WO2021122777A1

WO2021122777A1 - Method for surface hardening of a drive component having teeth

Info

Publication number: WO2021122777A1
Application number: PCT/EP2020/086466
Authority: WO
Inventors: Thomas HERTING
Original assignee: Güdel Group Ag C/O Güdel Ag
Priority date: 2019-12-17
Filing date: 2020-12-16
Publication date: 2021-06-24
Also published as: CH716959B1; CH716959A1

Abstract

The invention relates to a method for surface hardening of a toothed drive component (1) made of a hardenable steel, wherein surface hardening occurs by means of partial heating of a plurality of regions (14) of the drive component (1). Each of the regions (14) comprises at least two adjacent teeth (11.1, 11.2) of the toothing system (10), wherein all flanks (12.1b, 12.1c, 12.2b, 12.2c) of the teeth (11.1, 11.2) of the regions (14) and tooth roots (13.1) in the inside of the regions (14) are hardened by partial heating and tooth roots (13.0, 13.2) on the edges of the regions (14) are not hardened. The regions (14) do not overlap. Toothed drive components (1) can thus be produced which, at the given dimensions and required durability, enable higher feed forces than conventional components not hardened under the tooth root. Due to the remaining soft tooth roots, the warping of the workpiece for the drive component is nevertheless strongly reduced, such that, in particular in the case of linear drive components such as gear racks, a subsequent straightening is spared or is possible with significantly reduced effort. Reduced process time additionally results due to the simultaneous hardening of a plurality of teeth.

Description

Process for hardening the surface of a drive component with toothing

Technical area

The invention relates to a method for surface hardening of a drive component with toothing, wherein the drive component consists of a hardenable steel and the surface hardening by means of partial heating of several areas of the

Drive component takes place. The invention further relates to an induction tool for carrying out such a method and a drive component that can be produced using such a method. State of the art

Toothed drive components made of steel, such as racks, pinions, gears or steering spindles, are hardened to increase wear and fatigue strength.

Typically unalloyed or alloyed are used for drive components

Quenched and tempered steels, tool steels or roller bearing steels, spring steels or case-hardened steels can be considered. A carbon content of at least about 0.35% or more is required for hardenability, which in the case of case-hardening steels can also only be adjusted locally on the edge to be hardened via a previous carburization. The surface layer of the workpiece is in the austenitic state of the steel, i.e. H. at high temperature, enriched with carbon. The component is then quenched. A martensitic surface layer results (case hardening).

With other hardening processes, the components are only heated locally for a short time. The thermal effect and the subsequent quenching changes the structure of the material in the affected area, which leads to greater hardness. Compared to case hardening, these hardening processes have the advantage of low heat input and the resulting lower distortion of the components (hardening distortion).

In particular, the surface layer hardening through partial heating of the material to be processed and subsequent quenching is of great importance for drive components. In the case of suitable steels, this results in a martensitic surface layer with a hardness that is significantly higher than that of the initial configuration.

Various methods can be used for surface hardening. The material can be heated by means of direct heat from external heat sources, e.g. B. Gas burners (flame hardening with oxy-fuel burner technology), locally heated by means of laser or electron radiation, conductively or inductively.

With inductive surface hardening, a (cooled) coil is brought up to the workpiece. An alternating voltage applied to the coil causes eddy currents in the workpiece, which lead to heating up to a certain penetration depth. The latter depends in particular on the frequency of the alternating voltage, but also on other parameters such as the surface power density, the permeability of the material, the exposure time and the material geometry. The result can be influenced by a suitable choice of frequency and the superposition of different frequency ranges: High frequencies lead to shallower hardness zones, low frequencies, on the other hand, lead to greater depths of surface hardness.

Various inductive surface hardening processes for gears are known:

With single-tooth flank hardening, the flanks of the individual teeth are hardened one after the other in a discontinuous single-shot process using a form inductor. This method is suitable for components with a large module. It must be ensured that the shape inductor can be inserted into the tooth gaps, and the tempering effect must be limited to neighboring surfaces as much as possible. With single-tooth gap hardening, the gaps are hardened one after the other, again in a discontinuous single-shot process, using a mold inductor. In order to reduce the tempering effect, intensive cooling of the previously hardened flank is necessary in order to reduce the tempering effect. This method is also particularly suitable for components with a large module.

With all-tooth hardening, the teeth are hardened in a continuous process. The use of multi-frequency generators that superimpose high and medium frequencies enables conformal hardening down to the tooth root. This method is particularly suitable for components with a small module, because a larger module results in a less favorable distribution of heat, which can cause the tooth tip to overheat, with the risk of hardening cracks.

After hardening, the workpieces are tempered as soon as possible by heating them (locally if necessary) to a tempering temperature of typically 140-220 ° C for a sufficiently long holding time. The initially extremely hard martensite structure of the surface layer becomes more ductile again. Hardening and tempering give the component a high level of surface hardness and strength. The core, on the other hand, remains in a tough (tempered or annealed) state.

When producing surface-hardened drive components with toothing, the design of the hardening zone is of great relevance for the fatigue strength of the tooth root.

Conventionally, all teeth of a drive component are designed with a similar hardness pattern, which, compared to the respective main symmetry element, follows a profile that is uniform for each tooth. Rotary components (gears / pinions) have the same hardness pattern in the circumferential direction, and linear products (racks, steering spindles) have the same hardness pattern in the longitudinal direction.

If the surface hardening in the tooth root, higher values for the parameter s _{F ilm} (tooth root fatigue strength) are recognized, than teeth, where the tooth root remains uncured. If the tooth root remains unhardened, the reduced flexural strength of the respective Raw material in the delivery condition (normalized, tempered, soft annealed or similar).

On the other hand, the greater the proportion of hardened workpiece volume or the larger the hardening zones, the greater the distortion of drive components, since the structural transformation during hardening is always associated with a change in volume. In particular on workpieces with non-symmetrically arranged hardness zones, such. B. with racks, it comes as a result of an asymmetrical heat treatment with increasing hardening depth or hardening of additional molded elements to greater distortion. This results in greater manufacturing-related expenditure in the subsequent hard machining or during straightening.

In addition, the straightenability also decreases and the risk of cracking directly during hardening or during later straightening, the greater the relative proportions of the hardening zone on the cross-section. The challenge with hardening down to the tooth root is also the mass distribution in the toothing. While the tooth tips tend to accumulate heat or overheat due to their low mass, the introduction of heat into the tooth root is difficult due to the large mass.

Conventional hardening processes thus either enable high strength, but require a complex subsequent straightening process, or they only enable reduced strength. Presentation of the invention

The object of the invention is to create a method, belonging to the technical field mentioned at the beginning, for hardening the surface layer of a drive component with toothing, which method enables high fatigue strength with reduced manufacturing costs. The solution to the problem is defined by the features of claim 1. According to the invention, each of the areas comprises at least two adjacent teeth of the toothing, with all flanks of the teeth of the areas as well as tooth roots inside the Areas are hardened by partial heating and tooth roots are not hardened at the edges of the areas, whereby the areas do not overlap.

The areas each extend from the middle of a tooth root to the middle of another tooth root, the length of a region being at least two tooth pitches.

In other words, at least two adjacent teeth are subjected to the heat treatment at the same time. The areas can be edited one after the other, especially with the same tool, but it is also possible to edit several (or all) areas at the same time.

The process is characterized by the fact that in a given area all tooth flanks and the tooth root or the tooth roots between the teeth are hardened continuously along the toothing, while the first tooth root and the last tooth root, each at the border of the area, remain unhardened. This means that in the interior of the area, a hardened zone extends continuously from the first flank to the last flank along the treated surface of the drive component.

At least in the area of the inner tooth root or the inner tooth roots, the hardened zone thus extends under the tooth root. There is no hardening of the tooth root on the outer tooth roots. These areas remain soft. Because there is no overlap between the areas, the outer tooth roots are not hardened in subsequent heat treatment steps either, because - depending on the arrangement of the areas - they also form the edges of other areas or lie in regions of the toothing that are not heat-treated.

“Hardened” in this context means that the action of heat in a certain region has taken place in such a way that the desired structural change (e.g. to martensite) has taken place at least on the surface (and preferably to a predetermined depth). In other, "not hardened" areas, there is no structural change. However, it is possible that these other areas are also exposed to a certain amount of heat during the process. The method according to the invention thus results in a special design of the hardening zones in which hardened segments alternate with unhardened sections.

The method according to the invention can be applied to all surface hardenable steels. It is irrelevant here whether the steel can be hardened in its initial state as is the case with unalloyed heat treatable steels (C40, C45, C50, C55, C60, ...), alloyed heat treatable steels (42CrMo4, 50CrMo4, 58CrMoV4, 38MnB5, ...), Tool / roller bearing steels (10006, 100CrMo7, 100CrMnSi6-4, ...) or spring steels (510V4, 52CrMoV4) or whether the martensitic hardenability has been adjusted to a carbon content at the edge of at least 0.35% C at the edge, such as case-hardened steels (16MnCr5, ...).

With the method according to the invention, a new type of drive component made of hardenable steel with a toothing can be produced, the toothing comprising several areas with at least two teeth each, with all the flanks of the teeth of the areas as well as tooth roots being hardened in the interior of the areas and tooth roots being hardened at the edges of the areas are not hardened and the areas do not overlap.

In this way, both rotationally symmetrical drive components such as pinions or gears and linear drive components such. B. produce racks or their derivatives (e.g. steering spindles). With the method according to the invention, a toothed drive component can be produced which, due to the teeth hardened under the tooth root, allows higher feed forces than components not hardened under the tooth root, given the dimensions and the required fatigue strength. Due to the remaining soft tooth roots, the distortion of the workpiece for the drive component is nevertheless greatly reduced, so that subsequent straightening is unnecessary or possible with significantly less effort. Due to the simultaneous hardening of several teeth, there is also an economic advantage over the known methods of single tooth hardening due to a shortened process time. Because there is no overlapping heat treatment, the related problems do not arise - namely, there is no undesired tempering, as in known processes, where it cannot be avoided that certain areas are subjected to the hardening treatment twice. The drive component is advantageously a rack, with one module of the rack in particular being at least four. According to the current definition, the module corresponds to the pitch of the rack (in mm) divided by the number of circles p.

Since the hardness zones of toothed racks are usually only arranged on one side of the workpiece and there is usually no equalization hardening, the mentioned advantage of lower warpage and better straightenability comes into play here. In the case of racks with a comparatively large module, individual tooth hardening has primarily been used so far, so that the shortening of the process time is also an advantage here.

The toothing is preferably a helical toothing. The helical toothing results in a greater overlap in the longitudinal direction of the rack, so that several teeth are in mesh at the same time, which means that the soft tooth roots can be covered, especially when a soft (unhardened) tooth root is always followed by a hardened tooth root on both sides.

In the case of racks with helical gearing, the somewhat lower mechanical stability compared with continuously hardened racks is less of a consequence than with racks with straight gearing.

Other racks (with a smaller module and / or with straight teeth) and rotary drive components can also be manufactured in the manner according to the invention. B. in relation to the process time, the fatigue strength compared to components not hardened under the tooth root and the lack of overlaps during hardening.

Advantageously, the ends of the rack come to rest in hardened tooth roots. These ends are often particularly stressed mechanically, so that hardening under the tooth root there is an advantage. Such racks can be produced in hardened tooth roots, in particular by appropriately cutting them to length.

The areas are advantageously selected in such a way that all teeth of the toothing belong to exactly one of the areas. As a result, all the flanks of the drive component (at least in their wear area) are hardened, but not all tooth roots. A soft tooth root is followed by a hardened tooth root on both sides.

In a preferred embodiment, all areas have the same extent. This results in a uniform sequence of hardened and unhardened tooth roots and thus essentially uniform mechanical properties along the drive component. In addition, the freeing position can in principle be carried out with a single tool, with which the teeth of an area and the tooth roots (or the tooth root in between) can be machined at the same time.

Alternatively, drive components can also be produced in which not all teeth are hardened and / or areas of different dimensions are present. This is particularly useful when different mechanical requirements are placed on different regions of the drive component.

The lowering position according to the invention is particularly advantageous, for example, in the case of a helical toothed rack with a module of 4 or more, with the areas comprising 2 or 3 adjacent teeth and with all teeth being edge-hardened.

The partial heating is preferably carried out inductively. As a result, the workpiece surface can be machined precisely in the toothing area, and high flare values can be achieved. For inductive heating, frequencies in the range 10 - 400 kHz are used in particular, whereby it can be useful to superimpose several frequencies of different frequency ranges in order to obtain a desired heat distribution that is adapted to the mass ratios in the tooth tip, in the area of the tooth flank and in the tooth root . For this purpose, generators are available which are offset in time or even superimpose the flux and medium frequency components for inductive heating at the same time, cf. B. Fl. Gießmann, "Heat treatment of gear parts", 3rd edition, expert Verlag, 2019, pp. 142ff. Corresponding systems are z. B. offered by the providers EFD Induction GmbH, Freiburg im Breisgau, Germany ("Mehrfrequenzkonzept / MFC") or eldec Schwenk Induction GmbH, Dornstetten, Germany ("SDF - Simultaneous Dual Frequency").

Inductors adapted to the contour to be hardened are used as tools for inductive hardening.

The areas are preferably hardened one after the other by partial heating, that is to say in a discontinuous process. A single area or a group of areas is heated and then quenched. This is followed by the next area or group. In this way, the machining can be carried out with compact tools, and the same tools can be used, for example, for machining racks of different lengths (but with the same module and the same tooth geometry).

Alternatively, tools are used with which the entire workpiece can be heated in one step and then quenched. Continuously running processes are also conceivable, which run in such a way that the areas are processed according to the invention.

The induction tool preferably comprises at least three inductor areas for the simultaneous hardening of at least two teeth of a tooth system, the inductor areas at the edges of the induction tool each being designed for hardening one flank of a tooth of the tooth system and the inductor area or the inductor areas inside the induction tool each for hardening two flanks and a tooth root therebetween are formed.

The induction tool therefore couples to the teeth hardened within a range from the tooth flank up to and including the tooth root. At the beginning and end of the area, however, the induction tool is designed in such a way that only the wear areas on the flank are heated and hardened. In the root area there is no coupling or no heat input, so that the root areas in the tooth root are here stay soft. In addition, the influence of heat and thus a possible tempering effect are minimized as far as possible.

Correspondingly, with an area length of N teeth, such an induction tool has in each case N + 1 inductor areas.

The coupling distance refers to the distance of the lowest point of the induction loop in relation to the highest point of the workpiece surface, measured in a radial direction for rotationally symmetrical drive components or in a direction perpendicular to the longitudinal axis in the longitudinal center plane for linear drive components, in the operating position of the induction tool.

Due to the different dimensions and shapes, the induction tool couples to the teeth hardened within a range from the tooth flank up to and including the tooth root. At the beginning and end of the area, on the other hand, only the wear areas on the flank are heated and ultimately hardened. The induction tool is withdrawn here in relation to the workpiece surface, so that there is an increased coupling distance and thus little or no coupling and heat input.

In a preferred embodiment, the at least three inductor areas are provided by a single inductor loop, the inductor areas being connected to one another by curved connecting sections. The latter run to the side of the workpiece and therefore have no effect on the workpiece during operation because there is no coupling in these sections.

Such induction tools can be manufactured using additive manufacturing processes. From the company GH Induction Deutschland, Hirschhorn (Neckar), Germany, a method for manufacturing an inductor in the investment casting process using a wax mold is known in which the actual inductor loop is manufactured in an investment casting process from silver or a silver alloy (so-called "microfusion inductor"). . The additive manufacturing process is used here to manufacture a mold to enable the investment casting process. In addition, another method by the same company is known to Additive manufacturing of copper inductors using the "Electron Beam Melting" (EBM) process (so-called "3DPCoil").

The induction tool is connected to a cooling circuit via a connection in the inductive hardening system to protect the tool from overheating during operation. The inductor loop can, for example, have the usual wall thicknesses of approx. 0.6 - 1.2 mm, the cooling cross-section is dimensioned in such a way that the cooling function is guaranteed for a given line length.

Field amplifiers (so-called concentrators) are preferably attached to the induction tool in order to divert the heat input from the heads of the toothing and rather to direct it to the foot area. This results in an optimized hardness profile or an optimized inductor efficiency. As is customary in inductor construction, the concentrators are made of composite materials made of soft iron particles or fillers in conjunction with a polymer material binding phase. Corresponding semi-finished products are sold, for example, by the company Fluxtrol, Auburn Hills, MI, USA under the trade names “Ferrotron” or “Fluxtrol”. Alternatively, it can also be equipped with a package of transformer / pure iron sheets.

The induction tool preferably comprises an additional cooling device (“additional cooling shower”) for cooling a tooth of the toothing adjacent to the machined area during the action of the induction tool.

Depending on the process sequence, such a cooling device can be arranged upstream and / or downstream of the induction tool in the longitudinal direction of the workpiece.

Further advantageous embodiments and combinations of features of the invention emerge from the following detailed description and the entirety of the patent claims.

Brief description of the drawings

The drawings used to explain the exemplary embodiment show: Fig. 1 AC Schematic representations of the hardened surface layers in three

Embodiments of a rack produced with a method according to the invention;

2 shows a schematic cross-sectional view through a toothed rack produced according to the invention;

3 shows an oblique view of an induction tool according to the invention;

4 shows a plan view of the induction tool according to the invention; Fig. 5 shows a cross section through the induction tool, in the plane A-A;

6 shows an oblique view of the interaction of the induction tool according to the invention with a cooling spray on a toothed rack workpiece to be machined;

7 shows a plan view of the induction tool and the workpiece; and

8 shows a cross section through the induction tool and the workpiece, in the plane B-B of FIG. 7. Basically, the same parts are provided with the same reference numerals in the figures.

Ways of Carrying Out the Invention

FIGS. 1 AC are schematic representations of the hardened edge layers in three embodiments of a toothed rack produced using a method according to the invention. The first embodiment of the rack 1 according to FIG. 1A comprises a toothing 10 which extends over the entire length of the rack 1 and comprises a plurality of evenly shaped and distributed teeth 11. A tooth root 13 is formed between two adjacent teeth 11. The teeth are shown schematically with a trapezoidal cross-section. Each tooth 11 comprises a tooth tip 12a and lateral flanks 12b, 12c. The toothing 10 is divided into several areas 14 (hardness segments), with each of the areas 1 comprising two adjacent teeth 1 1.1, 1 1.2 and with adjacent areas always being arranged in direct succession, that is, each of the teeth 1 1 belongs to one of the areas 14.

Each area 14 comprises a hardened edge layer 16 or hardening zone, which, starting from a first flank 12.1b of the first tooth 11.1, extends over its tooth tip 12.1a, the second flank 12.1c, the tooth root 13.1, the first flank 12.2b of the second tooth 1 1.2, whose tooth tip 12.2a extends into its second flank 12.2c. The zone comprises the entire wear section of the first flank 12.1b of the first tooth 11.1 and the second flank 12.2c of the second tooth 11.2. The tooth roots 13.0, 13.2 adjoining the area 14 on both sides do not have a hardened edge layer.

The hardened edge layer 16 extends from the rack surface to a certain depth. An unhardened tooth core area 17 of the toothed rack 1 extends below a corresponding interface 15 (visible in cross section as a line). The interface 15 is formed continuously in each area 14. In the first embodiment according to FIG. 1A, it extends in the area of the inner tooth roots 13 into an area below the tooth root, but in the area of the teeth it does not run continuously below the tooth root.

The second embodiment of the rack 2 according to FIG. 1 B comprises a toothing 20 which extends over the entire length of the rack 2 and comprises several evenly shaped and distributed teeth 21. A tooth root 23 is formed between two adjacent teeth 21. The teeth are shown schematically with a trapezoidal cross-section. Each tooth 21 comprises a tooth tip 22a and lateral flanks 22b, 22c.

The toothing 20 is divided into several areas 24, with each of the areas 24 comprising three adjacent teeth 21.1, 21.2, 21.3 and with adjacent areas always being arranged in direct succession, ie each of the teeth 21 belongs to one of the areas 24. Each area 24 comprises a hardened edge layer 26 or hardness zone, which, starting from a first flank 22.1b of the first tooth 21.1, extends over its tooth tip 22.1a, the second flank 22.1c, the first tooth root 23.1, the first flank 22.2b of the second tooth 21.2, its tooth tip 22.2a, its second flank 22.2c, the second tooth root 23.2, the first flank 22.3b of the third tooth 21.3, whose tooth tip 22.3a extends into its second flank 22.3c. The zone comprises the entire wear section of the first flank 22.1b of the first tooth 21.1 and the second flank 22.3c of the third tooth 21.3. The tooth roots 23.0, 23.3 adjoining the area 24 on both sides do not have a hardened edge layer. The hardened edge layer 26 extends from the rack surface to a certain depth. An unhardened tooth core area 27 of the toothed rack 2 extends below a corresponding interface 25 (visible in cross section as a line). The interface 25 is formed continuously in each area 24. In the second embodiment according to FIG. 1B, it extends in the area of the inner tooth roots 23 into an area below the tooth root, but in the area of the teeth it does not run continuously below the tooth root.

The third embodiment of the rack 3 according to FIG. 1C comprises a toothing 30 which extends over the entire length of the rack 3 and comprises several evenly shaped and distributed teeth 31. A tooth root 33 is formed between two adjacent teeth 31. The teeth are shown schematically with a trapezoidal cross-section. Each tooth 31 comprises a tooth tip 32a and lateral flanks 32b, 32c.

The toothing 30 is divided into several areas 34, with each of the areas 34 comprising three adjacent teeth 31.1, 31.2, 31.3 and with adjacent areas always being arranged in direct succession, i. H. each of the teeth 31 belongs to one of the areas 34.

Each area 34 comprises a hardened edge layer 36 or hardness zone, which, starting from a first flank 32.1b of the first tooth 31.1, extends over its tooth tip 32.1a, the second flank 32.1c, the first tooth root 33.1, the first flank 32.2b of the second tooth 31.2, its tooth tip 32.2a, its second flank 32.2c, the second tooth root 33.2, the first flank 32.3b of the third tooth 31.3, whose tooth tip 32.3a extends into its second flank 32.3c. The zone comprises the entire wear section of the first flank 32.1b of the first tooth 31.1 and the second flank 32.3c of the third tooth 31.3. The tooth roots 33.0, 33.3 adjoining the area 34 on both sides do not have a hardened edge layer.

The hardened edge layer 36 extends from the rack surface to a certain depth. An unhardened tooth core area 3Z of the rack 3 extends below a corresponding interface 35 (visible in cross section as a line). The interface 35 in the rack 3 according to the third embodiment extends except at the edges of the area 34 below the tooth root. Thus the outer teeth 31.1, 31.3 are almost completely and the middle tooth 31.2 completely hardened.

FIG. 2 is a schematic cross-sectional view through the toothed rack produced according to the invention according to the first embodiment. The two teeth 11.1, 11.2 of a region 14 are shown. Again, the hardened edge layer 16 or hardness zone, the unhardened tooth core region 1 Z and the interface 15 are shown. The following requirements are met at five different test points p1 ... p5:

The surface hardness according to Vickers is determined in accordance with DIN EN ISO 6507: 2018. The surface hardness depth is determined in accordance with DIN EN 10328: 2005-04. The specified values for the surface hardness and the surface hardness depth refer to the condition after tempering. The illustrated course of the interface 15 corresponds to the specified hardness depths at which the specified minimum hardness is reached. An examination of the material shows that at least above the interface 15 the material is present as fine-needle to needle-like martensite in the area of the test points p1-p3 and is free of cracks.

FIG. 3 is an oblique view of an induction tool according to the invention, FIG. 4 shows a top view, and FIG. 5 shows a cross section in plane A-A.

The induction tool 100 has a first side S 1 facing a drive component when the induction tool 100 is used, and a second side S2 facing away from the drive component. The induction tool 100 comprises an inductor loop 110 and three concentrators 131, 132, 133, which are arranged on the inductor loop 110. The inductor loop 1 10 comprises three parallel and spaced apart straight sections 1 1 1, 1 13, 1 15, the first section 1 1 1 with the second section 1 13 and this in turn with the third section 1 15 via U-shaped connecting sections 1 12, 1 14 are connected. A cooling channel 120 runs in the inductor loop 110. This has a connection (not shown) at its beginning and at its end for introducing and discharging a circulating cooling liquid for cooling the inductor.

In the first straight section 1 1 1 and in the third straight section 1 15, the inductor loop 1 10 has the same cross section, the shape of the cross section in the third straight section 1 15 being mirror-symmetrical to the shape of the cross section of the first straight section 1 1 1. The shape of the cross section of the inductor loop 1 10 in the first straight section 1 1 1 and in the third straight section 1 15 results from a combination of a rectangle with a right-angled trapezoid. The trapezoidal part of the mold is in the direction of the second side S2 of the induction tool, while the rectangular part is in the direction of the first side S1. The side of the trapezoidal part of the shape that is not at right angles is the second facing straight section 13, the width of the trapezoidal part of the mold decreasing towards the second side S2 of the induction tool 100.

The cross section of the inductor loop 1 10 in the second straight section 1 13 is larger than that in the first straight section 1 1 1 and in the third straight section 1 15. The shape of the cross section in the second straight section 1 13 also differs and is a combination of one Rectangle and an isosceles trapezoid. The trapezoidal part of the mold is located in the direction of the first side S 1 of the induction tool 100, while the rectangular part is located in the direction of the second side S2.

The trapezoidal part of the shape of the cross section of the second section 1 13 protrudes further in the direction of the first side S1 than the rectangular part of the shape of the cross section of the first and third straight section 1 1 1, 1 15. This means that the inductor loop 1 10 In the second straight section 1 13 is closer to the drive component than in the first and third straight section 1 1 1, 1 15. Preferably, the inductor loop 1 10 in the second straight section 1 13 is 5.5mm closer to the drive component than in the first and third straight sections Section 1 1 1, 1 15.

In the connecting sections 1 12, 1 14, the cross sections of the straight sections 1 1 1, 1 13, 1 15 each merge steplessly into one another.

The concentrators 131, 132, 133 are assigned to the straight sections 1 1 1, 1 13, 1 15 of the inductor loop 1 10 and are supported and fastened there on the inductor loop 1 10. The concentrators 131, 133 in the first and in the third straight section 1 1 1, 1 15 encompass the inductor loop 1 10 essentially in a U-shape, in each case on their side surfaces not facing the second straight section 1 13. The side surfaces of the inductor loop 1 10 facing the second straight section 1 13 in the first and third straight section 1 1 1, 1 15 are exposed. In the direction of the first side S1 of the induction tool 100, the concentrators 131, 133 of the first and third straight sections 1 1 1, 1 15 have angled partial surfaces which are adapted to the geometry of the flanks of the teeth of the drive component (cf. FIG. 8) . The concentrator 132 of the second straight section 113 has a similar shape in cross section to the cross section of the inductor loop 110 in this second section 113, that is to say a combination of a rectangle with an isosceles trapezoid. The concentrator 132 comprises the inductor loop 1 10 in the second straight section 1 14, on its side facing the second side S2 of the induction tool 1 10. The concentrator 132 comprises only a portion of the rectangular part of the shape of the cross-section of the inductor loop 1 10 in the second section 1 13. That is, the trapezoidal part and a further sub-area of the rectangular part of the shape of the cross-section of the inductor loop 1 10 in the second section 1 13 are freely available. The concentrator 132 of the second straight section 113 protrudes less far in the direction of the second side S2 of the induction tool 100 than the concentrators 131, 133 of the first and third sections 1111, 1115.

FIG. 6 is an oblique diagram which illustrates the interaction of the induction tool according to the invention with a cooling shower with a workpiece to be machined for a straight toothed rack. FIG. 7 shows a plan view of a helical toothed rack and FIG. 8 shows a cross section through the induction tool and the workpiece, in plane B-B of FIG. 7.

The additional cooling shower 150 is arranged laterally on one side of the inductor loop 110 on the induction tool 100. The additional cooling shower 150 comprises four cooling nozzles 151, 152, 153, 154 which are arranged in a line, the line running parallel to the three parallel straight sections 1 1 1, 1 13, 1 15 of the inductor loop 1 10. The outlets of the four cooling nozzles 151, 152, 153, 154 are again directed obliquely downward, parallel to one another.

During operation, the induction tool 100 is fed onto the rack 1 and brought into a defined coupling distance to the rack 1 with respect to the three spatial axes. The three straight sections 1 1 1, 1 13, 1 15 penetrate into successive tooth gaps. The first straight section 1 1 1 faces the third tooth root 13.2, the second straight section 1 13 faces the second tooth root 13.1, and the third straight section 1 15 faces the first tooth root 13.0. The additional cooling shower 150 penetrates the again preceding tooth gap and acts on the flank of the preceding tooth 1 1.0, the has already been surface hardened in a previous processing step. The additional cooling prevents undesired tempering of the previously hardened area.

As can be clearly seen in FIG. 8, the coupling distance to the second tooth root 13.1 in the middle tooth gap is smaller than to the first or third tooth root 13.0, 13.2 in the outer gaps due to the larger cross section and thus the greater penetration depth of the second straight section 13 . The outer first and third straight sections 1 1 1, 1 15 are also not arranged symmetrically in the corresponding tooth gaps in the longitudinal direction of the rack 1, but in such a way that they are closer to the flank of the respective inner tooth 1 1.1, 1 1.2 than the opposite one Flank of the unprocessed teeth. The second straight section 113 located in the middle is positioned symmetrically in the middle tooth gap between the teeth 11.1, 11.2.

The geometry of the inductor loop 110 and the concentrators 131, 132, 133 is specifically adapted to the geometry of the helical toothing in order to achieve the desired coupling of the energy into the workpiece surface.

To clear the rack 1, the induction tool 100 is successively brought into engagement with the toothing 10 of the rack 1 in the manner shown in FIGS. 6-8, the position being shifted by two teeth after each step. When the induction tool 100 with the inductor loop 110 is in engagement with the rack 1, the inductor loop 110 is acted upon in a manner known per se with a superimposition of medium and high frequency alternating voltages. The choice of frequencies, amplitudes and duration of action depends on the geometry of the rack and the induction tool as well as on the material of the workpiece and takes place in a manner known per se. As a result, the rack 1 is heated at the desired points. Because it cannot be avoided that the previously hardened region also experiences a certain warming (in particular due to heat conduction in the workpiece), the affected area is cooled with the aid of the additional cooling shower 150 in order to prevent it from being left on again due to the effect of heat. After heating, which is approx. 0.5 - 2.5 s, the induction tool 100 is moved away from the rack 1 and the heated region is quenched with the aid of a box shower (not shown) (for approx. 1-6 s). For this purpose, a water-based solution or a water-based mixture with additions of polymeric quenching concentrates is used in a manner known per se. After these steps, the area is hardened on the surface.

The induction tool 100 is now advanced by two tooth pitches, after which a new hardening process can take place for the next two teeth. This procedure is repeated until the entire toothing 10 has been hardened. In order to obtain optimal strength properties, the rack 1 is finally cut to length in the area of the hardened tooth roots.

The invention is not restricted to the exemplary embodiments shown. As mentioned, in addition to racks of different geometries, other drive components can also be machined and designed accordingly, including rotary components such as pinions or toothed wheels.

In principle, other hardening processes can also be used, such as B. laser or electron beam hardening.

In summary, it can be stated that the invention creates a method for surface hardening of a drive component with toothing, which enables high fatigue strength with reduced manufacturing costs.

Claims

1. A method for surface hardening of a drive component with toothing, wherein the drive component consists of a hardenable steel and the surface hardening takes place by means of partial heating of several areas of the drive component, characterized in that each of the areas comprises at least two adjacent teeth of the toothing, with all flanks of the teeth of the areas as well as tooth roots inside the areas are hardened by partial heating and tooth roots are not hardened at the edges of the areas, whereby the areas do not overlap.

2. The method according to claim 1, characterized in that the areas are chosen so that all teeth of the toothing belong to exactly one of the areas.

3. The method according to claim 2, characterized in that all areas have the same extent.

4. The method according to any one of claims 1 to 3, characterized in that the partial heating takes place inductively.

5. The method according to any one of claims 1 to 4, characterized in that the areas are hardened one after the other by partial heating.

6. Induction tool for performing the method according to claim 4, comprising at least three inductor areas for the simultaneous hardening of at least two adjacent teeth of a toothing, wherein the inductor areas at the edges of the

Induction tool are each designed to harden a flank of a tooth of the toothing and the inductor area or the inductor areas in the interior of the induction tool are each designed to harden two flanks and an intermediate tooth root.

7. Induction tool according to claim 6, characterized in that the at least three inductor areas are provided by a single inductor loop, the inductor areas being connected to one another by curved connecting sections.

8. Induction tool according to one of claims 6 to 7, characterized by a

Cooling device for cooling a tooth of the tooth system adjacent to the machined area.

9. Drive component made of hardenable steel with a toothing, the toothing comprising several areas with at least two adjacent teeth each, with all flanks of the teeth of the areas and tooth roots in the interior of the areas being hardened and tooth roots at the edges of the areas not being hardened, with the areas do not overlap.

10. Drive component according to claim 9, characterized in that it is a rack, wherein a module of the rack is in particular at least 4.

1 1. Drive component according to claim 10, characterized in that the toothing is a helical toothing.

12. Drive component according to claim 10 or 1 1, characterized in that the ends of the rack come to rest in hardened tooth roots.