder 20 without the use of horseshoe shaped clips. Rather, the roller 18 is retained by way of retaining plates 21 screw fastened at each end of the cradle 19. Stubs 22 at each end of the roller 18 engage and are held in apertures 23 of the retaining plates 21 respectively. This form of attachment of the roller is particularly useful where the included angle of the shoulder of the punch or die to which the roller assembly is to be fitted is less than approximately 70 degrees and in which circumstances the holder encloses less than 180 degrees of the roller and so does not hold it in place vertically. In the embodiment shown in figures 13 and 14 the retaining plates provide the means for connecting the roller and holder to prevent the roller moving both vertically and along its rotational axis with respect to the holder. Another advantage of using retaining plates in the way shown is that the retaining plates only hold the roller to the holder. They do not fix the roller with respect to the body of the punch or die, meaning that no threaded hole has to be tapped in the punch or die. As previously described it is not economical to tap a threaded hole into a hardened steel punch or die. As the retaining plates are attached to the holder this problem is overcome. Referring to figure 15, in some embodiments the press tool may utilise a punch 23 which moves against a work piece 24 set on a die 25 which is without a cavity. The punch 23 has a removable roller assembly 26, which in turn has a removable roller as described for the other embodiments. Figures 16 and 17 show the punch 23 at progressively advanced stages of operation when used for shaping the work piece 24.

Figure 18 shows an embodiment of tool where the die 2 and punch 3 are each provided with roller assemblies in their shoulders. The provision of the multiple roller assemblies means that friction experienced on the shoulders of the die 2 and punch 3 during the forming operation is significantly less than if conventional static die and punch shoulders were used. The rollers also reduce marking on the work piece being formed.

While some preferred forms of the invention have been described by way of example it should be appreciated that modifications and improvements can occur without departing from the scope of the appended claims.