Patent Application
20090173129
The invention relates to a method for the production of a stamping with an enlarged functional surface, especially fine blanking a workpiece out of a flat strip, wherein the flat strip at closing is clamped between an upper part consisting of a shearing punch, a pressure pad for the shearing punch, an arranged on the pressure pad V-shaped projection and an ejector and a lower part consisting of a cutting die and an ejector and the V-shaped projection is pressed into the flat strip.
The invention further relates to devices for the production of a stamping with an enlarged functional surface, especially fine blanking a workpiece out of a flat strip, with a tool having two parts comprising at least a shearing punch, a pressure pad for the shearing punch, an arranged on the pressure pad V-shaped projection, an ejector, a cutting die and an ejector, wherein the flat strip is clamped between pressure pad and cutting die and the V-shaped projection is pressed into the flat strip.
Fine blanking and forming techniques are mainly used to process different steels. Within this, the multiplicity of used materials comprises general-purpose construction steels up to high-tensile fine-grained steels. The resource “material” during the last years gained large importance. With an optimal material utilization, the production costs of a component can be significantly influenced. The high-tensile steels allow for components with thinner walls with the same strength behavior.
In most of the cases, the cutting surface at fine blanking acts as a functional surface, and that is why the rollover is a cost factor.
Typical features of fine blanking parts are the edge rollover and the cutting burr. Especially in corner areas, the rollover occurs, and grows with decreasing corner radius and increasing sheet thickness. The depth of the rollover can be about 30%, and the width of the rollover, about 40% of the sheet thickness or more (see DIN 3345, Feinschneiden, August 1980). Thus the rollover depends on material thickness and quality, so that the possibility to control it is limited and often brings about a limited function of parts, for example, due to a lack of sharp edges of the corners at toothed parts or the caused change in the functional length of the parts.
The stamping rollover thus reduces the functionality of parts and urges the manufacturer to use a thicker raw material.
A number of solutions for trying to get rid of the edge rollover either by re-cutting (CH 665 367 A5), shaving (DE 197 38 636 A1) or shifting of material during the cutting (EP 1 815 922 A1) are known.
The known solutions according to CH 665 367 A5 and DE 197 38 636 A1 do not reduce the edge rollover, but largely rework the parts, so that on the one hand, significant costs for additional machining operations and tools are required and, on the other hand, a respective loss of material occurs due to the necessity of using thicker materials.
In the known solution according to EP 1 815 922 A1, the workpiece is machined in a single-step setup in at least two chronologically successive steps in different cutting directions, wherein during a first cutting process in a vertical working direction, a semi-finished product corresponding to the geometry of the workpiece with small rollover is cut out, and finally cut during at least one further cutting process in the opposite working direction. The rollover of the first partial step with this shall be filled up again at least in the corner area. But with this known method in the first instance, the projecting stamping burr is avoided. Also with this known solution, the rollover lastly is not avoided and material volume is shifted along the cutting line, which is accompanied by an increased risk of tearing.
At this state of the art, it is an object of the invention to largely, systematically avoid the edge rollover by creating a rollover corresponding to the volume within the part geometry, and at the same time, to maintain the functional surfaces at thinner fine blanking parts and to save material, without material being shifted along the cutting line.
This object is achieved by a method of the above mentioned kind, in accordance with which.
According to the invention, it is possible for the first time to economically apply the fine blanking technique for parts, for example toothed parts of medium and greater thickness, with sharp edges without finishing and material shifting along the cutting line.
This is achieved by carrying out, at the untreated clamped flat strip before the cutting starts, a negative with regard to the cutting direction preforming with a preforming element in the direction opposite to the cutting direction that corresponds to the expected edge rollover into the cutting die with regard to size and geometry at cutting including an allowance and generates a material volume at the side of the rollover in a mirror-inverted form. At the beginning and during the cutting the preformed area of the clamped flat strip is supported by the preforming element.
It is of special advantage that the process parameters for the preforming, for example, the geometry and the material volume of the area to be preformed, are determined depending on the material type, shape and geometry of the workpiece by a virtual forming simulation. This leads to a fast practical design of the preforming elements, especially regarding the preforming angles at the preforming elements.
But the process parameters for the preforming also can be determined iteratively by measuring real fabricated fine blanking parts, without leaving the frame of this invention.
The method according to the invention is variably applicable. So, for instance, the preforming can be carried out in a separate pre-stage as sequential cutting operation within a tool. But it can be also carried out without problems within a complex cutting operation in case the ejector at the same time is used as a preforming element, wherein the complex cutting operation according to the method of this invention is especially advantageous in case of thinner parts.
Thus, the method according to this invention covers fine blanking in a wide range of dimensions, for example, parts up to medium thicknesses and smaller parts up to medium-sized parts in complex cutting operations, and parts up to great thicknesses and dimensions in sequential cutting operations.
The devices according to this invention have a simple and sturdy structure. In case of the application of the sequential cut, at least one coining stamp arranged before the cutting stage acting against the cutting direction is provided to negatively pre-form a material volume on the rollover side corresponding to the expected edge rollover, wherein the coining stamp at its active side has a contour, respectively a preforming angle, which correspond with the geometry of the expected edge rollover plus an allowance.
For the complex cut, at least one stamp acting against the cutting direction is provided, allocated to the cutting stage ejector for negatively preforming a material volume on the rollover side corresponding with the expected rollover, wherein the ejector, at its active side, has a contour, respectively a preforming angle, which corresponds with the geometry of the expected edge rollover plus an allowance, wherein the ejector at cutting supports the preformed area.
The preforming angles for the coining stamp at the sequential cut and the ejector at the complex cut amount to about 20° to 40°.
Further advantages and details accrue from the following description with reference to the attached figures.
The invention in the following will be explained in more detail at the example of an embodiment.
a and 4b each is respectively a schematic view of the geometry of the edge rollover according to the state of the art and according to the preforming according to the invention;
The pre-stage is formed by a guided in the lower part 2 designed as preforming element V coining stamp 13, which on its active side 14, has a previously determined preforming angle a and a contour 15 (in a virtual forming simulation), corresponding to the geometry of the expected rollover plus an allowance resulting from experimental values (see
The process parameters for the preforming, for example the geometry, i.e., the height of the rollover and the width of the rollover, and the material volume, i.e., the volume of the rollover, are determined depending on the type of material, shape and geometry of the workpiece by a virtual forming simulation, wherein the material flow in the forming process is shown, extensions and reference stress values are analyzed to find out whether the forming can be realized and the tool elements can bear the loads. But the process parameters can be also determined at the real fine blanking part by individually measuring the height of the rollover, the width of the rollover and determining the volume of the rollover. That requires a series of tests and their analysis to be able to respectively design on this basis the coining stamp 13.
Instead of the separate pre-stage, here described in more detail it is possible of course to use the ejector 9 as preforming element for preforming of the clamped flat strip according to the expected geometry of the edge rollover.
The interrelationships to assist in an understanding of the method according to this invention are shown in the
a shows the occurring rollover at a fine blanking part fabricated without applying the invention. This rollover E according to DIN 6930 and VDI guide lines 2906 is defined by the edge rollover height h and the edge rollover width b and the occurring burr by the cutting burr height and the cutting burr width. It is secured knowledge that the burr volume with respect to the rollover volume V is many times smaller. So to speak, volume has been lost. This volume on the one hand clearly moves behind the outer contour of the part and on the other hand a small amount is lost because of the strain hardening of the material.
During shearing, applied tensile forces to the material are present which increase beyond the cohering forces in the atomic lattice. This leads to a slip between the adjoining planes of shearing punch 5 and cutting die 7. But before the real shearing, plastic deformations occur, leading to the edge rollover E.
For each geometry of a part to be fabricated according to the method of this invention, the dimensions and the volume V of the expected edge rollover are determined. This can be done either by forming simulation or direct measuring of real parts.
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 07018139.1 | Sep 2007 | EP | regional |
