Patent Application
20080188164
The invention relates to a method and a unit for grinding treatment of a cutting tool, in particular a knife.
As is well known, the blade or the edge of a cutting tool are to be finished by means of grinding. By such a grinding process, the blade of the cutting tool not only obtains its final shape, but also the surface quality of the blade or the cutting edge is finally set.
For the purposes of the invention, cutting tools are in particular knives. But also other cutting tools, as for instance scissors, are included in the method according to the invention.
For the purposes of the invention, the term “knife” is to be understood in its general form and comprises the most varied types of knives, as for instance kitchen knives, cooking knives, fish knives, meat knives, boner knives, chopping knives, etc., while this list is not final.
According to the method for grinding treatment known from the prior art, the edge finish for high-quality knives is obtained by a two-stage grinding process. In the first stage, the left and the right side of the blade or the edge of the knife are ground one after the other, such that a double conical cross-section is created. Within the scope of the grinding process, certain nominal dimensions, regarding for instance the thickness of the back or the thickness of the facet of the blade, are set. The grinding tool used are so-called cup wheels, where the grinding material is formed in the shape of a ring with a diameter of 450 mm to 710 mm, depending on the size of the knives. The cup wheel has a bevel, so that the knife is inclined by a certain angle with respect to the vertical of the grinding wheel axis. As a result of this geometric arrangement, the ground shape of the two sides of the blade are slightly convex in dependence on the diameter of the wheel. The geometry of the blade in longitudinal direction is also compellingly predetermined by the grinding wheel geometry. The reason why this arrangement known from the prior art is sensible is, among other things, because a certain stability of the blade against bending is achieved despite a thinly ground facet of the blade. Thus, this bending stiffness is compulsorily achieved from the spatial arrangement of the knife and the grinding wheel geometry.
In a second stage, the blade is dry-fined on both sides with a similar geometry. “Dry-fining” means that the surface roughness of the sides of the blade ground in the first stage is now levelled by means of a finer abrasive grain size. As a result of dry-fining, the roughness parameters decrease from approx. 10μ to approx. 2μ. The superposition of the grinding pattern with the dry-fining pattern results in a surface quality which is distinguished by an increased corrosion resistance of the blade surface due to decreased surface roughness.
The two-stage process known from the prior art, which is preferably carried out on robot-assisted machines, adversely runs up funds for machines and costs in relation to machine operation, consumption of abrasives, coolant supply, required floor space, and correspondingly causes frequent downtimes due to multiple set-up operations. Moreover, with the arrangement known from the prior art, it is not possible to individually form different blade or edge geometries. In addition, the process step of dry-fining generates a lot of dirt, requiring complex cleaning both of the machines and of the finished cutting tools.
Starting from the state of the art described above, it is the main objective of the invention to provide a method for grinding a cutting tool, in particular a knife, which allows the formation of individual blade or edge geometries and at the same time is comparatively less costly. In addition, the invention is supposed to propose a unit for grinding the blade of a cutting tool, in particular a knife.
For the solution of the aforementioned problem as regards the method, a method for grinding a cutting tool, in particular a knife, is proposed, where the cutting tool is brought into contact with the active surface of a grinding device, whereby the cutting tool and the grinding device are moved relative to each other in at least three degrees of freedom.
The execution of the method according to the invention advantageously allows the formation of any cutting tool geometries, i. e. blade and/or edge geometries. In addition, the cutting tool can be finished by means of the method according to the invention such that the process stage of dry-fining required according to the method known from the prior art can be omitted completely. Moreover, a very short processing time, i. e. treatment time, can be achieved by the method according to the invention in comparison with the prior art, so that the method according to the invention is extremely effective. Experiments have shown that the treatment time can be reduced by 50% by the method according to the invention.
The method according to the invention is characterised in that the cutting tool and the grinding device are moved relative to each other in at least three degrees of freedom. Depending on the unit used, this can be achieved in the most varied manners. It may be provided for instance that the cutting tool does not move at all. In this case, the grinding device moves rotationally around an axis of revolution on the one hand, and translatorily in at least two directions which are transverse to each other, on the other hand. By a superposition of these three motions of the grinding device, the cutting tool can be treated to form an individually predeterminable, i. e. arbitrarily predeterminable grinding geometry.
Alternatively to the execution of the method as described above, it may also be provided that the grinding device is stationary, i. e. it does not move. In this case, the cutting tool is moved both rotationally around an axis of revolution, and translatorily in two directions of motion which are transverse to each other. The result of this superposition of motions carried out by the cutting tool is also a cutting tool with an individually, i. e. arbitrarily formed geometry.
In a third alternative embodiment of the invention, both the cutting tool and the grinding device are moved. In this process, both the cutting tool and the grinding device are preferably moved rotationally around respective related axes of rotation. In addition, both the cutting tool and the grinding device are moved in a translatory manner, whereby it may be provided that the grinding device is moved translatorily in a first direction of motion, and the cutting tool is moved translatorily in a second direction of motion, whereby the first and the second direction of motion are transverse, preferably orthogonal to each other. It may also be provided that both the cutting tool and the grinding device are each moved translatorily in two directions of motion which are transverse to each other.
What is decisive for the method according to the invention is that the grinding device and the cutting tool are moved independent of each other, whereby an individual, i. e. arbitrarily predeterminable, final grinding geometry of the cutting tool is achieved by the superposition of the relative motions carried out by the grinding device and/or the cutting tool. With this in mind, the term “degree of freedom” means the relative degree of freedom resulting from the superposition of the possible motions of the cutting tool on the one hand and the grinding device on the other hand.
As already indicated above, the relative motion resulting between the active surface of the grinding device and the surface of the cutting tool to be treated can be generated in different ways. It may for instance be provided that the grinding device is moved rotationally and/or translatorily. It may also be provided that the cutting tool is moved rotationally and/or translatorily. It is not essential for the invention in which combination these possible movements are superposed. It is solely important that the grinding device and the cutting tool are moved rotationally or translatorily, respectively, so that as a result, a superposition of motions is achieved which is suitable to form the desired cutting tool geometry, in particular the blade geometry. For this purpose, it is provided according to a special feature of the invention that both the grinding device and the cutting tool are driven rotationally, and in the same direction, to be precise. Furthermore, the grinding device is movable in a direction transverse to the direction of motion of the cutting tool. Moreover, in order to form a special blade geometry, it may be provided that the cutting tool is moved rotationally around another rotational axis. To this extent, there are no limits to imagination.
According to a special design, the invention provides a method where the blade sides to be treated of a cutting tool clamped in a holding device are guided past a rotatably arranged grinding device, while the active surface of the grinding device is essentially brought into line contact with the blade side to be treated, and the grinding device moves translatorily and transversely to its axis of revolution in dependence on the blade geometry.
In accordance with this execution of the method, the blade side to be treated of the cutting device clamped in a holding device is guided past the active surface of the grinding device in a traversing movement. The grinding device is for instance formed like a rotating cylinder, preferably annular, whereby the face side surface of the annular cylinder comprises the abrasive as its active surface. In the course of guiding the blade side to be treated past the active surface of the grinding device, it is essentially brought into line contact with that active surface.
The holding device and the grinding device are driven in such a way that in the course of the execution the method, the line contact between the blade to be treated on the one hand and the grinding device on the other hand moves across the surface of the blade side to be treated in a direction transverse to the longitudinal extent of the blade. In the course of the execution of the method, the grinding device and/or the holding device travel, preferably computer-controlled, translatorily and transversely to the axis of revolution of the grinding device in dependence on the blade geometry to be produced, that is the grinding device and/or the holding device are moved back and forth in the direction of the blade side to be treated, or in the opposite direction. By a superposition of this translatory motion of the grinding device with the motion of the holding device, a blade geometry as desired can be produced in a favourable manner.
In accordance with a first alternative of the execution of the method as described above, it is provided that the holding device is rotatable and that the cutting tool is guided past the grinding device, i. e. the active surface of the grinding device, on an at least partially circular path. According to this embodiment, both the holding device and the grinding device are designed rotatably. In this context, the holding device and the grinding device are preferably driven in the same direction, so that the grinding device and the cutting tool supported by the holding device perform a contra-rotating relative movement in the area of their line contact.
In the course of the execution of the method, the area of the future facet of the blade to be treated is initially brought into line contact with the active surface of the grinding device. In order to be able to form as sharp, i. e. as thin a facet of the blade as possible, the grinding device is juxtaposed with the blade side to be treated. In the further course of the process, the blade side to be treated is guided past the active surface of the grinding device, while maintaining the line contact. In order to form for instance a convex blade geometry, the grinding device, in the course of being guided past the blade side to be treated, moves translatorily and transversely to its axis of revolution in a direction pointing away from the blade side to be treated. In the course of the execution of this method, a blade geometry with a thinly ground facet of the blade and an otherwise comparatively thickly ground blade or edge body is produced.
The advantage of the method described above is that, depending on the feed motion of the grinding device and/or of the holding device, any blade geometries can be formed. Contrary to what is known from the prior art, not only convex blade geometries can be formed, but it is rather possible to create arbitrary blade geometries. So for instance, wedge geometries with a pointed or truncated cross-section, trapezoidal geometries, or other geometries can be produced. In addition, it is possible to machine the transition between the blade side and the back of the blade for instance in the form of a rounding. Such possibilities for treatment do not exist with the methods for grinding known from the prior art.
Furthermore, it is of advantage that the wear of the grinding device can be compensated by a translatory adjustment motion transverse to the axis of revolution of the grinding device. The grinding result is therefore not affected by the wear of the grinding device. The feed motion and the adjustment motion of the grinding device are superposed within the scope of the execution of the method to form one overall movement, so that regardless of the wear of the grinding device, the grinding result is always the same.
Another advantage of the method according to the invention is that not only continuous blade geometries can be formed. It is also possible to form visible edges running in transverse or longitudinal direction of the blade. These visible edges are the result of a partly higher material density the effect of which, from a technical point of view, is a stiffening, similar to a stiffening rib or a bead. Such a design is advantageous in particular when forming comparatively thin blades or edges of cutting tools, since the general rule applies that a comparatively thin blade produces a much better cutting result than a thick blade. Thin blades, however, have the disadvantage that they have a low bending moment and torsional moment of area corresponding to the blade thickness. As a result, a thin blade is likely to bend during the cutting process, which is regarded as disadvantageous by the user, since he has less control of the knife as a whole. Grinding treatment according to the method of the invention remedies the matter. This method allows a reinforcement positioned outside of the area of the facet of the blade which will stiffen the cutting tool blade as a whole, so that it is less susceptible to bending or torsional stress. Comparatively thin tool blades or edges can thus be stiffened via the biaxial moment of area or the polar moment of area, respectively. As a consequence, knives can be produced which, due to the comparatively thin blade, have good cutting properties, while they are very rigid at the same time due to their stiffening, Such knives have previously not been known from the prior art. Blades with an asymmetric cross-section can also be produced with this method.
The transition between the blade side and the back of the blade can be formed as desired, for instance rounded. The grinding treatment of the transition between the blade side and the back of the blade is enabled by a feed motion of the grinding device in the direction toward the blade side to be treated, as a result of which the blade side is treated in the direction toward the back of the blade. Depending on the feed motion, a rounded transition or also a sloping transition between the blade side and the back of the blade can be formed.
Contrary to what is known from the prior art, the grinding device can be driven at a very high rotating speed. This is possible because the grinding device, contrary to what is known from the prior art, is essentially only brought into line contact with the blade side to be treated. The grinding device which is designed for instance in the form of a cylinder can therefore have a much smaller diameter than the cup wheels known from the prior art, which allows for a much higher speed. The advantage of the higher rotating speed is that, when using an appropriate abrasive which is arranged on the outer surface of the cylinder of the grinding device, the blade side to be treated can be ground in one process step in dry-fining quality. Contrary to what is known from the prior art, it is therefore not required to carry out the edge or blade finish in a two-stage grinding process when using the method according to the invention. Cost-intensive retooling processes can thereby be omitted in a favourable manner.
The grinding device is preferably designed as a conically tapering cylinder. This form of the grinding device automatically results in a blade geometry tapering toward the tip of the blade.
According to an alternative embodiment it is provided that the holding device is arranged movably in at least two directions which are transverse to each other, and that the cutting tool is guided past the active surface of the grinding device in a superposition of these two directions of motion. In contrast to the first alternative described above, the holding device is arranged not in a rotatable, but in an exclusively translatorily movable manner. At the same time, it is provided that the holding device is movable in at least two directions which are transverse to each other, so that by a superposition of these two directions of motion, the cutting tool accommodated by the holding device is preferably guided on an at least partly circular path. Although the holding device itself is not arranged in a rotatable manner, the cutting tool accommodated by the holding device is guided past the grinding device on a preferably circular, but at least partly circular path, whereby this path is the result of the superposition of the translatory motions of the holding device. The advantage of this embodiment is that the entire mechanical equipment, i. e. in particular the machine parts supporting the holding device, can be designed much stiffer. In this manner, deviations from the desired grinding geometry, which might possibly result from an insufficient stiffness of the entire unit, are avoided. Also with a superposed translatory motion of the holding device, the grinding result corresponds to that achieved by a rotatable holding device, so that the advantages already described above can also be achieved by the alternative embodiment of the invention. Regardless which variant of the method is used, what is solely crucial is that the grinding device is essentially brought into line contact with the blade side of the cutting tool to be treated and is moved translatorily and transversely to the axis of revolution of the grinding device in dependence on the blade geometry to be produced.
According to another feature of the invention, it is provided that in a first grinding treatment, one blade side, and in a second grinding treatment, the other blade side is finished in one step. The cutting tools to be treated are initially clamped into the holding device provided for this purpose for grinding one blade side. Then the grinding process is carried out in the manner described above. When this is completed, the cutting tools are re-clamped for treatment of the other blade side, and this still untreated blade side is treated in another grinding process.
If the holding device is designed in a rotatable manner according to the first embodiment of the invention, it may be provided that in addition, it is arranged translatorily movable transverse to its own axis of revolution. In this manner, the holding device including the clamped cutting tool can be moved toward the grinding device in the beginning of the grinding process. The feed motion effected within the scope of the grinding process is then realised solely via the translatorily movable arrangement of the grinding device. If according to the second alternative method, the holding device is arranged translatorily movable in at least two directions which are transverse to each other, the feed motion carried out in the course of the grinding process can be effected both via the translatorily movable arrangement of the grinding device and via the translatorily movable arrangement of the holding device. A combined movement of the holding device and the grinding device is also imaginable.
In accordance with another feature of the invention, it may be provided that the motions of the grinding device and/or of the cutting tool are carried out in an oscillating manner, namely as regards both the rotational and the translatory motion. The frequency of the oscillating motion can be adjusted in an advantageous manner and can also be changed during the grinding process. In relation to the rotary motion of both the grinding device and the cutting tool, it may be provided in this context that the oscillating motion is carried out around a specified angle, i. e. that the grinding device and the cutting tool, respectively, are moved up and down, so to speak. The same may be provided for one or more of the translatory motions, resulting in a back and forward motion.
For the solution of the aforementioned problem as regards the unit, a unit for grinding a cutting tool, in particular a knife, is proposed with a holding device for accommodating the cutting tool to be treated and a grinding device, whereby the holding device and the grinding device are arranged movable relative to each other with regard to at least three degrees of freedom.
As already described on the basis of the method according to the invention, the characteristic of the unit according to the invention consists in the fact that the holding device accommodating the cutting tool to be treated is movable relative to the grinding device, whereby the holding device and the grinding device are arranged movable relative to each other with regard to at least three degrees of freedom. This design makes it possible to position the active surface of the grinding device in any position relative to the cutting tool to be treated. As a result, an arbitrary cutting tool geometry can be formed using the unit according to the invention. In particular, the blade sides of the cutting tool can be treated, whereby it is possible to form convex, concave, prism-shaped blade sides and the like. To this extent, there are no limits to imagination. In addition, the blade sides may be provided with a visible edge which technically assumes the function of a reinforcing rib or a bead. In this manner, also relatively thinly ground edges can be produced which, thanks to the reinforcing rib or bead, have a high bending moment or torsional moment of area, so that the cutting tools are resistant to bending or torsion despite their relatively thin blade geometry.
According to a special feature of the invention, the holding device of the unit according to the invention is formed like a cylinder, preferably like a drum cylinder. The outer surface of the cylinder carries several holding elements for a preferable accommodation of several cutting tools to be treated.
The holding device is designed rotatably, whereby in case that the holding device is designed as a cylinder, a rotational movement of the holding device around the longitudinal axis of the cylinder is possible. During a rotational movement of the holding device, the cutting tools are guided past the active surface of the grinding device.
According to another feature of the invention, the grinding device is formed like an annular cylinder, whereby the outer surface of the ring forms the active surface of the grinding device provided with an abrasive. The grinding device is designed translatorily movable in a direction which is transverse to the axis of revolution, so that by the superposition with the traversing movement of the holding device, any point of the blade surface of the cutting tool can be travelled to.
According to another feature of the invention, it is provided that either the cutting tool or the grinding device can be tilted around the respective axis of revolution. In this manner, a skew orientation between the blade side of the cutting tool to be treated on the one hand and the active surface of the grinding device, on the other hand, can be set. This makes it particularly easy to form varying blade widths in the longitudinal direction of the cutting tool.
According to the invention, the unit comprises a computer unit for controlling the rotational and translatory traversing movements of the holding device and/or the grinding device. Therefore, the entire grinding process can be carried out computer-controlled in a fully automated manner.
The unit according to the invention proves to be advantageous in comparison with the prior art in particular because the cutting tool can be ground in a comparably short time. In contrast to the prior art, the grinding process can be shortened by up to 50% by the unit according to the invention. The unit according to the invention thus proves to be much more effective than the units known from the prior art.
Another advantage of the unit according to the invention is to be seen in the fact that the grinding device which is preferably formed as an annular cylinder can be driven at a comparatively high speed. Due to this circumstance, the active surface of the grinding device can be provided with a fine grit abrasive. As a consequence, the cutting tool to be treated with the unit according to the invention can be finished in only one process step. Reworking, for instance in the form of dry-fining, can be omitted completely. Therefore, the execution of the method using the unit according to the invention also proves to be very cost-effective.
Other features and advantages of the invention result from the description on the basis of the following figures. In these figures:
a is a schematic diagram of the unit according to the invention in accordance with a second alternative;
a is the exemplary design of a blade cross-section according to a fifth embodiment;
b is the exemplary design of a blade cross-section according to a fifth embodiment, as a variation of
The method according to the invention and the unit according to the invention are described in an exemplary manner on the basis of the following
The unit shown schematically in
As shown in
Grinding device 12 is formed like a conically tapering cylinder, as can be seen in particular from
The method for grinding according to the invention is carried out as described in the following:
For the purpose of machining the first side of blade 2, the knives 1 to be treated are clamped using the correspondingly formed holding elements on holding device 11. Subsequently, holding device 11 and grinding device 12 are set in rotary motion. Holding device 11 with the knives 1 arranged on it is moved toward grinding device 12. At this time, there is no contact between knife 1 and grinding device 12, yet.
Due to the rotary motion of holding device 11, the blade sides to be treated of the the knives 1 arranged on it are guided past grinding device 12 on a circular path. For the purpose of grinding, grinding device 12 is now brought into line contact 17 with the blade sides to be treated of knife 1; for this purpose, grinding device 12 is moved toward holding device 11 according to the direction of motion 14. As a result of the rotary motion of holding device 11, the knives 1 to be treated are initially brought into contact with grinding device 12 in the area of their future facet of the blade. While as a result of the rotary motion of holding device 11, the blade sides to be treated are guided past grinding device 12, the latter is translatorily moved away from holding device 11 in direction of motion 14. As a result of this motion of grinding device 12, blade 2 is provided with a geometry as is shown by way of example in
Alternatively to carrying out the method as described above, it may also be provided that the grinding device 12 is additionally moved in vertical direction 23.
According to an alternative variant of the unit shown in
As already described above on the basis of
The special advantage of the method according to the invention is that almost any arbitrary blade geometry can be formed, since it is based solely on the selected feed motion and the diameter of grinding device 12 in direction of motion 14. The closer grinding device 12 is brought to the knives to be treated in the course of the execution of the method, the more material will be removed. In addition, the future blade geometry can be determined precisely via the feed motion of grinding device 12, and thus for instance continuously extending blade sides can be formed, as they are shown for instance in
In contrast to what has been known from the prior art, according to the method according to the invention, the blade sides to be treated and the grinding device are essentially brought only into line contact. A full-surface treatment of blade 2 does not occur. It can be seen from
Grinding device 12 is designed as a conically tapering cylinder, resulting automatically in a blade geometry with a cross-section tapering in the direction of the blade tip. The outer cylinder surface 18 of grinding device 12 is provided with abrasives of a corresponding grain size. Since grinding device 12 is only in line contact with blade 2 to be treated, the outer diameter of grinding device 12 can be formed correspondingly small. This allows for a comparatively high rotating speed of grinding device 12. Due to the comparatively high rotating speed of grinding device 12, the abrasive particles arranged on the outer surface 18 can be of a very small size. In this manner, knife blade 2 can be ground and dry-fined in only one process step. Two-stage machining, i. e. initially grinding and then dry-fining, is advantageously not required.
When one side of blade 2 has been finished in accordance with the execution of the method described above, the knives I are to be re-clamped for treating the other blade side. Then the other side of blade 2 is treated in the manner described above.
a show exemplary representations of possible blade geometries.
It is also easily possible to produce asymmetrically formed blade geometries by the method according to the invention, as is shown by way of example in
The method according to the invention also makes it possible in an advantageous manner to machine the transition between the blade side on the one hand and the blade back 7, on the other hand. The latter can for instance be bevelled, as shown in
In addition, using the method according to the invention, the transition between blade 2 and bolster 3 can be treated in one process step. This transition, as can be seen from
In the course of the execution of the method, the grinding device 12 wears off. In order to always obtain consistent and reproducible grinding results, however, the wear of grinding device 12 must be compensated. According to the invention, this is achieved by adjusting the grinding device 12 in dependence on the occurring signs of wear, and/or adjusting it in direction of motion 14. Adjustment motion and feed motion of grinding device 12 are superposed to form a traversing movement to be overall performed, which is set automatically and computer-assisted. In order to determine the adjustment motion to be set for compensating the wear of the grinding device, corresponding sensors are provided, so that the method according to the invention can be operated fully automatically.
The workpiece unit 45 comprises the holding device 11, which in turn supports the cutting tool 1 to be treated or the cutting tools 1 to be treated, respectively. The holding device 11 is formed as a drum cylinder and accommodates on its outer surface side the cutting tools 1 to be treated.
The holding device 11 is coupled to a drive unit 38, which is for instance designed as a motor. The drive unit 38 drives the holding device 1 in a rotational manner, namely in the direction of motion 39 around the rotational axis 37.
Holding device 11 and the associated rotational drive 38 are flanged to a machine stand 36. This machine stand 36 is supported by a machine bed and can be moved translatorily in direction of motion 41. The machine stand 36 is translatorily movable around its vertical axis in direction of motion 40 and can be moved around the angle γ. Since holding device 11 is flanged to the machine stand 36, the motion of the machine stand 36 is transferred to holding device 11, so that the latter can be moved as a whole both rotationally and translatorily, as described above.
The tool unit 46 essentially comprises the grinding device 12. The latter is formed essentially annularly, whereby the outer surface of the ring carries the abrasive as active surface 29. The grinding device 12 is arranged rotatably around rotational axis 32, whereby a drive unit 31, preferably in the form of a motor, is provided to drive the grinding device 12.
In addition, grinding device 12 can be moved translatorily, namely in the direction of motion 30, which is transverse, preferably orthogonal, to rotational axis 32.
The tool unit 46 furthermore comprises a dresser 33. This dresser 33 is formed annularly, like the grinding device 12, and arranged rotatably around rotational axis 35 by means of a drive unit 34. The outer surface of the annular dresser can be brought into contact with the active surface 29 of grinding device 12, if required, in order to dress grinding device 12; for this purpose, grinding device 12 can be moved to the dresser 33 in direction of motion 30.
As a third component, the unit 28 comprises the operating unit 47. The latter essentially consists of a control cabinet 42 accommodating the electronic components. This control cabinet 42 is provided with a control panel 44, from which the entire device 28 can be computer controlled. As regards communications, the electrical control cabinet 42 is connected both with the workpiece unit 45 and with the tool unit 46 via corresponding cable connections which are routed in a cable duct 43.
An alternative embodiment of the unit according to the invention is shown in
Both in the embodiment according to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 043 157.4 | Sep 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2005/009462 | 9/2/2005 | WO | 00 | 2/6/2008 |
