Method for grinding small rotary cutting tools by grinding machine

Abstract

The invention relates to a method for machining a small rotary cutting tool (10) by a grinding machine, comprising: a) mounting a workpiece (10a) in a spindle (20) of the grinding machine; b) machining the calibration portion (CP) of the workpiece (10a) by making one or more marks (M1, M2, M3, M4) on the workpiece with one grinding wheel or with a corresponding plurality of grinding wheels (W1, W2, W3, W4) of different shapes, the one or each mark (M1, M2, M3, M4) comprising at least one geometric feature (R1, R2, a1, a2, L) and two positional features (D1, D2), each of the three-dimensional coordinates (D1w, D2w) corresponds to a geometric feature (R1w, R2w, a1w, a2w, Lw) of a corresponding grinding wheel to which a corresponding mark (M1, M2, M3, M4) has been ground and a 3D coordinate (D1w, D2w) in an XYZ coordinate system of the grinding machine; c) performing a measurement of the at least one geometric feature (R1, R2, a1, a2, L) and the two positional features (D1, D2) of the or each marker (M1, M2, M3, M4) of the calibration part (CP); d) generating a sequence of instructions for grinding the workpiece (10a) to a final and desired shape of the cutting tool (10) on the basis of the at least one geometric feature and the two positional features of the or each mark as measured in step c); and e) controlling the 3D coordinates of the one or more grinding wheels (W1, W2, W3, W4) in the XYZ coordinate system during a grinding operation on a workpiece or on another workpiece according to the instruction sequence to obtain the cutting tool (10).

Description

Technical Field

[0001] The present invention relates to a method for grinding small rotating cutting tools with very high accuracy. The cutting tool may, for example, include one or more spiral grooves having an outer diameter of less than 3 mm, with a minimum outer diameter as small as 50 microns, or even as small as 30 microns. These cutting tools may be, for example, milling cutters (such as end mills), drills or cutting tools of complex shapes. The present invention also relates to a computer-readable storage medium storing instructions to cause a grinding machine to perform a calibration routine and subsequently grind a cutting tool according to the method disclosed therein. Background Art

[0002] Trends in the areas of ultra-high precision and micro-manufacturing require a fresh look at new machine and process technologies.

[0003] For the production of cutting tools, the work carried out in a conventional manner essentially involves the following steps: i) setting the parameters of the cutting tool to be manufactured in specialized programming and simulation software for generating the profile of the cutting tool to be ground; ii) selecting and preparing by the operator the different types of grinding wheels necessary to perform the different grinding operations in order to machine the cutting tool into its final and desired shape; iii) measuring the shape of the selected grinding wheel on a preset optical measuring system; iv) performing a machine setup specific to the cutting tool to be manufactured; and v) performing iterative adjustments to the geometry of the cutting tool by consecutively grinding several cylindrical workpieces.

[0004] The smaller the size of the cutting tool to be produced, the greater the number of iterations required to obtain the final geometry. The geometrical deviations between the virtual tool programmed by the software and the first tool produced are due to different factors, in particular the inherent accuracy of the preset optical measuring system for measuring the shape of the grinding wheel, the inherent accuracy of the grinding machine (in particular its calibration), the quality of the settings by the operator, the type of grinding process and the inherent geometry of the cutting tool.

[0005] The most common way to correct dimensional deviations from the desired shape is to measure the cutting tool after completion and correct the incorrect values. This is inconvenient, not only because it requires multiple operations and is time-consuming, but also requires the use of several blanks of bars or cylindrical workpieces to produce a single cutting tool, resulting in excessive material waste.

[0006] The main challenge is to know with the highest possible accuracy the exact shape, size and position of each grinding wheel in the grinding environment, as defined by the XYZ coordinate system of the grinding machine.

[0007] Today, calibration measurement devices external to the grinding machine (such as preset devices or CNC machines with optical measurement) are used to measure the critical geometric features and 3D coordinates of the grinding wheel to calibrate its position and shape inside the grinding machine. These external measurement devices have an accuracy of the order of 10 microns.

[0008] Although an accuracy of the order of 10 microns is generally high enough for grinding cutting tools with an outer diameter of more than 3 mm, this accuracy is not enough to avoid fine-tuning the final geometry of the cutting tool by continuous trials in order to obtain a cutting tool with an outer diameter typically below 3 mm, for example as small as 50 microns or even as small as 30 microns. These inaccuracies lead to a lot of time loss and to the scrapping of a large number of blanks of rods or cylindrical workpieces used to produce cutting tools.

[0009] WO2019 / 197931 discloses a method for machining a workpiece including a desired spiral groove. The method comprises the following steps: grinding a calibration groove on the surface of the workpiece according to a predetermined spiral pattern of the desired spiral groove and with the aid of a grinding wheel of a grinding machine. The calibration groove has a calibration length equal to or less than the predetermined length of the desired spiral groove and a calibration depth less than the predetermined depth of the desired spiral groove. The method comprises the following steps: determining the grinding wheel size of the grinding wheel and its position by measuring the calibration depth; and grinding the desired spiral groove with the aid of the grinding wheel using the determined wheel size and position.

[0010] The method advantageously reduces the time required for calibrating the machine, since the calibration procedure is an integral part of the machining of the workpiece and no raw material is wasted.

[0011] However, machining the calibration groove requires a workpiece of the desired shape to have a certain diameter. Therefore, this solution is not suitable for calibrating grinding machines for grinding small rotary cutting tools, especially rotary cutting tools with an outer diameter of less than 3 mm, down to 50 microns or even down to 30 microns. Summary of the invention

[0012] It is therefore an object of the present invention to provide a method for grinding a rotary cutting tool such as a milling cutter, a drill or a tool of complex shape having an outer diameter less than 3 mm, and possibly as small as 50 microns, or even as small as 30-35 microns.

[0013] Another object of the present invention is to provide a method for grinding small rotary cutting tools which is easy to implement.

[0014] Another object of the present invention is to provide a method for grinding small rotary cutting tools which simplifies the manufacturing process of large quantities of cutting tools.

[0015] Another object of the present invention is to provide a computer-readable storage medium storing instructions which, when executed by a processing unit of a grinding machine, perform the method disclosed herein.

[0016] According to the invention, these objects are achieved in particular by means of a method for machining a rotating cutting tool, preferably with an outer diameter of less than 3 mm, by a grinding machine. The method comprises: a) mounting a workpiece in a spindle of the grinding machine and rotating the workpiece; b) machining a calibration portion of the workpiece by making one or more marks on the workpiece with a grinding wheel or with a corresponding plurality of grinding wheels of different shapes, wherein the one or each mark comprises at least one geometric feature and two position features, which correspond to the geometric features and 3D coordinates in the XYZ coordinate system of the grinding machine of the corresponding grinding wheel on which the corresponding mark has been ground; c) performing a measurement of the at least one geometric feature and the two position features of the one or each mark of the calibration portion; d) generating a sequence of instructions for grinding the workpiece to the final and desired shape of the cutting tool based on the at least one geometric feature and the two position features of the one or each mark as measured in step c), and e) controlling the 3D coordinates in the XYZ coordinate system of the one or more grinding wheels during a grinding operation on the workpiece or on another workpiece according to the sequence of instructions to obtain the cutting tool.

[0017] In an embodiment, at least one geometrical feature of the grinding wheel on which the marking has been ground corresponds to an angle or an edge radius of the grinding wheel.

[0018] In an embodiment, once the grinding of the calibration portion is completed, the measurement of the one or more geometric features and the two positional features of the one or each mark is automatically performed by a laser imaging system embedded in the grinding machine. For example, these measurements can be obtained by performing a laser scan along the calibration portion of the workpiece.

[0019] In an embodiment, each of the plurality of marks is ground using one of a corresponding plurality of grinding wheels of a different shape necessary to grind the workpiece to a final and desired shape of the cutting tool.

[0020] In an embodiment, the method further comprises the step of performing a direct measurement of one or more geometrical features of the or each of the grinding wheels by means of a preset device before machining the or each mark of the calibration portion in step b).

[0021] In an embodiment, the method further comprises the step of performing a measurement of the position of the workpiece along an axis of an XYZ coordinate system of the grinding machine. Based on said measured position of the workpiece along said axis and said two position features of said one or each corresponding mark of the calibration part performed in step b), determining the 3D coordinates of said one or each of said plurality of grinding wheels in the XYZ coordinate system of the grinding machine.

[0022] In an embodiment, the plurality of marks of the calibration portion are made on the workpiece adjacent to each other along a longitudinal axis of the workpiece or along a transverse axis extending from one end to an opposite end of the calibration portion.

[0023] In an embodiment, the measurements of the at least one geometrical feature and the two positional features for each mark performed in step c) are saved for each grinding wheel of the plurality of grinding wheels. These measurements are taken for performing at least two consecutive grinding operations on a workpiece to obtain the rotating cutting tool.

[0024] In an embodiment, the first position feature of the or each mark of the calibration portion defines a first position along a first axis of three coordinate axes of an XYZ coordinate system of the grinding machine.The first axis coincides with the longitudinal axis of the workpiece.

[0025] In an embodiment, the second position feature of the one or each mark of the calibration portion is used to determine the diameter of the corresponding grinding wheel used to make the one or each mark. The second position and the third position along the second axis and the third axis of the coordinate system respectively are determined based on the diameter to calculate the 3D coordinates of the corresponding grinding wheel.

[0026] In an embodiment, the calibration portion is machined at a distal portion of the workpiece.

[0027] In an embodiment, said rotary cutting tool is made from a workpiece which has been previously machined to obtain said calibration portion.

[0028] In an embodiment, the cutting tool comprises a helical groove. The helical groove is machined by controlling a 3D coordinate position of the sheave based at least in part on a first geometric feature and a second, different geometric feature of the sheave.

[0029] In an embodiment, the control of the 3D coordinate position of a sheave for machining a helical groove is further based on one or more of three additional different geometric features of the sheave.

[0030] In an embodiment, the cutting tool is an end mill including an end relief face that is machined by controlling a 3D coordinate of the end relief wheel based in part on a geometric feature of the end relief wheel.

[0031] In an embodiment, an end mill includes an end notch that is machined by controlling a 3D coordinate position of a notching wheel based in part on two different geometric features of the notching wheel.

[0032] In an embodiment, an end mill includes an OD relief land that is machined by controlling a 3D coordinate position of the OD relief wheel based in part on three different geometric features of the OD relief wheel.

[0033] In an embodiment, the cutting tool comprises a helical groove, and wherein the 3D coordinate position of each grinding wheel of the plurality of grinding wheels is continuously controlled to perform continuous grinding operations on the workpiece to a desired shape of the cutting tool having an outer diameter of less than 3 mm.

[0034] Another aspect of the present invention relates to a computer-readable storage medium storing instructions that, when executed by a computer of a grinding machine, cause the machine to execute a calibration routine and grind a cutting tool. The calibration routine includes: a) obtaining a first set of measurements of geometric features and positional features of a specific shape of one or each grinding wheel in a set of grinding wheels of different shapes, wherein the first set of measurements is obtained by a preset device; b) calculating a first instruction sequence for grinding one or more marks on a workpiece based on the first set of measurements; and c) obtaining and storing a second set of measurements of at least one geometric feature and positional feature of one or more marks made on the workpiece by the one or each corresponding grinding wheel in the set of grinding wheels. The cutting tool is obtained by: d) calculating a second instruction sequence based on a virtual cutting tool of a desired shape generated by software and the second set of measurements, and e) grinding the cutting tool by running the second instruction sequence.

[0035] In an embodiment, during a calibration routine, a first set of measurements is acquired in step a) for each of at least two grinding wheels, preferably each of at least three grinding wheels, of a set of grinding wheels of different shapes. The instruction sequence in step b) is calculated for grinding at least two marks, preferably at least three marks, adjacent to each other along the distal portion of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention will be better understood with the aid of the description of embodiments given by way of example and illustrated by way of illustration, in which: - Figure 1 shows a perspective view of a cutting tool in the form of an end mill; - Figure 2 Shows Figure 1 An enlarged perspective view of the end mill; - Figure 3 Shows Figure 2 Front view of the end mill; - Figure 4shows the installation for machining Figure 1 A side view of an end mill grinding a cylindrical workpiece in the spindle of a machine; - Figure 5 shows a side view of a workpiece in the form of a stepped bar including a pre-machined cylindrical portion, - Figure 5a yes Figure 5 A magnified view of the pre-machined part. - Figure 6 shows the workpiece after the calibration portion is ground at the distal end portion Figure 5 of the workpiece, - Figure 7 Shows Figure 6 an enlarged view of a calibration portion of a grinding wheel comprising different markings made by corresponding grinding wheels of a set of grinding wheels of different types, - Figure 8 The first type of grinding wheel is shown. Figure 7 A magnified view of one of the markers, - Fig. 9 shows a side view of a grinding wheel of the first type, - Fig.10 The second type of grinding wheel is shown. Figure 7 Another zoomed-in view of the mark - Fig.11 shows a side view of a grinding wheel of said second type, - Fig.11a shows a design to perform with Fig.11 A partial side view of a grinding wheel of the same type of grinding operation, - Fig.12 For use with the third type of grinding wheel Figure 7 Another zoomed-in view of the mark - Fig.13 shows a side view of a grinding wheel of the third type, - Fig.14 The fourth type of grinding wheel is shown. Figure 7 Another zoomed-in view of the mark, - Fig.15 shows a side view of a grinding wheel of the fourth type, - Figures 16a to 16d Schematically shows the first type, the second type, the third type and the fourth type of grinding wheels for obtaining Figure 7 A series of operations performed as part of the calibration - Fig.17 shows the pre-calibrated measurement of the grinding wheel by means of a pre-set device, - Fig.18Schematically illustrating the operations performed by a grinding wheel for grinding a spiral groove of a cutting tool according to the prior art, - Fig.19 Shows Fig.18 The cross section of the cutting tool, and - Fig. 20 It shows that according to the prior art Fig.18 Another schematic diagram of the operation performed by a grinding wheel for grinding a spiral groove. DETAILED DESCRIPTION

[0037] There is a need to reliably and cost-effectively manufacture small rotary cutting tools, in particular milling cutters, such as Figures 1 to 3 For machining cutting tools with such small diameters, conventional calibration methods as described above are not suitable, since they do not allow the shape of the grinding wheel to be determined with a very high level of accuracy.

[0038] The methods disclosed herein are suitable for calibrating a CNC grinding machine to grind rotary cutting tools having an outer diameter as small as 50 microns, or even as small as 30-35 microns.

[0039] refer to Figures 4 to 7 , a long workpiece (e.g., a cylindrical workpiece 10a) is mounted in the spindle 20 of the grinding machine. First, the workpiece is pre-machined into a stepped rod form having a distal portion 10c, such as Figure 5 and 5a As shown in , its diameter exceeds the outer diameter of the cutting tool to be ground by a value typically between 5 and 20 microns. For example, for a cutting tool with an outer diameter of 0.2 mm, the diameter of the cylindrical distal portion 10c is between 0.205 and 0.22 mm.

[0040] Then, a calibration portion CP is ground at the distal end of the portion 10c, as shown in FIG. Figure 6 and 7 . This calibration part CP allows not only the determination of the specific geometrical features of a set of grinding wheels W1, W2, W3, W4 of different shapes, but also the determination of the 3D coordinates of each grinding wheel in the Cartesian coordinate system of the grinding machine, and this with very high accuracy for both the geometrical features of the grinding wheel and its 3D coordinates. This high accuracy can advantageously have an accuracy of less than 3-4 microns, and preferably in the order of one micron. The step bar can be machined directly on the grinding machine used to grind out the calibration part CP for calibration of the grinding machine, or by another machine.

[0041] refer to Figure 7 , the calibration part CP comprises different distinguishing marks M1, M2, M3, M4 machined adjacent to each other. Figure 5aAs shown in FIG. 1 , these distinguishing marks can be ground along the longitudinal axis Z of the cylindrical workpiece 10 a or along a transverse axis A extending from one side of the pre-machined portion 10 c to the other side. T Grinding is performed. The number of marks and their corresponding specific geometric and positional features depend on the desired and final shape of the cutting tool 10. For some cutting tools with simple shapes, a unique type of grinding wheel may be sufficient for machining the cutting tool to the desired shape. In this case, for certain shapes of cutting tools, it may be sufficient to make only one mark on the calibration part, but in most cases, different distinguishing marks M1, M2, M3, M4 are required to identify different geometric features of the grinding wheel in order to grind the cutting tool to its final shape.

[0042] However, for most applications, Fig. 9 , Fig.11 , Fig.13 , Fig.15 A set of grinding wheels of different types shown in the figure is used to grind the cutting tool to the desired shape. In the embodiment shown, Figures 1 to 3 The end mills have been ground using four grinding wheels of different shapes, namely Fig. 9 The groove wheel W1, Fig.11 The outer diameter rear cutter wheel W2 (hereinafter referred to as the OD rear cutter wheel), Fig.13 The notch wheel W3 and Fig.15 The end of the rear cutter wheel W4.

[0043] In the context of the present invention, the term "groove wheel" is to be understood as a wheel having a specific shape suitable for grinding such as Figure 2 Any grinding wheel having a spiral groove of the end mill 10 shown in FIG. Fig. 9 As shown in FIG, the cutting wheel W1 is an example of a grinding wheel suitable for grinding spiral grooves. Similarly, the term "OD back cutter wheel" should be understood as having a specific shape suitable for grinding Figure 2 The outer diameter back edge of the end mill 10 is provided with a grinding wheel having 18. Fig.11 As shown in FIG, the grinding wheel W2 is an example of a grinding wheel suitable for grinding the outer diameter back edge band. Similarly, the term "slotting wheel" should be understood as having a specific shape suitable for grinding Figure 2 The end of the end mill 10 is notched 16 by any grinding wheel. Fig.13 An example of the shape of the scoring wheel W3 is shown in FIG. Similarly, the term "end back cutter wheel" should be understood as having a specific shape suitable for grinding such as Figure 3 Any grinding wheel of the end relief surface 14 of the end mill 10 shown in FIG. Fig.15 As shown in the figure, the cup wheel W4 is suitable for grinding Figure 3 An example of a grinding wheel with a clearance surface at the end of an end mill 10.

[0044] Additionally, the term "grinding operation" should be understood as one type of grinding operation among several types of operations required to grind a cutting tool to its final and desired shape. Grinding operations may include, for example, groove grinding, kerf grinding, end relief grinding, OD grinding, and the like.

[0045] A continuous grinding operation must be performed using several grinding wheels (e.g., using four different grinding wheels W1, W2, W3, W4) to grind the end mill 10 according to the embodiment having an outer diameter of less than 3 mm. In this case, the distal end portion 10c of the cylindrical workpiece or blunt tool is machined to make four different marks M1, M2, M3, M4 using the corresponding grinding wheels W1, W2, W3, W4 to obtain the calibration portion CP. Figure 7 The general shape of the calibration portion CP shown in FIG. 1 is merely an example of various other shapes that may characterize geometric and positional features of one or more grinding wheels of a particular shape.

[0046] Before carrying out a continuous grinding operation on the workpiece 10a for grinding a calibration portion CP whose geometry may depend on the final and desired shape of the cutting tool to be ground, the geometrical and positional characteristics of each of the set of grinding wheels W1, W2, W3, W4 necessary for grinding the cutting tool are measured by means of a preset measuring device. To this end, each grinding wheel is mounted, for example, on a support, the dimensions of which correspond to the dimensions of the spindle of the grinding machine on which the grinding wheel is intended to be mounted. Thus, when the grinding wheel is mounted on the support for grinding the cutting tool, it is positioned in exactly the same position relative to the support and relative to the spindle. The 3D coordinates D1 of the grinding wheel in the coordinate system of the grinding machine can thus be measured. w 、D2 w .

[0047] Fig.17 The pre-calibration measurement of each grinding wheel shown in FIG. 1 typically consists of measuring the profile of a continuous portion of the grinding wheel. From this profile, the values ​​of the key geometrical features of the grinding wheel (such as R1, R2, a1, a2) and the positional features Z and The values ​​of , where the accuracy is about 10 microns. These values ​​are used to estimate the key geometrical features of the grinding wheel and the 3D coordinates in the grinding machine in order to be able to grind the different markings M1, M2, M3, M4 of the calibration part CP.

[0048] In this example, if Figures 16a to 16d As shown in FIG. 1 , the calibration portion CP is obtained by performing a series of grinding operations on the distal end portion 10b of the cylindrical workpiece 10a. A first mark M3 is ground using a notching wheel W3, a second mark M4 is then ground using an end relief wheel W4, a third mark M2 is then ground using an OD relief wheel W2, and finally a fourth mark M1 is ground using a groove wheel W1.

[0049] Thus, each of these marks M1, M2, M3, M4 has geometrical features R1, R2, a1, a2, L and positional features D1, D2 that are specific to the grinding wheel on which it is ground. By measuring the geometrical features of the marks, the geometrical features of this specific grinding wheel can be determined with very high accuracy. In addition, additional geometrical features of each of these marks, referred to therein as positional features, can be used to determine the 3D coordinates D1 of the grinding wheel in the XYZ coordinate system of the grinding machine. w 、D2 w .

[0050] Various methods can be used to measure the geometric and positional features of different marks M1, M2, M3, M4 of the calibration part CP. In an advantageous embodiment, one or more geometric features and two positional features of each mark M1, M2, M3, M4 are measured using a laser imaging system embedded in the grinding machine. The laser imaging system has been used to regularly measure the diameter and external shape of the cutting tool to automatically perform any necessary corrections during grinding to ensure unattended automatic cycle production of the cutting tool. The laser imaging system, which has an accuracy of less than 3 to 4 microns and preferably on the order of one micron, can therefore perform on-site laser scanning along the longitudinal axis of the calibration part CP, thereby avoiding the need to remove the workpiece 10a from the spindle 20 in order to perform the measurement. This simplifies the manufacturing process because the cutting tool 10 can be ground to its final and desired shape immediately after performing the laser scan. This is particularly important when it is necessary to produce large quantities of cutting tools, in which the cutting tool will be automatically replaced by the workpiece used to produce the cutting tool once it has been ground to its final shape without any manual intervention.

[0051] Alternatively, the measurement of the geometrical and positional features of the different markings M1 , M2, M3, M4 of the calibration part CP may be performed outside the grinding machine, for example with the aid of a microscope having an accuracy also below five micrometers and preferably in the order of one micrometer.

[0052] Therefore, by measuring these different markings M1, M2, M3, M4, the geometrical features of each grinding wheel W1, W2, W3, W4 and its 3D coordinates in the Cartesian coordinate system of the grinding machine can be determined with high accuracy. This high-precision calibration is essential for machining small rotating cutting tools with an outer diameter of less than 3 mm, especially for cutting tools with an outer diameter of less than 100 microns (e.g., as small as 50 microns, or even as small as 30-35 microns).

[0053] refer to Figure 8 , Figure 7 The marking M1 of the exemplary calibration portion CP has been Fig. 9The marking M1 includes several distinguishing geometric features specific to the sheave, namely the radii R1 and R2, the angles a1, a2, the length L, which are specific to the sheave. Fig. 9 Different geometric features R1 of the sheave W1 shown in w , R2 w 、a1 w 、a2 w , L w The marking includes two additional position features D1, D2, which can be used to determine the 3D coordinates D1 of the groove wheel W1 in the Cartesian (XYZ) coordinate system of the grinding machine. w 、D2 w .

[0054] More specifically, the first position feature D1 is used to determine the z coordinate D1 of the sheave W1 w , i.e., its position along the first axis Z of the horizontal plane of the Cartesian coordinate system, and the second position feature D2 is used to determine the x-coordinate D2 of the sheave W1 w , that is, its position along the second axis X of the horizontal plane, because D2 w The second position feature D2 is also used to determine the y-coordinate of the grinding wheel W1 , ie its position along the third axis Y (vertical axis) of the Cartesian coordinate system, because the diameter of the grinding wheel W1 also corresponds to the third axis.

[0055] However, when the cylindrical workpiece 10a is mounted in the spindle 20 of the grinding machine, a measurement of the position of the cylindrical workpiece 10a must be completed in order to have a reference for determining the exact position of the workpiece 10a along the first axis Z. For example, this measurement can be completed using an embedded laser imaging system that senses the distal end of the cylindrical workpiece 10a. By knowing the exact position of the workpiece 10a along the first axis Z and the first position feature D1 and the second position feature D2, the exact 3D coordinate D1 of the grinding wheel W1 can be determined. w 、D2 w .

[0056] The instruction sequence is then calculated by the CNC grinding machine using the known mathematical models of the grinding wheel movements, which are corrected to take into account the deviations between the preset values ​​used by the mathematical models and the values ​​measured on the calibration part CP. These corrections are performed for one or more geometrical features and two positional features of each grinding wheel in a set of grinding wheels W1, W2, W3, W4 of different types / shapes required for performing different grinding operations to obtain cutting tools. The instruction sequence can be pre-programmed, for example, by means of software based on a given numerical model of the cutting tool of the desired shape.

[0057] Subsequently, the 3D coordinates of the different grinding wheels are controlled by a command sequence for performing consecutive and preferably different grinding operations on the workpiece in order to machine the cutting tool into the desired shape.

[0058] In the illustrated embodiment, Fig. 9 The grooved wheel W1 is used for grinding Figure 2 The groove 12 of the end mill 10 shown in FIG. For such small diameters, the 3D coordinates of the groove wheel W1 in the XZY reference system of the grinding machine must be as accurate as possible. This accuracy is crucial for the success of the machine setup and avoids grinding iterations several times until a tool within specifications and tolerances is obtained.

[0059] The 3D coordinates are calculated based on geometric features, which include at least the radius R1 of the sheave W1 w and angle a1 w , as in Figure 8 For a particular type of spiral profile, one or more of the following geometric features of the sheave may also be used in combination with the geometric features R1 and a1: Width L w 、Chamfer a2 w and transition radius R2 w .

[0060] The 3D coordinates of the groove wheel W1, which have been pre-measured by the preset device as described above, are adjusted based on the measurement of the position features D1, D2 of the marker M1, which accurately calibrates the position D1 of the groove wheel W1 in the Cartesian coordinate system of the grinding machine. w 、D2 w Using known mathematical models and based on the above geometrical features and the calibrated 3D coordinates of the sheave wheel W1 in the Cartesian coordinate system of the grinding machine, the movement of the sheave wheel W1 in the groove grinding operation is calculated.

[0061] refer to Fig.10 , Figure 7 The mark M2 of the exemplary calibration portion CP has been Fig.11 The marking M2 includes several distinguishing geometric features specific to the wheel, namely the radius R1 and the angles a1, a2, which are specific to the wheel. Fig.11 Different geometric features of the OD back wheel W2 shown in R1 w 、a1 w 、a2 w Like the mark M1 of the calibration part, the mark M2 includes two additional position features D1, D2, which, as explained above for the groove wheel, can be used to determine the 3D coordinate D1 of the OD back cutter wheel W2 in the Cartesian coordinate system of the grinding machine. w 、D2 w .

[0062] Using the known mathematical model and based on the above geometric characteristics R1 w 、a1 w 、a2 w And the calibrated 3D coordinate D1 of the OD back wheel W2 in the Cartesian coordinate system of the grinding machine w 、D2 w To calculate the movement of the OD back wheel W2 during the OD grinding operation. Figure 2 The end mill 10 shown in FIG. 1 is formed by an outer diameter relief land 18 .

[0063] refer to Fig.12 , Figure 7 The mark M3 of the exemplary calibration portion CP has been Fig.13 The marking M3 comprises at least two distinguishing geometric features specific to the wheel, namely the radius R1 and the angle a1, which are specific to the wheel. Fig.13 The corresponding geometric feature R1 of the notching wheel W3 shown in w 、a1 w Like the marks M1 and M2 of the calibration part, the mark M3 includes two additional position features D1, D2 which, as explained above for the grooved wheel, can be used to determine the 3D coordinate D1 of the notching wheel W3 in the Cartesian coordinate system of the grinding machine. w 、D2 w .

[0064] Using a known mathematical model and based on two or more geometric features R1 of the notching wheel W3 w 、a1 w And the 3D coordinate D1 w 、D2 w To calculate the movement of the notch wheel W3 during the notch grinding operation. Figure 2 As shown in FIG. 1 , the notch grinding operation consists of grinding the end notch 16 of the end mill 10 .

[0065] refer to Fig.14 , Figure 7 The mark M4 of the exemplary calibration portion CP has been Fig.15 The end back wheel W4 shown in FIG. is ground out. The mark M4 includes a geometric feature R1, which corresponds to Fig.15 The radius R1 of the end back cutter wheel W4 shown in w As explained above, like the marks M1, M2 and M3 of the calibration part CP, the mark M4 includes two additional position features D1, D2, which can be used to determine the 3D coordinate D1 of the end back cutter wheel. w 、D2 w .

[0066] Using a known mathematical model and based on at least the above geometric features R1w and 3D coordinates D1 of the end back cutter wheel W4 w 、D2 w To calculate the movement of the end flank wheel W4 during the end flank grinding operation. Figure 3 The end relief surface 14 of the end mill 10 shown in FIG.

[0067] The shape of a particular grinding wheel assigned to a particular type of grinding operation may vary significantly, as the technician himself decides what shape to give to the grinding wheel based not only on his experience, but also on the wheel he is using. Fig.11 The OD back wheel W2 shown in FIG. 1 may have another shape, such as Fig.11a and still be suitable for achieving the same grinding operation. In this case, Fig.11 Geometric feature R1 in w and a1 w Corresponds to Fig.11a Geometric feature R1 in w' and a1 w' .

[0068] Thus, the disclosed method for machining small rotary cutting tools can be used independent of the shape of the grinding wheel designed for a particular type of grinding operation.

[0069] For simple shaped cutting tools, only one or two grinding wheels may be sufficient to machine a cylindrical workpiece into its final shape. In the case of simple shaped cutting tools where only one grinding wheel may be needed to perform all grinding operations, in some cases, the grinding wheel may still need to make several marks on the calibration portion of the workpiece during calibration of the grinding machine in order to determine the different distinguishing geometric features of the grinding wheel necessary to perform all grinding operations. However, a single mark may be sufficient to characterize the geometric and positional features of the grinding wheel for grinding a particular simple shaped cutting tool.

[0070] The disclosed method has the advantage of calibrating all grinding wheels necessary to grind a cutting tool to its final and desired shape by grinding a calibration portion on a workpiece that will eventually be machined by different types of consecutive grinding operations to obtain the cutting tool, thereby reducing the waste of raw material.

[0071] The grinding machine includes software storing instructions which, when executed by a processing unit of the grinding machine, cause the machine to perform the method as described above for machining a small rotary cutting tool 10 having a core diameter of less than 3 mm. The method executed by the software can calibrate the geometric features and 3D coordinates of each grinding wheel W, W2, W3, W4 with high accuracy (e.g., down to microns).

[0072] In this regard, the software is configured to acquire key geometrical and positional features along a profile of at least one grinding wheel obtained by a preset optical device. The first set of measurements of Z. Fig.17 An example of such a profile is shown in . The key geometric features may be, for example, the first radius R1 and the second radius R2 and the first angle a1 and the second angle a2 of the grinding wheel. The number of executions of this operation is defined by the number of grinding wheels W1, W2, W3, W4 required to grind the cutting tool to its final and desired shape. The first set of measurements obtained by the preset optical device has an accuracy typically in the order of 10 microns, which is not accurate enough for grinding cutting tools having an outer diameter of less than 3 mm.

[0073] A first basic sequence of instructions is then calculated based on the first set of measurements to control the movement of each grinding wheel W1, W2, W3, W4 to make different marks M1, M2, M3, M4 along the longitudinal axis of the distal portion of the workpiece. The software then acquires a second set of measurements of at least one geometric feature and two positional features of each mark M1, M2, M3, M4 made on the workpiece, which are specific to a particular type of grinding wheel.

[0074] As mentioned above, the positions and geometrical features of the different marks M1, M2, M3, M4 can be measured by a laser imaging system embedded in the grinding machine. The laser imaging device is mounted to perform a laser scan along the longitudinal axis of the distal portion of the workpiece to obtain a second set of measurements without removing the workpiece from the spindle of the grinding machine.

[0075] The second set of measurements typically has an accuracy of about one micron. For tools having an outer diameter less than 3 mm, as small as 50 microns, or even 30-35 microns, this accuracy allows the dimensional deviation of the grinding of the cutting tool to remain within an acceptable range.

[0076] Alternatively, the measurement of the geometrical and positional features of the different markings M1, M2, M3, M4 of the calibration part CP can be performed outside the grinding machine, for example with the aid of a microscope, which also has an accuracy down to micrometers. In this case, the software can acquire data from these measurements, which will be sent to the computer of the grinding machine. In an alternative embodiment, the software can provide a user interface comprising a field for manually entering the second set of measurements.

[0077] A sequence of instructions for movement of one or more grinding wheels is then calculated based on a known mathematical model and in accordance with a second set of measurements for machining the cutting tool.

[0078] In an advantageous embodiment, a set of measurements corresponding to each grinding wheel in a set of grinding wheels of different types may be stored and retrieved for use in grinding additional cutting tools during cutting tool manufacturing that require any of these specific grinding wheels to grind a specific part.

[0079] In short, the method disclosed above usefully enables accurate setting of a grinding machine based on different geometrical features of one or more grinding wheels W1, W2, W3, W4, which are obtained by measuring one or more corresponding marks M1, M2, M3, M4 ground on a workpiece by the respective grinding wheel. Thus, the method advantageously enables the production of rotary cutting tools, in particular cutting tools with a helical groove, having an outer diameter of less than 3 mm, and as small as 50 microns, or even as small as 30-35 microns.

[0080] On the other hand, the step of grinding a calibrated groove on the surface of the workpiece according to a predetermined spiral pattern of the desired spiral groove as disclosed in WO2019 / 197931 does not allow the grinding machine to be set up as accurately as the method disclosed herein. In fact, the predetermined spiral pattern cannot be used to determine the geometrical features of the grinding wheel that has ground such a pattern. More specifically, when grinding a spiral groove, the geometry of the grinding wheel is never reflected in the groove. Fig.18 As shown in FIG, a simple grinding wheel W with a sharp edge at the end or an edge radius of a few microns is produced as Fig.19 Complex cross section of a cutting tool shown in .

[0081] No matter in which plane the tool section is produced, it will never reflect the original shape of the grinding wheel W. In addition, if Fig. 20 As shown in , in the case of a spiral groove, the inclination angle of the grinding wheel is always greater than the spiral angle of the groove. Therefore, it is impossible to obtain the geometric characteristics of the grinding wheel that has ground a spiral groove from the method disclosed in WO2019 / 197931, let alone the angle or edge radius of the grinding wheel.

[0082] In WO2019 / 197931, although direct measurement by probing the spiral grooves does not in any way lead to the calculation of the shape of the grinding wheel, it does provide an accurate indication of its position error in the XYZ workspace. In order to achieve this, the shape must first be entered into the calculation software as accurately as possible. This method is only suitable for cutting tools of sufficient size to know the exact shape of the grinding wheel in advance. Before the wheel is installed in the machine, a special measuring instrument is used to measure the shape.

[0083] In contrast, in the case of microtools, the shape of the grinding wheel that will produce the helical groove is only approximately known. The method disclosed herein is able to find not only the exact shape of the grinding wheel used to grind the helical groove, i.e., the specific critical geometric features, but also its exact position in the XYZ workspace.

[0084] It will be apparent to those skilled in the art that various modifications and variations of the embodiments of the invention may be made without departing from the scope of the invention as defined in the appended claims. For example, the above method may of course be adapted to any other rotary cutting tool, such as other types of milling cutters, such as slab milling cutters, face milling cutters, straight slot milling cutters, or different types of drills, such as multi-slot drills, straight slot drills, countersunk drills, etc. Reference List Cutting tool 10 (eg, end mill) Cylindrical workpiece 10a Distal portion 10c Screw groove 12 End flank 14 End cut 16 Outside diameter back blade band 18 Spindle 20 Calibration part CP Marking M1, M2, M3, M4 Marked geometric features R1, R2, a1, a2, L Marked position features D1, D2 Grinding wheels W1, W2, W3, W4 Wheel geometry R1 w , R2 w 、a1 w 、a2 w , L w Wheel position feature D1 w 、D2 w .

Claims

1. A method for machining a rotating cutting tool (10) by a grinding machine, comprising: a) installing a workpiece (10a) in a spindle (20) of the grinding machine; b) machining a calibration portion (CP) of the workpiece (10a) by making one or more marks (M1, M2, M3, M4) on the workpiece using a grinding wheel or using corresponding multiple grinding wheels (W1, W2, W3, W4) of different shapes, wherein the one or each mark (M1, M2, M3, M4) comprises at least one geometric feature (R1, R2, a1, a2, L) and two position features (D1, D2), which respectively correspond to the geometric features (R1) of the corresponding grinding wheel on which the corresponding mark (M1, M2, M3, M4) has been ground. w , R2 w 、a1 w 、a2 w , L w ) and the 3D coordinates (D1 w 、D2 w ); c) performing measurements of the at least one geometrical feature (R1, R2, a1, a2, L) and the two positional features (D1, D2) of the or each mark (M1, M2, M3, M4) of the calibration portion (CP); d) generating a sequence of instructions for grinding the workpiece (10a) to a final and desired shape of the cutting tool (10) based on the at least one geometrical feature and the two positional features of the or each mark as measured in step c), and e) controlling the 3D coordinates of the one or more grinding wheels (W1, W2, W3, W4) in the XYZ coordinate system to obtain the cutting tool (10) during a grinding operation on the workpiece or another workpiece according to the instruction sequence.

2. The method according to claim 1, wherein: At least one geometric feature (R1) of the grinding wheel (W1, W2, W3, W4) on which the marking has been ground w , R2 w 、a1 w 、a2 w , L w ) corresponds to the angle or edge radius of the grinding wheel.

3. A method according to any preceding claim, wherein: Once step b) is completed, measurement of one or more geometrical features (R1, R2, a1, a2, L) of the mark or each mark (M1, M2, M3, M4) and of the two position features (D1, D2) is automatically performed by a laser imaging system embedded in the grinding machine, for example by performing a laser scan along a calibration portion (CP) of the workpiece (10a).

4. A method according to any preceding claim, wherein: Each of the plurality of marks (M1, M2, M3, M4) is ground using one of the corresponding plurality of grinding wheels (W1, W2, W3, W4) of different shapes required to grind the workpiece (10a) to the final and desired shape of the cutting tool (10).

5. The method according to any preceding claim, further comprising the steps of: Before machining the one or each mark (M1, M2, M3, M4) of the calibration part (CP) in step b), direct measurement of one or more geometrical features of the one or each of the multiple grinding wheels (W1, W2, W3, W4) is performed with the help of a preset device.

6. The method according to any preceding claim, further comprising the steps of: a measurement of the position of the workpiece along an axis (Z) of the XYZ coordinate system of the grinding machine, wherein the 3D coordinates (D1, D2) of the one or each of the grinding wheels (W1, W2, W3, W4) in the XYZ coordinate system of the grinding machine are determined based on the measured position of the workpiece along the axis and the two position features (D1, D2) of the one or each of the markings (M1, M2, M3, M4) of the calibration part performed in step b). w 、D2 w ).

7. A method according to any preceding claim, wherein: The plurality of marks (M1, M2, M3, M4) of the calibration portion (CP) are arranged along a longitudinal axis (Z) of the workpiece or along a transverse axis (A) extending from one end of the calibration portion to an opposite end. T ) are made adjacent to each other on the workpiece (10a).

8. A method according to any preceding claim, wherein: Measurements of the at least one geometrical feature (R1, R2, a1, a2, L) and the two position features (D1, D2) for each marking (M1, M2, M3, M4) performed in step c) are saved for each of the plurality of grinding wheels (W1, W2, W3, W4), and wherein the measurements are obtained for performing at least two consecutive grinding operations on the workpiece to obtain the rotating cutting tool.

9. A method according to any preceding claim, wherein: The first position feature (D1) of the one or each mark (M1, M2, M3, M4) of the calibration portion (CP) defines a first position along a first axis (Z) of the three coordinate axes of the XYZ coordinate system of the grinding machine, the first axis coinciding with the longitudinal axis of the workpiece.

10. The method according to the preceding claim, wherein: The second position feature of the one mark or each mark (M1, M2, M3, M4) of the calibration part (CP) is used to determine the diameter (D2) of the corresponding grinding wheel (W1, W2, W3, W4) used to make the one mark or each mark, and wherein the second position and the third position along the second axis and the third axis of the coordinate system respectively are determined based on the diameter to calculate the 3D coordinates of the corresponding grinding wheel.

11. A method according to any preceding claim, wherein: The or each marking (M1, M2, M3, M4) of the calibration portion comprises at least one radius (R1, R2) for determining at least one radius of the corresponding grinding wheel (W1, W2, W3, W4).

12. A method according to any preceding claim, wherein: The calibration portion (CP) is machined at a distal end portion (10b) of the workpiece.

13. A method according to any preceding claim, wherein: The rotary cutting tool is made from the workpiece (10a) which has been previously machined to obtain the calibrated portion (CP).

14. A method according to any preceding claim, wherein: The rotary cutting tool comprises a helical groove (12) which is formed by at least a first geometric feature (R1) of the groove wheel based at least in part on w ) and the second different geometric feature (a1 w ) to control the 3D coordinate position of the groove wheel (W1) for machining.

15. The method according to the preceding claim, wherein: The control of the 3D coordinate position of the sheave (W1) for machining the helical groove is further based on three additional different geometric features of the sheave (L w 、a2 w , R2 w ) 16. The method according to any one of claims 1 to 13, wherein: The cutting tool is an end mill including an end relief face that is machined by controlling a 3D coordinate of the end relief wheel (W4) based at least in part on at least one geometric feature (R1') of the end relief wheel.

17. The method according to the preceding claim, wherein: The end mill includes an end notch that is machined by controlling a 3D coordinate position of a notching wheel (W3) based at least in part on two different geometric features of the notching wheel.

18. The method according to claim 16 or claim 17, wherein: The end mill includes an outer diameter relief land zone that is formed by three different geometric features (R1 w 、a1 w 、a2 w ) to control the 3D coordinate position of the outer diameter back cutter wheel (W2) for machining.

19. A computer readable storage medium storing instructions which, when executed by a computer of a grinding machine, cause the machine to perform a calibration routine and grind a cutting tool, the calibration routine comprising: a) Acquiring and storing geometric features (R1, R2, a1, a2) and position features of a specific shape of one or each grinding wheel in a set of grinding wheels (W1, W2, W3, W4) of different shapes a first set of measured values, wherein the first set of measured values ​​is obtained by a preset device, b) calculating a first instruction sequence for grinding one or more marks (M1, M2, M3, M4) on the workpiece based on the first set of measured values, c) obtaining and sorting a second set of measured values ​​of at least one geometric feature (R1, R2, a1, a2, L) and position feature (D1, D2) of one or more marks (M1, M2, M3, M4) made on the workpiece (10a) by the one or each corresponding grinding wheel of the set of grinding wheels (W1, W2, W3, W4), d) calculating a second instruction sequence based on the second set of measurements, and e) grinding the cutting tool by executing the second instruction sequence.

20. The computer-readable storage medium according to the preceding claim, wherein In step a), the first set of measurement values ​​is obtained for each of at least two grinding wheels, preferably each of at least three grinding wheels, of the set of grinding wheels (W1, W2, W3, W4) of different shapes, and the instruction sequence in step b) is calculated for grinding at least two marks, preferably at least three marks (M1, M2, M3, M4) adjacent to each other along the distal portion of the workpiece.

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