Patent Application
20130213198
The invention concerns a device for processing workpieces using ultrasound, comprising a first tool part and a second tool part, wherein the first tool part can be moved by a carriage in the working direction thereof, and towards the second tool part.
Devices for processing workpieces are disclosed in EP-A 1 108 494, EP-A 1 466 709, DE-A 696 21 134, DE-U 295 07 068, DE-A 35 29 686, DE-A 197 16 018, WO-A 96 109 919, EP-A 1 112 823, DE-A 195 81 256, DE-A 44 39 284, WO-A 96 014 202, DE-A 10 2004 013 050, DE-A 10 2004 013 049 and DE-U 202 06 561. Devices of this type are used to process (in particular cut) thermoplastic materials, fabrics, paper and the like. It is thereby desired to reduce the cutting forces and/or optimize the cutting edge by using ultrasound.
One conventional technique is the free cut, wherein an ultrasound tool is designed as a cutting tool, and a material sheet or a workpiece is cut without a counter tool. The ultrasound tool, which is designed as an ultrasound knife, thereby moves relative to the workpiece in the direction of the cutting line. The ultrasound tool may also be designed as a rotating knife. In this case, an additional rotary movement is performed. This free cut is mainly used for cutting fabric webs. In this method, the cutting force results mainly from the cutting speed, the cutting geometry, the cutting angle and the workpiece itself.
A further conventional technique is the shaped cut with a counter tool, wherein an additional cutting pressure is generated between the ultrasound tool and the counter tool. In this fashion, cutting forces of almost any strength can be generated through either a force-dependent feed motion or via a fixed gap between the ultrasound tool and the counter tool. The workpiece to be processed is forced through this gap.
A further technique is the continuously formed cut. The ultrasound tool may thereby be designed as for a free cut, e.g. as an ultrasound knife. However, an additional force is exerted on the workpiece to be processed by urging the workpiece between the ultrasound knife and the counter tool. The cutting pressure is thereby considerably increased. The counter tool may thereby be designed as a simple plate or a rotating cylinder. The ultrasound tool may also be designed without a cutting geometry, wherein the cutting geometry is provided in the counter tool.
In a further conventional technique, a cycled cut is performed. A cutting force is thereby generated in cycles between the ultrasound tool and the counter tool. The cutting geometry may thereby be provided in the ultrasound tool and/or in the counter tool. In this method, the workpiece is processed in one, two or even three dimensions. An oscillating amplitude of the tool having a predetermined resonance frequency of e.g. between 20 and 60 kHz is applied to the workpiece and counter tool which is in addition to and which overlies the cutting force. The ultrasound tool moves by one stroke length towards the counter tool during the cycle. In this case, the counter tool is rigidly installed and does not move. When the ultrasound tool and the counter tool contact, the workpiece is usually separated. The ultrasound tool may also be rigidly clamped and the force and travel path may be performed by the counter tool. In both variants, one tool is rigidly clamped and the feed motion and cutting force is provided by the other tool.
The travel path may also be limited. This can be effected e.g. using an end stop that can be exactly adjusted, or through carriages which can be exactly positioned and fixed, and are driven e.g. by a spindle having a servomotor. This permits adjustment of a certain weld gap. When the workpiece must be completely separated, this weld gap is adjusted to zero or almost zero.
These techniques have proven to be problematic in that, when the workpiece has been separated, the ultrasound tool and the counter tool contact each other. The cutting force urges the surfaces together, which meet with the prevailing frequency of 20 to 60 kHz. This produces uncontrolled forces, motion and oscillations which are i.a. also audible. The ultrasound tool and also the counter tool are worn within a very short time due to notches and deformations that are formed in the contact surfaces. This wear can be reduced, but not completely prevented through hardening of the contact surfaces, e.g. through a coating or a harder steel. Moreover, only a limited number of materials or degrees of hardness may be used for ultrasound processing, since the materials which can be used for the tools are very limited. The cutting quality greatly decreases with increasing wear of the tool. For this reason, the tool must be frequently replaced.
Electronic regulation is feasible to reduce wear, and has partially been realized. However, fast switching-off of the ultrasound, fast cancellation of the cutting force or fast removal of the ultrasound tool from the counter tool cannot prevent contact. There are still a relatively large number of contacts due to the high frequency of the ultrasound tools. If e.g. during processing with a frequency of 20 kHz, the return motion of the ultrasound tool is started within 1 ms, there will still be 20 contacts between the ultrasound tool and the counter tool during this 1 ms.
Moreover, it has turned out to be difficult to exactly adjust the ultrasound tool relative to the counter tool in order to solve the contact problem, since the position of the components relative to each other is influenced by a plurality of variables. When e.g. the ultrasound tool is heated, the gap height changes due to expansion which has a direct effect on the cutting quality. Other variables are the ambient temperature, the process temperature, force fluctuations etc.
It is therefore the underlying purpose of the invention to provide a device for processing workpieces using ultrasound and/or a method for operating such a device that improves the cutting quality and prolongs the service life of the tools.
This object is achieved witha device for processing a workpiece using ultrasound, which comprises:
In accordance with the invention, the resonance frequency of the anvil with counter tool is smaller than the resonance frequency of the oscillating structure, in particular by a factor 102 to 104, preferably by a factor 103. This design is substantially advantageous in that the working surface of the counter tool rests on the position of maximum deflection, i.e. at the apex of the working surface of the ultrasound sonotrode, since due to the low eigen frequency of the counter tool, the counter tool cannot follow the high-frequency motion of the ultrasound sonotrode. The eigen resonance of the anvil system is considerably smaller than the eigen resonance of the ultrasound oscillating structure, in particular, the ultrasound sonotrode. This prevents uncontrolled oscillation of the counter tool.
The first tool part is thereby an oscillating ultrasound structure with an ultrasound sonotrode or an anvil with a counter tool, and the second tool part is an anvil with a counter tool or an ultrasound oscillating structure with an ultrasound sonotrode.
A preferred embodiment of the inventive device offers the substantial advantage that the counter tool is not rigidly held, but exerts a force in the direction of the ultrasound sonotrode which means that the counter tool can give way even when this force is exceeded by the ultrasound sonotrode. When the clearance changes e.g. due to temperature fluctuations, the counter tool either follows or gives way to the ultrasound sonotrode, thereby maintaining high cutting quality and considerably reducing the wear on the working surfaces of the tools.
In a further development, the force of travel of the carriage is greater than the feed force of the force storage, in particular, by a factor of 1.2 to 5.0, preferably 1.5 to 2.0. For this reason, the counter tool gives way and not the ultrasound sonotrode when the ultrasound sonotrode is supplied and/or the workpiece is inserted between the ultrasound sonotrode and the counter tool. This prevents damage to the working surfaces. The force of travel of the carriage is thereby at least 50 N, in particular 200 N to 5000 N, preferably 800 N to 2000 N.
In accordance with an embodiment of the invention, the force storage is a pneumatic and/or hydraulic spring or a magnet, in particular, an electromagnet. The force to be provided by the force storage is thereby dimensioned to be much smaller than the force of travel of the carriage or of the ultrasound sonotrode, wherein the force provided by the force storage represents the cutting force.
Typical cutting forces range from 10 N to 2000 N. The cutting forces thereby increase with increasing thickness of the workpiece. The force storage formed by the mechanical spring may e.g. be a spiral spring, a plate spring or a leaf spring. In particular, the force of the force storage can be adjusted to desired values.
Oscillation is also advantageously reduced, when the anvil and, in particular, the force storage have a damping element for the counter tool. This damping element may also be generally disposed in the anvil system, e.g. as a damping element on the counter tool, in particular as a frictional damper. In another simple solution, the bearings are designed such that the bearing friction has the damping properties.
In accordance with a preferred embodiment, the ultrasound sonotrode and the counter tool can be moved exclusively coaxially towards each other. This is achieved through high-quality guidances within the ultrasound oscillating system and within the anvil system. The quality of the cut or welding is thereby substantially increased. The ultrasound sonotrode and/or the counter tool may thereby have a cutting edge and/or a welding edge.
In a further development, a fixed stop is provided for the carriage which moves the ultrasound sonotrode. This provides a defined feed and adjustment of the exact weld or cutting gap, and moreover optimally fixes the ultrasound sonotrode.
To further optimize the cutting speed and/or reduce wear of the tool, the transient time of the ultrasound system may be extended or the amplitude and/or cutting forces may be varied in dependence on time during the cut. At the end of the cut, the cutting force and/or the amplitude are e.g. reduced. Longer transient times are advantageous in view of wear, but prolong the cutting time.
The welding surfaces may additionally be provided in the same tool having the cutting edge, or additional tools having a welding surface may be provided.
The above-mentioned object is also achieved in accordance with the invention with a method for operating the above device, in that the ultrasound sonotrode moves the counter tool into a working position, in particular, via the workpiece, thereby exerting a feed force onto the workpiece.
The ultrasound sonotrode is thus fed until it contacts the workpiece and additionally also moves the counter tool, thereby pressing onto the workpiece with a predetermined feed force. During this process, the counter tool is moved by a working path. Deflection of the counter tool ensures that the workpiece, which is pressed onto the ultrasound sonotrode via the counter tool, is completely processed, in particular, completely separated. Temperature-related length changes can be neglected in the entire system. The small eigen frequency resulting from mass, spring rate and damping of the counter tool, prevents the working surfaces from being damaged, since the counter tool remains at the outermost apex of the ultrasound tool.
Further advantages, features and details of the invention can be extracted from the dependent claims and the following description which describes in detail two particularly preferred embodiments with reference to the drawing. The features shown in the drawing and mentioned in the description and the claims may thereby be essential to the invention either individually or collectively in arbitrary combination.
The ultrasound oscillating structure 14 and anvil 16 have parallel axes, and are, in particular, coaxial to each other. The adjusting device 36 can press the counter tool 42 onto the workpiece 12 with a predetermined force, in particular, a feed force FS. This feed force FS is stored in the force storage 40.
The figure also shows that the counter tool 42 is disposed in the machine frame 18 in a bearing 48, such that it can be moved in the direction of the vertical axis 46, wherein the bearing 48 has a bearing friction for damping D. The counter tool 42 has a mass m. The force storage 40 moreover has a spring constant c, which results in a resonance frequency fA=f(m,c,D) for the anvil 16 which is determined from the mass m of the counter tool 42, the spring constant c of the force storage 40, and damping D of the bearing 48.
The function of the device 10 in accordance with
The ultrasound sonotrode 32 is subsequently put into operation such that the working surface 34 oscillates with the adjusted ultrasound, as is indicated at 50. The workpiece 12 is thereby separated and the working surface 44 of the counter tool 42 penetrates into the workpiece 12. The cutting force FS is provided only by the counter tool 42, since the ultrasound sonotrode 32 abuts the fixed stop 26.
As soon as the workpiece 12 has been separated, the working surfaces 34 and 44 temporarily contact, wherein, however, the counter tool 42 remains in this position. The counter tool 42 cannot follow the high-frequency oscillating working surface 34 of the ultrasound sonotrode 32, since the eigen frequency or resonance frequency of the counter tool 42 is substantially lower, in particular by a factor 103, than the oscillating frequency of the ultrasound sonotrode 32. For this reason, the working surface 44 remains at rest. This can be obtained through suitable selection of the mass m, the spring constant c and damping D. Since contact between the working surfaces 34 and 44 cannot be prevented, they have a hardness of at least 55 HRC, which also prevents excessive wear thereof.
In one variant, the working surface 44 of the counter tool 42 is designed not only as a cutting edge but also has a welding surface, such that the counter tool 42 can be used to both cut and weld. In this fashion, workpieces 14 that consist of several layers can be simultaneously cut and the individual layers can be welded together. This is desirable in particular for hose bag systems, wherein the individual hose bags are filled and subsequently separated.
The anvil of
The converter 30 and the ultrasound sonotrode 32 have a mass m. The force storage 40 has moreover a spring constant c. This yields a resonance frequency fU=f(m,c,D) for the ultrasound oscillating structure 14, which is determined from the mass m of the converter 30 and the ultrasound sonotrode 32, the spring constant c of the force storage 40 and damping D of the bearing 48.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 020 429.8 | Apr 2006 | DE | national |
| 10 2006 041 655.4 | Aug 2006 | DE | national |
This application is a continuation of Ser. No. 12/588,063 filed Oct. 2, 2009 which is a divisional of 11/730,935 filed Apr. 5, 2007 and claims Paris Convention priority of DE 10 2006 020 429.8 filed Apr. 26, 2006 and DE 10 2006 041 655.4 filed Aug. 24, 2006 the complete disclosures of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11730935 | Apr 2007 | US |
| Child | 12588063 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12588063 | Oct 2009 | US |
| Child | 13850358 | US |
