EP0916429A1

EP0916429A1 - Method and device for forming a side wall on a base plate

Info

Publication number: EP0916429A1
Application number: EP98203771A
Authority: EP
Inventors: Franciscus Alphonsius Christianus M. Habraken
Original assignee: Wemo Nederland BV
Current assignee: Wemo Nederland BV
Priority date: 1997-11-12
Filing date: 1998-11-10
Publication date: 1999-05-19
Anticipated expiration: 2018-11-10
Also published as: PT916429E; ATE243578T1; DK0916429T3; EP0916429B1; DE69815790D1; NL1007527C2; DE69815790T2; ES2202737T3

Abstract

The invention relates to a method for forming a curved corner wall part (4c) on a baseplate (19), the curved corner wall part (4c) extending along a line of rounding (18) of the baseplate (19) and merging, at each end, into a side wall part (4a, 4b) which is formed on the baseplate (19). The method comprises the following steps:

forming at least two side wall parts (4a, 4b) on the baseplate (19) by turning up an edge region of the baseplate (19) through an angle of substantially 90° along a bend line (7a, 7b), which side wall parts (4a, 4b) extend as far as the corner region (5) of the baseplate (19) and merge into one another, in the corner region (5), via a crease-like transition (10) which is directed outwards,

deforming the crease-like transition (10) and a part of the corner region (5) which adjoins the crease-like transition (10) to form a conical spout (10a) which extends along the line of rounding (18) of the baseplate (19) and along a section of the bend lines (7a, 7b) which adjoin the line of rounding (18),

fitting a die (13) and a blank holder (16), which are substantially shaped so as to correspond to the conical spout (10a), around the conical spout (10a),

and deep-drawing the conical spout (10a) so that the curved corner wall part (4c) is formed, the die (13) and the blank holder (16) preventing creases from being formed in the conical spout (10a) during the deep-drawing.

Description

The invention relates to a method for producing, for example, a panel which may be used, by way of example, as a cupboard door, from a baseplate which is made of deformable material, for example metal. A panel of this nature has a planar plate part and, on the circumferential edge of the plate part, a side wall which is at an angle to the plate part, preferably at an angle of 90°.
Such panels are generally known and can be produced, for example, by deep-drawing the baseplate which is made of deformable material. In this method, an edge region of the baseplate is enclosed by a blank holder and a die. A punch then presses the baseplate into the die, the edge regions of the baseplate being drawn between the die and the blank holder and bent into the definitive form. There is a surplus of material in a corner region of the baseplate when the edge region is converted from the flat state into the state in which it is at an angle. Particularly in the corner region, the baseplate material which is present in this corner region becomes puckered. During deep-drawing of the panel, the blank holder prevents the formation of creases in the corner region.
In this way, a panel which has seamless transitions in the corner regions from the planar plate part to the side wall and between the side walls is obtained in a single step. However, for this method it is necessary to produce a new die, blank holder and punch for each panel of different dimensions. This has an adverse effect on the flexibility allowed in dimensioning the panels.
To eliminate these drawbacks, the side wall would have to be formed separately in a corner region of the baseplate. Such local deformation of a corner region of a baseplate is known perse. DE-40 09 466, for example, describes a method with which each corner region can be deformed separately in order to obtain a seamless transition between the plate part and the side wall. The side wall itself is also formed seamlessly. In this method, use is made of a roller which is shaped like a diabolo. In a first step, two edge regions of the baseplate, which adjoin a corner region, are turned up through a predetermined angle. The interim product obtained in this way is placed on a work holder, after which the diabolo roller is rolled over the corner region. The shape of the work holder determines the ultimate shape of the corner region.
A significant drawback of the method which is described in DE-40 09 466 is that during deformation the corner region is only supported by the work holder, so that while the corner region is being rolled considerable creasing occurs in the corner region which is yet to be deformed. These creases cannot be completely ironed out by the diabolo roller. The creasing is intensified by the fact that the interim product is of asymmetric shape in the corner region.
DE-35 30 513 gives a description of producing a rectangular shaped part by turning up the edge regions up to a distance from the corner region using a bending device of adjustable length so that the corner regions of the baseplate are not subjected to the bending. Then, a corner region which is enclosed between two edge regions is formed into the ultimate shape by deep-drawing. However, this publication provides no explanation whatsoever of what the deep-drawing tool looks like. Also, the problems caused by the material present in the corner region upsetting and drawing are not dealt with. The document certainly does not provide a solution which allows the upsetting and drawing in the corner region to take place in a controlled manner during the deep-drawing.
One object of the invention is to provide a method with which a corner region of a baseplate can be locally deformed in order to obtain a side wall which is substantially perpendicular to the baseplate and has seamless transitions but in which creasing is prevented as far as possible during deformation of the corner region and the upsetting and drawing takes place in a controlled manner.
In order to achieve this object, an important aspect of the method according to the invention is the fact that edge regions of the baseplate are turned up through an angle of substantially 90° along bend lines, forming side walls which continue at least as far as a corner region of the baseplate and which form a spout which projects outwards in the corner region.
Another important aspect of the method according to the invention is that the spout which is formed in this way, a part of the corner region which is defined by the bend lines and a line of rounding of the baseplate, and those parts of the side walls which continue into the corner region are deformed into a conical spout, the conical shape being recognisable in particular in that part of the conical spout which extends along the line of rounding. The conical spout is substantially symmetrical with respect to the bisector plane of the corner, which is included by the side walls adjoining the corner region. The interim product which has been produced in this way is positioned in a device which clamps the conical spout between a die and a blank holder. To this end, the blank holder and the die are of a three-dimensional shape which substantially corresponds to the shape of the spout. Then, a punch is used to press the corner region into the die, the spout being drawn between the die and the blank holder. The result is a continuous, rounded corner on the plate part with creasing being prevented and upsetting and drawing being limited to a minimum during the deep-drawing.
The invention furthermore relates to a method for forming a semi-finished product which is suitable for the method according to the invention.
The invention furthermore relates to a device with which the method according to the invention can be carried out.
A preferred embodiment of the method according to the invention will be explained in more detail below with reference to the drawing, in which:
Fig. 1 shows a corner part of a panel with side walls,
Fig. 2 shows a baseplate,
Fig 2a shows the baseplate in accordance with Fig. 2, with an edge region turned up as far as into the corner region,
Fig. 2b shows the baseplate in accordance with Fig. 2, with an edge region turned up over its entire length,
Fig. 3 shows the baseplate in accordance with Fig. 2a, with a second edge region turned up as far as into the corner region,
Fig. 3a shows the baseplate in accordance with Fig. 2b, with a second edge region turned up as far as into the corner region,
Fig. 4 shows a baseplate which has side wall sections which have been turned up and which is clamped between a punch and a mating punch,
Fig. 5 shows the situation in accordance with Fig. 4, in which a die and a blank holder are added,
Fig. 6 shows the situation in which the die and the blank holder are closed,
Fig. 7 shows the situation in which the die and the blank holder have been opened, so that the conical spout formed can be seen,
Fig. 8 shows the situation in which the punch and the mating punch, with the baseplate clamped between them, have been moved downwards with respect to the die and the blank holder.
Fig. 9 shows an optimized blank holder,
Fig. 10 shows the die which is associated with the blank holder of Fig. 9,
Fig. 11 shows two diagrammatic views of a simplified embodiment of a blank holder and a die according to the invention,
Fig. 12 shows a model of a surface which is employed for a calculation using the finite element method,
Fig. 13 shows the surface which is the result of the calculation using the finite element method,
Fig. 14 is a diagrammatic representation of a device which is suitable for the method according to the invention,
Fig. 15 is a plan view of a die and a mating punch,
Fig. 16 shows a diagrammatic cross-sectional view on the lines A-A, B-B, C-C and D-D in Fig. 15 at the start of the deep-drawing process,
Fig. 17 shows a diagrammatic cross-sectional view on the lines A-A, B-B, C-C and D-D in Fig. 15 halfway through the deep-drawing process, and
Fig. 18 shows a diagrammatic cross-sectional view on the lines A-A, B-B, C-C and D-D in Fig. 15 at the end of the deep-drawing process.
Fig. 1 shows a corner part of a panel which is produced using the method according to the invention. The panel is substantially in the form of a tray 1 with a flat bottom 2 and a side wall 4 which extends along an outer edge 3 of the bottom 2. In this example, the bottom 2 is rectangular with substantially straight edge sections 3a, 3b and a rounded edge 3c in a corner region 5 of the tray 1, which is denoted by dashed line 5a.
The bottom 2 may also be in the shape of a triangle, a hexagon or some other polygon, such as a trapezium. The edge section 3a, 3b are orientated at an angle to one another. The angles which are included by the various side wall sections are not necessarily equal to one another in a single panel.
In the present example, the edge sections 3a, 3b include an angle of 90°. The edge section 3a, 3b merge into one another via the rounded edge 3c. In general, the rounded edge 3c will describe part of the circumference of a circle. Other shapes, such as a part of the circumference of an ellipse, are also possible.
The side wall sections 4a, 4b which adjoin the edge section 3a, 3b merge into one another via a curved wall section 4c which adjoins the rounded edge 3c. In the present example, the curved wall section 4c is part of a cylinder and will be referred to in the text which follows as corner wall part 4c.
Fig. 2 shows part of a planar baseplate 19, which is the starting material for the tray 1 which is to be formed. A dashed line is used to indicate the outer edge 3 which is to be formed. The plate section 14 lying outside the outer edge 3 is intended to form the side wall 4. The side wall sections 4a, 4b are turned up, for example with the aid of a bending machine, through an angle of preferably 90° along bend lines 7a, 7b. The bend lines 7a, 7b extend as far as into the corner region 5 and include a predetermined angle. In this example, the angle included by the bend lines 7a, 7b is equal to 90°. However, other angles are also possible, although they will generally lie between 45° and 135°.
Fig. 2a shows the baseplate 19 in accordance with Fig. 2 with one turned-up edge region, forming the side wall section 4a. While this region is being turned up, the corner region 5 is not supported, so that the corner region 5 is able to deform freely. When the side wall section 4b is then formed, the result is the baseplate which is shown in Fig. 3 and has a crease-like transition 10 between the side wall sections 4a and 4b, which crease-like transition 10 is substantially symmetrical, the plane of symmetry substantially corresponding to the bisector plane of the angle which is included by the side wall sections 4a, 4b.
Fig. 2b shows the baseplate 19 in accordance with Fig. 2 in which one edge region has been turned up along its entire length, thus forming the side wall section 4a. While the side wall section 4b is being formed, the side wall section 4a is supported, so that the result is a baseplate as illustrated in Fig. 3a, with the crease-like transition 10 between the side wall sections 4a and 4b. The baseplate which is illustrated in Fig. 3a has the advantage that the crease-like transition 10 projects only on one side of the baseplate. This means that one side of the crease-like transition lies in the plane of the side wall section 4a. The baseplate which has the side wall sections 4a, 4b formed in this way is particularly suitable for an automated manufacturing processing for forming the corner wall part 4c. The side wall section 4a can be used as a reference in a production device and makes the baseplate suitable for moving along a guide.
A spout 10 is formed in the corner region 5 as a result of the side wall sections 4a, 4b being turned up (see Fig. 3). That part 25 of the corner region 5 which is enclosed by the bend lines 7a, 7b and a line of rounding 18 is to be formed into the corner wall part 4c together with those sections of the side wall sections 4a, 4b which extend into the corner region.
In order to achieve this, in a subsequent step the flat bottom 2 is clamped between a punch 11 and a mating punch 12, the side wall sections 4a, 4b bearing against the punch 11, as illustrated in Fig. 4. The punch 11 determines the curvature of the corner wall section 4c along the line of rounding 18. In order to obtain an advantageous distribution of material in the corner region 5, it is preferable for the crease-like transition 10 which is formed when the side wall sections 4a, 4b are turned up and the said part 25 of the corner region 5 to be shaped into a substantially conical spout 10a which extends along the rounded edge 3c, the bend lines 7a, 7b which extend into the corner region 5 being smoothed or straightened out as far as possible. This is achieved by moving a die 13 and a blank holder 16 towards one another, respectively along the mating punch 12 and the punch 11, the crease-like transition 10 being clamped between the die 13 and the blank holder 16 (see Fig. 5). The blank holder 16 is formed in such a manner that while it is moving towards the die 13 it folds open the crease-like transition 10 and pushes it, together with the part 25 of the corner region 5, into a recess 17 in the die 13. In the process, the material in the corner region 5 is deformed no more than is necessary, but rather is redistributed, so that surface irregularities are eliminated (see Fig. 6).
The semi-finished product which is manufactured in this way can be deformed, using the deep-drawing process, to form a flat bottom 2 with a side wall 4 which seamlessly adjoins the bottom 2. Fig. 7 shows the semi-finished product with the conical spout 10a. The conical spout 10a is symmetrical with respect to the bisector plane of the angle included by the side wall sections 4a, 4b.
The semi-finished product may also be produced in a separate step using a suitable die and blank holder, the punch and blank holder, on the one hand, and the die and mating punch, on the other hand, forming single entities.
The semi-finished product is then clamped back between the punch 11 and the mating punch 12, and the conical spout 10a is enclosed by the die 13 and the blank holder 16. The force with which the die 13 and the blank holder 16 are pressed towards one another is substantially constant. If a force in a downwards direction, perpendicular to the bottom 2, is now exerted on the punch 11 and the mating punch 12, the conical spout 10a is drawn out of a gap which is formed between the die 13 and the blank holder 16 and into a gap which is formed between the punch 11 and the die 13 (see Fig. 8). The width of the two gaps substantially corresponds to the thickness of the material which is to be deformed. The formation of creases is prevented by the fact that the conical spout 10a is enclosed between the die 13 and the blank holder 16. Fig. 1 shows part of the end product which is produced using the method according to the invention.
By means of the method according to the invention, a conical spout 10a is formed in the corner region 5, and this spout can be deformed without problems using the deep-drawing process. Enclosing the conical spout 10a and the adjoining parts of the side wall sections 4a, 4b between the die 13 and the blank holder 16 prevents the formation of creases and makes it possible to locally deform the plates which are relatively thin with respect to the height of the side wall and the rounding radius of the bottom 2 using the method according to the invention.
The shape of the die and the blank holder determine the ultimate quality of the end product. Ideally, the deformation of the corner region during the formation of the conical spout 10a is minimized by suitably selecting the shape of the die and the blank holder.
The costs of producing the die and the blank holder may play a role in selecting the shape of the die and the blank holder.
Fig. 9 illustrates an optimized blank holder 16. Fig. 10 shows the die 13 which is associated with the blank holder 16 shown in Fig. 9. The blank holder 16 has a surface 31, the width of which corresponds to the width of the conical spout 10a which is to be deformed. The surface 31 bears against an internal surface of the conical spout 10a to be deformed. The surface 31 is a so-called double-curved surface, the shape of which is calculated using the finite element method. With this method, it is possible to calculate a shape for the die 13 and the blank holder 16 in which the curvature of the surface is as small as possible. This method is generally known and can be used, for example, to calculate deformations in materials when they are exposed to forces or other external influences. A mathematical model is made of the area in question in order to carry out the calculation. Fig. 12 shows a model of a corner edge region which is divided into a number of region elements. If the size of the region and the size of the elements is selected appropriately, there is scarcely any, or no, deformation to the elements which lie next to circumferential edges 42, 43. A number of boundary conditions are also incorporated in the model. The selection of the boundary conditions determines the result of the calculation. The boundary condition for circumferential edge 41 is that there must be no displacement. By contrast, a displacement is imposed on the circumferential edges 42, 43. In this case, this displacement is a rotation through an angle of 90°. A boundary condition is also imposed on the normal of the elements which adjoin the circumferential edges 42, 43, a rotation of the normal through an angle of 90° being possible in only one direction. The requirement of continuity is imposed on the entire surface.
The result of the calculation is given in Fig. 13 and can be used to produce a blank holder 16 and the die 13 associated with the blank holder 16. The conical spout 10a which is clamped between a blank holder 16 and die 13 of this nature undergoes minimal deformation. As a result, a greater percentage of the deformability of the baseplate 19 is available for forming the corner wall part 4c. Furthermore, the optimized blank holder 16 and die 13 result in a gradual and continuous transition between the side wall section 4a, 4b and the corner wall part 4c. There will be no abrupt transition in the surface of the end product.
In practice, it is desirable for the conical spout 10a to be stretched slightly while it is clamped between the blank holder and the die in order to remove any surface irregularities. The irregularities present in the corner part may, for example, have been formed while the side wall sections 4a, 4b were being turned up. The geometry of the optimized die 13 and blank holder 16 can ensure that such surface irregularities are removed by stretching the material. Only low levels of force are required to achieve this, and a better result is obtained than that produced by, for example, rolling. In order to carry out the stretching, an expansion is applied to each element during the calculation.
Fig. 11 shows two diagrammatic, perpective views of a die 20 and a blank holder 21 for enclosing a conical spout 10a which is formed on a baseplate with side wall parts, which die and blank holder are simple to produce, for example using the wire spark erosion technique. To do this, a recess, the surface of which is formed by a cylindrical surface 24 and two tangent surfaces 22, 23 on the cylindrical surface 24, is arranged in the die 20, which determines the radius of the corner wall part to be formed. The axis of the cylindrical surface 24 lies in the bisector plane of the angle which is included by the side wall parts of the baseplate and forms an angle with the baseplate. This angle generally lies between 15° and 50°. The two surfaces 22, 23 which are tangent on the cylindrical surface 24 form an angle with one another which is selected to be such that virtually the entire conical spout 10a which is formed on the baseplate can be enclosed by the die 20 and the blank holder 21. On its side which faces towards the die 20, the shape of the blank holder 21 is substantially complementary to the die. When the die 20 and the blank holder 21 are moved towards one another, a gap is formed between the die 20 and the blank holder 21, the width of which gap substantially corresponds to the thickness of the baseplate 19 which is to be deformed. Owing to the simple geometry, a certain degree of flexibility is possible in terms of the width of the gap formed between the die 20 and the blank holder 21. Moreover, the die and the blank holder are simple and inexpensive to produce.
Obviously, in addition to the above-described shapes of the die 13 and the blank holder 16, other shapes which are able to fit around that section of the corner region which is to be deep-drawn are also possible.
Fig. 14 diagrammatically depicts a device 30 according to the invention. The device 30 comprises a punch 40 and a mating punch 41, by means of which a semi-finished product can be clamped and positioned in the device 30. Obviously, other means may conceivably be suitable for positioning the semi-finished product in the device 30. The device 30 furthermore comprises the die 20, which determines the shape of the finished product, and the blank holder 21. On their sides which face towards one another, the die 20 and the blank holder 21 each have a surface between which a gap can be formed. The shape of the surfaces substantially corresponds to the shape of the conical spout 10a of the semi-finished product. The device 30 is also provided with means (not shown) for exerting on the die 20 and the blank holder 21, or on the punch 40 and the mating punch 41, forces which are directed towards one another. Moreover, the device 30 is designed to move the punch 40 and the mating punch 41 with respect to the die 20 and the blank holder 21, so that the conical spout 10a is deep-drawn. Using a device 30 of this nature, it is possible to form and deep-draw the conical spout 10a in a single step.
Fig. 15 shows a plan view of the die 13 together with the recess 17 which is shaped on the basis of the result of the calculations carried out using the finite element method as described above. Furthermore, the mating punch 12, which accurately joins an internal wall 26 of the die 13 which determines the ultimate shape of the end product, is arranged in the die 13.
Fig. 16-18 diagrammatically depict various stages in the process of deep-drawing the conical spout 10a. Each stage is illustrated along the cross-sectional lines A-A, B-B, C-C and D-D in Fig. 15. Fig. 16 shows the clamping of the bottom 2 and the side wall section 4b at time t=0. The conical spout 10a is enclosed between the die 13 and the blank holder 16, the curvature of the conical spout 10a depending on the position with respect to the bisectrix of the angle which is included by the side wall sections 4a, 4b. During deep-drawing, the conical spout 10a is pulled out of the gap which is formed between the die 13 and the blank holder 16. In the process, the material which is present in the conical spout 10a is able to flow smoothly, and the entire region in which deformation may occur is enclosed by either the die 13 and the blank holder 16 or the die 13 and the punch 11, so that the formation of creases is effectively prevented. In Fig. 18, the deep-drawing process has been completed and the conical spout 10a has been completely formed into the corner wall part 4c (cf. d in Fig. 18).
The method according to the invention is particularly suitable for forming panels, such as cupboard doors, front panels of drawers and the like, from metal plates, a seamless transition being formed, in a corner region of the baseplate, between the baseplate and the side wall sections of the panel to be formed which meet in the corner region.
The method according to the invention can be carried out locally, so that one corner wall part at a time is formed. If appropriate, a plurality of dies and blank holders may be used, in which case the distance between the dies is adjustable, so that a plurality of corners can be formed simultaneously. The die and the blank holder are adapted to the corner which is to be formed.
The embodiments described above are given as non-limiting examples. It will be clear to a person skilled in the art that numerous modifications and amendments can be made to the method and the device according to the invention without departing from the scope of the invention as defined in the appended claims.

Claims

Method for forming a curved corner wall part (4c) perpendicular to a baseplate (19), the curved corner wall part (4c) extending along a line of rounding (18) in a corner region (5) of the baseplate (19) and merging continuously, at each end, into a side wall part (4a, 4b) which is formed on the baseplate (19), comprising the following steps:

forming at least two side wall parts (4a, 4b) on the baseplate (19) by turning up an edge region of the baseplate (19) through an angle of substantially 90° along a bend line (7a, 7b), which side wall parts (4a, 4b) at least extend as far as the corner region (5) of the baseplate (19) and merge into one another, in the corner region (5), via a crease-like transition (10) which is directed outwards,

deforming the crease-like transition (10) and parts of the corner region (5) which adjoin the crease-like transition (10) and the side wall parts (4a, 4b) into a curved spout (10a) which extends along the line of rounding (18) of the baseplate (19) and along a section of the bend lines (7a, 7b) which adjoin the line of rounding (18), in such a manner that the curved spout (10a) merges continuously into the side wall parts (4a, 4b) which adjoin the curved spout (10a),

fitting a die (13) and a blank holder (16) around the curved spout (10a) and the side wall sections (4a, 4b) which adjoin the curved spout (10a), the die (13) and the blank holder (16) being of a curved shape which is such that the curved spout (10a) and the side wall sections (4a, 4b) which adjoin the curved spout (10a) are enclosed in a gap which is formed between the die (13) and the blank holder (16) and has a substantially constant width, and

deep-drawing the curved spout (10a), so that the curved corner wall part (4c) is formed, the die (13) and the blank holder (16) preventing creases from being formed during the deep-drawing.
Method for forming a curved corner wall part (4c) on a baseplate (19), the curved corner wall part (4c) extending along a line of rounding (18) of the baseplate (19), comprising the following steps:

providing the baseplate (19) with side wall parts (4a, 4b) and a curved spout (10a) which is formed on the baseplate (19),

fitting a die (13) and a blank holder (16) around the curved spout (10a) and the side wall sections (4a, 4b) which adjoin the curved spout (10a), the die (13) and the blank holder (16) being of a curved shape which is such that the curved spout (10a) and the side wall sections (4a, 4b) which adjoin the curved spout (10a) are enclosed in a gap which is formed between the die (13) and the blank holder (16) and has a substantially constant width, and

deep-drawing the curved spout (10a), so that the curved corner wall part (4c) is formed, the die (13) and the blank holder (16) preventing creases from being formed during the deep-drawing.
Device for forming a curved corner part (4c) on a baseplate (19), the curved corner wall part (4c) extending along a line of rounding (18) of the baseplate (19) and merging, at each end, into a side wall part (4a, 4b) formed on the baseplate (19), the device comprising a die (13) and means for positioning the baseplate (19) in the die (13), the device being provided with a blank holder (16) which is designed, together with the die (13), to fit around a curved spout (10a) which is formed on the baseplate (19) and side wall sections (4a, 4b) which adjoin the curved spout (10a) and to clamp said spout and side wall sections in place, and the device furthermore comprising a punch (11) which is able to push the baseplate (19) into the die (13) in order to draw the curved spout (10a) between the die (13) and the blank holder (16) and to form the curved corner wall part (4c) between the punch (11) and the die (13).
Device according to claim 3, in which the shape of those surfaces of the die (13) and the blank holder (16) which fit around the curved spout (10a) are determined with the aid of the finite element method, in order to ensure that there is minimal deformation of the curved spout (10a) while it is enclosed.
Device according to claim 3, in which those surfaces of the die (13) and the blank holder (16) which fit around the curved spout (10a) are determined by a cylindrical surface, the axis of which lies in the plane of symmetry of the corner wall shape defined by the die (13) and forms an angle with the baseplate (19), and two tangent surfaces on the cylindrical surface, which form an angle with one another which is selected to be such that the die (13) and the blank holder (16) completely enclose the curved spout (10a).