DE102011122539A1 - Method for producing a bore in a workpiece - Google Patents

Abstract

The invention relates to a method for producing a bore (1) in a workpiece (3) in which a pilot hole (7) having a diameter (D1) is first produced with a drilling tool, which is subsequently provided with a fine machining of the pilot hole (7 ) formed clamping tool (11) to a desired final diameter (D2) is increased. The cutting tool (11) has at least one cutting edge (15) extending at least approximately perpendicularly to a central axis (M2) of the cutting tool (11) in the region of a tool tip (13) and cutting edges extending on the circumferential side.

Description

The invention relates to a method for producing a bore in a workpiece according to the closer defined in claim 1.

From practice, methods are known with which very close tolerances having holes can be made in workpieces. Here, a pilot hole with a diameter which is smaller than a desired final diameter is first produced with a pilot drill. Since a desired position tolerance may not be met in this case, in a subsequent method step, a position correction must be performed, for example with a Ausspindelwerkzeug, so that a central axis of the bore is within the desired position tolerance. In a subsequent subsequent process step, for example, a reamer is used to bring the pilot hole to the desired final diameter and thereby to achieve good surface properties within the bore. The Ausspindelprozess is necessary because the reamer is guided in the bore and centered in the diameter enlargement due to oblique, arranged in the region of a tool tip cutting in the given hole.

Until the bore is brought to the final diameter, the process described thus requires many process steps with different tools, so that the production of the bore is time-consuming and cost-intensive.

The present invention is therefore based on the object to provide a method by means of which a high-precision bore can be produced quickly and inexpensively.

According to the invention this object is achieved by a method having the features of claim 1.

A method is proposed for producing a bore in a workpiece, for example a blind bore or a through bore, in which a pilot hole is first used to produce a pilot hole having a diameter, which is subsequently machined to a desired final diameter with a cutting tool designed for material-removing fine machining of the pilot hole is increased, wherein the cutting tool has at least one at least approximately perpendicular to a central axis of the cutting tool extending edge in the region of a tool tip and circumferentially extending cutting edges.

A bore can be produced with the inventive method in a simple, fast and thus cost-effective manner while maintaining close position and diameter tolerances with high surface quality in fewer steps than with conventional methods produced holes. In addition, fewer tools are needed for this. This results from the fact that the pre-drilling can be expanded to the desired final diameter with the cutting tool both by performing a position correction and achieving a high surface quality. Due to the cutting edge in the region of the tool tip, which in the method according to the invention has a point angle of at least approximately 180 °, a substantially radial force-free fine machining of the pilot hole is possible, i. H. In contrast to the reamers used in known methods, which center in the pilot hole due to their oblique cutting edges, a position correction can be carried out with the cutting tool. About the peripheral cutting edges high surface quality of the bore can be achieved.

In an advantageous embodiment of the method according to the invention, it is provided that a bevel is produced on an insertion side of the cutting tool into the workpiece, which is produced in particular in one step with the pilot hole. The chamfer can be produced in a simple manner together with the bore, in particular with a step drill. Alternatively, it is also possible to use a separate tool for producing the chamfer. The chamfer can be created before or after a use of the cutting tool in the workpiece.

In the production of a through hole, a rear chamfer can be produced on a side of the workpiece facing away from the insertion side of the cutting tool. This step may be performed before or after the use of the cutting tool.

In an advantageous embodiment of the method according to the invention a protective chamfer or rounding is provided in the region of the cutting edge of the cutting tool, which is designed in particular smaller than a radial allowance of the bore relative to the pilot hole. The protective chamfer or the rounding serves to protect the cutting edge, since corners or exposed areas of the cutting edge are avoided by the protective chamfer or rounding, in which large amounts of heat accumulate and thus material damage to the workpiece or the tool could occur.

If at least one circumferential cutting edge of the cutting tool at least partially over its direction of extension a has defined Rundschlifffase, a particularly narrow end diameter tolerance of the bore to be produced is maintainable. In the field of Rundschlifffasen the cutting edges have a low wear. Due to the low wear, the diameter of the cutting tool remains very constant in the region of the cutting edges, so that the cutting tool has a long service life and a high process capability of the bore end diameter is achieved.

If the Rundschlifffase of the cutting edges has a width between 0.02 mm and 0.1 mm, in particular a width of 0.05 mm, a high surface quality at the same time good diameter tolerance of the cutting tool can be achieved. The round grinding bevel forms part of a lateral surface of the cutting tool. Together with the cutting edge in the area of the tool tip, the round grinding bevel on the outside diameter of the cutting tool results in a high guiding accuracy of the cutting tool.

As an alternative to the provision of round grinding bevels, at least one circumferential cutting edge can have a first clearance angle in the range of 2 ° to 4 ° at least in regions over its direction of extent. The clearance angle has a comparable effect as the Rundschlifffase, so that good surface properties of the bore while maintaining close diameter tolerances are achieved with a relatively low wear of the cutting edges.

In an advantageous development of the method according to the invention, it is provided that the at least one cutting edge in a region adjoining the first clearance angle has a second clearance angle which is greater than the first clearance angle. The second clearance angle adjoins the first clearance angle of the cutting edges in the circumferential direction, wherein a width of the cutting edge in the region of the first clearance angle in particular has a value in the range of about 0.2 mm and 0.5 mm. However, this value may also be larger or smaller depending on the present diameter of the cutting tool.

Further alternatively, it can be provided that the peripheral cutting edges have a radial course or a radial clearance, whereby a comparable effect as with the use of one or more clearance angle is achieved.

In particular, all cutting edges of the cutting tool located on the tool circumference are provided with a round grinding bevel or a clearance angle or a radial clearance clearance. The front cutting edge and possibly attached protective chamfers or edge rounding are in particular provided with one or more clearance angles.

In particular, the cutting tool has four to eight circumferential cutting edges, so that a ratio of feed to a number of cutting edges is very small. The total feed can thus be chosen to be relatively large, as a result, a feed per cutting edge is low. As a result, a short processing time can be achieved. Furthermore, a uniform distribution of the acting cutting forces over the circumference of the tool is achieved by the high number of blades. Due to the high number of cutting edges, a service life of such a cutting tool is advantageously large. The number of cutting edges is selected such that flutes arranged between adjacent cutting edges are sufficient for removing chips arising during the chip removal process.

Stable cutting edges can be achieved if the peripheral cutting edges of the cutting tool have a helix angle of less than 30 °, in particular less than 20 ° and preferably greater than 15 °. The smaller the helix angle, the better the heat dissipation at the cutting edge in use and the greater the durability of the cutting tool. In addition, a cutting force increases with decreasing helix angle.

In an advantageous embodiment of the method according to the invention, the peripheral cutting edges of the chipping tool have an axial length less than six times a diameter of the chipping tool, in particular three to five times the diameter of the chipping tool. As a result, the cutting tool is designed to be short overall and inherently stable.

An improvement in the surface finish of the bore can be achieved by the cutting tool having a diameter taper in the axial direction in the area of the peripheral cutting edges, the largest diameter being provided in the region of the tool tip. The diameter decrease in the form of a cone angle in particular has a value less than 60% of a bore tolerance. The effect of rubbing the cutting edges on a bore surface is thereby reduced.

In order to be able to dissipate heat arising during the cutting process effectively from the cutting tool, a cooling device can be provided, by means of which the cutting tool is cooled during a cutting process, in particular from the inside.

A dimensional accuracy of the bore to be produced is also determined by a concentricity of the cutting tool and the tool holder. In particular, the use of hydraulic expansion chuck, precision shots or the like is suitable.

With the method according to the invention, bores, such as blind bores or through bores, can be produced in all materials, with it being possible to optimize the bore with regard to positional accuracy, bore diameter and surface quality. For example, holes can be made in flanges on rotating components of rotors, disks or the like, the components being made of, for example, Udimet, Inconel, titanium or nickel base alloys.

The cutting tool can be designed in the manner of a milling tool, a Reibfräswerkzeugs or the like.

Both the features specified in the claims and the features specified in the subsequent embodiments of the method according to the invention are each suitable for use alone or in any combination with each other to develop the subject invention. The respective feature combinations represent no limitation with respect to the development of the subject matter according to the invention, but essentially have only an exemplary character.

Further advantages and advantageous embodiments of the method according to the invention will become apparent from the claims and the embodiments described in principle below with reference to the drawings.

It shows:

1 a simplified sectional view through a drilling tool and a workpiece in a first method step for producing a through hole, wherein the drilling tool a pilot hole and a chamfer on an insertion side of the drilling tool are generated in the workpiece;

2 a simplified sectional view through a cutting tool and the workpiece of 1 in a second method step, wherein a position correction and an extension of the pilot hole to a desired final diameter are performed with the chipping tool;

3 a simplified sectional view through a milling device and the workpiece of 2 during a third process step, wherein on the side facing away from the insertion side of the workpiece with the milling device, a rear chamfer is generated;

4 a simplified three-dimensional representation of the cutting tool of 2 in isolation;

5 a simplified shown sectoral section of a sectional view through the cutting tool of 4 along the line VV; and

6 a simplified shown sectoral section of a sectional view through an alternative designed clamping tool.

In the 1 to 3 are partially optional process steps for producing a high-precision bore 1 in a workpiece 3 shown, with the respective tools and the workpiece 3 each shown greatly simplified in a sectional view.

First, with a in the 1 simplified illustrated drilling tool 5 a pilot hole 7 with a diameter D1 about a central axis M1 in the workpiece 3 generated. The drilling tool 5 , which is formed here in the manner of a stepped drill, is for this purpose with a rotational movement along the arrow P1 and a feed movement along the arrow P2 in the direction of the workpiece 3 emotional. From the drilling tool 5 is thus here in one step through the entire workpiece 3 reaching pre-drilling 3 in the manner of a through hole and a front chamfer 9 generated, which on an insertion side of the drilling tool 5 in the workpiece 3 is arranged.

For the production of the front bevel 9 larger tolerances are allowed compared to the final hole position, so that these together with the pilot hole 7 can be produced. An advantage of the step drill shown 5 is that this to create the front chamfer 9 not fully or bluntly engages the workpiece, but in the present case at an angle of about 45 °. As a result, a uniform increase in a cutting force, a smooth tool run and a long tool life can be achieved.

The front chamfer 9 can also be produced with a separate tool in an alternative embodiment of the invention.

In one to the preparation of the pilot hole 7 subsequent process step is according to the 2 the pilot hole 7 with a cutting tool 11 to a desired final diameter D2, which is greater than the diameter D1 of the pilot hole, extended. The cutting tool made of a hard metal, a hard metal-ceramic mixture or other known cutting materials 11 , which in the 4 and 5 is closer, turns for this purpose in the direction of an arrow P3 and has a feed direction along an arrow P4, which is the feed direction of the drilling tool 5 equivalent.

At least one in the area of a tool tip 13 arranged main or end cutting edge 15 of the cutting tool 11 In this case, it is substantially perpendicular to a center axis M2 of the cutting tool 11 educated. The cutting edge 15 runs over the entire diameter range D1 of the pilot hole 7 perpendicular to the central axis M1 and M2. This has the advantage that at a widening of the diameter D1 of the pilot hole 7 through the cutting tool 11 no forces in the radial direction of the cutting tool 11 act, so with the cutting tool 11 a position correction of the center axis M1 can be performed and the center axis M2 of the bore relative to the center axis M1 of the pilot hole can be offset.

Accordingly, a first radial allowance R1 on a in the sectional view of 2 left side of the workpiece 3 from a second radial allowance R2 on a right side in the sectional view of the workpiece 3 differ.

That in the 4 in a three-dimensional side view fragmentary cutting tool shown 11 points next to the main cutting edge 15 several circumferentially extending cutting edges 17 on, these present have a positive helix angle DW of about 15 °. Due to the relatively small helix angle DW of the cutting edges 17 is the tool tip 13 relatively blunt, so that the cutting tool has a good durability and the cutting edges 17 are stable. In addition, a heat dissipation from the area of the tool tip 13 very effective.

There are present six cutting edges 17 provided by the high number of minor cutting edges 17 a feed can be made very large, since a ratio of feed to a cutting edge number by the large cutting edge number is relatively small. In addition, has the large number of cutting edges 17 the advantage that a very uniform distribution of cutting forces acting during the cutting process on the entire circumference of the cutting tool 11 is achieved. The large number of cutting edges 17 also has a beneficial effect on the life of the cutting tool 11 ,

The individual cutting edges 17 Here, in each case over their extension along the cutting tool 11 a Rundschlifffase 19 on. Like in the 5 is closer, is a part of the cutting edge 17 through the Rundschlifffase 19 a lateral surface 21 of the cutting tool 11 at least approximately or is part of the lateral surface 21 , so that a dimensional accuracy of the cutting tool 11 over a long period is very high and tight diameter tolerances can be met. Through the Rundschlifffase 19 , which in this case is a width B of about 0.04 mm, an undefined cutting edge is produced, which allows the exact adherence to a desired final diameter D2. On the other side is the Rundschlifffase 19 chosen so small that a surface 23 the bore 1 is not damaged in the chip process.

Together with the cutting edge 15 lead the Rundschlifffasen the cutting edges 17 to that the cutting tool 11 has a high guidance accuracy.

Alternative to the Rundschlifffase 19 can the cutting edges 17 also - as in the 6 visible - with otherwise unchanged clamping tool 11 be formed with a first clearance angle FW1, which is about 2 ° to 4 °. In the present case, the first clearance angle FW1 is in the circumferential direction of the cutting tool 11 extending width of about 0.2 mm to 0.5 mm. The first clearance angle FW1 is adjoined by a second clearance angle FW2 which is greater than the first clearance angle FW1 and is selected to be similar to a clearance angle of a cutter geometry. Through the use of cutting edges 17 with clearance angles FW1, FW2 is a very good surface finish of the bore 1 achievable.

The cutting tool 11 is in the range of a useful length NL of the cutting tool 11 in the present case cone-shaped, ie a diameter D3 in the region of the tool tip 13 is greater than a diameter D4 in one of the tool tips 13 facing away from the clamping tool 11 , This is achieved by a cone angle, which in the 4 is not clear. A rejuvenation of the cutting tool 11 in the present case is about 60% of a bore diameter tolerance over the effective length NL of the cutting tool 11 , This causes a rubbing effect of the minor cutting edges on the surface 23 the bore 1 reduced and an improvement of a surface finish of the bore 1 achieved.

In the 4 is a circumferential corner rounding 25 in the area of the tool tip 13 it can be seen which for the protection of the cutting tool 11 is provided. The corner rounding 25 , which in particular has a radius in the range of 0.05 mm to 0.1 mm, is preferably chosen such that it is smaller than the smaller radial allowance R1 or R2, so that by the corner rounding 25 no radial forces in the area of the tool tip during the cutting process 13 Act.

Alternative to the corner rounding 25 It is also possible to provide a peripheral protective bevel in the area of the tool tip, which is likewise preferably designed to be smaller than the smallest radial allowance.

To tight tolerances in the production of the bore 1 To be able to comply, it is advantageous to have a cutting tool 11 and to use a tool holder with a high concentricity.

With the cutting tool 11 Having features of a conventional milling cutter and a positive twisted reamer, can thus be dispensed with the use of a separate tool for position correction of the pilot hole and another tool for widening the diameter of the pilot hole to the desired final diameter.

After the possibly necessary position correction and the production of the bore 1 with the desired final diameter is present with a in the 3 apparent milling device 27 a rear chamfer 29 on one of the front bevels 9 opposite side of the workpiece 3 generated. The milling device 27 has for such a small diameter D5 at its widest point that they pass through the hole 1 can be passed.

LIST OF REFERENCE NUMBERS

1

drilling

3

workpiece

5

drilling

7

pilot hole

9

front chamfer of the workpiece

11

Spanungswerkzeug

13

Tool tip of the cutting tool

15

Cutting edge of the cutting tool

17

Cutting edge of the cutting tool

19

Rundschlifffase the cutting edge

21

Lateral surface of the cutting tool

23

Surface of the hole

25

Corner rounding of the cutting tool

27

milling device

29

rear chamfer of the workpiece

B

Width of the Rundschlifffase

D1 to D5

diameter

DW

angle of twist

FW1, FW2

clearance angle

NL

Effective length

M1, M2

central axis

P1 to P4

arrow

R1, R2

radial allowance

Claims (14)

Method for producing a bore ( 1 ) in a workpiece ( 3 ), in which initially with a drilling tool ( 5 ) a pilot hole ( 7 ) is produced with a diameter (D1), which subsequently with a material-removing fine machining of the pilot hole ( 7 ) trained clamping tool ( 11 ) is increased to a desired final diameter (D2), wherein the cutting tool ( 11 ) at least one at least approximately perpendicular to a central axis (M2) of the chipping tool ( 11 ) running edge ( 15 ) in the area of a tool tip ( 13 ) and peripherally extending cutting edges ( 17 ) having. Method according to claim 1, characterized in that on an insertion side of the cutting tool ( 11 ) in the workpiece ( 3 ) a chamfer ( 9 ), which in particular in one step with the pre-drilling ( 7 ) will be produced. Method according to one of claims 1 or 2, characterized in that a through-bore ( 1 ) is produced, wherein at one of the insertion side of the cutting tool ( 11 ) facing away from the workpiece ( 3 ) a rear chamfer ( 29 ) is produced. Method according to one of claims 1 to 3, characterized in that in the region of the cutting edge ( 15 ) of the cutting tool ( 11 ) a protective chamfer or rounding ( 25 ) is provided, which in particular smaller than a radial allowance (R1, R2) of the bore ( 1 ) opposite the pilot hole ( 7 ) is trained. Method according to one of claims 1 to 4, characterized in that at least one peripheral cutting edge ( 17 ) at least in regions over its direction of extension a defined Rundschlifffase ( 19 ) having. A method according to claim 5, characterized in that the Rundschlifffase ( 19 ) of the cutting edge ( 17 ) a width (B) between 0.02 mm and 0.1 mm, in particular a width (B) of 0.05 mm. Method according to one of claims 1 to 4, characterized in that at least one peripheral cutting edge ( 17 ) has a first clearance angle (FW1) in the range of 2 ° to 4 ° at least in regions over its extension direction. Method according to claim 7, characterized in that the at least one cutting edge ( 17 ) has in a region adjacent to the first clearance angle (FW1) a second clearance angle (FW2) which is greater than the first clearance angle (FW1). Method according to one of claims 1 to 8, characterized in that the cutting tool ( 11 ) four to eight peripheral cutting edges ( 17 ) having. Method according to one of claims 5 to 9, characterized in that all circumferential cutting edges ( 17 ) of the cutting tool ( 11 ) with a Rundschlifffase ( 19 ) or a clearance angle (FW1, FW2) are provided. Method according to one of claims 1 to 10, characterized in that the peripheral cutting edges ( 17 ) of the cutting tool ( 11 ) have a helix angle (DW) of less than 30 °, in particular less than 20 ° and preferably greater than 15 °. Method according to one of claims 1 to 11, characterized in that the peripheral cutting edges ( 17 ) of the cutting tool ( 11 ) has an axial length less than six times a diameter (D3) of the cutting tool ( 11 ), in particular three to five times the diameter (D3) of the cutting tool ( 11 ), exhibit. Method according to one of claims 1 to 12, characterized in that the cutting tool ( 11 ) in the region of the peripheral cutting edges ( 17 ) at least partially in the axial direction has a diameter taper, wherein the largest diameter (D3) in the region of the tool tip ( 13 ) is provided. Method according to one of claims 1 to 13, characterized in that a cooling device is provided, by means of which the cutting tool ( 11 ) is cooled during a Spanungsvorgangs especially from the inside.

Images