Stretching and bending measuring device to simulate the stamping of a metal

Abstract

A stretch and bend measuring apparatus comprises: a sheet metal strip stretching tool (11) and a tensile force measurement; 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 rod (35) and a female rod (36) for clamping the sheet metal strip at its distal end, a measurement of the clamping force, and defining a direction of restraint force for the sheet metal strip; and the stretching support causing the sheet metal strip to form an angle between the stretching force and the restraint force; the stretching support further comprising a measurement of the sheet metal slip relative to the rods and a restraint force measurement (39). Figure to be published with the abbreviation: Fig 1

Description

Title of the invention: Stretching and bending measuring apparatus for simulating the stamping of a metal technical field

[0001] The present invention relates to a stretch and bend measuring device for simulating the stamping of a metal. State of the art

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

[0003] To avoid this phenomenon, it is common practice to test different stamping configurations until a configuration without the defect is obtained. This has the disadvantage of being costly in terms of time and materials.

[0004] Therefore, it would be desirable to have a simulation tool that allows for a virtual search for the best solution. To create a model reflecting metallurgical reality, it is then necessary to be able to measure the various parameters that can influence the appearance of a slip line.

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

[0006] The inventors have, however, found in use that this device has a number of limitations regarding the possibilities of parameterizing operations and the completeness of the measurements necessary to create a model that correctly reflects the reality of 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 overcome one or more of the aforementioned drawbacks, according to a first embodiment, a stretch and bend 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 gripping surface at 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; • 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 its stretching; • a stretching support mounted on the mounting plate and adapted to mount a male and a corresponding female rod holder, each comprising a male and a female rod respectively, and a compression means adapted to compress the rod holders in order to clamp the sheet metal strip between them via the rods when present, said stretching support further comprising a clamping force measuring sensor for measuring the clamping force of the rods on the sheet metal strip; and the stretching support defining a direction of retaining force for the sheet metal strip when clamped by the rods; and • the mounting plate is pivotally mounted on the fixed base and includes means for fixing to the fixed base so that an angle 0 between the longitudinal direction of the fixed base and the direction of the holding force of the stretch support can be selected from a field of values; • the stretching support further comprising a sensor for measuring the slippage of the sheet metal relative to the rods during the application of the tensile force and a sensor for measuring the holding force.

[0009] Thus, the device can measure all the forces around the sheet metal strip and its possible displacements near the clamping area of ​​the rods, thus allowing for a more complete feeding of the stamping simulation models.

[0010] Specific features or embodiments, usable alone or in combination, are: • the cam has a cylindrical shape with a substantially triangular cross-section whose vertices are formed by arcs of circles, each arc of circle having a radius of curvature different from the radii of curvature of the other two arcs of circles; • the cam holder includes an axis support adapted to allow the cam to pivot around its axis and a removable holding tool to lock the cam in a predetermined position; • the means for measuring contact force are configured to measure the force vector in a 3D space; • The cam carrier 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 according to angle 0, the normal to the radius of curvature of the cam is tangent to the sheet metal strip; • The stretching support includes rails allowing the rod holders to translate along the axis of the holding force; and / or • The rod holders and rods are configured to receive shims and compensators adapted to allow the sheet metal strip to slide between the rods when tensile force is applied.

[0011] In a second embodiment, a measurement system includes an apparatus as described above and a test 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 upon reading the following description, given solely by way of example, and with reference to the figures in the appendix in which: • [Fig.1] represents an isometric view of a stretching and bending measuring device according to one embodiment; • [Fig.2] represents a front view of the device in [Fig.1]; • [Fig.3] represents a view according to section AA' of the apparatus of [Fig.1]; • [Fig.4] represents a view according to section BB' of the apparatus of [Fig.1]; and • [Fig 5 shows an isometric view of a cam used in the device of Fig. 1. Methods of implementation

[0013] The described embodiment presents a device for directly measuring various movements and forces acting on a sheet metal strip during a stretching and bending operation. This device is preferably used with a tensile testing machine such as those commonly found in a metallurgy or mechanical engineering laboratory.

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

[0015] The test machine includes 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 a vertically upward tensile force Ft. The machine includes means for controlling and measuring this tensile force Ft.

[0016] The sheet metal strip 11 serves as a test specimen. Depending on the measurement requirements, it can be made of aluminum, steel, or any other metal or alloy on which measurements are relevant. The thickness can also vary, typically 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 a horizontal axis 13 perpendicular to the vertical plane of the fixed base 3, allowing rotation through an angle θ (theta) about the vertical chosen by the experimenter. This angle can be called the winding angle, as it defines the winding of the sheet metal strip 11 around an arc of a cam described below. Bolts 15, integral with the mounting plate 9 and able to pass through a circular slot 17 or holes 18 in the fixed base 3, clamp the mounting plate 9 onto the fixed base 3 at the predetermined angle θ. Figures 1 to 4 show the apparatus with an angle θ of 0°.

[0018] A cam carrier 19 is fixed to the mounting plate 9. The cam carrier includes a module 21 adapted to adjust the 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 with a substantially triangular cross-section, and each of its three vertices 51, 53, 55 forms an arc of a circle whose radius of curvature differs from the radii of curvature of the arcs of the other two vertices. Each flat face of the cylinder has, approximately at its center, a tapped hole 57. At the ends of the cylinder's axis, two shafts 59 are formed to allow rotation about the axis when the cam is installed in the cam support 25. This rotation allows the selection of which of the three vertices the sheet metal strip 11 will bend around during the measurement. A bolt 41, [Fig. 4], integral with the cam support 25, is fixed in the tapped hole 57 of the cam 23, thus preventing rotation and holding the cam 23 in position.

[0020] The cam support 25 has the general shape of a rectangular parallelepiped without apex or base, the two elongated faces of which are parallel to the vertical plane of the fixed base 3 and include a bore to receive the cam shafts 59 and thus allow 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 include, on one side, a hole for the passage of the bolt 41 and, on the other, the attachment of a worm gear 43. This worm gear, in conjunction with a sliding support of the cam support 25 integrated into the module 21, allows translational adjustment of the cam 23 to position it in contact with the sheet metal strip 11.

[0021] The cam holder 19 pivots 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. This advantageously allows for choosing an angle different from O for the cam holder 19 and, in particular, once the mounting plate 9 is positioned at angle O, to position the normal to the radius of curvature of the cam 23 in tangent to the sheet metal strip 11.

[0022] The cam carrier 19 also includes 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 includes rails 29 to guide a carriage 31 in translation along a direction of translation passing through the axis 13.

[0024] The carriage 31 includes a male ring holder 33 and a female ring holder 34 in which a male ring 35 and a female ring 36 are fixed face to face respectively. Two screws face to face 37, 38 serve as compression means to compress the ring holders in order to clamp the sheet metal strip 11 at its distal end via the rings.

[0025] The stretching support 27 further includes a clamping force sensor (not shown) for measuring the clamping force of the rods on the sheet metal strip and a device (not shown) for measuring any slippage of the sheet metal strip at the rods 35, 36. This is, for example, a piezo-resistive displacement sensor whose base is fixed to the rod holders and whose sensing element is connected to the body of the sheet metal strip.

[0026] It also includes a sensor 39 for the holding force Fr, that is, the resistance force produced by the stretching support to the tensile force. This holding force is therefore oriented along the same axis of translation 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 tensile force Ft, the holding 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 slippage 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 displacements present on its surface.

[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 angle 0 is at 0.

[0032] The sheet metal strip 11 is positioned vertically and its upper or proximal end is clamped with the gripping means of the tensile machine.

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

[0034] We then check that the sheet metal strip 11 is indeed vertical so that the force traction must be properly applied along its extension.

[0035] The cam is approached by translation of the cam support 23 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 rotated 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 description is to be considered illustrative and given by way of example and not as limiting the invention to this single description. Numerous embodiments are possible.

[0041] Thus, depending on the material of the sheet metal strip 11, rods 35, 36 of different shapes are used. Furthermore, the height of the rods can be adjusted using shims. When sliding of the sheet metal strip relative to the rods is desired, the height of the rods relative to the rod holders is lowered, and this adjustment may be further adjusted using compensators whose thickness is equal to 110% of the thickness of the sheet metal strip. Conversely, when no sliding is desired, shims are used to increase the height of the rods relative to the rod holders.

Claims

1. Demands A 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 stretching tool having a gripping surface of 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 stretching 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 its stretching; • a stretching support (27) mounted on the mounting plate and adapted to mount a corresponding male rod holder (33) and female rod holder (34), each comprising a male rod (35) and a female rod (36), respectively, and a compression means (37, 38) adapted to compress the rod holders in order to clamp the sheet metal strip between them via the rods when present, said stretching support further comprising a clamping force sensor for measuring the clamping force of the rods on the sheet metal strip; and the stretching support defining a direction of retaining force for the sheet metal strip when clamped by the rods; and • the mounting plate is pivotally mounted on the fixed base and includes means for fixing (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 holding force of the stretch support can be selected from a field of values; • the stretching support further comprising a sensor for measuring the slippage of the sheet metal relative to the rods during the application of the tensile force and a sensor for measuring the restraining force (39).

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

3. Device according to claim 2, wherein the cam holder includes an axis support adapted to allow pivoting of the cam around its axis and a removable holding tool to lock the cam in a predetermined position.

4. Apparatus according to claim 1, 2 or 3, wherein the means for measuring the contact force are configured to measure the force vector in a 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 one of the preceding claims, further comprising a stereovision system configured to record displacement fields on the surface of the sheet metal strip during the stretching of the sheet metal strip.

8. Apparatus according to any one of the preceding claims, wherein the drawing 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 when the tensile force is applied.

10. A measuring system comprising an apparatus according to any one of claims 1 to 9 and a test 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.

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