Background to the Invention It is known to use a mechanical clamp or holder to hold a work piece such as a drill blank or other component during processing of the work piece. For example, drill blanks from which drills, sometimes called drill bits, are made are conventionally held in steel carriers which have a plurality of holes or recesses for receiving the cylindrical drill blanks. The holes are normally aligned vertically so that when the drill blanks are inserted they are substantially upright.

The drill blanks are often inserted into the carrier by hand. Automated"pick and place"apparatus could be used but generally the apparatus is not able to pick and place fast enough to keep up with downstream processing throughput such as heat treatment in a furnace.

When the carrier has been fully loaded, it is placed on a conveyor which takes the carrier and drill blanks into a furnace and carries them through the furnace over a predetermined time. Whilst in the furnace, the carrier

and drill blanks are exposed to thermal radiation to heat treat the drill blanks.

As well as holding the drill blanks, the carrier shields those parts of the drill blanks that have been inserted into the steel carrier. The steel carrier therefore acts as a radiation shield as well as a holder. It absorbs radiation from the furnace and acts as a heat sink by dissipating the absorbed energy throughout the bulk of the carrier. It also dissipates heat that flows by conduction from the exposed part of the drill blank to the lower shielded part. So, the carrier prevents direct heating by radiation and reduces indirect heating by conduction of those parts of the drill blanks that are inserted into the holes of the carrier.

Of course, those parts of the drill blanks that are exposed, i. e. sticking out from the carrier, will be heated by the radiation.

The reason for wanting to heat only one part of the drill blank is that it is desirable to heat treat only a pre- determined length of the drill blank which will subsequently be machined into the fluted or cutting end of the drill. This part is called the body of the drill.

The remaining portion will form the shank of the drill and it is desirable not to heat treat the shank. This process of selective heat treatment is known as differential or partial hardening.

The holes in conventional steel carriers must therefore be of the correct dimensions to accommodate the drill blanks so that only the desired amount of drill blank is

exposed and so that the lower part is adequately shielded. This latter requirement means that there must be a close fit between the drill blank and the walls of the hole. This requires precision engineering and also makes it more difficult to insert the drill blank into the hole.

Indeed, the present inventors have noted that the problem of inserting large numbers of drill blanks into close fitting holes in the steel carrier is particularly marked in the case of small diameter drill blanks. Given the need to heat treat large numbers of drill blanks as quickly and efficiently as possible, any difficulty in getting the drill blanks into the holes in the first place has a significant commercial impact.

Furthermore, in order to accommodate a wide range of drill blank sizes, it is necessary to make a correspondingly large number of different sized holes in the carrier. In practice this means that a large number of carriers must be made, e. g. some have large holes, for large drill blanks, others have smaller holes for smaller drill blanks. Generally, a given carrier only has holes to accommodate drills having a diameter within a 1mm range, e. g. 9.6 to 10.6mm.

Also, when a new size of drill blank needs to be heat treated, it is necessary to make a new carrier.

This inflexibility adds significantly to the cost of the heat treatment step.

Similarly, the use of mechanical clamps, e. g. of the sort

having two clamping surfaces that can be moved closer together to hold a work piece, also has drawbacks such as the need to adjust or tighten each clamp. Furthermore, such clamps can have a temperature dependent clamping strength that is caused by clamping surfaces and clamping mechanism expanding and contracting during heating.

Summary of the Invention The present inventors have found that the drawbacks of existing methods of holding work pieces, in particular the use of steel carriers for drill blanks, can be addressed by the present invention.

At its most general, the present invention proposes that a particle bed can be used to support and"clamp"a work piece without needing any further supporting means.

In a first aspect, the present invention provides a method of holding a work piece in a desired orientation, the method including the step of inserting the work piece into a particle bed, so that at least a part of the work piece is immersed in the particles and the work piece is held in the desired orientation by the particles.

An advantage of using a particle bed that"clamps"the work piece is that no further mechanical support is needed-once the work piece has been released the particles clamp the work piece and keep it in the desired orientation. This means that the particle bed can be uncovered (i. e. no lid or cover) which makes it easier to insert the work piece, and to remove it.

Preferably the work piece is supported only by the particle bed.

The work piece can be a bore cutting tool blank or bore cutting tool. It is particularly useful when the bore cutting tool or blank is to undergo differential hardening, particularly where the bore cutting tool has a shank which it is desired not to heat treat, as discussed above. The term bore cutting tool as used herein means a cutting tool for making a bore (or hole) in a work piece or machining the bore once it has been formed. Examples of such tools include twist drills, slot drills and taps and the like.

The method is particularly useful when the work piece is a drill blank and this is preferred.

In the case of drill blanks, the drill blank is preferably inserted into the particles so that a lower shank portion of the drill blank is covered by the particles. This means that the shank portion should lie beneath the upper surface of the particle bed, eg. it is submerged in the particles.

The method may include the step of inserting a plurality of work pieces, e. g. a plurality of drill blanks, into the particle bed. For example, two work pieces that are to be joined together may be held in the particle bed in the desired orientation, e. g. so that they are touching. The two pieces may be joined, e. g. by applying adhesive to the upper pieces before or after inserting them into the particle bed to fix them together, or applying heat to cause softening of at least one part of one or both work pieces to bond them together.

In the case of drill blanks, tens, hundreds or even thousands of drill blanks may be inserted into a particle bed. Preferably, the step of inserting the work piece is automated. Suitably, insertion is done by robots. To speed up processing, preferably groups of work pieces are inserted at approximately the same time. The method may include the step of moving the work piece or plurality of work pieces from a start point to the particle bed, prior

to inserting them into the particle bed.

The method preferably includes the step of processing the work piece whilst it is held in the particle bed. For example, the work piece may be heated, cooled or coated.

The particle bed is preferably part of a universal jig.

The universal jig typically includes a container for containing the particles. The universal jig may include sufficient particles to at least partially fill the space within the container, e. g. to fill at least 30%, preferably at least 50%, more preferably at least 70% of the space within the container.

The universal jig may be static, in the sense that it does not move during the method, or mobile so that it is moved during the method. A static universal jig may, for example, include a large container fixed to a work surface.

In the case of a static universal jig, work pieces could be inserted into the particle bed and then, for example, sprayed with a coating. The coated work pieces could then be removed from the particle bed and a new set of work pieces inserted in their place.

A mobile universal jig may, for example, include a container that is not fixed to anything and can be traversed through a furnace, e. g. on a conveyor. Work pieces held by particles in the container will move through the furnace with the universal jig, e. g. to harden them.

A preferred processing step after inserting the work pieces into the particle bed is heating the work pieces.

Suitably, this is done in a furnace or oven. Preferably the temperature of the heat treatment is at least 800°C, more preferably at least 1000°C, most preferably at least 1100°C.

Preferably heating is effected by applying thermal radiation to the work pieces. In which case, the particle bed preferably acts as a radiation shield to attenuate radiation reaching the parts of the work piece covered by the particles.

Suitably, the universal jig traverses through the furnace, preferably on a conveyor.

The container can have a depth (top to bottom) of 5 cm to 100 cm, preferably 5 cm to 50 cm, more preferably 10 cm to 30 cm. The container can have a length and width independently selected from 5 cm to 500 cm, preferably 20 cm to 100 cm, more preferably 30 cm to 100 cm.

The container is typically metallic, e. g. steel or aluminium.

The container preferably has an open top, i. e. there is no lid or cover.

The furnace preferably has radiation emitting elements such as silicon carbide elements.

The work piece (s) can be inserted into the particle bed by simply pushing the work piece into the particles, for

example by hand or by programming a robot to do it.

However, the particles may have significant resistance to the insertion of a work piece and so insertion can be made easier by fluidising the particle bed.

The particle bed can be fluidised by expanding the particle bed, e. g. by passing gas though the particles.

Suitably the gas is introduced at the bottom of the particle bed so that it flows around the particles as it rises to the top of the bed. Accordingly, the universal jig preferably includes a gas inlet for receiving fluidisation gas.

The universal jig may include a mesh or gauze at the bottom of the particle bed through which a fluidising gas can be passed. The mesh serves to direct the gas flow evenly over the bottom of the particle bed, so as to fluidise the particles more evenly. This can aid insertion at any place in the particle bed. The mesh size is selected so as to permit the flow of gas but prevent particles falling through the mesh. Preferably, the universal jig includes a container for containing the particles and a lower wall of the container includes a mesh as discussed above. Suitably, the mesh supports the particles during use. The container may include a ledge or shoulder on which the mesh is supported.

The mesh has a further advantage of providing an end stop for the work pieces to limit the extent of insertion.

Preferably the container also includes at least one gas inlet below the mesh.

The container may be a single piece of unitary construction but it can also include two or more parts.

For example, an upper part may include a peripheral wall for containing the particles, and a shoulder or annulus extending from a lower portion of the peripheral wall for supporting a mesh. The mesh may be integral with the container.

A lower part may include one or more gas inlets and have means for engaging the upper part to form a substantially gas tight fit. The means for engaging can include a step or shoulder for receiving the lower portion of the upper part. It may include a seal, preferably a heat resistant seal. An o-ring seal may be used where temperature permits.

The universal jig may include a gas flow controller.

Alternatively, the gas flow controller may be separate.

The gas flow rate is selected to fluidise the particle bed such that the resistance of the particles to insertion of a work pieces is reduced.

Alternatively, or additionally the particle bed may be fluidised by vibrating the particles. This is suitably achieved by placing the universal jig on a vibrating surface, e. g. a vibration table.

The universal jig may include vibrating means, which may be integral, for vibrating the particles. Alternatively, the vibration means may be separate, e. g. a vibrating table as noted above. Preferably the vibrating means include control means for selecting the frequency of vibration and/or the magnitude of vibration.

Other known methods for fluidising particles may also be used.

The particle bed is preferably fluidised throughout insertion of the work piece (s). Suitably, the fluidisation is stopped when insertion is complete. This causes the particles to set'around the work piece and hold or clamp it in place.

The insertion step preferably includes holding the work piece, inserting it into the particle bed, stopping fluidisation and then releasing the work piece. In other words the work piece is held in the correct orientation and at the desired depth until the fluidisation is stopped, at which point it can be released.

In the case of drill blanks, the drill blanks are suitably held at the desired depth corresponding to the shank length until fluidisation is stopped.

Where a robot is used to insert the drill blanks, the robot is preferably programmed to keep hold of the drill blanks until fluidisation is stopped.

Preferably, the drill blanks are held upright until fluidisation is stopped.

It is desirable to keep the drill blanks upright and as near as possible to vertical during heat treatment because the drill blanks can bend or distort if they are not vertical. The clamping effect of the particles over a wide range of temperatures is therefore particularly

advantageous in this respect.

The nature of the particles can be selected to provide a strong holding or clamping action around a work piece. the idea is that the particles support the work piece, i. e. hold it at the desired orientation, without any other supporting means.

The inventors have noted that the force needed to remove a work piece from the particle bed (i. e. the clamping force) can vary as a function of the size of the work piece. In particular, wider diameter drill blanks can be more difficult to remove from the particle bed than smaller diameter drill blanks. If a greater force is needed it is an indication the clamping effect is greater, which is desirable.

Particle size and shape can be selected to alter the clamping effect of the particle bed.

Typically, the particles have a mean particle size in the range of 20 to 500 pm, preferably 50-200 hum and more preferably 75-150 pm. The particle bed can be a powder bed. A mean particle size of about 100 zm is preferred.

Generally, the present inventors have found that the flow characteristics of larger particles, eg. mean particle size greater than about 50 pm. are better than smaller particles. In particular, larger particles can flow better than finer particles.

Suitably, the particle bed responds to small displacements of the work piece by flowing to fill the displacement, thereby maintaining the clamping effect.

The particle shape can be regular, such as spherical, or irregular. A combination of regular, e. g. spherical, and irregular shaped particles is also possible. Irregular particles may have re-entrant angles.

Irregular shapes are preferred because they may provide a stronger clamping effect. This may be because irregular particles"lock"together more effectively than, eg. spherical particles. The higher surface area of irregular particles may also improve clamping The material from which the particles are made can be selected according to the type of work pieces that are to be held by the particle bed and the conditions which the particle bed is to be exposed to.

So, for example, if the particle bed is to pass though a furnace at elevated temperature, the particles should have a melting temperature higher than the furnace temperature.

Similarly, if the particles are to provide functions in addition to holding the work piece in the desired orientation they must be made of an appropriate material.

For example, where the particle bed is to be used as a radiation shield for the shank portions of drill blanks, the particles must not be transparent to thermal radiation. Preferably they are also thermal conductors so that they can act as a heat sink for heat travelling down the drill blanks from the exposed upper portions.

The particles can be metallic or non-metallic. Examples

of suitable metallic particles include steel, stainless steel, aluminium, cobalt and copper particles, and alloys and combinations. thereof. Examples of non-metallic particles include oxides, ceramics and polymers.

Combinations of different particle types may also be used.

For drill blank processing, the particles are preferably metallic. High melting point metals including alloys are preferred, for example high temperature steel and copper particles. Preferably the particles are dry so that they can flow more easily.

In a second aspect, the present invention provides apparatus for holding a work piece in a desired orientation, the apparatus including a particle bed, and inserting means for inserting a work piece into the particle bed so that the work piece is held in the desired orientation by the particle bed.

Preferably the work piece is held in the desired orientation only by the particle bed.

Preferably the apparatus includes fluidising means for fluidising the particle bed to aid insertion of the work piece.

The particle bed is particularly suited for use in drill blank processing or other work piece processing where the work piece is heated and then cooled or quenched because the clamping effect is maintained over a wide range of temperatures, as noted above. One method of quenching involves the use of cooling zones in a processing

apparatus, for example as disclosed in US6,632, 302.

Preferably the apparatus includes control means to prevent the release of the work piece by the inserting means whilst fluidisation is occurring. The control means can ensure that the inserting means only releases the work piece once insertion is complete and fluidisation has stopped.

Optional and preferred features of the other aspects also apply to the second aspect.

In a third aspect the present invention provides a universal jig for holding a work piece in a desired orientation, the universal jig including a particle bed for holding the work piece in the desired orientation while at least a part of the work piece is immersed in the particles and held in the desired orientation by the particles; and a container in which the particle bed is contained.

Additional support means are not required.

Optional and preferred aspects of the other aspects also apply to the third aspect.

Brief Description of the Drawings Embodiments of the invention and tests and experiments illustrating the principles of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 shows a steel carrier of the prior art ; Figure 2 shows a universal jig of the present invention and; Figure 3 shows apparatus used to test the clamping effect of different particle beds.

Detailed Description of Embodiments of the Invention and Supporting Experiments Figure 1 shows a steel carrier 1 of the type used to hold drill blanks 2 in conventional methods of heat treating drill blanks. As can be seen, vertical bores 3 are needed to ensure the drill blanks are held upright. The depth of the bores must be selected to correspond with the shank length 4 of the drill blank. This means that, in practice, a given vertical bore is only useful for one size of drill blank.

Figure 2 shows a universal jig 10 of the present invention including a container 12 having a base 14 and sidewalls 16, and a particle bed 18.

The container is about 50 cm long, 50 cm wide and 15 cm deep. The container does not have a lid or cover, the surface of the particle bed is uncovered. The particle bed 18 is contained within the container 12. The particle bed includes a very large number of particles 20 which have a mean particle size of about 100 jjm. The particles are steel and have an irregular shape.

The particle bed 18 holds a drill blank 22 in an upright

position. The drill blank 22 is held upright without any further supporting means. In this embodiment, the drill blank 22 has been inserted so that it touches the base 14. In other embodiments the depth of insertion may be less, eg. 3/4 or 1/2 of the particle bed depth. The depth of insertion corresponds to the shank length 24 which is the part of the drill blank that will form the shank.

The shank length 24 is shielded by the particle bed 18 from thermal radiation inside the furnace. Exposed upper portion 26 is not shielded and will be heat treated in the furnace. The particles 20 are metallic and the particle bed 18 conducts heat away from shank length 24 as it moves down from hot upper portion 26.

The particles 20 are copper particles with a mean size of about 100 um. They have an irregular shape. Universal jig 10 is mobile and can be placed on a conveyor as part of a drill blank processing apparatus.

Clamping Effect The magnitude of the clamping effect provided by the particle bed was investigated by measuring the drill blank's resistance to movement through the particle bed.

Figure 3 shows the apparatus used. Universal jig 10 is fixed (eg. by screws) on top of dynamometer 30.

Dynamometer 30 includes a steel block 32 containing three sensors 34,36, 38 for measuring the force exerted on the block 32 in each of the X, Y and Z directions.

A pneumatic pusher 40 having a piston 42 was used to apply a force to one side of the exposed upper portion 26 of the drill blank. The piston 42 moved at a fixed rate in the X direction against the drill blank throughout the experiment. The movement of the piston was intended to cause the drill blank to move away from its upright position and"fall"through the particle bed in response to the force applied by the piston.

Any resistance to movement of the drill blank, as a result of the clamping effect of the particle bed, would result in the transmission of forces from the drill blank to the dynamometer 30 via particle bed 18 and container 12.

Any such forces applied to dynamometer 30 were detected by sensors 34,36, 38 as a change in voltage.

Force profiles were generated by plotting the duration of the experiment (and hence extension of piston 42) against the detected voltage from the sensors.

The important readings were those from the X direction sensor 34 and the Y direction sensor 36, since any resistance to movement in the X direction (direction of motion of piston 42) resulted in the transfer of force in that direction to the dynamometer (especially after the drill blank started to move in the X direction. Force was also transferred in the Y direction as a result of the the pivot effect of the drill blank about its lower end point 44.

A force profile was measured for a range of particle

types, including aluminium particles, copper particles, steel particles and cobalt particles.

The results of the test showed that irregular particles, for example irregular copper particles, provide good clamping of a drill blank.

Particle sizes are preferably 20 to 500 pm with 50-200 pm and in particular 75-150 jum producing good results.

The inventors found that generally the clamping effect increases as the diameter of the drill blank increases. this makes the method particularly suitable for large work pieces.

These preferred embodiments have been described by way of example and it will be apparent to those skilled in the art that many alterations can be made that are still within the scope of the invention.