METHOD FOR PRODUCING A CAMSHAFT

Abstract

A method for producing a camshaft may include: providing at least two metallic components; and welding the at least two components to one another via a combined induction/friction welding method. According to an implementation, one of the at least two components is a camshaft tube and the other of the at least two components is a drive element.

Claims

1. A method for producing a camshaft comprising: providing at least two metallic components; and welding the at least two components to one another via a combined induction/friction welding method.

2. The method according to claim 1, wherein providing the at least two components includes arranging a drive element as one of the at least two components on a longitudinal end of a camshaft tube as the other of the at least two components.

3. The method according to claim 1, wherein the combined induction/friction welding method includes: heating opposite surfaces of the at least two components via an induction heater to a predetermined temperature that is greater than a re-crystallization point of the at least two components in a non-oxidizing atmosphere; continuously moving at least one component relative to the other component of the at least two components parallel to the opposite surfaces; bringing together the opposite surfaces of the at least two components to be connected to one another with an axial force while at least one of the at least two components is in motion to weld the opposite surfaces of the at least two components to one another, wherein at least approximately 90% of the welding energy is contributed by the induction heater and the equalizing welding energy is contributed by common friction welding, and wherein a loss of total length of the at least two components is less than 1.0 axial millimeters per millimeter of a wall thickness of the at least two components.

4. The method according to claim 3, wherein heating the opposite surfaces of the at least two components to the predetermined temperature is performed in a time of less than approximately 30 seconds.

5. The method according to claim 1, wherein the combined induction/friction welding method welding opposite surfaces of the at least two components to one another in approximately one second after heating the opposite surfaces to a predetermined temperature, and maintaining an axial force of the at least two components held against one another for approximately five seconds.

6. The method according to claim 1, wherein the combined induction/friction welding method includes rotating at least one of the at least two components and welding opposite surfaces of the at least two components to one another in less than approximately four rotations after heating the opposite surfaces to a predetermined temperature, and maintaining an axial force of the at least two components held against one another until a welding temperature falls below the predetermined temperature.

7. The method according to claim 1, wherein the combined induction/friction method includes inductively heating opposite surfaces of the at least two components to a predetermined temperature that is greater than a re-crystallization point of the at least two components in a time of less than approximately ten seconds.

8. Method according to claim 1, wherein the combined induction/friction welding method includes heating opposite surfaces of the at least two components via an induction heater at a frequency of approximately 10 Kilohertz or more.

9. The method according to claim 1, wherein the combined induction/friction welding method overflowing opposite surfaces of the at least two components with a non-oxidizing gas composed of predominantly nitrogen gas while heating the opposite surfaces to a predetermined temperature greater than a re-crystallization point of the at least two components via an induction heater.

10. The method according to claim 1, wherein welding the at least two components to one another includes keeping opposite surfaces of the at least two components substantially in a vacuum atmosphere.

11. The method according to claim 10, wherein welding the at least two components to one another further includes heating the opposite surfaces in a vacuum to a predetermined temperature greater than a re-crystallization point of the at least two components via an induction heater.

12. The method according to claim 1, further comprising precoating opposite surfaces of the at least two components with a metallurgically compatible material and a thickness of less than 0.025 mm after heating the opposite surfaces to a predetermined temperature greater than a re-crystallization point of the at least two components via an induction heater.

13. The method according to claim 1, wherein welding the at least two components to one another includes: continuously moving at least one of the at least two components in a rotational movement.

14. A camshaft, comprising: a camshaft tube and a drive element, the drive element joined to a longitudinal end of the camshaft tube at a combined induction/friction welded connection.

15. The method according to claim 1, further comprising inductively heating opposite sides of the at least two components to a predetermined temperature that is greater than a re-crystallization point of the at least two components in a time of less than approximately ten seconds before welding the at least two components to one another.

16. The method according to claim 1, further comprising: inductively heating opposite surfaces of the at least two components to a predetermined temperature greater than a re-crystallization point of the at least two components; and overflowing opposite surfaces of the at least two components with a non-oxidizing gas while the at least two components are at the predetermined temperature.

17. The method according to claim 16, wherein the non-oxidizing gas is composed of predominately of nitrogen gas.

18. The method according to claim 3, wherein the induction heater is arranged between the opposite surfaces of the at least two components during the heating.

19. The method according to claim 7, wherein the opposite surfaces of the at least two components are parallel to one another.

20. A method of producing a camshaft, comprising: welding a drive element to a longitudinal end of a camshaft tube via a combined induction/friction welding technique, the combined induction/friction welding technique including inductively heating opposite surfaces of the drive element and the camshaft to a predetermined temperature that is greater than a re-crystallization point of the at least two components at a frequency of approximately 10 Kilohertz or more.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In each case schematically:

[0029] FIG. 1A shows a partial longitudinal section of a camshaft, which is welded according to a common friction welding method;

[0030] FIG. 1B shows a partial side cross sectional view of a camshaft, which is welded according to the solid state welding method of the invention;

[0031] FIG. 1C shows a partial longitudinal section of a second embodiment according to a camshaft, which is welded according to the solid state welding method of the invention,

[0032] FIG. 2A shows a longitudinal section of an area of the device for the solid state welding method,

[0033] FIG. 2B shows a sectional illustration along the sectional plane B-B,

[0034] FIG. 3 shows a camshaft, which is welded by means of the method according to the invention.

DETAILED DESCRIPTION

[0035] FIG. 1A illustrates a welded camshaft 111, which is produced according to common friction welding techniques, such as, e.g., common flywheel friction welding. The camshaft 111 thereby has a component 11, for example a camshaft tube, and a component 10, for example a drive element, which are welded to one another by means of friction welding by rotating one of the components 10, 11 relative to the other component 11, 10 by simultaneously pressing against one another. In response to the friction welding, the opposite surfaces heat to the hot work temperature. The excess welding burr material thereby forms the largest problem of such friction welded connections, both on the inner and on the outer sides of the welded connection, which has the appearance of a double torus.

[0036] In particular in the case of camshafts 111, this welding burr detail F1 must be removed, which is associated with additional effort or which is disadvantageous, respectively, with regard to notching effect, dirt trap or increased corrosion risk (inner side), respectively. As specified above, the large welding burr volume results from the loss of length in the welding interface as a deterioration of the welded connection strength due to concentration of non-metallic inclusions. The solid state welding method according to the invention thus does not only reduce the material loss and the length during the welding cycle, but also improves the structural integrity.

[0037] FIGS. 1B and 1C represent the characteristic profiles of welded connections established according to the method according to the invention.

[0038] In FIG. 1C, the induction coil 9 is dimensioned appropriately, which results in a completely connected outer welding burr F4. The total quantity of welding burr material F4 and F5 can also be reduced. The welding burr volume and the loss of length was reduced significantly in both embodiments illustrated in FIGS. 1B and 1C, and the integrity of the welded connection was improved.

[0039] The combined induction/friction welding method according to the invention thereby comprises the following steps: [0040] heating opposite, in particular parallel surfaces of the components 10, 11, by means of an induction heater 40 to a first temperature, which is above the re-crystallization point of the components 10, 11 of a non-oxidizing atmosphere, in that the induction heater 40 is in particular arranged between the opposite surfaces, [0041] continuously moving at least one component 10, 11 relative to the other component 10, 11 parallel to the opposite surfaces, [0042] bringing together the opposite surfaces of the components 10, 11, which are to be connected to one another, with an axial force, while at least one of the components 10, 11 is still moved, in order to weld the opposite surfaces of the components 10, 11 to one another, wherein a portion, preferably at least approximately 90% of the welding energy, is contributed by the induction heater 40 and the equalizing welding energy is contributed by common friction welding, and wherein a loss of total length of the components 10, 11 is less than 1.0 axial millimeters per millimeter of the wall thickness of the components 10, 11.

[0043] It is a particular advantage of the production method according to the invention that only a fraction of the axial length is used, whereby a much smaller volume of welded connection burr is generated. In contrast to the previous friction welding methods, the welding method according to the invention does in fact start before the two matching components come into contact. The induction heating phase, which provides the majority of the required welding energy, runs together with the acceleration of the rotating component 10, 11 and ends a few tenth of a second before the contact of the two components 10, 11 takes place. This is necessary in order to ensure retraction of the induction coil 9 between the components 10, 11 and the subsequent closing of the axial gap to the contact.

[0044] In the example of the bringing together of two components 10, 11, which are embodied with clean, smooth, straight-cut parallel ends, the induction coil 9 can be arranged between opposite longitudinal ends of the two components 10 and 11, which leaves a small gap 12 and 13 on each side. The induction coil 9 is normally a coil, which is wound once and is formed of hollow rectangular copper pipe in order to allow cooling water to circulate during the induction-heating cycle.

[0045] In the alternative, it is also conceivable to attach the induction heater 40 on the outside, so that it encompasses the opposite surfaces, which are to be welded to one another, or surrounds them in a ring-shaped manner, respectively. The induction coil 9 thereby forms a ring, which surrounds the camshaft 111.

[0046] The induction coil 9 is connected to a high frequency power supply either by means of flexible power supply cables or in the alternative by means of rotary or sliding joints. The size of the gap 12 and 13 is normally adjusted to the possible minimum value prior to the beginning of the physical contact and/or prior to the flashover between the induction coil 9 and one of the components 10 and 11, either during the heating phase or during the retraction. If the two components 10 and 11 have the same diameter, wall thickness and metallurgy, the induction coil 9 is arranged at the same distance between the opposite ends of the components 10, 11. In uses, where one or a plurality of these three parameters between the two components 10, 11 of the camshaft 111 are different, the equalization of the heat supply to the two components 10, 11 is attained by moving the induction coil 9 closer to the component 10 or 11, which requires the extra heat supply. It is the primary goal of the gap adjustment to ensure that both components 10, 11 reach their respective hot work temperature at the same time. The gap 12, 13 can either be determined and adjusted prior to the start of the induction heating phase or, in the alternative, continuously during the induction heating by means of a non-contact temperature sensor.

[0047] The gaps 12 and 13 serve two purposes. First of all, they avoid physical contact between the induction coils 9 and one of the components 10 and 11, which would lead to a contamination of the component surface and an electrical short-circuit of the induction coil 9. In addition, they represent a path for the flow of a protective gas 14, which avoids an unwanted oxidation of the heated ends of the components 10 and 11. Even though nitrogen is preferred in many uses for the above-specified reason, the protective gas can be nitrogen, carbon dioxide, argon or other non-oxidizing gases or mixtures thereof, chosen according to the metallurgical requirements and availability at the workplace. On the outer side, the gas is surrounded by a flexible curtain 15, which abuts closely around the outer circumference of each component 10, 11, whereby the gas 14 is forced to flow radially inwards and thus continuously displaces any oxygen away from the released component ends. Provision is furthermore made for allowing a retraction of the induction coil 9, while the flexible curtain 15 is held in position.

[0048] The selection of a suitable protective gas 14 depends primarily on the metallurgy of the components 10, 11 and on the high temperature ionization properties of the gas 14. Nitrogen is sufficient for most of the uses, which relate to ferrous compounds and nickel-based alloys. For certain metallurgies, however, a different gas may be necessary, e.g. in the case of titanium compounds. Even though it is preferred to use a suitable protective gas 14, it should be recognized that the components 10, 11 can be protected against harmful gases by alternative and additional methods, such as, e.g. precoating. For this purpose, the opposite surfaces of the components 10, 11 can be precoated directly with a protective barrier substance, such as, e.g., a chloride-based flux material, which preferably rules out hydrogen.

[0049] FIG. 3 now shows a camshaft 111, which is produced according to the method according to the invention, comprising a drive element and a camshaft tube.