Method and device for grinding fluted tools

Abstract

The invention relates to a method and device for grinding fluted tools (10) that have an essentially circular envelope curve, in particular, for grinding spiral fluted tools. The device provided with a steady for guiding the tool to be ground comprises a guideway (8) with at least two inner lateral faces. The lateral faces each extend in planes in a manner that is essentially parallel to the longitudinal axis of the tool to be ground and they form an angle for accommodating the tool to be ground, whereby the tool to be ground rests each time with at least two circumferential points (a11, a12) of its essentially circular envelope curve at least on two of the inner lateral faces of the guideway. In order to carry out the inventive method, a tool to be ground is appropriately clamped and pressed into the guideway by means of at least one grinding wheel (41) while the flutes are ground.

Description

[0001] The present invention relates to a method and a device for grinding fluted tools, in particular for grinding spiral fluted tools.

[0002] The device and method as described are generally suited for manufacturing spiral fluted tools. What is described in particular in detail hereinafter is the manufacturing of twist drills.

[0003] It is generally known in the prior art that fluted tools, in particular twist drills, are ground in sleeves for accommodating and guiding the tools. This approach requires a separate locating sleeve for each tool diameter, which sleeve has been adapted to the nominal diameter of the tool to be manufactured. Consequently, a lot of individually adapted accessories of the actual grinding machine are required for clamping and grinding the tools to be manufactured. Consequently, for producing other tools which may be of a different diameter, the machine will thus have to be reset and/or retooled in a number of ways by substituting various parts. Should the tools to be manufactured be of different nominal diameters, a separate locating sleeve each will have to be available for every nominal tool diameter at least. The extensive resetting and retooling work as well as the high number of specific accessories is also time-consuming and costly, which will increase the overall costs of the tool manufacturing process.

[0004] The use of sleeves for guiding the tools to be ground furthermore results in the problem of insufficient accuracy of the guide. An inherent feature of this system is that the adapted sleeve diameters exhibit a play of 1-2 hundredth of a millimetre with respect to the actual diameter of the tool to be manufactured. When in the process of grinding the tool to be manufactured, the grinding wheel is made to contact the tool to be ground for grinding a flute, for example, the influence of the shear forces will urge said tool into punctual or extended (i.e. along a line) contact with the inner face of the guiding sleeve on which said tool will rest essentially only with one circumferential point to counter the shear forces. The guide is thus not fixed spatially and depends on the geometry and the direction in which force is exerted on the tool to be ground by the grinding wheel. This will result in increased tolerances in the finished tool.

[0005] It is the object of the present invention to provide a device and a method which will allow the manufacturing of spiral fluted tools to be ground in the same or less time, at the same time improving quality and reducing costs.

[0006] This object is accomplished by a device according to claim 1 and by a method according to claim 16.

[0007] Preferred embodiments of the invention are defined in the respective subclaims.

[0008] The device of the invention serves for grinding fluted tools that have an essentially circular envelope curve, in particular for grinding spiral fluted tools, by means of grinding wheels. Twist drills can be ground as well as similar other tools such as milling cutters, drills in general and possibly also reamers. In accordance with the invention, the device for grinding fluted tools comprises a steady for guiding the tool to be ground. According to the invention, said steady is provided with a guideway with at least two inner lateral faces which each extend in planes in a manner that is essentially parallel to the longitudinal axis of the tool to be ground and they form an angle for accommodating the tool to be ground, whereby the tool to be ground rests each time with at least two circumferential points at least on two of the inner lateral faces of said guideway, i.e. one each of said at least two circumferential points rests on one each of said at least two inner lateral faces.

[0009] In general, the tools to be ground may taper conically, in particular slightly conically, along their length. In particular, they may taper conically from their fronts to their shanks. For making such a tool to be ground rest on the at least two inner lateral faces of said guideway according to the invention, the latter essentially follow a slight taper of the tool, then extending in planes in a manner that is essentially parallel to the longitudinal axis of the tool to be ground. In the case of a non-tapering tool to be ground in which the diameter of the envelope curve will not vary along its length (usually, with slight taper at best, by a few hundredth millimetres), said at least two lateral faces of said guideway will extend in parallel. Where the tool to be ground tapers more, the course of said at least two inner lateral faces of said guideway may essentially follow the tool contour in a longitudinal section, with the planes of said lateral faces being correspondingly tilted towards each other in space, which tilt may also differ in sections along the length.

[0010] The inventive design of the device in which the tool to be ground is guided in a guideway of a steady and rests with at least two circumferential points on and in said guideway, will allow play-free mounting and feed of the tool to be ground. In the prior art, by contrast, the tool is guided in a sleeve and, viewed in cross-section of the tool to be manufactured, only rests with one point on the lateral wall of said sleeve—which will not allow secure guiding. Contrary to the sleeve of the prior art, the present invention provides for at least two lateral faces of the guideway to form an angle in which the tool to be ground is guided, and the invention makes it possible to grind tools of differing diameters, since the guideway, viewed in cross-section, including these lateral faces essentially opens in a widening, e.g. a V-shaped, manner for accommodating the tool. The tools rest on and are guided by at least two lateral faces of said guideway, whereby—depending on the work step performed or on the diameter of the tool to be ground—the respective point of rest may be at a different place, and/or the tool may rest on the guideway in a line-shaped manner, with at least two lines. Thus, the special design for guiding the tool to be ground according to the invention eliminates the need for using different locating sleeves depending on the diameter of the tool to be ground as well as the need for keeping a lot of individual parts available. Furthermore, for a change-over to a different tool to be ground which may be of a different diameter for example, the grinding machine will not necessarily have to be reset or retooled in a time-consuming manner.

[0011] In accordance with the invention, the tool to be ground is usually guided via the at least two circumferential points resting on and in the guideway of the steady and urged against the lateral faces by the grinding forces, e.g. by means of a grinding wheel—which will result in a particularly good guide since the grinding pressure will act on the guideway via said at least two circumferential points. The direction of the force of the grinding pressure will thus be divided into partial forces in the direction of at least two circumferential points of the tool to be ground, especially in the shape of a parallelogram, which is determined by the geometry and thus by the position of these points.

[0012] It is now considered particularly advantageous according to the invention that the device for grinding additionally includes a clamping lever, besides said guideway, which may be moved in the direction of the guideway for urging the tool to be ground into contact therewith and/or for clamping it. This will ensure particular secure guiding, free of play in this case, too, of the tool to be ground when machining the front of fluted tools, in particular of spiral fluted twist drills.

[0013] It is to be noted that the length of the guideway and thus also the length of the clamping lever correspond to at least the length of a pitch of a flute spiral of the tool to be ground. This is considered particularly advantageous since it makes sure that essentially always at least part of the circular envelope curve of the tool to be ground will rest with at least two circumferential points on the lateral faces.

[0014] Said steady including said guideway and said clamping lever, but also said guideway and/or said clamping lever, may of course be designed to be movable in the axial direction of the tool to be ground for use in manufacturing tools of excessive length, in particular twist drills, in order to thus ensure optimum support and guiding of the tool to be ground in the area where the respective grinding work is being performed on it.

[0015] It is considered particularly advantageous to also make the position of the steady and/or of the guideway, and naturally also the position of the clamping lever where necessary, adjustable with respect to the diameter of the tool to be ground, in which case the position of the longitudinal axis of the tool to be ground may be given and may in particular result from the geometry of the grinding machine used with the respective grinding units. This will allow fast and at the same time precise manufacturing of the tools to be ground in a particularly flexible manner, involving only little resetting and retooling work.

[0016] This advantage is also obtained in a particularly preferred manner in that said guideway may be adapted as a function of the diameter of the tool to be ground. In particular, it may be advantageous to provide an exchangeable guideway for tools to be ground of larger or smaller diameters, in particular when there are vast differences in diameter between individual tool batches to be manufactured. It may also be particularly preferred to make the angle variable for adjustment, for example by providing an adjusting mechanism. This will also increase the flexibility of the device, at the same time maintaining the good and exact guiding of the tools to be ground.

[0017] Whereas an angle of 90° is preferred, any angle smaller than 180° is essentially possible in principle.

[0018] Said guideway is preferably made of super-speed steel. Said clamping lever may also be made of super-speed steel.

[0019] In another preferred embodiment of the device, it is advantageous to make at least the surface of the guideway and/or the surface of the clamping lever, in particular of the portion of the clamping lever which will rest on the tool to be ground as such is being pressed into the guideway, of hard metal. It is possible for example to provide this hard metal in the form of strips or rails which will be mounted on the respective surface of the guideway and/or of the clamping lever.

[0020] For grinding, in particular hard metal tools, the surface of the guideway and at least the surface of the clamping lever may also be made of polycrystalline diamond (PCD).

[0021] By appropriately selecting the material for the guideway and/or for the clamping lever, it is possible to ensure a secure guiding matched to the material of the tool to be ground, in particular without the danger of the tool to be ground running into the guideway and/or the clamping lever in the area of its circumferential contact points. Nevertheless, and especially for this reason, the costs of the inventive device may be kept as low as possible.

[0022] In general, the device may be provided for grinding tools made of super-speed steel and/or for grinding hard metal tools. For tools made of super-speed steel, conundrum grinding wheels and/or CBN grinding wheels may preferably be used. For grinding hard metal tools, diamond grinding wheels are preferably used as grinding means.

[0023] The grinding method of the invention relates to the manufacturing of fluted tools that have an essentially circular envelope curve, in particular to the grinding of spiral fluted tools, by means of grinding wheels. This will allow the grinding of twist drills, but also of other similar tools such as milling cutters, drills in general and possibly reamers as well.

[0024] In accordance with the invention, in the method for grinding twist drills, the tool to be ground is clamped such that a steady including a guideway with at least two inner lateral faces which each extend in planes in a manner that is essentially parallel to the longitudinal axis of the tool to be ground and which form an angle for accommodating the tool to be ground, in particular a steady including a guideway as claimed in claim 1, will guide the tool to be ground via at least two circumferential points which each rest at least on two of said inner lateral faces of said guideway. According to the invention, the tool to be ground is pressed into the guideway by means of at least one grinding wheel while the flutes are ground.

[0025] Preferably, if a back of the tool to be ground is to be ground, in this case the tool to be ground is also pressed into the guideway during grinding.

[0026] For guiding the tool to be ground in a particularly secure manner when grinding front cutting edges and/or when grinding the front of the tool in general, the tool to be ground is additionally pressed into the guideway by means of a clamping lever.

[0027] It is particularly preferred to grind the tool to be ground, in particular front cutting edges, flutes and possibly the back of the tool, in one chucking.

[0028] The invention is explained hereinafter in more detail based on an embodiment with reference to the accompanying drawings, in which

[0029] FIG. 1 is a top view of a grinding machine including a device according to an embodiment of the invention;

[0030] FIG. 2 a sectional view taken along line B-B of FIG. 1; and

[0031] FIG. 3 is a cross-sectional view of an embodiment of the device, in which different working steps of the method of the invention are illustrated using the example of the grinding of a twist drill.

[0032] FIG. 1 is a top view of a grinding machine and a device for grinding fluted tools in an embodiment of the invention.

The grinding machine consists of the following main components: the machine column 1, the grinding spindle head 2 including a pivotable grinding spindle unit 3 and an HF grinding spindle 4, the grinding table 5 including a workpiece spindle head 6, the steady with the guideway 8, and the wheel trueing attachment 9.

[0033] The rear area of said machine column 1 has a grinding spindle head 2 which may be moved by means of a CNC axis (axis X). Furthermore, the grinding spindle unit 3 which may be swivelled about an axis (axis A) may travel vertically along its height along an axis (axis Y). In the front area of said machine column 1, the grinding table 5 is mounted on guides (not shown), which table can travel in the direction of an axis (axis Z). Mounted on said grinding table 5 is the workpiece spindle head 6 which is provided with a collet chuck closer 61. Said collet chuck closer 61 is mounted on a sleeve which is driven to rotate about a CNC axis (axis C). According to the invention, for supporting the tool to be ground, the steady with the guideway 8 is mounted on said grinding table 5. Further mounted on said grinding table 5 is the wheel trueing attachment 9 with a rotatorily driven diamond wheel 91 for trueing the grinding wheels used. All aforementioned axes take the form of CNC axes.

[0034] FIG. 2 shows a section along line B-B of FIG. 1. This view shows the HF grinding spindle 4 swivelled up at a 90° angle about axis A, in contrast to the view of FIG. 1. As in FIG. 1, axes X, Y and A are each marked in and shown symbolically.

[0035] The HF grinding spindle 4 is firmly connected to the grinding spindle unit 3 which can be swivelled. The front area of said HF grinding spindle 4 accommodates grinding wheels 41, 42, 43, with said HF grinding spindle 4 being designed to accept both conundrum and CBN or diamond grinding wheels. For grinding tools made of super-speed steel, either CBN or conundrum grinding wheels are predominantly used as grinding means whereas diamond grinding wheels are preferably used for grinding hard metal (HM).

[0036] Shown in the front area of the machine column 1 is the grinding table 5 on which the steady including the guideway 8 is mounted. For guiding and supporting the tool 10 to be ground, the circumference of the tool rests on the guideway 8 of said steady. For grinding front cutting edges, for example into the shape of an envelope of a cone, the clamping lever 83 is swung in the direction of the guideway for improved guiding of the tool 10. For adjusting the position as a function of the diameter of the tool to be ground, the steady and/or the guideway can be adjusted manually in the direction of arrow 85.

[0037] FIGS. 3 to 6 are cross-sectional or top views, as viewed from the front of the tool to be ground, of the design of the device of the invention, in particular of the steady, including the guideway 8, and the advantageous use of the device is illustrated in more detail based on the example of grinding twist drills. In this context, FIGS. 3 to 6 show the design of the steady in the clamping area.

[0038] In the present case, the tool to be ground 10 is a twist drill. One shank end of the twist drill to be ground is clamped in the workpiece spindle head 6 by means of a collet chuck. Here, chucking only serves for transferring torque, since the actual guiding is accomplished by means of the steady including the guideway. To this end, the shank of the tool 10 to be ground which freely projects from the collet chuck rests on said guideway 8. The tool 10 is supported via its free shank length on the surface area 11 or the circumference of the essentially circular envelope curve with at least two circumferential points of the envelope curve of the tool 10 to be ground on at least two inner lateral faces of said guideway which—in the embodiment of FIGS. 3 to 6—is essentially prismatic in cross-section. The fact that the tool rests with two circumferential points on the guideway results in a free-of-play guiding of the tool 10 to be ground. Said guideway may be made of super-speed steel, or may be provided with hard metal or PCD strips. As already set out with reference to FIG. 2, guiding and pressing the tool 10 to be ground into contact may be further improved by swiveling a clamping lever 83 into this area—if the grinding wheel does not operate in the respective area—so as to allow guiding or clamping the tool to be ground without play between three circumferential points which, viewed in cross-section, are arranged triangularly around the circumference of the tool to be ground.

[0039] When the tool to be ground is guided in a sleeve according to the prior art, by contrast, said sleeve will always allow some play of approx. 0.01—0.02 mm between the sleeve interior and the tool to be ground, resulting in the tool resting on a single point or linearly along its length on the sleeve interior. This point or line of contact and their direction are directly related to the grinding direction, and said point or line will always be on the opposite side of the grinding contact, since the force from there is supported linearly on the respective point or line against the guiding sleeve. In a sleeve of the prior art, the tool to be ground is thus only supported partially and only guided at one point. The radial force is accepted as a geometric error. The fact that the tool to be ground is not 100% clamped and guided also results in a diminished service life of the tool machining the actual tool to be ground.

[0040] FIG. 3 shows a tool to be ground which is clamped and guided according to the invention along the length of its shank by means of a clamping lever 83 swivelled into the closed position. The contact lines are illustrated as points A11, A12 and A13. While the tool is being machined, the tool 10 to be ground is rotated radially about axis C of the workpiece spindle head 6. The tool 10 to be ground is clamped by means of the collet chuck 61. In doing so, the latter must be precisely aligned with the guideway. The length of the guideway is determined by the length of the tool to be ground, by the shape and the length of the flutes, as well as by the pitch of the spiral flutes. The flute pitch takes an influence in that at least one complete flute spiral must be covered by the length of the guideway. However, it is possible to design the steady including the guideway and/or the clamping lever such that it can also be moved in the direction of the longitudinal axis of the tool to be ground so as to allow the machining of overly long twist drills or generally fluted tools of excessive length.

[0041] In the chucked state shown in FIG. 3, the front cutting edges of a twist drill may for example be ground into an envelope of cone shape by means of grinding wheel 41.

[0042] FIG. 4 shows the guideway of the steady 8 with the clamping lever 83 (not shown) in the open position, with the shear forces produced by the grinding wheel pressing the tool 10 to be ground in the illustrated flute grinding process into contact with the guideway at two contact lines. This will guarantee a secure and play-free mounting of the tool to be ground during grinding even without the clamping lever 83. In the present case, grinding is performed by means of the grinding wheel 43 which is offset corresponding to the flute pitch angle to be ground from the position of the longitudinal axis 11 of the tool to be ground.

[0043] FIG. 5 illustrates the grinding of the back of a twist drill which is being machined by means of grinding wheel 41. Here, the central axis of the HF grinding spindle 4 preferably extends in parallel to the longitudinal axis of the tool 10 to be ground.

[0044] FIG. 6 shows the pointing of the transverse cutting edge of the tool 10 to be ground, a twist drill in this case, which working step is performed by means of grinding wheel 42. This machining is performed on the front or tip of said twist drill, with the clamping lever 83 being moved into the closed position again for clamping the tool to be ground.

[0045] All the work steps illustrated in FIGS. 3 to 6 are only schematically shown and the machining is illustrated by the lines in the top view of the front of the tool or twist drill to be ground. The essentially circular envelope curve of the tool is also shown. The work steps are all performed in one chucking.

Claims

1. A device for grinding fluted tools with an essentially circular envelope curve, in particular spiral fluted tools, by means of grinding wheels, characterized in that a steady for guiding the tool to be ground includes a guideway (8) with at least two inner lateral faces which each extend in planes in a manner that is essentially parallel to the longitudinal axis of the tool (10) to be ground and which form an angle for accommodating the tool to be ground, said tool to be ground with at least two circumferential points (A11, A12) of the essentially circular envelope curve each resting on at least two of said inner lateral faces of said guideway (8).

2. The device of claim 1 characterized in that a clamping lever (83) can be swivelled into the closed position for pressing the tool (10) to be ground into contact in the direction of the guideway (8).

3. The device of claims 1 or 2 characterized in that the position of the steady and/or of the guideway (8) may be adjusted as a function of the diameter of the tool (10) to be ground with respect to the position of the longitudinal axis of the tool (10) to be ground.

4. The device of claims 1 or 3 characterized in that said angle may be varied as a function of the diameter of the tool (10) to be ground.

5. The device of one of claims 1 to 4 characterized in that said device is designed for grinding tools (10) made of super-speed steel.

6. The device of one of claims 1 to 5 characterized in that said device is designed for grinding tools (10) made of hard metal.

7. The device of one of claims 1 to 6 characterized in that said guideway (8) is made of super-speed steel.

8. The device of one of claims 2 to 7 characterized in that said clamping lever (83) is made of super-speed steel.

9. The device of one of claims 1 to 8 characterized in that said guideway (8) includes at least one hard metal surface.

10. The device of one of claims 2 to 9 characterized in that said clamping lever (83) includes at least one hard metal surface.

11. The device of one of claims 1 to 8 characterized in that said guideway (8) includes at least one surface made of polycrystalline diamond (PCD).

12. The device of one of claims 2 to 8 or of claim 11 characterized in that said clamping lever (83) includes at least one surface made of polycrystalline diamond (PCD).

13. The device of one of claims 5 to 12 characterized in that said grinding wheels are conundrum grinding wheels.

14. The device of one of claims 5 to 12 characterized in that said grinding wheels are CBN grinding wheels.

15. The device of one of claims 6 to 12 characterized in that said grinding wheels are diamond grinding wheels.

16. A method for grinding fluted tools with an essentially circular envelope curve, in particular spiral fluted tools, which are clamped such that a steady including a guideway that has at least two inner lateral faces which each extend in planes in a manner that is essentially parallel to the longitudinal axis of the tool to be ground and which form an angle for accommodating the tool to be ground, guides the tool to be ground via two circumferential points at least which rest on at least two of said inner lateral faces of said guideway, and the tool to be ground is pressed into contact with and into the guideway by means of at least one grinding wheel while the flutes are ground.

17. The method of claim 16 wherein, for grinding the back, the tool to be ground is pressed into contact with and into the guideway by means of at least one grinding wheel.

18. The method of one of claims 16 or 17, wherein, for grinding the front cutting edges, the tool to be ground is additionally pressed into contact with and into the guideway by means of a clamping lever.

19. The method of claim 18 characterized in that front cutting edges, flutes and backs are ground in one chucking.