EP2825341A1

EP2825341A1 - Method and tool for producing an exact-fit cylindrical bore by removal of material from an existing bore with a finishing allowance

Info

Publication number: EP2825341A1
Application number: EP13711572.1A
Authority: EP
Inventors: Peter Kopton; Eugen Maurer
Original assignee: Audi AG
Current assignee: Audi AG
Priority date: 2012-03-16
Filing date: 2013-03-15
Publication date: 2015-01-21
Also published as: CN104302430A; US20150158132A1; DE102012007514A1; US9919389B2; WO2013135392A1; CN104302430B

Abstract

The provided method and material-removing tool serve for producing an exact-fit cylindrical bore with a high degree of surface quality and a length that may be a multiple of the diameter from an existing bore with a finishing allowance. In order to reduce the time taken for the finishing by means of a reamer to be performed, it is proposed to use a tool in the form of an impact ram (10), which is formed at the front end with a circular or substantially circular cutting edge (14), the diameter of which corresponds to the nominal diameter of the bore to be produced, and which tapers from directly behind the cutting edge (14) or behind a front region (16) of a certain length.

Description

Method and tool for machining a precisely fitting, cylindrical bore from an existing bore with

Finish machining allowance

The invention relates to a method and a tool for machining a precision, cylindrical bore with high surface quality and a length which can be a multiple of the diameter, from an existing bore with a radius related finishing allowance.

For the preparation of non-circular holes, z. B. with square cross-section, keyways or splined profile, broaches and Räumdorne be used, which usually staggered from front to rear have a plurality of stepped further projecting cutting teeth. Broaching tools are typically used for profiling, not the finishing and finishing of cylindrical holes with high surface quality.

If cylindrical bores are to be finished in the last work step, reamers are used, with which an existing bore, which still has a friction allowance of a few tenths of a mm, is bored out. The rubbing is a relatively slow process in which the reamer is driven axially along the bore axis and simultaneously rotating. If the axial feed z. B. 0.1 mm per revolution, ie 380 revolutions are needed for the rubbing of a 38 mm long hole, and worked with 800 rpm, the operation takes about half a minute. The long processing time is particularly significant when large-scale workpieces such. As engines are produced, each having a variety of very accurate and with high surface quality to be machined holes, for example, for the management of the intake and exhaust valves of the cylinder of a four- or six-cylinder engine.

CONFIRMATION COPY The invention is therefore an object of the invention to provide a method and tool of the type mentioned, which allows a significant reduction in processing time compared to the conventional rubbing without loss of precision and surface quality of the cylindrical bores to be produced.

The above object is achieved in terms of the method according to the invention essentially in that the finishing allowance is peeled off during an axial stroke of a Stoßstempels with a circular or substantially circular cutting edge at its front end to the nominal diameter of the finished bore.

More particularly, the invention relates to a method of machining a precision-machined, high-surface-area cylindrical bore having a length that can be a multiple of the diameter from an existing bore with a finishing allowance that is characterized by the finishing allowance during axial machining Working stroke of a Stoßstempels is peeled with a circular or substantially circular cutting edge at its front end to the nominal diameter of the finished bore, wherein the axial stroke is superimposed by a rotational movement, either the ratio of stroke and speed is constant or varied.

For carrying out the method according to the invention, a tool is proposed according to the invention, which has the shape of a Stoßstempels, which is formed at the front end with a circular or substantially circular cutting edge whose diameter corresponds to the nominal diameter of the bore to be produced. The ram preferably tapers immediately behind the cutting edge or behind a front region of a certain length. By a substantially circular cutting edge is here to be understood a cutting edge which produces a substantially cylindrical bore for accurately receiving and guiding a cylindrical shaft or axis, wherein small projections for the production shallow traits in the surface of the bore, which only affect the lubricating film locally, are disregarded.

For the finishing of the pre-machined hole a length of z. B. 38 mm requires the push only a single forward and return stroke and a processing time of z. B. about 0.6 sec. That is only about 1/50 of the duration of the exemplified Reibbearbeitung with a reamer. During the pre-stroke, the cutting edge of the thrusting die peels the grinding or finishing allowance from the bore wall so that it expands to the nominal diameter. During the return stroke, the material of the bore wall can be compacted and smoothed by the impact ram. This results in a high percentage of support. Traces and surface structures left by the tool on the bore wall during the forward and return strokes extend axially, i. H. in the direction of the movement of the valve stems, provided that a purely axial impact movement is performed. In contrast, the tracks and surface structures run after processing by means of a reamer transverse to the direction of movement of the valves, so that it already comes when retracting the motor due to the friction of the valve stems transverse to the surface structures to a first wear.

The cutting speed in the finishing of the bores with the punch can easily be 5 m / min to 150 m / min, preferably 30 to 60 m / min or more.

The thickness of the finishing allowance depends on the diameter of the bore and the material. It must peel off with a single stroke, so shock, and then the cut surface must have the predetermined surface quality. For bore diameters up to 20 mm, the finishing allowance will normally be 0.01 mm to 0.5 mm, based on the radius, but it may also be smaller or larger. So that the impact punch can push out the chips peeled off from the bore wall itself from the bore, the impact punch is preferably slightly longer than the bore to be produced. The chip formation takes place at the cutting edge at the front end of the Stoßstempels. Starting either immediately behind the cutting edge or behind a front, cylindrical portion of certain length, z. 0.1-0.4 mm, the impactor is tapered relative to its cross-section at the cutting edge. The amount of taper should, on the one hand, be sufficient to prevent it from rubbing against the bore wall beyond a front portion of a certain length, while remaining stiff enough to guide the cutting edge safely.

A guide of the impact punch also takes place on the bore wall, namely on the front part of the impact punch, where the diameter is as large as or only slightly smaller than the diameter of the cutting edge. Therefore, the front part of the bumper can also take over the function, during the return stroke material that has been displaced during the cutting process radially outward and then pushed back into the bore to push back to the outside and thereby solidify and smooth. This applies not only to tools whose thrusting dies are tapered only behind a front region of a certain length, but also to those in which the taper already begins immediately behind the cutting edge but is still very weak there.

A special feature applies to tools for relatively long, narrow holes. Here it has been found to be advantageous to reduce the outer peripheral surface of the Stoßstempels on some relatively narrow, axial webs, over whose length in the region of the bore no or only a very small radial taper is made, so that all or a large part of Length a support and leadership of the Stoßstempels can be done on the bore wall. In the peripheral regions between the webs are preferably sinkers with a depth of a few hundredths to some tenths of mm work, z. B. grind. In a preferred embodiment of the invention, coolant lubricant channels open in the front regions of the depressions, in another embodiment alternatively or additionally also in the front end surface of the impact plunger. In order to promote the lubrication of the valve stems in the bore, a further improvement of the tool according to the invention may be that in the front region of the Stoßstempels, behind the front end formed cutting edge, distributed over the circumference, a plurality of radial projections are mounted, the z. B. 1 to 3 hundredths of mm protrude radially beyond the cutting edge and cut or push corresponding trains in the cylindrical bore wall, which can hold a small amount of oil. The projections may be formed on the impactor, mounted or machined by laser from radially outside the cutting edge existing material.

A similar result can be obtained if the cutting edge formed at the front end of the bumper is a polygonal approximated to a circular shape, the radius in the corner regions of the polygon z. B. about 2 to 3 hundredths of a mm greater than in the central peripheral regions between the corner regions.

In a preferred embodiment, the last mentioned radial projections or the corner regions of a substantially total circular, polygonal cutting edge helical axial extensions on the peripheral surface of the Stoßstempels and this is not only axially in the production of the bore, but also at the same time according to the pitch of the screw flights driven in the direction of rotation. In this way, twisted trains are created in the bore wall which can cause a valve to be slightly rotated at each stroke and thereby more evenly loaded over the circumference.

In order to avoid or reduce static friction, that is to say essentially to achieve sliding friction, it is provided that a rotational movement is added to the impact movement which is generated by the stroke of the impact punch. The rotational movement can be synchronous or asynchronous with the thrust movement. Synchronous means that the impact movement is superimposed by the rotational movement, whereby the ratio of stroke and rotational speed is constant. In the case of an asynchronous progression, there is no reference between the impact speed and the rotational speed, ie a constant ratio not before. The speed may correspond to a common engine speed between 1 and 22,000 rpm. Turning speeds of 30,000 rpm or more may also be suitable. The stroke amounts in particular to 5 m / min to 60 m / min or more.

A further preferred embodiment of the invention provides that the front end of the Stoßstempels with the cutting edge and possibly also the front region with the same or only slightly smaller diameter without or with radial projections of carbide, polycrystalline diamond (PCD), cubic boron nitride ( CBN), or a CVD (Chemical Vapor Deposition) produced diamond layer. The diamond layer is available as a solid material and is either soldered to a subcarrier or directly on the impactor, in particular in a vacuum. The thickness of the layer produced by the CVD method may be 0.5 mm.

The cutting material provides adequate service life of the proposed tool for high volume production.

In particular, it is provided that the impact stamp is made entirely of hard metal or has a front side forming a cutting edge cylindrical disc made of hard metal or a cylindrical disc of cutting material, such as PCD or CBN or a diamond layer produced by CVD method. At least the cutting material PKD and CBN is applied to a support made of hard metal as soldered, which in turn with the impact stamp z. B. is connected cohesively by soldering. In this case, the connection and soldering zone should extend at least at a distance of at least 3 mm, in particular at a distance of between 3 mm and 8 mm to the end face, which consists of the cutting material. At least in the connection and soldering zone, the impact punch has a smaller diameter compared to the support, so that the connection and soldering zone is located outside the conforming zone, ie the region in which the material in which the bore is to be made, to the Clinging tool could. If a diamond layer produced in the CVD-V is used as the cutting material, it is either connected to a carrier made of hard metal and then soldered onto the bump or directly on the bump, in particular in a vacuum. The connection as well as the soldering zone should also be outside the conforming zone.

Furthermore, it is provided in an embodiment of the invention that the thickness of the cutting material, ie the hard metal as the cutting material or the layer thickness of the PCD, CBN or the diamond layer produced by the CVD method is between 0.1 mm to 3 mm or more, where the thickness should be determined as a function of the elastic fitting of the workpiece through which the bore is to be pushed. This is to ensure that the pusher can be easily withdrawn regardless of the nestling of the material to the ram in the range of the cutting material.

If the cutting edge is the peripheral region of a planar surface consisting of the cutting material, which is the end face of the impact stamp, then a ring made of the cutting material can also be used, which extends on the front side of the tool.

All of the aforementioned embodiments allow influencing the cutting conditions and chip formation by properly designing the front end face of the impact punch to selectively form a positive or negative rake angle at the cutting edge. Also independent of the particular embodiment, the tool can be integrally, z. B. carbide or tempered tool steel, or two parts, z. Example, consist of a rear clamping shaft made of steel and a front impact die made of hard metal, soldered into a matching hole in the clamping shaft and possibly at the front end by soldering with an insert from z. B. PCD is connected to a support layer of hard metal.

Further details, advantages and features of the invention will become apparent not only from the claims, the features to be taken from them - for themselves and / or in Combination - but also from the following description of the drawing to be taken preferred embodiments.

Show it:

Fig. 1A is a central longitudinal section through a cutting tool for

Finishing of guide bores for motor vehicle valves, FIG. 1B a section of FIG. 1A in the region of the cutting edge of the

Tooling on a larger scale,

FIG. 1C is a perspective view of the tool of FIG. 1A; FIG.

Fig. 1D shows a detail of Fig. IC in the region of the front end of

Tool on a larger scale;

Fig. 2A is a central longitudinal section through a compared to FIG. 1 modified to the effect tool that his push punches axial webs and between these depressions, in which

Coolant lubricant channels open,

Fig. 2B shows a cross section through the impact die of the tool according to

Section line C-C in Fig. 2C,

2C is a side view of the tool of FIG. 2A,

FIG. 2D is a perspective view of the tool of FIGS. 2A-C; FIG.

3A shows a central longitudinal section through a comparison with FIG. 2A to the effect modified embodiment that the front end of

Bumper made of PCD,

3B shows a cross section through the impact stamp according to section line C-C in FIG.

3C,

3C is a side view of the tool of FIG. 3A,

FIG. 3D is a perspective view of the tool of FIGS. 3A-C; FIG.

4A is a central longitudinal section through a modified compared to FIG 3A, the tool that behind the cutting edge radial projections are present, which generate in the bore wall trains,

4B is a side view of the tool of FIG. 4A, 00803

9 shows a cross section through the impact stamp according to section line C - C in FIG. 4B, FIG.

an enlarged section of a cross section of the Stoßstempels after

Section line E-E in Fig. 4B,

a detail from FIG. 4B on a larger scale,

a section of an end view of the Stoßstempels in larger

Scale,

a perspective view of the tool of Figure 4A - F, the front end of the Stoßstempels of Figure 4G on a larger scale. 1 shows a longitudinal section through a tool modified relative to FIG. 1A in that the impact stamp has a polygonal cutting edge which approximates a circular shape and in the front region of the impact stamp coolant coolant channels open in the peripheral surface, a side view of the tool according to FIG. 5A, FIG.

a partial cross section through the front, polygonal region of the Stoßstempels according to section line C - C in Figure 5B on a larger scale, a perspective view of the tool of Figure 5A - C, the front end of the Stoßstempels of Figure 5D on a larger scale. a middle longitudinal section through a modified compared to FIG 1A to the tool that axially before the formed at the front end of the Stoßstempels cutting edge a milling head with Ideinerem diameter for face milling of the bottom of a machined with the impact punch blind bore attached or is formed,

an end view of the milling head of the tool of FIG. 6 A,

Side view and end view of a drill head used instead of the milling head of FIG. 6 A, B,

Side view and front view of a mounted directly in front of the bump or trained milling head for face milling of the bottom of a blind hole and

Side view and front view of a drill head used instead of the milling head of Fig. 6 E, F. The tool shown in Fig. 1A consists of a circular cross-section impact die 10 made of hard metal, which is soldered with its rear end in a matching hole in a clamping shank 12. The clamping shaft 12 is z. B. from a tempered tool steel. The tool is a pre-drilled hole in a workpiece z. B. brass or steel bronze by machining ablation of a Reibzugabe of z. B. 0.1 to 0.5 mm thickness to the nominal diameter of the finished bore and thereby the surface quality can be achieved as in a processing with a reamer. Such quality requirements are z. B. provided to holes for valve guide in internal combustion engines.

The impact stamp according to Fig. 1A is formed at its front end with a substantially circular cutting edge 14 whose diameter corresponds to the nominal diameter of the bore to be produced. As shown in Figure 1B, the cutting edge 14 is followed by a forwardmost portion 16 having an axial length of e.g. 0.1-0.2 mm, in which the plunger 10 is formed cylindrically with the same diameter as the cutting edge 14. Behind the cylindrical portion 16 then the further circular cross-section impact stamp 10 tapers conically, wherein the inclination angle a between a straight line in the circumferential surface lying in the straight line and a parallel to the central longitudinal axis in the example is 0.5 °. The conical taper extends over a greater length than the length of the bore to be made, e.g. over 40.5 mm with a bore length of 38 mm. By the taper is achieved that the ram does not rub with its rear portion on the bore wall.

Other than described above, the taper of the impact punch may also begin immediately at the cutting edge 14. The conicity of the taper will then be much smaller, for. B. only one to two μ on lengths of 20 mm. In this case, the taper immediately after the cutting edge only minimally affects, so that it can be assumed that the foremost portion 16 of FIG. 1B pralctisch still the same diameter as the circular cutting edge 14. Therefore, also retains in this version of the front portion 16 of the Stoßstempels 10 its leading and smoothing function. In contrast to FIG. 1A, in the embodiment of FIG. 2A the impactor 10 is not circular in cross-section but has an outer peripheral surface which is reduced to a plurality of axially extending webs 18 (see FIGS. 2B-D). Between these webs are depressions 20 with a depth of z. B. 0.05 to 0.5 mm, which may possibly also be shallower or deeper, preferably in each of whose front areas a coolant lubricant channel 22 opens. The cooling lubricant channels 22 are connected to a central supply channel 24 extending centrally through the impact punch. The same applies to the radially outer surface of the webs 18 as for the peripheral surface of the impact stamp 10 according to FIG. 1A. Also starting along the webs 18, in particular on the cutting edge 14, takes place from the front to the rear, a radial taper, but this is preferably made only small, eg only one to two μ to 20 mm in length. With this embodiment, it is endeavored to drive the punches on a large part of its length at the bore wall, especially for long holes with a relatively small diameter. The friction occurring is reduced by the supplied with coolant depressions 20 between the webs 18.

The circumferential surface of the Stoßstempels 10 should be according to the illustration of FIG. 1 A - D cutting edge free outside the frontal cutting edge.

The embodiment of Fig. 3A is similar to that of Fig. 2A, but has the advantage that the front end of the impact punch 10, where the cutting edge 14 is located, from a layer or plate 15 of polycrystalline diamond (PCD) or a other extremely hard cutting material such as cubic boron nitride (CBN) or a CVD diamond layer. Also, the PCD or the CBN is mounted on a support, which consists in particular of hard metal and has the geometry of a cylindrical disc. Such is indicated in Fig. 3 A with 15 '.

The thickness of the layer of PCD or CBN or a diamond layer produced in the CVD method should be between 0.1 to 3 mm, without thereby affecting the invention is restricted. The thickness of the layer depends on the material in which the bore is to be introduced, that is of its elasticity, so that when retracting the impact punch 10, the elastic nestling of the material essentially acts on the cutting material. Furthermore, the distance between the connection such as soldering zone 15 "and the hard metal carrier 15 ', which is materially connected to the plunger 10, at a distance between 3 and 8 mm from the end face of the hard metal layer 15 extend to unwanted forces during retraction by In particular, the distance should be at least 3.2 mm or more The connection and soldering zone 15 "extends in the region of the shaft of the impact punch 10, in which this in the Compared to the cutting edge has a smaller diameter.

If, on a case-by-case basis, it also turns out that even the foremost portion of the impact punch wears in the area where the diameter is still substantially the same size as the diameter of the cutting edge 14, because the taper only becomes noticeable behind it, then it is desirable to make the whole thing strong claimed front section of the Stoßstempels made of extremely hard cutting material.

The tool shown in Fig. 4A-F, which largely coincides with that of FIG. 3A-D, is obtained by the fact that the bumper at its front end behind the soldered there plate 15 made of PCD on hard metal pad on a portion 17 of z. B. 4 mm in length initially has a slightly larger diameter (eg 6.05 mm) than the cutting edge (eg 6.0 mm) made of PCD. Then, evenly distributed over the circumference, on the said peripheral portion 17, lying adjacent to each other on the circumference, for example, 20 axially extending recesses 26 are incorporated with laser, each lying in its central region below the diameter of the cutting edge 14, while between the recesses 26th remain radial protrusions 27, for example, 0.01 to 0.5 mm radially projecting beyond the diameter of the cutting edge 14 (see Fig. 4D, F, H). They therefore produce during the working stroke of the tool flat tractions in the bore wall, which is used for the lubrication of the valve stems are advantageous. The radial projections 27 between the lasered recesses 26 on the front portion 17 of the Stoßstempels 10 of FIG. 4D, F need not necessarily extend axially straight line, but may be helical as shown in FIG. 4H. If the tool is rotated during the forward and return strokes, twisted lines will be generated in the bore wall, which may have a positive effect on the movement of the valves in the bores produced.

Instead of the recesses 26 incorporated by means of laser, as shown in FIGS. 4D, F, by machining the circumference of the impact punch 10 in the said region 17 a similar formation of protrusions protruding radially beyond the diameter of the cutting edge could be obtained.

In the embodiment according to Fig. 5A-E, the cutting edge 14 is already ground so that it has a circular diameter larger than the nominal diameter Dn (for example, 6 mm) approximating a circular shape with larger diameter (z B. 10 mm) and corners 27 'composite, polygonal shape receives. This is achieved by the tool 10, 12 when grinding the cutting edge 14 sequentially z. B. can rotate about 12 eccentric axes of rotation, the z. B. on a circle with 2 mm diameter about the central longitudinal axis of the tool 10, 12, so that during a revolution in each case the distance between the center of the grinding wheel and the central longitudinal axis of the Stoßstempels 10 changes and through the 12 grinding operations a total of polygon 12 convex side edges 26 'and a little outside the nominal diameter Dn lying corners 27' is formed.

The polygonal shape of the cutting edge is best seen in Fig. 5C and is also clearly expressed in Fig. 5E. This shape of the tool also lends itself to creating non-tangle or twisted features in the bore wall to be made by forming the corners 27 'with either an axially rectilinear or a helical extension. The only example called number of 12 convex side edges of the polygon can also be chosen smaller or larger.

Has been explained above that for the production of a precisely fitting bore of the cutting edge 14 having impact stamp 10 substantially exclusively ausfuhrt an axial stroke, which if necessary. Superimposed by a swirl in the inner wall of the bore forming rotational movement is such that in the inner wall of the Hole spiraling grooves or trains result, the pitch angle should be between 1 ° and 75 °, preferably between 10 ° and 15 °.

In addition to the lifting movement and a rotational movement in particular should be carried out at high speed. The rotational movement can be synchronous or asynchronous with the thrust movement. Synchronous means that the impact movement is superimposed by the rotational movement in such a way that the ratio of lifting speed and rotational speed is constant. In an asynchronous process, the ratio of impact speed and speed varies. As a result, feed and retraction can be facilitated. It is a stiction avoided or reduced to an extent that basically only a sliding friction occurs. Thus, it is possible, the impact stamp 10 during the impact with a speed of z. B. 2,000 rev / min or more or less, in particular rotations of 30 000 rev / min or more to rotate. The stroke should be in the range of 5 m / min or more, in particular up to 150 m / min. Due to the numerical values, however, the teaching according to the invention is not restricted.

It may be appropriate or necessary in a particular case to form a finished with a push stamp bore to be machined as a blind hole. For such applications, a tool according to Fig. 6A-H is proposed. It has an impactor 10 of Figures 1A-D, 2A-D or 3A-D having the above-described characteristics, variations and functions. The ram 10 is only combined with a milling head 30 for face milling of the bottom of the blind bore or with a drill head 32, the cutting edges of a vertex angle of eg 90 ° or 120 ° or any other suitable acute or obtuse angle. You could also be ground rounded so that the bottom of the blind bore thus obtained is not the shape of a hollow cone but a dome.

The milling or drilling knob 30 and 32 may be formed integrally with the push-10 or made individually and fixedly attached to the front end of the push-10, z. B. soldered. It should not be larger in diameter, preferably slightly smaller than the cutting edge 14. In the exemplary embodiments according to FIGS. 6A-D, an annular recessed transition region 33 is provided between the cutting edge 14 and the milling or boring head 30, 32; in the embodiments according to FIGS. 6E, F and 6 G, H, the milling head 30 is located It is understood that the blind bore is finished as far as but butt and accurate fit, as the ram 10 axially advances. A certain section of the bore wall will remain up to its bottom without this finishing. Experiments have shown that the ram 10 with milling or drilling head 30 and 32 can also be driven in rotation during the shock stroke, preferably at low speed.

Since the surface of the bottom of the blind hole is machined by rotary drive with axial feed of the tool, the mentioned in connection with Fig. 4A-H and Fig. 5 AE trains in the bore wall to influence the lubrication and possibly to achieve a twist only on the length portion of the bore can be realized, which pass over the nominal diameter protruding projections 27 and polygonal corner regions 27 'radially during the shock stroke of the Stoßstempels 10.

Claims

claims

A method of machining an accurate, high surface quality, cylindrical bore having a length that can be many times the diameter from an existing bore with a finishing allowance, characterized in that the finishing allowance is circular during an axial working stroke of a ram (10) or substantially circular cutting edge (14) is peeled off at its front end to the nominal diameter of the finished bore.

A method of machining an accurate, high surface quality, cylindrical bore having a length that can be many times the diameter from an existing bore with a finishing allowance, characterized in that the finishing allowance is circular during an axial working stroke of a ram (10) or substantially circular cutting edge (14) is peeled at its front end to the nominal diameter of the finished bore, wherein the axial stroke is superimposed by a rotational movement, wherein either the ratio of stroke and speed is constant or varied.

A method according to claim 1 or 2, characterized in that the cutting speed during the working stroke 5 m / min to 150 m / min, in particular 30 to 90 m / min, with bore diameters up to 20 mm, preferably 50 to 80 m / min.

Method according to at least one of claims 1 to 3, characterized in that the front end (16) of the impact punch (10) is guided behind the cutting edge (14) on the bore wall during the working stroke.

5. The method according to at least one of claims 1 to 4, characterized in that during the following on a working stroke return stroke of the Stoßstempels (10) the surface of the bore wall by the axially adjacent to the cutting edge (14), in diameter as large as the nominal diameter the bore or only slightly smaller than this sized portion (16) of the impact punch is compressed and / or smoothed.

6. The method according to at least one of claims 1 to 5, characterized in that during the working and return stroke, the friction between the bore wall and the ram (10) is limited by its taper on its front end (16).

7. The method according to at least one of the preceding claims, characterized in that distributed over the circumference, on the bumper (10) behind the cutting edge (14) arranged only a few hundredths of a mm radially beyond these protruding projections (27) the lubricant film in the finished Hole affecting trains are generated in the bore wall.

8. The method according to at least one of claims 1 to 7, characterized in that distributed over the circumference, on the cutting edge (14) formed only a few hundredths mm radially beyond the nominal diameter outstanding projections (27 ') the lubricant film in the finished bore affecting trains are generated.

9. The method according to at least one of claims 1 to 8, characterized in that during the working and return stroke by rotation of the push ram (10) trains are generated with a twist in the bore wall, in particular a train with a slope of z. B. 1 ° to 75 °, in particular 10 ° to 15 ° is generated.

10. The method according to at least one of the preceding claims, characterized in that the chip formation during the working stroke of the Stoßstempels (10) is influenced by the design of the front end face in the outer peripheral region as a cone or Hohlkonunsfläche.

11. The method according to at least one of the preceding claims, characterized in that for producing a blind bore an optionally rotationally driven impact stamp (10) with an axially in front of the cutting edge (14) mounted milling or drilling head (30, 32) is used by the the bottom of the blind hole is machined.

12. The method according to at least one of the preceding claims, characterized in that the axial working stroke is superimposed with a rotational movement between 1 U / min and 10,000 U / min or more.

13. The method according to at least one of the preceding claims, characterized in that the impact punch (10) is rotated during the power stroke, wherein the rotation is preferably at least 2,000 U / min, preferably at least 30,000 U / min.

14. Chip removing tool, in particular for carrying out the method according to at least one of claims 1 to 13 for producing a precisely fitting, cylindrical bore with high surface quality and a length which may be a multiple of the diameter, from an existing bore with a finishing allowance, characterized in that the tool is in the form of a bumper (10) formed at the front end with a circular or substantially circular cutting edge (14) whose diameter corresponds to the nominal diameter of the bore to be produced and which begins immediately behind the cutting edge (14). 14) or behind a front portion (16) of a certain length, tapered.

15. A tool according to at least claim 14, characterized in that the taper of the Stoßstempels (10) behind a front portion (16) starts with an axial length of 0.1 mm to 0.4 mm. 19

16. A tool according to at least claim 14, characterized in that the taper is conical and, measured in the central longitudinal section through the push ram (10) as an angle between the peripheral surface performing line and the central longitudinal axis, 0.3 ° to 0.7 ° ,

17. A tool according to at least one of claims 14 to 16, characterized in that the taper of the Stoßstempels (10) immediately behind the cutting edge (14) begins, has a conical shape and, measured at the radius, preferably 1 μ to 10 μ on 20th mm length is.

18. Tool according to at least one of claims 14 to 17, characterized in that the peripheral surface of the Stoßstempels (10) distributed over a plurality of circumferentially, axially extending webs (18) is reduced, the height corresponding to the taper from front to back and between which are depressions (20) having a depth of preferably 0.05 mm to 0.5 mm below the nominal diameter of the bore to be produced.

19. Tool according to at least claim 18, characterized in that in the front region of the depressions (20) supply channels (22) open for a cooling lubricant.

20. Tool according to at least one of claims 14 to 20, characterized in that axially behind the at the front edge of the Stoßstempels (10) formed cutting edge (14), distributed over the circumference, a plurality of radial projections (27) are present, the 0, 01 mm to 0.5 mm beyond the radius of the cutting edge and produce correspondingly flat traction in the cylindrical bore wall.

21. Tool according to at least one of claims 14 to 20, characterized in that at the front end of the Stoßstempels (10) formed cutting edge (14) is a circular shape approximate polygon (26 ^' , 27 ^' ), wherein on the central longitudinal axis of Pushstamp (10) related radius in the Corner regions (27 ') of the polygon is 0.01 mm to 0.5 mm larger than in the central peripheral regions (26') between the corner regions (27 ').

22. Tool according to at least claim 20 or 21, characterized in that the projections (27) or polygonal ^' corner regions (27') are formed with a helical, axial extension for generating trains with swirl in the bore wall.

23. Tool according to at least one of claims 14 to 22, characterized in that the cutting edge (14) at the front end of the Stoßstempels (10) and preferably also its front portion (16) made of hard metal, hard cutting material such as PCD, CBN or in the CVD method produced diamond layer consists.

24. A tool according to at least one of claims 13 to 23, characterized in that the hard cutting material is mounted on a preferably in the form of a cylindrical disc having carrier (15) which is in particular connected by soldering to the shaft of the Stoßstempels (10), wherein Distance between connection as soldering zone (15 ") and cutting edge (14) in particular at least 3 mm, preferably between 3 mm and 8 mm.

25. The method according to at least claim 24, characterized in that the diameter of the connection as soldering zone (15 ') is smaller than the diameter of the circular or substantially circular cutting edge (14).

26. Tool according to at least one of claims 14 to 25, characterized in that the front end face of the Stoßstempels (10) by hollow grinding on the cutting edge (14) forms a positive rake angle.

27. Tool according to at least one of claims 14 to 26, characterized in that the front end face of the Stoßstempels (10) at the cutting edge (14) forms a negative rake angle. Tool according to at least one of claims 14 to 27, characterized in that for machining the bottom of a blind bore in front of the cutting edge (14) of the bumper (10) a milling or drilling knob (30; 32) is formed or mounted, the diameter of which at most large as the diameter of the cutting edge (14).