Patent Application
20200030866
The present invention relates to a method for the optimized production of a component, in particular of steel, with at least one ancillary formed element, in particular a collar or a flange, which is characterized in particular by the fact that the geometry of the ancillary formed element is deliberately adjustable and the component can therefore be manufactured individually very precise and for various applications. The component is further characterized by the fact that it is formed in one piece with the ancillary formed element and has a very high stability also in the region of the formed edges.
In the following, a blank or sheet metal blank shall be understood as relating to a cut of a sheet metal, in particular a sheet steel. The sheet metal blanks can be uncoated or provided with a metallic and/or organic corrosion protection coating.
In the following, a component shall be understood to relate to a component which is produced from a sheet metal blank by being formed using a forming tool at ambient temperature. Sheet metal materials include any formable metal materials, in particular steel however.
Such components are predominantly used in the automotive construction, but also applications in the home appliance industry, in mechanical engineering or civil engineering or in the field of yellow are possible.
The hotly contested automotive market forces the manufacturers to continuously look for solutions to reduce their fleet consumption while maintaining a highest possible comfort and occupant protection. Not only weight savings of all vehicle components play hereby a crucial role, but also a most beneficial behavior of the individual components at high static and dynamic stress during operation as well as in the event of a crash.
Suppliers of source material attempt to meet the required material demands by reducing the wall thicknesses of high strength and super high strength steels, while at the same time improving component behavior during production and operation.
These steels must therefore meet comparatively strict demands in terms of strength, deformability, toughness, energy absorption capability and corrosion resistance as well as their workability, for example during cold forming with respect to the fatigue behavior and during welding.
Among the afore-stated aspects, the production of components of higher and high strength steels with yield strengths above 400 MPa, advantageously above 600 or above 800 MPa to about 1800 MPa or even more, increasingly gains importance. For example, ferritic or bainitic or dual phase steels with the following alloy composition in weight-% find application:
0.2-4.0%
0.5-4.0%
with optional addition of Cr, Ni, Mo, B, balance iron, including impurities resulting from smelting.
It is known for the production of a component to first cut to size a sheet metal blank of hot or cold strip at room temperature. Cutting processes involve oftentimes mechanical separation processes, such as e.g. shearing or punching, but less common also thermal separation processes, such as e.g. laser cutting. Thermal separation processes are significantly more cost-intensive compared to mechanical separation processes, so that their use is contemplated only in exceptional cases.
After cutting, the cut blank is placed in a forming tool and the finished component, such as e.g. a chassis carrier, is produced in single or multi-stage forming steps.
During forming operation, the cutting edges, in particular when being raised or placed up, e.g. collar operations in perforated blanks, are particularly exposed to stress.
Before forming operation, various other optional manufacturing steps, such as e.g. punching and cutting operations, are implemented on the blank.
The cutting edges may have various preliminary damages. These are caused on one hand by strain hardening of the material, as a result of the mechanical separation, which represents a total deformation up to material separation. On the other hand, a notch effect may be encountered, which is due to the topography of the cut surface.
Especially with the steels considered here, an increased crack probability in the edge regions of these cutting edges is thus encountered during the subsequent forming process.
The afore-mentioned preliminary damages to the sheet edges can lead to premature failure during subsequent forming operations or during operation of the component.
To minimize the edge crack sensitivity during cold forming of shear-cut or punched sheet edges, approaches are known, for example, involving changing of the alloy composition and material processing (e.g. targeted adjustment of an optimized microstructure) or relating to process engineering during cold trimming of the blank (e.g. via modifications of cutting gap, speed, multiple trimming, etc.).
These measures are either expensive and complex (e.g. multi-stage cutting operations, maintenance of 3-D cutting tools, etc.), or do not yet yield optimal results.
Furthermore, it is known from laid-open publication DE 10 2009 049 155 A1 to heat at least the region of the cutting edge to a defined temperature and to execute the cutting process at this temperature in order to improve the formability of the cut edges and to thereby reduce or avoid the strain hardening in the region of the cutting edge. The disadvantage here is the required high technical and economic complexity to heat the metal sheet on one hand, and the forced coupling of heating of the blank with immediately subsequent cutting process, thus rendering the production inflexible on the other hand.
Laid-open publication DE 10 2011 121 904 A1 further discloses to cold-form a shear-cut sheet and, prior to further forming operations, to locally heat the strain-hardened regions by means of a laser with the objective of partial softening. The disadvantage here is in particular the local softening, which represents a discontinuity in terms of the often used high strength and super high strength material, especially in stress situations and under oscillatory stress. In addition, it is unclear where exactly heating should occur and how the local heating with temperature and time sequence should actually be implemented. Furthermore, it is unclear how and to what extent partial softening is able to improve formability of the already cold-formed metal sheet.
Laid-open publication DE 10 2014 016 614 A1 describes a method for the production of a component by forming a blank of steel, wherein a cut blank, following optional punching and/or cutting operations in the regions of the shear-cut edges, undergoes a short temperature treatment (max. 10 seconds) of at least 600° C. The heat-treated edges are then cold formed at any time after being heated. Even though this method is basically capable to increase formability of strain-hardened mechanically separated sheet edges when compared to other previously known methods, it is still desirable to be able to define and deliberately adjust geometric boundary conditions of an ancillary formed element produced by forming, in order to achieve a more precise configuration and increased stability of the ancillary formed element.
Laid-open publication DE 11 2007 000 239 T5 discloses a method for producing a wheel disc. A flat disc blank is formed into a bowl-shaped wheel disc. The bowl-shaped wheel disc is formed to form spoke-forming regions adjacent to window-forming regions. A window is formed in each of the window-forming regions in a substantially vertical direction, wherein each window has a respective outer edge proximate a continuous outer band around a periphery of the wheel disc. The windows define a plurality of spokes between adjacent windows. A circumferential length of each of the windows along the outer band is preferably greater than a circumferential length of each of the spokes. The outer edge is partially formed by means of a forming tool for forming a cylindrical shape, wherein the forming tool has an engagement surface with an intermediate ledge for receiving a peripheral edge of the outer band to reduce undulated deformations of the outer band. The outer edge is then fully brought into a substantially cylindrical shape by a cylindrical punch by being pulled axially along its outer edge. With the invention, grooves and undulations should be prevented when forming the collar.
Also this known method is not yet able to deliberately and individually adjust the geometric boundary conditions, such as wall thickness and wall height of a produced ancillary formed element.
It is therefore the object of the present invention to provide an alternative method for the production of a component, in particular of steel with formed-on ancillary formed element, wherein the geometric boundary conditions, e.g. the wall thickness and/or the wall height of ancillary formed element, can be adjusted deliberately and individually.
The invention solves this problem with the features of the claims and in particular by providing a method for the optimized production of a component having at least one ancillary formed element with the steps of
a) providing a blank cut from a strip or metal sheet at room temperature and optionally produced with recesses and/or openings by punching or cutting operations;
b) temperature treatment of selected edge regions of the blank that have been strain-hardened by the punching or cutting operations, wherein the edge regions are heated to a temperature of at least 600° C. for a period of maximal 10 seconds;
c) forming the temperature-treated edge regions of the blank at ambient temperature to obtain a component with raw ancillary formed element;
d) calibration step for obtaining the component with ancillary formed element, wherein the raw ancillary formed element is formed at ambient temperature into an ancillary formed element which has increased and/or homogenized wall thickness compared to the raw ancillary formed element.
As ambient temperature, both the room temperature, for example 20° C., and the temperature of the forming tool are considered. The temperature of the forming tool may lie well above the room temperature.
The blank provided in step a) of the method according to the invention has in the regions of its shear-cut edges an unwanted strain-hardening, which considerably reduces formability of the blank. This applies to both the shear-cut edge regions when cut from the metal sheet or strip and the edge regions which are shear-cut by a closed section or a punching operation and also the edge portions which are shear-cut by an open cut or a cutting operation.
For the purposes of the invention, a closed cut is understood to relate to a punching operation or a cutting operation having a starting point which is identical to the end point. The result of such a closed section is therefore an opening in the blank, for example a circular or polygonal, e.g. quadrangular opening. By contrast, an open cut is a cutting operation having a starting point which is not identical to the end point. The result of such an open cut is therefore a shear-cut contour of any geometry.
The process of shear cutting causes in the regions of the involved edges a strain hardening in the respective material, which is known to often lead to cracking in subsequent forming processes.
As a result of the temperature treatment according to the invention according to step b), the unwanted strain hardening can be eliminated or at least greatly reduced, so that the material can also be formed in the regions of the shear-cut edges, without encountering an increased susceptibility to cracking. A short temperature treatment for a period of maximal 10 seconds is already sufficient to eliminate or reduce strain hardening. Preferably, the temperature treatment lasts for a period of 0.02 to 10 seconds, and more preferably for a period of 0.1 to 2 seconds.
The process window for the temperature to be reached in the cutting edge region is moreover very large and includes a temperature range of above 600° C. up to the solidus temperature of approx. 1500° C., e.g. a range between the transformation temperature Ac1 and the solidus temperature.
In any case, it is crucial that the temperature treatment eliminates as far as possible the strain hardening introduced by the cutting process. The heat treatment according to the invention results in the region of the cutting edge in a same or higher hardness compared to non-heat-treated base material. For example, the Vickers hardness increases by up to 1000 HV.
Due to the elimination of strain hardening, the temperature-treated edge regions of the blank in step c) of the method according to the invention can be formed at room temperature into a raw ancillary formed element with demanding geometry, for example to a collar with a large collar height or a flange with a large flange height. The production of such a demanding geometry is not possible with most conventional methods, since the strain hardening caused by the shear cutting of the edges allows only a deformation of the edges to a relatively small extent.
While the method described in DE 10 2014 016 614 A1 is generally also able to produce collars with a large collar height and flanges with a large flange height, since this method also includes the steps a to c of the method according to the invention. However, it has been found that the wall thickness of the collar and flanges thus produced is often not uniform. Furthermore, this method is unable to allow adjustment of a defined height of the ancillary formed elements, since the edge regions are formed comparably undefined by the use of a widening tool, for example a conical or cylindrical punch. In particular, due to their undefined height and their non-uniform wall thickness, the ancillary formed elements produced in this way are referred to herein as “raw ancillary formed elements”.
The invention now provides for a calibration step d) for producing an ancillary formed element with a defined geometry, e.g. with defined and uniform wall thickness and/or wall height. This is an additional forming step at room temperature, which chronologically takes place after the first forming step (step c of the method according to the invention).
Surprisingly, it has been shown that in the calibration step d) by forming in a direction which is at least partially in opposition to the forming direction in step c), properties of the ancillary formed element can be advantageously altered.
The forming process in step c) is usually implemented by applying a forming tool in a so-called widening direction. For example, to produce a collar or a flange, a punch is inserted into a shear-cut or punched opening in the component, wherein by drawing the punch in widening direction through the opening, the edge regions are bent upward.
Since it is generally advantageous for various applications of components but still difficult to achieve the highest possible height of the respective ancillary formed element, it is first of all absurd to again reduce this once realized height of ancillary formed element by an additional forming step, e.g. by applying a force on the height of the ancillary formed element in a direction that counteracts the widening direction wholly or partially. That this is possible at all is due only by the temperature treatment according to the invention and the forming of the shear-cut edge regions in accordance with the invention, by which ancillary formed elements, e.g. edges, collars or flanges, can be produced with significantly higher than average height. These ancillary formed elements still have a sufficient height even after being formed in opposition to the widening direction, and are characterized by improved properties. It has been found that this forming process, which corresponds in principle to a compression, enables homogenization of the wall thickness of the ancillary formed element on one hand and increase thereof on the other hand, which both positively affect the properties of the component, e.g. its stability and life. Furthermore, the additional forming step, realized by a force applied in opposition to the preceding forming direction, renders it possible to generate a defined height of the ancillary formed element, in particular a defined edge height, flange height or collar height. As a result of the implementation of a defined adjustment of geometric boundary conditions of ancillary formed elements by the additional forming step, this forming step is referred to in accordance with the invention as a calibration step.
A calibration step is also to be understood as a shaping of edge regions with a force which is applied not completely but only partially in opposition to the preceding forming operation in the widening direction. Such a calibration step renders possible the production of, for example, ancillary formed elements with edges that are angled by 90°. As a result of this calibration cut, adjustment of the conicity and/or the cylindricity can advantageously be tailored, so that expensive reworking processes can be reduced to a minimum.
In concrete terms, a defined adjustment of geometric boundary conditions, for example of a collar, can be:
1. the height of the collar
2. the wall thickness over the circumference and the height of the collar
3. the shape accuracy (cylindricity/conicity) of the collar, achieved by:
According to an advantageous refinement of the invention, the method according to the invention has a further forming step, in which selected edge regions of the blank, strain hardened by the punching or cutting operations, can be formed at room temperature. This further forming step takes place after cutting of the blank and possible punching and/or cutting operations and prior to the temperature treatment of the edge regions. As a result of the additional forming step, the strain hardening, encountered by the cut and the optional punching and/or cutting operations in the material, is even further increased, but eliminated again by the subsequent temperature treatment according to the invention.
In a modified embodiment, the method according to the invention includes between steps a) and b) not only the one additional forming step, but also any number of further consequences of the inventive temperature treatment of the edge regions at a temperature of at least 600° C. for a period of maximal 10 seconds and another forming step. In this way, it is possible to further form the material in each forming step, and to remove the interfering factors caused by the forming process, such as strain hardening, microstructure damages, and adverse contour changes such as, e.g. microcracks.
The individual forming and temperature treatment steps of the method according to the invention can be implemented at any time, i.e. temporally decoupled from one another.
The forming steps of the method according to the invention can advantageously be executed with forming tools, e.g. cylindrical or conical punches, that already exist in the production. As a result, no expensive investment costs for carrying out the method according to the invention are necessary.
The method according to the invention is particularly applicable to any shear-cut material edges, in particular to punched holes and edges with any contour. As a result of the increased formability in accordance with the invention, it becomes possible to also produce complex geometries that require, for example, several forming steps. Even complex components can be produced in one piece, eliminating the need for additional joining operations.
The temperature treatment is preferably carried out in the method according to the invention over the entire thickness of the blank and in plane direction of the blank in a region which corresponds at most to the thickness thereof. The duration of the temperature treatment depends on the type of heat treatment process.
Heating itself can be implemented in any desired manner, for example, conductively, inductively via radiation heating, or by laser processing. Especially suitable for temperature treatment is conductive heating, as used for example in the automotive industry in many cases as demonstrated by the example of spot welds.
Advantageously, the use of a spot welding machine for example with rather short treatment times for the treatment of punched holes in the blank is suitable, whereas at longer edge portions to be treated, the inductive method, radiation heating or laser processing with longer treatment times are considered.
Thus, the heat input is very concentrated into the shear-affected cutting edge regions and is therefore accompanied with a comparatively little energy consumption, in particular with regard to processes in which the entire blank is subjected to a heating or which find application in a stress relief heat treatment that is more time consuming by orders of magnitude.
According to one embodiment of the method of the invention, the blank has a metallic and/or organic coating. This coating may contain or be made of zinc, magnesium, aluminum and/or silicon. The blank itself can e.g. be rolled flexibly with different thicknesses or be joined from cold or hot strip of same or different thickness and/or quality. The invention is applicable to hot or cold rolled steel strips of soft to high strength steels.
As higher strength steels, all single-phase as well as multi-phase steel grades find application. These include micro-alloyed, higher strength steel grades as well as bainitic, ferritic or martensitic grades as well as dual phases, complex phases and TRIP steels.
According to a possible embodiment of the method, to protect against oxidation during and optionally before and/or after the temperature treatment, the region around the location of the temperature treatment can be flushed by an inert gas.
In view of the short temperature treatment period of maximal 10 seconds, the method according to the invention can be integrated as an intermediate operating step in a series production which specifies a clock rate in the range of 0.1 to 10 seconds. In particular, the production of sheet metal components in the automotive sector in several successive steps thus represents a predestined field of application of the method according to the invention.
The invention also relates to a component having at least one ancillary formed element with high and/or homogeneous wall thickness, wherein for the production of the component a blank is provided which has been cut at room temperature from a strip or sheet metal and has been optionally produced by punching or cutting operations with recesses and/or openings, wherein a temperature treatment of selected edge regions of the blank that have been strain hardened by the punching or cutting operations is carried out, with the edge portions being heated to a temperature of at least 600° C. for a period of maximal 10 seconds, wherein the temperature-treated edge regions of the blank were formed at room temperature to obtain a component with raw ancillary formed element, and wherein the raw ancillary formed element was formed to obtain the component with ancillary formed element at room temperature into an ancillary formed element of increased and/or homogenized wall thickness compared to the raw ancillary formed element.
In an advantageous refinement of the invention, it is provided that the formed edge regions are repeatedly heat-treated and reshaped.
Preferred components are e.g. chassis components of hot sheet or cold sheet with attached ancillary formed elements, in particular collar, flanges and/or edges, which are obtainable by a method according to the invention.
Finally, the invention also relates to the use of a blank of steel for producing a component with at least one ancillary formed element, wherein the blank previously cut at room temperature from a strip or a metal sheet is subjected after optional further manufacturing steps are carried out at room temperature, such as e.g. punching or cutting operations for realizing recesses or openings, in selected edge regions that were strain hardened by the punching or cutting operations to a temperature treatment in which the edge regions are heated of at least 600° C. for a period of a maximal 10 seconds, wherein the temperature-treated edge regions of the blank are formed at room temperature to obtain a component with raw ancillary formed element, and wherein the raw ancillary formed element is formed at room temperature into an ancillary formed element having a wall thickness which is increased and/or homogenized compared to the raw ancillary formed element. In an advantageous refinement of the invention, it is provided that here too the formed edge regions are repeatedly heat-treated and reshaped.
The features of the invention as disclosed in the above description and in the claims may be essential individually as well as in any desired combinations for the realization of the invention in its various embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 103 743.8 | Feb 2017 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/051680 | 1/24/2018 | WO | 00 |
