CA2773343A1

CA2773343A1 - Method and device for increasing the bearing area ratio of a fine-blanked part having a tooth, tooth section or the like

Info

Publication number: CA2773343A1
Application number: CA 2773343
Authority: CA
Inventors: Andreas Marti; Ulrich Schlatter
Original assignee: Feintool Intellectual Property AG
Current assignee: Feintool Intellectual Property AG
Priority date: 2011-04-05
Filing date: 2012-04-05
Publication date: 2012-10-05
Also published as: EP2508274B1; JP2012218071A; EP2508274A1

Abstract

For producing a flat part having a tooth or other projection of augmented thickness, a fine blanking stage is followed by a forming stage in which the thickness of the tooth or other projection is increased by application of force to at least one surface of the tooth or other projection perpendicular to the flat faces of the part. Transfer of the part from the fine blanking stage to the forming stage is effected by a cross slide.

Description

METHOD AND DEVICE FOR INCREASING THE BEARING AREA RATIO OF A FINE-BLANKED PART HAVING A TOOTH, TOOTH SECTION OR THE LIKE
Background of the Invention The invention relates to a method for increasing the bearing area ratio of a flat fine-blanked part having a tooth, a tooth section or the like, and in particular a parking-gear pawl for automatic transmissions, in which a blank is integrally cut from a flat strip clamped between the upper part and the lower part of a tool in a fine-blanking stage, is captured by a cross slide, which is moved horizontally into the opened tool, and is carried, correctly positioned, into a forming stage in a direction opposite to the feed direction of the flat strip, the cross slide then moving out of the tool into the home position thereof, whereupon the tool closes.

The invention further relates to a device for carrying out the method using a tool having an upper part and a lower part, comprising a fine-blanking stage provided for cutting a blank having at least one tooth from a flat strip, and comprising a forming stage having an upsetting head, a plate-shaped holder, a clamping plate, an ejector and a control pin for partially upsetting the blank, wherein a cross slide carries the blank, correctly positioned, out of the fine-blanking stage into the forming stage.

In fine-blanking and metal forming technology, primarily steels are processed.
The diversity of materials that are used ranges from simple constructional steels to high-strength, fine-grained steels. The aspect of "materials" has gained considerable importance in recent years. The production costs of a component can be significantly influenced by utilizing materials in an optimal manner. High-strength steels make it possible to obtain thinner-walled components having the same strength behavior.
In fine-blanking, the sheared edge acts as a functional surface in most cases, and therefore rollover is a cost factor.

Typical features of fine-blanked parts are the edge rollover and the burr. The rollover notably forms in corner sections, and increases as the corner radius decreases and the sheet thickness increases. Rollover depth can amount to approximately 30% of the sheet thickness and rollover width can amount to approximately 40% or more of the sheet thickness (see DIN
3345, Fine-blanking, Aug. 1980). Rollover is therefore dependent on the thickness and quality of the material, and so control thereof is limited and is often associated with restrictions on part function, such as in terms of the corners not having sharp edges in the case of fine-blanked parts having tooth geometries, such as parking-gear pawls, or terms of changes in the functional length of the parts.
Thus, punched rollover reduces part function and makes it necessary for the manufacturer to use a thicker starting material.

An entire series of solutions is known, which attempt to either eliminate the edge rollover by shaving (CH 665 367 A5) or scraping (DE 197 38 636 Al), or to compensate therefor by shifting material during cutting (EP 1 815 922 Al), negative deformation (EP 2 036 631 B1) or thickening the functional surfaces (DE 102009001305A1).
The known solutions according to CH 665 367 A5 and DE 197 38 636 Al do not reduce the edge rollover, but rather re-machine the parts in a complex manner, thereby requiring considerable costs for additional machining processes and tools, and result in a related material loss due to the need to use thicker material.
In the known solution according to EP 1 815 922 Al, the workpiece is machined in a single-stage system, in at least two chronologically successive step sequences in different cutting directions, wherein, in a first cutting process, a semi-finished product matched to the workpiece geometry, which has a slight rollover, is cut in the vertical working direction and, in at least one further cutting process, the final cutting of the part is carried out in the opposite working direction. The rollover from the first partial step should be refilled, at least in the corner section.
This known method, however, primarily avoids the protruding burr; the rollover is ultimately not eliminated, but rather a material volume is shifted along the cutting line, which increases the risk of crack formation.
The known method according to EP 2 036 631 B1 attempts to compensate for the edge rollover in that, before the cutting starts, deformation that is negative with respect to the cutting direction is carried out at the clamped, untreated flat strip, using a preforming element opposite to the cutting direction that corresponds to the expected edge rollover into the cutting die, in terms of size and geometry at cutting, including an allowance, and generates a material volume at the side of the rollover in a mirror-inverted form.
In the known method according to DE 10 2009 001 305 Al as well, before cutting, the edge region of a sheet metal part is subjected to a permanent deformation, that is, upsetting.
Solid-blank forming carried out before fine-blanking has the fundamental disadvantage, however, that the dimensional stability of the finished parts can be unfavorably influenced. This means that the forming devices must adhere to very narrow tolerances to ensure plane parallelism in the upset regions, which is indispensible for fine-blanking.

Summary of the Invention In this state of the art, the object of the invention is to markedly increase the bearing area ratio of the functional surfaces at the tooth geometry of a fine-blanked part, and simultaneously reduce the sheet thickness, while saving material and ensuring economic advantages, and to further improve the dimensional stability of the parts.

The basic idea of the solution according to the invention is that of avoiding solid-blank forming, which influences the tolerances of the material strip, before fine-blanking, and performing solid-blank forming at the functional surfaces of the tooth geometry of the finished cut part, with the requirement of carrying out a desired partial thickening.
This is achieved by the following steps, which take place in the forming stage:
a) clamping the blank, at the flat sides thereof, between a clamping plate and an ejector in such a way that the tooth of the blank is not clamped and remains accessible for a forming operation, b) upsetting the tooth by application of a compressive force suited to the material of the blank and the tooth shape in such a way that the force is directed, by an upsetting head, horizontally to the flat sides into the core of the tooth, whereby the tooth is symmetrically thickened by up to 30% relative to the starting thickness of the blank.

It is advantageous for the compressive force to be introduced perpendicularly into the tip surface of the tooth, thereby permitting the material to flow uniformly and symmetrically in the tooth region.

In a preferred embodiment of the method according to the invention, the upsetting head is driven mechanically or hydraulically by way of a wedge drive. This is associated with the advantage of achieving a flat and compact design for the forming stage.

It has proven advantageous to adjust the compression at the partially thickened surfaces of the tooth geometry to values between 1.25 and 1.625, and to match the upsetting head to the tooth shape. This ensures that the thickening takes place substantially symmetrically at the tooth, thereby markedly increasing the thickness of the tooth with respect to the thickness of the remaining blank and reducing the moment of inertia.

It is particularly advantageous that the process parameters for upsetting, such as the geometry and the material volume of the upsetting region, can be determined according to the material type, and the shape and geometry of the workpiece, by way of a virtual forming simulation. This results in a faster, realistic setting of the compressive force.
The process parameters for upsetting can also be iteratively determined by measuring real fine-blanked parts, without the scope of the invention being limited as a result.

According to a further preferred embodiment of the invention, and in particular of the device according to the invention, the holder has a receiving opening matched to the shape and size of the blank, which encloses the blank except for the tooth, whereby the blank is held in the receiving opening in a clamped manner at the flat sides thereof, between a clamping plate and an ejector, but the tooth is not clamped, and the upsetting head is aligned with the tooth in the forming stage and is disposed so that the upsetting direction thereof is oriented horizontal to the flat sides, and perpendicular to the tooth tip surface of the non-clamped tooth.

In a further advantageous embodiment of the device according to the invention, the upsetting head comprises a wedge drive, having wedge elements with two opposing wedge surfaces, the first wedge element being disposed so that it is displaceable perpendicular to the feed direction of the flat strip in the forming stage below the die plane (ME), and the second wedge element being disposed so that it is displaceable perpendicular and horizontal thereto, wherein the wedge element carries the upsetting head, which brings about the perpendicular motion of the upsetting head onto the tooth tip surface by way of the displacement of the wedge element along the wedge surfaces.

In a further embodiment of the device according to the invention, the forming stage comprises a mechanical and/or hydraulic drive system, which is independent of the fine-blanking stage.

The solution according to the invention is characterized in that it is possible to thicken fine-blanked parts at the functional surfaces thereof, partially, and in a well-defined manner, without the precision of the fine-blanked parts being influenced by the forming process.

Further advantages and details will become apparent from the description that follows, with reference to the accompanying drawings.

The invention is described in greater detail in the following with reference to an exemplary embodiment.

Brief Description of the Drawings Shown are:

FIG. 1 a perspective view of the blank for a parking-gear pawl according to the prior art;

FIG. 2 a schematic view of the rollover at a fine-blanked tooth;

FIG. 3 a perspective view of a parking-gear pawl manufactured using a method according to the invention;

FIG. 4 a schematic view of the device according to the invention;

FIG. 5 a perspective view of the blank placed into the plate-shaped holder, having a tooth that is freely accessible for forming, and FIG. 6 a schematic view of the upsetting head comprising a drive.
Detailed Description of the Invention FIG. 1 shows a fine-blanked parking-gear pawl 1 according to the prior art, for an automatic transmission. The parking-gear pawl 1 has a tooth geometry in the form of a tooth 2.
This tooth 2 is designed such that it fits into a tooth space of a parking gear, which is not shown, when the parking-gear pawl 1 is engaged with the parking gear.

The parking-gear pawl 1 is made of case hardening steel, of the grade 16MnCr5, and has a thickness s of 10 mm and a moment of inertia with respect to the centroid of 29958 kgmm2. As shown in FIG. 1, the parking-gear pawl 1, as a component, has a uniform thickness in the width and length directions, and therefore the tooth 2 also has this thickness.

Due to the rollover produced in fine-blanking, the bearing area ratio at the functional surfaces F of the tooth 2 is reduced. In other words, the available thickness is reduced by the amount of the rollover, which results from the height h and the width b of the rollover. These relationships are depicted in FIG. 2, in which the bearing area ratio TA of the functional surface F is shaded, and the lost surface is labeled VF.
To ensure that the required bearing area ratio is available at the functional surfaces for the transmission of moments, the starting thickness of the strip material must be increased accordingly. This leads to a higher weight and all the associated disadvantages for the technical parameters of the transmission, as well as economic disadvantages, such as higher costs.

In the present example, a parking-gear pawl, as shown in FIG. 3, shall be produced using the method according to the invention and the device according to the invention.
The reference characters used above are retained in the following description.
The parking-gear pawl 1 should have a thickness s of 8 mm and reach a thickness SZD of 10 mm in the region of the tooth. The moment of inertia should be 23187 kgmm2.

FIG. 4 schematically illustrates an example of a device according to the invention, with which the parking-gear pawls 1 are produced. The device according to the invention comprises a fine-blanking stage 3 and a forming stage 4, which are coupled to one another by a cross slide 5, which, in the opened state of the device, moves between the upper part and the lower part, captures the blanks 7 that were integrally cut from the flat strip 6 in the fine-blanking stage 3, and moves to the forming stage 4. The cross slide 5 is shown in the non-engagement position in FIG. 4.
The fine-blanking stage 3 primarily comprises a guide plate 8, a die 9, a shearing punch 10, an ejector 11, an inner form punch 12, and an ejector 13, which are disposed in the upper part 0 or the lower part U of the device according to the invention, in accordance with the function they perform.
The guide plate 8, the shearing punch 10, the ejector 11, the inner form punch 12 and the ejector 13 are connected by way of a piston/cylinder unit, which is not shown in greater detail, to a hydraulic system 14, which generates the appropriate pressure forces for the fine-blanking operations and applies them to the operative elements. The fine-blanking stage 3 otherwise corresponds to the prior art, and therefore a more detailed depiction can be omitted.

The forming stage 4 primarily comprises a holder 15 in the form of a thin plate, a pressure plate 16 in the form of an anvil, an ejector 17, an upsetting head 18 and a control pin 24. The pressure plate 16 and the ejector 17 are driven directly, and the upsetting head 18 is driven indirectly, by way of a mechanical wedge drive 21, by an auxiliary hydraulic system 19, which is independent of the hydraulic system 14. The control pin 24 moves against the wedge element 23, which moves the upsetting head 18 with the compressive force PSK
against the tooth tip surface ZKF. The holder 15 is aligned with the die plane ME of the fine-blanking stage 3, thereby enabling the cross slide 5 to move the blank 7 horizontally between the fine-blanking stage 3 and the forming stage 4. The holder 15 has a receiving opening 20, which is matched, in terms of size and shape, to the contour of the blank 7 for the parking-gear pawl 1 (see FIG.

5). The receiving opening 20 is designed so that it can receive the entire blank 7 except for the tooth 2. The tooth 2 is therefore not enclosed by the holder 15 and is freely accessible from the outside for relevant forming operations.
The holder 15 has a thickness T, which is slightly greater than the thickness s of the blank 7.
The blank 7, which is captured by the cross slide 5, is deposited into the receiving opening 20 of the holder 15, and therefore one flat side FSB of the blank 7 lies flat on the ejector 17, and the other flat side FSD faces the pressure or clamping plate 16.
When the tool is closed, the clamping plate 16 moves against the flat side FSD
of the blank, and the ejector 17 moves against the flat side FSB of the blank 7. The blank 7 is therefore held in the receiving opening 20 of the holder 15, clamped between the pressure plate 16 and the ejector 17. The clamping force applied by the auxiliary hydraulic system 19 is lower than the compressive force PSK applied by the upsetting head 18.

The upsetting head 18, with the wedge drive 21 thereof, is depicted schematically in FIG. 6. The wedge drive 21 comprises two wedge elements 22 and 23, wherein each of the wedge elements 22 and 23 has a wedge surface KI and K2, respectively. Wedge surfaces K1 and K2, which are displaceable towared one another, are provided at wedge elements 22 and 23. The wedge element 22 is disposed below the die plane ME so that it can be displaced vertically, and the wedge element 23 is disposed so that it can be displaced vertically and horizontally with respect to the strip feed direction VS of the flat strip 6.
The displacement of the wedge element 23 is brought about by the control pin 24 moving against the wedge element 23, and therefore the wedge surface K2 moves along the wedge surface K1, and the upsetting head 18, which is carried by the wedge element 23, moves in the direction of the tooth 2, which is exposed for forming.

The upsetting head 18 and the compression direction thereof are oriented parallel to the flat sides FSB and FSD of the clamped blank 7, perpendicular relative to the tooth tip surface ZKF
of the exposed tooth 2, and therefore the compressive force PSK is directed into the core of the tooth 2 in a uniform manner and causes the material in the tooth 2 to flow. A
symmetrical thickening of the entire tooth geometry results, which is to say at the flat sides of the tooth 2 and at the functional surfaces, which allows the bearing area ratio at the functional surfaces of the tooth 2 to be increased in a well-defined manner.

The method according to the invention is carried out as follows. The blank 7, which is blanked in the fine-blanking stage 3, is clamped except for the tooth 2 thereof in the forming stage 3, at the flat sides thereof, between the pressure plate 16, which is in the form of an anvil, and the ejector 17, and is held in the clamped state in the receiving opening 20 of the holder 15.
The tooth 2 is not clamped and remains freely accessible to a forming operation, in a plane disposed below the die plane ME.
The clamping force PK is established such that the blank 7 without the tooth 2 retains the shape and form obtained in the fine-blanking operation, and deformation is prevented in the clamped region of the blank 7.
In the next method step, the freely accessible tooth 2 is upset by application of a force adjusted in accordance with the material and the tooth geometry in such a way that the compressive force PSK is directed by the upsetting head 18 into the core of the tooth 2, perpendicular to the tooth tip surface ZKF, and parallel to the flat sides of the blank 7. To this end, the upsetting head 18 is moved by way of the wedge drive 21 thereof in the manner described heretofore against the tooth 2 and creates a partial thickened region of the tooth 2.
The method according to the invention makes it possible to easily obtain partial thickened regions, of up to 30% relative to the starting dimension, whereby the weight reductions reach considerable levels. The partial compression achieved in the tooth region are in the range of 1.25 to 1.625.

Claims

1. A method of producing a flat fine-blanked part having a tooth or other projection of increased bearing area, comprising producing an initial configuration of the part in a fine blanking stage, capturing and transferring the fine blanked part to a forming stage, and reconfiguring the tooth or other projection of the fine blanked part in the forming stage, wherein the fine blanking stage comprises integrally cutting a part having flat sides from a flat strip fed in a feed direction and then clamped between an upper part and a lower part of a fine-blanking tool, the capturing and transferring comprises capturing the fine blanked part in a cross slide which is moved horizontally from a home position into the tool when the tool is open, and carrying the fine blanked part in the cross slide, in an orientation suitable for the forming and in a direction opposite to the feed direction of the flat strip, to the forming stage, depositing the fine blanked part in said orientation in the forming stage, and moving the cross slide into said home position, and the forming stage comprises clamping the fine blanked part at the flat sides thereof between a clamping plate and an ejector so that the tooth or other projection is not clamped and is accessible for a forming operation, and upsetting the tooth or other projection by application of a compressive force directed by an upsetting head against at least one surface of the tooth or other projection perpendicular to the flat sides and into an interior of the tooth or other projection, whereby the tooth or other projection is symmetrically thickened by up to 30% relative to a starting thickness of the fine blanked part.

2. The method according to claim 1, wherein the compressive force is applied perpendicularly to a tip surface of the tooth or other projection.

3. The method according to claim 1, wherein the clamping of the blank is carried out hydraulically.

4. The method according to claim 1, wherein the upsetting head is driven mechanically and/or hydraulically by a wedge drive.

5. The method according to claim 1, wherein the compression of the tooth or other projection by application of the compressive force is from 1.25 to 1.625.

6. The method according to claim 1, wherein the upsetting head is configured to mate with surfaces of the tooth or other projection.

7. The method according to claim 1, wherein the fine blanked part is a parking gear pawl having a tooth.

8. Apparatus for producing a flat fine-blanked part having a tooth or other projection of increased bearing area, comprising a fine-blanking stage, a forming stage, and a device for capturing a part which has been fine-blanked and transferring the part to the forming stage, wherein the fine-blanking stage includes a fine-blanking tool comprising an upper part and a lower part for clamping a flat strip therebetween and integrally cutting from the strip a flat part having a tooth or other projection, the forming stage comprises a clamping plate and an ejector for clamping therebetween of the fine-blanked part with the tooth or other projection not being clamped and being accessible for a forming operation, and an upsetting head arranged, with respect to a predetermined orientation of the fine-blanked part, for applying to at least one surface of the fine-blanked part perpendicular to flat faces of the fine-blanked part a compressive force sufficient to thicken the tooth or other projection by up to 30%, and the capturing and transferring device comprises a cross-slide for capturing the fine-blanked part in the fine-blanking tool after the upper and lower parts thereof have opened following the integral cutting of the stip to produce the fine-blanked part and for then transferring the fine-blanked part to the forming stage, the cross-slide being movable horizontally from a home position to positions in the fine-blanking stage and the forming stage and the cross-slide being arranged for transferring the fine-blanked part to the forming stage in said predetermined orientation.

9. The apparatus according to claim 8, further comprising a wedge drive for the upsetting head, the wedge drive comprising first and second wedge elements having opposed oblique wedge surfaces, the first wedge element carrying the upsetting head in opposing proximity to said at least one surface of the tooth or other projection, and a drive member positioned for engagement with the first wedge element to drive the first wedge element so that the first wedge element is guided by engagement of the wedge surface of the first wedge element with the wedge surface of the second wedge element to cause the upsetting head to bear against said at least one surface of the tooth or other projection.

10. The apparatus according to claim 8, wherein the forming stage comprises a mechanical and/or hydraulic drive system which is independent of the fine-blanking stage.

11. The apparatus according to claim 8, wherein the upsetting head is matched to the geometry of the tooth.