The invention refers to an impact cutting device for adiabatic separation of workpieces, a cutting unit for an impact cutting device as well as a method for accelerating an impact element in an impact cutting device.
During high-speed impact cutting a high impulse is imparted to a moveable matrix being laterally displaced along a stationary matrix by means of the impulse. The workpiece is clamped between the matrices in a passage through the matrices, wherein their cross-section corresponds to the cross-section of the workpiece to be separated. Observations show that the workpiece to be cut can be separated almost without plastic deformation by very short, but heavily interacting impulse. Thereby the displaceable matrix is displaced by only few tenths of millimeters relative to the stationary matrix. Herein it is problematic on the one side to transmit a reproducible impulse of accurate power to the moveable matrix, and on the other side to damp the impulse energy, which has not been transformed into separation energy, in such a manner that the impact cutting device is also applicable for permanent use.
DE 695 19 238 T2 (corresponding to EP 0 833 714 B1) describes an impact machine, in which the workpiece is clamped between a stationary and a moveable matrix. On the stationary matrix rests an impact bolt, onto which an impact impulse is transmitted by means of a hydraulically moved piston. It is the object herein to achieve a cutting rate as high as possible, so that for example a high cutting rate for wire nails of a certain length is achieved. In order to achieve the high cutting rate by means of the hydraulically operated piston a particular piston/cylinder arrangement is proposed.
Also U.S. Pat. No. 4,840,236 suggests a hydraulic-pneumatic actuator for transmitting high impulses to a workpiece to be compressed or cut. Besides a cylinder arrangement for a high acceleration of the piston also an arrangement for slowing down the piston is proposed.
It is an object of the invention to provide an impact cutting device and a method therefor, in which the acceleration of an impact element may be accurately set and the impact impulses minimally affect the acceleration device.
This object is achieved by the features of claims 1, 25 and 32. Advantageous embodiments are subject matter of the dependent claims.
The conventional impact cutters are optimized to separate a workpiece (mostly in form of a wire and being of a specific basic material having a given thickness) by a very high impact rate so that many wire nails can be produced for further processing. When rigging the machine, the system is optimized by tests in that on the one side a clear material separation is carried out and on the other side there is a preferably low transformation of the impact impulse into shock waves within the apparatus. The optimization time is justified by means of the subsequently long use of the machine with the optimized parameters. Such an optimization phase is however not justified for frequently changing workpiece types (form of material, thickness of material, used material etc.). Therefore it is aspired to achieve a change in the impulse of the impact element and the optimization of the impact energy in a manner as simple and reproducible as possible. Due to the dynamic processes in a pneumatic or hydraulic system this is very extensive and depends on the oil temperature, on the oil type, its contamination, the wear of sealing elements and the like. Further, in conventional impact cutters the moving impact element and the acceleration element are connected to each other also during the impact phase so that on the one hand the acceleration device has to be correspondingly mechanically stable and on the other hand undergoes a strong mechanic stress, which may result in a fast wear.
In the impact cutting device according to claim 1 it is proposed that the impact element transmitting the impulse to an impact unit is releaseably coupled to an acceleration unit. Before the impact element impinges on the cutting unit a decoupling between the acceleration unit and the impact element is carried out by a coupling device. By decoupling the operations ‘impacting’ and ‘accelerating’ the impact process and the acceleration process can be optimized independently from each other, wherein, particularly by decoupling the acceleration unit from impacting, the acceleration unit undergoes considerably lower mechanical stress. Further, the acceleration may be interrupted exactly then, when the impact element has the impulse required for the workpiece to be processed, so that e.g. the slowing down of the acceleration unit in turn has no effect on the impact element and its impulse. By means of the forceless ‘flight path’ of the impact element when approaching the cutting unit also an exact adjustment between the acceleration unit and the cutting unit is not necessary for reproducing a given impact impulse.
A carrier of the acceleration unit advantageously grips into the impact element and carries this at least during the acceleration phase and over the acceleration distance, respectively. Via the carrier on the one hand the acceleration power is transmitted to the impact element and on the other hand a secure guiding of the impact element is achieved. The coupling ‘at least’ over an acceleration distance means herein that either the carrier is coupled to the impact element only during the acceleration phase and over the acceleration distance, respectively, and directly after the acceleration a decoupling takes place. Or a coupling is maintained for another given time and distance, respectively, after the acceleration, so that the carrier couples to the impact element free of force. In this phase the system of the impact element/acceleration unit may relax free of force on the one hand and on the other hand the carrier may be decoupled from the impact element by minimizing the frictional forces or the like.
A guiding of the carrier advantageously runs at least over the acceleration distance parallel to the track of the impact element so that no offset between the carrier and the impact element is necessary over the acceleration distance and the acceleration phase, respectively. In a particularly advantageous embodiment the carrier is decoupled from the impact element in that the track of the carrier deviates from the track of the impact element after the acceleration distance and, if applicable, a relaxation distance. Thereby the carrier and the impact element are spatially separated from each other and by means of a spatial separation of the impact element from the cutting unit an interaction between those two is excluded during the impact phase.
If the carrier is arranged on a strip- or cordlike element the carrier may be accelerated by means of pulling and, if applicable, pushing on the strip- or cordlike element. Further, the track of the carrier may be easily changed by deflecting the strip- or cordlike element. The striplike element is advantageously a belt, for example a tooth belt, or a chain, which may transfer high acceleration and pulling forces, respectively, to the carrier.
If the striplike element is endless and guided over at least two deflecting elements, a nearly constant stress is enabled by means of the striplike element, when the striplike element is uniformly driven—nearly independent of the position of the carrier. The striplike element is in particular advantageously driven by at least one of the deflecting elements so that the construction of the acceleration device is simplified.
If the impact element comprises a recess for supporting the carrier and if a ramp element is adjacent to the recess, the carrier may be traced back into the recession over the ramp by means of lateral deflection of the carrier when retracting the carrier. After decoupling and carrying out the impact to the cutting device, it is thus enabled that by means of easily feeding the carrier into the recession the carrier is re-coupled to the impact element and then the impact element may be retracted in reverse acceleration direction in the original or a new position. For example, the carrier is arranged on a striplike element and when traveling the ramp the carrier is displaced laterally to the impact element by perpendicularly retracting the carrier to the acceleration direction, until it re-engages with the recess. The inverse embodiment may of course be provided in which the carrier comprises a recess and a protruding element of the impact element engages with the recess of the carrier.
If the coupling of the impact element and the acceleration unit comprises several coupling locations and if these are symmetrically arranged as regards the acceleration direction, a tilt moment due to the acceleration power on the impact element is prevented during the acceleration.
If the impact element is guided in a guiding device during its movement towards the cutting unit, a sliding element reduces the friction when guiding along the guiding device. If the sliding element is moveably supported in a recession on the impact element, decoupling is provided between the impact vibration when the impact element impinges on the cutting device. Additionally, a damping element is advantageously arranged between the moveable sliding element and the impact element so that the vibration movement is not directly transmitted from the impact element to the guiding device of the impact element. Alternatively and/or additionally the cutting unit is supported on a mineral cast support structure for vibration damping. The mineral cast shows excellent damping features and reduces the shock propagation to the workhall floor or the acceleration unit.
In particular two impact elements are advantageously accelerated from opposite directions to the cutting unit and impinge on it. If the cutting unit comprises for example two moveable matrix elements, which are vibrantly supported, the two impulses compensate themselves in symmetrically impinging pulse intensities, which are ideally transformed completely into heat and separation energy. This also reduces the shock wave resulting from impact cutting.
Advantageously an acceleration unit is used in the impact and reverse impact arrangement which synchronizes the acceleration of the impact and reverse impact element. Or two acceleration units are synchronized with each other by mutual coupling.
If the impact element comprises a shape tapered towards the impact surface of the impact element, the deceleration impulse of the impact element towards the impact surface is concentrated and amplified.
In the cutting unit according to claim 25 between a moveable matrix element and a supporting structure for the cutting unit a damping device is arranged between the side opposing to the impact side of the moveable matrix and the supporting structure. By means of the damping element excessive energy from the impact is damped, if the impact energy could not be transformed completely into separation energy and heat energy. By means of an annular spring as a damping device the excessive energy is advantageously transformed into heat energy within a very short distance. If additionally or alternatively an air gap is provided as damping device and if compressed air is fed into the air gap, contaminations are discharged from the air gap on the one hand and on the other hand the continuous air flow serves for cooling the cutting unit.
If the moveable matrix is supported in a recess having lateral guiding, the air fed into the air gap also causes the reset of the moveable matrix element. This can be assisted in that in the case of the displaced matrix element the air can hardly discharge from the air gap and thus an air pressure is build up which resets the matrix with increased power.
If at least one moveable matrix element is supported in a recess having side boundary walls and if pressurized air is supplied to the side boundary walls, then contaminations are discharged on the one hand and the air cussion serves as air conduction bearing for guiding the moveable matrix element in the recession.
If in the moveable matrix element the cross-section of the opening enlarges from the separation rim to the feeding or removing side of the workpiece, then not the whole workpiece held in the matrix has to undergo the lateral acceleration effected during the impact operation. Thus the impulse energy acting on the cutting location is increased.
The embodiments of the invention are explained by means of drawings which show:
In the acceleration unit 30 runs a chain 32 over an upper driving wheel 33 and a lower deflecting wheel 34. The upper driving wheel 33 is driven by a NC-controlled servodrive 82 (
For inserting the carrier 36 into the recess 28 during the coupling of the hammer 21, the chain guiding is pulled back so that the chain can be laterally deflected:
In an embodiment not shown herein the chain 32 is alternatively or additionally driven by the lower wheel 34, so that the chain between the lower and the upper wheel 33, 34 is under tension and stiffened over the acceleration distance.
The second passage 15 of the moveable matrix 13 opens from the intersection to the input and output 17, respectively. Thereby the workpiece is held free of clearance in the area of the cutting edge, while for longer workpieces a displacement of the end of the workpiece outside the matrix 13 is avoided during impact cutting. Thereby the mass to be accelerated during the impact is reduced and the required impulse-energy for longer workpieces is widely independent from the length of the workpiece to be separated.
In the recess 18 a damping element 19 is arranged which absorbs the impact impulse or the part of the impact impulse, which has not been transformed into separation and deformation energy during the impact, and transforms it into heat. The damping element 19 countervails with very high power against the displacement of the moveable matrix 13, so that it is completely slowed down within a very short deflection distance, even if there is excessive energy.
After performing an impact onto the moveable matrix element 13 the return of the matrix 13 is carried out by the damping element 19. The retraction may alternatively or additionally be carried out by generating a pneumatic cussion below the moved matrix element 13, as shown in
In addition a sensor 58 is associated to the tool holder 11, which detects the vibrations of the tool holder 11 and/or measures the air pressure in the recess 18. Thus, the presence and the level of the vibrations can be measured while performing the impact. The level of the vibrations is a measurement for the excessive impact energy which has not been transformed for the separation of the workpiece. As excessive energy has to be preferably avoided, the signal of the sensor 58 is used for optimization of the parameters of the impact cutting machine as well as for controlling the function of impact cutting. As shown in
The acceleration of the hammer 21 (the same applies for the hammers 69, 70) is carried out in that the hammer and carrier 36, respectively, is in the starting position and the acceleration operation starts by means of the motor 82. Therein, also with small required impact impulses (for example with a thin workpiece) it is possible to start from a maximal retraction position in order to be able to accelerate over a long acceleration distance with low acceleration power. If however a high impact frequency is required, an acceleration distance as short as possible (low starting position of the hammer 21) is chosen in accordance with the required impact impulse, so that the acceleration and retraction operation can be carried out in a short time. A high acceleration acts then on the hammer.
On the level of the lower deflecting wheel the deflection of the chain 32 causes the slide 36a being pulled back and thus the carrier 36 being retracted from the recess 28 (e.g.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP03/02177 | 3/4/2003 | WO | 9/1/2005 |