METHOD FOR GRINDING ROTARY CUTTING TOOLS WITH A SINGLE CLAMPING ON A SINGLE MACHINE

Abstract

 The present invention relates to a method for grinding, with a grinding machine (100), a rotary cutting tool (20) comprising a cutting part (22) and a shank (26). The grinding machine (100) comprises a headstock (102) with a spindle (104) arranged to receive one end portion of a workpiece (10) to rotate said workpiece about a rotation axis (X), and a guiding support (50) to support a portion of the workpiece (10) during grinding of the cutting part. The guiding support (50) comprises a guiding surface (52) having a cross-section, within a plane orthogonal to said rotation axis, of an incomplete annulus. The method comprises the following steps: i) mounting said one end portion of the workpiece (10) into the spindle (104) and rotating said workpiece about the rotation axis (X); ii) performing sharpening operations, on a portion of the workpiece intended to become to the cutting part (22) of the final cutting tool with grinding wheels (W2, W3, W4) to obtain a sharpen segment, and iii) grinding the sharpen segment down to a final diameter including the back taper with another wheel (W5) to obtain the cutting part (22) of the cutting tool (20). The portion of the workpiece intended to become to the cutting part (22) of the final cutting tool is supported by the guiding support (50) during steps ii) and iii).

Description

Field of the invention

[0001] The present invention relates to a method for grinding rotary cutting tools, in particular reamers and drills, with a single clamping on a single machine. These cutting tools comprise a cylindrical part, called the shank, and a useful part, generally called the cutting part whose dimensional tolerance is generally very tight and features a back taper.

Description of related art

[0002] Cutting tools, such as reamers and drills, with conventional and reinforced shanks are shown in Figures 1b and 1c. In particular, the cutting tool of Figure 1c comprises a reinforced shank 26 whose diameter corresponds to the diameter of the blank bar 10 of Figure 1a of known diameter and from which the cutting tool is ground, with for example a diameter of 6mm. The cutting tool of Figure 1b has a conventional shank 26 whose diameter corresponds to the diameter of the blank bar 10 from which the cutting tool is ground, with a diameter of a few hundredths of millimeters larger than the diameter of the cutting part 22 of the cutting tool with its final shape. In this case, the diameter of the blank bar may be for example of 5mm while the diameter of the cutting part may be for example of 4.98mm.

[0003] Conventionnel methods, for manufacturing a reamer or a drill are generally two-steps methods. These methods comprise a first step consisting in preparing the cutting part of the tools from a blank bar by grinding circular parts including the back taper to prevent the reamer or drill from jamming in the hole. The first step is followed by a second step consisting in sharpening the cutting part to obtain the cutting tool.

[0004] More particularly, the first step of manufacturing the cutting part from the blank bar is obtained through different alternative known methods. One method consists in grinding the cutting part of the tool including the back taper while turning the workpiece WP between centers as shown in Figure 2. This methos uses a headstock HS supporting one end of the workpiece directly or through a chuck CK and a tailstock TS supporting the opposite end of the workpiece WP. In order to transmit torque from the spindle to the workpiece, a lathe dog LD is used. The lathe dog is driven by a drive plate affixed to the spindle nose.

[0005] This method has the disadvantage of likely bending the workpiece in the case of a large length/diameter ratio. Moreover, for cutting tools with a reinforced shank, the material to be removed must be carried out in several roughing passes and then, after changing the grinding wheel, one finishing pass must be performed. Finally, a center point must be ground on both ends of the bar by means of a center point grinding machine. All these steps have a negative impact on the production output in particular when large batches of cutting tools are to be produced.

[0006] Another method of carrying out the first step of the machining of the cutting part from the blank bar consists in carried out in a single pass with a roughing wheel Wa and a finishing wheel Wb working simultaneously as disclosed in US5865667 and schematically shown in Figure 3. Back taper is automatically achieved during this process.

[0007] The second step of manufacturing the cutting part of the tool comprises sharpening operations including grinding straight or helical coils, peripheral relieves and tool tip sharpening. These operations are carried out on another machine, i.e. a sharpening machine, which usually comprises five or six numerical axes. The bar is generally held in place by a tailstock.

[0008] In a nutshell, manufacturing a reamer or a drill using the conventional methods requires two machines, and is therefore produced in two clamping operations. These two-steps conventional methods comprise several drawbacks. Preparation of the bar by grinding between points induces bending of the bar, and therefore additional difficulty in accurately producing the back taper of the cutting part. Moreover, for both methods (inter-point or peel grinding as disclosed in US5865667), the two clamping operations requires the setup of two separate machines. Finally, for between-point bar preparation, it is necessary to create center points at both ends of the bar. This operation is carried out on a special machine called a "center point grinding machine".

[0009] The above-described methods are therefore time-consuming and difficult to implement which have a direct negative impact on the production costs of the reamers and drills.

[0010] These tools can also be machined in one clamping on a 5-6-axis grinding machine equipped with a tailstock. This set-up enables to produce the cutting part, including the back taper, by grinding and, at the same time, to carry out the sharpening operations, i.e., grinding of straight or helical flutes, grinding of peripheral undercuts and sharpening the tool tip.

[0011] As described in the previous methods, the disadvantage of this approach is that the bar is likely to bend when the back taper is ground. This method also requires a center to be ground on a special machine by means of a center point grinding machine thereby increasing the time and production costs of these tools.

Brief summary of the invention

[0012] An aim of the present invention is therefore to propose a method for grinding rotary cutting tools exempt of the limitations of the prior art.

[0013] In particular, an aim of the present invention is to provide a grinding method that streamlines the production of cutting tools.

[0014] According to the invention, this aim is achieved notably by means of a method for grinding, with a grinding machine, a rotary cutting tool comprising a cutting part and a shank. The grinding machine comprises a headstock with a spindle arranged to receive one end portion of a workpiece to rotate said workpiece about a rotation axis, and a guiding support to support a portion of the workpiece during grinding of the cutting part. The guiding support comprises a guiding surface having a cross-section, within a plane orthogonal to said rotation axis, of an incomplete annulus. The method comprises the following steps: i) mounting said one end portion of the workpiece into the spindle and rotating said workpiece about the rotation axis; ii) performing sharpening operations, on a portion of the workpiece intended to become to the cutting part of the final cutting tool with grinding wheels to obtain a sharpen segment, and iii) grinding the sharpen segment down to a final diameter including the back taper with another wheel to obtain the cutting part of the cutting tool. The portion of the workpiece intended to become to the cutting part of the final cutting tool is supported by the guiding support during steps ii) and iii).

[0015] In an embodiment, longitudinal threads run along flutes and form together parts of a circle corresponding to the original diameter of the workpiece at any cross-section along the longitudinal axis of the cutting part both during sharpening operations and when said sharpening operations are completed. These longitudinal threads are in contact with the guiding surface of the guiding to provide a reference point and to support the cutting part of the cutting tool during steps ii) and iii).

[0016] In an embodiment, the method further comprising, after performing step i) and prior to performing steps ii) and iii), the following steps: a) grinding with a first grinding wheel of the grinding machine an opposite end portion of the workpiece down to a first diameter for calibration of the position of said first grinding wheel; b) measuring said first diameter, and c) moving the first grinding wheel to grind a cylindrical segment of the workpiece down to a second diameter and according to the measurement of the first diameter. The length of the cylindrical segment corresponds to the length of the workpiece intended to become the cutting part of the final cutting tool. During step ii), the sharpening operations are performed on said cylindrical segment, The grinding wheels are different from the first grinding wheel (W1).

[0017] In an embodiment, longitudinal threads extend along flutes and form together parts of a circle corresponding to the second diameter of the workpiece at any cross-section along the longitudinal axis of the cutting part both during sharpening operations and when said sharpening operations are completed. These longitudinal threads are in contact with the guiding surface of the guiding support to provide a reference point and to support the cutting part of the cutting tool during steps ii) and iii).

[0018] In an embodiment, the first diameter is less than 0.1mm larger than the second diameter of the cutting part of the cutting tool.

[0019] In a preferred embodiment, the first diameter is not larger than 0.04mm of the second diameter.

[0020] In an embodiment, the sharpening operations comprise a step of grinding flutes of the cutting part with one grinding wheel of said other grinding wheels.

[0021] In an embodiment, the sharpening operations comprise another step of grinding outer diameter relief lands of the cutting part with another grinding wheel of the other grinding wheels.

[0022] In an embodiment, the sharpening operations comprise another step of grinding the distal end of the cutting part with another grinding wheel of the other grinding wheels.

[0023] In an embodiment, the first diameter is measured in-situ by an electronical probe or by optical means such as a laser.

[0024] In an embodiment, the headstock of the grinding machine moves along the rotating axis of the workpiece while the guiding support remains fixed while grinding the length of the segment down to said second diameter.

[0025] In an embodiment, the headstock of the grinding machine remains fixed while the guiding support moves along the rotating axis while grinding the length of the segment down to said second diameter.

[0026] In an embodiment, the grinding machine further comprises a V-guide for supporting the workpiece and to correct any concentricity errors during grinding of the cylindrical segment down to the second diameter and during sharpening operations of the cutting part.

[0027] In an embodiment, the diameter of the incomplete annulus of the guiding support is between one to ten micrometers larger than the second diameter of the cylindrical segment, preferably between two and five micrometers.

[0028] In an embodiment, the diameter of the incomplete annulus of the guiding support is between one to ten micrometers larger than the known diameter of the workpiece before grinding, preferably between two and five micrometers.

Brief Description of the Drawings

[0029] The invention will be better understood with the aid of the description of embodiments given by way of examples and illustrated by the figures, in which:

• Figures 1a, 1b and 1c show a side view of respectively a blank bar, and a cutting tool with respectively a reinforced shank and a conventional shank after completing sharpening operations;
• Figure 2 shows a schematic side view of a first step of manufacturing the cutting part from a blank bar including the back taper of a method according to the prior art discussed above ;
• Figure 3 shows a schematic side view of a first step of manufacturing the cutting part from a blank bar including the back taper of another method according to the prior art as discussed above;
• Figure 4 shows a side view of a grinding machine comprising different grinding wheels (only one is visible), a headstock with a spindle to receive one end of a workpiece and a guiding support to support the workpiece during grinding operations;
• Figure 5 shows a perspective view of the guiding support comprising a guiding surface having a cross-section, within a plane orthogonal to said rotation axis, of an incomplete annulus, when the guiding support is mounted onto a fixed base of the grinding machine;
• Figure 6 shows a view similar to Figure 4 while a distal end portion of the workpiece is ground down to a first diameter for calibration of the position of a first grinding wheel according to a grinding method for cutting tools with reinforced shank;
• Figure 7 shows a view similar to Figure 6 while the first grinding wheel is griding a cylindrical segment of the workpiece down to a second diameter as a function of the measurement of the first diameter;
• Figure 8 shows a view similar to Figure 7 during a sharpening operation of the cutting part with another grinding wheel,
• Figures 9a, 9b and 9c show different sharpening operations of the cutting tool performed prior completing the back taper grinding,
• Figure 10 shows a view similar to Figure 8 while another grinding wheel is grinding the sharpen segment down to a final diameter including the back taper to obtain the cutting tool with the reinforced shank, and
• Figure 11 shows the cutting part of the cutting tool once the sharpening operations are completed, wherein longitudinal threads run along the flutes of the cutting part for ensuring contact with the guiding surface of the insert during sharpening operations and back taper grinding.

Detailed Description of possible embodiments of the invention

[0030] The complete grinding of a cutting tool, in particular a reamer or a drill as shown in Figures 1b and 1c with alternative methods disclosed therein is carried out in a single clamping on a single grinding machine 100 as shown for example in Figure 4. In this respect, the grinding machine 100 comprises a headstock 102 with a spindle 104 arranged to receive one end portion of a workpiece 10 in the form of a blank bar 10 as illustrated in Figure 1a. The spindle 104 is arranged to rotate the blank bar 10 about a rotation axis X coaxial with its longitudinal axis.

[0031] The grinding machine 100 comprises, conventionally, a V-guide 60 for supporting the blank bar 10 during grinding and to correct any concentricity errors. The grinding machine 100 further comprises an interchangeable insert 50 which acts as a guiding support. As illustrated in Figure 5, the insert 50 comprises a guiding surface 52 having a cross-section, within a plane orthogonal to the rotation axis, of an incomplete annulus, when the insert is fixed to a removable or fixed base 54 such that the guiding surface 52 of the insert 50 support the workpiece during grinding and sharpening operations as shown in Figures 7, 8 and 10, according to an embodiment, and further discussed thereafter. The insert 50 supports the bar 10 very precisely during a large part of the machining operations.

[0032] In an embodiment, the method is adapted to grind a cutting tool 20 with a reinforced shank 26 as shown in Figure 1c. A cylindrical segment of the bar 10 must first be ground to a very precise diameter which must be slightly smaller than the diameter of the incomplete annulus, within a range from one micrometer to ten micrometers, preferably between a range from two micrometers to five micrometers, for example three micrometers. This allows the guiding surface 52 of the insert 50 to be used as a reference point for most of the grinding operations of the cutting part 22 of the cutting tool 20.

[0033] With reference to Figure 6, to reach such accurate diameter of the cylindrical segment of the bar 10, a distal end portion 12 of the bar is ground with a first grinding wheel W1 of the grinding machine 100 down to a first diameter d1 along a length of a few millimeters, for example five millimeters, for calibration of the position of the first grinding wheel W1. In the case of a cutting tool of 5mm diameter to be produced, the diameter of the blank bar 10 of Figure 1a may be for example 6mm and the first diameter d1 is a few hundredths of a millimeters larger than the final diameter, for example a diameter of 5.04mm.

[0034] This diameter d1 is then measured in-situ for example by an electronical probe or by optical means such as a laser.

[0035] The first grinding wheel W1 is then moved for grinding a cylindrical segment of the workpiece 10 to a second diameter d2 as close as possible to 5.02mm, within a tolerance of a few microns, generally 2 microns. The 5.02mm diameter is a few micrometers smaller than the incomplete annulus of the insert 50 as previously mentioned.

[0036] The difference in diameter between d1 and d2 must be less than 0.1mm and preferably not higher than 0.04mm. The principle of a thickness in excess of the diameter d2 is fundamental for successfully machining a reamer or a drill using this method, as it is necessary that longitudinal threads p1, p2, p3 run along the helical flutes 23 and form together parts of a circle of diameter d2 at any cross-section along the longitudinal axis of the cutting part once the sharpening operations are completed as illustrated in Figure 11. Without these longitudinal threads p1, p2, p3, contact with the guiding surface 52 of the insert 50 would be lost and it would be impossible to grind the back taper without supporting the cutting part 22 of the tool.

[0037] Reamers have in general four, five of six cutting edges or teeth as illustrated in Figure 11 while drills have in general only two cutting edges or teeth. To successfully grind any type of reamers or drills with the method disclosed therein, it essential to have as many longitudinal threads p1, p2, p3...pn as the number of cutting edges or teeth of the cutting part 22 of the tool to be ground.

[0038] During the step consisting in grinding the cylindrical segment down to the second diameter d2, the trajectory of the first grinding wheel W1 is calculated by a dedicated software as a function of the measurement of the first diameter d1 to reach this second diameter d2. The distal end portion of the cylindrical segment is then fitted into the guiding surface 52 of the insert 50 and the total length of the cylindrical segment corresponding to the length of the cutting part 22 (Figure 1b) of the cutting tool 20 to be produced is ground to the second diameter d2 by displacing the headstock 102 along the rotating axis X of the workpiece while the insert 50 remains fixed as shown in Figure 7. The guiding surface 52 of the insert 50 (Figure 5) supports a portion of the segment and is used as a reference point.

[0039] In an alternative embodiment, the headstock 102 of the grinding machine remains fixed and the total length of the segment corresponding to the length of the cutting part 22 of the cutting tool 20 is ground to the second diameter d2 by displacing the insert 50 along the rotating axis X towards the headstock 102.

[0040] It is important to note that cylindrical grinding of the total length of the segment that eventually become the cutting part 22 of the cutting tool 22 is performed without back taper. The first grinding wheel W1 is slightly offset from the insert 50 and the bar slides along the guiding surface 52, thus avoiding bar flexion. The offset of the first grinding wheel W1 in relation to the guiding surface 52 of the insert 50 can vary from a few tenths to a few millimeters.

[0041] The sharpening operations of the cutting tool are carried out also using the guiding surface 52 of the insert as 50 a reference point as shown in Figure 8. More particularly, a second grinding wheel W2, as shown in Figure 9a, is used for grinding helical flutes 23 as illustrated in Figure 11. Once flute grinding is completed, a third grinding wheel W3, as shown in Figure 9b, is used for grinding the outer diameter relief lands 24, as illustrated in Figure 11. Once outer diameter relieving is completed, a fourth grinding wheel W4, as shown in Figure 9c, is used for end teeth grinding. Each of these sharpening operations uses the guiding surface 52 of the insert 50 as a reference point and for supporting a portion of the workpiece during grinding to avoid any flexion.

[0042] The cutting tool 20 is then ground to the final diameter, for example 4.988mm, including the back taper, using a finishing grinding wheel W5 as shown in Figure 10 by moving the headstock 102 or the removable or fixed base 54 of the insert 50 while the guiding surface 52 is used as a reference point and support a portion of the cutting part.

[0043] In another embodiment, the method is adapted to grind a cutting tool 20 with a conventional shank 26 as shown in Figure 1b. With a blank bar of a diameter of 5mm for example, the sharpening operations are directly performed with grinding wheels W2, W3, W4 as shown in Figures 9a to 9c while the portion of the blank bar intended to become the cutting part is supported by the guiding support 50 to obtain a sharpen segment. As for the embodiment for grinding reamers and drills with reinforced shank, longitudinal threads remain along the helical flutes forming together parts of a circle corresponding to the original diameter of the blank bar at any cross-section along the longitudinal axis of the cutting part both during sharpening operations and when said sharpening operations are completed.

[0044] The sharpen segment is then ground down to a final diameter of the order of 4.988mm including the back taper with another wheel to obtain the cutting part 22 of the cutting tool 20. During the sharpening operations and the final step during which the back taper is ground, the above longitudinal threads are continuously in contact with the guiding surface 52 of the insert 50 to provide a reference point and to support the cutting part 22 of the tool.

[0045] In a nutshell, the method disclosed therein allows to manufacture a cutting tool 20, in particular a drill or a reamer in one clamping operation on a single machine. The back taper is carried out as the final operation, on a tool that has already been sharpened. This method is only possible with the use of the insert describe above which act as a single reference point for all grinding operation while at the same time eliminating the problem of bending and increases precision.

[0046] Multiple inserts with different diameters of the partial annulus may be used to produce cutting tools, in particular drills and reamers, of different diameters.

Claims

1. Method for grinding, with a grinding machine (100), a rotary cutting tool (20) comprising a cutting part (22) and a shank (26), the grinding machine (100) comprising a headstock (102) with a spindle (104) arranged to receive one end portion of a workpiece (10) to rotate said workpiece about a rotation axis (X), and a guiding support (50) to support a portion of the workpiece (10) during grinding of the cutting part, said guiding support (50) comprising a guiding surface (52) having a cross-section, within a plane orthogonal to said rotation axis, of an incomplete annulus, the method comprising the following steps:

i) mounting said one end portion of the workpiece (10) into the spindle (104) and rotating said workpiece about the rotation axis (X);

ii) performing sharpening operations, on a portion of the workpiece intended to become to the cutting part (22) of the final cutting tool with grinding wheels (W2, W3, W4) to obtain a sharpen segment, and

iii) grinding the sharpen segment down to a final diameter including the back taper with another wheel (W5) to obtain the cutting part (22) of the cutting tool (20)

wherein said portion of the workpiece is supported by the guiding support (50) during steps ii) and iii).

2. Method according to claim 1, wherein longitudinal threads (p1, p2, ,p3) extend along flutes (23) and form together parts of a circle corresponding to the original diameter of the workpiece (10) at any cross-section along the longitudinal axis of the cutting part (22) both during sharpening operations and when said sharpening operations are completed, and wherein said longitudinal threads are in contact with the guiding surface (52) of the guiding support (50) to provide a reference point and to support the cutting part (22) of the cutting tool (20) during steps ii) and iii).

3. Method according to claim 1, further comprising, after performing step i) and prior to performing steps ii) and iii), the following steps:

a) grinding with a first grinding wheel (W1) of the grinding machine an opposite end portion (12) of the workpiece down to a first diameter (d1) for calibration of the position of said first grinding wheel (W1);

b) measuring said first diameter (d1); and

c) moving the first grinding wheel (W1) to grind a cylindrical segment of the workpiece (10) down to a second diameter (d2) and according to the measurement of the first diameter, wherein the length of the cylindrical segment corresponds to the length of the workpiece intended to become the cutting part (22) of the final cutting tool, and

wherein in step ii) the sharpening operations are performed on said cylindrical segment and wherein said grinding wheels (W2, W3, W4) are different from the first grinding wheel (W1).

4. Method according to the preceding claim, wherein longitudinal threads (p1, p2, ,p3) run along flutes (23) and form together parts of a circle corresponding to the second diameter (d2) of the workpiece (10) at any cross-section along the longitudinal axis of the cutting part (22) both during sharpening operations and when said sharpening operations are completed, and wherein said longitudinal threads (p1, p2, ,p3) are in contact with the guiding surface (52) of the guiding support (50) to provide a reference point and to support the cutting part (22) of the cutting tool (20) during steps ii) and iii).

5. Method according to claim 3 or 4, wherein said first diameter (d1) is less than 0.1mm larger than the second diameter (d2) of the cutting part (22) of the cutting tool (20) and preferably not larger than 0.04mm of said second diameter.

6. Method according to any preceding claim, wherein said sharpening operations comprise a step of grinding flutes (23) of the cutting part (22) with one grinding wheel (W2) of said other grinding wheels (W2, W3, W4).

7. Method according to the preceding claim, wherein said sharpening operations comprise another step of grinding outer diameter relief lands (24) of the cutting part (22) with another grinding wheel (W3) of said other grinding wheels (W2, W3, W4).

8. Method according to the preceding claim, wherein said sharpening operations comprise another step of grinding the distal end of the cutting part (22) with another grinding wheel (W4) of said other grinding wheels (W2, W3, W4).

9. Method according to any preceding claim and claim 3, wherein said first diameter (d1) is measured in-situ by an electronical probe or by optical means such as a laser.

10. Method according to any of the preceding claim and claim 3, wherein the headstock (102) of the grinding machine (100) moves along the rotating axis (X) of the workpiece (10) while the guiding support (50) remains fixed while grinding the length of the segment down to said second diameter (d2).

11. Method according to any of claims 1 to 9 and claim 3, wherein the headstock (102) of the grinding machine (100) remains fixed while the guiding support (50) moves along the rotating axis (X) while grinding the length of the segment down to said second diameter (d2).

12. Method according to any of the preceding claim and claim 3, wherein the grinding machine (100) further comprises a V-guide (60) for supporting the workpiece and to correct any concentricity errors during grinding of the cylindrical segment down to the second diameter (d2) and during sharpening operations of the cutting part (22).

13. Method according to any preceding claim and claim 3, wherein the diameter of the incomplete annulus of said guiding support (50) is between one to ten micrometers larger than the second diameter (d2) of the cylindrical segment, preferably between two and five micrometers.

14. Method according to claim 1, wherein the diameter of the incomplete annulus of said guiding support (50) is between one to ten micrometers larger than the known diameter of the workpiece before grinding, preferably between two and five micrometers.

Drawing