DE20307124U1 - Tool suitable for working at inside of metal workpiece, comprising shaft with longitudinal slot and particularly designed cutting head - Google Patents

Abstract

The tool (10) has a shaft (12) of hard metal with a slot (14) with a rectangular cross section located alongside. The cutting head (16) has a semi-cylindrical tip (18) gradually transforming into a rectangular base (20) and soldered to the top of the slot (14) in an eccentric position. The tip (18) is made of an axial arranged layer of cubic bornitride (CBN) (22) positioned at the outside of the cutting head (16) and a layer of hard-metal (24) adjacent to the bottom of the slot (14).

Description

WITTE, WELLER & PARTNER

Patent attorneys

Rotebühlstraße 121 D-70178 Stuttgart

Applicant: 25 April 2003

MAS Sales Company 3467G100 - CS/ad

for machining technology with

limited liability

Glemseckstrasse 69

71229 Leonberg

Germany

Tool for internal machining of hardened metal workpieces

The present invention relates to a tool for internal machining of hardened metal workpieces, with a base section for fastening the tool to a holder, a machining section which can be inserted into an opening of the workpiece in a feed device for internal machining, and a cutting body which has a layer of a hard machining material, in particular CBN.

Such a tool is generally known, for example from the brochure "Carbide turning tools" by Sumitomo Electric, pages 157 to 163, printing note MD 08/02.

In recent years there has been a trend to bring hardened metal workpieces to a final dimension not by grinding but by turning.

Interchangeable cutting plates are known as turning tools, into which a cutting body is soldered that is suitable for hard machining.

The currently common material for hard machining of metal workpieces is cubic boron nitride (CBN or PCBN).

CBN is a very hard but also very brittle material. The cutting bodies are therefore generally manufactured by sintering CBN powder onto a carrier material layer, particularly made of hard metal. The sintered flat blank produced in this way is brought into the appropriate shape, for example by erosion. A triangular shape is usually chosen for use in cutting plates. The cutting body is then attached to the carrier plate, usually by soldering. The cutting body is then finished. However, it is also known to manufacture cutting bodies in the form of indexable inserts entirely from CBN.

While this technology has proven itself in the external machining of hardened workpieces, for internal machining

For such workpieces, special boring tools are often manufactured, especially for small bore diameters.

The boring tools essentially consist of a cylindrical shaft section. A rear section of this shaft is designed to be attached to a holder. The holder in turn is clamped into a chuck of a machine, e.g. a lathe.

The holder is usually a cylindrical body with a continuous axial bore into which the shaft section of the boring tool can be inserted. Fastening is achieved using grub screws or similar.

At the front machining section of the boring tool, material is removed in such a way that the cross-section is approximately semicircular.

In one corner of the surface thus formed, a cutting body is fixed by soldering. In such boring tools, the cutting body is aligned in such a way that a parting plane between the hard machining layer and the carrier layer of the cutting body runs approximately perpendicular to the axis of the shaft section.

A conventional arrangement for internal machining of hardened workpieces by means of a boring tool of the type mentioned is shown in Fig. 8.

A chuck 102 is provided on a spindle 100 of a machine tool (lathe). A holder 104 of the type described is clamped into the chuck 102.

A boring bar 106 is inserted and fixed into a front axial bore of the holder 104.

The boring bar 106 has a front machining section 106a and a rear base section 106b which is received in the axial bore of the holder 104.

For internal machining of a workpiece 108, the machining section 106a is inserted into an unspecified opening of the workpiece 108.

The inner diameter of the opening of the workpiece 108 is designated 112 in Fig. 8, the outer diameter of the machining section 106a is designated 110. As described in the prior art, the minimum inner diameter 112 is in the range of 2.5 mm.

At the front end of the machining section 106a, a cutting body 114 is fixed by soldering.

The cutting body 114 has a front CBN layer 116 and a rear hard metal layer 118. The two layers 116, 118 are separated from each other by a parting plane which runs approximately perpendicular to the feed direction V of the boring bar 10 6.

Another example of the prior art is shown schematically in Fig. 9 in a plan view and a sectional view.

A cutting plate 120 has an approximately diamond shape in plan view. A cutting body 114' is fixed to one corner of the diamond by soldering, with an upper CBN layer 116' being aligned approximately flush with an upper side of the cutting plate 120. The hard metal layer 118' is soldered flat into a holder of the cutting plate 120.

If boring bars are selected for internal machining with a cutting plate detachably attached to the front end, internal diameters down to 5 mm can be machined.

Users request that even smaller inner diameters be hard machined.

In the current state of the art, this would mean that the diameter of the shank section of the boring tool would have to be reduced. On the other hand, the cutting body would have to be made even smaller. This not only leads to problems in the manufacture of the cutting body, but also in the attachment of the cutting body to the shank section.

It is therefore the object of the present invention to provide a tool for the internal machining of hardened metal workpieces, with which even very small inner diameters can be machined, wherein the tool should be easy to manufacture.

This object is achieved in the tool mentioned at the outset for the internal machining of hardened metal workpieces in that a front section of the cutting body forms the machining section and protrudes freely from the base section, and that a rear section of the cutting body is fixed to the base section.

Furthermore, the above object is achieved by a cutting body made of a layer of a hard machining material, in particular CBN, and preferably a further layer of a carrier material, in particular hard metal, wherein the cutting body is formed elongated with a front machining section and a rear section.

Finally, the above object is achieved by a base body, wherein the base body is designed as an elongated shaft section and has a longitudinally continuous groove which is designed to receive a rear section of an elongated cutting body.

The basic idea of the present invention is to design the cutting body itself as a machining section, whereby only the cutting body or its front section can be inserted into the opening of the workpiece.

This makes it possible to provide the machining section, which is formed by the front section of the cutting body, with a particularly small cross-section or external diameter. This means that particularly small diameters can be machined internally.

Accordingly, the present invention departs from the idea of supporting the part of the cutting body used for machining by a base section, for example by the front part of a shank of a boring tool or by the plate-like base body of a cutting plate.

To fix the cutting body whose freely projecting front section is used as the machining section, a rear section of the cutting body is fixed to the base section. In this way, a stable positioning of the front section of the cutting body in relation to the base section can also be achieved.

The cutting body has a layer made of a hard machining material, in particular CBN. In the present context, this should be understood to mean that the cutting body can be made entirely of solid CBN material. Such a cutting body is manufactured separately and then attached to the base section. However, it is also within the scope of the present invention to prepare the base section and the cutting body essentially as a one-piece element made of hard metal and to sinter a CBN layer onto the front section of the cutting body.

It is considered particularly preferred if the cutting body has, in addition to the layer of hard machining material, a further layer of a carrier material, in particular hard metal.

This allows the relatively brittle hard machining material layer to be supported. Furthermore, such a cutting body can be produced relatively easily, for example from a CBN hard metal plate as described at the beginning.

It is also particularly advantageous if the tool is rod-shaped, with the base section being designed as an elongated shaft section.

In this embodiment, the tool as a whole generally has the shape of a boring tool or a boring bar, with an elongated shaft as a base section and a cutting body, the rear section of which is fixed to the base section and the front section of which protrudes relative to it and forms a machining section.

This design of the base section allows the tool to be inserted into known holders.

It is particularly advantageous if the cutting body is elongated.

This measure makes it possible to make both the front and rear sections relatively long. As a result, a relatively large internal machining depth can be achieved. The rear section can also be made sufficiently long to be securely and, above all, rigidly attached to the base section.

It is also advantageous if a parting plane between the hard machining material layer and the carrier material layer of the cutting body is arranged parallel to the feed direction.

By this measure, the desired elongated shape of the cutting body can be achieved from a conventional, generally flat cutting body blank.

According to a further preferred embodiment, the front section of the cutting body forming the machining section is approximately semicircular in cross section.

This makes it possible to achieve a precise cutting edge from a generally cuboid-shaped section of the cutting body blank in a comparatively simple manner.

According to a further preferred embodiment, the rear portion of the cutting body is polygonal in cross section, in particular rectangular.

This measure makes it possible to rigidly fix the rear section of the cutting body to the elongated shaft section.

Overall, it is preferred if the rear portion of the cutting body is positively secured to the shaft portion in the circumferential direction.

This allows the cutting body to be securely fixed to the shaft section.

Furthermore, the cutting body should be positively secured to the shaft section in the direction of rotation about its longitudinal axis due to the polygonal shape of its rear section.

According to a further preferred embodiment, the rear portion of the cutting body is brazed to the shaft portion.

Since the rear section of the cutting body can be made comparatively large compared to a cutting body that is designed for particularly small diameters in a conventional boring tool, this fastening process can be implemented in a cost-effective manner in terms of production technology.

It is also advantageous if the elongated shaft section has a longitudinal groove in which the rear section of the cutting body is fixed.

This makes it possible to form a cost-effective holder for the rear section of the cutting body on the elongated shaft section (which is preferably also made of a hard metal).

It is particularly advantageous if the longitudinal groove is continuous over the length of the shaft section.

With this measure, the longitudinal groove can be produced by a simple erosion process, for example by wire erosion. Such a shaft-shaped base section with a groove running through the longitudinal direction is considered to be an independent invention.

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Overall, it is also advantageous if the diameter of the front section of the cutting body is smaller than the diameter of the shaft section.

This makes it possible for the shaft section to have a diameter suitable for commercially available holders, whereas the diameter of the front section of the cutting body is designed for particularly small inner diameters on the workpiece to be machined.

Preferably, the diameter of the front portion of the cutting body is in the range of 0.5 to 3 mm, in particular in the range of 1 to 3 mm.

This measure therefore allows holes with inner diameters of corresponding dimensions to be machined internally.

According to an alternative embodiment, the tool is designed as a cutting plate, wherein the base portion is plate-shaped.

In this embodiment, the inventive concept is applied to cutting plates, in particular interchangeable cutting plates.

It is particularly advantageous if the front section of the cutting body protrudes freely from the plate-shaped base section.

This makes it possible for only the front section of the cutting body to be inserted into openings in workpieces for internal machining.

It is also advantageous if a separation plane between the hard machining material layer and the carrier material layer of the cutting body is aligned parallel to the plate-shaped base section.

This allows the cutting body to be fixed to the plate-shaped base section in the usual way.

However, since only the front section of the cutting body is inserted into openings of workpieces for internal machining, the rear section of the cutting body can be made comparatively large, so that a flat and stable attachment to the plate-shaped base section is possible.

It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

Embodiments of the invention are shown in the drawing and are explained in more detail in the following description. They show:

Fig. 1 is a schematic perspective view of a first embodiment of the tool according to the invention;

Fig. la shows a modification of the cutting body of the tool of Fig. 1;

Fig. 2 is a side view of a second embodiment of the tool according to the invention;

Fig. 3 is a front view of the tool of Fig. 2;

Fig. 4 is a plan view of the tool of Fig. 2;

Fig. 5 is a perspective view of the tool of Fig. 2;

Fig. 6 shows a detail VI of Fig. 5;

Fig. 7 is a schematic sectional view of another embodiment of a tool according to the invention;

Fig. 8 is a schematic diagram to explain the internal machining of hardened metal workpieces according to the prior art; and

Fig. 9 is a plan view or a schematic sectional view through a cutting plate according to the prior art.

In Fig. 1, a first embodiment of the tool according to the invention is generally designated 10.

The tool 10 has an approximately cylindrical shaft 12 on which a continuous longitudinal groove 14 is provided.

The shaft 12 is usually made of hard metal and the longitudinal groove 14 can be formed in a comparatively simple manner by wire erosion.

The tool 10 further comprises an elongated cutting body 16.

The cutting body 16 has a front section 18 and a rear section 20. The rear section 20 is fixed in the region of a front side of the shaft 12 in the longitudinal groove 14. This can be done, for example, by soldering. Alternatively, it is also possible to detachably fix the rear section 20 to the shaft 12, for example by screwing or the like.

As shown, the longitudinal groove 14 is approximately rectangular or square in cross-section. In the same way, the rear section 20 of the cutting body 16 is approximately cuboid-shaped, so that it can be inserted into the groove 14 with a clearance fit in order to then carry out a soldering process with which three outer surfaces of the rear section 20 are fixed flat to the shaft 12. The relative dimensions can be selected so that the solder flows into the gap between the rear section 20 and the longitudinal groove 14 by capillary effects.

The front portion 18 of the cutting body 16 projects beyond the front face of the shaft 12.

A front area of the front section 18 is approximately semicircular in cross section. In a rear

In the area of the front section 18, which borders on the rear section 20, there is a transition from the semicircular shape to the rectangular shape of the rear section 20.

The cutting body 16 has a CBN layer 22 and a hard metal layer 24, which are separated from each other by a parting plane 26. In this case, the parting plane runs approximately centrally through the cutting body 16, specifically along its longitudinal axis. Consequently, the parting plane 26 also runs approximately parallel to the longitudinal axis of the shaft 12. However, the parting plane can also run off-center.

The CBN layer is arranged radially on the outside so that it is approximately flush with the outer circumference of the shaft 12. The hard metal layer 24 is arranged radially on the inside so that it is adjacent to the bottom of the longitudinal groove 14.

The diameter of the front portion 18 is designated by d in Fig. 1 and is generally in the range of 0.5 to 3 mm, in particular in the range of 1 to 3 mm.

The diameter of the shaft 12 is generally designated D in Fig. 1 and is, for example, in the range from 3 to 10 mm, in particular in the range from 4 to 8 mm.

In general, the cutting body 16 is thus aligned approximately parallel to the shaft 12, but eccentrically to it. The depth of the longitudinal groove 14 is preferably smaller than the radius (D/2) of the shaft 12.

The cutting body 16 is made from a sintered blank. The sintered blank is generally a flat plate with the CBN layer and the hard metal layer. The elongated shape of the cutting body 16 is first eroded out of this. The front section 18 is then shaped, for example also by eroding.

It is understood that the thickness of the blank must generally be greater than the diameter d of the front section 18. Preferably, the thickness of the blank is as close as possible to the value of d or is identical to the value of d. This ensures that as little material as possible is lost from the blank to produce the basic shape of the cutting body 16.

When machining the inside of hardened workpieces, the shaft 12 is inserted into a holder which can be designed similarly to the holder 104 of the prior art described at the beginning.

It is understood that the internal machining of small diameters of the workpiece can only be carried out to a depth that corresponds approximately to the length of the front section 18 of the cutting body 16. Since it is often only necessary to machine relatively flat holes internally, it is generally sufficient if the front section 18 protrudes by 2 to 6 mm from the front side of the shaft 12. In particular with such lengths, it is possible that the support provided by the hard material layer 24 is sufficient for the comparatively brittle CBN layer 22.

In Fig. la, a modification of the cutting body of the tool 10 of Fig. 1 is generally designated 16'. The general dimensions and the general structure of the cutting body 16' correspond to that of the cutting body 16 of Fig. 1. The cutting body 16' is, however, made of solid CBN, and thus has no carrier material layer.

Such a cutting body 16' is suitable if the CBN or another hard machining material has sufficient strength to be used alone as a cutting body.

Fig. 1a further shows a further modification of the cutting body 16 of Fig. 1, which is generally designated 16''.

In this embodiment, the cutting body 16'' is made entirely of hard metal and a CBN layer is sintered onto the area of the machining section, as shown schematically at 22''. In this embodiment, it is understood that the cutting body 16'' can also be formed in one piece with the shaft 12. In this case, it is also not necessary to provide a groove 14 on the shaft 12.

Figures 2 to 6 show a further embodiment of a tool according to the invention.

The tool shown in Figs. 2 to 6 is generally of similar construction to the tool 10 of Fig. 1, so that like elements are provided with like reference numerals.

However, it is shown that the section of the shaft 12 adjacent to the front section 18 of the cutting body 16 can also be bevelled in order to facilitate insertion, for example, into countersunk holes in the workpiece.

Finally, in Fig. 7, a third embodiment of the tool according to the invention is generally designated 10'.

The tool 10' is a cutting plate 30 which has a carrier plate 32. The carrier plate 32 has, in a conventional manner, a bore for receiving a fastening screw or the like.

Furthermore, a cutting body 34 is fixed to the carrier plate 32.

The cutting body 34 in the tool 10' is generally flat, for example with a triangular shape, as shown in Fig. 9.

In this case, only a rear portion 20' of the cutting body 34 is fixed to the carrier plate 32, whereas a front portion 18' of the cutting body 34 protrudes freely from the carrier plate 32.

A CBN layer 22 of the cutting body 34 lies approximately flush with an upper side of the carrier plate 32. A rear section of the hard metal layer 24 is fixed to the carrier plate 32, for example by soldering.

In this embodiment, it is possible that only the front section 18' is used for the internal machining of hardened metal workpieces, so that comparatively small internal diameters can also be machined by means of a cutting plate 30.

The extent of the projection by which the front portion 18' projects relative to the carrier plate 32 is designated K in Fig. 7. The extent of K can be, for example, in the range from 1 to 6 mm, in particular in the range from 2 to 5 mm.

From the above it follows that the cutting body 34 can also be made of solid CBN. It is also possible for the cutting body 34 to consist essentially of carrier material onto which a CBN section is sintered. In this case, the cutting body 34 can also be formed in one piece with the carrier plate 32.

Claims (21)

1. Tool ( 10 ) for internal machining of hardened metal workpieces ( 108 ), with - a base section ( 12 ; 32 ) for fastening the tool ( 10 ) to a holder ( 104 ), - a machining section ( 18 ; 18 ') which can be inserted into an opening of the workpiece ( 108 ) for internal machining in a feed direction (V), and - a cutting body ( 16 ; 34 ) having a layer ( 22 ) of a hard machining material, in particular CBN, characterized in that
a front section ( 18 ; 18 ') of the cutting body ( 16 ; 34 ) forms the machining section ( 18 ; 18 ') and projects freely relative to the base section, and that a rear section ( 20 ; 20 ') of the cutting body ( 16 ; 34 ) is fixed to the base section ( 12 ; 32 ). 2. Tool according to claim 1, characterized in that the cutting body ( 16 ; 34 ) further comprises a layer ( 24 ) made of a carrier material, in particular hard metal. 3. Tool according to claim 1 or 2, characterized in that the tool ( 10 ) is rod-shaped, wherein the base portion ( 12 ) is designed as an elongated shaft portion ( 12 ). 4. Tool according to claim 3, characterized in that the cutting body ( 16 ) is elongated. 5. Tool according to claim 2 and 4, characterized in that a parting plane ( 26 ) between the hard machining material layer ( 22 ) and the carrier material layer ( 24 ) of the cutting body ( 16 ) is arranged parallel to the feed direction (V). 6. Tool according to claim 4 or 5, characterized in that the front section ( 18 ) of the cutting body ( 16 ) forming the machining section ( 18 ) is approximately semicircular in cross section. 7. Tool according to one of claims 4-6, characterized in that the rear portion ( 20 ) of the cutting body ( 16 ) is polygonal in cross section, in particular rectangular. 8. Tool according to one of claims 3-7, characterized in that the rear portion ( 20 ) of the cutting body ( 16 ) is fixed to the shaft portion ( 12 ) in a form-fitting manner in the circumferential direction. 9. Tool according to one of claims 3-8, characterized in that the rear portion ( 20 ) of the cutting body ( 16 ) is soldered to the shaft portion ( 12 ). 10. Tool according to one of claims 3-9, characterized in that the elongated shaft portion ( 12 ) has a longitudinal groove ( 14 ) in which the rear portion ( 20 ) of the cutting body ( 16 ) is fixed. 11. Tool according to claim 10, characterized in that the longitudinal groove ( 14 ) is continuous over the length of the shaft portion ( 12 ). 12. Tool according to one of claims 3-11, characterized in that the diameter of the front portion ( 18 ) of the cutting body ( 16 ) is smaller than the diameter of the shaft portion ( 12 ). 13. Tool according to one of claims 3-12, characterized in that the diameter of the front portion ( 18 ) of the cutting body ( 16 ) is in the range of 0.5-3 mm, in particular in the range of 1-3 mm. 14. Tool according to claim 1 or 2, characterized in that the tool ( 10 ') is designed as a cutting plate ( 30 ), wherein the base portion ( 32 ) is plate-shaped. 15. Tool according to claim 14, characterized in that the front portion ( 18 ') of the cutting body ( 34 ) projects freely from the plate-shaped base portion ( 32 ). 16. Tool according to claim 2 and according to claim 14 or 15, characterized in that a parting plane ( 20 ') between the hard machining material layer ( 22 ') and the carrier material layer ( 24 ') of the cutting body ( 34 ) is aligned parallel to the plate-shaped base section ( 32 ). 17. Cutting body ( 16 ), in particular for a tool ( 10 ) according to one of claims 3-13, made of a layer ( 22 ) of a hard machining material, in particular CBN, and preferably a further layer ( 24 ) of a carrier material, in particular hard metal, wherein the cutting body ( 16 ) is elongated with a front machining section ( 18 ) and a rear section ( 20 ). 18. Cutting body according to claim 17, wherein a parting plane ( 26 ) between the hard machining material layer ( 22 ) and the carrier material layer ( 24 ) of the cutting body ( 16 ) is aligned parallel to the longitudinal axis of the cutting body ( 16 ). 19. Cutting body according to claim 17 or 18, wherein the rear portion ( 20 ) is polygonal in cross section, in particular rectangular. 20. Cutting body according to one of claims 17-19, wherein the front portion ( 18 ) of the cutting body ( 16 ) is approximately semicircular in cross section. 21. Base body ( 12 ), in particular for a tool ( 10 ) according to one of claims 3-13, wherein the base body ( 12 ) is designed as an elongated shaft section ( 12 ) and has a longitudinally continuous groove ( 14 ) which is designed to receive a rear section ( 20 ) of an elongated cutting body ( 16 ).