Patent Application
20080209976
The present invention relates to a forming tool, a method of modifying the surface of a work-piece or a ductile compound wherein at least one surface of the work-piece or the ductile compound comes into contact with the surface of a forming tool at least once and a method of structuring the outer surface of a forming tool.
In the materials processing industries there are many types of forming operation. In the metals industry forming operations can include, for example:
an extrusion process which is defined as the process of shaping material, such as aluminium, by forcing it to flow through a shaped opening in a die. Extruded material emerges as an elongated piece with the same profile as the die opening.
a wire drawing process, which is a metal-reducing process in which a wire rod is pulled or drawn through a single die or a series of continuous dies, thereby reducing its diameter. Because the volume of the wire remains the same, the length of the wire changes according to its new diameter.
In the plastics industry forming operation can include, for example:
a polymer processing such as calendering.
A work-piece is a unformed or pre-formed body of determinate or indeterminate size and shape. For example a solid block of metal or plastic is a work-piece. In an extrusion process 08-182 the work-piece is e.g. a billet. In a wire drawing processes the work-piece is e.g. a rod. In polymer processing the work-piece is e.g. a monofilm made of a plastic or a multi-layer film having at least one layer made of plastic.
A ductile compound is an unformed material in a solid to semi-solid state. In polymer processing the ductile compound is e.g. an at least partially softened, melted or even flowable mass, sheet, plate or film material made of plastic or having at least a plastic surface layer.
In this invention a structured surface is meant to be where the surface is not intended to be smooth. Of course most surfaces are not perfectly smooth, but it will be readily understand what is covered by the meaning of a structured surface if it is defined as one possessing deliberate roughness, patterns, protuberances, depressions, ridges and troughs or engraving-like features, such features to be transmitted to the surface of the work-piece such that the work-piece surface is also not smooth.
A forming operations like this can be applied to polymer processing. During such forming operations, the appearance of the surface of the work-piece which was in contact with the forming surface of the forming tool after forming is typically the same as or similar to the surface appearance of forming surface of the forming tool. The surface on the work-piece can not be an exact replica of the surface of the forming tool because various factors like the amount of load applied through the forming tool or the physical properties of the material of the work-piece have an influence on the extent of deformation. It is routine practice to adjust forming conditions to take account of such factors. Often the surface of the forming tool can be exaggerated in order to ensure the final surface on the work-piece is produced.
There are also many situations where the surface of a work-piece is desirably modified in order to bring about specific benefits. The surfaces of work-pieces can be modified for purely decorative reasons. The surface of a work-piece can also be modified in order to attain desirable physical characteristics with the aim of improving the performance of an article in a specific application, where that performance depends strongly on the surface characteristics of the work-piece.
The forming tools can have on their surface a textured surface prepared by one of a variety of methods. Such known methods include EDT (Electro Discharge Machining) texturing, sand blasting or shot peening, mechanical brushing, structured Cr deposition (also known as Topocrom), and so on. These methods result in a working surface which is stochastic in nature and after the forming process this surface structure is substantially transferred to the surface of the work-piece. Other known methods include laser beam or electron beam texturing and these can produce a deterministic structure. A deterministic structure would show a pattern, or would be one where a specific design is present and could include, for example, an imprint of wording, a drawing, a grating or an imprint of a trade mark. In the case of multiple pass embossing, deterministic structures can lead to interference effects whilst stochastic structures generally will not.
In work rolls used in the above mentioned polymer processing, a deterministic structure could be imparted into the surface of the work roll by a machining operation, but this would be expensive and such work rolls have a limited life whereafter they need to be refurbished or re-machined, operations which can be expensive and time consuming. Furthermore, the quality of indentation of the deterministic structure into the surface of the work-piece can deteriorate over time due to wear of the forming surface of the forming tool leading to variable quality in the final product over long production runs.
In most of the forming operations mentioned above there is eventually a need to replace the tools used for forming, or to refurbish the same.
The life of a forming tool is often extended by adding a protective layer to that surface of the forming tool that comes into contact with the work-piece. In forming operations using dies and punches, such protective coatings are usually deposited onto the working surface of the tool without any subsequent profiling step, i.e. they are applied in such a way that the shape required is still derived from the shape defined by the main body and profile of the forming tool itself.
It is possible to provide them with very fine detailed designs of a deterministic nature. Smaller surface features are interesting because they can lead to interesting effects. One known effect is the creation of images from complex diffraction patterns. In order to create complex diffraction patterns, the cut lines are sub-micron in width and it is not possible with conventional tooling methods to obtain this level of resolution within a deterministic structure directly on the surface of a forming tool.
The prior art surface structuring approaches possess a number of disadvantages. Eventually forming tools wear out and are either expensive or difficult to refurbish. Also, it is difficult and sometimes impossible to produce deterministic structures. It is especially difficult to produce very fine, sub-micron, deterministic structures within the coating on a forming tool. Furthermore, forming tools are generally used for single purposes, that is, with one kind of shape or surface structure in mind. They do not provide flexibility in the sense of it being easy and straightforward to change the surface of the forming tool.
It is an object of this invention to provide a new forming tool, one that can have its surface easily modified and one that can be produced with deterministic structures and very fine deterministic structures, the said surface features being transferable to a work-piece.
It is a further object of this invention to provide a new method of modifying the surface of a work-piece using a forming tool that itself has a structured surface.
It is a further object of the invention that the surface of the forming tool can be easily and inexpensively produced and eventually refurbished and to provide a method of preparing and refurbishing such forming tools.
The problem is solved by providing a forming tool made of metallic glass or containing at least a metallic glass layer wherein the forming tool forms one of:
a) a forming tool of an extrusion press
b) a die of a wire-drawing machine
c) a roll of a polymer processing unit.
In first embodiment the mentioned tool of the extrusion press contains at least a body, which is the substrate, and at least a metallic glass layer according to the invention, which is directly or indirectly applied on the tool body. The metallic glass layer is applied at least at the working surface. The extrusion tool having a metallic glass layer can be a tool, which is directly involved in the forming process of the work-piece, such as an extrusion die, a die assembly (tool stack) or a mandrel. A die assembly can comprise a die, a bolster, a backer, a feeder, a die mandrel or a die cap. Moreover, the mentioned extrusion tool having a metallic glass layer can also be a tool, which is indirectly involved in the forming process of the work-piece, such as a container (wall), a press plunger, a press ram or a dummy block. The substrate of these tools can be of one of a hard cast-iron or hard steel.
In second embodiment the above mentioned extrusion tools can also be completely made of a metallic glass. Hence the metallic glass is used as bulk material.
The working surface of the tool, which is made of metallic glass, is wear resistant and therefore durable. Moreover the metallic glass surface makes it easier to rework the tool by heating the worn surfaces and rebuilding the metallic glass surface.
The extrusion press according to the invention can be used to produces profile sections made of metal, in particular made of aluminium or an aluminium alloy. It is also possible to use the extrusion press having extrusion tools according to the invention to produce profiles made of plastics.
The tools of a wire drawing machine containing a metallic glass layer according to the invention can be as already mentioned dies or drawing plates. The metallic glass layer is applied on the tool at least at its working surface. The substrate of these tools can be of one of a hard cast-iron, hard steel, diamond or ruby. It is also possible that the complete forming tool (die) is made of a metallic glass. Hence the metallic glass is used as bulk material.
The machine can be a continuous wire-drawing machine or a single-block machine. The continuous wire-drawing machine comprises a series of dies, whereby the work-piece, i.e. metallic rod, is reduced to the desired diameter and properties by repeated drawing through progressively smaller dies.
The working surface of the dies, which is made of metallic glass, is wear resistant and therefore durable. Moreover the metallic glass surface makes it easier to rework the tool by heating the worn surfaces and rebuilding the metallic glass surface.
The wire drawing unit according to the invention can be used to produce wires made of metal, e.g. aluminium, aluminium alloy, copper, copper alloy, iron, or steel.
The polymer processing can be a calender process where the tool coated with a metallic glass according to the invention is one or more work rolls of a calender unit with a smooth or a deterministic, structured surface.
The polymer processing can be a casting of thin films, sheet or plates on, preferably chilled, rolls. The rolls can be embossed and the structure of the bulk material glass would be transferred onto the molten or soft polymer to give patterns or topographies. The polymer is solidified after being embossed. The plastic material can be extruded. One of the main application can be packaging materials made of single- or multilayer-films.
The polymer processing can also be a coating process, where a sheet material is coated with a plastic layer. In such a process a sheet material, e.g. a packaging film, is coated with a plastic material. The sheet material can be a single- or multi-layer film composed of different materials. The coating can be an extrusion coating process, a coating by means of a coating knife, a dip coating, coating by means of rolls (roll-coater), or a calender coating process. In all these processes the tool containing a metallic glass layer according to the invention is one or more rolls with a smooth or a deterministic, structured surface.
The polymer processing can also be a surface treatment process of a coated sheet material, a laminated sheet material or a monofilm or even a sheet or plate containing at least a surface layer made of plastic. Such a surface treatment process can be based on an embossing calender. In this case the tool containing a metallic glass layer according to the invention can be an embossing roller, preferably a chilled embossing roller with a deterministic, structured surface.
The working surface of the roll(s), which is made of metallic glass, is wear resistant and therefore durable. Moreover the metallic glass surface makes it easier to rework the tool by heating the worn surfaces and rebuilding the metallic glass surface. Further the possibly structured surface of the roll(s) can easily be modified according to another template. The body of the rolls can be made of metal.
The work-pieces or ductile compounds formed in a polymer processing unit can be in the form of a film, sheet, plate or flowable bulk material. The film, sheet or plate material can be made of a single plastic layer or can be a multi-layer system containing at least one layer, preferably at least one surface layer, made of plastic. Other materials of a multi-layer system can be other plastic materials, metal foils, reinforcing fibres or fibre fabrics. The plastic material is preferably a thermoplastic.
In a forming process more than one forming tools can be coated with or be made of metallic glass. The tools of such a processing unit can be coated with or made of the same or different metallic glass materials.
Accordingly a first aspect of the invention is a forming tool characterised in that it comprises a substrate and a metallic glass layer on at least the working surface of the forming tool and the metallic glass layer possesses a structured surface for the purpose of reproducing the structured surface of the metallic glass layer in the surface of a work-piece.
It will be readily appreciated that the metallic glass layer need not be directly adjacent to the working surface of the forming tool and that other intermediate and functional layers can be incorporated, for example a compliant layer to accommodate differences in thermal expansion coefficients.
Metallic glasses are multi-component metallic alloys that, when cooled from a molten state at a fast enough rate, preferably retain an amorphous state when solid. Metallic glasses can also be slightly or partially crystallised when solid after cooling. These materials can be up to twice as strong as steel, have greater wear and corrosion resistance and have higher elasticity values than steel.
Metallic glasses suitable for the purpose herein described can be, for example, any one of the following group of general alloy systems: Au—Pb—Sb, Pd—Ni—P, La—Al—Ni, La—Al—Cu, La—Al—Ni—Cu, Mg—Cu—Y, Zr—Al—Ni—Cu, Zr—Ti—Cu—Ni—Al, Zr—Ti—Cu—Ni—Be, Zr—Ti—Nb—Cu—Ni—Be, Pd—Cu—Ni—P, Ni—Nb—Ta, Al—Co—Zr, Al—Ni—Ce—B, Al—Ni—Y—Co—B. These alloy systems are particularly useful because they can be cooled at slower rates than other metallic glasses yet still retain their amorphous state. One specific alloy that could be used is one containing, by weight percent, Zr 56.2, Ti 13.8, Nb 5, Cu7, Ni 5.5, Be 12.5. They can be cooled such that thickness of the metallic glass is of the order of 0.01 to 10 mm. This is important in this invention because the glass coating is on a substrate and the combined thermal mass means that extremely fast cooling rates are not always possible. In many situations the substrate itself can be used as an effective heat sink, either alone or in combination with other cooling means.
Where the intention is to make very fine deterministic structures the thickness of the metallic glass layer need not be very high. For example it could be a thin layer between 0.001 mm and 2 mm thick. Where the surface structure desired contains more prominent features then the metallic glass layer will preferably be thicker, between 0.5mm and 30 mm thick. For many applications there is no need to have a large excess of glass because that would simply be a waste of material but there needs to be enough to enable the required structure to be formed within its surface. The lower thickness limit of the metallic glass is e.g. 0.001 mm and preferably 0.5 mm. The upper thickness limit of the metallic glass depends on the intended application but is e.g. not more than 30 mm, preferably 20 mm, more preferably 8 mm, and even more preferably 5 mm.
The substrate could comprise any suitable shape typical of conventional forming tools that might be used in any of the forming methods previously mentioned. Also there is no particular requirement that the shape of the surface onto which the metallic glass is deposited to be of a certain kind. The metallic glass layer need not be deposited on the whole of the forming tool, merely on that face which comes into contact with the work-piece to be formed or modified, herein referred to as the working surface. In other words, the working surface is that face of the forming tool through which load is applied to the work-piece. The working surface could be substantially planar or profiled, (in the sense that its shape face varies in at least two dimensions). Alternatively the shape of the working surface can be at least a segment of the surface of a cylinder, as would be the case with a work roll for a polymer processing unit. In the latter case the substrate itself can be at least partly cylindrical or it could be a complete cylinder.
A particular advantage of the invention is that the structured surface of the metallic glass layer can be provided with a very fine deterministic structure. It is a preferred embodiment of the invention that the structured surface be deterministic and a more preferred embodiment that the deterministic structured surface contain features which are sub-micron in size.
A second aspect of the invention is a method of modifying the surface of a work-piece wherein at least one surface of the work-piece comes into contact with the structured surface of a forming tool at least once, characterised in that the forming tool is comprised of a substrate and a metallic glass layer on at least the working surface of the forming tool and the metallic glass layer possesses a structured surface whereby the structured surface of the metallic glass layer reproduces in the surface of the work-piece.
The nature of the metallic glass layer in terms of its composition and thickness are typically the same as those described above in connection with the forming tool. Likewise, the structured surface can be stochastic in nature but it is preferred that it is deterministic and even more preferred that it contains features which are sub-micron in size.
Often forming operations of this nature take place in a number of repeat actions and therefore another embodiment of the invention is that this method involves a plurality of contracts between the work-piece and forming tool. This is often desirable because the transfer of the structural features from the surface of the forming tool to the work-piece is rarely perfect and more than one impression can be needed to generate the final desired surface on the work-piece.
In addition the transfer of the structure from the forming tool to the work-piece can take place under very low loading such that there is little or no reduction in the thickness of the work-piece. This is particularly useful in embossing operations.
A preferred embodiment involves the use of this method in the processing of plastic material where the forming tool is a work roll of a polymer processing unit.
A further aspect of the invention is a method of structuring the outer surface of a forming tool characterised in that the forming tool comprises a substrate and a metallic glass layer comprising the steps of:
heating at least the outer surface of the metallic glass layer to a temperature above its glass transition temperature,
bringing the outer surface of the metallic glass layer into contact with the structured surface of a template for a period of time and under pressure such that the structured surface of the template is reproduced in the outer surface of the metallic glass layer to create a structured outer surface on the metallic glass layer,
at least the structured outer surface of the metallic glass layer is cooled down at a rate sufficient to retain an amorphous structure or mostly amorphous structure throughout the metallic glass layer,
and the forming tool and the template are separated, the features of the structured surface of the template being retained within the structured outer surface of the metallic glass layer,
It has been surprisingly found that the surface of metallic glasses can be heated up until they are soft and can then be pressed against a template, the template possessing on its surface the structure or pattern desired in the surface of the metallic glass. After coming into contact with the template, at least the outer surface of the metallic glass layer is cooled and separated from the template. Of course the bulk of the metallic glass layer itself will also cool to some extent, it can even cool at a rate similar to the cooling rate of the outer surface. The cooling rate is sufficient such that the amorphous state is retained throughout the metallic glass. The surface structure of the template, which has been reproduced in the surface of the metallic glass, is retained after cooling in the outer surface of the metallic glass layer. Where the surface structure of the template contains large impressions or indentations then some of the bulk of the metallic glass layer can also be deformed so that the metallic glass layer as a whole displays the same external profile. A forming tool with a metallic glass layer thus formed is then used to modify the surface of the chosen work-piece.
The template could be made from conventional materials such as copper, aluminium or steel but is preferably made from a material that is able to withstand the high temperatures and pressures involved. Therefore steel or nickel templates are preferred. In order to facilitate the release of the template from the metallic glass at the relatively high temperatures in question a release agent can be applied to the surface of the template prior to coming into contact with the softened metallic glass.
The metallic glass, after coming into contact with the template, has to be cooled down at a rate fast enough to ensure that the metallic glass retains its amorphous structure below the glass transition temperature. The cooling rate necessary for this will depend on the metallic glass used but will normally be >10° .C/sec, preferably >100° C./sec, more preferably >200° C./sec. In some situations, for example where the metallic glass has a large critical casting thickness, or the thickness of the metallic glass is small, effective cooling can be achieved by using forced gas, as for example air but in other situations it can be necessary to use means such as a fluid, as for example water or a water spray to bring about faster cooling rates. Other cooling means are solid materials having a high thermal conductivity such as metals, preferably copper and the like.
The invention will now be illustrated by reference to the following examples.
In
In
In another embodiment the template can be fed round another series of rolls (not illustrated) back to the start in a continuous loop. In such a case the length of template can be carefully controlled to correspond to the diameter of the substrate cylindrical work roll, especially if the structure to be created is deterministic. The diameter of the cylindrical work roll is not critical. The forming tool and the template are separated in the region of point B. In some circumstances, for example when the glass transition temperature is high and there is a danger of the metallic glass and the template sticking together, a suitable release agent is applied to the structured surface of the template to make separation easier.
A typical heater would be an induction heater, heating by conduction or convection heater as an infrared heater but can also include for example contact heaters, flame heaters, Joule effect heaters or any other adequate heating device.
The structured surface of the metallic glass layer and the metallic glass layer itself can start to cool down even as the template and forming tool are in contact, i.e. before they are separated in this case. The cooling can be effected by the bulk of the substrate itself acting as a heat sink, which can be improved with the use of a cooling system built into the substrate. It is common for cylindrical work rolls to contain a chilled fluid such as a water system and this can be used to help provide the fast cooling required. Cooling can be further enhanced by forced gas, for example air cooling, applied on the exit side in the vicinity of the area marked B.
The forming tool with its surface structured according to the method illustrated by
The tool and processes according to the invention offer a range of advantages. They allow a greater degree of reproducibility from one manufacturing plant to another. For example, two similar forming tools can be created in different locations because the same template can be used to produce almost identical tools. The template can be moved from one manufacturing plant to another and the working surface of the forming tool can be structured in exactly the same way at different locations. This will ensure consistency in the final form of the work-pieces being manufactured. Further, the very first structured forming tool can be used as a master tool and it can be used to generate a number of templates for use in other locations, again making production consistent from one manufacturing facility to another.
The processes described enable the creation of very small and deterministic surface features in a simple and effective way. This will have a wide range of benefits in many forming industries and has the potential to eliminate some subsequent processing steps. For example, if the forming operation also enables marking of the work-piece, a subsequent marking or printing step using another process can be dispensed with. This provides the user with the means to individualise their manufactured products more easily and distinctively.
The tool and processes according to the invention facilitate longer forming tool life. The properties of the metallic glass layer are well suited to prolonging tool life. Their high elastic strain limits, combined with high strength and high toughness means that the metallic glass layer remains in the fully elastic range during forming operations, far away from the metallic glass yield strength. As a result the structured surface of the metallic glass layer retains its integrity for much longer than other forming tool protective layers.
Furthermore, by re-heating the metallic glass surface layer and refurbishing the structure in exactly the same way as it had previously been formed, the life of the forming tool and its working surface can be further extended and any deterioration in the quality of the surface structure can be easily corrected.
In addition, the same conditioning and refurbishing process allows the manufacturer to change the structure of the working surface with a minimum of effort. This provides enhanced flexibility in design and production scheduling.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 047 801.8 | Oct 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/009629 | 9/8/2005 | WO | 00 | 3/18/2008 |
