EP3993927A1

EP3993927A1 - Method and device for induction hardening

Info

Publication number: EP3993927A1
Application number: EP20753356.3A
Authority: EP
Inventors: Heiko Schwibode
Original assignee: Liebherr Components Biberach GmbH
Current assignee: Liebherr Components Biberach GmbH
Priority date: 2019-08-09
Filing date: 2020-08-07
Publication date: 2022-05-11
Also published as: WO2021028343A1; US20220186332A1; DE102019127231A1; CN114502750A

Abstract

The invention relates to a method for the induction hardening of a workpiece, in particular a toothed and/or corrugated and/or ribbed workpiece such as a gear or saw blade, wherein a matchingly shaped induction loop is guided or set over the workpiece surface to be hardened, the induction loop being formed layer-by-layer by the additive application of material, and the induction loop being shaped to match the surface to be hardened.

Description

Method and device for inductive hardening

The present invention relates to a method and a device for inductive hardening of a workpiece, in particular a toothed and / or corrugated workpiece such as a gear, chain wheel or saw blade, a shape-adapted induction loop being guided or set over the surface to be hardened.

In the case of inductive hardening, as is known, an induction loop is brought close to the surface of a workpiece to be hardened or leads over it, whereby by applying an alternating voltage or possibly by relative movement to a magnetic field, a voltage is induced that induces eddy currents in the workpiece and the workpiece is partially heated. With sufficiently large work pieces, the heat flows sufficiently quickly into the rest of the still cold work piece so that hardening occurs, although quenching can also be carried out if necessary. By controlling the frequency, the depth of penetration or hardness can be controlled, and the degree of heating can be influenced by the current strength and duration of the current supply. Overall, even more complex contoured workpieces can be specifically heated to the required hardening temperature in limited areas through inductive hardening and thus partially hardened. In order to achieve a uniform hardening result over the contour profile on more complex surfaces such as toothing or corrugations or corrugations, the shape of the induction loops is adapted to the tooth or shaft contour or the surface contour to be hardened in order to keep the distance between the surface contour to be hardened and the contour as constant as possible to achieve the induction loop or to vary this distance specifically over the length of the induction loop if a correspondingly non-constant course of the hardening depth is desired.

Usually, the induction loops are made hollow on the inside in order to be able to cool the induction loops with water or another cooling medium during the hardening process. Accordingly, the induction loops are made by bending and connecting individual tubes, which usually have a rectangular or square cross-section. Depending on the required contour of the induction loop, various pieces of pipe are cut to size, sawn off, bent and connected to one another by soldering in order to adapt the contour of the induction loop to the shape of the surface contour of the workpiece to be hardened. Due to said cutting, sawing off, bending and soldering, however, the freedom of geometry of the induction loops is limited or the production of the desired induction loop contour is very difficult and expensive.

The induction loop must not touch the workpiece during the hardening process and is separated by a predetermined gap between the workpiece and the induction loop. The gap width is determined by adapting the induction loop to the contour of the workpiece or its surface to be hardened. Due to the limited geometrical adaptability of the induction loop to the workpiece, induction loops are currently only adapted to individual segments of the workpiece, with the workpiece being inductively hardened on its individual segments. For example, when hardening the toothing of a gear or a rack, induction loops are usually used, which are usually only matched to a tooth gap between two adjacent tooth flanks or to a maximum of two to three such tooth gaps. The induction loop is moved parallel to the axis of rotation of the Gear or transversely to the longitudinal direction of the rack through the tooth gap, then the induction loop or the gear or the rack is set a little further and the induction loop is passed through a tooth flank that is still unhardened by a renewed feed movement. In this way, the toothing is induction hardened piece by piece.

With the cited tooth gap hardening, the induction loop is thus adapted in shape to at least two adjacent tooth flanks as well as the root area lying in between. In contrast to single tooth hardening, the above-mentioned tooth gap hardening has the advantage that even hardening is achieved in the highly stressed tooth root area and hardness irregularities due to the cyclical reassembly of the induction loop in the next tooth gap or the next tooth gap group only occur in the area of the tooth tip . Nonetheless, in the case of more complex gear geometries, it would be desirable to be able to avoid hardness irregularities both in the tooth root area and in the tooth tip area.

In principle, it would also be desirable to be able to inductively harden a larger group of teeth or tooth gaps or similar wave or general surface contours at the same time, on the one hand to shorten the total production time required for the hardening process and on the other hand to reduce the number of irregularities in hardness caused by renewed application the induction loop. Equally, it is desirable to be able to control the course of hardness as precisely as possible by keeping deviations in shape between the induction loop and the surface contour to be hardened as small as possible or the distance between the induction loop and the surface contour can be maintained as precisely as possible.

In order to be able to harden several teeth or tooth gaps of a gear at the same time, the document EP 23 10 542 B1 proposes to use several induction loops or Härtein ductors, which are arranged distributed around the circumference of the gear, at a distance from each other an integer multiple of Corresponds to the sector angle of two adjacent teeth. If the gear is rotated further in accordance with the pitch of the toothing, several induction loops can be driven through the tooth gaps at the same time. However, it remains with the hardness irregularities in the area of the tooth tips. In addition, the hardening time remains considerable, since a large number of hardening cycles and the corresponding revolving movement of the gear or hardening device are necessary.

The document EP 22 64 192 A1 proposes induction hardening of gears under protective gas, the protective gas should at least surround the sector to be hardened in order to prevent scaling of the tooth flank surfaces. The shape of the induction loop is adapted to the tooth gap to be hardened.

The document DE 10 2011 053 139 A1 proposes to use an induction coil for hardening the toothing of racks, which has an S-shaped curved course in order to direct the induced current at least partially orthogonally to the tooth flanks.

In order to achieve a uniform hardness depth even with more complex toothing geometries, the document DE 10 2008 041 952 B4 proposes providing simultaneous application of different frequencies.

Further devices for the inductive hardening of gears are known from the documents DE 956 259 B and DE 969 927 B.

The present invention is based on the object of creating an improved method and an improved device for inductive hardening of workpieces, avoiding the disadvantages of the prior art and further developing the latter in an advantageous manner. In particular, a homogeneous hardening result without undesired hardness irregularities or even for complex contoured workpieces should be achieved -variations with an efficiently feasible, short production times require the hardening process to be achieved without incurring excessive tool costs.

According to the invention, the stated object is achieved by a method according to claim 1 and a device according to claim 7. Preferred embodiments of the invention are the subject matter of the dependent claims.

It is therefore proposed that the induction loop used for the hardening of the respective workpiece be built up in layers in the required contouring through additive application of material, thereby eliminating the geometry restrictions of conventional induction loops, such as those given by sawing, bending and soldering pipe sections . According to the invention, the induction loop is formed in layers by additive application of material, in particular built up in layers and, for example, thermally solidified, and thereby adapted in shape to the surface of the workpiece to be hardened. Due to the additive application of material and the resulting layer-by-layer contour, the induction loop can be precisely adapted in shape to more complex surface contours such as toothing, so that the gap or distance to be maintained between induction loop and workpiece surface during hardening can be precisely formed.

In particular, the induction loop can be produced by means of a 3D printing process, with the induction loop being built up, for example, by building up layers in the 3D printer and, if necessary, solidifying it by thermal post-treatment.

In particular, layers of material can be liquefied and / or solidified one after the other by means of an energy beam. For example, one or more materials can be applied in layers in powder and / or paste and / or liquid form and accordingly melted or solidified and / or cured and / or brought to a chemical reaction by a laser beam or electron beam or plasma beam in layers Layer to form. Due to the layer-by-layer design, the induction loop can be precisely adapted in shape to difficult contours with changing curvatures and / or angular transitions between different straight lines and / or curved contour sections, even with small surface contours, in order to accommodate the gap between the induction loop and the workpiece surface during hardening Keeping it constant over the surface contour or being able to vary it in the desired manner, whereby very homogeneous hardening results can be achieved.

In an advantageous development of the invention, the induction loop can be adapted to the surface to be hardened over many tooth, wave or corrugated contours, whereby hardness irregularities can be avoided, for example at the tooth tip or even in a tooth root. In particular, the induction loop on more than three or more than five or even more than ten or also on any number of - preferably adjacent - tooth gaps or Wel lentäler or teeth or waves or dents or bumps or protrusions and sinks or generally depressions or elevations or changes in shape of the workpiece are simultaneously adapted in shape by the induction loop being shaped in the cited manner by means of additive material application and in the process being adapted in shape to the surface contour. By means of such an induction loop, the aforementioned more than three or more than five or even more than ten tooth gaps or corrugations or depressions and projections can be hardened at the same time. The simultaneous hardening of such a large number of surface contour segments, on the one hand, significantly reduces the production time required for hardening. On the other hand, hardness irregularities are avoided, such as those that arise when an induction loop that is adapted to the shape of only one tooth gap is reattached to the teeth cyclically.

In particular, by means of the induction loop mentioned, more than 25% or more than 50% or more than 75% of the entire toothing and / or corrugation and / or surface contour to be hardened from the induction loop can be timely enclosed or covered and hardened at the same time. In a further development of the invention, provision can also be made for the shape of the induction loop to be adapted to the entire surface contour to be hardened and for the entire surface contour of the workpiece to be hardened to be hardened at the same time. For example, if a gear is hardened, the induction loop can surround a third or two thirds of the circumference or even the entire circumference of the gear and be adapted to the contours of the tooth gaps or tooth flanks and tooth tips exactly or in the desired manner, so as to be uniform or to have the distance between the induction loop and the toothed profile contour varying in the desired manner and accordingly to achieve a homogeneous hardening result.

If, on the other hand, a rack is hardened, the induction loop can extend, for example, over a quarter or half or three quarters of the length or the entire length of the rack or the toothed area of the rack and thereby to the covered tooth gaps and tooth flanks and tooth pointed to be shaped.

Advantageously, the induction loop can be designed to be hollow on the inside as a result of the additive application of material in layers in order to form a coolant channel inside the induction loop. Cooling medium located in the coolant channel or flowing through the coolant channel, such as a water-polymer solution mixture or oil or some other liquid cooling medium, can cool the induction loop or protect it from overheating or keep it at the desired temperature during hardening. Despite a possibly complex loop contour, a hollow loop profile with a coolant channel inside can be formed in 3D printing.

The invention is explained in more detail below with reference to preferred exemplary embodiments and associated drawings. In the drawings show:

Fig. 1: a side view of an induction loop of a device for inductive hardening of a gear, which extends over the entire outer circumference of the gear and is precisely adapted to the contour of the tooth gaps and teeth, the viewing axis corresponding to the representation of the axis of rotation of the gear,

2: a perspective representation of the gear to be hardened surrounding the induction loop in a viewing direction at an angle to the axis of rotation of the gear, which shows the contour of the induction loop, which is adapted to the toothing,

3: a side view of a gear and an induction loop which is adapted to the shape of its toothing, which, in contrast to the embodiment according to FIGS. 1 and 2, is only adapted to three or more tooth gaps and has inlets and outlets for a coolant at the end,

FIG. 4: a perspective illustration of the induction loop from FIG. 3 partially surrounding the gear to be hardened in a viewing direction at an angle to the axis of rotation of the gear,

5: a side view of a gear wheel and an induction loop adapted to its toothing, the induction loop comprising two partial induction loops for simultaneous hardening and being contoured in such a way that the gap between the induction loop and the toothing surface contour has a non-constant, predetermined gap dimension course ,

FIG. 6: a perspective view of the gear and the surrounding induction loop from FIG. 5 in a viewing direction at an angle to the axis of rotation of the gear,

Fig. 7: a side view of a two-stage toothed gear for simultaneous hardening and one on the different toothed areas shape-adapted induction loop for simultaneous hardening of the various tooth step areas, and

FIG. 8: a perspective illustration of the multi-stage gear rim and the induction loop adapted to it from FIG. 7 in a viewing direction at an angle to the axis of rotation of the gear rim.

As FIGS. 1 and 2 show, the induction loop 2 can be used for partially hardening the toothing 8 of a toothed workpiece 1, wherein the toothed workpiece 1 mentioned can be a toothed wheel or a rack. As explained at the beginning, however, other workpieces with similar wave or groove contours or surfaces with different contours can also be inductively hardened in a corresponding manner.

Advantageously, the induction loop 2 can cover at least a large part of the toothing 8 at the same time, in particular also the entire toothing 8, as FIGS. 1 and 2 show.

The induction loop 2 is produced in an additive material application process, in particular with a 3D printing process, the induction loop being built up in layers in the 3D printer and possibly solidified by thermal post-treatment. The induction loop is constructed before geous enough from an electrically conductive, in particular metallic material.

The induction loop 2 can be designed with a round or rounded, flattened, for example elliptical, but also an angular, in particular rectangular or square cross-section. Furthermore, the induction loop can have any cross section if this is required by the geometric conditions of the workpiece to be hardened. As FIGS. 1 and 2 show, the induction loop 2 can be precisely adapted to the shape of the toothing 8 by the additive, layer-by-layer application of material, in particular the shape of the tooth gaps 5 and the teeth 6 of the toothing 8, so that a gap 9 between the induction loop 2 placed over the toothing 8 and the tooth and tooth gap contours can be kept exactly constant, so that a gap dimension along the longitudinal extension of the induction loop 2 remains at least essentially constant. In this way, a desired hardening result, for example a uniform hardening depth, can be achieved.

The induction loop 2 can be formed by the additive application of material and the layer-wise training, however, also specifically deviating from the contour of the surface to be hardened, in particular the toothing 8, in order to achieve a defined course of the gap size of the gap 9, for example at the tips of the Teeth 6 have a slightly larger gap than at the bottom of the tooth gaps 5, as shown in FIGS. 5 and 6. In particular, the induction loop 2 can be shaped in the 3D printing process in such a way that the gap dimension along the induction loop 2 changes continuously and / or cyclically in order to achieve the desired hardening depth profile.

As FIGS. 1 and 2 show, the induction loop 2 can extend over the entire circumference of the gearwheel and / or extend over the entire toothing 8 and thereby be adapted to the contours of the teeth and tooth gaps.

As shown in Figures 1 and 2, the width of the induction loop 2 can be smaller than the thickness of the workpiece 1. During the inductive hardening process, the induction loop 2 can be guided by a feed movement over the entire width of the workpiece 1, such a feed movement in the direction the axis of rotation of the gear from the induction loop 2 and / or from the workpiece 1 to be hardened can be performed. The induction loop 2 is parallel to the Tooth flanks of the teeth 6 or parallel to the sole of the tooth gaps 8 pushed over the work piece 1 away to harden the teeth 8 over the entire width.

Alternatively, however, it would also be possible to make the induction loop 2 wider, so that the width of the induction loop 2 corresponds to the thickness of the workpiece 1 or is also greater.

As FIGS. 1 and 2 show, the induction loop 2 can advantageously have a coolant supply 3 and a coolant discharge 4 in order to be able to introduce it into a coolant channel 7 which extends inside the induction loop 2, in particular to be able to circulate through the said coolant channel 7 can and to cool the induction loop 2 by the coolant in the coolant channel 7 during hardening.

Said coolant channel 7 is formed in the interior of the induction loop 2 when the induction loop 2 is formed in layers by additive material application.

As FIGS. 3 and 4 show, the induction loop 2 can, however, also cover only a partial section of the toothing 8, for example extending over three adjacent tooth gaps 5. Here, too, it can advantageously be provided that the induction loop 2 fits snugly against the contours of the tooth gaps 5 and the teeth 6 delimiting the tooth gaps 5, so that a gap 9 with a constant gap size is achieved. The gap size mentioned can be essentially constant from the bottom of the tooth gaps 5 via the tooth flanks to the tips or heads of the teeth 6, as FIG. 3 shows.

In order to harden the entire toothing 8, after the hardening cycle of the tooth gaps 5 covered by the induction loop 2, the workpiece 1 can be rotated further by an angle which corresponds to the angle between the outermost tooth gaps detected by the induction loop 2. In other words it becomes the gear rotated by three teeth further to introduce the induction loop 2 into three tooth gaps 5 not yet hardened can. Alternatively, the gear can also be rotated further by an integral multiple of the angle mentioned, for example by six or nine teeth. As an alternative or in addition to rotating the gear wheel further, the induction loop 2 can also be rotated accordingly, that is to say it can be moved further in the circumferential direction of the gear wheel.

As FIGS. 5 and 6 show, the induction loop 2 can also be adapted to the contour of the toothing 8 in such a way that the gap 9 between the induction loop 2 and the toothing 8 does not remain exactly constant, but varies, in particular continuously and / or steadily larger and again becomes smaller in order to achieve 8 different hardness results, in particular special different hardness depths, at different sections of the toothing.

Independently of this, as FIGS. 5 and 6 show, two or more induction loops 2 can also be used at the same time, wherein each of the induction loops 2 can have a coolant inlet 3 and a coolant outlet 4. Advantageously, the coolant supply connections 3 and the Kühlmit telabfuhran connections 4 can each be fed by a common inductor foot.

As FIGS. 7 and 8 show, separate contour sections that are separate from one another can also be hardened simultaneously on a workpiece 1. One or more induction loops 2 can be adapted in shape to different contour sections of the workpiece 1, the contour sections mentioned in particular having different diameters and / or being able to be axially spaced from one another.

As FIGS. 7 and 8 show, a toothed workpiece 1 can have two separate toothings 8 which, for example, can have different numbers of teeth and / or different pitch circle diameters. For example, a Stu fenzahnkranz with two gears 8 can be hardened by both Verzahnun gene 8 at the same time an induction loop 2 is assigned. Any induction loop 2 can be precisely matched to the toothing contour in the manner mentioned, if necessary with a desired variation of the gap size.

Advantageously, the induction loop 2 can completely surround both toothings 8, but if necessary, similar to FIGS. 3 to 6, only a partial sector can be covered by the induction loop 2 in one or both toothings 8.

As FIGS. 7 and 8 show, two separate induction loops 2 can be used, each of which can have a coolant supply 3 and a coolant discharge 4, which can be fed from a common inductor base. Alternatively, however, it would also be possible to train a continuous induction loop 2, which encloses both toothings 8 in a correspondingly adapted shape.

Claims

1. A method for inductive hardening of a workpiece (1), in particular a toothed and / or corrugated and / or corrugated workpiece such as a gearwheel, chain wheel or saw blade, a shape-adapted induction loop (2) being guided or set over the surface of the workpiece to be hardened, characterized in that the induction loop (2) is formed in layers by the additive application of material and is adapted in shape to the surface to be hardened.

2. The method according to the preceding claim, wherein the induction loop (2) is formed by means of a 3D printing head in the 3D printing process and adapted to the shape of the surface to be hardened, the induction loop being built up in layers in the 3D printer and possibly by thermal post-treatment is solidified.

3. The method according to any one of the preceding claims, wherein the induction loop (2) is adapted to more than three or more than five or more than ten tooth gaps (5) or wave troughs of the workpiece (1) and more than three or more than five or more than ten tooth gaps (5) of the workpiece (1) are hardened at the same time by said induction loop (2).

4. The method according to any one of the preceding claims, wherein the induction loop (2) is made hollow in layers by the additive material application such that a coolant channel (7) running through the induction loop (2) is formed, and through in the coolant channel (7 ) be sensitive cooling medium during hardening the induction loop (2) is cooled.

5. The method according to any one of the preceding claims, wherein more than 25% or more than 50% or more than 75% of the entire toothing and / or corrugation and / or corrugation contour to be hardened by the induction loop (2) and simultaneously are hardened at the same time.

6. The method according to any one of the preceding claims, wherein the induction loop (2) by the additive application of material in layers to two ver different, axially spaced and / or different diameter toothing contours of the toothed work piece adapted and the said different Verzahnungskontu ren of the toothed workpiece (1) simultaneously hardened by the induction loop (2).

7. Device for inductive hardening of a workpiece (1), in particular a toothed and / or corrugated workpiece such as a toothed wheel, chain wheel or saw blade, with at least one induction loop (2) adapted to the shape of the surface of the workpiece (1) to be hardened, characterized in that, that the induction loop (2) is designed as a layered structure, the material layers of which are solidified individually layer by layer.

8. Device according to the preceding claim, wherein the induction loop (2) is made by means of a 3D printer in the 3D printing process.

9. Device according to one of the two preceding claims, wherein the induction loop (2) in its interior has a coolant channel (7).

10. Device according to one of the preceding claims, wherein the Indukti onsschleife (2) on more than three or more than five or more than ten tooth gaps or wave troughs of the toothed or corrugated workpiece and more than three or more than five or surrounds more than ten neighboring tooth gaps or wave troughs at the same time.

11. Device according to one of the preceding claims, wherein the Indukti onsschleife (2) has at least one portion with a continuously changing curvature.

12. Device according to one of the preceding claims, wherein the Indukti onsschleife (2) has at least one straight and at least one curved portion, which are verbun by a bent portion to each other.

13. Device according to one of the preceding claims, wherein the Indukti onsschleife (2) sits on different, mutually different diameter having sectors of a gear shape-adapted loop sections be.

14. Device according to one of the preceding claims, wherein the induction loop (2) is adapted to a plurality of tooth gaps (5) and a plurality of teeth (6) so that a gap (9) between the induction loop (2) and the toothing (8) has a constant, constant gap dimension over the several tooth gaps (5) and several teeth (6).

15. Device according to one of claims 7 to 13, wherein the induction loop (2) is adapted to a plurality of tooth gaps (5) and a plurality of teeth (6) in such a way that a gap (9) between the induction loop (2) and the toothing (8 ) across the multiple tooth gaps (5) and multiple teeth (6) a constantly changing, cyclically larger and smaller gap be seated.

16. Device according to one of claims 7 to 15, wherein the induction loop (2) extends over more than 25% or more than 50% or more than 75% of the length of the toothing (8) of the workpiece (1).

17. Device according to one of claims 7 to 16, wherein the induction loop (2) extends over the entire toothed circumference of a gear or over the entire length of the toothing of a rack.

18. Device according to one of the preceding claims, wherein the Indukti onsschleife (2) has two separate induction loop sections which are axially spaced from each other and limit envelope contours of different diameters such that the two induction loop sections are adapted to different toothings (8) of a toothed ring.

19. Device according to the preceding claim, wherein each induction loop section surrounds more than three tooth gaps (5), preferably in each case enclosing the entire toothing (8).

20. Device according to one of the preceding claims, wherein the Indukti onsschleife (2) has at least one coolant channel inside.