WO2020147935A1 - Method and arrangement for changing the shape of a sheet-like workpiece - Google Patents

Abstract

The present invention relates to a method for changing the shape of a sheet-like workpiece (10), which has a shaped recess formed by reducing the thickness of the material, comprising arranging the workpiece (10) on at least two spaced-apart supporting elements (12) of a machine bed (13), shaping the workpiece (10) into a final form by step-by-step free bending, in that the steps of bending a part of the workpiece (10) by lowering an upper die (14) between the supporting elements from a waiting position into a shaping position (15), raising the upper die (14) into the waiting position and moving the position of the workpiece (10) relative to the machine bed (13) are performed repetitively in at least one infeeding direction, and is distinguished by the fact that, before the workpiece (10) is shaped into the final form, a filling element (18) adapted to the shaped recess and designed to make up the material thickness is created and is arranged in the region of the shaped recess. The invention also relates to such an arrangement.

Description

Method and arrangement for changing the shape of a plate-like workpiece

Description

The present invention relates to a method for changing the shape of a plate-like workpiece, which has a recess formed by reducing the thickness of the material, comprising arranging the workpiece on at least two spaced apart support elements of a machine bed, shaping the workpiece into a final shape by step-by-step bending by the steps of bending one Partial section of the workpiece by lowering an upper tool between the support elements from a waiting position into a forming position, lifting the upper tool into the waiting position and moving the position of the workpiece relative to the machine bed can be repeated in at least one infeed direction.

Furthermore, the invention relates to an arrangement for changing the shape of a plate-like workpiece, which has a shape recess formed by reducing the thickness of the material, comprising at least two spaced apart support elements arranged for arranging the workpiece on a machine bed, one for reshaping the workpiece into a final shape by stepwise , repetitive free bending set-up device with an upper tool, which can be lowered from a waiting position into a forming position so that it can be moved in a taxable manner for bending a partial section of the workpiece, and with positioning means which are designed to move the position of the workpiece relative to the machine bed in at least one infeed direction.

Such methods and arrangements are used in particular in the processing of large sheets which serve as the outer lining of aircraft. The metal sheets have to be shaped according to the outer contour of the fuselage and often a workpiece with several different radii has to be produced. The sheets are often brought into the desired final shape by means of roll forming, that is to say formed when various rolls pass through. The formed sheets are then regularly machined in order to make rivet holes, pockets and cutouts in the already formed workpiece.

Document DE 10 201 1 1 14 927 A1 discloses a method for bending large sheets to a target radius. The round bending takes place by means of a folding bench by multiple edges with a round stamp.

A disadvantage is that only known workpieces can be machined using the known methods and arrangements. Machining machined work pieces, which therefore already have pockets, rivet holes or recesses for windows, for example, cannot be processed satisfactorily with the known methods and arrangements, since such recesses in the workpiece lead to uncontrollable deformations of the workpiece in the area of these recesses when using the known forming methods .

Because of this, it is necessary to first shape the workpieces in a bending process and only then to machine them in order to produce the desired shape recess. Due to the spatially extending workpiece geometry obtained after the bending process of the workpiece, the use of 5-axis portal milling is inevitable for the subsequent machining, which is associated with large space requirements and high acquisition and maintenance costs.

It is therefore an object of the present invention to propose a method by means of which plate-like workpieces which have already been machined can be formed inexpensively, with high precision and repeatability by step-by-step bending. Furthermore, the task is to propose a corresponding procedure.

The object is achieved by a method having the features mentioned at the outset that, prior to the shaping of the workpiece into the final shape, a filler element adapted to the shape and set up for material thickness compensation is created and arranged in the region of the shape recess. The method according to the invention offers numerous advantages over the methods known from the prior art. For the first time, a method is create that allows the bending of workpieces that have already been machined. The workpieces can now be machined before the bending process due to their plate-like geometry. For this, the use of a three-axis cutting machine is sufficient, which in particular also significantly reduces the effort required to clamp the workpiece compared to complex machining using a 5-axis portal milling machine on an already bent workpiece. In this way, the workpieces can be machined much cheaper. In addition, a high-precision bending process, in particular in the area of the shape recesses, that is to say in the area of milled pockets, rivet holes, window cutouts or the like, is ensured by means of the filling element and an extremely good repeatability of the entire bending process is thus achieved.

A preferred development of the invention is characterized in that the filling element is at least essentially created as a negative form of the mold recess. In other words, the filling element is designed in such a way that it fits into the mold recess in a form-fitting or essentially form-fitting manner. The Füllele element thus forms a reusable intermediate layer, which is located between the upper tool and the workpiece. The filling element ensures a uniform introduction of the forces acting during the bending process into the workpiece and compensates for the different forming behavior depending on the material thickness during the bending process. In this way, the entire workpiece is bent precisely and with high precision and repeatability, despite the existing shape recess.

According to a further preferred embodiment of the invention, the filling element has a minimum thickness in areas of the mold recess with reduced material thickness, which corresponds at least to the extent of the reduction in material thickness of the workpiece in this area. The filling element is consequently set up as a compensating element that exactly compensates for the material removal by the previously performed machining process on the workpiece, so that there is always an essentially flat contact between the upper tool and the workpiece or the filling element arranged thereon during the forming process. According to a further expedient embodiment of the invention, the filling element is created in such a way that it, arranged in the mold recess, ends flush with the upper side of the workpiece, forming an at least substantially smooth pressure surface. According to a further preferred embodiment, the filler element is created in a pre-defined cantilever area in relation to the pressure surface. As a result, locally higher bending forces act on the workpiece in the corresponding cantilever areas during the forming process. In this way, the return behavior of the material, which is dependent on the respective local material thickness of the workpiece, is compensated for and the bending process is also carried out with extremely high precision in areas of different material thickness of the workpiece. In other words, the cantilever areas of the filling element are designed and set up to compensate for the return behavior.

Alternatively or in addition, the areas of elevation are formed by a pressure-resistant film which is arranged on the pressure surface of the filling element. In this way, compensation of undesired return behavior of workpiece areas can be achieved in a particularly simple and inexpensive manner. For this purpose, the film is advantageously glued on and is also secured in this way against undesired slipping.

A preferred development of the invention is characterized in that the filling element is made of acrylonitrile butadiene plastic (ABS). ABS is machinable, comparatively inexpensive and has the physical properties required for the forming process. On the one hand, ABS has the flexibility required to return to its original shape after the bending process.

On the other hand, ABS has the necessary hardness to transfer the forces generated during the forming process from the upper tool to the workpiece to be formed without significantly deforming itself. The filling element is preferably produced by machining. In this way, the filling element is inexpensive and can be manufactured with high precision.

An expedient embodiment of the invention is characterized in that a resilient support surface element is arranged between the support elements of the machine bed and the workpiece. The resilient support surface element forms a spring-loaded machine bed. During the forming process, the support surface element is deformed elastically and thus supports the workpiece over the entire surface. Advantageously, on the one hand, workpieces with a low material thickness can be formed, and on the other hand, it is also possible to shape the end regions of the workpieces with high precision, since the end regions are always supported during the forming process. The object is also achieved by the arrangement mentioned at the outset, which is distinguished by the fact that it further comprises a filling element which is adapted to the mold recess and is set up to compensate for material thickness and is arranged in the region of the mold recess before the workpiece is formed into the final shape to become. In order to avoid repetition of the advantages associated therewith, reference is made to the above explanations regarding the method according to the invention. The advantages described there also apply in an analogous manner to the arrangement according to the invention and to the further advantageous embodiments of the arrangement according to the invention mentioned below.

Another expedient embodiment of the invention is characterized in that the filling element is at least essentially designed as a negative shape of the mold recess.

According to a further preferred embodiment, the filling element in areas of the mold recess with reduced material thickness each has a minimum thickness which corresponds at least to the extent of the reduction in material thickness of the workpiece in this area.

A further expedient embodiment of the invention is characterized in that the filling element is designed in such a way that it is arranged in the mold recess and ends flush with the top of the workpiece, forming an at least substantially smooth pressure surface.

A preferred further development of the invention is characterized in that the filling element is set up in a predetermined cantilever area relative to the pressure surface before jumping. Another expedient embodiment of the invention is characterized in that a pressure-resistant film is arranged on the pressure surface to create the cant areas.

According to a further preferred embodiment, the film is connected to the pressure surface by an adhesive connection. Another expedient embodiment of the invention is characterized in that the filling element consists of acrylonitrile butadiene plastic (ABS).

Another expedient embodiment of the invention is characterized in that a resilient support surface element is arranged between the support elements of the machine bed and the workpiece.

Further preferred and / or expedient features and configurations of the inven tion result from the subclaims and the description. Particularly preferred embodiments are explained in more detail with reference to the attached drawing.

The drawing shows:

1 is a schematic view of the arrangement according to the invention according to a first embodiment,

Fig. 2 is a schematic view of the forming process by means of the arrangement according to the Invention, and

Fig. 3 shows a further advantageous embodiment of the arrangement according to the invention with a support surface element.

The method according to the invention and the arrangement according to the invention are described in more detail below on the basis of preferred embodiments. Because of the analogy between the method and the arrangement, the respective statements made regarding the method also apply to the arrangement according to the invention and vice versa.

FIG. 1 shows a plate-like workpiece 10 with a recess formed by reducing the thickness of the material. For example, the workpiece is a sheet or large sheet for use as a flight outer skin, in particular made of aluminum alloys with copper and / or magnesium components with high tensile strengths in the range from 400 to 450 N / mm ² . Such sheets have dimensions of 800 x 800 mm up to 6000 x 6000 mm, for example. The maximum material thickness of the workpiece 10 varies between 0.5 and 16 mm, depending on the application. The method according to the invention and the device according to the invention are for reshaping Workpieces 10 made of plastic or metal, such as aluminum and steel sheets, are suitable.

The workpiece 10 has a shaped recess which is formed by reducing the material thickness. As can be seen from the schematic view in FIG. 1, the workpiece 10 has areas 11 of reduced material thickness. These areas 1 1 form the shape recess. When the workpieces 10 are used in the aircraft industry as aircraft outer skin, also referred to as “skins”, these regions 11 are introduced into the workpiece 10, for example, through rivet holes, pockets for weight saving, cutouts for windows or the like. The machining of the work piece for introducing the mold recess is carried out by machining, for example on the plate-like, ie flat workpiece 10 by means of three-axis machining machines.

To change the shape, for example in order to adapt the workpiece 10 to the desired aircraft contour, it is preferably arranged on at least two spaced apart support elements 12 of a machine bed 13. The forming process into the final shape is carried out by step-by-step bending. For this purpose, a section of the workpiece 10 is brought by lowering an upper tool 14 between the support elements 12 from a waiting position (not shown in the drawing) into a forming position 15.

The upper tool 14 is then raised, that is to say moved back into the waiting position in the z direction 16. Now the position of the workpiece 10 is moved relative to the machine bed in at least one feed direction 17. Figure 2 shows the workpiece 10 schematically after one or more forming operations. The steps described above are repeated until the desired final shape is achieved by multiple forming.

Further preferably, the positioning means (not shown in the drawing) are formed and set up not only to move the workpiece 10 in the feed direction 17 shown, but also to move it in a further direction perpendicular to the setting direction 17. As far as possible, the workpiece can be positioned and moved anywhere in the XY plane. In addition, it is possible to incline the upper part 14 relative to the Z direction 17. In this way, the workpieces can be twisted to a certain extent during forming. By specifying the immersion depth of the upper tool 14, which is determined by the lowering path, the desired local bending radius is specified in each case during a forming process. Repeatedly performing this forming process, the workpiece 10 is formed into the desired final shape. By specifying individual immersion depths for each bending process, different radii can be introduced into the workpiece 10.

Before the workpiece 10 is formed into the final shape, a filling element 18 which is adapted to the shape recess and is set up to compensate for the material thickness is created and arranged in the region of the shape recess. As shown in FIGS. 1 and 2, the filling element 18 is arranged on the workpiece 10 to be formed and thus fills in particular the regions 11 of reduced material thickness of the mold recess.

This makes it possible for the first time to subsequently shape machined workpieces 10 with the mentioned shape recesses by free bending, without obtaining forming results in these areas due to the already introduced areas of reduced material thickness in these areas, which contradict the tightly specified tolerances.

The upper tool 14 advantageously has a sword end 22 which comes into contact with the workpiece 10 or the filling element 18. This is preferably made of plastic and has a large radius, preferably greater than 50 mm, on the one hand to bend the workpiece 10 gently and on the other hand to ensure the smoothest possible transitions of the bending radii.

The filling element 18 is preferably created as a negative shape or essentially as a negative shape of the shape recess. In other words, the filling element 18 has a shape that corresponds to the shape of the regions 11 of reduced material thickness, so that the filling element 18 arranged on the workpiece 10 preferably fills the entire recess and completely compensates for the material removal of the workpiece 10 in the region of the mold recess. The filling element 18 thus forms a flat or smooth contact surface 19 with the workpiece 10 on the upper tool side. It is also possible to design the filling surface element 18 such that it only partially covers the selected area of the workpiece 10. The filling element 18 further preferably has a minimum thickness in regions 11 of the mold recess with reduced material thickness, which corresponds at least to the extent of the reduction in material thickness of the workpiece 10 in this region. The workpiece 10 thus forms, with the filler elements 18, the flat pressure surface 19 described above, so that in the forming process there is basically a flat contact between the upper tool 14 and the workpiece 10 or the filler element 18.

The filling element 18 is therefore created in such a way that it, arranged in the mold recess, ends flush with the upper side 20 of the workpiece 10, forming the at least substantially smooth pressure surface 19.

According to a preferred development (not shown in the drawing) of the invention, it is provided that the filler element is created in a predetermined cantilevered areas relative to the pressure surface 19. The workpiece 10 has a different return behavior depending on the respective local material thickness. Depending on the respective local material thickness and the selected bending radius, the material of the workpiece springs back to different degrees after the forming process.

According to the invention, this springback behavior is determined simulatively before the forming process and the springback behavior of the entire workpiece 10 to be formed is forecast on the basis of this simulation. On the basis of this prognosis, the cantilever areas are then determined, at which the filling element is to be made correspondingly wider, so that it has the cantilever areas mentioned.

In these elevation areas, an increased immersion depth is achieved compared to the remaining areas of the filling element, and in this way in the elevation areas the force exerted on the workpiece is increased compared to the remaining areas during the bending process. As a result, the workpiece 10 is bent locally to such an extent that the rebound behavior of the material is compensated for and the workpiece 10 is precisely formed into the desired final shape in all areas.

For example, a process simulation using a program for analysis using the finite element method (FEM) is used to determine the areas of superelevation. By modeling the geometry of the upper tool 14 and the machine bed 13 and the material properties of the workpiece 10 and the filling element 18, the bending process can be simulated and the overall geometry of the filling element 18 can be determined in such a way that the exact forming results mentioned are achieved.

As already stated above, the filling element 18 is preferably milled from solid based on the determined geometry of the filling element 18. Alternatively and / or in addition, it is possible to arrange a flameproof film on the pressure surface 19 of the filler element in order to create the cantilever areas and thus adjust the material thickness of the filler element 18 accordingly in the respective cantilever areas. The film is further preferably glued onto the pressure surface 19 of the filling element 18 and thus secured against undesired slipping.

The filling element 18 is preferably made of acrylonitrile butadiene plastic (ABS). This material has a modulus of elasticity of 2400 MPa and thus has the necessary flexibility to form elastically on the one hand during the forming process and on the other hand to return to its original shape after the end of the forming process. In this way, the filling element 18 can be used for a large number of forming operations. The ABS plastic preferably has a hardness of 90 shore and is suitable for machining.

Alternatively, the filling element 18 can be made from other plastics, fiber composite materials, cast resin or spring steel. In addition to machining, depending on the material used, casting or laminating processes are used to produce the filling element 18.

FIG. 3 shows a further advantageous embodiment of the arrangement according to the invention, on the basis of which the method according to the invention is also explained below. A resilient support surface element 21 is arranged between the support elements 12 of the machine bed 13 and the workpiece 10. The workpiece 10 is therefore supported on the at least two support elements 12 via the resilient support surface elements 21. The support surface element 21 is consequently designed as a spring machine bed and is elastically deformed during the shaping process of the workpiece 10, but automatically returns to its original shape after the bending process has been completed. The workpiece 10 is supported over the entire surface by the support surface element 21.

Claims

Expectations A method for changing the shape of a plate-like workpiece (10) which has a shape recess formed by reducing the material thickness, comprising Arranging the workpiece (10) on at least two spaced apart support elements (12) of a machine bed (13), Forming the workpiece (10) into a final shape by step-by-step bending by the steps - Bending a section of the workpiece (10) by lowering an upper tool (14) between the support elements from a waiting position into a forming position (15), - Lifting the upper tool (14) into the waiting position and - The position of the workpiece (10) relative to the machine bed (13) can be repeated in at least one infeed direction, characterized in that prior to the shaping of the workpiece (10) into the final shape, an adjustment adapted to the shape and set up for material thickness compensation Filling element (18) is created and arranged in the area of the mold recess. A method according to claim 1, characterized in that the filling element (18) is created at least substantially as a negative shape of the mold recess. Method according to one of claims 1 or 2, characterized in that the filling element (18) in areas (1 1) of the mold recess with reduced Material thickness each has a minimum thickness that corresponds at least to the extent of the reduction in material thickness of the workpiece (10) in this area. 4. The method according to any one of claims 1 to 3, characterized in that the filling element (18) is created such that this, arranged in the mold recess, forming an at least substantially smooth pressure surface (19) with the top (20) of the Completes the workpiece (10) flush. 5. The method according to claim 4, characterized in that the filling element (18) in predetermined areas of elevation relative to the pressure surface (19) is created in advance. 6. The method according to claim 5, characterized in that a pressure-resistant film is arranged on the pressure surface (19) of the filling element (18) to create the cant areas. 7. The method according to claim 6, characterized in that the film is glued on. 8. The method according to any one of claims 1 to 7, characterized in that the filling element (18) is made of acrylonitrile butadiene plastic. 9. The method according to any one of claims 1 to 8, characterized in that the filling element (18) is produced by machining. 10. The method according to any one of claims 1 to 9, characterized in that a resilient support surface element (21) is arranged between the support elements (12) of the machine bed (13) and the workpiece (10). 1 1. Arrangement for changing the shape of a plate-like workpiece (10) which has a recess formed by reducing the thickness of the material, comprising at least two spaced-apart support elements (12), one for forming, for arranging the workpiece (10) on a machine bed (13) of the workpiece (10) in a final shape by step-by-step, repetitive free bending forming device with an upper tool (14), which is from a waiting position in a forming position (15) Steuerbe movable lowerable for bending a portion of the workpiece (10) and a Positioning means which are designed to move the position of the workpiece (10) relative to the machine bed (13) in at least one infeed direction, characterized in that the arrangement further comprises a filling element (18) which is adapted to the shape recess and is set up for material thickness compensation, which is set up before the workpiece (1 0) to be arranged in the final shape in the area of the mold recess. 12. The arrangement according to claim 1 1, characterized in that the filling element (18) is at least substantially formed as a negative shape of the mold recess. 13. Arrangement according to one of claims 1 1 or 12, characterized in that the filling element (18) in areas (1 1) of the mold recess with reduced material thickness each has a minimum thickness which is at least the measure of the reduction in material thickness of the workpiece (10) in corresponds to this area. 14. Arrangement according to one of claims 1 1 to 13, characterized in that the filling element (18) is designed such that this, arranged in the mold recess, forming an at least substantially smooth Pressure surface (19) with the top (20) of the workpiece (10) closes flush. 15. The arrangement according to claim 14, characterized in that the filling element (18) in predetermined areas of elevation relative to the pressure surface (19) is set up in advance. 16. The arrangement according to claim 15, characterized in that for creating the Elevation areas a pressure-resistant film on the pressure surface (19) is arranged. 17. The arrangement according to claim 16, characterized in that the film with the Pressure surface (19) is connected by an adhesive connection. 18. Arrangement according to one of claims 1 1 to 17, characterized in that the filling element (18) made of acrylonitrile-butadiene plastic. 19. Arrangement according to one of claims 1 1 to 18, characterized in that a resilient support surface element (21) is arranged between the support elements (12) of the machine bed (13) and the workpiece (10).