DE202021101050U1 - Combination tool for fine machining of bores - Google Patents

Abstract

Tool (10) for fine machining of an inner wall (6) of a cylindrical workpiece (2), in particular a bore (4) in a tubular workpiece, with a tool body (12) which comprises a honing section (20) with honing stones (23), thereby characterized in that the tool body (12) additionally comprises a roller burnishing section (30).

Description

The invention relates to a tool for the fine machining of inner walls of cylindrical workpieces, in particular pipes.

Tubular precision components such as hydraulic cylinders and cylinder tubes are often subject to high loads during operation. This is why high demands are placed on the functional surfaces of such components in terms of dimensional accuracy and surface quality. Precision steel tubes are used as the starting material for the production of such components, the cylindrical inner walls of which typically have a machining allowance of about 0.5 to 1 mm in diameter and are finely machined using a combined peeling and roller burnishing tool. A combination tool for fine machining such components is, for example, from EP 1 512 492 B2 known. The combination tool comprises a peeling head with usually two peeling knives and a roller burnishing head arranged axially behind the peeling head. The combination tool is inserted into a chuck of a machine tool and processes the inner surface of the component in a combined rotary and feed movement.

In this machining process with the aid of a peeling head and cutting inserts, the pipe to be machined must typically have an allowance of 0.5 to 1 mm in the inside diameter in order to ensure reproducible chip formation; With a lower machining allowance, the formation of short flow chips could not be reliably ensured when machining with a geometrically determined cutting edge, so that problems arise in terms of machining accuracy, process reliability and chip evacuation.

Thanks to advanced manufacturing processes, output tubes with fitting dimensions of H9 / H8 and roundness deviations of <0.03 mm are now available, with which significantly less material has to be removed in the fine machining. This holds the possibility of considerable time and cost savings in fine machining. However, the processing of such starting tubes with a significantly lower machining allowance (<< 1/10 mm) is technologically not possible with the known peeling / roller burnishing tool for the reasons mentioned above.

The invention is therefore based on the object of proposing a tool for the fine machining of cylindrical cavities with which workpieces with a small machining allowance (<< 1/10 mm) can be machined reliably.

This object is achieved by a tool with the features of independent claim 1. The subclaims relate to advantageous developments and variants of the invention.

A tool according to the invention for fine machining an inner wall of a cylindrical workpiece, in particular for fine machining a bore in a tubular workpiece, comprises a tool body which comprises a honing section and a burnishing section, the burnishing section being arranged axially behind the honing section. To designate the interior of the workpiece to be machined, the term “hole” is also used in the following, although this interior was not usually produced by drilling.

The honing section is used for machining the cylindrical interior. For this purpose, honing stones are provided in the honing section, with the aid of which the diameter of the cylindrical interior is enlarged to the desired dimension. The roller burnishing section serves to strengthen the inner surface of the bore, which has been pre-machined by honing, and to produce a final surface roughness. In this way, a surface with high dimensional accuracy and a high percentage of contact can be produced.

While in the prior art the machining of the workpiece is carried out by peeling, that is, with a geometrically defined cutting edge, when using the tool according to the invention, the fine machining of the bore is carried out by honing, that is, with a geometrically indefinite cutting edge. In contrast to peeling machining, a minimum material removal can be achieved with honing with high accuracy and process reliability. By means of the tool according to the invention, workpieces with a low machining allowance can thus be machined reliably and in high quality. The tool is therefore particularly suitable for the fine machining of the inner surfaces of precision steel tubes, whose fitting dimensions and roundness deviations in the initial state come very close to the desired final dimensions, and which therefore only require very little material removal during machining. The use of honing for machining such components with a greatly reduced machining allowance enables - compared to conventional peeling of tubes with a significantly larger machining allowance - a significant increase in the work feed rate (by approx. 100%), which leads to a considerable increase in productivity.

The roller burnishing section is used for surface hardening and comprises a plurality of roller elements which are rotatably held in a cage. In order to be able to adjust these rolling elements to the diameter variations of the workpiece to be machined, is in the roller burnishing section preferably a mechanical expansion system is provided. This expansion is preferably controlled with the aid of a push rod guided in the interior of the tool body. In the simplest case, the push rod is only used to bring the rolling elements into their working position and to pull them in or out of the bore.

During the honing of a bore, the honing stones wear continuously, with the result that the honing stone coating (and thus also the outer diameter of the honing section) is progressively reduced as the machining progresses. When machining a long tubular workpiece, this means that the inside diameter of the bore produced by the honing process continuously decreases as the penetration depth of the tool increases due to the wear of the honing stones, until it finally lies outside the required tolerance range. If you want to achieve a bore diameter with the desired dimensional accuracy over long machining distances, it is therefore necessary to compensate for the wear of the honing stone lining, which can be achieved in particular by moving the honing stones radially. For this purpose, the tool is expediently provided with a mechanical expansion system by means of which such radial displacements of the honing stones can be realized.

In a particularly advantageous embodiment, the expansion system comprises a servomotor integrated in the tool body, with which the honing stones can be moved radially. An expansion cone, which is guided displaceably in the interior of the tool body and can be moved in the axial direction with the aid of the servomotor, is preferably used. The honing stones are attached to trapezoidal base elements, which are shifted in the radial direction when the expansion cone is axially displaced, so that activation of the servomotor causes radial displacements of the honing stones. This makes it possible to compensate for honing stone wear without having to interrupt the machining process. The complete integration of the adjustment mechanism of the expansion system into the tool has the advantage that the axial displacement of the honing stones takes place independently of the machine tool used and the tool can therefore be used on different machine tools.

It is particularly advantageous if the honing stone wear is compensated for in a control loop during the process. To achieve this, a measuring system is provided on the tool body with which the inside diameter of the bore is determined. A tactile measuring system is expediently used for this. Alternatively, it is possible to use a pneumatic measuring mandrel, in this case, however, an air pressure supply must be provided for the tool, which means additional expenditure on equipment. Furthermore, a pneumatic measurement only delivers _{reliable measured values up to a surface roughness of R z} <4 µm. In addition, for example, flooding the pipe to be processed with cooling lubricant can lead to incorrect measurements in pneumatic measuring systems.

The measuring system is advantageously arranged between the honing section and the roller burnishing section, so that the bore diameter is measured immediately after the honing operation. In contrast to a (alternatively also possible) measurement of the bore diameter after rolling, i.e. a positioning of the measuring system on the side of the roller burnishing section facing away from the honing section, a higher surface roughness is accepted in the measurement here. However, the measurement between honing and rolling has the advantage that the measured values are recorded closer to the actuator of the control loop (i.e. the expansion system of the honing section) and without being influenced by the rolling elements. Furthermore, when using a tactile measuring system, measuring errors due to traces of the probe on the rolled-smooth surface are excluded.

In order to ensure a tool-internal regulation of the radial displacement of the honing stones, the tool can additionally comprise a storage and control unit. In the control unit, the expansion system is controlled during the process, depending on the diameter values supplied by the measuring system. Process data (measured values from the tactile measuring system, delivery parameters, etc.) can be stored in the memory unit. After finishing the machining of the existing pipe, this data can be transferred to an external computer and used, for example, for evaluations of the quality and the condition of the honing stone.

The actuators used in the control loop (servomotor for moving the expansion cone in the honing section) and sensors (tactile measuring device) and the associated process electronics are advantageously integrated into the fine machining tool according to the invention. This enables a regulated iterative radial adjustment of the honing stones depending on their wear and thus the achievement of the dimensional accuracy of the machined bore through an in-process control. This represents a significant advance compared to conventional tools, with which only machining with fixed tool diameters, i.e. without process-integrated wear compensation, is possible.

To supply energy to the storage and control unit, the sensors and the servomotor of the expansion system, the tool advantageously has an integrated energy store (battery). This is charged between successive machining processes.

A method for fine machining a cylindrical inner wall of a workpiece, in particular a bore in a tubular workpiece, uses a machining tool with a tool body on which a honing section with honing stones and a measuring system for recording measured values of the diameter of the machined cylindrical interior space are arranged. Based on the measured values supplied by the measuring system, radial displacements of the honing stones in the honing section are carried out with the aid of an expansion system integrated in the honing section. This shifting of the honing stones is preferably carried out in a control process with threshold value control.

In this way, a process-integrated, regulated compensation of tool wear on the honing stones can be ensured. Due to the in-process measurement, there is no subsequent measurement. Furthermore, through the continuous acquisition and evaluation of process data, an improved constant quality and process stability can be achieved, whereby an increase in the feed rates and thus a reduction in the processing times are possible. Compared to conventional honing tools, the tool life of the honing stones can be increased and a constant surface quality can be achieved through constantly conditioned honing stones. The improvement in the manufacturing process also goes hand in hand with an increase in component quality. Furthermore, the operating and tool data recorded in the course of processing can be integrated into a production management system.

In addition to improved process stability, the control process described also enables an increase in the degree of automation in the manufacture of precision steel tubes. In addition, it is independent of the machine control, which enables quick and uncomplicated adaptation to a large number of existing machine tools.

The tool according to the invention is particularly suitable for the fine machining of welded and drawn precision bores, which are subject to the highest requirements in terms of size and shape, roundness and roughness of the inner pipe surface and which are used, for example, as hydraulic cylinders for the automotive industry, mechanical engineering, etc.

• 1 eine perspektivische Ansicht eines erfindungsgemäßen Werkzeugs;
• 2 eine schematische Schnittansicht des Werkzeugs der 1 ;
• 3 eine schematische Schnittansicht durch ein mit Hilfe des erfindungsgemäßen Werkzeugs feinbearbeitetes Rohr.

Exemplary embodiments and variants of the invention are explained in more detail below with reference to the drawing. Show it

• 1 a perspective view of a tool according to the invention;
• 2 a schematic sectional view of the tool of FIG 1 ;
• 3 a schematic sectional view through a pipe finely machined with the aid of the tool according to the invention.

1 and 2 show a perspective view or a schematic sectional view of a tool according to the invention 10 for fine machining of a cylindrical inner wall 6th of a tubular workpiece 2 with an interior 4th , hereinafter also referred to as “Bohr 4th “Although it was not necessarily made by drilling. The tool 10 includes a tool body 12th , which has a honing section 20th and a roller burnishing section 30th for processing the inner wall 6th having. Beyond the roller burnishing section 30th there is a tool shank 14th , the end of which (not shown in the figures) is received during machining in a machine tool (not shown in the figures). On the tool body 12th are support strips 18th for guiding the tool 10 in the hole 4th provided during processing. The length of the tool shank 14th is the length of the hole to be machined 4th customized.

With the help of the honing section 20th becomes the hole 4th of the workpiece 2 that have an inside diameter at the start of machining D ₀ has, to an inner diameter D _F elevated; a layer of material with a thickness of 1/10 mm is typically removed. Furthermore, in the course of the honing process, the inner wall 6th the hole 4th provided with a surface structure suitable for roller burnishing. The honing section 20th comprises a plurality of honing stones 23 that with the help of an expansion system 25th can be adjusted radially. The expansion system 25th includes an expansion cone 28 with the help of an inside the tool body 12th recorded servomotor 26th via a worm gear 27 can be moved horizontally. The honing stones 23 are (for example via soldered connections) with trapezoidal base elements 24 connected to their honing stones 23 averted sides - as in 2 shown - one of the angle of the expansion cone 28 have a corresponding slope. By an axial shift 29 of the expansion cone 28 can thus cause a radial displacement of the honing stones 23 (and thus a change in an outside diameter 22nd of the honing section 20th ) can be achieved.

The roller burnishing section 30th serves to create an edge layer 8th of the machined hole 4th to solidify and produce a final surface roughness (Rz <1 µm). For this purpose, the roller burnishing section includes 30th a plurality of rolling elements 32 that rotates in a cage 33 being held. The rolling elements 32 have a cylindrical or conical shape and roll on a conical body 36 with opposite cone. The basic body 36 can with the help of an in the shaft 14th displaceably mounted push rod 37 be shifted in the axial direction (direction arrow 39 in 2 ) what with a radial displacement the rolling elements 32 goes hand in hand. Due to the axial displaceability of the base body 36 thus becomes an expansion system 35 created that an adjustment of the outer diameter 31 of the roller burnishing section 30th enables. In particular, the push rod 37 used to do this, the rolling elements 32 to move radially between a working position and a retracted or extended position.

The machining of the inner wall 6th the hole 4th through the honing section 20th of the tool 10 leads to wear of the honing stones 23 what with a reduction in the outer diameter 22nd of the honing section 20th goes hand in hand. The diameter created by the honing operation D. the hole 4th thus decreases continuously as the processing path progresses. In order to avoid (especially with long machining paths) that the diameter D. a minimum value specified by the tolerance requirements D _min the honing stones must 23 therefore be readjusted radially. This is done in the tool 10 with the help of a control loop in which the diameter D. is measured during the machining process and the honing stones 23 can be readjusted depending on the measured values.

To this end, the tool body has 12th a measuring section 40 on that between honing section 20th and roller burnishing section 30th is arranged and in which there is a tactile measuring system 42 for measuring the inside diameter D. is located. The measuring system 42 comprises a plurality of measuring cells 44 on the circumference of the tool body 12th are attached. The ones from these measuring cells 44 determined measured values of the inside diameter D. are about one in the tool body 12th integrated data line 46 to one (also in the tool body 12th integrated) storage and control unit 50 with arithmetic unit 56 , Data storage 54 and energy storage 52 forwarded. A target / actual comparison of the measurement data with threshold values takes place there D _min , D _max which are based on the required dimensions / tolerances of the finished workpiece 2 are matched.

Are the honing stones 23 worn so far by the progressive machining that the measuring system 42 Diameter determined during the process D. below a predetermined lower threshold value D _min is the mechanical expansion system 25th of the honing section 20th put into operation. The servomotor 26th of the expansion system 25th then moves the expansion cone 28 in the axial direction and thus presses the honing stones 23 in the radial direction outwards; this can accompany the process for honing / rolling the workpiece 2 so that the finishing process does not have to be interrupted. An increasing axial displacement of the expansion cone 28 and the associated radial displacement of the honing stones 23 leads to a progressive enlargement of the outer diameter 22nd of the honing section and thus also to an increase in the inner diameter D. of the machined hole 4th . This axial shift is continued until the measuring system 42 determined measured values for the diameter D. the honed inner wall 6th the hole 4th an upper threshold D _max achieved; then the servomotor 26th stopped so that the honing stones 23 are fixed in the reached radial position.

An example of a pipe machined in this way 2 ' with a hole machined in this way 4th is in 3 shown, with all variations of pipe diameter D. are shown here strongly exaggerated. The pipe 2 ' has a total length L. of 12 m and an inside diameter of 80 mm. The inner wall 6th of the pipe 2 ' was by means of the tool 10 in one by the arrow 60 marked machining direction honed and rolled smooth. At the beginning of processing (i.e. at the right end 2a of the pipe 2 ' ) were the honing stones 23 of the honing section 20th adjusted in such a way that the bore 4th honed to an inside diameter D = D _{max by the fine machining.} When further processing the pipe 2 in the feed direction 60 there was continuous wear of the honing stones 23 , which is an increasing reduction in the inner diameter D. resulted in. The honing stones were at a penetration depth L ₁ 23 rubbed off so much that the inside diameter D. of the pipe 2 the lower threshold D _min had achieved. Hence the mechanical expansion system 25th turned on that the honing stones 23 Shifted radially outwards until the desired upper threshold value again at a penetration depth L ₂ D _max reached and the expansion system 25th has been switched off. This brief actuation of the expansion system 25th repeated at the penetration depths L ₃ and L ₄ , so that the inner wall 6th of the pipe 2 this in 3 has stepped profile shown. During the fine machining, in the present example, the 12 m long pipe 2 ' a feed rate of 3 m / min was achieved, resulting in a total machining time of about 4 minutes. As in 3 The honing stones were shown 23 Delivered a total of three times in order to maintain a tolerance range ΔD = D _max - Dmin of 25 µm; In this example, the dimensional tolerance became complete using a threshold control exploited. To achieve closer tolerances and to increase process reliability, the infeed of the honing stones should 23 however, are repeated at shorter time intervals.

List of reference symbols

2

(tubular) workpiece

2a

Pipe end

2 '

finished tube

4th

Interior ("hole")

6th

Inner wall

8th

Edge layer of the hole

10

Tool

12th

Tool body

14th

shaft

18th

Support strips

20th

Honing section

22nd

Outside diameter honing section

23

Honest tea

24

trapezoidal base element

25th

Expansion system

26th

Servomotor

27

Worm gear

28

Expansion cone

29

Axial displacement of the expansion cone

30th

Roller burnishing section

31

Outside diameter roller burnishing section

32

Rolling element

33

Cage

35

Expansion system

36

Conical body

37

Push rod

39

Axial displacement of the expansion cone

40

Measuring section

42

Tactile measuring system

44

Measuring cells

46

Data line

50

Storage and control unit

52

Energy storage

54

Data storage

56

Arithmetic unit

60

Directional arrow feed

D.

Inside diameter of the hole

D0

Inside diameter before machining

DF

Inside diameter after machining

Dmin

lower threshold

Dmax

upper threshold

L.

Length of pipe

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 1512492 B2 [0002]

Claims (11)

Tool (10) for fine machining of an inner wall (6) of a cylindrical workpiece (2), in particular a bore (4) in a tubular workpiece, with a tool body (12) which comprises a honing section (20) with honing stones (23), thereby characterized in that the tool body (12) additionally comprises a roller burnishing section (30). Tool after Claim 1 , characterized in that the roller burnishing section (30) comprises a mechanical expansion system (35). Tool after Claim 2 , characterized in that the mechanical expansion system (35) of the roller burnishing section (30) can be activated using a push rod (37) guided in an interior (16) of the tool body (12). Tool after one of the Claims 1 to 3 , characterized in that the honing section (20) comprises a mechanical expansion system (25). Tool after Claim 4 , characterized in that the mechanical expansion system (25) of the honing section (20) comprises a servomotor (26) integrated in the tool body (12) for the radial displacement of the honing stones (23). Tool according to one of the preceding claims, characterized in that the tool body (12) comprises a measuring system (42) for measuring the inside diameter (8) of the bore (4). Tool after Claim 6 , characterized in that the measuring system (42) is a tactile measuring system. Tool after Claim 6 or 7th , characterized in that the measuring system (42) is arranged between the honing section (20) and the roller burnishing section (30). Tool after Claim 4 , characterized in that the tool body (12) comprises an integrated storage and control unit (50) for controlling the expansion system (25). Tool after one of the Claims 6 to 9 , characterized in that the tool body (12) comprises an integrated data memory (54), in particular for storing the measured values supplied by the measuring system (42). Tool according to one of the preceding claims, characterized in that the tool body (12) comprises an integrated energy store (52).

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