BACKGROUND OF THE INVENTION Generally, the invention relates to the so- called dieless forming of a sheet metal. A method and apparatus for dieless cold forming of a sheet metal are known in prior art e. g. from publication JP 07- 132329 and EP 0 970 764 Al (Amino Corp. ) A sheet metal is herein used to mean a metallic sheet metal. A di- eless forming is used to mean that the method and ap- paratus do not use two complementary dies defining the three-dimensional shape, of which one is a movable pressing device and the other one is a counter support against which the pressing device is moved, as is done in a conventional deep drawing method. Instead, the pressing device is a forming tool that forms in a point-form manner or in a small area, which tool is moved with respect to the sheet metal.

From the aforementioned publications, an ap- paratus is known that has a holding mechanism for clamping the sheet metal by its edge. A fixed counter support is arranged underneath the sheet metal and de- signed to be in contact with the lower surface of the sheet metal. An upright means of conveyance is ar- ranged to move the holding mechanism in the vertical direction for moving the sheet metal with respect to the fixedly supported counter support. The apparatus further comprises a pressing device which is a bar

provided with a spherical point and which is arranged above the sheet metal for applying a stretching and bending force to the sheet metal on the upper surface thereof. The pressing device is connected to a three- axis portal robot which is able to move the pressing device and to press it against the top surface of the sheet metal with a forming force that stretches and bends the sheet metal. The control device of the appa- ratus is provided with program means for numerically controlling the movements of the upright means of con- veyance and of the portal robot.

In the known method, the lower surface of the sheet metal is contacted with a fixed pressing device.

Then the pressing device is used to apply pressure to the sheet metal in the vicinity of the contact point between the pressing device and the sheet metal, and the pressing device is moved based on the desired shape along a predetermined, e. g. a spiral path in the horizontal direction around the contact point between the pressing device and the sheet metal so that the pressing device moves on the top surface of the sheet metal, while at the same time pressing the sheet metal with a stretching and bending forming force.

The problem is that as the pressing device is connected to a three-axis portal robot, the pressing device only has three degrees of freedom, i. e. the possibilities of movement in the x, y and z direc- tions, when the sheet metal is supported on the x-y plane; and the pressing device may therefore only move against the x-y plane in the perpendicular z direction in addition to the x and y directions. The forming force is thus always directed only downwards, and its direction cannot be changed. Therefore, a known device cannot be used to form in the sheet metal straight an- gles or inwards turning shapes (as shown in the accom- panying figures 3,6 and 8-10), instead one must use a release that is at least of the order of 15°-30°. This

fact imposes a significant limitation on the fact of what kind of three-dimensional shapes it is possible to form in the sheet metal by means of the apparatus.

One further problem is that to make deep shapes in the sheet metal, one must use in the forming a prolonged-arm pressing device, which results in bending and vibration of the arm, which cause measur- ing errors and crinkling of the sheet metal.

OBJECTIVE OF THE INVENTION The objective of the invention is to elimi- nate the drawbacks referred to above.

One specific objective of the invention is to disclose a method and apparatus that enable inclining of the pressing device for applying the forming force to the sheet metal in a desired angle and for forming inwards turning shapes in the sheet metal.

One further objective is to disclose a method and apparatus that enable measuring errors as small as possible and a smooth forming imprint.

SUMMARY OF THE INVENTION The method in accordance with the invention is characterised by what is presented in claim 1. Fur- ther, the apparatus in accordance with the invention is characterised by what is presented in claim 18.

According to the invention, in the method, the movement of the pressing device is controlled by at least a five-axis principle.

Correspondingly, in the apparatus in accor- dance with the invention, the second means of convey- ance, which moves the pressing device, is at least a five-axis robot. The program means controlling the ap- paratus include instructions for controlling the robot

in such a manner that the pressing device has at least five degrees of freedom.

The invention has the advantage that the five-axis degrees of freedom of the pressing device enable inclining of the pressing device so that the forming force can be applied to the sheet metal in the desired direction, and it is possible to form in the sheet metal inwards turning shapes. The forming force can be applied perpendicularly towards the sheet metal. In addition, the pressing device arm can be short-arm and sturdy, which reduces the bending and vibration of the pressing device arm and results in a bigger forming accuracy, and there will be no non- desired crinkling of the sheet metal.

The other advantages and features of the in- vention are apparent from the dependant claims, as well as from the following description of preferred embodiments.

LIST OF FIGURES In the following, the invention is described in detail with reference to the accompanying drawing, wherein Fig. 1 is a schematic side view of a first embodiment of the apparatus in accordance with the in- vention in the initial phase of a forming method in accordance with the invention, Fig. 2 represents section II-II of Fig. 1.

Fig. 3 represents the apparatus of Fig. 1 in another phase of the forming, Fig. 4 represents a second embodiment of the apparatus in accordance with the invention, Fig. 5 represents a third embodiment of the apparatus in accordance with the invention, Fig. 6 represents a fourth embodiment of the apparatus in accordance with the invention,

Fig. 7 represents a fifth embodiment of the apparatus in accordance with the invention, Fig. 8 schematically represents two different pressing devices of the apparatus in accordance with the invention in inclined positions, according to the invention, as they form a sheet metal at two points of a model being formed, Figs. 9 and 10 represent a roller press in inclined positions, according to the invention, as they form a sheet metal, Fig. 11 is a side view illustrating a roller press, and Fig. 12 is schematic side view illustrating a counter support which consists of support elements lo- cally supporting the sheet metal.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows an apparatus that can be used to form complicated three-dimensional shapes in a sheet metal 1. A rectangular sheet metal 1 is attached to position so as to be horizontal with a frame-like holding mechanism 2, which clamps the edge of the sheet metal along the whole periphery (see also Fig.

2).

Arranged in the lower part of the sheet metal 1 is a counter support 3. The counter support 3 is in this example a die 3 having a shape corresponding to the desired final three-dimensional shape of the sheet metal. Advantageously, the apparatus can include a cooling device 16 for cooling the die 3 during the forming, especially when the sheet metal is heated as the forming goes on. The die 3 that is illustrated in Fig. 1 as being cross-sectioned includes a schematic illustration of a cooling medium channel 28, via which the cooling device 16 circulates the cooling medium.

In addition, the die 3 can be provided with suction

ducts 15, in which a vacuum device 14 creates a vac- uum. The suction ducts 15 open on the outer surface of the die 3 for sucking the sheet metal tightly against the outer surface of the die 3. The apparatus includes a first means of conveyance 6, which is herein a hoisting device 6 which lifts the die in the vertical direction and by means of which the die is lifted up- wards during the forming. The hoisting device 6 in- cludes e. g. a horizontal support plate 29 to be moved in the vertical direction by means of a ball-race screw drive, on top of which plate the die 3 is at- tached. During the forming, the die 3 is in contact with the lower surface 5 of the sheet metal 1 and sup- ports the sheet metal 3 during the forming.

Arranged in the upper part 8 of the sheet metal 1 is a means of conveyance 10, to which the pressing device 7 is connected for moving the pressing device and pressing against a second surface 9 with a forming force stretching and bending the sheet metal.

The second means of conveyance 10 is an articulated arm robot 10'to be controlled by a six-axis principle, the robot being a so-called industrial robot. The base 23 of the robot 10'is attached to a fixed frame 22.

The base 23 is placed from the sheet metal 1 to be formed to such a distance that allows the articulated arm of the robot 10'to be stretched as straight as possible during the forming process. This is advanta- geous because an articulated arm robot produces a pressing force as big as possible when kept as straight as possible.

The articulated arm robot 10'is controlled by a control device 11 which has a computer program for numerically controlling the movements of the means of conveyance and the second means of conveyance. The program contains predetermined instructions for con- trolling the robot 10'in such a manner that the press- ing device 7 has at least five degrees of freedom, ad-

vantageously at least degrees of freedom, which are needed in order that the pressing device 7 can be in- clined into a suitable angle at each point so that the forming force is directed substantially perpendicu- larly against the surface of the die 3, and thus against the thickness direction of the sheet metal 1.

By suitably inclining the pressing device 7, it is possible to form shapes in the sheet metal, such as inwards turning shapes and straight angles, which were impossible to form using the previous pressing devices having three-axis degrees of freedom.

The apparatus can include a heating device 13 which is installed in the second means of conveyance 10'in the vicinity of the pressing device 7 for apply- ing a local heating to the sheet metal 1. The heating device 13 can include means for applying hot air, com- bustion gas, radiation or the like to the sheet metal, or the heating device 13 can be an electrical heating element. The points to be heated can be determined based on a CAD model corresponding to the desired shape, as can be done with the path of movement of the robot 10 as well, so that heating is used just at points in which it is specifically needed.

The objective of the heating is to soften and plastify the material of the sheet metal to be formed to ease the forming. Soft metallic sheet metals, such as aluminium sheet metals, can be formed even without heating, but e. g. a steel sheet may need heating.

By means of the predetermined instructions defined in the control device 11 it is possible to get the hoisting device 6 and the articulated arm robot 10'to mutually cooperate during the forming. To begin with, the highest point of the die 2 and the lower surface 5 of the sheet metal are contacted with one another. Then the pressing device 7 is pressed against the upper surface 9 of the sheet metal at a point which is in the vicinity of the contact point between

the die and the sheet metal. The pressing device 7 is moved on the upper surface of the sheet metal 1 based on the desired shape along a predetermined path which is growing in respect of its radius, the path being illustrated by a dot-and-dash line 30 in Fig. 2, around the aforementioned contact point in such a man- ner that the pressing device presses the sheet metal with a stretching and bending force, which results in a permanent transformation of the sheet metal 1. The hoisting device 6 is used to lift the die 3 upwards as the forming goes on.

The instructions for controlling the path of movement of the pressing device 7 and the local heat- ing are generated based on the CAD model that defines the desired three-dimensional shape. The program means of the control device 11 are arranged to generate, based on the CAD model, a first set of instructions for controlling the movement of the pressing device 7 by a five-axis principle, and then to determine, based on the CAD model, the additional information that is related to an additional degree of freedom and local heating, which cannot be controlled by the first set of instructions. Further, the program means are ar- ranged to generate, based on the first set of instruc- tions and the additional information, a second set of instructions which control the movement of the press- ing device 7 by at least a six-axis principle, and in addition control the second heating device 13 to apply a local heating to the sheet metal at the necessary points.

Fig. 3 illustrates a situation in which the forming has reached a phase in which the pressing de- vice 7, which is controlled in the aforementioned man- ner, has been used to form in the sheet metal 1 a shape corresponding to the die 3.

Fig. 4 represents an embodiment of the appa- ratus that differs from the embodiment of Fig. 1 in

that the articulated arm robot 10 that moves the pressing device is disposed next to the sheet metal 1 to be formed. In addition, the base 23 of the robot 10 is supported on guide elements 24, under whose control the robot 10 is wholly controlled so as to be movable in a direction parallel to the plane as shown in Fig.

4. An actuator 25 moves the robot 10 under the control of the guide elements 24.

Fig. 5 represents an embodiment in which as the second means of conveyance 10 that moves the pressing device, a six-axis pusher arm robot 10"is used, which is marketed with the trademark Tricept (SMT Tricept Ab, Sweden). A Tricept pusher arm robot enables one to achieve a sufficiently big pressing force that remains as constant as possible throughout the whole machining area.

Fig. 6 represents an embodiment of the appa- ratus in which the sheet metal 1 is supported with a holding mechanism 2 into an upright position. Instead of a die, a counter support 3 that supports the sheet metal 1 in a small area is used, which counter support is moved by a first means of conveyance 6, which is herein an articulated arm robot that works on the first side 4 of the sheet metal. The pressing device 7 is moved by a second means of conveyance 10, which also is an articulated arm robot. Both robots 6 and 10 are controlled by at least a five-axis principle, ad- vantageously a six-axis principle, and synchronically in cooperation so that the counter support substan- tially follows the path of movement of the pressing device 7. One or both of the articulated arm robots 6 and 10 can be substituted by a Tricept pusher arm ro- bot as shown in Fig. 5. The counter support 3 and the pressing device 7 are e. g. roller presses which are explained in more detail in the following with refer- ence to Fig. 8.

Fig. 7 illustrates a schematic diagram from which it can be seen that the apparatus can also be applied to mass production, although dieless forming has been conventionally used for making individual ar- ticles and prototypes. The sheet metal 1 can be con- veyed e. g. from a coil 26 along a horizontal path by means of some kind of conveyor 21, which conveys the sheet metal 1 to a forming station 27. If the sheet metal 1 is to be preheated, the apparatus may include e. g. an electrical heating device 12, which heats the sheet metal 1 on both sides thereof at least through- out the whole surface area to be formed.

The pressing device 7 as shown in the upper part in Fig. 8 includes a spherical fixed or rotating forming point 18. As can be seen from the pressing de- vice 7 as shown in the upper part in the figure, the pressing device 7 can be a roller press, in which case it includes an arm part 19 which can be attached to the robot, and a forming roller 20 which is rotably mounted on the arm part using bearings. As can be seen from Fig. 11, in the roller press, the arm part 19 is advantageously mounted with bearings on the robot's arm so as to rotate freely. The rotation axis of the arm part 19 is disposed at a distance s aside from the rotation axis of the forming roller 20, thanks to which the rotation level of the roller automatically keeps to the direction of movement of the roller.

Figs. 8-10 show that by suitably inclining the pressing device 7, it is possible to form e. g. straight angles and inwards extending shapes, which were impossible to form using the previous apparatuses and methods of dieless forming.

Furthermore, Fig. 12 illustrates that instead of a die, it is possible to use as the counter support 3 several fixed support elements 17, each of which lo- cally supports the sheet metal at different points of the desired three-dimensional shape.

The invention is not limited merely to exam- ples of its embodiments, instead many variations are possible within the scope of the invention defined by the claims.