TECHNICAL FIELD

The present invention relates to a method for manu¬ facturing a tool which is suitable for use for shearing, clipping, cutting and/or parting a workpiece for example, and which includes a functional surface operative to effect the work for which the tool is intended, and a material which forms said surface.

The invention also relates to a tool which is prefer¬ ably manufactured in accordance with the method and which can be used to shape and/or to cut a workpiece.

The invention can be used to advantage within a number of technical fields, of which the following are examples of the most prominent fields in the present context: extrusion; plastic moulding; compression moulding; swaging, drop-forging, stamping; pressure hardening; powder compaction; shearing, clipping; sheet-metal shaping; section, rolling; wire drawing; seamless tube drawing; section drawing.

BACKGROUND ART

Various methods are known to the art for manufacturing high-grade tool steel. In principle these methods can be divided into two main groups, namely pyrometallurgiσal processes and powdermetallurgical processes.

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For example it has been found that high-speed tool steel of good quality, e.g. so-called. ASP-steel can be produced by means of powder' metallurgical processes.

It can also be mentioned that the- isostatic pressing technique has been developed within the field of powder technology to such an extent that it is possible, on the basis of past experience, to forecast with a high degree of accuracy the dimensional changes which will take place in the tool body during the process. The methods applied today in the manufacture of shaping tools are both time and cost intensive, however.

The two methods at present preferred for the manu¬ facture of shaping tools are: a) rough cutting of soft-annealed tool blanks, which are then heat treated to the desired degree of hard¬ ness/toughness, whereafter the tool blank is subjected to a comprehensive and expensive finishing process, primarily including a grinding and polishing process; b) pre-fabrica ion of hardened and tempered tooi blanks, which can be finalized with the aid of deep spark- machining techniques.

Although the method referred to in b) is more modern than the method referred to in a) , the method of b) is highly time and cost demanding. As a result hereof the method referred to under b) has been preferred in practice solely in respect of plastics shaping tools.

For example, in the case of injection moulding processes it is far easier to select and shape a suitable compromise alloy capable of satisfying the majority of requirements than hot forging metal for example.

The arrangement illustrated and described in Swedish

Patent Application 7803485-7 forms part of the art discussed here. In this known arrangement part of a mould corresponding to part of the root of a ^• turbine blade is filled with a nickel-based powdered alloy of standard particle size through a filling opening intended therefor. This powder

is then compacted and consolidated by vibration, to achieve uniform distribution of 70% compacted, state in the said mould part. The upper part of the mould, which corresponds to the aerofoil part of the turbine blade is then filled with a powdered alloy which has previously been treated to deform the powder particles, whereafter the mould is again, vibrated to pack the metal powder into the aerofoil mould part. Subsequent to filling the mould with metal powder and compacting said powder, the mould, or tube, is connected to a vacuum pump and air is removed from the mould until a low pressure prevails. The aforesaid filling opening is then closed with the aid of a conical ceramic plug or like stopper, so as to seal-off the mould, and the mould is placed in an autoclave for isostatic hot pressing of the powder.

The Swedish Patent Specification No. 146 531 describes a method and apparatus for producing composite sintered bodies having sections of mutually different properties. According to this specification a mould is provided with partitions which divide the mould, at right angles to the powder entering the mould or tube, into chambers having a form which corresponds to the desired form of the aforesaid composite body sections. These chambers are intended to receive quantities of powder of mutually different charac- ter, and the powder quantities in respective chambers are compressed and sintered into fusion with one another. According to the aforementioned Swedish patent specification the partitioning walls are made of a material such that the walls remain in place during the initial stage of the process, but melt away or otherwise disappear during the sintering process.

DISCLOSURE OF THE INVENTION TECHNICAL PROBLEM One qualified technical problem in this respect is that of providing ways and means whereby a. shaping tool of the kind mentioned in the introduction can be manufactured readily and cheaply.

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Another qualified problem is one of creating condi¬ tions such that the shaping tool also obtains, an improved function in relation to earlier known, techniques.

One problem in the present context is that even a so-called shape permanent material will lose some of its shape when hardened and annealed, making it necessary to subsequently work tools which have been manufactured from such materials, in order to produce tools to the correct dimensions. This tool finishing process can only be effected by fine grinding or spark-machining the tools, which is quite a comprehensive task.

One qualified technical problem in connection with the manufacturing of hardened shaping tools is that of creating conditions which reduce subsequent treatment of the tools to a minimum.

Consequently an extremely complicated technical problem is^one of creating conditions such that technical demands placed on the manufacture of such tools from the point of view of production do not disproportionately influence the design and function of the tools.

In certain instances an advantage can be obtained when the operative or functional surface of the tool exhibits completely different material characteristics and properties to the remainder of the tool, or its bulk parts. It has been found unsatisfactory when using a unitary material to force a compromise between the properties of the material forming the functional surfaces and those of the bulk material.

Another technical problem encountered in the manu- facture of such shaping tools when a compromise has to be made with regard to the material used therefor resides in the necessity of coating or layering the functional surfa¬ ces which in use are subjected to high working loads with a material which is highly resistant to wear, e.g. stellite. In the efforts to find a solution to the aforesaid problem a further technical problem has arisen in the necessity of dividing the tool into various parts or

sections, each comprising material which exhibits proper¬ ties different to the other.

It is often desired to incorporate in a shaping tool functions that are secondary to the principle shaping function of the tool, such as a tool-attachment function for example. The inclusion of such secondary functions can only be achieved with great effort, however, when the material used to produce the tool deforms when hardened.

One technical problem in this respect is that attach- ment of a tool must normally be effected with the aid of clamp joints, which are bulky and thus require more space, besides which a clamp joint normally results in a tool attachment of poorer stability than previously known methods. A further technical problem resides in the fact that through-bolts, or screwthreads formed in the tool body,, cannot be used efficiently due to the fact that the bolt holes are moved out of alignment when heat treating the tool, and because of damage to the screwthreads, which are cut prior to the hardening process, caused inter alia by deformation of threads in the heat treatment process and the deleterious effect of said treatment thereon.

A highly qualified technical problem encountered in this art is one of maintaining a tool at a set temperature, so that each tool produced has desired and repetitive properties. To this end there is desired a method whereby a cooling or heating medium can be introduced into the tool in order to adjust and control the temperature there¬ of. This is particularly desirable, of course, in tools of the kind used to work a substance or a material whose temperature differs from the normal tool temperature.

In previously known tools this has been associated with a qualified technical problem of creating conditions whereby such temperature control can be incorporated therein.

When such temperature control is required, another qualified technical problem is one of forming suitable

channels herefor, e.g. by drilling or- in- some other way, in the hard tool materials used, these ^* material not normally being easily machined or worked.

It has been proposed to form these channels prior to hardening the tool material. This is also difficult to achieve since even when unhardened,hardenable steel is still difficult to work.

Although at present temperature regulation is only applied as a matter of form in plastics forming or shaping tools and tools for the compression moulding of metal workpieces, it ^can be expected that the temperature control of such tools will have an increasing significance in the future, inter alia in the further development of pressure hardening techniques, precision forging techniques, etc..

SOLUTION

The present invention relates to a method of manufac¬ turing a tool for working a material blank, for example shearing, clipping, cutting and/or parting said blank, which tool incorporates a functional surface operative to perform actual work on the workpiece and a material which forms this surface. The method according to the invention comprises the steps of: a) placing in a pressure sintering chamber a compressible, enlarged model having a form which exhibits a surface corresponding to, or substantially corresponding to, the functional working surface of the tool; b) applying to said model a powder which will sinter under pressure thereby to form the body of the tool; c) pressure sintering the powder to form said tool; d) removing subsequent hereto the model, which has been compressed during the sintering process; and e) optionally heat treating the tool in a manner to impart desired properties to the material thereof, for example hardening the material.

In accordance with the invention the outer surface layer of the functional surface can be produced by applying

to the model a powder, which is particularly adapted for said outer surface layer and applying ^* onto, said powder in a second layer a powder particularly adapted to the bulk of the tool. It has been found that particularly advantageous results are obtained when the powder forming the interface or boundary layer between the enlarged model and the tool body comprises a material which, during the sintering process, will not adhere to one or both of the surfaces forming the interfaces or boundary layers or which can be removed after sintering.

It is proposed in accordance with the invention that the enlarged model is formed with the aid of a powdered material, preferably a loose, pre-compacted and/or pre- sintered powder.

In order to provide for simpler attachment of the tool to a tool holder intended therefor, it is proposed that there is introduced into the tool body one or more inserts made of a material which, subsequent to the pressure sintering process and optionally also the heat treatment process, can be readily machined or worked, e.g. drilled and tapped with screwthreads.

It is also proposed in accordance with the invention that a temperature regulating coil or like device is posi- tioned in the proximity of said surface prior to said sintering process, and that the coil or like means is suitably formed by placing a wire or tubular element in the powdered mass prior to sintering the powder, and removed therefrom after sintering, e.g. by leaching. The invention also relates to a tool which is prefer¬ ably manufactured in accordance with the method and which includes a functional surface for effecting the actual work for which the tool is intended and a material forming said surface, and the tool of which body comprises pressure sintered powdered material.

According to the invention the aforesaid tool surface is a cavitated. surface and/or the surface material thereof

has properties which are different to the properties exhibited by the material in the remainder of the tool.

The invention also relates to a tool having a functional surf ce for effecting the actual work for which the tool is intended in which there is incorporated in the tool body one or more inserts which comprise a material which can be readily worked or machined after the pressure sintering process and after the optional heat treatment process. In addition hereto there is proposed in accordance with the invention a tool which presents in, or in the proximity of, said functional surface a spiral channel, loop or like passage, preferably a cooling coil or loop, which is preferably formed by inserting a wire or tubular element into the powder mass forming the tool and removing said element, either totally or partially, subsequent to said pressure sintering process.

In this way it is possible to apply to the compressible enlarged model a layer of highly wear resistant material, for example a layer of stellite- owder. The temperature regulating coil configuration can be placed in the vicinity of the aforesaid surface, preferably in the bulk material, prior to said sintering process. It is also proposed that a low-alloy powder capable of being machined or worked after the sintering process is incorporated in the bulk material.

It is particularly proposed in accordance with the present invention that the aforesaid pressure sintering process is effected in accordance with thermo-isostatic pressure sintering or powder-compacting principles.

Upon termination of the sintering process the model is removed and the thus exposed surface can, if required, be further worked, for example hardened or spark-machined, to form the surface precisely as desired. Prior to sintering, cavity formers may be introduced into the powder mass so as to form cavities, voids, and channels in given locations in the finished tool.

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ADVANTAGES

Those advantages primarily afforded by a method and a tool according to the present invention reside in the fact that subsequent to manufacturing the shaping tool no subsequent finishing work is required thereon, or only a limited amount of such finishing work, for example such work as face grinding and calibration and possibly deep spark-machining for surface smoothing purposes. In addition hereto the tool can be produced so that the shaping surface has properties particularly suitable to the surface material while the bulk material has properties particularly suitable therefor.

The method of manufacturing the shaping tool also enables temperature control loops or like passage configu- rations to be readily incorporated therein, while the bulk tool material can have incorporated therein different materials capable of being worked with the aid of plasti¬ cally shaping or chip-cutting working methods, subsequent to hardening the tool, such as cutting screwthreads for example.

The primary characterizing features of a method according to the present invention are set forth in the characterizing clause of the ollowing Claim 1 , while the main characterizing features of a tool according to the- present invention are set forth in Claims 8,9 and 10.

BRIEF DESCRIPTION OF THE DRAWINGS

A forming tool according to the present invention at present preferred and a method for its manufacture will now be described with reference to the accompanying drawings in which

Figure 1 is a side view taken in section of a prior art shaping tool;

Figure 2 is a side view taken in section of a shaping tool constructed in accordance with the invention; and

Figures 3-7 illustrate the procedural sequences when carrying out a method for ^* manufacturing a shaping tool according to thepresent invention.

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DESCRIPTION OF AN EMBODIMENT AT PRESENT PREFERRED

Figure 1 is a- side view taken in- section of a shaping tool of known construction. The illustrated shaping tool 1 comprises a workpiece shaping surface 2 and bulk material 3 forming said surface. As will clearly be seen from

Figure 1 the surface 2 and also the bulk material 3 comprise one and the same material structure.

It will be obvious that with the aid of special arrangements when hardening the surface 2 can be given different properties to the bulk material. he properties of the surface 2, however, cannot be selected totally inde¬ pendently of the properties of the bulk material 3.

The reference 4 identifies a discrete coating, for example stellite, which is welded to the surface 2 and intended to increase the wear resistance of said surface in connection with the coating 4. As will be seen from Figure 1, the bulk material 3 has two clamping shoulders 5, 5' formed therein. Each clamping shoulder co-acts with a clamping bolt 6 ¹ and 6" having associated nuts 6 and a clamp fitting 7. Also provided is the requisite support block 8.

Not only are the outer dimensions of the shaping tool illustrated in Figure 1 large, due to the clamping means (5, 6', 6, 7,8), but it is also difficult to render the tool sufficiently stable.

Figure 2 illustrates a shaping tool manufactured in accordance with the invention, this tool comprising a surface 2 which is functional in effecting the actual shaping work, and a bulk material 3 supporting the material of said surface.

The material 10 forming the surface 2 is selected from a material exhibiting good wear resistance, high compression strength and/or high heat resistance. The bulk material 3 on the other hand, is chosen for its toughness, good compression strength and/or low price. It should be noted that the interface 9 between the material 10 of the surface 2 and the bulk material 3 is formed by an atomic

or diffusion bond.

The material 10 orming the sur ace 2 comprises a highly strong, hard and/or heat durable, and/or. wear resistant tool steel, while the bulk material.3 comprises a hardened tool steel of tough structure.

Placed in the bulk material 3 are. steel zones 11 which can be plastically shaped or cut to form screw¬ threads 12, even subsequent to hardening the tool 1. It will be understood that other machining operations than screw-thread forming operations can be carried out if desired.

Located in the vicinity of the surface 2 is one or more temperature control channels 13 through which a heating or cooling medium is passed. As clearly shown in Figure 2, the channels 13 are formed in the bulk material 3. It will be understood that such temperature control can also be effected by incorporated electrically insula¬ ted heating loops directly in the material.

It is also possible to apply to the surface 2 a stellite coating or layer 4 in the case of surfaces where a high degree of wear can be expected.

One method of manufacturing a shaping tool according to Figure 2 will now be described with reference to Figures 3-7. As beforementioned, the shaping tool comprises a functional surface 2 operative to effect the actual shaping work and bulk material 3 which supports the material forming the surface 2. The shaping tool is manufactured by: a) placing in a pressure sintering chamber or vessel 15,16, a compressible enlarged model 14 exhibiting a shape having a surface 14' and 14" corresponding to or substantially corresponding to the functional working surface of the tool; b) applying to the model 14 a suitable pressure sintering powder 10' to form the surface 10 of the tool and a powder 3" to form the bulk material of the tool. When required the bulk material 3' is introduced into the

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part 11" to simplify subsequent machining or working of the tool; c) pressure sintering the powder to. form the- tool; d) upon completion of the sintering ^* process removing the model 14, which is compressed during said sinte¬ ring process; and e) optionally imoartinα to the tool desired material properties by suitable heat-treatment, for example hardening. According to the invention it is proposed that the surface layer of the surface 2' is produced by applying to the model a powder 10' which is particularly adapted for said surface layer. This powder may be an iron-base alloy, nickel-base alloy, chromium-base alloy or the like. Against this powder there is applied a powder particularly adapted for the bulk of the tool in a further layer 3' .

The boundary layer 2' between the enlarged model 14 and the powder 10' forming the tool body comprises a material which, during the sintering process, will not fuse or bind together against a surface or the surfaces forming the boundary layer or permit themselves to be removed after sintering. The enlarged model is formed with the aid of a powder preferably comprising a loose, pre- compacted and/or pre-sintered oowder. In the illustrated method there is introduced into the tool body one or more inserts 11' made of a material which can be machined or cut subsequent to said pressure sintering process and said optional heat treatment process. It is also proposed that a temperature control loop or coil 13 is positioned in the vicinity of the surface prior to the pressure sintering process and that the coil is formed by a wire or tubular element shaped to provide one or more loops, and that the wire or tubular element is removed subsequent to the sintering process. This removal can be effected by leaching for .example.

In the procedural step illustrated in Figure 5 it is shown, however, that a temperature control loop or coil 13 is incorporated in the bulk material 3* in the vicinity

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of the powder 10'. There is nothing, however, to prevent the coil 13 being placed in the surface material 10 and/or in the boundary or interface 9.

Figure 5 also indicates the incorporation in the bulk material 3' of a low-alloy powder which is capable of being worked or machined subsequent to a pressure sintering and hardening process, this low-alloy powder being refe¬ renced 11'.

It is now proposed that the pressure sintering process is effected in accordance with the principles of thermo- isostatic pressure sintering or powder compaction with thin-wall vessels. It is also proposed that the porosity of the various powders is the same or substantially the same. Thus, the powder of the Figure 5 embodiment will be compressed to the form illustrated in Figure 6. The linear change in length occurring in conjunction with the afore¬ said compaction may be between 5 and 20 %, normally about 12-14%.

Upon completion of the pressure sintering process the model 14 is removed and the thus exposed surface 2 may be subjected to a subsequent working or machining process, for example a deep spark machining process.

Although the described embodiment proposed the insertion of powder sections 11' in the bulk powder 3' it will be understood that the powder sections 11 * may be replaced with cores or like elements. In addition, cavity formers effective to form cavities, voids and channels may also be incorporated. Material parts having mutually diffe¬ rent properties may also be incorporated in predetermined sites in the final tool.

Figure 7 illustrates subsequent working of the surface 2 and the formation of a screwthread 12 in the powder section 11 , this screwthread being intended to co-operate with a bolt to hold the tool in a shaping tool machine. When powder compaction is employed it is advantageous that the powder materials and the model have the same or substantially the same porosity.

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It is also of value that the. various ^* materials used to produce the tool have the same or substantially the same plastic deformation properties at the pressure and temperature or combinations of pressure and temperatures used when the porous powder mass is to be consolidated to the totally dense tool.

Thus, the surface layer 2 may comprise a wear resistant strong and/or heat durable steel, some other heat durable metal, ceramic and the like. The surface material 10 and the bulk material 3 may, in accordance with the invention,be selected so that the materials are optimized in relation to their function independently of one another. The condition that they can be bonded to one another must, of course, be fulfilled. This bond can also be effected with the aid of a special bonding alloy introduced between the different materials.

The invention also includes a product produced by a shaping tool of the aforementioned kind and/or produced in a shaping tool manufactured in accordance with the afore- described method.

Although the description refers to both surface material 10 and bulk material 3 it will be understood that this is not necessarily a single material selection but that the surface material may comprise one or more materials or material compositions in mixture, and similarly also the bulk material.

In the above description reference has been made to the use of a chamber. In practice this chamber may have the form of a vessel, a capsule or container. The invention is not restricted to the aforedescribed embodiment and modifications can be made within the scope of the following claims.