GB2498099A

GB2498099A - Milling cutter and method of use

Info

Publication number: GB2498099A
Application number: GB1223441.5A
Authority: GB
Inventors: Siegmar Neuner; Gregor Kappmeyer; Thorsten Deusinger; Hubert Kilb
Original assignee: Rolls Royce Deutschland Ltd and Co KG
Current assignee: Rolls Royce Deutschland Ltd and Co KG
Priority date: 2011-12-27
Filing date: 2012-12-27
Publication date: 2013-07-03
Anticipated expiration: 2032-12-27
Also published as: GB2498099B; DE102011122539A1; GB201223441D0

Abstract

A method for making a hole (1) in a workpiece (3) is described, in which a drilling tool is initially used to make a pilot hole (7) having a diameter (D1, fig 1) which is then enlarged to a required final diameter (D2) using a metal-cutting tool (11) designed for precision machining of the pilot hole (7). The metal-cutting tool (11) has in the area of a tool tip (13) at least one cutting blade (15) extending at least approximately vertically to a central axis (M2) of the metal-cutting tool (11), and cutting edges helically extending on the circumferential side. There may be four to eight such cutting edges and the clearance angle of said cutting edges may range from 2 4 DEG.

Description

Method for making a.hole in a workpiece This invention relates to a method for making a hole in a workpiece in accordance with the type defined in greater detail in patent Claim 1.

From practical experience, methods are known by which holes having very close tolerances can be made in workpieces. To do so, first a pilot drill is used to create a pilot hole with a diameter smaller than a required final diameter.

Since it might not be possible here to conform to a required positional tolerance, a positional correction must be performed in a subsequent process step, for example using a finish-boring tool, so that a central axis of the hole is within the required positional tolerance. in a further subsequent process step, a reamer for example is used to enlarge the pilot hole to the required final diameter while obtaining good surface properties inside the hole. The finish-boring process is needed since the reamer is guided in the hole and is centered in the given hole while the diameter is being widened due to oblique cutting blades arranged in the area of a tool, tip.

The method described thus entails many process steps with various tools until the hole has been increased to its final diameter, so that making the hole is time-consuming and cost-intensive.

The object underlying the present invention is to provide a method using which a high-precision hole can be made quickly and inexpensively.

It is a particular object of the present invention to provide solution to the above problematics by a method in accordance with the features of patent Claim 1.

A method is proposed for making a hole in a workpiece, for example a blind hole or a through-hole, in which a drilling tool is initially used to make a pilot hole having a diameter which is then enlarged to a required final diameter using a metal-cutting tool designed for stock-removing precision machining'of the pilot hole, said metal-cutting tool having in the area of a tool tip at (east one cutting blade extending at least approximately vertically to a central axis of the metal-cutting tool, and cuffing edges extending on the circumferential side.

A hole can be made using the method in accordance with the invention in a simple, quick and hence inexpensive manner while conforming to close positional and diameter tolerances with a high surface quality, in fewer process steps than for holes made using conventional methods. in addition, fewer tools are needed to do so. This results from the fact that the pilot hole can be widened using the metal-cutting tool to the required final diameter while performing a positional correction and also achieving a high surface quality.

Thanks to the cutting blade in the area of the tool tip, which has in the method in accordance with the invention a tip angle of at least approximately 1800, precision machining of the pilot hole is possible substantially free of radial forces, i.e. a positional correction can be performed with the metal-cutting tool, unflke in known methods where reamers are used which are centered inside the pilot hole due to their oblique cutting blades. A high surface quality can be achieved for the hole using the cutting edges on the circumferential side.

In an advantageous embodiment of the method in accordance with the invention, it is provided that a chamfer is created on an insertion side of the metal-cutting tool into the workpiece and is in particular made in one step with the pilot hole. The chamfer can. in particular be made in simple manner together with the hole using a step drill. Alternatively, it is also possible to use a separate tool to make the chamfer. The chamfer can be created before or after use of the metal-cutting tool in the workpiece.

When making a through-hole, a rear chamfer can be created on a side of the wcrkpiece facing away from the insertion side of the metal-cutting tool. This step can be performed before or after the use of the metal-cutfing tool.

In an advantageous embodiment of the method in accordance with the invention, a protective chamfer or fillet is provided in the area of the cutting blade of the metal-cutting tool and is designed in particular smaUer than a radial allowance of the hole relative to the pilot hole. The protective chamfer or fillet serves to protect the cutting blade, as the protective chamfer or fillet prevents corners or exposed areas of the cutting blade in which large quantities of heat could build up and as a result cause damage to the material of the workpiece or tool.

If at least one circumferential-side cutting edge of the metal-cuffing tool has at least in some areas a defined circular grinding chamfer over its extension direction, a particularly close final diameter tolerance for the hole to be made can be maintained. In the area of the circular grinding chamfers, the cutting edges are subject to low wear. Due to this low wear, the diameter of the metal-cutting tool in the area of the cutting blades remains very consistent, so that the metal-cuthng tool has a long service life and a high process capability of the final hole diameter is achieved.

If the circular grinding chamfer of the cutting edges has a width between 0.02 mrri and 0.1 mm, in particular a width of 0.05 mm, a high surface quality can be achieved at the same time as a good diameter tolerance of the metal-cutting tool: The circular grinding chamfer represents a part of a lateral surface of the metal-cutting tool. Together with the cutting blade in the area of the tool tip, a high guidance accuracy of the metal-cutting tool isachieved with the circular grinding chamfer on the outer diameter of the metal-cutting tool, Alternatively to the provision of circular grinding chamfers, at least one circumferential-side cutting edge can have at least in some areas over its extension direction a first clearance angle in the range from 2° to 4°. The clearance angle has an effect comparable to that of the circular grinding chamfer, so that good surface properties of the hole are achieved with relatively ow wear on the cutting edges while conforming to close diameter tolerances.

In an advantageous development of the method in accordance with the invention, it is provided that the at (east one cutting edge has in an area adjacent to the first clearance angle a second clearance angle larger than the first clearance angle. The second clearance angie adjoins the first clearance angle of the cutting edges in the circumferential direction, with a width of the cutting edge ri the area of the first clearance angle in particular having a value in the range from around 0.2 mm to 05 mm. This value can however also be greater or smaller depending on the actual diameter of the metal-cutting tool.

In a further alternative, it can be provided that the cutting edges on the circumferential side have a radial contour or a radial neck; so that an effect comparable to that by using one or more clearance angles is achieved.

In particular, all cutting edges on the circumference of the metal-cutting tool are provided with a circular grinding chamfer or a clearance angle or a radial neck.

The front cutting blade and the possibly provided protective chamfers or edge fillets are in particular provided with one or more clearance angles.

The metal-cutting tool has in particular four to eight cutting edges on the circumferential side, so that a ratio from a feed to a number of cutting edges is very low. The total feed can thus be selected relatively large, since a feed per cutfing edge is low as a result. This permits a short machining time to be achieved. Furthermore, a uniform distribution of the effective cutting forces over the circumference of the toot is achieved by the high number of cutting edges.

Thanks to the high number of cutting edges, a service life of a metal-cutting toot of this type is advantageousLy long. The number of cutting edges is selected such that chip flutes arranged between adjacent cutting edges are sufficient for the removal of chips created during the metal-cutting process.

Stable cutting edges can be achieved when the cutting edges on the circumferential side of the metal-cutting tool have a twist angle smaller than 300.

TpartcuIar smaller than 200 and preferably larger than 15°. The smaller the twist angle, the better a heat discharge at the cutting edge currently in use and the greater the durability of the metal-cutting tool. in addition, a metal-cutting force rises as the twist angle decreases.

In an advantageous embodiment of the method in accordance with the invention, the cutting edges on the circumferential side of the metal-cutting toot have an axial length less than six times a diameter of the metal-cutting tool, in particular three to five times the diameter of the metal-cutting tool. The metal-cutting tool is as a result designed short and intrinsically stable overall.

An improvement in a surface finish of the hole can be achieved in that the metal-cutting tool has, in the area of the cutting edges on the circumferential side at least in some zones, a tapering diameter in the axial direction, with the largest diameter being present in the area of the tool tip. The diameter decrease in the form of a cone angle has a vaiue in particular smaller than 60 % of a hole tolerance. The effect of friction by the cutting edges on a hole surface is reduced as a result.

For effective discharge from the metal-cutting tool of heat generated during the metal-cutting operation, a cooling device can be provided using which the metal-cutting tool is cooled in particular from the inside during a metal-cutting operation.

Dimensional accuracy of the hole to be made is also determined by the true running accuracy of the metal-cutting tool and of the tool holder. In particular, the use of hydraulically expanding clamping chucks, precision mountings or the

like is suitable.

With the method in accordance with the invention, holes such as blind holes or through-holes can be made in all materials, where optimization of the hole with respect to its positional accuracy, hole diameter and surface quality is enabled.

For: example, holes can be created in flanges in rotating components of rotors, disks or the like, these components being made for example from Udimet, Inconel, titanium alloy or nickel-based alloys.

The metal-cutting tool can be designed here as a milling tool, as a reaming/milling tool or similar.

Both the features stated in the patent Claims and the features stated in the following exemplary embodiments of the method in accordance with the invention are each suitable, singly or in any combination with one another, to develop the subject matter of the invention. The respective feature combinations do not represent any restriction with regard to the development of the subject matter in accordance with the invention, but have substantially only exemplary character.

Further advantages and advantageous embodiments of the method in accordance with the invention become apparent from the patent Claims and the exemplary embodiments described En principle in the following with reference to the accompanying drawing. In the drawing, Fig. 1 shows a simplified sectional view through a drilling tool and a workpiece in a first process step for making a through-hole, where a pilot hole and a chamfer are generated using the drilling tool in the workpiece on an insertion side of the drilling tool, Fig. 2 shows a simplified sectional view through a metal-cutting tool and the workpiece of Fig. 1 in a second process step, where a positional correction and a widening of the pilot hole to a required tinal diameter are carried out using the metal-cutting tool, Fig. 3 shows a simplified sectional view through a milling device and the workpiece of Fig. 2 in a third process step, where a rear chamfer is generated using the mUting device on a side of the workpiece facing away from the insertion side, Fig. 4 shows a simplified three-dimensional view of the metal-cutting tool of Fig. 2 in stand-alone position, Fig. 5 shows a partial area of a sectional view in simplified representation through the metal-cutting tool of Fig. 4 along line V-V. and Fig. 6 shows a partial area of a sectional view in simplified representation through an alternatively designed metal-cutting tool.

Figures 1 to 3 show in part optional process steps for making a high-precision hoLe 1 in a workpieCe 3, with the respective tools and the workpiece 3 each being shown in a greatly simplified sectional view.

Firstly, a pilot hole 7 having a diameter Dl is created around a central axis Ml in the workpiece 3 using a driflirig tool 5 shown in simplified form in Fig. 1. The drilling tool 5, here designed in the manner of a step drill, for that purpose makes a rotary motion along the arrow P1 and a feed movement along the arrow P2 in the direction of the workpiece 3. with the drilling toot 5, therefore: the pilot hole 7 extending through the entire workpiece 3 in the manner of a through-hole, and a front chamfer 9 which is arranged on an insertion side of the drilling tool 5 inside the workpiece 3, are generated in one step.

For making the front chamfer 9, larger tolerances are permissible when compared with the final hole position, so that it can be made together with the pilot hole 7. An advantage of the step drill 5 shown is that for creating the front chamfer 9 it does not engage full-surface or obtusely with the workpiece, but in the present case at an angle of around 450* This permits achievement of a uniform increase in a cutting force, smooth tool action and a tong service life of the tool In an alternative.embodiment of the invention, the front chamfer 9 can also be created using a separate tool.

En a process step subsequent to the making of the pilot hole 7, said pilot hole 7 is, in accordance with Fig. 2, widened using a metal-cutting tool 11 to a required final diameter D2 which is larger than the diameter Dl of the pilot hole. The metal-cutting tool 11, made from a carbide, a carbide-ceramic mixture or other known cutting materials and shown in more detail in Figs 4 and 5, rotates for that purpose in the direction of an arrow PS and has a feed direction along an arrow P4 corresponding to the feed direction of the drilling tool 5.

At least one main or front cutting blade 15 arranged in the area of a tool tip 13 of the metal-cutting tool 11 is in the present case designed substantially vertical to a central axis M2 of the metal-cutting tool 11. The cutting blade 15 extends over the entire diameter area Dl of the pilot hole 7 vertically to the centrat axis Ml and M2. This has the advantage that during a widening of the diameter Dl of the pilot hole 7 by the metal-cutting tool 11, no forces act in the radial direction of the metal-cutting tool 11, so that a positional correction of the central axis Ml can be performed with the metal-cutting tool 11, and the central axis M2 of the hole can be offset relative to the central axis Ml of the pilot hole.

Accordingly, a first radial allowance Ri on one side of the workpiece 3 shown on the left in the sectional view in Fig. 2 can differ from a second radial allowance R2 on one side of the workpiece 3 shown on the right in the sectional view.

The metal-cutting tool 11 shown in sections in Fig. 4 in a three-dimensional side view has, besides the main cutting blade 15, several cutting edges 17 extending on the circumferential side, these having in the present case a positive twist angle DW of around 15°. Due to the relatively small twist angle OW of the cutting edges 17, the tool tip 13 is relatively blunt, so that the metal-cutting tool has a good durability and the cutting edges 17 are stable. In addition, heat discharge from the area of the tool tip 13 is very effective.

Six cutting edges 17 are provided in the present case, where due to the high number of secondary cutting edges 17 a teed can be selected very large, since a ratio of feed to a cutting edge number is relatively low due to the large number of cutting edges. The large number of cutting edges 17 also has the advantage that a very uniform distribution is achieved of the cutting forces acting during the metal-cutting process over the entire circumference of the metal-cutting tool 11.

The large number of cutting edges 17 also has an advantageous effect on the service life of the metal-cutting tool 11.

The individual cutting edges 17 each have in the present case over their extent along the metal-cutting tool 11 a circular grinding chamfer 19. As shown in more detail in Fig. 5, one part of the cutting edge 17.is at least approached by the circular grinding chamfer 19 of a lateral surface 21 of the metal-cutting toot 11 or is a part of the lateral surface 21, so that a dimensional accuracy of the metal-cutting tool 11 over a long period is very high, and close diameter tolerances can be complied with. Due to the circular grinding chamfer 19, which in the present case has a width B of around 0.04 mm, an undefined cutting edge is created which permits precise compliance with a required final diameter D2. On the other hand, the circular grinding chamfer 19 is selected so smaJl that a surface 22 of the hole 1 is not damaged during the metal-cutting process.

Together, with the cutting blade 15, the circular grinding chamfers of the cutting edges 17 lead to the metal-cutting tool 11 having a high guidance accuracy. -10-

iternatively to the circular grinding chamfer 19, the cutting edges 17 can also -as seen in Fig. 6 -be designed with a first clearance angle FW1 which is around 2° to 4° while the metal-cutting tool ii is otherwise unchanged. In the present case, the first clearance angle FW1 has a width of around 0.2 mm to 0.5 mm extending in the circumferential direction of the metal-cutting tool 11. A second clearance angle FW2 is adjacent to the first clearance angle FW1 and is selected larger than the first clearance angle FW1 and similar to a clearance angle of a milling tool geometry. Thanks to the use of cutting edges 17 with clearance angles FW1, FW2, a very good surface finish of the hole 1 can be achieved.

The metal-cutting too) 11 is in the present case designed conical in the area of an effective length NL of the metal-cutting tool 11, i.e. a diameter D3 in the area pf the tool tip 13 is larger than a diameter D4 in an area of the metal-cutting tool 11 facing away from the tool tip 13. This is achieved by a cone angle which is not shown in greater detail in Fig. 4. A tapering of the metal-cutting tool 11 is in the present case about 60 % of a hole diameter tolerance over the effective length NL of the metal-cutting tool 11. This reduces a friction effect of the secondary cutting edges on the surface 23 of the hole 1 and achieves an improvement in the surface finish of hole 1.

Fig. 4 shows a continuous corner fillet 25 in the area of the tool tip 13 and intended to protect the metal-cutting tool it The corner fillet 25, which in particular has a radius in the range from DM5 mm to 0.1 mm, is preferably *èelected such that it is smaller than the smaller radial allowance Ri or P2 respectively, so that during the metal-cutting operation no radial forces act in the area of the tool tip 13 due to the comerfillet 25.

Alternatively to the corner fillet 25, a continuous protective chamfer can also be provided in the area of the tool tip, and is likewise designed preferably smaller than the smallest radial allowance.

To conform to close tolerances when making the hole 1, it is advantageous to use a metal-cutting tool 11 nd a tool holder with a high true running accuracy.

With the metal-cutting tool 11, which has features of a conventional milling tool and of a positive-twist reamer, the use of a separate toot for positional correction of the pilot hole, and of a further tool for widening of the pilot hole diameter to the required final diameter, can be dispensed with.

After the possibly necessary positional correction and the making of the hole 1 with the required final diameter, a rear chamfer 29 is created in the present case on a side of the workpiece 3 facing away from the front chamfer 9 using a milling device 27 shown in Fig 3. The milling device 27 has for that purpose a diameter D5 so small at its widest point that it can be passed through the hole 1.

:sãt0f reference numerals 1 Hole 3 Workpiece Drilling tool 7 Pilot hole 9 Front chamfer of workpiece ii Metal-cutting tool 13 Tip of metal-cutting tool Cutting blade of metal-cutting tool 17 Cutting edge of metal-cutting tool 19 Circular grinding chamfer of cutting edge 21 Lateral surface of metal-cutting tool 23 Surface of hole Corner fillet of metal-cutting tool 27 Milling device 29 Fear chamfer of workpiece B Width of circular grinding chamfer Dl to D5 Diameter DW Twist angle FW1, FW2 Clearance angle NL Effective length Ml, M2 Central axis Fl to P4 Arrow Ri, R2 Radial allowance

Claims

<claim-text>Claims Method for making a hole (1) in a workpiece (3), in which a drilling tool (5) is initially used to make a pilot hole (7) having a diameter (Dl) which is then enlarged to a required final diameter (D2) using a metal-cutting tool (11) designed for stock-removing precision machining of the pilot hole (7), said metal-cutting tool (11) having in the area of a tool tip (13) at least one cutting blade (15) extending at least approximately vertically to a central axis (M2) of the metal-cutting tool (11), and cutting edges (17) extending on the circumferential side.</claim-text> <claim-text>2. Method in accordance with Claim 1, characterized in that a chamfer (9) is created on an insertion side of the metal-cutting tooL (11) into the workpiece (3) and is in particular made in one step with the pilot hole (7).</claim-text> <claim-text>3. Method in accordance with one of the Claims 1 or 2, characterized in that a through-hole (1) is made, with a rear chamfer (29) being created on a side of the workpiece (3) facing away from the insertion side of the metal-cutting tool (11).</claim-text> <claim-text>4. Method in accordance with one of the Claims 1 to 3, characterized in that a protective chamfer or fillet (25) is provided in the area of the cutting blade (15) of the metal-cutting tool (11) and is designed in particular smaller than a radial allowance (Ri, R2) of the hole (1) relative to the pilot hole (7).</claim-text> <claim-text>5. Method in accordance with one of the Claims 1 to 4, characterized in that at least one circumferential-side cutting edge (17) has at least in some areas a defined circular grinding chamfer (19) over its extension direction.</claim-text> <claim-text>6. Method in accordance with Claim 5, characterized in that The circular grindtng chamfer (19) of the cutting edge (17) has a width (B) between 0 02 mm and 0 1 mm, in particular a width (B) of 0 05 mm 7. Method in accordance with one of the Claims 1 to 4, characterized in that at least one circumferential-side cutting edge (17) has at least in some areas over its extension direction a first clearance angle (FW1) in the range from 2° to 4° 8. Method in accordance with Claim 7, characterized in that the at least one cutting edge (17) has in an area adjacent to the first clearance angle (FWI) a second clearance angle (FW2) larger than the first clearance angle (EW1).9. Method in accordance with one of the Claims 1 to 8, characterized in that the metal-cutting toot (11) has four to eight cutting edges (17) on the circumferential side.10. Method in accordance with one of the Claims 5 to 9, characterized in that all cutting edges (17) on the circumferential side of the metal-cutting tool (11) are provided with a circular grinding chamfer (19) or a clearance angle (FW1, FW2).11. Method n accordance with one of the Claims 1 to 10, characterized in that the cutting edges (17) on the circumferential side of the metal-cutting tool (11) have a twist angle (DW) smaller than 30°, in particular smaller than 20° and preferably larger than 15°.. Method in accordance with one of the Claims ito 11, characterized in that the cutting edges (17) on the circumferential side of the metal-cutting tool (11) have an axial length less than six times a diameter (D3) of the metal-cutting tool (11), iii particular three to five times the diameter (D3) of the metal-cutting tool (11).13. Method in accordance with one of the Claims ito 12, characterized in that the metal-cutting tool (ii) has, in the area of the cutting edges (17) on the circumferential side at least in some zones, a tapering diameter in the axial direction, with the largest diameter (03) being present in the area of the toot tip (13).14. Method in accordance with one of the Claims 1 to 13, characterized in that a coolihg device is provided using which the metal-cutting tool (11) is coo(ed in particular from the inside during a metal-cutting operation.</claim-text>