DE102006016099B4 - Method for producing a transmission hollow shaft - Google Patents

Abstract

Rest Eisen einschließlich erschmelzungsbedingter Verunreinigungen.A method for producing a gear hollow shaft, which is composed of axially successive shaft sections (1-5), wherein at least two shaft sections (1, 2, 4) with a toothing (6, 7, 8) are provided and wherein the toothing (6, 7, 8) is produced without cutting by means of toothed rollers, the shaft sections (1-5) being provided with toothing prior to assembly, completely finished and joined together by friction welding after production of the toothing (6, 7, 8), with adjacent shaft sections (1-5) are arranged with respect to their rotational angle positioning in a predetermined target angular position, wherein the deviation from the target angular position less than 30 arc seconds, wherein the shaft sections are made of air-hardening steels of different properties and at least one shaft portion (1-5) a yield strength of greater than 850 MPa and a strength greater than 1,000 MPa t, wherein at least one shaft portion (1-5) is made of a steel having the following alloy components in weight percent: C: 0.1% -0.3% Si: Max. 0.8% Mn: 1.3% -2.5% Cr: 0.8% -1.8% Not a word: Max. 0.3% Nb: Max. 0.06% Ti: Max. 0.06% B: Max. 0.004% Remaining iron, including impurities caused by melting.

Description

The invention relates to a method for producing a transmission hollow shaft:
In general, three shafts are needed in a vehicle transmission, the drive shaft, countershaft and output shaft. The unit weights of these shafts in car transmissions amount to about 2 to 5 kg in a massive version, which is still predominantly usual. The global demand for transmission shafts for vehicle transmissions was approximately 262 million units in 2000, of which about 50% are car transmissions (Pannasch, Lorenz; substitution trends and trends in die-forged parts and methods for their production on the basis of future motor vehicle production; Study, IWU Chemnitz, 1996, unpublished). The main requirements of a modern vehicle transmission include a small volume and a low intrinsic mass with a high reliability and low cost (Goll; Development tendencies in the transmission technology for cars and commercial vehicles, transmission in vehicles '98, VDI report 1393, p. 41-58) , In order to realize these lightweight construction requirements, there are in principle three ways, the use of new materials or composite materials that guarantee the same component properties for smaller masses (lightweight fabric construction), the use of stress-designed steel components (constructive lightweight construction) and the targeted utilization of process-related improved functional properties Components (technological lightweight construction).

By Use of hollow shafts in car transmissions can achieve considerable lightweight potential become. It is known that in a possible reduction of the resistance moments to 10% with a hollow shaft opposite a solid shaft can result in a material saving of around 30%, because the stress of these waves on the near-surface Focused area while that Nuclear material is negligible (Neugebauer, Glass, Hoffmann cleaning; Incremental Forming of Hollow Shapes, steel research international 76 (2005), no. 2/3). According to this fact, on the one hand to recognize the constructive potential in the application of Hollow shafts, on the other hand derive new requirements to the production of such waves.

These However, potentials are not yet fully exploited for cost reasons, because the theoretically optimal hollow shaft according to the load distribution at individual lengths of a Transmission shaft different requirements, eg. B. material properties, Heat treatments, residual stresses or cross-sections, presupposes that by single reshaping or also basic machining procedures economically can not be displayed. Aim of all research in the field Hollow shaft production is therefore among the most technologically-economical Restrictions meaningful approach to this theoretical optimal execution.

Forming Procedures allow this due to their process properties one over the component length uniform wall thickness course and, in the case of warm and cold forming, a load-conforming fiber formation in the material. The inner contour follows approximately the outer contour and is thus better adapted to the local load distribution than this can be achieved during machining. Notch effects are largely reduced.

Commercial vehicles (trucks) -Hohlwellen can through a combination of forming processes or process combinations be generated. The literature describes different process chains. The limits of the individual procedures lie in the realizable Wall thickness, the possible Material accumulations, in the sometimes necessary high number of stages, in necessary interim treatments and achievable accuracies (Neugebauer, Lorenz; Production of hollow gear shafts by forming technology manufacturing processes; FVA Research Report 2001; Neugebauer, Lorenz, Kolbe, Glaß; Hollow Drive Shafts - Innovation by Forming Technology; Society of Automotive Engineers, Inc., Detroit, 2002, 02M-54). Due to the dimensions of the waves dominate Method of hot massive forming. The process goal is so focused on the mass reduction and net-shape manufacture.

in the On the other hand, passenger car shafts are preferably cold and warm forging processes to apply that allow near-net-shape qualities. The usual to be considered wall thicknesses in the range of 5 mm limit the achievable shape changes, bound to the wall thickness-diameter ratio are a. Material accumulation, as for the gear main body the Festradwellen are required, can be applied with the Do not create process and from the semi-finished products to be used. The substitution of massive waves by hollow waves requires consideration These restrictions in the passenger car sector, the application of hybrid process chains on the production of integrated components.

By the EP 0 473 061 B1 counts a built camshaft for internal combustion engines to the prior art. The cam-carrying functional part is made of gray cast iron and has a ferritic-pearlitic or a purely pearlitic matrix. At this function part can z. Example, by means of friction welding a drive part made of steel to be welded. While the functional part with the cams may possibly have a hollow end, the drive part is designed as a hollow shaft with an inner form-locking element serving internal teeth, in which, for example, auxiliary units to the camshaft, preferably a cam adjustment can be used with counter-form-locking elements. The combination of gray cast iron and steel offers some advantages in the production of a camshaft, but it is not fully suitable for the production of hollow shafts, since the individual segments or sections of the hollow shaft transmission are subjected to very different load conditions.

A friction welded shaft is the subject of DE 696 30 979 T2 , This document discloses two different length shaft sections, which are each provided with an external toothing. In the production of the shaft, a first engagement means in the form of teeth is preferably case hardened in order to achieve the necessary surface hardness of the tooth flanks. The first shaft portion is then welded to the second shaft portion by friction welding, after which the teeth in a portion of the second shaft portion are machined. Subsequently, the second shaft portion is induction hardened in the area where the teeth have been formed. Since the first shaft portion has been case hardened prior to the welding operation, the entire shaft need not be subjected to the relatively expensive case hardening operation. Although savings are possible in the context of this invention, the manufacturing process as a whole is relatively expensive, in particular since cutting processes and hardening processes alternate several times.

From the DE 33 46 056 A1 For example, a method of manufacturing a composite camshaft is known. The processing of the individual elements of the camshaft is carried out essentially to final dimension. Only on the bearing surfaces and on the cam surfaces excess is provided to be brought to the final dimension after assembly of the camshaft. The connection of the individual elements takes place temporally successively in a predetermined sequence and predetermined angular position to each other in a common longitudinal axis by friction welding.

Subject of the DE 10 2005 036 681 A1 is a transmission in which shafts can be used, which are composed of several components and in particular are interconnected by laser welding or friction welding. Gears can be made by so-called axial forming.

In the EP 0 052 077 B1 a method for producing a rotationally symmetrical hollow shaft is described by means of the friction welding process. The individual shaft parts are produced by cold extrusion, wherein at least one shaft part is stepped in diameter.

From the DE 90 14 280 U1 a hollow shaft is known, which is composed of shaft sections of steels of different properties. The elements can be joined together by friction welding.

A method for braking friction welding machines in the friction welding of parts with exact angular position after welding is the subject of DE 32 26 362 C2 , This publication deals with the fact that known electronic position control systems do not achieve the positioning accuracies of <0.5 ° required in friction welding machines within the permissible positioning time of approximately 300 ms.

Also in the DE 195 23 240 C1 describes a method and a device for friction welding of materials, which is suitable for joining materials that have significant differences in the material properties, in particular the hardness and / or the melting temperature.

In the DE 2 122 483 A For example, there is proposed a method and a device for welding, wherein the burr formed at the welding sections of the workpieces during the friction welding process is already removed during the welding process.

Of these, The invention is based on the object, a method to show the production of a hollow shaft transmission, wherein the process steps are coordinated so that a nacharbeitsarme, hybrid Process chain is formed, which optimizes according to economic criteria is.

These Task is in a method according to the features of the claim 1 solved.

advantageous Further developments of the inventive concept are the subject of the dependent claims.

In the method according to the invention, a gear hollow shaft is composed of axially successive shaft sections, wherein at least two shaft sections are provided with a toothing, wherein the toothing is produced by means of toothed rollers without cutting, the shaft sections are provided completely finished before joining with a toothing and wherein the individual shaft sections after producing the teeth are joined together by friction welding. It is essential that adjacent shaft sections with respect to their rotational angle positioning in a previously predetermined target angular position are arranged, wherein the deviation from the target angular position is less than 30 arc seconds. Preferably, a deviation from the desired angular position of less than 5 seconds of arc is set, whereby the possibility is created by high-precision friction welding to connect locally optimized, ready-to-install shaft sections with no, but at least no significant rework is required. The shaft sections are made of air-hardening steels of different properties and at least one shaft section has a yield strength of greater than 850 MPa and a strength of greater than 1,000 MPa, at least one shaft section being made of a steel having the following alloy components in weight percent: C: 0.1% -0.3% Si: Max. 0.8% Mn: 1.3% -2.5% Cr: 0.8% -1.8% Not a word: Max. 0.3% Nb: Max. 0.06% Ti: Max. 0.06% B: Max. 0.004% Remaining iron, including impurities caused by melting.

Important is that a faithful positioning of the shaft sections in axial, radial and angular position is guaranteed, that is, that the axial offset and the radial offset as well as the angle error between the central longitudinal axes one another adjacent wave sections is minimized. The axial offset is preferably in a range less than 10 microns, in particular less than 5 microns. Also the radial offset is preferably in a range less than 5 microns.

By a servo-electric real-time control in precision friction welding is allows, also toothed and provided with any functional surfaces shaft sections in terms of their angular position with sufficient accuracy against each other align what it allows, individually configured and preconfigured to the particular function and loading condition To connect shaft sections with each other. In particular, the Shaft sections made of steels different properties, in particular different Strengths are produced.

One Shaft section in the sense of the invention may be both a longitudinal section or segment of the shaft shaft, for torque transmission or Storage serves. As a shaft section but also a functional section understood, for example, with an adjacent over the diameter shaft ends protruding high toothing is provided. It can thus at the shaft portion also to act a gear whose tooth width of the length of corresponding shaft section can correspond. Of course it is also possible, only a portion of a longer one Shaft section to be provided with a toothing, so this Shaft section as wave shaft and at the same time because of the gearing can function as a functional part. A toothing in the context of the invention is a radial inside or outside arranged engagement means for transmitting a torque.

Corresponding the different load conditions, the individual shaft sections therefore not only from steels be made of different properties, but also on based on different production methods. Come in accordance with the invention non-cutting machining chipless production process for use.

By Gear rolls is a highly accurate forming of spur gears with Straight and helical gearing in the entire application-typical dimension range without cutting pre-machining possible. The training nacharbeitsarmer and nacharbeitsfreier in subordinate applications Gears with highest gear quality and high tooth root strengths can be realized by toothed rollers become.

Gear teeth rolling is understood to be a process which is carried out as precision roughing of preformed toothings with edge-corrected rolling tools or as shaping rolling in pre-turned solid bodies. For the latter variant, it was possible for the first time to provide the basic proof of rolling gear-typical high-speed gears. The realization of gearing qualities 6 - 7 seems feasible. Thus, the very decisive advantage of rolled teeth, which consists in the contour-adapted fiber flow and the hardness increases in the flank and Tooth base area and leads to a higher dynamic load capacity and carrying capacity of gears produced, remain largely preserved.

Shaft sections designed as shaft shafts can also be realized by means of spinning rollers with high dimensional accuracy, low coaxiality and accurate mass distribution in the wall. The spin forming has the advantage of shortening the stage sequence for circular cross sections, as required in hollow gear shafts. By means of pressure rollers, it is possible, exclusively supported by the kinematics of the tools, to produce stepped wave-like contours on pipes. The thereby possible The omission of an application of shape memory tools leads to a considerable cost reduction and a very high flexibility of the method, in particular for applications to smaller or frequently changing production lots. The localization of the forming zone on the force application point of the forming tools and the resolution of the change in shape in incremental steps allows a lowering by an order of magnitude forming force and thus the use of relatively small forming machines with correspondingly low investment costs, which promotes the acceptance of the process significantly. Due to the associated improvement in the wall thickness distribution and the targeted formation of load-dependent adjustable different wall thicknesses in individual shaft sections, the method includes a clearly recognizable value-added potential for hot tubes.

swaging has for producing shank portions of the hollow shaft transmission the advantage that ready-to-use functional surfaces and of the circular shape deviating form elements the targeted local material accumulations be created.

through of hole pressing can ready-to-install interior profiles for high torque transmission be created. Minimizing the dimensions of the bearings By producing heavy duty inner profiles is another advantage of this Forming process. One for the production of molds new process is the bore pressing. This Method offers an alternative to the previously preferred deep hole drilling. The advantage is to be seen in the fact that for all applications for which no Semi-finished tubes available stand, hollow preforms with a homogeneous mass distribution in the Wall can be generated. Productivity surpasses while that of drilling by a whole order of magnitude. In addition, the Material input codes of the ablation methods far undercut become.

Furthermore could prove the principle for the manufacturability of internal profiles are provided on the basis of the associated surface hardening and the adapted fiber flow are highly resilient and thus considerable lightweight potentials for develop appropriately designed waves.

In Combination with the high precision friction welding, because of the high accuracy, it is almost unbalance-free Connecting individual shaft sections, it becomes possible, completely finished shaft sections, in particular with a toothing to add provided shaft sections as finished parts. This can be the benefits the demanding precision forming process for the Optimization of separately manufacturable shaft sections are exhausted. The mutual influence of the manufacturing processes is minimized and the transmission hollow shafts can sections technology and function optimized. For later applications is an optimal production structure with short lead times, high specialization and very high flexibility.

Although in the method according to the invention as far as possible Finished shaft sections by friction welding together In particular, it can be used to remove a in certain circumstances disturbing Bead, the friction welding incurred, it will be necessary to remove this subsequently machined.

When Materials for Gear hollow shafts produced by this method can basically the usual Materials in gearbox construction, z. 16 MnCr5 and 20 MnCr5 and 20 MoCr4 be used. However, these have the disadvantage that it is in the field the heat affected zone the weld to a hard waste comes, which generally requires a subsequent heat treatment.

at the method according to the solution are therefore called air-hardening steels used. They do not have this disadvantage, so that one following the friction welding Heat treatment not is required, with the result that the process chain continues shortened becomes.

Air hardening steels show even at slow cooling rates a structure with high levels of martensite or bainite. Usually, air-hardening steels are used Alloy made with the elements Mn, Cr, Mo, Ti, B.

New Developments have surprisingly revealed that a steel with Mo contents below 0.3 wt .-% by a suitable variation of Si, Cr and Mn high strengths above 1000 MPa, in particular above 1200 MPa in the air-hardened or friction welded State shows.

The Of course, shaft segments designed as gearwheels can be hollow for reasons of weight saving be designed. in principle but it is also conceivable to produce them from round blanks. Such Transmission hollow shaft is not hollow throughout, but at least in those shaft sections which are designed as shaft shafts, so that the advantage of weight savings over the much larger length ranges the transmission hollow shaft is maintained.

The invention is described below with reference to egg Nes in the drawings schematically illustrated embodiment explained in more detail. 1 shows semi-finished products in the form of pipes and steel bars of different strength and accuracy requirements, eg. As well as hot rolled steels, especially air-hardening steels. The individual semi-finished products are the basis for each wave section 1 - 5 , wherein each semi-finished product is subjected to an individual, transforming further processing.

2 shows that the shaft sections 1 . 3 and 5 undergo a height enhancement by reshaping further processing. Preferred forming methods are the projection pressing or rotary kneading, pressure rolling and bore pressures. The advantages of these methods were explained at the beginning. With a broken line, the respective inner contours of the shaft sections configured as hollow shafts 1 . 3 . 5 to recognize.

3 shows that the left in the image plane end of the first shaft portion with an external spline 6 has been provided. The second shaft section configured as a gear 2 is with a straight high toothing 7 and the shaft section 4 with a helical toothing 8th Mistake. All gears 6 . 7 . 8th are preferably produced by toothed rollers.

Only when all shaft sections 1 - 5 are finished, the welding connection of the individual shaft sections takes place finally 1 - 5 by friction welding. As a result, the finished parts are joined with the highest precision in the axial, radial and circumferential directions, so that finally the finished gear hollow shaft is created. The Reibverschweißten areas are marked with R.

1

shaft section

2

shaft section

3

shaft section

4

shaft section

5

shaft section

6

gearing

7

gearing

8th

gearing

R

friction welded area

Claims (9)

Method for producing a hollow gear shaft consisting of axially successive shaft sections ( 1 - 5 ), wherein at least two shaft sections ( 1 . 2 . 4 ) with a toothing ( 6 . 7 . 8th ) and where the gearing ( 6 . 7 . 8th ) is produced by means of toothed rollers without cutting, wherein the shaft sections ( 1 - 5 ) provided before joining with a toothing, completely finished and after making the toothing ( 6 . 7 . 8th ) are joined together by friction welding, whereby adjacent shaft sections ( 1 - 5 ) are arranged with respect to their rotational angle positioning in a predetermined target angular position, wherein the deviation from the target angular position is less than 30 seconds of arc, wherein the shaft sections are made of air-hardening steels of different properties and at least one shaft section ( 1 - 5 ) has a yield strength of greater than 850 MPa and a strength greater than 1,000 MPa, wherein at least one shaft portion ( 1 - 5 ) is made of a steel with the following alloy components in weight percent: C: 0.1% -0.3% Si: Max. 0.8% Mn: 1.3% -2.5% Cr: 0.8% -1.8% Not a word: Max. 0.3% Nb: Max. 0.06% Ti: Max. 0.06% B: Max. 0.004% Remaining iron, including impurities caused by melting. Method according to claim 1, characterized in that that a deviation from the target angular position of less than 5 arc seconds is set. Method according to claim 1 or 2, characterized that an axial offset of less than 10 microns is set. Method according to one of claims 1 to 3, characterized that a radial offset of less than 5 microns is set. Method according to one of claims 1 to 4, characterized in that one with a toothing ( 6 . 7 . 8th ) shaft portion ( 1 . 2 . 4 ) is made from a round blank. Method according to one of claims 1 to 5, characterized in that at least one shaft section ( 1 . 3 . 5 ) is processed by friction rollers before the friction welding. Method according to one of claims 1 to 6, characterized in that at least one shaft section ( 1 . 3 . 5 ) is worked by rotary swaging before friction welding. Method according to one of claims 1 to 6, characterized in that at least one shaft section ( 1 . 3 . 5 ) before friction welding Bore press is processed. Method according to one of claims 1 to 8, characterized that one when friction welding emerging bead is removed by cutting.