DE102010017625A1 - Cutting tool, in particular cutting wheel and method for its production - Google Patents

Abstract

The invention relates to a cutting tool, in particular cutting wheel and a method for its production. For smoothing the surfaces and sharpening the cutting edge, a method is used in which at least one side surface is subjected to a laser beam at least in a region adjacent to the cutting edge and in which the laser beam is aligned at a shallow angle to the surface of the side edge. Thus, cutting tools can be produced with improved properties that meet at least one of the following parameters: straightness deviation of less than 2 .mu.m, in particular of less than 1 .mu.m, cutting edge waviness of less than 0.5 .mu.m, in particular less than 0.3 .mu.m , Negative cutting edge blunting on and / or starting distance of the edge rounding of less than 4 microns, especially less than 2 microns.

Description

The invention relates to a cutting tool, in particular cutting wheel and a method for its production. Cutting tools and cutting wheels of the type in question are used in particular for cutting or scoring brittle materials, such as ceramic and / or glass.

To increase performance in such processing and cutting processes defined and preferably along the edge of the tool reproducible or uniform edge geometries are sought. In particular, it is difficult to produce a uniformly sharp geometry.

Previously known from the prior art cutting wheels aim at the smoothest possible cutting edge. This smooth cutting edges can be achieved in particular in glass workpieces.

The patent EP 0 773 194 B1 discloses a cutting wheel made of polycrystalline material, in particular of diamond material, which is provided with a tooth structure along the cutting wheel circumference. With this embodiment of the cutting wheel to slippage of the Schneidrädchens on the surface of the material to be cut during the rolling process caused during the rolling process is to be prevented to improve the cutting result in particular.

A method of manufacturing a cutting wheel having a tooth structure is disclosed in the patent application EP 1 666 426 A1 discloses, according to which the tooth structure is ground by means of a grinding tool in the cutting edge of the cutting wheel. A disadvantage of these known from the prior art cutting wheels, however, is that the cracks generated by the cutting process in the material to be cut lead to breakage edges with an edge quality that is not always optimal for today's applications.

The WO 2009/036742 discloses a cutting wheel having a peripheral structure of protruding teeth and intervening interdental spaces showing improved cutting performance. The WO 2009/036743 discloses a method of manufacturing such a cutting wheel in which, by means of a pulsed laser beam, the surface of a prefabricated cutting wheel without tooth structure is removed at predetermined locations along the cutting edge and in the region of the side surfaces adjacent to the cutting edge. In this structuring of the laser beam is applied substantially at right angles to the side surface in order to achieve the most intensive removal of material and to reduce the production times.

In the manufacture of cutting wheels by means of grinding or laser machining, there is generally the problem of rounding or local breakouts just along the cutting edge and the side surfaces adjacent thereto. These roundings or outbreaks are locally different due to the manufacturing process.

In the manufacture of cutting wheels for scribing glass, there are special requirements for the cutting edge in some problems. If a reproducible but deliberately rough cut is used in some applications - combined with local breakouts along the cutting edge - then in other applications an ideally uniform and sharp cutting edge is sought. Such applications exist for example in cutting wheels for scribing thin glass, which is used for example in the display industry. The invention therefore preferably relates to cutting tools and in particular cutting wheels for the latter application.

Due to the grinding process or by the laser processing occurs in the prefabricated cutting wheels a rounding already in a relatively large compared to the penetration depth of the cutting wheel distance to the cutting edge, which is referred to in this description "start distance Schneidkantenverrundung".

The real center cutting edge thereby recedes from the approximated central cutting edge by a distance, referred to in this specification as "cutting edge blunting".

Due to the irregularity of the cut or the laser processing, the straightening deviation and the cutting edge waviness are quite high.

Thus, the present invention, the technical problem underlying the macrogeometry already prefabricated side surfaces of a cutting tool, in particular a cutting wheel, and a cutting edge formed by the side surfaces to be treated so that the sharpest possible and uniform surfaces having cutting edge.

The technical problem indicated above is achieved by a method for smoothing a surface of a prefabricated cutting tool, in particular a cutting wheel having two side surfaces which run at an angle to each other and form a cutting edge, wherein at least one side surface is at least in an area adjacent to the cutting edge one Laser beam is applied and in which the laser beam is aligned at a shallow angle to the surface of the side edge.

The method according to the invention can therefore also be referred to as laser grinding or laser smoothing. A laser beam is understood to mean a directed beam of electromagnetic radiation, wherein the wavelength does not necessarily have to be in the visible range, but also wavelengths in the infrared or ultraviolet range can be used.

The starting point for the present invention are the previously described cutting wheels for working brittle materials, such as ceramic and / or glass. However, the invention generally relates to cutting tools, which require a high degree of precision of the cutting surfaces and the cutting edges for cutting any materials. Thus, the invention described below can also be applied to tools such as knives, saws, drills, milling tools, cutting inserts and similar tools. In all tools, the processing effect occurs through a sharp-edged cutting edge, even if the process itself is not always referred to as cutting, but as sawing, drilling, machining or turning / milling. The following description of the invention is based on the exemplary application to cutting wheels for working brittle materials, such as ceramics and / or glass, but the invention is not limited to this application.

According to the invention, it has been recognized to remove material by means of a suitable beam guidance in such a way that sharper and more uniform cutting edges can be produced in comparison with the prior art. In this case, places with large Schneidkantenabundungen as well as places with little rounding in about the same edge geometry to be transferred. For this purpose, bumps are smoothed on the two side surfaces of the prefabricated cutting wheel and selectively removed at the cutting edge, especially in areas with large Schneidkantenabrundungen less material.

The effect of smoothing out unevennesses on the two side surfaces and deliberately removing less material at the cutting edge, particularly in areas with large cutting edge roundings, is achieved by guiding the laser beam at a shallow angle, ie relatively tangentially to the surface of the side surfaces of the cutting wheel , Projecting tips on the side surfaces thus provide a large attack surface for the laser radiation, recessed areas and in particular rounding on the cutting edge a smaller attack surface. As a result, the effect of smoothing unevenness on the side surfaces and sharpening of the cutting edge occurs.

In the present case, a low angle is understood to mean angles in an angular range of less than 45 °, preferably of 5 ° to 45 °, in particular 10 ° to 30 °. The exact adjustment of the angle depends on the boundary conditions such as material, size of the material removal to be achieved, laser power and wavelength, cutting angle and / or radius of the cutting wheel.

The tilt of the incoming laser beam to the side surface of the cutting wheel should therefore be adjusted within an angular range in order to ensure the success of the invention. As a result, the focus in the longitudinal axis is increased by about 2-fold to 12-fold, depending on the angle of incidence. In order to achieve a sufficient intensity for a sufficient removal of material, a beam expansion is preferably performed, which reduces the focus diameter in the subsequent focusing, here for example to about 10 to 50 microns.

The method can lead to an improved geometry of the cutting edge just by the application on a side surface. However, it is preferred to apply the method according to the invention on both side surfaces.

The method is preferably carried out so that the laser beam is focused on the region of the side surfaces adjacent to the cutting edge. As a result, a sufficient removal rate is applied to the cutting wheel in the area important for the quality of the cutting edge.

At the same time, there is only a lesser intensity at the side surfaces at a greater distance from the cutting edge, and the intensity which becomes smaller with increasing distance, is finally no longer sufficient.

The method described above can be carried out with different laser sources, which may vary depending on the application and material of the cutting tool or cutting wheel. It has proven to be advantageous to use a pulsed laser. The pulsed laser beam has the advantage that within each laser pulse a sufficient power density can be achieved. By using a pulsed laser, the side surface of the cutting wheel is only detected selectively and only for a short period of time in each case in the area covered by the focus. However, it can be achieved by a suitable process management, that the entire sections of the side surfaces to be machined be largely uniformly applied with laser light.

The invention is not limited to the application of a pulsed laser. Thus, it is possible to use a continuous wave laser for materials that require less laser power for removing material. In this case, a particularly uniform processing is achieved, since no single-spaced laser pulses of fine structure in the side surface and the cutting edge can occur.

Preferably, during the application of the laser beam, regardless of whether the laser beam is pulsed or unpulsed, the cutting wheel is rotated in such a way that substantially the area of the side surface to be machined is exposed to the laser beam. For this purpose, the cutting wheel can be rotated continuously or in separate steps.

Furthermore, during laser processing, the relative position of the laser focus to the side surface can be adjusted continuously or in individual steps. By adjusting the laser beam relative to the side surface is ensured that a portion of the side surface, which is wider than the focal length, is applied successively with the laser beam.

When changing the relative position of the laser beam on the side surface, there are various possibilities as to whether and how the alignment of the laser beam is tracked. For the respective tracking suitable, known per se optics are used.

First, it is possible that the laser beam is adjusted parallel to the propagation direction while maintaining the angle to the side surface. By the same angular orientation of the laser beam a largely uniform processing of the side surface is achieved, even if some areas of the side surfaces are less than others in focus, if the focus is not tracked.

Alternatively, the angle of the laser beam during the adjustment of the laser beam relative to the side surface can be changed. Thus, for example, the angle in the region of the cutting edge can be set smaller, that is, flatter than in the regions which are arranged at a distance from the cutting edge.

In addition to adjusting the beam alignment of the laser beam, the relative distance of the focus to the side surface can either be maintained or changed. If in each case the focus distance is tracked and maintained substantially the same, this also results in a more uniform processing. If, on the other hand, the focus distance is changed or not tracked at all, the effect of the laser beam on different areas of the side surface can be changed. For example, it is thus possible to increase the intensity of the laser beam in the region of the cutting edge and to reduce it in the direction of a greater distance to the cutting edge.

The machining of the surface with a stepwise or continuous adjustment of the position of the focus relative to the side surface of the cutting wheel can advantageously be carried out during a continuous rotation of the cutting wheel. As a result, either separate tracks are processed or the laser beam travels a spiral curve from the outside, so starting from a greater distance from the cutting edge on the cutting edge to the cutting edge or beyond. The track offset should be selected so that one side surface leaves enough laps (turns) to achieve a completely overlapping processing of the side surface. The laser beam can be focused approximately on the cutting edge in order to have a maximum power density of the laser radiation here. One of the beam guidance changes already described above may also be selected during machining.

The above-indicated technical problem is solved according to the invention by cutting tools and in particular cutting wheels, which differ by different independent features from the prior art. These various features arise for the first time by the application of the method according to the invention, but can also be achieved by other manufacturing methods.

Furthermore, for all features of the cutting tool described below, the parameter values are determined from a three-dimensional measurement of the spatial profile of a section of the cutting edge. The measuring range has, for example, and the invention not limiting a length in the direction of the cutting edge of about 500 microns and a width across the cutting edge on both sides of about 250 microns, ie a total of about 500 microns. For example, for the white light interferometer can be used, which can determine the spatial shape of the side surfaces and the cutting edge with an accuracy of about 1 micron. If confocal microscopy is preferably used, the lateral resolution is approximately 1 μm or less than 1 μm, depending on the objective, while the depth resolution is less than 1 μm. From the data of a measurement can then for any given sections of the Side surfaces and / or the cutting edge, in particular line or surface, the real history and mean values are formed, which are then brought into relation and derived features of the cutting tool.

The invention relates first to a cutting tool, in particular cutting wheel for cutting brittle materials, such as ceramic and / or glass, with two mutually at a predetermined angle to each other extending side surfaces and a cutting edge formed by the side surfaces, which is characterized in that the side surfaces a mean cutting angle to each other, which is determined by the angle of two sections delimited on either side of the cutting edge from the cutting edge to a first distance from the cutting edge, and that the angle between two portions of the side surfaces which is in a range between a second distance are limited near the cutting edge and a relation to the first distance smaller third distance, smaller than the average cutting angle.

In other words, the two portions of the side surfaces in the immediate vicinity of the cutting edge are steeper than the mean cutting angle to each other, which is determined over a wider range. Since it arrives at the foremost portion of the cutting edge when penetrating the cutting edge, it is advantageous if this area is steeper so sharper than the adjoining part of the side surfaces. For example, during glass processing with a cutting wheel, the cutting edge penetrates between 10 μm and 30 μm, depending on the glass thickness, on both sides of the cutting edge into the glass surface. The resulting area where the glass undergoes damage is also called scratch width. If, in particular in this width, the side surfaces converge at a more acute angle than the rest of the side surfaces, this has a positive effect on the quality of the cutting process and on the service life of the cutting tool.

The invention also relates to a cutting tool, in particular cutting wheel for cutting brittle materials, such as ceramic and / or glass, with two side surfaces extending at a predetermined angle and with a cutting edge formed by the side surfaces, which is characterized in that the cutting edge of a straight line deviation less than 2 microns, in particular less than 1 micron.

For the determination of the magnitude of the straightness deviation, the measured spatial progression of the cutting edge is compared with an interpolated linear course of the cutting edge.

For this purpose, the section of the highest elevation, ie the largest elevation values, is first determined on the basis of the line of the recorded measurement data running transversely to the cutting edge, and its center is defined as the position of the cutting edge in this line. This results in the actual course of the cutting edge over a length of approx. 500 μm from the measured data. From these values, which fluctuate around an ideal cutting line, an interpolated, ie smoothed, linear course is first determined. Thereafter, for each measured value of the course of the cutting edge, the distance to the interpolated linear curve is calculated, and the standard deviation of the real curve from the interpolated curve then represents the value of the straight line deviation.

The specified values according to the invention of less than 2 μm and in particular less than 1 μm for the straightness deviation have the advantage that the cutting line of such a tool runs so straight that the disturbance introduced during cutting into the material of the workpiece to be cut extends along that contained in the material Structures can spread. Thus, the cutting, so the separation of the material can be performed easier and with less force. The precision of the cutting is thereby also improved.

The invention further relates to a cutting tool, in particular cutting wheel for cutting brittle materials, such as ceramic and / or glass, with two mutually at a predetermined angle to each other extending side surfaces and with a formed by the side surfaces cutting edge, characterized in that the cutting edge of a Schneidkantenwelligkeit of less than 0.5 microns, in particular less than 0.3 microns.

For the determination of the value of the cutting edge waviness, the measured spatial progression of the cutting edge is compared with a circular arc approximated to an interpolated course of the cutting edge.

For this purpose, the section of the highest elevation, ie the largest elevation values, is first determined on the basis of the line of the recorded measurement data running in each transverse to the cutting edge. This results, for example over a length of about 500 microns, the real history of the cutting edge as a result of height values. From these height values, which fluctuate radially around an ideal circular-arc-shaped cutting line, the course of the cutting edge is first approximated with the least error by a circular cutout. To the In the case of a round cutting tool such as a cutting wheel, the interpolated course approximates a circular arc which represents the ideal radial course of the cutting edge. In straight cutting edges, however, a straight line is approximated to the interpolated course. Thereafter, for each measured height value of the radial path of the cutting edge, the distance to the approximated ideal path is calculated, and the standard deviation of the real path from the approximate path then represents the value of the cutting edge waviness.

The stated values of the cutting edge waviness of less than 0.5 μm, in particular of less than 0.3 μm, have the advantage that the cutting edge deviates so little from an ideal cutting edge in the direction transverse to the snow direction that the cutting edge rests uniformly during the cutting process can penetrate the workpiece to be cut. For a cutting wheel this means that the cutting edge deviates very little from an ideal arc.

The invention also relates to a cutting tool, in particular cutting wheel for cutting brittle materials, such as ceramic and / or glass, with two side surfaces extending at a given angle to each other and with a cutting edge formed by the side surfaces, which is characterized in that the cutting edge is a negative Schneidkantenabuntpfung having.

The cutting edge blunting represents a measure of how far the mean value of the maximum values of the real cutting edge determined from the measurement data in the radial direction deviates on average from the radial profile of the middle cutting edge. The profile of the middle cutting edge results from the intersection of the two averaged spatial courses of the side surfaces which form the cutting edge. The value of the cutting edge blunting is positive when the real cutting edge is below the middle cutting edge, that is blunted. The value is negative if the real cutting edge runs above the middle cutting edge, that is, protrudes further. It is obvious that a negative cutting edge blunting results in a better cutting result because the cutting edge causes the first contact with the surface of the workpiece to be cut at a more acute angle.

The invention further relates to a cutting tool, in particular cutting wheel for cutting brittle materials, such as ceramic and / or glass, with two side surfaces extending at a predetermined angle to each other and having a cutting edge formed by the side surfaces, which is characterized in that the cutting edge a starting distance the cutting edge rounding of less than 4 microns, in particular less than 2 microns.

The starting distance of the cutting edge rounding is determined by starting from the cutting edge in the case of the real average over the measuring range and, depending on the distance to this left and right, determining the local slope. From the pitch curve defined in this way, the local angle profile is determined as a function of the distance to the cutting edge. From this, starting from the cutting edge, the distance is determined at which the angle is for the first time only 1 degree above the value determined over the entire side edges. This distance value is the starting distance of the cutting edge rounding. In other words, starting at the starting distance from the cutting edge, the rounding of the cutting edge begins. The position of the starting distance can also be optionally determined on both side surfaces and then the mean value can be used as starting distance.

The smaller the value of the start distance of the cutting edge rounding, the sharper the cutting edge is formed. At each cutting edge, there is a transition between the two side surfaces, where at one point the cutting angle is 180 °. Since this angle of 180 ° can not be detected metrologically, the starting distance is defined as a measure to characterize the extent of the rounding of the cutting edge. However, the narrower the transition region is formed, the sharper the cutting edge.

The described cutting tool according to the invention, in particular the cutting wheel, has a starting distance of less than 4 μm and in particular less than 2 μm. Thus, the area of the rounding of the cutting edge represents only a small proportion of the above-mentioned scribe width. The advantageous effect is thus further improved at values of less than 2 μm. The values of the starting distance to be achieved also depend on the material structure of the material of the cutting tool.

The previously described embodiments of the invention have been described for a continuous cutting edge. On the other hand, it is also possible that the cutting edge is provided with a sequence of teeth and interdental spaces and that the properties of the cutting edge explained above apply at least to the teeth.

Generally applies to cutting, especially for cutting wheel, that at shallow, ie blunt cutting angles, the ripple less than at acute cutting angles fails. In contrast, the straightness deviation is greater at blunt cutting angles. Conversely, these are at sharp ends Cutting angles make the waviness greater and the straightness deviation lower.

The inventive method therefore has an advantageous effect on the design of cutting wheels for scribing thin glass, as they are needed in the display production. Because in this application, cutting wheels with pointed cutting angles (eg 105-125 ° cutting angle) are used at low penetration depth into the thin glass to be doctored. The inventive method therefore leads to the improvement of these cutting wheels over the prior art, just by the ripple is reduced in these cutting wheels, at the same time the straightness is improved.

The invention will be explained with reference to embodiments, reference being made to the drawing. In the drawing show

1 a cutting wheel in a side view,

2 a schematic diagram for a first embodiment of a method according to the invention,

3 a schematic diagram of a second embodiment of a method according to the invention,

4 a schematic diagram to illustrate the implementation of the method according to the invention,

5 a schematic diagram of a third embodiment of a method according to the invention,

6 an input image of a three-dimensional height structure of a cutting wheel,

7 a grayscale image showing the deviations of the measured surface from an ideal surface of a prefabricated cutting wheel known from the prior art,

8th a grayscale image representing the deviations of the measured surface from an ideal surface of a cutting wheel produced by the method according to the invention,

9 Diagrams for explaining the parameter of the straightness deviation,

10 a diagram for explaining the parameter of the cutting edge waviness,

11 another diagram for explaining the parameter of the cutting edge waviness for a cutting wheel produced by the method according to the invention,

12 a diagram for explaining the parameter of the Schneidkatenabstumpfung for a prefabricated, known from the prior art cutting wheel,

13 a diagram for explaining the parameter of the Schneidkatenabstumpfung for a cutting wheel produced by the method according to the invention,

14 3 is a diagram for explaining the parameter of the starting distance of the cutting edge rounding for a prefabricated cutting wheel known from the prior art,

15 a diagram for explaining the parameter of the starting distance of the cutting edge rounding for a cutting wheel produced by the inventive method.

1 shows a schematic side view of a cutting wheel 2 with along the entire circumference extending cutting edge 4 , The cutting wheel 2 has in this example rotational symmetry with respect to an axis A, which is the axis of rotation of the cutting wheel 2 is used during the cutting process.

The cutting edge 4 is made of two side surfaces which taper in a wedge shape in axial cross-section 6a . 6b , each having truncated cone shape, formed. The side surfaces 6a . 6b include a cutting edge angle X between them. The cutting edge angle X can in the cutting wheel of the 1 for example 135 °. The cutting wheel 2 may also be made of a polycrystalline material, in particular polycrystalline diamond material or of a hard metal, for example tungsten carbide.

By the convergence of the side surfaces 6a . 6b is with the cutting edge 4 also formed a circumferential line, which is essentially a plane 8th arranged in this representation perpendicular to the plane considered and therefore spanned as a line. The level 8th the circumferential line in the present case runs perpendicular to the cutting wheel axis A.

In the 1 illustrated cutting edge 4 is continuously formed, the cutting edge 4 Thus, it runs along a line and thus can exert the substantially same effect on the material to be cut at each angular position. In addition, it is known from the prior art mentioned that the cutting edge with Teeth and interdental spaces may be formed so that a regular or irregular tooth structure is given. In particular, up to the outer diameter of the Schneidrädchens 2 protruding teeth must have the best possible cutting edge, since the teeth represent the essential elements for cutting the material. In addition, the interdental spaces may have their own, slightly recessed cutting edge, provided that they penetrate into the material in addition to the teeth during the cutting process.

2 shows a schematic representation of an embodiment of a method according to the invention. In the diagram, a triangle-like line is drawn in micrometer resolution, which shows the irregular course of the surface of a prefabricated cutting wheel in section.

Coming from diagonally lower right is the course of a laser beam shown. The middle dot-dash line 10 shows the axis of the laser beam, while the slightly curved lines 12 and 14 illustrate the waist of the focus F of the laser beam. The focus of the laser beam is in the area of the cutting edge 4 that is, at the top of the triangle-like line. In this position, only half of the laser beam strikes the surface of the cutting wheel. Because the axis 10 the laser beam only affects the upper end of the cutting edge 4 so that the upper half of the laser beam radiates beyond the cutting edge. Therefore, the upper line 12 consistently drawn throughout, while the bottom line 10 to the left of the cutting edge 4 only indicated by dashed lines. There, of course, comes because of the shading by the cutting edge 4 no light from the laser beam (except by diffraction) on.

The axis of the laser beam is opposite the right side surface 6a the cutting wheel inclined, wherein the inclination angle is flat and can be set less than 45 °, in particular between 5 ° and 45 °. In the illustration after 2 By way of example, an angle α ₁ of slightly more than 15 ° has been selected.

In the in 2 Top view of the cutting wheel in the region of the cutting edge shown above 4 is the relative position of the focus F to recognize as an elongated oval. On the side edge shown on the right 6a you can see the light spot on the surface. Left of the cutting edge 4 If the oval is shown in dashed lines to indicate the symmetrical course of the focus F, of course the laser beam does not hit the left side surface 6b on.

The oval is all the more stretched, the shallower the angle of the axis of the laser beam is set to the surface. As a result, the light power concentrated in the focus of the laser beam is distributed over a larger surface area. Therefore, the laser beam must not impinge on the surface at too low an angle, since otherwise not enough light energy density is applied to the surface in order to be able to remove material.

If the focus of the laser beam as in 2 is positioned in the region of the cutting edge, then there is the effect that in the region of the cutting edge, about half a focal length of the entry of light energy in total less than in further from the cutting edge 4 distant areas when the laser beam is positioned and focused there. Presumably by this effect and the associated different removal of the material of the side surface 6a it comes to a special design of the cutting edge 4 , Because this points directly to the cutting edge 4 immediately adjacent region a sharper cutting angle than over a larger area of the side surface 6a . 6b calculated mean cutting angle on. This feature will be further explained below. This effect is probably based on the described different energy input, but it can also by diffraction effects on the cutting edge 4 or by another unrecognized effect.

However, the angle of incidence must not be too steep for the method according to the invention. Because the desired effect of the method is that projecting tips on the side surfaces provide a larger attack surface for the laser radiation as receding areas and in particular rounding at the cutting edge. As a result, the effect of smoothing unevenness on the side surfaces and sharpening the cutting edge occurs. If the angle is set too large, the laser light falls too steeply on the side surface and the smoothing and sharpening effect is reduced.

3 shows a different constellation. Here, the laser beam is not on the area of the side edge 4 focused, but at a distance. In addition, the axle points 10 of the laser beam an angle α ₂ of about 30 ° to the side surface 6a on.

By varying the angle, the distance of the focus to the cutting edge and the distance of the focus relative to the surface of the side surface of the inventive method can be varied. In particular, areas of the side surface 6a greater than the extent of the focus of the laser beam, are processed by positioning the laser beam relative to the cutting edge and to the side surface to be machined 6a . 6b is changed. If at the same time the cutting wheel is rotated, the entire can machining area of the side surface are smoothed in one process step.

4 shows a schematic representation of another embodiment of a method according to the invention, in which the oval-shaped impingement of the focus of the laser beam in separate tracks on the side surface 6a is positioned during rotation of the cutting wheel. The spaced tracks are shown with the vertical arrows and numbered n-4 through n + 2. The laser beam is sequentially adjusted to each of these tracks, with the track n coming closest to the cutting edge, ideally coinciding therewith substantially within the setting accuracy. Since the oval processing spots formed by the focus of the laser beam in each track have a greater longitudinal extent than the distance between the tracks, the processing areas of the individual tracks overlap, so that the overlapping positioning results in the area-wide processing on the side surface.

Im in 4 illustrated embodiment, the oval focus has a width of about 20 microns and a length of about 120 microns, so one to about 6 times greater length. If the tracks have a distance of approx. 10-20 μm, then the surface areas are processed several times and therefore very evenly when the entire side surface is scanned, ie they are smoothed or ground with the laser.

5 shows another example of a cutting wheel, which is processed by the method according to the invention. In contrast to the 2 and 3 has the cutting wheel in the illustrated cross-section in the region of the cutting edge 4 ' the side surface 6a a setback paragraph 20a and the side surface 6b a paragraph 20b on. The step leads to a set-back structure with a width which is indicated by the double arrow B and which has already been referred to above as the interdental space. Thus one can the 2 as a cross-section of the same cutting wheel understand, in which the cross-section shown an area with a to the cutting edge 4 protruding tooth shows while 5 the arranged between each two teeth interdental space shows.

As 5 is detected, the laser beam irradiated at a shallow angle on the heel 20a a little shadowed. But this shadow does not sit down to the cutting edge 4 ' so that at this point no or only slight deterioration of the smoothing of the surface structure occurs. The influence of shading can be reduced by the fact that the paragraph 20a further spaced from the cutting edge 4 ' is arranged and / or by the angle of the laser beam is increased within the possible limits.

Another difference to the 2 and 3 is that the scaling of the illustrated diagram shows a larger width of the cutting wheel over a little more than 600 μm.

The laser to be used must always be adapted to the application. Therefore, the following description of laser parameters is purely exemplary. The power of for editing in the 1 to 5 The cutting wheel shown used of polydiamantenem material laser is a maximum of 2.8 watts at 500 kHz and a pulse length of 10 picoseconds.

Due to the high pulse frequency of this laser, the cutting wheel can rotate during processing at a comparatively high speed. If the cutting wheel diameter, for example, 2 mm and the speed 20 U / sec. or 1200 rpm, the resulting local pulse spacing between two successive pulses is about 0.25 μm, which is far below a beam diameter. The individual pulses can thus not be recognized on the laser-machined cutting wheel surface, that is to say the side surface, or only to a very limited extent.

In the following, various characteristics of the cutting blade smoothed and sharpened by the method described above will be described.

The 6 to 15 show measured data and evaluations of the measured data for an untreated, in the context of this description referred to as "prefabricated" cutting wheel, as is known from the prior art, and for a cutting wheel according to the invention processed according to the invention. These cutting wheels have a rather large cutting angle of about 140 °. However, the invention is not limited to cutting wheels with such a cutting angle.

From this description the differences and the associated advantages become clear. There are therefore various parameters for characterizing the geometry and surface condition of the cutting edge and the adjacent sections of the side surfaces, which can be used individually or else linked together in any combination.

6 shows a three-dimensional structure of a cutting wheel in a micrometer-accurate resolution, which has been detected with a camera device. The three-dimensional height structure was determined by white light interferometry using confocal microscopy. The measured structure reproduces, with an accuracy in the range of approximately 1 μm, the three-dimensional shape of a section of the cutting edge whose characteristic and quality is to be determined. In this case, the individual pixels each indicate a specific value for the respectively associated subarea on the surface. In the measurements made, the lateral resolution was about 1 μm or less than 1 μm, depending on the objective, while the depth resolution was less than 1 μm.

The grayscale in 6 represent different elevation values, with equal gray levels at the bottom and at the cutting edge not being equal height values. The black-and-white representation was obtained from a colored representation, with red colors at the cutting edge and blue colors at the bottom, which gave the same gray tones in the black and white representation.

Both from the measured three-dimensional data as well as derived from it two-dimensional views, such as in 8th and 9 geometry can be analyzed, both qualitatively and quantitatively.

In the following, it is assumed that the cutting edge runs from top to bottom within the input image that is being evaluated. When recording the three-dimensional structure, therefore, the cutting wheel is therefore arranged as centrally as possible.

At the beginning of the evaluation, the horizontal position of the cutting edge or the vertical position of the cutting wheel axis is first of all searched for in the input image and, therefore, the evaluation range is determined symmetrically.

Furthermore, the geometry of the cutting wheel can be determined in more detail from the measured data. In the analysis of the evaluation range, the geometry of the cutting wheel is first approximated by an ideally round, and on the opposite cutting edges flat, smooth cutting wheel.

7 shows an evaluation for a prefabricated, known from the prior art cutting wheel. Shown is the height difference between the measured geometry of the cutting wheel in the evaluation area, ie in the input image described above 6 , and the geometry approximated by an ideally round and unstructured cutting wheel. Different gray levels represent different deviations from the ideal shape. Clearly visible in the center of the image is the brighter area of the almost vertical cutting edge. This is already a first indication that the cutting edge in the area of the tip deviates significantly from the ideal shape.

From the approach to an ideally round and unstructured, so no tooth structure exhibiting cutting wheel, first of all the cutting angle and the diameter of the cutting wheel can be determined.

Furthermore, in 7 Two vertical lines are drawn at a given distance from the left and right edges of the evaluation area. These lines symbolize the expected scribe spacing of +/- 10 μm and +/- 20 μm, ie the area of the cutting edge and the side surfaces which are responsible for the scoring of the material. The scratch distance thus represents the contact width with the material, for example the glass.

8th shows the same evaluation for a processed with a method according to the invention cutting wheel. The shades of gray are the same and at that compared to 7 more regular structure of the grayscale is recognizable that the side surfaces are much smoother. In addition, it can be seen in the area of the cutting edge that it differs only slightly from the ideal shape. The cutting edge is thus significantly sharper than the prefabricated cutting wheel.

When analyzing the evaluation range, the straightness deviation of the cutting edge can be determined as an important parameter. The cutting edge is first defined by the horizontal position of the highest points of each line in the evaluation area. Since the cutting edge runs partly diagonally through the evaluation area, depending on the orientation of the input image, the straight-line deviation is determined as a deviation from an interpolated linear cutting edge.

In 9a and 9b Details of the determination of the value for the straightness deviation are shown. 9a shows the progression of the measured data 2 derived position of the cutting edge in each row over a range of 500 microns. A curve running in steps of the measurement resolution of about 1 μm can be seen, which runs slightly inclined, since the input image has not been exactly aligned.

9a further shows a linear interpolation of the measured values, which in this case result from the pixel resolution of approximately 1.6 μm and run in stages. The interpolation can also be performed by a low-pass filter. The course of the Cutting edge is thus smoothed and approximated with a straight line.

9b then shows the deviation of the measured values from the linear interpolation 9a , As dashed horizontal lines is in 9b additionally the area of the standard deviation is drawn. The value of this standard deviation, ie the distance of the dashed line from the zero line in 9b , is then taken as the value for the straightness deviation. The cutting edge accordingly has a straightness deviation of less than 2 μm, in particular approximately 1 μm. This value can be further improved by optimizing the parameters of the machining of the side surfaces and the cutting edge according to the invention.

In 10 Details are given for determining the interpolated cutting edge of the cutting wheel machined by a method according to the invention. For this purpose, the measured height values along the course of the cutting edge are obtained from the data of the three-dimensional shape from the input image 6 derived and as a line 30 drawn. 10 thus represents the radial profile of the cutting edge with the radial waviness to be determined along the measured portion of the cutting wheel.

The wavy curve below the measured values at a distance 32 represents the averaged cutting edge. From the approximation by an ideally round wheel with flat side surfaces, this averaged cutting edge becomes a circular arc curve 34 determined because a circular cutting edge is to be produced. The distance between the measured data 30 and the circular arc curve 34 gives the details below 13 described negative cutting edge blunting again, so that the real course of the cutting edge is above the average cutting edge.

11 now shows the deviations of the measured values of the curve 30 in 10 from the circular curve fitted to the interpolated cutting edge 34 with the values fluctuating to a certain extent around the zero line. The difference curve does not fluctuate around zero because of the negative cutting edge blunting, but around the value of the cutting edge blunting. The curve in 11 However, for the determination of the standard deviation, it was corrected by the value of the negative cutting edge truncation and thus made averaging. This results in the 11 , The two horizontal dashed lines represent the standard deviation, wherein the distance of the dashed line from the zero line represents the determined value of the cutting edge waviness. The cutting edge accordingly has a cutting edge waviness of less than 0.3 μm, in particular of approximately 0.2 μm.

The 12 to 15 show evaluations based on the sharpness of the cutting edge 4 which serve to obtain parameters for the sharp-edged check.

The 12 and 13 give evaluation results for the averaged in the evaluation of the input image sharpness or quality of the cutting edge or the cutting edge for a prefabricated cutting wheel and for a machined by a method according to the invention cutting wheel again.

In the 12 and 13 For an evaluation of the measured cutting edge shape, these are triangular lines approximated to an ideal cutting edge shape 40 respectively. 50 drawn. This is, as above to 7 has been described which uses geometry approximating an approximately circular and unstructured cutting wheel. The curves 40 respectively. 50 thus represent the approximation of the left and right cutting wheel flanks by two balancing straight lines that meet at the cutting edge.

In 12 sets the curve for a prefabricated cutting wheel 42 is the line-average averaged shape of the cutting edge, the average shape of the cutting edge being obtained from all lines by averaging over all the "pixels" of the image having the same corrected distance from the cutting edge. In this case, it has been taken into account that the cutting edge in each row of the evaluation region varies along the cutting edge laterally or radially to the cutting axis. In 13 is the corresponding line 52 drawn for the processed with the inventive method cutting wheel.

Two different averaging methods are preferably used.

In a first alternative, the line-average averaged shape of the cutting edge is represented by the values of the measured profile with respect to the maximum value in each line, i. H. determined based on a non-straightened cutting edge.

In a second alternative, the line-average averaged cutting edge shape is determined with respect to the circular arc approximated to an interpolated cutting edge shape. The approximate circular arc shape was above in relation to the 10 has been described. The line-average averaged edge shape thus appears somewhat blunt in the second alternative of interpolation compared to the first alternative. From the approximation of an ideal cutting wheel thus results in a curve for each line. In the 12 and 13 is this Curve course and the measured course of a line are shown.

How out 12 can be seen, deviates the line-average averaged cutting edge shape 42 especially in the area of the cutting edge of the ideal shape. A significant dulling over a width of about +/- 3-4 microns to the side of the cutting edge (x = 0 microns) can be seen.

On the other hand shows 13 a line-wise averaged cutting edge shape 52 for the cutting wheel machined by the method according to the invention, which projects beyond the shape of the geometry approximating the ideal round and unstructured cutting wheel in the area of the cutting edge. The measured cutting edge has just in the range +/- 30-50 microns around the cutting edge around an exaggerated pointed shape. In addition, the course of the curve 52 much smoother than the curve 42 in 12 , which again gives an indication of the smoothing effect of the method according to the invention.

The difference between the two curves 40 and 42 as well as the difference between the two curves 50 and 52 at the position of the cutting edge (x = 0 μm) is used as a measure of the cutting edge blunting. This results for 12 a positive value while the cutting edge blunting for 13 is negative. For an ideal cutting edge, both curves would be identical and the cutting edge blunting would be zero.

The 14 and 15 show an evaluation of the measured over all lines angle of the measured cutting edge compared to an approximated to an ideal round and unstructured cutting wheel geometry. This approximate geometry is based on 8th been explained.

The scaling has been chosen the same in both diagrams, so that the curves of the individual curves can be directly compared with each other.

The in the 14 and 15 contained dot-dash line 60 respectively. 70 at an angle of about 138 ° in 14 and from about 141 ° represents the formed in the approximate geometry between the two edge portions cutting angle.

The in the 14 and 15 drawn lines 62 and 72 represent the cumulative cutting angle. To calculate the cumulative cutting angle, the height value of the cutting edge averaged over all lines is first calculated. Thereafter, the mean vertical value on the side surface, which is averaged over all rows, is determined on both sides of the edge of the snow at equal intervals on the right and left. The cumulative angle is then the angle defined by the two straight lines that run between the averaged height value of the cutting edge and the two averaged values at the left and right of the cutting edge.

The curve shape of the lines 62 and 72 is therefore symmetrical to the cutting edge (x = 0 μm). The shape of the cumulative cutting angle is to be interpreted as follows.

In 14 The cumulative cutting angle for large distances of about +/- 50 microns from the cutting edge is only slightly above the approximated to the ideal shape angle of the line 60 , The closer the distance to the cutting edge is reduced, the more the cumulative angle increases until it reaches 180 ° at x = 0 μm. Even though the waveform conveys a peak, in the illustration the cutting angle increases to larger values in the y-direction.

The width of the curve 62 gives an indication that the cumulative cutting angle already increases sharply from +/- 20 μm and at +/- 10 μm exceeds the angle of approx. 150 °, ie becomes flatter. The shallower angles are therefore a measure of the blunting of the cutting edge. When scribing thin glasses, the scribe width is considerably lower compared to scribing thick glasses. If the scribe width on the left and right of the cutting edge is, for example, only 10 μm, then the edge angle coming into contact with the glass is in 14 slightly more than 151 °, with a scratch width left and right of the cutting edge of 20 μm about 144 °. In 15 In addition, significantly lower fluctuations in the surface structure occur.

On the other hand, the curve runs 72 in 15 for larger distances up to approx. +/- 50 μm, initially below the ideal shape. approximate angle of the line 70 , This means that in this area the cutting edge has a steeper angle than the shape approximated to the ideal geometry. Only from values below +/- 5 μm the cumulated angle exceeds the value of approx. 150 °. The cutting edge therefore rounds off only at significantly smaller values than is the case in the prior art. Even with minor scoring, as is common in scribing thin glass, the cutting angle in the area of contact of the cutting wheel with the glass is comparatively constant and sharp compared to that of the prefabricated one.

In the 14 and 15 make the lines 64 and 66 respectively. 74 and 76 the angle that results from the two mean local slopes left and right of the cutting edge as a function of the distance to the cutting edge. Here is the dashed curve 64 respectively. 74 the one about Pixel pitch determined local slopes and the continuous curve 66 respectively. 76 the first 2 pixels in the immediate vicinity of the cutting edge are not filtered (first pixel) or only with a 2 × 1 low-pass filter (second pixel).

A comparison between the amplitudes of the two curves 64 and 74 results in a significantly smoother surface for the cutting wheel machined by the method according to the invention.

From the course of the curve 66 respectively. 76 the starting distance of the cutting edge rounding can be derived, which defines the distance to the cutting edge at which the continuous curve 66 respectively. 76 starting from the cutting edge for the first time a value of 1 degree above the dashed curve 60 respectively. 70 reached. This value is additionally marked with a cross. For distances to the cutting edge, which are smaller than this starting distance of the cutting edge rounding, the local cutting angle is thus consistently greater than 1 ° greater than the average, approximated to the ideal cutting edge form cutting angle. This is interpreted as meaning that the rounding of the cutting edge starts from this point.

Out 14 It can be seen that the starting point of the cutting edge rounding for the prefabricated cutting wheel is at values of +/- 7-10 μm. In contrast, the value of the starting point of the cutting edge rounding in the processed by the inventive method cutting wheel after 15 at values of +/- 3-4 μm. This value also represents a measure of the sharpness and accuracy of the cutting edge.

From the 15 the following can also be read. The side surfaces have a mean cutting angle to each other, which is limited by the angle of two sections, which are limited to both sides of the cutting edge of the cutting edge to a first distance, here about +/- 250 microns to the cutting edge. This corresponds to the width of the input image and the angle corresponds to the mean cutting angle of the line 70 , The angle between two portions of the side surfaces, which is limited in a range between a second distance near the cutting edge, here the starting point of the cutting edge rounding, and a relation to the first distance smaller third distance, here at +/- 50 microns, is smaller than that average cutting angle. Because the curves 74 and 76 run in this section below the line 70 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0773194 B1 [0004]
• EP 1666426 A1 [0005]
• WO 2009/036742 [0006]
• WO 2009/036743 [0006]

Claims (12)

Method for smoothing a surface of a prefabricated cutting tool, in particular a cutting wheel having two side surfaces which run at an angle to one another and form a cutting edge, - In which at least one side surface is acted upon at least in a region adjacent to the cutting edge with a laser beam and - In which the laser beam is aligned at a shallow angle to the surface of the side edge. Method according to Claim 1, in which the flat angle is set in an angular range of less than 45 °, preferably 5 ° to 45 °, in particular 10 ° to 30 °. A method according to claim 1 or 2, wherein the laser beam is focused on the area adjacent to the cutting edge. Method according to one of claims 1 to 3, wherein the cutting wheel is rotated continuously or in separate steps. Method according to one of claims 1 to 4, wherein the relative position of the laser focus to the side surface is adjusted continuously or in individual steps. The method of claim 5, wherein the laser beam is parallel to the propagation direction while maintaining the angle to the side surface and maintaining the relative position of the focus of the laser beam is adjusted. The method of claim 5, wherein the angle of the laser beam to the side surface is adjusted while maintaining the relative distance of the focus of the laser beam to the side surface. The method of claim 7, wherein the angle of the laser beam to the side surface at the cutting edge is set less than in the remote from the cutting edge region. Cutting tool, in particular cutting wheel for cutting brittle materials, such as ceramic and / or glass, - with two at a predetermined angle to each other extending side surfaces ( 6a . 6b ) and - with one through the side surfaces ( 6a . 6b ) formed cutting edge ( 4 ), characterized in that - the side surfaces ( 6a . 6b ) have an average cutting angle to each other, which is determined by the angle of two sections which are on both sides of the cutting edge ( 4 ) from the cutting edge to a first distance to the cutting edge ( 4 ), and - that the angle between two sections of the side surfaces ( 6a . 6b ) defined in a range between a second distance near the cutting edge and a third distance smaller than the first distance is smaller than the average cutting angle. Cutting tool, in particular cutting wheel for cutting brittle materials, such as ceramic and / or glass, - with two at a predetermined angle to each other extending side surfaces ( 6a . 6b ) and - with one through the side surfaces ( 6a . 6b ) formed cutting edge ( 4 ), characterized in that - at least one of the following parameter indications a) to d) is fulfilled: a) the cutting edge ( 4 ) has a straightness deviation of less than 2 microns, in particular less than 1 micron, b) the cutting edge ( 4 ) has a cutting edge waviness of less than 0.5 μm, in particular less than 0.3 μm, c) the cutting edge ( 4 ) has a negative cutting edge blunting, d) the cutting edge ( 4 ) has a starting distance of the edge rounding of less than 4 microns, in particular less than 2 microns. Cutting tool according to claim 9 or 10, characterized in that the cutting edge is continuous. Cutting tool according to claim 9 or 10, that the cutting edge is provided with a sequence of teeth and interdental spaces and that the properties of the cutting edge according to claim 10 or 11 apply at least to the teeth.

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