Method for producing stamped parts

Abstract

A stamped or fine-blanked, workpiece is inserted in an embossing device, and the burr created on the workpiece during stamping or fine blanking is rounded by way of a die of the embossing device and the height of the rollover created during stamping or fine blanking is decreased using the same stroke of the embossing device by way of which the burr rounding is carried out.

Claims

1. A method for producing a finished part having teeth, comprising: producing a partially finished part having teeth by stamping or fine blanking a workpiece resulting in a burr on a first face of the partially finished part having teeth and a rollover on a second face of the partially finished part having teeth and a sheared edge extending between the burr and the rollover, the sheared edge forming an acute angle with the first face and an obtuse angle with the second face of the partially finished part having teeth; providing an embossing device comprising an embossing die; arranging the partially finished part having teeth in the embossing device for engagement of the partially finished part having teeth with the embossing die, and effecting a stroke of the embossing die in a direction orthogonal to the first and second faces of the partially finished part having teeth so that the embossing die engages the partially finished part having teeth; wherein the embossing die comprises an annular first die part and arranged coaxially therewith a second die part configured to be received in the first die part with a sliding fit; wherein a radially outermost interior diameter of the first die part is greater than a radially outermost diameter of the partially finished part having teeth and corresponds to a predetermined outermost diameter of the finished part having teeth; wherein regions of at least one of the first and second die parts corresponding to regions of the partially finished part having teeth which are a root region of each tooth of the partially finished part having teeth and regions between the teeth of the partially finished part having teeth are undersized relative to said regions of the partially finished part having teeth; wherein the first die part comprises a face facing the first face of the partially finished part having teeth and the second die part comprises a face facing the second face of the partially finished part having teeth; wherein the respective faces of the first and second die parts facing the respective first and second faces of the partially finished part having teeth are so configured that distance between the respective faces of the first and second die parts continuously decreases in a radially outward direction over a radial distance corresponding to a predetermined annular region extending radially to the predetermined outer extremity of the finished part having teeth; wherein the first die part has a lateral annular wall parallel to the axis of the embossing die and a transition between the annular wall and the face of the first die part facing the first face of the partially finished part having teeth has a radius of curvature corresponding to a predetermined radius of curvature of a transition from the first face of the finished part having teeth and lateral walls of the finished part having teeth; wherein an annular outermost edge portion of the face of the second die part facing the second face of the partially finished part having teeth has a radius of curvature corresponding to a predetermined radius of curvature of a transition from the second face of the finished part having teeth and the lateral walls of the finished part having teeth and less than a radius of curvature of the rollover; and wherein during a stroke of the embossing die the second die part is received in the first die part with a sliding fit and material of which the partially finished part having teeth is constituted is displaced laterally and axially to completely fill spaces that existed between the partially finished part having teeth and the embossing die, and in the regions of the partially finished part having teeth corresponding to the undersized regions of at least one of the first and second die parts an angle of a tangent of edges of the part having teeth with respect to a normal of the part having teeth is reduced, the burr is mashed to conform to the curvature of the transition between the lateral annular wall of the first die part and the face of the first die part facing the first face of the partially finished part having teeth, and the rollover is engaged by the annular outermost edge portion of the face of the second die part facing the second face of the partially finished part having teeth and thereby shaped to conform to the curvature of the annular outermost edge portion of the face of the second die part facing the second face of the partially finished part having teeth, thereby to form a finished part having teeth having annular walls which are orthogonal to a radial plane of symmetry of the finished part having teeth first and second faces which converge continuously in a radially outward direction in the annular region extending radially to the outer extremity of the finished part having teeth.

2. The method according to claim 1, wherein the annular region corresponds to at least a tip region of each of the teeth of the part having teeth.

3. The method according to claim 2, wherein the annular region corresponds to the entirety of each of the teeth of the part having teeth.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B are schematic representations of the prior art;

(2) FIGS. 2A, 2B, 2C are schematic representations of an embodiment of the invention;

(3) FIGS. 3A, 3B are schematic representations of another embodiment of the invention; and

(4) FIGS. 4A, 4B are schematic representations of yet another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIGS. 1A and 1B show the existing prior art, essentially according to WO 97/32678 (U.S. Pat. No. 6,212,930) by the same applicant, for a comparison with the advantageous invention, which will be apparent later.

(6) The workpiece W1 is apparent on the left side of FIG. 1A, which in this example was produced in the stamping stage of a fine blanking device. The rollover E, customary with fine blanking or with stamping in general, is apparent on the die-roll side, which is at the bottom here. On the burr side of the workpiece W1, which is at the top here, the typical burr G extends at a height h.

(7) After stamping or fine blanking, the workpiece W1 is transferred into an embossing stage. Using a die, which is not shown in FIG. 1A, the burr G is rounded, using the radius R here, and with this step, workpiece W2 is produced from workpiece W1. The die-roll side, and in particular the height of the rollover E, remains unchanged here.

(8) An orientation of the sheared edge SF not parallel to the stroke direction or workpiece normal is not illustrated in FIG. 1A, but always exists for reasons related to the design principle. This orientation remains unchanged in the prior art by the rounding of the burr, which represents only a minor forming step.

(9) FIG. 1B shows the rounding of the burr in conjunction with a die GS. The workpiece W1, which is fine-blanked in this example, but optionally may only be stamped in the traditional manner, is shown on the left side of FIG. 1B; however, the non-parallel slanted position of the sheared edge SF is illustrated here as well, compared to FIG. 1A.

(10) With an identical dimension or oversized dimension between the workpiece W1 and the die GS symbolized by the arrow P1 and the line L1, during the stroke, the die moves from the burr side over the workpiece and rounds the burr G by way of the embossment rounding PR, with which the lateral surface of the die transitions into the bottom surface of the die.

(11) The identical dimension or oversized dimension exists here in the upper burr-side workpiece plane between the burr-side sheared edge and the inner die lateral surface. In this illustrated case, these are aligned along line L1.

(12) The right side of FIG. 1B furthermore shows that the rounding of the burr, and the material displacement associated therewith, in addition to the rounded burr, also results in a bead, which in actuality causes an increase in the cross-sectional surface area of the embossed workpiece W1 just below the burr-side workpiece surface plane, as compared to the unembossed workpiece W1. It is furthermore apparent here that the slanted position of the sheared edge with respect to the normal of the workpiece surface is unchanged.

(13) Overall, the embossed workpiece W2 thus shows considerable differences in geometry, and in particular differences in the surface area sizes of the burr-side and die-roll-side workpiece surfaces, as well as a non-parallel sheared edge SF with respect to the workpiece normal, so that a workpiece thus embossed requires a finishing operation, for example by way of a grinding process, to be ready for use.

(14) FIGS. 2A,2B show an embodiment of the invention.

(15) According to FIG. 2A, the stamped or fine-blanked workpiece W1 is clamped between two ejectors A1 and A2. The die GS has a bell-shaped design here, surrounds the upper ejector A1, and can be moved in the stroke direction H relative to the two ejectors and the clamped workpiece W1 so as to carry out the embossing step.

(16) Again, the rollover E, the burr G and the sloped sheared edge SF, which is not parallel to the normal, are apparent here. In FIG. 2A, the embossing device is open, which is to say the embossing step has not yet been carried out.

(17) FIG. 2B shows the closed embossing device after the embossing step according to the invention has been carried out. The bell-shaped die GS has moved from the burr side over the burr G and has rounded the same in accordance with the embossment rounding PR.

(18) According to the above definitions, the die has an identical dimension or oversized dimension in relation to the workpiece, however here this also causes a reduction, and preferably even an elimination, of the angle , which in this sectional view is enclosed between the sheared edge SF and the die lateral surface and corresponds to the angle, described in the hereinabove discussion of the prior art, between the aforementioned tangent on the sheared edge and the workpiece normal WN. This also results in a reduction in the rollover E.

(19) It is apparent from FIG. 2B that the sheared edge SF rests against the die lateral surface, and thus the angle has been eliminated here, and apart from the burr-side rounded edge and the edge of the workpiece having reduced rollover on the die-roll side, the sheared edge SF is thus parallel to the workpiece normal WN.

(20) Both the rollover reduction and the angular reduction on the sheared edge here can be attributed to the die GS having moved, with the die bottom surface GSB thereof, in a closing stroke direction over the burr-side workpiece surface, and thus the thickness of the workpiece has been decreased by the die GS in an edge region along the cutting contour. This thickness reduction causes a material displacement in the axial direction and radially outwardly, whereby the angular reduction and rollover reduction are achieved. This may also result in strain hardening of the material in the zones Z close to the edge, radially inwardly in relation to the sheared edge SF.

(21) FIG. 2C shows a detail of the embossed edge GR on the burr-side workpiece surface. The width of the edge GR can preferably be in the range of 0.1 to 1 mm, for example. The thickness reduction of the workpiece thickness in this edge region can likewise preferably be 0.1 to 1 mm.

(22) Here, the invention can furthermore provide that the radius of the embossment rounding PR is at least substantially identical to the height of the reduced rollover on the embossed workpiece W2.

(23) This results in an embossed workpiece that, apart from the embossed edge, is substantially identical on the burr side and the die-roll side of the workpiece and has a sheared edge SF parallel to the workpiece normal WN. Such a workpiece W2 does not require any finishing. Grinding processes for adapting the workpiece to the desired geometry can thus be dispensed with.

(24) FIGS. 3A,3B show another embodiment of the method according to the invention, which can also be combined with the step of edge embossing according to FIGS. 2A, 2B.

(25) Based on the line L1 and the arrow P1, FIG. 3A illustrates that the die GS has an undersized dimension in relation to the workpiece W1. Here, this results from the die lateral surface GSSF of the die being disposed radially inwardly in relation to the burr G, with the outer cutting contour shown here. In the case of an inner cutting contour, conversely the die lateral surface would be disposed radially outwardly in relation to the burr. Due to the abutment taper of the die GS directed toward the burr G, however, it is still possible to move the die over the workpiece W1 during the embossing stroke.

(26) FIG. 3B shows the situation after the embossing stroke has been carried out. Here, the die has displaced material of the workpiece W1 radially inwardly and axially, and thereby has both decreased the rollover and reduced, or here eliminated, the angle of the sheared edge SF with respect to the die lateral surface GSSF. The die bottom surface here has moved only into the planes of the burr-side workpiece surface, so that no edge was embossed here, as is described in FIGS. 2A, 2B. Nonetheless, such edge embossing would additionally also be possible.

(27) The reduction in the sheared edge angle and rollover height in this embodiment is thus primarily due to the effect of the undersized dimension between the die and the workpiece W1, so as to form the embossed workpiece W2, which is preferably directly ready for use without finishing.

(28) The embossment rounding PR can also be selected here such that the rounded burr has a radius that at least substantially corresponds to the reduced rollover height. Preferably, deviations between this radius and the reduced rollover height of less than 25% are achieved.

(29) FIGS. 4A, 4B show a particularly preferred embodiment, which can be used, for example, with n-fold rotationally symmetrical workpieces, such as transmission disks or gear wheels, and preferably sprockets. It is likewise possible to produce non-symmetrical workpieces or such that comprise teeth only in sections, and in particular in at least one section of the stamped or fine-blanked circumferential contour. FIG. 4A shows a sectional view of the embossing device parallel to the stroke direction or parallel to the workpiece normal WN. The still unembossed workpiece W1 shown here again has a rollover having the height E, a burr G, and a sloped sheared edge SF non-parallel to the workpiece normal WN.

(30) The workpiece W1 is surrounded by a die here, which comprises an upper die part GSO and a lower die part GSU. In the sections A1 and A2, the two die parts GSO and GSU each have an embossment rounding PR. The embossment rounding PR of the lower die part GSU is used to mash the burr using a desired radius, wherein the embossment rounding PR of the upper die part GSO limits the rollover reduction to the value E1 since material pressed during embossing is thus limited in terms of flow.

(31) It is apparent in this sectional view A-A, which corresponds to the cutting plane A-A of FIG. 4B, that the die parts have an oversized dimension in relation to the workpiece W1 or the sheared edge SF thereof. It is apparent from the comparison with FIG. 4B, where the die is shown with dotted lines, that this oversized dimension is only present in a tooth tip region of a workpiece W1 comprising teeth, for example a workpiece comprising teeth only in at least a partial region, such as a seat adjustment element of a motor vehicle, or a workpiece W1 stamped or fine-blanked in the form of a gear wheel, and preferably a sprocket.

(32) Both figures furthermore indicate an embodiment essential to the invention, according to which the distance between the two die parts in the stroke direction H decreases in the direction of the sheared edge, viewed from inside the workpiece. This reduction in the distance is present in the region B of both die parts which extends over the tooth tip according to FIG. 4B. This region may also extend over the entire tooth height, where necessary, but is at least provided in the tooth tip region.

(33) This embodiment causes not only the burr G to be rounded and the rollover E to be decreased to E1 during embossing, but additionally implements a workpiece thickness reduction on the workpiece W1, with a thickness reduction, increasing from radially inside toward radially outside, on a respective tooth of the workpiece comprising teeth, and in particular a gear wheel. The material pressed out of the region B in the workpiece finds room in the spaced region between the sheared edge and the die lateral surface, due to the oversized dimension present there.

(34) Such a thickness reduction which is generated in an identical manner both on the burr side and on the die-roll side on each tooth of the workpiece comprising teeth, and in particular a gear wheel, can form a lead-in region on the workpiece tooth for facilitated lead-in of the tooth into a respective chain link.

(35) FIG. 4B furthermore shows that the die has, or the two die parts GSO and GSU have, an undersized dimension in the respective tooth root region or tooth base region, which is to say the die lateral surfaces GSF of the die parts are located inside the workpiece W1, viewed in the stroke direction.

(36) As a result of abutment tapers, it is again made possible that the die, and in particular the lower die part GSU thereof, can move over the burr G of the workpiece during the embossing step, and thus embosses the same, and also reduces, or preferably eliminates, the angle of the sheared edge SF with respect to the workpiece normal through material flow. In this way, the sheared edge can be made parallel to the workpiece normal in the tooth root region, and in particular in the region that is, for example, up to 50% of the tooth height over the tooth root region, and in particular can thus improve the engagement between the tooth surfaces there and a chain link axis.

(37) Preferably, this method variant also yields a workpiece that can be used immediately after the embossing step, in particular a workpiece comprising teeth, and preferably a sprocket, and requires no reworking or only reworking that is considerably reduced over the prior art.