Patent Grant
9919351
This application is a National Stage of International Application No. PCT/EP2013/056712 filed Mar. 28, 2013, claiming priority based on Swiss Patent Application No. 0455/12 filed Apr. 2, 2012, the contents of all of which are incorporated herein by reference in their entirety.
The present invention relates to a method for producing pot-shaped components from a planar blank, and to corresponding components.
In the production of pot-shaped parts in a deep-drawing method, in particular from metal and for example for use in the automotive sector, the thickness of the part bottom is limited by the thickness of the starting material. This means that, in order to produce a part with a predetermined bottom thickness, it is necessary to use a starting material which has at least this desired thickness of the bottom.
Often, however, parts are required which, although they have a large bottom thickness, should have a wall thickness which is as small as possible in the region of the frame. It has not previously been possible to produce such components in a deep-drawing method; rather, it has been necessary to produce them by joining two parts, namely a thin-walled sleeve and a “thick bottom disk”. The problem is, in particular, that it is generally not possible to reduce the wall thickness in the frame region to less than half the starting material thickness, otherwise the shaping capacity of the material would be exceeded.
The object of the present invention is, inter alia, to at least partially overcome this limitation of the deep-drawing process. Specifically, the proposed method is intended for producing parts whose bottom thickness is greater than the thickness of the starting material. To this end, a typically cylindrical bowl is firstly produced by a deep-drawing process and subsequently pressed into a conical die, so that thickening of the bottom part is achieved. This effect can be increased further by carrying out such a process sequence repeatedly.
First, in other words, a round bowl is preferably drawn from a planar round (blank), and this bowl is subsequently pressed into a conical die. The bowl may subsequently be pressed into a conical die again, in order to achieve further thickening of the bottom, or a cylindrical bowl may again be shaped from the conical workpiece by a further deep-drawing step.
In tests and FEM simulations, it is found that, in particular, the corner radius of the workpiece is of crucial importance for being able to achieve large thickening in the bottom region. To this end, it is important for the ejection force to be dosed correctly. If it is too low, then when the bowl is pressed in there is an excessive corner radius, so that efficient thickening is prevented. If this force is too great, then a kind of undercut is formed, which likewise prevents efficient thickening. Furthermore, the bottom of the part should be clamped above during the thickening, in order to prevent it from bulging, since this would likewise counteract a thickening process. By means of the strength of the clamping force, it is also possible to influence the extent to which the bottom is thickened in the region of the clamping. This is beneficial in terms of process technology, inter alfa when this region is subsequently intended to be provided with a hole, or have a step. With respect to the ratio of the ejection and clamping forces, it may be stated that the clamping force should in principle be less than the ejection force. In order to achieve an optimal result, the level of the difference of the two forces is important, and its optimal value depends on the specific geometry of the process, the tribo system and the material of the workpiece.
On the basis of the shaping introduced in the region of the bottom, the proposed method also achieves material strengthening, so that the component also has a greater strength than the base material in this region, which is not possible in a conventional deep-drawing process.
In the scope of the tests, it is furthermore found that, by a suitable sequence of deep-drawing and ironing operations after the thickening of the bottom, it is possible to produce parts which have very sharp corner radii for parts produced in a deep-drawing method.
Specifically, the present invention relates to a method for producing a pot-shaped component from a flat blank, wherein the pot-shaped component has an essentially planar bottom region and a circumferential frame adjacent thereto, rising from the bottom region. The blank has a first material thickness D essentially over its entire area, and the bottom region has a second material thickness D9, which is greater than the first material thickness D.
The method is, in particular, characterized by at least the following steps
a) shaping the planar blank in at least one deep-drawing step to form a pot-shaped raw component having an essentially planar bottom region and a circumferential frame adjacent thereto, rising from the bottom region,
b) shaping this pot-shaped raw component in a tool having a conically tapering die and a preferably path-controlled shear element (instead of this, however, the die may be path-controlled) exerting a shear on the circumferential surface of the frame of the raw component in the axial direction against the conically tapering die.
During this second step b), the bottom region of the raw component is clamped at least locally between an ejector and a retainer. Furthermore, the conically tapering die encloses the bottom region of the raw component, guiding this bottom region radially on the outside and in a diameter-reducing manner in the tool stroke.
By this management of the process, in the second step b) on the one hand the frame is compressed to a certain extent by the shear, and possibly swaged in a thickening manner. At the same time, however, the bottom region is pushed together in a thickening manner radially with respect to the symmetry axis.
A similar method may also be carried out for a step section, either in addition to the above-described formation of a thicker bottom region or instead thereof. Such a step section is a section in which a component plane is arranged perpendicularly to the axis of the component, and such a region can likewise be correspondingly thickened. Preferably, in such a case of a step section, since it is not continuous in the direction of the central axis in contrast to a bottom section, in the scope of step b) the internal aperture of the step section is stabilized by a punch engaging through the former, so that the region is in fact thickened and not simply pushed radially inward. When the bottom region is referred to below, this also includes such a step section.
It is moreover possible that, before or after step b), optionally for example in the scope of step a), holes and/or cutouts are formed in the bottom region, or also in the frame, or that these elements are formed in a stepped fashion, with horizontal, vertical or conical steps. Specifically in the case of horizontal steps, these, as mentioned above in the context of step sections, may likewise be thickened. Particularly when holes are formed in the bottom region before step b), it is preferred for the internal aperture of this hole to be stabilized by a punch engaging through it in the scope of step b), so that the bottom is actually thickened and not simply pushed radially inward with reduction of the hole.
When deep drawing is referred to below, this generally means a process in which the drawing gap is not limited, that is to say the drawing gap is wider than the material guided through it at the start. When ironing is referred to below, this includes actual ironing using a sharp edge at an angle of typically 12-18°, but it also includes deep drawing with limitation of the drawing gap, that is to say other methods in which the wall thickness is tapered in a controlled way but a sharp ironing edge is not necessarily used. Correspondingly also included are processes using a smoothing die, in which in contrast to a deep-drawing die the radius of the rounded region merges into the cylindrical region not tangentially but at an angle, typically 5-20°, normally 12-18°.
In principle, the method may be carried out under thermally regulated conditions both in the scope of step a) and particularly in the scope of step b), that is to say at a temperature at which an increased ductility of the material can be used. This is possible, for example, by heating the starting material and/or the tool parts in a controlled way. Hot forming, particularly in the scope of step b), or optionally subsequent steps, may even be envisioned.
In order not to hinder this thickening of the bottom by an excessive clamping force between the ejector and the retainer in the scope of step b), it is preferable that the retaining force of the retainer during the shaping tool stroke in step b) is less than the counterforce of the ejector. The difference between the two forces in absolute value is preferably adjusted in such a way that the defect states represented below in
Another preferred embodiment is characterized in that step a) comprises at least one first deep-drawing step for forming a rising frame, and optionally at least one second shaping step, in which the radius of the transition region between the bottom region and the frame is reduced. The frame is preferably pressed and/or deep-drawn in a wall thickness-reducing manner or height-increasing manner in the scope of this step or in the scope of at least one further step. In particular, it may prove important that, before step b), the radius in the transition region between the bottom region and the frame is already small enough to ensure, for this step b), sufficiently controlled displacement of the material in the plane of the bottom surface toward the symmetry axis.
Another preferred embodiment is characterized in that, following step b), the component is subjected to at least one shaping step in which the frame is converted from an orientation conically tapering toward the bottom region into a cylindrical, preferably circular-cylindrical, orientation at least over a part of the height, preferably over the entire height, of the frame. Preferably, at the same time or in the scope of one or more additional processing steps, the frame is pressed and/or deep-drawn so as to increase its height.
The result of step b) is normally a component which has a frame widening upward. Such a design is suitable for certain applications, but in other designs, if the frame is intended to extend parallel, such a subsequent step is then necessary.
Normally, the pot-shaped component is rotationally symmetrical.
According to a preferred embodiment, the second material thickness D9 is the same essentially over the entire bottom region. The material thickness may, however, also be controlled deliberately by the clamping, that is to say it may be formed in a stepped manner because of the clamping between the retainer and the ejector. By corresponding structuring, for example stepping of the clamping surface of the retainer and/or ejector, it is also possible to impose a very controlled surface structure in this clamping region.
Another preferred embodiment is characterized in that the second material thickness D9 is at least 1.25 times as great as the first material thickness D, preferably at least 1.5 times as great as the first material thickness D, particularly preferably at least 1.75 times as great than the first material thickness D.
It is thus possible, according to another preferred embodiment, that in the resulting component after step b) or optionally after further subsequent steps, as mentioned above and explained in detail below, the second material thickness D9 is at least 1.5 times as great as the material thickness D9′ of the frame, preferably at least 1.75 times as great, particularly preferably at least 2 times as great.
Typically, the blank consists of metal, preferably steel, or in particular metals preferably selected from the following group:
The conically tapering die preferably has a cone angle in the range of 3-20°, preferably in the range of 5-15°. If lower values are selected, the displacement of material into the bottom region is insufficient and the steps have to be repeated too often. If larger values are selected, then, particularly in the case of relatively high frames, difficulties are to be expected since the frame warps, or the like. The precise setting depends on various parameters, for example process speed, tool temperature, component temperature, friction on the tool, wall thicknesses, material, etc. An optimum setting of the parameters, in particular cone angle, clamping forces of retainer and ejector, etc., can be made without an unreasonable effort by the person skilled in the art, on the basis of visual or tactile checking of the resulting components, cf. below.
Another preferred embodiment, in which the thickness of the bottom is further increased, is characterized in that step b) is carried out at least two times, either immediately after one another or with at least one intermediate deep-drawing step, in which preferably the frame is converted from an orientation conically tapering toward the bottom region into a cylindrical, preferably circular-cylindrical, orientation at least over a part of the height, preferably over the entire height, of the frame.
Such a method may be carried out in a continuous or quasi-continuous process, preferably from a roll, by starting material being supplied and the blank being cut, particularly preferably stamped, from the starting material in at least one processing step which precedes step a).
Lastly, the present invention also relates to a pot-shaped component, in particular made of a metallic material, having an essentially planar bottom region and a circumferential frame adjacent thereto, rising from the bottom region, and produced by a method as described above, wherein the material thickness D9 of the bottom region is preferably at least 1.5 times as great as the material thickness D9′ of the frame, preferably at least 1.75 times as great, particularly preferably at least 2 times as great. In this case, furthermore, owing to the shaping-induced strengthening of the material in the bottom region, component properties are produced which—for a given base material—cannot be achieved by other production methods. For a specimen component produced from the material DC04LC (yield point about 210 MPa, HV1 about 107 to 111), the yield point of the bottom region was increased in two deep-drawing steps to about 240 MPa. In the subsequent first thickening step (1.1 mm to 1.3 mm), the yield point in the bottom region was increased to about 400 MPa (HV10 about 151 to 166) and in a second thickening step (1.3 mm to 1.7 mm) to about 450 MPa (HV10 about 176 to 181), the corresponding values of the yield points (except for the base material) being determined with the aid of FEM shaping simulations, as explained in more detail below, and the hardness values being measured on the real components. In general, the specific increase in the strength compared with the base material is dependent on the specific geometry of the component, on the material used and on the shaping temperature. The resulting strength may, however, already be determined at least approximately in advance from the comparative shaping factors in the bottom region and the corresponding creep curve of the base material. In the case of cold forming, the creep curve may, for example, be determined approximately with the aid of the formula which is specified in Standard EN10139:1997 Annex B under B1.2: σ=K*ϵn, where σ stands for the yield stress and ϵ stands for the comparative strain. K and n represent material parameters, K standing for a material-dependent constant in MPa and n being the dimensionless hardening exponent. Furthermore, there are a multiplicity of other hardening laws for determining the yield stress, which may correspondingly also take the effect of temperature into account. As examples, the Johnson-Cook model (G. R. Johnson, W. H. Cook, A constitutive model and data from metals subjected to large strains, high strain rates and high temperatures, 7th International Symposium on Ballistics, 541-547 (1983)) and the Kocks-Mecking model (H. Mecking and U. F. Kocks, Kinetics of flow and strain hardening, Acta Metall. 29 (1981) 1865-1875). It is furthermore possible to determine the corresponding creep curve experimentally, for example in a tensile or compressive test. The comparative shaping factor may be determined either in simple cases with the aid of analytical approximation formulae or with the aid of FEM shaping simulations. The yield stress determined in this way corresponds to the new yield point in the bottom region. Furthermore, the component is free of joins.
For such a component according to the invention, the yield point of the material in the bottom region—yield point as a measure of its strength—is increased relative to the corresponding value of the starting material, in such a way that it corresponds to an increase in the comparative plastic extension of at least 5%, preferably at least 10%, in particular at least 25% in the corresponding creep curve of the starting material. As the creep curve, the technical or actual stress/strain curve may be taken as a reference, and preferably the actual stress/strain curve.
Other embodiments are specified in the dependent claims.
Preferred embodiments of the invention will be described below with reference to the drawings, which are merely used for explanation and are not be interpreted as restrictive. In the drawings:
In this process, a blank in the form of a circular planar stamping 1 of metal (round) is provided. Such a stamping may for example be supplied in a continuous supply method from raw material on a roll, and stamped. In a first working step as represented in
Although this is not the case in this method represented in
The pot-shaped component 17, which is the result of the shaping step represented in
The result of this second step is pot-shaped component 30, which again has a circumferential rising region 31, moreover, since the gap width of the gap 33 is here set to be more than the thickness of the starting material, it is not only shaped but simultaneously also pressed, i.e. by this process the circumferential region 31 is to some extent drawn in length. The section 34 has thus been tapered in the scope of this step by using a limited drawing gap, and the transition region from the bottom region 32 to the circumferential rising region 31 of the pot-shaped component 30 has also been reduced in its radius. The bottom region 32 still, however, essentially has the material thickness of the starting material.
In a next processing step, which is represented in
Respectively on the left-hand side of represented
Now, in addition, a shear element 75 is provided, which bears with a radial shear surface 76 on the circumferential surface or upper edge 84 of the side wall. This shear element 75 is path-controlled, while the other tool parts 70, 71, 72 are adjusted by corresponding spring forces (the tool part 71 need not be spring-mounted). Now, the unit consisting of the retainer 70, ejector 72 and shear element 75 moves downward together with the clamped component 50, while the conical outer brace 71 remains essentially stationary. During this movement, the transition region 56 formed with a small radius comes to bear between the bottom section 52 and the rising section 54 with the cone surface 77.
By the successive further downward movement with pressure on the upper edge 84 by the shear element 75, as shown particularly in
At the same time, moreover, the rising region is deformed owing to the conical brace of the die 71 to form a rising region widening upward, as represented for the finished component by the reference 81. Since this side wall region is also pressed in a swaging fashion by the shear element 75, the component is possibly also thickened in this region as well.
The positioning and the shape of the retainer 70 are important in this case, as is in particular its radius. By the shear force directed radially inward, which is applied by the conicity of the die 71, the bottom may under certain circumstances also yield to this pressure by bulging upward, so that bulging instead of material thickening then results. Typically, the retainer should preferably cover at least one third of the radius of the bottom region at the starting time of the step, but it may also have a smaller radius. This, of course, is generally not desired, and correspondingly in this step it is important for the dimensioning and the clamping force of the retainer 70, in particular the clamping force between the retainer 70 and the ejector 72, to be set just in such a way that, although this bulging is prevented, the thickening of the material is nevertheless also made possible not only in the region where the retainer 70 does not bear, but also in the clamping region. Only if the distance between the retainer 70 and the ejector 72 can be modified in an increasing way in the course of the method step according to
The result of this important processing step according to
If an excessive force is exerted by the shear element 75 (cf.
With the aid of the different states of a component in the scope of a sequence of steps,
This stage sequence starts with a blank 1 having a thickness D. In a first step, this component is deep-drawn, the bottom optionally being very slightly thinned (D1) during this method step, while the frame retains the thickness of the original material and is set up to a height h1. This component, as represented in
In a next step, which corresponds essentially to step 3 as described above, shaping is carried out by swaging the corners, in other words the transition radius between the bottom region and the frame is greatly reduced. This is a preparation for the step, represented above in the scope of
In a fourth step, the result of which is represented in
A further step is now carried out, the result of which is represented in
This finally results in a component in which the ratio between the wall thickness in the bottom region and the wall thickness in the frame region lies in the region of 3 to 1, starting from a starting material thickness which is substantially less than the thickness in the bottom region, and greater or even substantially greater than the final thickness in the frame region.
A component resulting from this process is represented, particularly in order to illustrate the corner region 103, with very small edge radii in
| Number | Date | Country | Kind |
|---|---|---|---|
| 455/12 | Apr 2012 | CH | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/056712 | 3/28/2013 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2013/149938 | 10/10/2013 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4562719 | Budrean | Jan 1986 | A |
| 5722282 | Mine | Mar 1998 | A |
| 8037810 | Leidecker | Oct 2011 | B2 |
| Number | Date | Country |
|---|---|---|
| 935 186 | Nov 1955 | DE |
| 2 315 832 | Oct 1974 | DE |
| 0 919 305 | Jun 1999 | EP |
| 2 387 706 | Nov 1978 | FR |
| 60-72617 | Apr 1985 | JP |
| 2001-047175 | Feb 2001 | JP |
| 2002-102980 | Apr 2002 | JP |
| 2005349433 | Dec 2005 | JP |
| 2007-014978 | Jan 2007 | JP |
| 2009248092 | Oct 2009 | JP |
| 2010-120061 | Jun 2010 | JP |
| 2010-214381 | Sep 2010 | JP |
| Entry |
|---|
| English machine translation of FR2387706A1 dated Dec. 16, 2016. |
| Machine Translation of JP2009-248092, Translated May 15, 2017, 16 Pages. |
| Machine Translation of JP2005-349433, Translated May 15, 2017, 15 Pages. |
| Written Opinion dated Oct. 2, 2014, issued by the International Searching Authority in application No. PCT/EP2013/056712. |
| International Search Report for PCT/EP2013/056712 dated May 16, 2013. |
| Written Opinion for PCT/EP2013/056712 dated May 16, 2013. |
| Number | Date | Country | |
|---|---|---|---|
| 20150093591 A1 | Apr 2015 | US |
