Quenching a wheel comprising a hub

Abstract

The invention relates to a component in the form of a wheel comprising: a hub portion, a rim portion with an outer rim flange and an inner rim flange, a plurality of circumferentially distributed spokes extending between the hub portion and the rim portion, wherein the spokes and the hub portion are arranged offset with respect to a wheel center plane towards the outer rim flange and have an inner side facing the wheel center plane and an outer side directed away from the wheel center plane, wherein the outer rim flange has greater tensile residual stresses at least in a partial region than at least a partial region of the inner rim flange.

Claims

1. A method of quenching a component, wherein the component is configured in form of a wheel comprising a hub portion, a rim portion, and a plurality of circumferentially distributed spokes extending between the hub portion and the rim portion, wherein the rim portion comprises an outer rim flange, a rim bed and an inner rim flange, with a wheel center plane defined between the outer rim flange and the inner rim flange, wherein the spokes and the hub portion are arranged offset with respect to the wheel center plane towards the outer rim flange and have an inner side facing the wheel center plane and an outer side facing away from the wheel center plane, wherein the method comprises: quenching the spokes; and then quenching the hub portion after quenching the spokes has started.

2. The method of claim 1, wherein the method comprises: quenching the hub portion and then quenching the rim bed after quenching the hub portion has started.

3. The method according to claim 2, wherein quenching is carried out with a pressure of at least 30 bar.

4. The method according to claim 1, wherein the method comprises: quenching the inner rim flange and then quenching the rim bed after quenching the inner rim flange has started.

5. The method according to claim 1, wherein quenching is carried out by a liquid-gas mixture.

6. The method according to claim 1, wherein quenching is carried out with at least four separately controllable cooling units which are controlled in time sequence.

Description

BRIEF SUMMARY OF THE DRAWINGS

(1) Exemplary embodiments are explained below with reference to the figures of the drawings. Herein:

(2) FIG. 1 shows a wheel in perspective view from obliquely outside;

(3) FIG. 2 shows the wheel of FIG. 1 in axial view;

(4) FIG. 3 shows the wheel according to section line III-III of FIG. 2;

(5) FIG. 4 shows the wheel according to section line IV-IV of FIG. 2;

(6) FIG. 5 shows the wheel of FIG. 1 in radial view with residual stresses drawn on the inner and outer rim flange;

(7) FIG. 6 schematically shows the residual stress distribution in an edge layer of the outer side of a spoke;

(8) FIG. 7 shows the wheel with residual stresses in the region of a spoke and a rim portion;

(9) FIG. 8 shows the wheel in FIG. 1 in a radial view with the rim bed cut open;

(10) FIG. 9 shows a wheel in a modified embodiment in semi-longitudinal section with residual stress distribution schematically drawn in the edge layer of the outer side and the inner side of a spoke;

(11) FIG. 10 shows the wheel of FIG. 9 in a radial view with the rim bed cut open;

(12) FIG. 11 shows a device for quenching a wheel, in a schematic longitudinal section;

(13) FIG. 12 shows a time-temperature diagram during quenching according to the invention; and

(14) FIG. 13 shows a time-temperature diagram during quenching not according to the invention.

DESCRIPTION

(15) FIGS. 1 to 10, which are described together below, show an exemplary component in the form of a wheel 2.

(16) The wheel 2 has a hub portion 3, circumferentially distributed spokes 4 connecting thereto and a rim portion 5. The hub portion 3 serves for centering and fastening the wheel 2 to a vehicle wheel hub. For this purpose, the hub portion 3 has a central centering hole 6 and a plurality of circumferentially distributed through holes 7, which jointly are also referred to as a hole circle and through which respective fasteners can be inserted. According to an alternative embodiment, instead of a hole circle, the hub may also be configured with only one central hole for centering and simultaneous fastening. The rim portion 4, also referred to as the rim for short, is configured to receive a tire. The rim 4 comprises an outer rim flange 8, a rim bed 9 and an inner rim flange 10. The wheel 2 has an axis A about which it can rotate in a mounted condition.

(17) In particular, it can be seen in FIG. 3 that the hub portion 3 and the spokes 4, together also referred to as the wheel spider, are offset with respect to a wheel center plane E lying between the two rim flanges 8, 9. The wheel 2 has an outer side 12 which is visible when the wheel is mounted, and an inner side 13 which faces the vehicle when the wheel is mounted.

(18) FIG. 4 shows a half-longitudinal section through a spoke 4 of the finished component. FIG. 5 shows the rim 2 in a radial view with schematically drawn residual stresses S8 in the outer rim flange 8 and schematically drawn residual stresses in the inner rim flange 10. FIG. 6 shows the residual stress distribution in an edge layer of the outer side 12 of a spoke 4, wherein the outer contour K1 in FIG. 5 represents the raw component with production oversize, while the inner contour K2 represents the contour of the finished component. All the features described herein can refer both to the raw component, for example a raw casting or a raw forging, and to the finished machined component.

(19) As can be seen in particular from FIG. 5, the wheel 2 is produced such that the outer rim flange 8 and the inner rim flange 10 respectively have, at least in partial regions, tensile residual stresses effective in the circumferential direction about the longitudinal axis A, which are shown schematically by small arrows S8, S10. It is provided that the tensile residual stresses S8 of the outer rim flange 8 are greater than the tensile residual stresses S10 of the inner rim flange 10. It is understood that the outer rim flange 8 can have tensile residual stresses only in circumferential partial regions and can be free of residual stresses in others and/or that the inner rim flange 10 can be free of residual stresses or be subject to compressive residual stresses at least in circumferential partial regions. In this case, the tensile residual stresses of the outer rim flange 8 are greater than the residual stresses of the inner rim flange 10, at least in a circumferential partial region.

(20) It can further be seen in FIG. 6 that the spokes 4 have compressive residual stresses in the radial direction in at least one edge layer 14 of the outer side 12, which are shown by small arrows S14. It is provided that the compressive residual stresses in the edge layer 14 of the outer side 12 are greater than in the edge layer 15 of the inner side 13. This may relate to a section of the radial extension of a respective spoke 4 or to the entire radial extension of the spoke. It is possible that the compressive residual stresses vary over the radial extension of the spokes 4. In the unloaded state, preferably the edge layer 14 of the entire outer side 12 of the spokes 4 is subject to compressive residual stress and/or is free of tensile residual stress.

(21) In the present embodiment, not only sections of the spokes 4 are subjected to compressive residual stresses, but the entire spokes as such are each subjected to compressive stresses. In other words, according to a theoretical model, the spokes are clamped between the hub portion 3 and the rim ring 5, that is, forces directed radially outwardly from the hub portion 2 act on the inner ends of the spokes 4, while forces directed radially inwardly from the rim ring 5 act on the outer ends of the spokes 4. This applies at least to an edge layer of the outer side 12. In an edge layer of the inner side 13, lower compressive residual stresses are present than in the edge layer of the outer side 12, wherein tensile residual stresses may also be present here. Overall, the spokes 4 are thus under radial compressive load, at least in the region of the outer side 12, whereas the rim 5 is under tensile load in the circumferential direction. These load conditions are shown in FIG. 7, in which, by way of example, the compressive load in a spoke 4 is represented by arrows F4 acting towards each other and the tensile load in the rim 5 is represented by dashed arrows F5 pointing away from each other.

(22) Such a load condition can be determined, for example, by means of the free-cutting method. In this case, the rim bed 9 is axially cut open between two spokes 4 adjacent in the circumferential direction. When the rim portion 5 is under tensile load in the circumferential direction, and/or the spokes 4 are under compressive load, the cut-open ends of the rim portion 5 spring open. FIG. 8 shows the wheel 2 in radial view with the rim portion 5 cut open. The slit 16 created by the springing open of the free-cut rim segments 17, 18 is clearly visible. The slot 16 opens from the inner rim flange 10 in an axial direction towards the outer rim flange 8. This means that the tensile residual stresses S8 at the outer rim flange 8 are greater, respectively were greater before cutting, than the residual stresses 10 (compressive or tensile residual stresses) of the inner rim flange 8.

(23) FIGS. 9 and 10 show a component for a wheel 2 in a modified embodiment. This corresponds to a wide extent to the embodiment according to FIGS. 1 to 8, to the description of which reference is made in this respect. The same details are provided with the same reference signs as in the above figures.

(24) In common with the above embodiment, the wheel 2 shown in FIGS. 9 and 10 has residual compressive stresses S14 in the edge layer of the outer side 14 of the spokes 4. In contrast, the spokes 4 in the edge layer 15 of the inner side 13 are under tensile residual stresses S15. The wheel 2 has a variable residual stress distribution over the axial extension L of the spokes 4, which changes from compressive residual stresses S14 to tensile residual stresses S15 starting from the edge layer 14 of the outer side 12 to the edge layer 15 of the inner side 13. Inside the spokes 4 is a residual stress-free transition layer, in which the stresses change from compressive to tensile residual stresses. In this embodiment, as a theoretical model, the spokes 4 are clamped in the outer edge layer 14 between the hub portion 3 and the rim ring 5. Consequently, on the axially outer side 12 of the wheel 2, radially outwardly directed forces act from the hub portion 3 on the radially inner ends of the spokes 4, while radially inwardly directed forces act from the rim ring 5 on the radially outer ends of the spokes 4. In contrast, tensile residual stresses S15 are present in the edge layer 15 of the inner side 13, that is, on the axially inner side of the rim spider, forces directed radially inwardly act from the hub portion 3 on the radially inner ends of the spokes 4, while forces directed radially outwardly act from the rim ring 5 on the outer ends of the spokes 4. Overall, the spokes are thus under radial compressive load in the region of the outer side 14 and under radial tensile load in the region of the inner side 13. Accordingly, the rim portion 5 is subjected to tensile loading in the circumferential direction in the region of the outer rim flange 8, while it is subjected to compressive loading in the circumferential direction in the region of the inner rim flange 10.

(25) In this embodiment with the residual stresses mentioned, the result of cutting free the rim bed 5 in the circumferential region between two spokes 4 is that the cut-free ends 17, 18 of the rim bed spring open in the axial region of the outer rim flange 8, while they approach each other in the axial region of the inner rim flange 10. Overall, this embodiment results in a gap 16 tapering from the outer rim flange 8 towards the inner rim flange 10, as shown in FIG. 10, whereby the opening angle of the gap is greater here than in the above embodiment.

(26) For both embodiments described above, the material used for the wheel may be, for example, a light metal such as aluminum or an aluminum alloy or magnesium or a magnesium alloy, without being limited thereto. For example, a cast aluminum alloy may comprise at least 93.0 weight percent aluminum, 3.5 to 5.0 weight percent silicon, 0.2 to 0.7 weight percent magnesium, and optionally other alloying elements of up to 1.5 weight percent.

(27) After the blank has been produced, for example by casting, forging or milling, it is heat treated, in particular subjected to a solution annealing. After the heat treatment, the component is quenched, wherein the component 2 can be precooled after the solution annealing and before the quenching. The quenching is carried out in particular such that the desired residual stress distribution is produced in the component.

(28) FIG. 11 shows a device 20 according to the invention for quenching a component in the form of a wheel 2. It can be seen that the device 20 comprises a plurality of cooling units 21, 22, 23, 24, 25 for quenching the wheel 2. In the present embodiment, at least one cooling unit 21, 25 for quenching the hub 3; at least one cooling unit 22 for quenching the spokes 4; at least one cooling unit 23 for quenching the outer sides 12 of the rim 5; and at least one cooling unit 24 for quenching the inner rim flange 10 are provided. There may further be provided at least one cooling unit for quenching the outer rim flange 8 and/or at least one cooling unit for quenching the inner side 13 of the rim 5 (not shown).

(29) The cooling units 21, 22, 23, 24, 25 are configured to respectively spray a cooling medium onto the wheel. They are separately controllable by a control unit (not shown) with respect to the start and duration of the cooling and, optionally, at least one further parameter influencing the quenching effect, such as temperature or pressure of the cooling medium. The cooling medium used is, for example, steam or a liquid-gas mixture, in particular water or a water-air mixture. The cooling units 21, 22, 23, 24, 25 comprise corresponding nozzles through which the spray mist is sprayed onto the component 2 at high pressures. In this respect, the quenching can be carried out with high nozzle pressures of at least 30 bar, in particular at least 80 bar. High cooling rates of at least 75 K/s, in particular with at least 90 K/s or even more than 100 K/s can be achieved with the device 20.

(30) It can be seen that the quenching device 20 comprises a first device part 31 on which the cooling units 24, 25 are arranged that act on the inner side 13 of the wheel 2, and a second device part 32 on which the cooling units 21, 22, 23 are arranged that act in a cooling manner on the outer side 12 of the wheel 2. In the present embodiment, the second device part 32, which may also be referred to as the upper part, is configured to be axially movable relative to the first device part 31, which may also be referred to as the lower part, as indicated by the arrow P on the right-hand side. The two device parts 31, 32 are configured in a housing-like manner. The wheel 2 is placed on a support element 33 of the first device part 31, then the upper device part 32 is lowered towards the wheel 2 until the desired distance is reached. Finally, the quenching process begins. The lower device part 31 may comprise a rotating unit for rotationally driving the wheel 2 during quenching.

(31) The cooling units for quenching the wheel 2 may, for example, be actuated in the following order: the cooling units 22 for cooling the outer side 12 of the spokes 4 before the cooling units 21 of the hub portion 3, then the cooling units 22 for cooling the inner side 13 of the hub portion 2, then the cooling units 25 for cooling the inner side 13 of the rim bed 9 and/or of the hub portion 3, and then the cooling units 23 for cooling the outer side 12 of the rim bed 9. The cooling units 24 for cooling the inner rim flange 10 can be activated in time with the cooling of the outer side 12 of the spokes 4, timely before the cooling units 21, 25 of the hub portion 2 and/or before the cooling units 23 of the rim bed.

(32) The cooling respectively quenching with the individual cooling units starts in the above-mentioned sequence, but can then continue at least partially with time overlap of the individual cooling units, namely respectively until the desired target temperature is reached in the wheel region to be cooled. Quenching may be carried out for example until the ageing out temperature is reached. After ageing, the wheel can be cooled to room temperature, in particular by means of water.

(33) FIG. 12 shows a time-temperature diagram during quenching according to the invention from the initial temperature Ts after solution annealing to the room temperature T. The time is plotted on the x-axis, the temperature T is plotted on the y-axis. Four curves are drawn, namely a first one for temperature T312 in the area of hole circle 3 on the outer side 12, a second one for temperature T313 in the area of hole circle 3 on the inner side 13, a third one for temperature T4 in a spoke 4 and a fourth one for temperature T10 at the inner rim flange 10. It can be seen that the four curves run adjacent to each other and substantially equidistant to each other, that is to say that the maximum temperature differences occurring in the wheel 2 at a respective time are particularly small. This leads overall to low residual stresses, respectively a favorable distribution of residual stresses in the wheel 2, which in turn contributes to a long service life.

(34) Compared with this, FIG. 13 shows a time-temperature diagram during quenching for a conventional quenching process, i.e. not according to the invention, in a water bath. Six curves are drawn, namely a first one for the temperature T312 in the area of the hole circle on the outer side, a second one for the temperature T313 in the area of the hole circle on the inner side, a third one for the temperature T4 in a spoke and a fourth one for the temperature T10 at the inner rim flange, a fifth one for the temperature T8 at the outer rim flange and a sixth one for the temperature T9 at the rim bed. It can be seen that the six curves fall at different times, meaning that cooling starts at different times in the different areas. In addition, starting from the starting temperature Ts (approximately solution annealing temperature), the temperature curves diverge significantly from one another as time increases. These two facts lead to particularly high maximum temperature differences Tmax in wheel 2 and thus to high residual stresses in wheel 2.

LIST OF REFERENCE SIGNS

(35) 2 wheel 3 hub portion 4 spokes 5 rim portion 6 center hole 7 through holes 8 outer rim flange 9 rim bed 10 inner rim flange 12 outer side 13 inner side 14 edge layer 15 edge layer 16 slit 17 cut-free end 18 cut-free end 20 device 21-25 cooling units 31 device part 32 device part 33 support element A axis E plane K contour L extension P arrow S residual stress T temperature t time