Stretch and bend measuring device for simulating metal stamping

Abstract

A stretching and bending measuring apparatus comprises: a tool for stretching a sheet metal strip (11) and a measurement of the tensile force; a cam (23) positioned tangentially to the sheet metal strip and comprising a measurement of the contact force exerted on the cam by the sheet metal strip; a stretching support (27) comprising a male snap ring (35) and a female snap ring (36) for clamping the sheet metal strip at its distal end, a measurement of the clamping force and defining a direction of retaining force for the sheet metal strip; and the stretching support causing the sheet metal strip to form an angle between the tensile force and the retaining force; the stretching support further comprising a measurement of the sliding of the sheet metal relative to the snap rings and a measurement of the retaining force (39). Figure to be published with the abstract: Fig 1

Description

Title of the invention: Stretching and bending measuring device for simulating the stamping of a metal Technical field

[0001] The present invention relates to a stretching and bending measuring apparatus for simulating the stamping of a metal. State of the art

[0002] When stamping a sheet metal, an aesthetic defect called a skid line may appear. This phenomenon, which is similar to the presence of a second "parasitic" style line in parallel with the desired one, is considered to be an appearance defect that is more or less penalizing depending on its prominence.

[0003] To avoid this phenomenon, it is customary to carry out tests of different stamping configurations until a configuration is obtained which does not present the defect. This has the disadvantage of being costly in terms of time and materials.

[0004] Also, it would be desirable to have a simulation tool that allows the best solution to be virtually searched for. To create a model reflecting metallurgical reality, it is then necessary to be able to measure the different parameters that can influence the appearance of a skid line.

[0005] To this end, US patent 8511175 describes a measuring device for measuring certain parameters during a stretching operation for simulating stamping.

[0006] The inventors have however noted in use that this device has a certain number of limitations concerning the possibilities of parameterizing the operations and the exhaustiveness of the measurements necessary for the creation of a model correctly reflecting the reality of the stamping.

[0007] There is therefore a real need for a new measuring device which resolves all or part of the aforementioned drawbacks. Description of the invention

[0008] To resolve one or more of the drawbacks cited above, according to a first embodiment, a stretching and bending measuring device for simulating the stamping of a metal comprises: • a fixed base defining a longitudinal direction comprising means for attachment to a tensile testing machine, said testing machine comprising a sheet metal drawing tool having a surface for gripping a proximal end of a sheet metal strip and a sensor for measuring the tensile force when the sheet metal strip is pulled by the gripping surface of the stretching tool in the longitudinal direction; • a mounting plate mounted on the fixed base; and • a cam holder mounted on the mounting plate and adapted to position a cam tangentially to one of the two surfaces of the sheet metal strip and comprising a sensor for measuring the contact force exerted on the cam by the sheet metal strip during the stretching thereof; • a stretching support mounted on the mounting plate and adapted to mount a male snap ring holder and a corresponding female snap ring holder comprising respectively a male snap ring and a female snap ring and a compression means adapted to compress the snap ring holders in order to clamp by means of the snap rings the sheet metal strip between them when it is present, said stretching support further comprising a clamping force measuring sensor for measuring the clamping force of the snap rings on the sheet metal strip; and the stretching support defining a direction of retaining force for the sheet metal strip when it is clamped by the snap rings; and • the mounting plate is pivotally mounted on the fixed base and comprises means for attachment to the fixed base such that an angle 0 between the longitudinal direction of the fixed base and the direction of the retaining force of the stretching support can be selected from a field of values; • the stretching support further comprising a sensor for measuring the sliding of the sheet metal relative to the rods during the application of the tensile force and a sensor for measuring the retaining force.

[0009] Thus, the device can measure all the forces around the sheet metal strip and its possible movements near the clamping zone of the rods, thus making it possible to more fully supply the stamping simulation models.

[0010] Particular characteristics or embodiments, usable alone or in combination are: • the cam has a cylindrical shape of substantially triangular section whose vertices are formed by arcs of a circle, each arc of a circle having a radius of curvature different from the radii of curvature of the other two arcs of a circle; • the cam holder comprises an axle support adapted to allow the cam to pivot around its axle and a removable holding tool for locking the cam in a predetermined position; • the contact force measuring means are configured to measure the force vector in a 3D space; • the cam holder includes means for rotating and translating the cam on the mounting plate • the rotation means are configured so that, once the stretching support is positioned at angle 0, the normal to the radius of curvature of the cam is tangent to the sheet metal strip; • the stretching support comprises rails allowing translation of the rod holders in the axis of the retaining force; and / or • the rod holders and rods are configured to receive shims and compensators adapted to allow sliding of the sheet metal strip between the rods when the tensile force is applied.

[0011] In a second embodiment, a measuring system comprises an apparatus as described above and a testing machine comprising a sheet metal drawing tool having a gripping surface of a proximal end of a sheet metal strip and a sensor for measuring the tensile force when the sheet metal strip is pulled by the gripping surface of the drawing tool in the longitudinal direction. Brief description of the figures

[0012] The invention will be better understood on reading the following description, given solely by way of example, and with reference to the appended figures in which: • [Fig.l] represents an isometric view of a stretching and bending measuring device according to one embodiment; • [Fig.2] represents a front view of the device of [Fig.l]; • [Fig.3] represents a view along section AA' of the device of [Fig.l]; • [Fig.4] represents a view along section BB' of the device of [Fig.l]; and • [Fig 5 represents an isometric view of a cam used in the apparatus of Fig. 1. Methods of implementation

[0013] The described embodiment presents an apparatus for directly measuring various movements and forces acting on a sheet metal strip during a stretching and bending operation. This apparatus can preferably be used with a tensile testing machine such as can be regularly found in a metallurgical or mechanical laboratory.

[0014] With reference to Figs 1 to 4, an apparatus 1 comprises a fixed base 3. This fixed base 3 is fixed to the horizontal plate 5 of a testing machine by brackets 7. The fixed base 3 thus forms a vertical plane on which a mounting plate 9 is mounted.

[0015] The testing machine comprises gripping means (not shown), generally in the form of a clamp, adapted to firmly hold the proximal end of a sheet metal strip 11 and apply to it a tensile force Ft oriented vertically upwards. The machine comprises means for controlling and measuring this tensile force Ft.

[0016] The sheet metal strip 11 acts as a test specimen. Depending on the measurement requirements, it may be made of aluminum, steel or any other metal or alloy on which measurements are relevant. The thickness may also typically vary from a few tenths of a millimeter to a few millimeters, for example from 0.3 mm to 2 mm.

[0017] The mounting plate 9 is fixed to the fixed base 3 by an axis 13 horizontal and perpendicular to the vertical plane of the fixed base 3 allowing a rotation of an angle 0 (theta) with respect to the vertical chosen by the experimenter. This angle can be called the winding angle, because it defines the winding of the sheet metal strip 11 around an arc of a circle of a cam described below. Bolts 15 secured to the mounting plate 9 and able to pass through a circular slot 17 or holes 18 of the fixed base 3 hold the mounting plate 9 on the fixed base 3 by tightening with the determined angle 0. Figs 1 to 4 represent the apparatus with an angle O of 0°.

[0018] A cam holder 19 is fixed to the mounting plate 9. The cam holder comprises a module 21 adapted to adjust the translational position of the cam 23 relative to the sheet metal strip 11 by means of a cam support 25.

[0019] The cam 23, [Fig. 5], has a cylindrical shape whose section is substantially triangular and each of the 3 vertices 51, 53, 55 forms an arc of a circle whose radius of curvature is different from the radii of curvature of the arcs of the other two vertices. Each flat face of the cylinder comprises approximately in its center a tapped hole 57. At the ends of the axis of the cylinder, two shafts 59 are formed so as to allow rotation around the axis when the cam is installed in the cam support 25. This rotation makes it possible to choose which of the three vertices will bend the sheet metal strip 11 during measurement. A bolt 41, [Fig. 4], integral with the cam support 25 is fixed in the tapped hole 57 of the cam 23 thus making it possible to prevent rotation and to hold the cam 23 in position.

[0020] The cam support 25 has the general shape of a rectangular parallelepiped without top or bottom, the two elongated faces of which are parallel to the vertical plane of the fixed base 3 and comprise a bore for receiving the shafts 59 of the cam and thus allowing its rotation. At least one elongated face is removable to allow the installation of the cam 23. The two faces perpendicular to the elongated faces comprise, for one, a hole allowing the passage of the bolt 41 and for the other the attachment of a worm screw 43. The latter, associated with a sliding support of the cam support 25 integrated in the module 21, allows a translational adjustment of the cam 23 to position it in contact with the sheet metal strip 11.

[0021] The cam holder 19 is pivotable around the axis 13 and is held at the chosen angle by two bolts / nuts 45, 46 passing through two slots 47, 48 in an arc of a circle. This thus advantageously makes it possible to choose an angle different from O for the cam holder 19 and in particular, once the mounting plate 9 is positioned at the angle 0, to position the normal to the radius of curvature of the cam 23 at a tangent to the sheet metal strip 11.

[0022] The cam holder 19 also comprises a sensor (not shown) for measuring the force along the 3 axes of space generated by the sheet metal strip 11 and received by the cam 23.

[0023] A stretching support 27 is also fixed to the mounting plate 9. The stretching support comprises rails 29 for guiding a carriage 31 in translation in a translation direction passing through the axis 13.

[0024] The carriage 31 comprises a male snap ring holder 33 and a female snap ring holder 34 in which a male snap ring 35 and a female snap ring 36 are fixed face to face respectively. Two screws 37, 38 facing each other serve as compression means for compressing the snap ring holders in order to tighten the sheet metal strip 11 at its distal end by means of the snap rings.

[0025] The stretching support 27 further comprises a sensor (not shown) for measuring the clamping force to measure the clamping force of the rods on the sheet metal strip as well as a device (not shown) for measuring any sliding of the sheet metal strip at the level of the rods 35, 36. This is, for example, a piezo-resistive displacement sensor whose base is integral with the rod holders and the sensitive element is connected to the body of the sheet metal strip.

[0026] It also comprises a sensor 39 of the retaining force Fr, that is to say of the resistance force produced by the stretching support to the tensile force. This retaining force is therefore oriented along the same translation axis as that of the carriage 31 and in the opposite direction to the cam 23.

[0027] Thus, the system makes it possible to measure the traction force Ft, the retaining force Fr, the force received by the cam as well as the clamping force of the distal end of the sheet metal strip 11. In addition, it measures the sliding of the sheet metal strip at least at the level of the clamping zone by the rods.

[0028] It is also possible to provide a stereovision system, perpendicular to the sheet metal strip 11 to access the movements present on the surface thereof.

[0029] The operation of the device is as follows.

[0030] A cam 23 is chosen and positioned with the desired radius of curvature in the cam holder 25.

[0031] The mounting plate is placed so that the angle 0 is at 0.

[0032] The sheet metal strip 11 is positioned in a vertical position and its upper or proximal end is gripped with the gripping means of the traction machine.

[0033] The distal end of the sheet metal strip 11 is clamped between the rods 35, 36.

[0034] It is then checked that the sheet metal strip 11 is vertical so that the force traction is well applied in its extension.

[0035] The cam support 23 is approached by translation until contact is obtained between the sheet metal strip 11 and the cam 23 using the worm screw 43.

[0036] The mounting plate 9 is then inclined according to the predefined winding angle ©.

[0037] The cam support 23 is adjusted in rotation so that the normal to the radius of curvature of the cam is perpendicular to the tangent of the sheet metal strip 11 using the bolts 45, 46 and the slides 47, 48.

[0038] The displacement sensor is installed and the calibration of all sensors is checked.

[0039] The tensile test is carried out.

[0040] The invention has been illustrated and described in detail in the drawings and the preceding description. This should be considered as illustrative and given by way of example and not as limiting the invention to this description alone. Numerous alternative embodiments are possible.

[0041] Thus, depending on the material constituting the sheet metal strip 11, rods 35, 36 having different shapes are used. Furthermore, the height of the rods can be adjusted by sets of shims. When it is desired to obtain a sliding of the sheet metal strip relative to the rods, the height of the rods is lowered relative to the rod holders and this adjustment is possibly completed by compensators whose thickness is equal to 110% of the thickness of the sheet metal strip. Conversely, when it is desired that there is no sliding, shims will be used to increase the height of the rods relative to the rod holders.

Claims

1. Claims Stretch and bend measuring device for simulating the stamping of a metal comprising: • a fixed base (3) defining a longitudinal direction comprising means for attachment to a tensile testing machine, said testing machine comprising a sheet metal drawing tool having a surface for gripping a proximal end of a sheet metal strip (11) and a sensor for measuring the tensile force when the sheet metal strip is pulled by the gripping surface of the drawing tool in the longitudinal direction; • a mounting plate (9) mounted on the fixed base (3); and • a cam holder (19) mounted on the mounting plate and adapted to position a cam (23) tangentially to one of the two surfaces of the sheet metal strip and comprising a sensor for measuring the contact force exerted on the cam by the sheet metal strip during the stretching thereof; • a stretching support (27) mounted on the mounting plate and adapted to mount a male snap ring holder (33) and a corresponding female snap ring holder (34) comprising respectively a male snap ring (35) and a female snap ring (36) and a compression means (37, 38) adapted to compress the snap ring holders in order to clamp by means of the snap rings the sheet metal strip between them when it is present, said stretching support further comprising a clamping force measuring sensor for measuring the clamping force of the snap rings on the sheet metal strip; and the stretching support defining a direction of retaining force for the sheet metal strip when it is clamped by the snap rings; and • the mounting plate is pivotally mounted on the fixed base and comprises fixing means (13, 15, 17, 18) to the fixed base so that an angle 0 between the longitudinal direction of the fixed base and the direction of the retaining force of the stretching support can be selected from a field of values; • the stretching support further comprising a sensor for measuring the sliding of the sheet metal relative to the rods during the application of the tensile force and a sensor for measuring the retaining force (39).

2. Apparatus according to claim 1, in which the cam has a cylindrical shape of substantially triangular section whose vertices are formed by circular arcs, each circular arc having a radius of curvature different from the radii of curvature of the other two circular arcs.

3. Apparatus according to claim 2, wherein the cam holder comprises an axis support adapted to allow pivoting of the cam about its axis and a removable holding tool for locking the cam in a predetermined position.

4. Apparatus according to claim 1, 2 or 3, wherein the contact force measuring means is configured to measure the force vector in 3D space.

5. Apparatus according to claim 1, 2, 3 or 4, wherein the cam holder comprises means for rotating and translating the cam on the mounting plate.

6. Apparatus according to claim 5, wherein the rotation means are configured so that, once the stretching support is positioned at angle 0, the normal to the radius of curvature of the cam is tangent to the sheet metal strip.

7. Apparatus according to any preceding claim, further comprising a stereovision system configured to record the displacement fields at the surface of the sheet metal strip during stretching of the sheet metal strip.

8. Apparatus according to any one of the preceding claims, in which the stretching support comprises rails allowing translation of the rod holders in the axis of the retaining force.

9. Apparatus according to any one of the preceding claims, wherein the rod holders and the rods are configured to receive shims and compensators adapted to allow sliding of the sheet metal strip between the rods upon application of the tensile force.

10. A measuring system comprising an apparatus according to any one of claims 1 to 9 and a testing machine comprising a sheet metal drawing tool having a surface for gripping a proximal end of a sheet metal strip and a sensor for measuring the tensile force when the sheet metal strip is pulled by the gripping surface of the drawing tool in the longitudinal direction.

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