Clamping device

The invention concerns a clamping device for a device for the production of metal parts by forming with a closed forming tool, the clamping device comprising at least

The invention concerns a clamping device for a device for the production of metal parts by forming with a closed metal forming tool as well as a device for the production of metal parts by forming with a closed forming tool which is provided with the clamping device specified in the invention. The invention also concerns a structural component for a clamping tool of a device for the production of metal parts by forming with a closed forming tool.

As used in the invention, the designation of “metal forming with a closed forming tool” defines all metal forming procedures during which the application of a force to the workpiece to be formed occurs inside a forming tool which is essentially composed of several parts but which is substantially closed at the moment of the application of the force, and during which the forces to lock the forming tool are regularly higher than 3 MN, an example of such a forming procedure being the so-called hydroforming process using forming tools which are parted in a longitudinal direction.

In hydroforming processes, the devices used will generally be powered by hydraulic systems. The arrangement of such devices is largely determined by the workpiece to be produced, and the original forming body will always be a tube-shaped hollow body. The main cylinders used for power transmission to the tube extremities will be arranged either in an upright or a horizontal position so that they act in opposite directions in the direction of the initial tube axis. One of these cylinders will generally be provided with a hollow bore and a high pressure connection which is generally connected to the pressure intensifier by means of a pipe joint.

The forming tool has at least two components. In the simplest scenario of a two-part forming tool, one tool component is secured to the machine table, whilst the other is powered and performs an opening and closing motion as defined by the working cycles. Depending on the desired workpiece geometry, the devices can optionally take up forming tools which are either parted in the longitudinal or cross direction; where clamping forces of more than 3 MN will generally require forming tools which are parted in a longitudinal direction. Mostly, those devices will only be of economic value where higher numbers of pieces are produced, that is especially where short working cycles are used.

In many cases, the devices for hydroforming processes which are provided with a forming tool which is parted in the longitudinal direction down the tube axis are designed as multicolumn presses or frame presses. The forming tool is mounted so that the plunger of the press moves one component of the forming tool up during tool change. During the forming process, the plunger should compensate the force resulting from the workpiece surface area projected and the interior pressure and apply a force of at least the same value or higher to the forming tool. Due to the high interior pressures used in the process (generally more than 1000 bar), the clamping forces required in this respect which are higher than 3 MN must be ensured by the steel structure of the device, which will require relatively high constructional heights and much space for assembly and operating purposes when using multicolumn presses or frame presses. The device will involve costly foundation work and large space requirements where the forces to be absorbed are 3 MN or higher and the dead mass generally resulting from such structures is accordingly high. Any tool change, including that of the forming tool, will be subject to high technological expenditure.

The publication DE 1 602 475 B2 describes a pressing device for the production of hollow workpieces constructed of sheet metal under interior hydraulic pressure by cold forming processes where the moveable parts of the parted mould encompassing the workpiece are locked together by means of pivotable clamping hooks during cold forming. Where such a pressing device is required to ensure clamping forces of more than 1 MN, in particular more than 3 MN, the clamping mechanism, in particular the clamping hooks or joints which are needed for the pivoting motion of the clamping hooks, must be sufficiently dimensioned. Such devices of a dead mass of several metric tons must be based on expensive foundations and will have large overall construction heights. The clamping hooks, as far as they are able to guarantee the required clamping forces in the first place, can only be operated with heavy forces and high energy.

The short cycle times of between 20 and 40 seconds which are an economic necessity for a profitable operating of the device within industrial manufacturing processes, are not realistic in view of the high moments of inertia occurring. This solution will result in the formation of gaps between the components of the forming tool produced during the forming process proper, which mainly results from the elastic deformation of the material used for the clamping hooks, and which will lead to an undesired deformation of the workpiece during power build-up.

It is the aim of the invention to provide both a device and a component of such a device which have a lower construction height and a low dead mass and will require a lower expenditure regarding the amounts of investment, maintenance and operation and can be operated in an economical way and which are not subject to forming gaps between the components of the forming tool during forming.

The requirement of the invention is met because the clamping device according to the invention comprises at least:several tension hoops2, these tension hoops2each being provided with a tension frame2.2of a closed contour, the tension frame being provided with two segments2.3arranged opposite each other at some distance, between which a forming tool12can be arranged, each of these segments2.3being provided with at least either one bearing surface2.1or one bearing surface2.4, and the tension hoops2being each linked by at least one articulated joint8in order to be pivoted, the material of the tension frame2.2mainly consisting of materials of tensile strengths between 1500 N/mm2and 4200 N/mm2, an endurance strength of between 1200 N/mm2and 3000 N/mm2and a density of between 1.2 and 2.5 g/cm3,a bearing surface3.1which is arranged above or on the upper surface of forming tool12and is used as support for a bearing surface2.1of a tension hoop2, anda device5which produces a clamping force of more than 3 MN and is composed of several power-generating elements, the clamping force being applied between the bearing surfaces2.1and2.4of the tension hoops2and at least one surface area located beneath forming tool12.

The selection of materials of the invention and the constructional design of the material will, on the one hand, allow for a technically easy pivoting of the tension hoops using a low amount of energy in order to obtain reasonable cycle times, and, on the other, result in the occurring of a low amount of dynamic forces.

The fact that the invention makes use of and selects materials as construction materials, the properties of which are described in the first patent claim, makes way for new constructive solutions and/or new machine designs, as compared to the materials used in forming technology up to date, including structural steel.

The tensile strength of a carbon fiber compound is, for instance, of approx. 2950 N/mm2(structural steel of approx. between 320 and 690 N/mm2), the endurance strength of approx. 1950 N/mm2(structural steel of approx. 350 N/mm2), and the density of approx. 1.8 g/cm3).

By designing the element of clamping mechanism as a tension hoop which will provide the required clamping force the invention makes a purposeful use of the improved material properties of the materials preferred in the invention, such as carbon fiber compounds, which results in the proportion between the strength of the design and the tension frame mass being 800, for instance.

The depending Patent claims2to8indicate advantageous further developments and improvements of the clamping device under the invention.

The requirements of the invention are furthermore met by a device for the production of metal parts by hydroforming which comprises at least one parted forming tool and a device as described under Patent claims1to8.

The requirements of the invention are furthermore met by a structural component for a clamping tool of a device for the production of metal parts by hydroforming where a closed forming tool as described under Patent claims10is used.

The depending Patent claim11describes advantageous developments and improvements of the structural component as described in the invention.

FIG. 1shows a side view of a clamping device1under the invention which is a constituent part of a device for the production of metal parts by hydroforming which contains a two-part forming tool12. A machine base6is secured on a foundation13, the machine base substantially consisting of a box-shaped structural steel construction. A frame6.3is bolted down to another frame6.1by means of a column6.2. The column6.2is provided with two articulated joints8which are rigidly mounted in the direction of the longitudinal axis of the machine base6. The two tension hoops2are so linked to the articulated joints8that these tension hoops2can be pivoted in an almost parallel way to the longitudinal axis of the machine base6. Two hydraulic pivoting cylinders9which are located on the frame6.3activate the pivoting motion of the tension hoops2. The four corners of frame6.3are provided with four lifting cylinders4which rest on the frame6.3and are connected to crossbeam3.

Crossbeam3is provided with plane bearing surfaces3.1on which the equally plane bearing surfaces2.1belonging to tension hoops2which are arranged parallel to those can rest when they are positioned. The upper part of the two-part parted-in-length forming tool12is mounted to the Crossbeam3. The lower part of the forming tool12is bolted down to machine table7. The machine table7loosely sits on the piston bearing surfaces of the four pressing cylinders which constitute the power-generating elements of device5.

The pressing cylinders are mounted to the frame6.1so that these power-generating elements of device5acting on the same tension hoop2, preferably comprising several hydraulic high-pressure cylinders, are arranged so that the central power-applying lines generated by these power-generating elements of device5run almost parallel and along a plane which is not substantially different from the plane separating the tension hoop2in an axial direction. The segments2.3are largely constructed from some light metal material, such as aluminium alloys. The tension frames2.2mainly consist of a carbon fibre compound, e.g. an intermodular fiber of a volume portion of fibres of approx. 50/65% in an epoxy resin matrix.

The functional sequence of the above device is described in its context in the following.

After placing the workpiece into the opened forming tool12, the latter is closed by lowering the pistons of lifting cylinders4until both parts of forming tool12come to rest. The pivoting cylinders9are now used to pivot the two tension hoops2to the vertical condition in order to create a gap which is necessary to allow a contact-free positioning of tension hoops2, the gap being located between the bearing surfaces3.1of crossbeam3and the bearing surfaces2.1of the tension hoops2. The pressing cylinders are now used to apply clamping forces on to forming tool12along machine table7. The machine table7and the whole forming tool12are now lifted until the contact is made between the bearing surfaces of crossbeam3and the tension hoops2. Both parts of the forming tool12are then subjected to the required clamping force, which results in the forming tool12being clamped.

FIG. 2shows an alternative scenario of the clamping device with the opened die in a perspective view (FIG. 2aand/orFIG. 2b). The machine base6mainly consists of a box-shaped steel construction. A bottom frame6.3is bolted down to another frame6.1by means of four vertically arranged beams. A tension hoop beam10which is connected with four spring guides11to the frame6.3is mounted between these two frames. The two articulated joints8are mounted to tension hoop beam10. The articulated joints8are provided with the two tension hoops2which are linked to their lower ends in order to enable these to pivot parallel to the longitudinal axis of the machine base6. Two hydraulic pivoting cylinders9which are located on frame6.3are used for the pivoting of the tension hoops2. The four corners of frame6.1are provided with four vertically arranged lifting cylinders4which are connected to crossbeam3. Crossbeam3is provided with plane bearing surfaces3.1on which the equally plane bearing surfaces2.1arranged parallel to those of tension hoops2can rest when they have been positioned (FIG. 2a). The two tension hoops2each consist of two semicircular segments2.3arranged opposite each other, the almost semicircular contours of the upper and lower segment2.3each facing different directions. The annular rigid tension hoop2.2wraps around the semicircular contours of the upper and lower segment2.3and is connected to these. The upper part of the two-part forming tool12is fixed to crossbeam3. The lower part of the forming tool12is bolted down to frame6.1to the base of which the four pressing cylinders5protruding downwards are mounted. The pressing cylinders5will move through the four openings of the tension hoop beam10and press down on the bearing surfaces2.4of the lower segments2.3(?). The pressing cylinders are mounted to the frame6.1so that the central power-applying lines generated by these power-generating elements of device5run almost parallel and along a plane which is not substantially different from the plane parting the tension hoop2in an axial centerline direction when tension hoop2is positioned (FIG. 2a).

The functional sequence of the above device is described in its context in the following:

After placing the workpiece into the opened forming tool12, the latter is closed by lowering the lifting cylinders4until both parts of forming tool12come to rest. The pivoting cylinders9are now used to pivot the two tension hoops2to their vertical position in order to create a gap which is necessary to allow a contact-free positioning of tension hoops2, the gap being located between the bearing surfaces3.1of crossbeam3and the bearing surfaces2.1of the tension hoops2. The pressing cylinders are now used to apply forces on to the bearing surfaces2.4of the tension hoops2. Tension hoop2is lowered until the bearing surfaces3.1;2.1of the crossbeam3and the tension hoop2come into contact. The required clamping force which is applied by the pressing cylinders is now applied so that the forming tool12is clamped with the help of these clamping forces and the parts of forming tool12can no longer open during the forming process.

FIG. 3contains a side view of a component part for a clamping tool1as a constituent part of a device for the production of metal parts by hydroforming which is provided with a two-part forming tool12. A machine base6is bolted down to a foundation13, the machine base mainly consisting of a box-shaped construction made of structural steel. A frame6.3is bolted down to another frame6.1by means of a column6.2. The column6.2is provided with two articulated joints8which are rigidly mounted in the direction of the longitudinal axis of the machine base6. The two tension hoops2and therefore a pair of the design structure described in the invention are linked to the articulated joints8in a manner that these tension hoops2can be pivoted in a almost parallel way to the longitudinal axis of the machine base6.

As an alternative scenario which is not described inFIG. 3the tension hoop2can be located so that it can be axially shifted towards tool12.

Two hydraulic pivoting cylinders9which are mounted to the frame6.3are used to activate the pivoting motion of the tension hoops2. The four corners of frame6.3are provided with four lifting cylinders4which rest on the frame6.3and are connected to crossbeam3. Crossbeam3is provided with plane bearing surfaces3.1on which the equally plane bearing surfaces2.1belonging to tension hoops2which are arranged parallel to those can rest when they have been positioned. The upper part of the two-part parted-in-length forming tool12is mounted to the Crossbeam3. The lower part of the forming tool12is bolted down to machine table7. The machine table7loosely sits on the piston bearing surfaces of the four pressing cylinders which constitute the power-generating elements of device5. The pressing cylinders are mounted to the frame6.1in such a way that these power-generating elements of device5, preferably several hydraulic high-pressure cylinders, acting on the same tension hoop2are arranged so that the clamping force or the clamping forces act on the tension hoop2in such a way that the net force of the power-applying lines runs almost parallel and along a plane which is not substantially different from the plane parting the tension hoop2in a centerline axial direction. The segments2.3are largely constructed from some light metal material, such as aluminium alloys. The tension frames2.2mainly consist of a nonmetal compound material with embedded reinforcements, here of a carbon fibre compound, e.g. an intermodular fiber of a volume portion of fibres of approx. 50/65% in an epoxy resin matrix.

The functional sequence of the above device is described in its context in the following:

After placing the workpiece into the opened forming tool12, the latter is closed by lowering the lifting cylinders4until both parts of forming tool12come to rest. The pivoting cylinders9are now used to pivot the two tension hoops2to their vertical position in order to create a gap which is necessary to allow a contact-free positioning of tension hoops2, the gap being located between the bearing surfaces3.1of crossbeam3and the bearing surfaces2.1of the tension hoops2. The pressing cylinders are now used to apply the clamping forces on to the forming tool12along the machine table7. The machine table7and the whole forming tool12are lifted until the contact is made between the bearing surfaces of crossbeam3and the tension hoops2. Both parts of the forming tool12are now subjected to the required clamping force, which results in the forming tool12being clamped.

The component part described in the invention can also be used as an integral element of a clamping tool for the forming or interior forming of plastic, metal, ceramic or glass parts.

The workpiece can be formed inside by blow moulding or injection moulding of larger plastic parts, for instance. The structural unit described in the invention, provided with one or several components described in the invention, could be used for the gap-free closing of a two-part blow mould. The principle of the invention can easily be transferred by a specialist engineer according to known procedures after having adjusted the usual parameters.

A further example for the use of the invention due to its principle is offered by the casting of metal, ceramic or glass parts according to known procedures.