Patent Publication Number: US-2015075246-A1

Title: Thermoforming tool with distinct cooling feature

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application, Serial No. 10 2013 110 299.9, filed Sep. 18, 2013, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference in its entirety as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a tool for hot forming and press hardening metallic steel structures, and to a deep drawing tool for hot forming and optional press hardening of metallic steel structures. 
     The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
     It is generally known to shape a metal sheet, especially of steel sheet, by a forming process to manufacture a three-dimensional sheet metal product. Metal sheet products of this type are used in particular in the automobile industry to manufacture body components or also to produce motor vehicle control arms or housing components for example. 
     To satisfy the demand for motor vehicles to have little consumption while still exhibiting a vehicle body of increased stiffness, high-strength or ultra high-strength steel materials have been developed. This involves steel alloys that are heated to temperatures above the AC3 point, formed in hot state to a specific shape and then rapidly cooled down so as to produce a substantially martensitic microstructure and to thereby establish high-strength or also ultra high-strength properties in the steel structure. This manufacturing process is also known as hot forming and press hardening. 
     Heating of a metal sheet to a pliable forming temperature is normally implemented in a furnace, in particular a continuous furnace or also in a temperature-controlled station. The thus-heated metal sheet is transferred to a thermoforming tool and formed to a specific shape while being at the pliable forming temperature. Combined hot forming and press hardening tools are also constructed to cool down the metal sheet that is formed in hot state and held between an upper tool and a lower tool of the thermoforming tool. Cooling is realized in the thermoforming tool by cooling channels through which a coolant flows to attain the intended cooling rate. 
     Upper and lower tools are normally made of tool steel which is expensive because of its material properties and difficult to work with because of its high strength characteristics. 
     It would therefore be desirable and advantageous to provide an improved tool which obviates prior art shortcomings, is easy and cost-effectively to manufacture and exhibits little tool wear, while being capable to realize an effective cooling capacity and to produce distinct regions of different strengths in a structure. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a thermoforming tool for hot forming and press hardening a steel structure includes an upper tool and a lower tool, each having a base body made of highly heat conductive material and comprised of at least two segments, wherein the base body of at least one of the upper and lower tools has a cooling channel, and a wear protection shield arranged on the base body of at least one of the upper and lower tools. 
     In accordance with the present invention, a thermoforming tool is provided which is capable to manufacture motor vehicle components, such as A pillars, B pillars, C pillars or D pillars or also transmission tunnels or outer vehicle components such as engine hood or vehicle door, using a forming process. The upper tool can normally be lowered in a direction of the lower tool, with a cavity being defined between the upper and lower tools, when the thermoforming tool is closed. The cavity is sized to substantially correspond to the metal sheet thickness of the sheet metal part to be shaped. The base body of both the upper tool and the lower tool is made of highly heat conductive material, with both the upper tool and the lower tool being covered by a wear protection shield. It is, of course, also conceivable to provide only the upper tool or only the lower tool with such a wear protection shield. 
     According to another advantageous feature of the present invention, the base body can be made of a light metal alloy, e.g. of an aluminum alloy, as highly heat conductive material. 
     According to another aspect of the present invention, a deep drawing tool for hot forming and optional press hardening a steel structure, includes an upper tool, a lower tool in opposition to the upper tool, and a downholder configured to hold a workpiece to be deep drawn between the upper and lower tools, each of the upper and lower tools being made in one of two ways, a first way in which the upper tool and the lower tool have each a base body which is made of a light metal alloy, and a wear protection shield arranged on the base body of at least one of the upper and lower tools, a second way in which the upper tool and the lower tool have each a base body which is comprised of at least two segments, and a wear protection shield arranged upon the at least two segments, wherein at least one of the at least two segments of the base body of at least one of the upper and lower tools has a cooling channel, wherein the base body with the one segment having the cooling channel is made of highly heat conductive material. 
     Thus, the present invention provides a deep drawing tool that can be used not only for realizing a pure press forming but also a deep drawing process and can be manufactured in a cost-effective manner. The base body may initially be made of a material that can easily be machined, e.g. of a light metal. Placed on this base body is the wear protection shield which can be made of a material that has a higher strength than the material of the base body, e.g. of a tool steel. Advantageously, the wear protection shield is replaceable. A deep drawing tool can thus be manufactured in accordance with the present invention that is cost-effective and requires little maintenance since it is only required to replace the wear protection shield when worn off. Advantageously, the wear protection shield is threadably engaged and/or bonded onto the base body. 
     The deep drawing tool can have a base body which is constructed in segments. At least one of the segments can have one or more cooling channels, and the base body may be made of highly heat conductive material. In this way, the workpiece being deep drawn, especially when press hardened after undergoing hot forming, can be provided with regions of different strengths. These regions can be realized by different cooling rates and/or cooling temperatures in the respective segments. 
     According to another advantageous feature of the present invention, the segments can be arranged in spaced-apart relation to define a separation gap so that the segments are physically and thus thermally separated from one another. As a result, the workpiece can be tailored to have distinct regions with sharp edges. As a result of the high heat conductivity of the material of the base body together with the presence of cooling channels provides high heat dissipation. The cooling channels can advantageously be formed as throughbores extending through the base body, advantageously in a straight line. Some cooling channels may be spaced at a greater distance from the surface of the wear protection shield and thus have a greater distance to the workpiece being cooled down. The presence of a cooling throughbore, especially rectilinear throughbore, enables a reduction in the manufacturing costs of the tool, especially of the base body as there is no need to provide a complicated branched channel system. 
     It will be understood that the afore-described properties are true for the thermoforming tool as well as for the deep drawing tool. Thus, any reference to a “tool” in the following description is used here in a generic sense and the principles described in the following description apply to both a thermoforming tool and a deep drawing tool. 
     In accordance with the present invention, the base body is made of at least two parts so that the base body is divided in segments. The segments may be disposed in spaced-apart relationship to define a separation gap there between which may configured as a slot and extend in orthogonal relation to the wear protection shield. Advantageously, an insulation material may be arranged in the separation gap between the segments. Of course, the separation gap may also be configured substantially slot-free. In any event, any heat conduction between the segments should be greatly decreased or avoided. In this way, it becomes possible to maintain the segments of the base body at different temperatures in order to be able to establish different strength properties with sharply defined transition zones, as the structure or workpiece is cooled. Transition zones of less than 100 mm, or less than 80 mm, or less than 50 mm, or even less than 30 mm can be attained. 
     As the segments of the base body have cooling channels in the form of throughbores, the base body can be manufactured of a light metal alloy by way of a casting process or by a material removing machining process. Tool costs and manufacturing costs are relatively low compared to a base body made of tool steel, and the formation of cooling channels is also easy and cost-effectively to realize. Machining processes such as drilling or milling methods, are applicable and there is no need for a complex channel system. The cooling channels can be made as throughbores from one side of the base body to extend continuously to the other side since sufficient heat dissipation is realized in view of the high heat conducting properties of the base body or respective segment. At the same time, the presence of the separation gap between two adjacent segments ensures that each segment reaches its individual desired temperature, especially with respect to the quenching behavior during the press hardening process. Cooling channels can thus be manufactured especially cost-effectively, thereby further greatly reducing the overall tool manufacturing costs, when compared to a conventional thermoforming tool made of tool steel. 
     Examples of a coolant include especially fluidic media, e.g. cooling liquids, such as water. The use of water is possible because light metal alloys exhibit only slight corrosion susceptibility. Other examples of coolant include also air or compressed air or other gaseous media. The cooling rate necessary for the respective region of the structure can also be influenced by the size or cross sectional area of the cooling channels and/or pressure of the coolant and/or flow rate of the coolant through a respective segment. A tensile force can be adjusted in some areas, depending on the alloy, between 1,500 and 2,000 MPa, and in some areas between 750 and 1,050 MPa. Thus, two adjacent segments of the upper tool and/or the lower tool can be provided with different cool-down rates to establish different strength properties in the structure. 
     According to another advantageous feature of the present invention, the wear protection shield can be made of high-strength or ultra high-strength steel material. Advantageously, the wear protection shield is attached to the base body of the tool in such a way that it is simply exchangeable after a certain production time to maintain dimensional precision of the structures to be manufactured, without any need to replace the upper tool or lower tool or the overall thermoforming tool. Advantageously, the wear protection shield is replaceably or detachably connected to the base body or segments of the base body. The wear protection shield may hereby be attached on the base body by bonding and/or by a form fit, in particular by riveting or bolted connection. 
     According to another advantageous feature of the present invention, a heat conducting paste can be placed between the wear protection shield and the base body. In this way, an intense heat transfer is realized by heat conduction and quenching of the thermoformed structure can be tailored. 
     According to another advantageous feature of the present invention, the wear protection shield can be comprised of at least two wear protection shield segments disposed in spaced-apart relation to define a separation gap there between. In this way, the transition zone in the structure can be provided with even sharper edges when the structure is quenched differently in various regions, and it is possible to use the segmented wear protection shields to suit the respective thickness of the metal sheet that may have jumps in thickness and thus involves a tailored material that undergoes shaping and hardening as tailored material in a correspondingly defined cavity. The separation gap between adjacent wear protection shield segments may have the shape of a slot or may be slot-free, and insulating material may also be placed into the separation gap. 
     According to another advantageous feature of the present invention, the wear protection shield can have a marginal area configured to at least overlap at least one area of the base body so as to embrace a marginal area of the base body. The term “marginal area” relates hereby to a circumferential area or to an area extending all-around. By embracing the border of the base body, the wear protection shield is securely fixed by a form fit upon the base body, especially in horizontal direction. In particular, when a deep drawing tool is involved, the marginal area between wear protection shield and base body will not get damaged, when the metal sheet to be formed is misaligned so that the wear protection shield is prevented from inadvertently detaching from the base body in the event the metal sheet is tilted or skewed. 
     According to another advantageous feature of the present invention, a downholder can be provided for arrangement on opposite sides. The downholder may hereby be arranged on both sides so as to be placed entirely next to the upper tool or lower tool and may be configured for movement separately from the upper tool and/or lower tool. As an alternative, the downholder may also be configured such as to be arranged on one side only, for example approaching from the lower tool or from the upper tool and to clamp the metal sheet to be formed as it contacts the upper tool or the lower tool. The downholder is also in this case movably constructed independently from the upper and lower tools. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
         FIGS. 1   a ,  1   b  show a cross section and a longitudinal section of a first embodiment of a thermoforming tool according to the present invention; 
         FIGS. 2   a ,  2   b  show a cross section and a longitudinal section of a second embodiment of a thermoforming tool according to the present invention; 
         FIGS. 3   a ,  3   b  show a cross section and a longitudinal section of a third thermoforming tool according to the present invention for shaping tailored blanks; 
         FIGS. 4   a ,  4   b  show a cross section and a longitudinal section of a fourth embodiment of a thermoforming tool according to the present invention, depicting segmented wear protection shields; 
         FIGS. 5   a ,  5   b  show a cross section and a longitudinal section of a fifth embodiment of a thermoforming tool according to the present invention for making tailored blanks; 
         FIGS. 6   a ,  6   b  show a cross section and a longitudinal section of a sixth embodiment of a thermoforming tool according to the present invention, depicting a through opening in the wear protection shields; 
         FIGS. 7   a ,  7   b  show a cross section and a longitudinal section of a seventh embodiment of a thermoforming tool according to the present invention, depicting the presence of a passively cooled base body; 
         FIGS. 8   a ,  8   b  show a cross section and a longitudinal section of an eight embodiment of a thermoforming tool according to the present invention, depicting the presence of a passively cooled base body; 
         FIG. 9   a  shows a cross section of a ninth embodiment of a thermoforming tool according to the present invention, taken along the line A-A in 
         FIG. 9   b  and depicting the presence of a passively cooled base body; 
         FIG. 9   b  shows a longitudinal section of the thermoforming tool of  FIG. 9   a;    
         FIG. 10  is a plan view of the thermoforming tool of  FIGS. 9   a ,  9   b;    
         FIGS. 11   a ,  11   b  show a cross section and a longitudinal section of a first embodiment of a deep drawing tool according to the present invention, depicting a downholder on one side; 
         FIGS. 12   a ,  12   b  show a cross section and a longitudinal section of a second embodiment of a deep drawing tool according to the present invention, depicting a downholder on both sides; 
         FIGS. 13   a ,  13   b  show a cross section and a longitudinal section of a third embodiment of a deep drawing tool according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
     Turning now to the drawing, and in particular to  FIGS. 1   a  and  1   b , there are shown a cross section and a longitudinal section of a first embodiment of a thermoforming tool according to the present invention, generally designated by reference numeral  1 . The thermoforming tool  1  includes an upper tool  2  and a lower tool  3 , with the upper tool  2  and the lower tool  3  each having a base body  4 ,  5  made of highly heat conductive material, e.g. light metal alloy such as aluminum alloy. Currently preferred is a heat conduction of &gt;130 W/mK. Arranged on the base body  4 ,  5  of the upper and lower tools  2 ,  3  are wear protection shields  6 ,  7 , respectively. As shown in the cross sectional view of  FIG. 1   a , both the lower tool  3  and the upper tool  2  have formed therein a cooling channel  8  which extends in close proximity to the wear protection shield  6 ,  7  through the base body  4 ,  5 . 
     As shown in  FIG. 1  b by way of the longitudinal section of the thermoforming tool  1 , both the lower tool  3  and the upper tool  2  are each comprised of three segments  9   a,    9   b,    9   c;    10   a ,  10   b,    10   c.  Adjacent segments  9   a,    9   b,    9   c;    10   a ,  10   b ,  10   c  are separated by separation gaps  11 , shaped here in the form of slots. Insulating material may be placed into the separation gaps  11  to prevent heat conduction between the segments  9   a,    9   b,    9   c;    10   a,    10   b,    10   c.  The cooling channels  8  extend in the non-limiting example shown here only in the middle segment  9   b  of the upper tool  2  and the middle segment  10   b  of the lower tool  3 . As a result, it is primarily the middle segments  9   b;    10   b  in the upper and lower tools  2 ,  3 , respectively, that are coolable so as to realize an even heat dissipation of the upper and lower tools  2 ,  3  only in the respective region of the structure (not shown) being shaped. Adjacent regions in the segments  9   a,    9   c;    10   a,    10   c  remain unaffected by the cooling. The wear protection shield  6 ,  7  is continuous, with the separation gap  11  between the segments  9   a,    9   b,    9   c;    10   a,    10   b,    10   c  inhibiting a respective heat introduction. As a result, a structure is produced having a distinct transition zone with sharply defined border. 
       FIGS. 2   a ,  2   b  show a cross section and a longitudinal section of a second embodiment of a thermoforming tool according to the present invention, generally designated by reference numeral  1   a . Parts corresponding with those in  FIGS. 1   a ,  1   b  are denoted by identical reference numerals and not explained again. The description below will center on the differences between the embodiments. In this embodiment, provision is made for cooling channels in the form of throughbores  12 . As a result, the throughbores  12  can advantageously be formed in a base body blank by a material removing drilling process. As an alternative, the throughbores  12  may also be realized by tubes in the base body  4 . The throughbores  12  thus do no longer extend in close proximity to the wear protection shield  6 ,  7 . This, however, is insignificant in view of the high heat conducting capability of the material of the base body  4  and is more than balanced by the benefit of reduced manufacturing costs of the structure. 
       FIGS. 3   a ,  3   b  show a cross section and a longitudinal section of a third thermoforming tool according to the present invention, generally designated by reference numeral  1   b  and useful for forming tailored blanks. In this embodiment, the wear protection shield  6  on the upper tool  2  and the wear protection shield  7  on the lower tool  3  are each formed with a thick region  13  and a thin region  14 . As a result, the structure being shaped can be exposed to a greater surface pressure in the thick region  13 , when the thermoforming tool  1   b  is closed to thereby ensure high heat dissipation. Air gaps remain deliberately in the thin region  14  between the structure being shaped and the wear protection shield  6 ,  7  so as to establish here a lesser heat dissipation. 
       FIGS. 4   a ,  4   b  show a cross section and a longitudinal section of a fourth embodiment of a thermoforming tool according to the present invention, generally designated by reference numeral  1   c . In this embodiment, provision is made for a wear protection shield having wear protection shield segments  6   a,    6   b,    6   c;    7   a,    7   b,    7   c  in correspondence to the subjacent base body  4 ,  5 . Adjacent wear protection shield segments  6   a,    6   b,    6   c;    7   a,    7   b,    7   c  are separated by a separation gap to inhibit heat conduction between the wear protection shield segments  6   a,    6   b,    6   c;    7   a,    7   b,    7   c  and to receive an insulating material  17 . As an alternative, or in addition to the cooling channels  8 , shown in  FIGS. 1   a, b , provision may also be made for heating elements  16 , for example in the form of heating cartridges, in the tool segments  9   a ,  9   c;    10   a,    10   c  to maintain the temperature in particular regions. 
       FIGS. 5   a ,  5   b  show a cross section and a longitudinal section of a fifth embodiment of a thermoforming tool according to the present invention, generally designated by reference numeral  1   d  and useful for making a tailored blank  18 . In this embodiment, the wear protection shield  6  of the upper tool  2  and the wear protection shield  7  of the upper tool  3  are provided with protrusions  19  so that the cavity that forms as the thermoforming tool  1   d  is closed has a contour that complements the contour of the tailored blank  18 . As shown in particular in  FIG. 5   b , the wear protection shields  6 ,  7  have varying thicknesses D1, D2, with the thickness D1 being smaller than the thickness D2. 
       FIGS. 6   a ,  6   b  show a cross section and a longitudinal section of a sixth embodiment of a thermoforming tool according to the present invention, generally designated by reference numeral  1   e.  In this embodiment, each of the wear protection shields  6 ,  7  has an opening  20  via which, for example, the shaped structure can be perforated subsequently or in the thermoforming tool  1   e . When being perforated subsequently, the opening  20  causes reduced heat dissipation, cooling rate and thus strength in this region so that the perforation can be implemented at relatively slight force, tool wear and without risk of microcracks. 
       FIGS. 7   a ,  7   b  show a cross section and a longitudinal section of a seventh embodiment of a thermoforming tool according to the present invention, generally designated by reference numeral  1   f.  In this embodiment, the segments of the base body  4 ,  5 , are not directly and actively cooled through provision of cooling channels; Rather, a bottom plate  21  is attached to the base body  4 ,  5  and provided with a plurality of cooling channels  8 . Heat is thus dissipated via the wear protection shields  6 ,  7  through the base bodies  4 ,  5  and the bottom plates  21 . In view of the high heat conduction of the base body  4 ,  5 , a desired heat dissipation is again rendered possible. 
       FIGS. 8   a ,  8   b  show a cross section and a longitudinal section of an eight embodiment of a thermoforming tool according to the present invention, generally designated by reference numeral  1   g.  In this embodiment, provision is made for the individual segments  9   a,    9   b,    9   c;    10   a,    10   b,    10   c  of the upper tool  2  and the lower tool  3  to be formed on bottom plates  21 , respectively, with the segments  9   a,    9   b,    9   c;    10   a ,  10   b,    10   c  having a substantially constant or even reduced volume ratio for heat dissipation in relation to the bottom plate  21 . Thus, the individual segments  9   a,    9   b ,  9   c,    10   a,    10   b ,  10   c  are made in accordance with the present invention of highly heat conductive material to ensure adequate heat dissipation of the wear protection shield  6 ,  7 . The segments  9   a,    9   b,    9   c;    10   a,    10   b,    10   c  can easily be provided with the desired contour and the thermoforming tool  1   g  can be cost-effectively manufactured in combination with the wear protection shield  6 ,  7 . The presence of the bottom plate  21  also imparts the thermoforming tool  1   g  with a necessary stiffness, when applying the forming forces. As can be seen in particular in  FIG. 8   b , the middle. segments  9   b,    10   b  are provided with cooling channels  8  in the form of rectilinear throughbores  12 . As alternative, tubes may be cast into the middle segments  9   b;    10   b  during production. 
       FIGS. 9   a ,  9   b  show a cross section and a longitudinal section of a ninth embodiment of a thermoforming tool according to the present invention, generally designated by reference numeral  1   h.  In this embodiment, provision is made for heating elements  16  in the tool segments  9   a,    9   c;    10   a,    10   c,  and both the upper tool  2  and the lower tool  3  are each provided with a solid bottom plate  21 . In addition, the middle segment  9   b  is provided with a cooling channel  8  which is fluidly connected to a central cooling channel  22  in the bottom plate  21  so that coolant can be fed to the bottom plate  21  and flow via the cooling channel  22  to the segments  9   b;    10   b  of the upper tool  2  and the lower tool  3 . 
       FIG. 10  is a plan view of the thermoforming tool  1   h,  depicting the bottom plate  21  of the upper tool  2  with segments  9   a,    9   b,    9   c.  The heat zone and the cold zone are separated from one another by a respective separation gap  11 . Illustration of the wear protection shield  6  is omitted here for sake of simplicity. The segments  9   a,    9   b,    9   c  may be coupled onto the bottom plate  21  by a form fit and/or interference fit and/or material joint. 
       FIGS. 11   a ,  11   b  show a cross section and a longitudinal section of a first embodiment of a deep drawing tool according to the present invention, generally designated by reference numeral  23 . Parts corresponding with those in  FIGS. 1   a ,  1   b  are denoted by identical reference numerals and not explained again. In this embodiment, provision is made for a downholder  24  or sheet metal holder which is coupled to the lower tool  3  and movable in relation thereto. The downholder  24  is constructed to clamp the not shown workpiece as it contacts the upper tool  2  via the wear protection shield  6  in opposition to a spring force acting on the downholder  24 . Attached to the base body  4  of the upper tool  2  is wear protection shield  6  and attached to the base body  5  of the lower tool  3  is wear protection shield  7 . Both the upper tool  2  and the lower tool  3  have formed therein cooling channels in the form of throughbores  12  so that the formed structure can be quenched after conclusion of the deep drawing process. 
     As shown in particular in  FIG. 11  b by way of the longitudinal section through the deep drawing tool  23 , the base body  4  of the upper tool  2  and the base body  5  of the lower tool  3  are each comprised of the three segments  9   a,    9   b,    9   c;    10   a ,  10   b,    10   c.  The segments  9   a,    9   b,    9   c;    10   a,    10   b,    10   c  are respectively separated from one another by separation gaps  11 . The segments  9   b,    9   c  of the upper tool  2  and the segments  10   b,    10   c  of the upper tool  3  have throughbores  12 , whereas the segment  9   a  of the upper tool  2  and the segment  10   a  of the lower tool  3  are devoid of any cooling channels. 
       FIGS. 12   a ,  12   b  show a cross section and a longitudinal section of a second embodiment of a deep drawing tool according to the present invention, generally designated by reference numeral  23   a.  As shown in particular in  FIG. 12   a , a metal sheet  25  to be formed is clamped by a downholder  24  between an upper downholder part  24   a  and a lower downholder part  24   b.  The downholder  24  is movable separately in relation to both the upper tool  2  and the lower tool  3 . The wear protection shield  6  of the upper tool  2  and the wear protection shield  7  of the lower tool  3  are hereby configured to embrace the base bodies  4 ,  5  at least in some areas of their marginal areas. As a result, added lateral securement is realized with respect to the horizontal direction H, and the metal sheet  25  is prevented from sliding off in press stroke direction or vertical direction V via the border-side folded region of the wear protection shields  6 ,  7 . The wear protection shields  6 ,  7  thus embrace the marginal area of the base bodies  4 ,  5 , respectively on two opposite sides. 
     The longitudinal section of  FIG. 12   b  clearly shows that only the segment  9   b,    10   b  of the upper and lower tools  2 ,  3  has cooling channels in the form of throughbores  12 , whereas the segments  9   a,    9   c;    10   a,    10   c  are made of a material that is different than the material of the segment  9   b;    10   b.  For example, the material of the segments  9   a,    9   c;    10   a,    10   c  may have a heat conductivity which is smaller than the heat conductivity of the material for the segments  9   b;    10   b.  Taking into account the thermal separation as a result of the separation gap  11  between adjacent segments  9   a,    9   b,    9   c;    10   a,    10   b,    10   c,  heat dissipation into the segments  9   a,    9   c;    10   a ,  10   c  is significantly decreased. The wear protection shields  6 ,  7  do not embrace the base bodies  4 ,  5  according to the longitudinal section of  FIG. 12   b , although this is, of course, conceivable within the scope of the invention so that the marginal area of the base bodies  4 ,  5  is embraced all-around. 
       FIGS. 13   a ,  13   b  show a cross section and a longitudinal section of a third embodiment of a deep drawing tool according to the present invention, generally designated by reference numeral  23   b.  Also in this embodiment, provision is made for a downholder  24  which is coupled to the lower tool  3  and movable in relation thereto. The downholder  24  can hereby clamp the not shown metal sheet as the upper and lower tools  2 ,  3  are moved in relation to one another to bring the metal sheet into contact with the wear protection shield  6  of the upper tool  2 . Wear protection plate  7  is attached to the base body  5  of the lower tool  7 . Both the upper tool  2  and the lower tool  3  have cooling channels in the form of throughbores  12  so that the formed structure can be quenched after conclusion of the deep drawing process. 
     The longitudinal section of  FIG. 13   b  through the deep drawing tool  23   b  clearly shows that the base body  4  of the upper tool  2  and the base body  5  of the lower tool  3  are each comprised of three segments  9   a,    9   b,    9   c;    10   a,    10   b    10   c.  Unlike in the embodiment of  FIGS. 11   a ,  11   b , the segments  9   a,    9   b,    9   c;    10   a,    10   b    10   c  are free of gaps. The segments  9   a,    9   b,    9   c  of the upper tool  2  and the segments  10   a,    10   b,    10   c  of the lower tool  3  have throughbores  12  for cooling the deep drawing tool  23   b  and thus the steel component, not shown. 
     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 
     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: