Abstract:
A tool for machining a workpiece may comprise multiple parts that have different temperatures when the tool is being operated. To reduce or, in some cases, eliminate thermal radiation between the multiple parts, the tool may incorporate one or more devices that manipulate the thermal radiation. Such devices may be disposed along one or more of the multiple parts and, in some examples, between two or more parts of the tool. These devices may also help reduce and, at times, eliminate thermal radiation between the tool parts and the surrounding environment.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to prior filed German Patent Application No. DE 102015100100.4 filed Jan. 7, 2015, the entire contents of which are hereby incorporated by reference herein. 
       FIELD 
       [0002]    The present disclosure relates to tools and methods for selectively hardening certain regions of a workpiece. 
       BACKGROUND 
       [0003]    Tools for converting sheets into desired shapes by means of hot forming are known. For instance, the sheets are placed into the tool and acquire their final shape through hot forming. To this end, regions of the tool are typically heated to high temperatures (several hundred degrees). At such temperatures, a considerable amount of heat is transmitted to the environment and thus lost. Means for heating portions of the tool, for instance, heating cartridges, must therefore constantly offset this loss by re-heating, which reduces energy efficiency throughout the sheet forming process. Moreover, parts of tools that operate more optimally at or require a lower temperature are inadvertently heated. 
         [0004]    In order to reduce heat transfer between hot parts of tools and the environment or a machine, as well as between parts of tools that have different temperatures, the prior art, such as in US Patent Publication No. 2011/0030442A1, for instance, discloses inserting a gap between tool parts with different temperatures to reduce direct heat transfer between the tool parts during hot forming of the workpiece. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0005]      FIG. 1  is a diagrammatic view of an example tool for selectively hardening certain regions of a workpiece. 
           [0006]      FIG. 2  is a diagrammatic view of an example tool having an example surface character for manipulating thermal radiation. 
           [0007]      FIG. 3  is a perspective view of an example tool having multiple parts separated by a gap for reducing and/or eliminating heat transfer. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    As those having ordinary skill in the art will appreciate, although certain example apparatus and methods are disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents. 
         [0009]    One example object of the present disclosure is to provide a tool in which the heat transfer between tool and environment or between individual tool parts that are heated to different temperatures for hardening is further improved in relation to the prior art. Likewise, the present disclosure enables more energy-efficient use of tools such as, for instance, in the hot forming of sheets. 
         [0010]    Various objects of the present disclosure are achieved by a tool for the hot forming of a workpiece. In some examples, the tool comprises a first tool part and/or a second tool part, wherein, for heating of the workpiece, the first tool part for heating of the workpiece assumes a different temperature from the second tool part or from an environment of the tool, wherein the tool has a device for manipulating the thermal radiation. As those having ordinary skill in the art will understand, “first tool part” and “second tool part” may be shortened, respectively, to “first part” and “second part.” 
         [0011]    The tool provides a device for manipulating thermal radiation, with which the loss of heat, induced by thermal radiation, between the first tool part and the environment, or the transfer of heat from the first to the second tool part, can be advantageously reduced in relation to the prior art. In this way, the maintenance of an existing temperature difference between the tool parts and of the temperature control of the entire tool can be supported, so that a particularly energy-efficient use of the tool is ultimately enabled. Through the reduction of heat transfer, a temperature profile along the first or second tool part can also be advantageously improved in terms of spatial homogeneity. In addition, in the tool can be obtained spatially clearly discernible temperature zones, which, in the course of the hardening, advantageously lead to narrow transition regions between workpiece regions of different hardness. 
         [0012]    The tool may be designed for hot forming or for “tailored tempering.” In particular, with the first and the second tool part, the pre-heated workpiece is maintained during the forming at a certain temperature on a regionally selective basis, or is cooled only down to tool temperature and is subsequently kept at the appropriate temperature. For instance, the workpiece is a sheet that is heated to a temperature within the range from 720° C. to 900° C., is subsequently arranged in the tool, and acquires its final shape through the forming effected by the tool. In this case, by virtue of the tool parts at different temperatures, and the therewith associated different cooling rates or dwell times, purposefully different material properties are obtained in the regions of the workpiece. In addition, the tool may have a die-like tool effective area, against which in the operating state the workpiece bears and by the action of which the workpiece is then worked. Further, the shape of the tool effective area may be tailored to the subsequent shape of the formed workpiece. In particular, the tool may be designed at least partially as a press. In this example, the device for manipulating the thermal radiation is, at least in some regions, part of the first and/or second tool part, or can be disposed between the first and the second tool part. In particular, the device may be a feature of the first and/or second component. 
         [0013]    In some examples, a surface character of the first tool part, in particular of the tool effective area, and/or of the second tool part for manipulating the thermal radiation, may be modified. In such examples, by virtue of the surface character, the device for manipulating the thermal radiation is formed. In particular, the first and/or the second tool part, following a treatment, in particular an after-treatment, such as, for example, polishing, coating or roughening, may have at least in some places an altered surface character. In particular, the surface characters of the tool parts at different temperatures, e.g., of the first and the second tool part, can mutually differ. Through the modification of the surface character, the quantity of thermal radiation exchanged between the tool parts at different temperatures, as well as delivered to the environment, can be advantageously controlled or manipulated. 
         [0014]    In other examples, the first tool part and the second tool part may be at least partially spatially separated from each other by a gap. By virtue of the gap, a direct heat transfer from the second tool part to the first tool part is advantageously reduced. In particular, the device for manipulating the thermal radiation may be disposed within the gap. The device may then be introduced into and/or arranged exchangeably in the gap for the manipulation of the thermal radiation, whereby the device for manipulating the thermal radiation can be adapted as optimally as possible to the prevailing circumstances. In a further example, a device of this type can likewise be disposed between tool parts and the environment. 
         [0015]    In some examples, the tool for manipulating the thermal radiation has a coating. The coating in this example forms the device for manipulating the thermal radiation. Such a coating can be advantageously applied comparatively easily to the first and/or the second tool part and takes up little space. The coating may be designed such that the coating absorbs or reflects the thermal radiation. In particular, the coating may be tailored to a spectral distribution of the thermal radiation, wherein the coating absorbs or reflects over a wide band within the infrared spectral range. By adapting the coating to the spectral distribution of the thermal radiation, it is possible to manipulate the thermal radiation particularly effectively. In addition, the coating is chosen such that it at least partially co-determines an emission of the thermal radiation. In particular, the first or the second tool part is coated with a material having a specific emission coefficient in order to manipulate the emission radiating from the first or second tool part. In this example, the coating may be comprise a lacquer and/or a structured primer. In particular, the coating can advantageously have the effect that the thermal radiation between the tool parts at different temperatures is manipulated, in particular reduced. 
         [0016]    In some examples, the first tool part has a coating which varies from the coating of the second tool part. In particular, the second tool part has a higher temperature than the first tool part and, as a result of the coating, the second tool part assumes or has at least in part a darker colour than the first tool part, in particular is coloured black. The second tool part thereby becomes, for instance, a type of black body, and as much radiation as possible is absorbed by the coating of the first tool part. Moreover, if the first tool part has a lower temperature than the second tool part, the first tool part may assume or have at least in part a lighter colour than the second tool part, by virtue of the coating, for example. The first tool part thereby becomes, for instance, a type of white body, which reflects as much radiation as possible. 
         [0017]    In some examples, a secondary surface of the second tool part may have a greater roughness compared to a primary surface of the first tool part. As a result of the increased roughness of the secondary surface, its ability to absorb thermal radiation is advantageously further enhanced. The primary surface, on the other hand, may be polished and may reflect the thermal radiation in the direction of the first tool part. 
         [0018]    In some examples, the secondary surface may lie opposite the primary surface. In particular, the secondary surface and the primary surface lie at least partially opposite each other along the gap. The secondary surface and the primary surface may be of complementary configuration. In particular, the secondary surface may be rougher and, in terms of colouring, darker than the primary surface. This can advantageously have the effect of reducing the heat transfer from the second tool part to the first tool part. 
         [0019]    In some examples, a device is arranged between the first tool part and the second tool part that reflects thermal radiation. In particular, the device reflecting the thermal radiation, such as a mirror, for example, may be disposed within the gap. The reflective properties of the device may be tuned to the anticipated, spectral distribution of the thermal radiation. The device reflecting the thermal radiation may reflect over a wide band within the infrared spectral range. In addition, the device reflecting the thermal radiation may be arranged exchangeably in the gap. As a result, a device, tuned to the desired operating temperature, for manipulating the thermal radiation can be inserted into the gap. 
         [0020]    According to some examples, a reflective side of the device reflecting the thermal radiation may be directed towards the second tool part. Further, the device reflecting the thermal radiation may have on its rear side an absorbent part, which absorbs the thermal radiation emanating from the first tool part. Through the alignment of the device reflecting the thermal radiation, a heat transfer between the tool parts at different temperatures is advantageously reduced. 
         [0021]    A further subject of the present disclosure is a method for the regionally selective hot forming of a workpiece with a tool, wherein in a method step a the heated workpiece is disposed in the tool, wherein in a method step b the workpiece is worked, and/or at least in some regions maintained at a certain temperature or cooled at different speeds, with the first tool part and/or the second tool part, and wherein in a method step c the workpiece is removed and, if need be, after-treated for further microstructure adjustment. The workpiece may be cooled at different speeds via tool parts at different temperatures, for instance the first and second tool part, or may be maintained at a certain temperature, whereby material properties, such as hardness or ductility, on the shaped and ultimately hardened workpiece can be purposefully co-determined. 
         [0022]    With reference now to the figures, like parts are provided with like reference symbols and are therefore also generally respectively named or mentioned only once. In the figures, the curved lines are used to indicate that only a detail from the respective tool is viewed. Furthermore, the representations are heavily simplified for better comprehension and are not necessarily to scale or proportion. As merely an example, in many cases a second tool part  12  does not encompass a first tool part  11 . 
         [0023]      FIG. 1  depicts an example tool  1 . In this example, the tool  1  serves to hot-form a workpiece  10 , such as a steel sheet, for example and without limitation. That is to say, the tool  1  maintains the heated workpiece  10  at or above a certain temperature and works the workpiece  10  into a shaped workpiece  10 ′. In this example, the tool  1  may at least partially have a die-like configuration. To this end, the tool  1  may comprise a shaping tool effective area, which in an operating state enters into operative connection with the workpiece  10  such that the workpiece  10  is at least partially worked and, in particular, assumes a shape predefined by the tool effective area. The tool effective area in this example forms one side of the tool  1 , against which the workpiece  10  bears. 
         [0024]    The deformation may be performed, e.g., pressed, at a pressure that acts on the workpiece  10 . The heated workpiece  10 , in a method step a, may be placed into the tool  1 . In a method step b, the workpiece  10  may be worked and in some regions may be maintained at a certain temperature or cooled at different speeds. To this end, the tool may have a first tool part  11  and a second tool part  12 , with which different regions of the workpiece  1  may be brought to different temperatures, in some cases within the range from 450° C. to 550° C., after which, in a method step c, the workpiece  10  may in some cases be removed from the tool  1  and cooled external to the tool  1 . The workpiece  10  in this example may be cooled by the air surrounding the tool  1 . 
         [0025]    With continued reference to  FIG. 1 , a part of the tool  1  and a part of the workpiece  10  are shown. The part of the tool is represented in which the first tool part  11  and the second tool part  12  are disposed adjacent to each other. For instance, the second tool part  12  comprises at least partially a tool effective area with which the workpiece  10  is worked. In particular, the first and the second tool part  11  and  12  comprise tool effective areas with which the workpiece  10  can be worked. As a result, tool regions which have been heated to different temperatures can respectively be worked with the appropriate tool parts. In order to avoid heat losses, the tool  1  may comprise a device for manipulating the thermal radiation  2 . 
         [0026]    In particular, in the example shown in  FIG. 1 , it is provided to prevent, with the device for manipulating the thermal radiation  2 , the transfer of heat in the form of thermal radiation  2  from the second tool part  12  to the first tool part  11 , wherein the second tool part  12  for controlling the temperature of the workpiece is warmer than the first tool part  11 , e.g., possesses a higher intrinsic temperature than the first tool part  11 . In this example, the second tool part  12  and the first tool part  11  are mutually separated by a gap  4 , and in the gap  4  is arranged a device  5  which reflects the thermal radiation  2 , such as a mirror for the reflection of infrared light, for example. In another example, the tool comprises the device for manipulating the thermal radiation in order to prevent the heat loss to the environment. The device  5  reflecting the thermal radiation  2  may comprise a side that is highly reflective for the thermal radiation  2  radiating from the second tool part  12 . This highly reflective side may in some examples be directed towards the second tool part  12 , so that the thermal radiation  2  is reflected back onto the second tool part  12 . The highly reflective side may comprise a material and/or a coating  3  for the reflection of infrared light. In addition, the highly reflective side may be tailored to an operating temperature assumed by the second tool part  12  in the operating state, and the therewith associated spectral distribution of the thermal radiation  2 , in that, for instance, a wavelength for which the highly reflective side provides maximum reflection falls into a wavelength range in which the workpiece  10 , at operating temperature, most emits thermal radiation  2 . 
         [0027]    By virtue of the highly reflective side, a heat loss of the second tool part  12  can be advantageously avoided, which ultimately ensures an efficient operation of the total tool  1 . Further, the device  5  reflecting the thermal radiation  2  may have an absorbent side that lies opposite the highly reflective side and is directed towards the first tool part  11 . In particular, the absorbent side is tailored to the thermal radiation radiating from the first tool part  11 , in particular to the spectral thermal radiation profile thereof. As a result of the manipulation of the thermal radiation  2  between the first and the second tool part  11  and  12 , a temperature difference can be advantageously maintained in an energy-efficient manner. Apart from the device for manipulating the thermal radiation  2  between the first and the second tool part  11  and  12 , an insulating layer may be installed. 
         [0028]      FIG. 2  shows another example tool  1  according to the present disclosure. The tool  1  shown in  FIG. 2  differs from that shown in  FIG. 1  by the measure which is adopted to manipulate the thermal radiation  2 . Those having ordinary skill in the art will recognize that different measures for manipulating the thermal radiation  2  may be combined. Furthermore, as shown in  FIG. 2 , a surface character of the tool  1  may be designed to manipulate the thermal radiation  2 . In particular, the first tool part  11  may be coated or coloured white. As a white body, thermal radiation can thereby be advantageously reflected, and thus radiation losses avoided. For instance, the second tool part  12  for lowering the thermal radiation emission is at least partially coated with a black coating  3 , whereby the second tool part  12  advantageously at least partially assumes the thermal radiation emission characteristics of a black body. The surface of the second tool part  12  may be roughened and the thermal radiation  2  that is potentially transferable from the second tool part  12  to the first tool part  11  is thereby reduced. The surface character along a secondary surface may be modified, e.g., roughened or coated, wherein the secondary surface is disposed opposite a primary surface of the first tool part  11  along the gap  4 . 
         [0029]    In addition, in some instances, the surface character of the first tool part  11  may be at least in part, along the primary surface, complementary to the modified surface character of the second tool part  12 . In particular, the surface of the second tool part  12  has along the primary surface a smooth surface, or is coated or lined with a reflective coating  3 . The absorbent coating  3  may be at least partially white, whereby the first tool part  11  advantageously assumes the thermal radiation emission characteristics of a white body. 
         [0030]      FIG. 3  shows another example tool  1 . The tool  1  shown in  FIG. 3 , in the form of a warm punch, comprises a first tool part  11  and, in the form of a cold punch, comprises a second tool part  12 , wherein the first tool part  11  is separated from the second tool part  12  by a gap  4 . In this example, the workpiece  1 , in the region of the first tool part  11 , can be maintained at a certain temperature or only intended to be cooled to a tool temperature. As a result of the different cooling speeds or dwell times, different microstructures are formed in the workpiece, whereby the material properties can be adjusted. In this example, the tool may interact with a die-like, companion part of the tool  1 , wherein the first tool part  11  comprises an effective area. Via this effective area, heat energy is lost whenever the tool  1 , for instance for the reception of the workpiece  10 , is opened, e.g., the companion part is distanced from the effective area. Therefore, the thermal radiation  2  to the environment is lessened, wherein principally that heat loss is lessened which occurs via the effective area to the environment, in particular when the tool  1  is open. Likewise, the thermal radiation between the first tool part  11  and the second tool part  12  is lessened, wherein the temperature exchange between the first tool part  11  and the second tool part  12  is reduced.