Patent Application
20130283881
The invention relates to a process of producing metal blanks which, along their length, comprise different thicknesses.
From DE 197 04 300 A1 a process is known of producing sheet metal blanks with different thicknesses by deforming an approximately uniformly thick starting material. The starting material is first heated in an induction heating device to a temperature above the re-crystallization temperature. Subsequently, the starting material is subjected to a process of partial rolling deformation wherein the thicknesses vary in the rolling direction.
Document DE 198 46 900 A1 proposes a process of and device for producing a metal band. The differently thick regions of the band are produced by hot rolling in that portions of the band, prior to the hot rolling process, are set to a different temperature by being cooled or heated. As a result, the band, in its individual portions, as a result of the different temperature settings, is provided with different flow stress values, while experiencing different thickness reduction rates with the rolling force substantially remaining constant.
The disadvantage of the processes in use at present is the high expenditure involved in heating the coils and the complexity of the roll stands for rolling the coils and sheet metal blanks heated to different degrees in certain regions for the purpose of producing different thicknesses in certain regions.
It is the object of the present invention to propose a simplified process of producing metal blanks with different thicknesses, which process permits specific regional changing of temperature of sheet metal blanks and rolling the sheet metal blanks by means of a simple and cost-effective roll stand to different thicknesses in different regions.
The objective is achieved by a process of producing metal blanks with different thicknesses from a metallic material, having the following process stages:
The advantage of the process with the given sequence of individual process stages consists in that a regional change in temperature results in different temperature zones. As a result of the different temperature zones, the different regions of the metal blanks comprise different flow resistance values. The hotter regions have a lower flow resistance and are therefore rolled down to a greater extent than cooler regions of the sheet metal blanks. During the subsequent rolling operation portions with different thickness are produced in the sheet metal blank, due to the different flow resistance values. The regions which, prior to the rolling operation, were heated to a greater extent, comprise, after the rolling operation a smaller thickness than the regions heated to a lesser extent. Overall, the inventive process ensures that by setting suitable temperature zones for the metal blank in advance of the rolling process, there are obtained optimum blank thicknesses after the rolling process, which thicknesses are adapted to the subsequent component requirements.
A metal blank is meant to be a sheet metal element which is produced from a band material or a coil, respectively. This means that the process stage of regionally changing the temperature of the metal blank is preceded by the production of the metal blank from a band material. It is understood that between cutting individual blanks from the band material and the regional change in temperature of the blank, other process stages can take place, for instance a heat treatment process. For producing the metal blanks from the band material or coil, any method can be applied, which method depends on the end contour of the blank to be produced. For example, the metal blanks can be produced by simply cutting to lengths the band material into individual elements with at least two parallel side edges or by cutting or punching individual elements with individual circumferential contours out of the band material. Said cut-out elements with individual circumferential contours can also be referred to as profile cuts or contour cuts.
The advantage of using metal blanks for regionally changing the temperature consists in that it is also possible to generate temperature gradients transversely to the direction of production and to the subsequent direction of rolling, respectively. During rolling, said temperature gradients lead to blank deformation which is asymmetric with reference to the direction of rolling, which would not be the case with band material. Thus, in an advantageous way, there is achieved a maximum degree of flexibility as regards the geometry of the sheet metal blank to be produced and, respectively, of the end product to be produced from the blank.
The rolling operation which takes place after the blanks have been cut from the band material takes place with a constant roll gap. This means that when the blanks pass through the rolling tool, the roll gap setting remains substantially constant, preferably in an uncontrolled process. In this context, roll gap refers to the roll opening, including an expansion step, at the faces of contact of the material to be rolled with the rolls along the rolling bale length. Expansion step refers to an increase in the roll opening when the material to be rolled passes through; this is due to an elongation, respectively compliance of parts of the roll stand. In contrast to the roll gap, the rolling force can change when the sheet metal blank passes through. The transitions between the blank portions with different thicknesses occur as a result of the temperature distribution in the blank and can be kept very short by suitably regionally changing the temperature prior to the rolling operation, in contrast to controlled roll stands. The force/work requirements are greatly reduced as a result of the temperature-dependent flow resistance, so that sheet metal blanks with different plate thicknesses can be produced economically in wide widths.
According to a preferred embodiment, the different temperature regions are produced in accordance with the required thicknesses of the sheet metal blank. In principle, the shape and extension of the temperature regions in the longitudinal and transverse direction can be selected such that, after the rolling operation, the blank has the required thickness profile.
More particularly, according to a simple first embodiment, it is proposed that of the regions with different temperatures, at least one region, preferably a plurality of regions, are heated or cooled to a constant temperature transversely to the direction of rolling. Thus, the blank regions which are positioned side by side in the longitudinal direction of the blank and which each comprise a different temperature relative to the adjoining region, lead to a change in the thickness of the blank in the longitudinal direction, respectively in the rolling direction of the blank during the rolling process. The number and distribution of the regions with different temperatures, respectively the temperature profile can, in principle, be freely selected depending on the required thickness profile of the blank, with the number, more particularly, ranging between two and six.
According to a second possibility it is proposed that, at least one region, if necessary also several regions, are subjected to a variable temperature transversely to the direction of rolling. In this way it is ensured that, during the subsequent rolling process, the sheet metal blank experiences a respective change in thickness transversely to the direction of rolling. In this case, too, the number and distribution of the regions with different temperatures can be set as a function of the required thickness profile.
According to a third possibility, which constitutes a combination of the first and of the second possibility, it is possible to produce temperature regions which extend at a uniform temperature transversely to the direction of rolling, as well as temperature regions which comprise an additional temperature gradient transversely to the direction of rolling. The latter third possibility offers a maximum degree of flexibility in respect of the later thicknesses of the sheet metal blank after the rolling process in the longitudinal and transverse directions. More particularly, it is possible to achieve a three-dimensional thickness structure of the blank.
According to a first embodiment, the regional change in temperature starts from a homogenous first temperature of the sheet metal blank by heating at least one region of the blank to a higher second temperature. In this regard, homogenous first temperature means that prior to the regional change in temperature, the sheet metal blank comprises the same temperature everywhere. “At least one region” means that one region or several regions are heated to an individual temperature. If exactly one region is heated, there are obtained two regions whose temperatures differ from one another. The temperature level to which the sheet metal blank is heated essentially depends on the material and, respectively, on the strength of the material. If a steel material is used, then at least one region of the sheet metal blank is preferably heated to a second temperature of 400° C. to 1250° C., more particularly to 600° C. to 800° C. If an aluminum material is used, the sheet metal blank is preferably heated to a second temperature of 150° C. to 500° C.
The process of regionally heating the sheet metal blank can be carried out for example by a punch which is moved into contact with the blank such that the blank at least approximately assumes the temperature of the punch, in which case the punch would be provided in the form of a heating punch which preferably comprises differently controlled temperature zones. Alternatively, regionally heating can be effected by induction by one or several current-conducting rolls through which the blanks are guided, and more particularly it is proposed that the different temperature zones of the sheet metal blanks are produced by varying the power of the current-conducting rolls when the sheet meal blanks pass through.
According to a second embodiment, the regional change in temperature, while starting from a homogenous first temperature of the blank, is effected by cooling. For this purpose, the metal blanks are initially heated homogenously to a higher first temperature prior to the temperature of certain regions of the metal blank being varied. Subsequently, the regional change in temperature takes place by cooling at least one region of the blank to a lower second temperature. Because at least one region is cooled, there occur at least two regions whose temperatures differ from one another. It is understood that it is also possible to cool any number of regions to an individual temperature. When a steel material is used, the homogenous first temperature to which the sheet metal blank is heated ranges between 950° C. and 1250° C. During the subsequent regional process of cooling the regions, the temperatures are set to lower second temperatures which, more particularly, range between 400° C. and 950° C., preferably between 600° C. and 800° C.
The regional cooling of the metal blanks is preferably carried out by a punch which is brought into contact with the blank such that the blank at least approximately assumes the temperature of the punch, in which case the punch would be provided in the form of a cooling punch. The punch can preferably comprise individually controllable cooling zones, so that the temperature zones of the sheet metal blank can be adapted individually to the thickness profile to be produced at a later state.
According to a preferred process which applies to both embodiments, i.e. both to partial heating and also partial cooling, the blanks are subjected to a heat treatment, preferably to normalizing, after having been rolled. For this purpose, the blanks, if a steel material is used, are preferably heated to a temperature of 950° C. and 1250° C. and if an aluminum material is used to a temperature of 150° C. and 550° C. Heating preferably takes place in a heating furnace. This type of heat treatment ensures a uniform structure in the sheet metal blank across all portions of different thicknesses.
After completion of the heat treatment, the sheet metal blank is processed further into an end product. The subsequent process stage preferably comprises a deformation process such as deep drawing. Subsequently, the component can be hardened or subsequently quenched and tempered. It is particularly advantageous to use a hot forming process in the course of which the sheet metal blank is formed in a hot forming tool into the proposed shape and hardened. In connection with the hot forming process it is also conceivable that only partial regions of the hot forming tool are cooled, so that only those partial regions of the tool are hardened which come into contact with the cooled partial regions of the hot forming tool. The remaining partial portions of the tool retain their low hardness level. For hot forming with simultaneous hardening it is necessary to provide a cooled forming tool which, in the blank portions to be hardened and, respectively, of the end product to be produced therefrom, comprises cooled regions or, optionally, is fully cooled.
Another solution to the above-mentioned objectives consists in a device for producing metal blanks with different thicknesses from a metallic material in accordance with the inventive process with one or several of the above mentioned process stages, wherein the device, in the sequence as given, comprises the following: a tool for separating sheet metal blanks from a band material; a temperature-changing tool by means of which regions with different temperatures can be produced in the metal blanks; and a rolling tool with a constant roll gap setting by means of which the partially temperature-changed blanks can be rolled, so that, due to the different temperature regions, portions with different thicknesses can be produced in the sheet metal blanks.
The inventive device has the same advantages as the process so that, to that extent, reference can be made to the above description. More particularly, the constant roll gap setting of the rolling tool, preferably in an uncontrolled process, is advantageous in respect of a simple and effective production process. The change in the material thickness is achieved entirely as a result of the different roll expansion steps of the rolling tool while the blanks pass through, which, in turn, is due to the different flow resistance values in the blank material and to the different temperatures of the material in certain regions. Because a tool for separating band material into blanks is disposed upstream the temperature-changing tool, there is achieved a maximum degree of flexibility for the geometry of the sheet metal blank to be produced and for the end product to be produced therefrom. It is thus also possible to produce sheet metal blanks and products with a variable thickness profile transversely to the direction of rolling.
According to a preferred embodiment, the temperature-changing tool comprises at least one punch which can be heated or cooled. The punch is used to partially increase or decrease the temperature of the sheet metal blank in one partial region or several partial regions relative to other regions. The size and shape of the punch preferably depends on the temperature zones to be produced and on the thickness profile of the blank to be produced in connection with the rolling process. The punch preferably comprises a plurality of regions in which the temperature can be set individually. It is thus possible to produce different temperatures zones on the blank with one single punch.
In a first possibility according to which the punch is provided in the form of a heating punch, the punch is preferably provided with heating wires which can heat the punch at least in partial regions.
In a second possibility in the case of which the punch is provided in the form of a cooling punch for partially cooling the sheet metal blank, the punch preferably comprises channels through which a cooling medium can flow in order to cool the punch. For variably setting the different temperature zones in the blank it is particularly advantageous if the through-flow speed of the cooling medium through the channels can be controlled. In a preferred embodiment, the punch is provided with a plurality of cooling circuits through which the cooling medium flows. By individually setting the through-flow speed of the cooling medium in every single channel, it is possible, by means of one cooling punch, to produce different temperature zones. It is thus possible, for example, with one cooling punch to produce a first region with 600°, a second region with 750° C. and a third region with 900° C. in the sheet metal blank. The same does, of course, apply analogously to a heating punch according to the first possibility which, accordingly, can comprise different heating zones.
According to a preferred embodiment, which applies to both possibilities, the at least one punch is produced from a metallic material with a good thermal conductivity, more particularly from copper or a copper containing material.
The rolling tool is preferably designed in such a way that the gap width is constant during the rolling operation. As a result, the force/work requirements can be kept very low, which advantageously affects production costs and production times. However, it is understood that it is also possible to use a tool with flexible rolls by means of which a particularly high degree of flexibility is achieved with reference to the thickness profile of the blanks to be produced.
According to a preferred embodiment, the device furthermore comprises a heat treatment facility which follows the rolling tool. In the heat treatment facility which, more particularly, can be provided in the form of a heating furnace, the sheet metal blanks can be heat-treated, preferably normalized.
According to an advantageous further embodiment, the heat treatment facility can be provided in the form of a forming tool which is preferably provided as a hot forming tool in which the sheet metal blanks can be formed and at least partially hardened. The combination of changing the temperature of the blanks in certain regions, of the subsequent rolling process, heating and hot forming is particularly advantageous because it permits a very efficient production of sheet metal blanks with variable thicknesses along their length and width. The heat input into the sheet metal blank during production, i.e. while the material passes through the individual stations of the device can be kept low, which, in turn, advantageously affects the production speed and production costs. It is particularly advantageous if the sheet metal blanks in those regions which, after the region-wise change in temperature, comprise the highest temperatures always comprise a temperature in excess of 500° C., more particularly in excess of 600° C. for steel materials during the subsequent process stages of rolling and heat treatment up to the point of being inserted into the forming tool.
Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.
“Metal blank 10”, in this context, refers to a sheet metal element which, more particularly, is produced from a band material, respectively from a coil. The sheet metal blank can be produced by simply cutting the band material into individual elements or by cutting out or punching out individual elements from the band material.
In process stage A1, the sheet metal blank 10 is treated by a temperature-changing tool 30, with the blank 10 being given various regions 11, 12, 21 which comprise different temperatures. In the present example, the region 11 has a temperature of 800° C., the second region 12 a temperature of 600° C. The transitional region 21 positioned between the first region 11 and the second region 12 comprises a variable temperature which decreases from the first region 11 to the second region 12.
The temperature curve with a continuous line as shown in
After the sheet metal blank 10 has been temperature-treated in certain regions, it is subjected to a rolling process in process stage A2. This is carried out by means of a rolling tool 40 which comprises a plurality of rolls 41, 42. As a result of the different temperature regions 11, 12, 21 produced during process stage A1, the sheet metal blank 10 comprises different flow resistance values. The hotter first region 11 comprises a lower flow resistance so that it is rolled down to a greater extent. Compared thereto, the cooler second region 12 of the blank 10 comprises a higher flow resistance, so that it is rolled down to a lesser extent. As a result of said different flow resistance values, there are produced portions 112, 122, 212 with different thicknesses in the blank 10. After the rolling process, the sheet metal blank 10 is provided with subscripts 2. It can be seen that after having passed through the rolling tool 40, the sheet metal blank 102 comprises a first portion 112 with a smaller thickness and a second portion 122 with a greater sheet thickness, as well as an intermediate transitional portion 212.
When the sheet metal blank 10 passes through the rolling tool 40, the roll gap setting remains constant, i.e. the distance between the rolls while the sheet metal blank 10 passes through is not changed. The thickness profile is obtained entirely as a result of the different temperature regions 11, 12, 21 of the blank 10. Overall, there is thus achieved a lower force/work effort. However, it is understood that it is also possible to use a flexible rolling process wherein the roll gap setting is varied during the rolling process. This results in an even greater degree of flexibility and further possibilities for producing different individual thickness profiles in the sheet metal blank 10.
b) shows the temperature curve TA before, after and during the rolling process. Again, the continuous line shows the temperature curve for region 11 and for the portion 112 obtained after the rolling process. Prior to the rolling operation, the temperature increases slightly and decreases to a greater extent during the rolling process until a temperature of approximately 700° has been reached. After the rolling process, the rolled blank 102 continues to cool, so that the temperature is reduced accordingly. The temperature curve TA2,12 for the second region 12 is largely parallel to the temperature curve TA2,11 for the first region 11, with the temperature being reduced by approx. 200° C.
During the following process stage A3, the rolled sheet metal blank 102 is subjected to a heat treatment. After the heat treatment the sheet metal blank and, respectively, its portions are provided with the subscript 3. The heat treatment preferably takes place in a furnace 50. As a result of the heat treatment, any material solidifications which occurred during the rolling operation are reduced or eliminated and the rolled sheet metal blank 103 again comprises a higher ductility and elongation capacity. In consequence, the blank 103 can be processed more easily during the subsequent process stages, and in addition, the material properties of the end product to be manufactured are influenced positively. It is understood that the heat treatment in process stage A3 is of an optional nature only, which means that, in principle, the sheet metal blank 102 can be processed further without undergoing the subsequent heat treatment.
As can be seen in
After completion of the heat treatment according to process stage A3, the blank 103 can be processed further, one example being a forming operation in a hot forming tool 60. In view of the hot forming process, the sheet metal blank and its portions have been provided with the subscript four. During the hot forming process in accordance with process stage A4, the sheet metal blank 104 is subjected to a forming operation and at the same time, it is considerably cooled and hardened respectively. This is also confirmed by the temperature curve which, for the thinner first portion 114 (temperature TA4,11) indicates a considerable temperature drop from 950° C. to below 200° C. The thicker second blank portion 124 cools somewhat more slowly, as indicated by the dashed line (Temperature TA4,12). It is understood that other hot forming processes can also be used for forming purposes. By way of example, pressing or deep-drawing processes could be mentioned.
a) and 2b) show an inventive process of producing a sheet metal blank with different thicknesses according to a second process stage B. This process largely corresponds to the processes according to
A specific feature of process B according to
b) shows the temperature curve TB of the sheet metal blank 101 and, respectively, of the first region 11 and of the second region 12 as a function of time. The continuous line represents the temperature curve TB,11 for the first region 111, whereas the dashed line represents the temperature curve TB,12 as a function of time for the second region 12. With reference to the second process stage B1 it can be seen that the first region 111 of the sheet metal plate 101 is cooled down from 950° C. to approximately 800° C. (temperature curve TB1, 11). The second region 121 experiences a higher cooling rate in that it is cooled to approximately 600° C. (temperature curve TB1, 12).
The product existing at this point in time corresponds to the sheet metal blank 101 originating from the first process stage A according to
Another specific feature of the present embodiment according to
The punch is preferably produced from a metallic material with a good thermal conductivity rate, for instance from copper or from a copper-containing material.
It is understood that the two embodiments for the different regions of the sheet metal blank 10 which are shown in
b) shows the sheet metal blank 10 in a side view before the rolling process, i.e. in profile in a greatly exaggerated form. It can be seen that the blank 10 comprises a uniform thickness along the length of same before rolling.
c) shows the sheet metal blank 102 after having been rolled in accordance with process stages A2 according to
a and b), which will be described jointly below, show a sheet metal blank 10 in a further possible embodiment after the temperature has been regionally changed, prior to the rolling process according to
Because the temperature in region 15 is variable in the direction extending transversely to the direction of rolling, the blank is rolled non-uniformly. It can be seen in
By producing different temperature regions T15, even transversely to the rolling direction R, a maximum degree of flexibility is achieved as regards the thickness profile. In an advantageous way, the sheet metal blanks 10 to be produced can be adapted individually to the thickness profile to be required for the subsequent end product. The advantage of the process described in connection with
The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102011051345.0 | Jun 2011 | DE | national |
