JOINT-SITE STRUCTURE FOR COMPONENTS TO BE CONNECTED BY MEANS OF OVERLAP FRICTION WELDING, AND METHOD FOR CONNECTING COMPONENTS BY MEANS OF FRICTION WELDING

Abstract

A joint-site structure for components to be connected by overlap friction welding. At least one step of at least one component, on which an axially set-back ring-shaped joining surface is situated, is provided with a radial undercut, in such a manner that on the face side, a region of this step that is unchanged in diameter forms a radial support ridge, which is connected with the at least one component by way of a heat throttle that is reduced in cross-section. The length of each step is designed in such a manner that when the face surface of the one component makes contact with the ring-shaped joining surface of the other component, the other face surfaces of these components, which surfaces lie opposite one another in the same radial position, are still exposed until completion of the friction-welding process.

Claims

1. A joint-site structure comprising: first and second components having first and second ends, respectively, to be connected using a friction welding process; wherein the first end has a first thin-walled coaxial insertion region and the second end has a second thin-walled coaxial insertion region; wherein the first thin-walled coaxial insertion region has at least one step having a smaller diameter as compared with an outside diameter of the first component; wherein the at least one step forms a ring-shaped face surface set back axially relative to a first face surface of the first component and is configured as a joining surface for friction welding; wherein the second component has a second face surface abutting against the joining surface; wherein the first thin-walled coaxial insertion region has a first mantle surface and the second thin-walled coaxial insertion region has a second mantle surface; wherein the first and second mantle surfaces engage into one another and a radial gap is situated between the first and second mantle surfaces; wherein the at least one step is provided with a radial undercut so that on a face side a region of the at least one step is unchanged in diameter and forms a radial support ridge connected with the first component by way of a heat throttle having a reduced cross-section; and wherein the at least one step has a length designed so that when the first face surface of the first component makes contact with a ring-shaped joining surface of the second component, other face surfaces of the first and second components lying opposite one another in an identical radial position remain exposed until completion of the friction-welding process.

2. The joint-site structure according to claim 1, wherein the first and second components have an identical number of steps.

3. The joint-site structure according to claim 1, wherein each of the first and second components has at least first and second steps, and a respective radial undercut introduced into each of the first steps viewed from the first face surface of the first component and a second face surface of the second component, respectively.

4. The joint-site structure according to claim 1, wherein the ring-shaped joining surfaces are configured as a truncated cone.

5. The joint-site structure according to claim 1, wherein the undercut has a first flank comprising a radial extension of the ring-shaped joining surface of the first component.

6. The joint-site structure according to claim 5, wherein the undercut has a second flank lying opposite the ring-shaped joining surface of the first component and extending at an angle of less than 90° relative to a longitudinal axis of the first and second components.

7. The joint-site structure according to claim 1, wherein the at least one step has a first wall thickness amounting to at least 0.6 times the wall thickness of the first component in the first thin-walled coaxial insertion region.

8. The joint-site structure according to claim 7, wherein the heat throttle of the first component has a second wall thickness amounting to 0.1 to 0.3 times the first wall thickness of the at least one step of the first component in the first thin-walled coaxial insertion region.

9. The joint-site structure according to claim 1, wherein the support ridge of the first component has a third wall thickness less than or equal to a difference of the wall thickness of the first component in the first thin-walled coaxial insertion region and 1.1 times the first wall thickness of the at least one step of the first component.

10. A method for connecting first and second components using overlap friction welding comprising: providing first and second components having first and second ends, respectively, wherein the first end has a first thin-walled coaxial insertion region and the second end has a second thin-walled coaxial insertion region, wherein the first thin-walled coaxial insertion region has at least one step having a smaller diameter as compared with an outside diameter of the first component, and wherein the at least one step forms a ring-shaped face surface set back axially relative to a first face surface of the first component and is configured as a joining surface for friction welding; first, inserting the first and second thin-walled coaxial insertion regions of the first and second components, respectively, axially into one another until the first face surface of the first component abuts against a joining surface of the second surface, wherein a radial gap forms between mantle surfaces of the first and second thin-walled coaxial insertion regions that engage into one another; subsequently putting at least one of the first and second components into rotation and pressing the first and second components against one another by an axially acting process force until material of at least one of the first and second components softens; wherein the at least one step is provided with a radial undercut so that on a face side of a region the at least one step is unchanged in diameter and forms a radial support ridge connected with the first component by way of a heat throttle having a reduced cross-section; wherein the at least one step has a length designed so that at a beginning of a friction welding process, a wide axial ring gap is present between the first face surface of the first component and a second face surface of the second component lying opposite in an identical radial position; and wherein the wide axial ring gap is reduced to a minimum width during action of the axially acting process force on the first and second components at an end of the friction-welding process.

11. The method according to claim 10, wherein hollow shafts are used as first and second components that are connected with one another using overlap friction welding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings which show a preferred exemplary embodiment of the object according to the invention, using a connection between two pipes, and will be explained in greater detail below. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

[0033] In the drawings,

[0034] FIG. 1a shows the starting geometry of a joint-site structure according to the invention, of two pipes to be welded together, each having two steps,

[0035] FIG. 1b shows the joint-site structure from FIG. 1a in an enlarged representation,

[0036] FIG. 1c shows the joint-site structure from FIG. 1a and FIG. 1b with identification of the wall thicknesses,

[0037] FIG. 2a shows the two welded pipes after completion of the friction-welding process,

[0038] FIG. 2b shows the joint site from FIG. 2a in an enlarged representation,

[0039] FIG. 3a shows the starting geometry of a joint-site structure according to the invention, of two pipes to be welded together, of which only one has an inner step,

[0040] FIG. 3b shows the joint-site structure from FIG. 3a in an enlarged representation,

[0041] FIG. 4a shows the starting geometry of a joint-site structure according to the invention, of two pipes to be welded together, of which only one has an outer step,

[0042] FIG. 4b shows the joint-site structure from FIG. 4a in an enlarged representation,

[0043] FIG. 5a shows the starting geometry of a joint-site structure according to the invention, of two pipes to be welded together, which both have only one step and are flush at their outer circumference,

[0044] FIG. 5b shows the joint-site structure from FIG. 5a in an enlarged representation,

[0045] FIG. 6a shows the starting geometry of a joint-site structure according to the invention, of two pipes to be welded together, which both have only one step and are flush at their inner circumference, and

[0046] FIG. 6b shows the joint-site structure from FIG. 6a in an enlarged representation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0047] FIGS. 1a and 1b show the starting geometry of a joint-site structure according to the invention, of two pipes 1 and 2 that have rotation symmetry, are to be connected at their face sides by means of friction welding, and have the same wall thickness and weld seam preparation on both sides. The pipes can also be configured as hollow shafts, for example.

[0048] The first pipe 1 has a two-stair-step inner step on its face side that faces the second pipe 2 (this arrangement is equivalent to two inner steps having different diameters), so that on the face side, three ring-shaped face surfaces form, namely an outer face surface 3.1, a center face surface that is set back relative to the former and is referred to as a joining surface 4.1, which will still be explained below, and an inner face surface 5.1 that is once again set back axially relative to the joining surface 4.1. The joining surfaces 4.1 and 4.2 are structured conically in the present example.

[0049] The term “inner step” refers to the location of the step in the interior of the pipe 1, while the term “outer, center, and inner face surface” refers to their distance from the center axis 6 of the two pipes 1, 2. The second number after the period, within the reference number, in each instance, identifies the respective pipe 1 or 2, to which the characteristic identified by the first number belongs.

[0050] The second pipe 2 has a two-stair-step outer step (which is equivalent to two outer steps having different diameters) on its face side that faces the first pipe 1, which step has a coaxial counter-shape to the two-stair-step inner step of the first pipe 1, so that the two pipes 1, 2 can be easily inserted into one another with their steps before the start of the friction-welding process. The term “outer step” refers to the location of this step on the outer circumference of the pipe 2. On the face side, three ring-shaped face surfaces also form on the second pipe 2, by means of the two-stair-step outer step, namely an outer face surface 3.2, which lies opposite the outer face surface 3.1 of the pipe 1 in the same radial position, a center face surface, which is referred to as a joining surface 4.2 and will be explained below, and lies opposite the joining surface 4.1 of the first pipe 1, and an inner face surface 5.2, which lies opposite the inner face surface 5.1 of the first pipe 1 in the same radial position.

[0051] From FIG. 1b, it is evident that an undercut 7 that proceeds from the mantle surfaces of the stair steps, in each instance, is worked into the first stair step of the outer and inner step seen from their face sides, in each instance, in other words into the stair step having the greatest inside diameter, in the case of the first pipe 1, in other words into the step having the smallest wall thickness, and into the stair step having the smallest outside diameter in the case of the second pipe 2, in other words also into the step having the smallest wall thickness, so that a ring-shaped cross-section remains.

[0052] In the present example, the undercut 7 is structured as a radial extension of the conical joining surfaces 4.1 and 4.2 of the pipes 1 and 2, outward and inward, respectively, in each instance. The opposite flank of the undercut 7 is configured conically both in the case of the first pipe 1 and in the case of the second pipe 2.

[0053] At the deepest location of the undercut 7, in each instance, where the remaining ring-shaped cross-section of the steps of the pipes 1, 2 is smallest, a heat throttle 8 forms, in each instance, while the region of the steps that increases in cross-section again, in each instance, toward the outer face surface 3.1 of the first pipe 1 and toward the inner face surface 5.2 of the second pipe 2, or the region of the steps that is not affected by the undercut 7 forms a support ridge 9. An uninterrupted mantle surface of a step or of a stair step of the other pipe 1, 2, in each instance, lies radially opposite every support ridge 9, in each instance.

[0054] From FIG. 1b, it is furthermore evident that a radial gap 10 is present between the support ridge 9 of the first pipe 1 and the radially opposite uninterrupted mantle surface of the outer step of the second pipe 2, as well as between the support ridge 9 of the second pipe 2 and the radially opposite mantle surfaces of the inner step of the first pipe 1, in each instance. The radial gaps 10 have an axial connection with the respective undercut 7.

[0055] An additional characteristic that is essential to the invention is also evident from FIG. 1a and FIG. 1b, which show the position of the two pipes 1, 2 to be connected with one another, at the beginning of the friction-welding process: the two pipes 1, 2 touch only in the region of their center face surfaces, which simultaneously also form the joining surfaces 4.1 and 4.2 of the two pipes 1, 2. This result is achieved in that the axial length of the stair steps of the two-stair-step steps is also predetermined.

[0056] It can be seen that radially opposite steps of the two pipes 1, 2 are configured to have different lengths axially, so that a wide outer axial ring gap and a wide inner axial ring gap 11, 12 form between the respective opposite face surfaces of these steps when the joining surfaces 4.1 and 4.2 of the two pipes 1, 2 touch.

[0057] The outer axial ring gap 11 extends between the outer face surface 3.1 of the first pipe 1 and the outer face surface 3.2 of the second pipe 2. The inner axial ring gap 12 extends between the inner face surface 5.1 of the first pipe 1 and the inner face surface 5.2 of the second pipe 2.

[0058] The axial length of the steps or stair steps is determined by the parameters of the friction-welding technology that is provided for connecting the two pipes 1, 2. In this regard, it is decisive that the starting length of the axial ring gaps 11, 12 must be selected in such a manner that the width of the axial ring gaps 11, 12, which becomes shorter during the friction-welding process due to plastification of the center face surfaces of the pipes 1, 2, which touch one another, does not become less than or equal to zero by the end of the friction-welding process, i.e. that the outer face surfaces 3.1 and 3.2 as well as the inner face surfaces 5.1 and 5.2, which lie opposite one another in the radial position, do not touch or at most just touch even after the friction-welding process is concluded. In this way, it is guaranteed that solely the center face surfaces of the steps or stair steps, which surfaces have a direct connection to the respective undercut 7, function as joining surfaces 4.1 and 4.2, i.e. make contact from the beginning to the end of the friction-welding process and soften under the effect of the friction-welding process.

[0059] FIG. 1c shows the joint-site structure in the wall region of the friction-weld connection shown in FIG. 1a and FIG. 1b, with the variables essential to the joint-site structure according to the invention. The wall thickness of the pipes 1 and 2 was indicated as s.sub.1 and s.sub.2. Proceeding from the wall thickness s.sub.1, s.sub.2 of the pipes 1 and 2, a first step having the wall thickness a.sub.1 and a.sub.2 follows, which forms the inner horizontal insertion region of the joining structure. A second step having a wall thickness c.sub.1 or c.sub.2 follows the first step in the axial direction. The radial expanse of the joining surfaces 4.1, 4.2, which can run conically or also at a right angle to the pipe axis, results from the ratio of a.sub.1,2 to s.sub.1,2. The radial difference of the steps having the wall thicknesses a.sub.1 and a.sub.2 represents the overlap 13 of the joining surfaces. The wall thickness of these steps is reduced to a minimal wall thickness, namely the wall thickness b.sub.1 or b.sub.2 of the heat throttle 8, by means of the radial undercut 7 worked in at the transition from the first to the second step. The region of the second step, which follows the heat throttle 8 axially, represents the support ridge 9, so that the wall thickness c.sub.1 or c.sub.2 of the latter corresponds to the thickness of this step.

[0060] For a sufficient cross-section of the weld seam and for force transfer, the overlap 13, in other words the radial overlap of the face-side joining surfaces 4.1 and 4.2, must have a minimal size. For an overlap 13 of at least 20% of the wall thickness s.sub.1, 2 of the pipes 1 and 2, as well as for optimal action of the heat throttle 8 and easy insertion of the pipes 1 and 2 into one another, the following dependencies occur for the joint-site structure shown in FIG. 1a, FIG. 1b and FIG. 1c:

0.6s≦a≦0.8s

0.1a≦b≦0.3a

b≦c≦s−a.

[0061] The dependencies indicated hold true for both pipes 1 and 2, so that at the stated size ratios, no differentiation using the indices takes place at the wall thicknesses a, b, c and s.

[0062] Using the joint-site structure according to the invention as described above, as well as FIG. 2a and FIG. 2b, the method of effect of the invention will be explained in greater detail below, in connection with the description of the method for connecting the two pipes 1, 2 by means of friction welding.

[0063] To join the two pipes 1, 2, these are inserted into one another with their ends provided with the two-stair-step steps, along their common axis of rotation 6, until their center face surfaces, in other words their joining surfaces 4.1 and 4.2, bump up against one another, wherein the radial gap 10 forms between the support ridges 9 and the uninterrupted mantle surfaces of the step stair-steps that lie radially opposite them.

[0064] The aforementioned axial ring gaps 11 and 12 are present between the outer and inner face surfaces 3.1 and 3.2 as well as 5.1 and 5.2, which lie opposite one another at an axial distance. The friction-welding process begins in that at least one of the pipes 1, 2 is put into rotation and driven coaxially onto the other, possibly non-rotating pipe under the effect of axial process forces. Friction heat is released by the friction process under an increased axial force, which heat heats up the material in the region of the joint site, in other words at the joining surfaces 4.1 and 4.2, to almost the melting temperature of the material that has the lower melting temperature. The material desolidifies and begins to flow, whereupon a bead 14 is pressed out of the joint site due to the axial force, and, as is evident from FIG. 2b, is accommodated by the cavity of the undercut 7, which lies adjacent to the respective joining surface 4.1, 4.2, and essentially functions as a bead chamber here. Process gases as well as contaminants and chips can escape or be pressed outward by way of the radial gaps 10 and furthermore by way of the outer ring gap 11, and into the interior of the pipes 1, 2 by way of the inner ring gap 12.

[0065] The pipes 1, 2 become constantly shorter once bead formation starts. Due to the shortening of the pipes 1, 2, the support ridges 9 move along their radially opposite mantle surfaces of the step stair-steps, and thereby the outer and inner face surfaces 3.1 and 3.2 as well as 5.1 and 5.2 move toward one another.

[0066] After a certain reduction in length has been achieved, which is less than the starting width of the axial ring gaps 11, 12, rotation is braked to a stop and the pipes 1, 2 are compressed at the same or a greater axial process force. To state it differently, the welding process is continued until the outer and inner axial ring gap 11, 12 is almost closed.

[0067] The bead chambers, which are predetermined by the undercuts 7 in the pipes 1, 2, partially fill with the friction-weld bead 13 from the joint site during this process. Due to termination of the rotation movement, the joint site no longer receives any energy in the form of friction heat, and the material cools down and solidifies again. The axial process force is maintained until the compression shortening is saturated and the pipes 1, 2 are connected with one another with material fit. In this regard, as is evident from FIG. 2b, the width of the axial ring gaps 11, 12 is reduced to a minimum. It is also possible, however, that the outer and inner face surfaces 3.1 and 3.2 as well as 5.1 and 5.2 just touch one another. FIG. 2b shows that the radial gaps 10 are also still maintained even after completion of the friction-weld connection.

[0068] As is furthermore evident from FIG. 2a and FIG. 2b, a conical joining surface 15, indicated in FIG. 2b by a broken line, which surface is larger than the original contact surface of the conical joining surfaces 4.1 and 4.2 of the pipes 1 and 2, has formed after completion of the friction-welding process. The heat throttles 8 formed by the undercuts 7 in the outer and inner steps ensure that the support ridges 9 remain in the cold, solid state during the friction phase, and thereby are able to balance out or absorb the radial and tangential tensions caused by the friction-welding process. This feature is expressed by the inside and outside diameters of the two pipes 1, 2 being maintained.

[0069] In FIG. 3a to FIG. 6b, four different embodiments of the joint-site structure according to the invention for friction welding pipes using one-sided weld seam preparation are shown, which maximally have one step. The figures show the joint-site structure before the beginning of the friction-welding process, in each instance.

[0070] The items in these figures, which agree with the items shown in FIG. 1a to FIG. 2b, were given the same reference numbers as in FIG. 1a to FIG. 2b. Thus, FIG. 3a to FIG. 4b show two pipes 1, 2, to be connected by means of friction welding, only one of the two of which has a step, namely an inner step in FIG. 3a and FIG. 3b and an outer step in FIG. 4a and FIG. 4b, wherein in these figures, the pipe that has the step was given the reference number 1, and the pipe without such a seam preparation was given the reference number 2.

[0071] In each case, however, the undercut 7 that forms the heat throttle 8 and the support ridge 9 is provided in the mantle surface of this one step. The joining surfaces 4.1 (FIG. 3) and 4.2 (FIG. 4) are formed by the set-back inner face surface of the first pipe 1 (FIG. 3) and the set-back outer face surface of the second pipe 2 (FIG. 4).

[0072] In both embodiments, no axial gap is present, because there is no other face surface that lies opposite the outer face surface 3.1 of the first pipe 1 and the inner face surface 5.2 of the second pipe that form the joining surface 4.1 and 4.2, in each instance.

[0073] In the joint-site structures shown here, however, no radial flushness of the pipes 1, 2 is achieved in the outer mantle surface (FIG. 3) or the inner mantle surface (FIG. 4). For a sufficient cross-section of the weld seam for force transfer, the overlap 13, in other words the radial overlap of the face-side friction surfaces 4.1 and 4.2, must have a minimal size. For an overlap 13 of at least 20% of the wall thickness s.sub.1 of the pipes 1 and 2, as well as for optimal action of the heat throttle and easy introduction of the pipes 1 and 2 into one another, the following dependencies occur for the joint-site structure shown in FIG. 3a to FIG. 4b:

0.1s.sub.1≦b≦0.3s.sub.1

b≦c≦0.8s.sub.1

s.sub.2≧s.sub.1−c

[0074] The indices 1 and 2 were assigned to the respective pipe 1 or 2.

[0075] Radial flushness of the pipes 1, 2 is always achieved if at least one of the diameters of the pipes 1, 2 is the same size, the number of steps in the region of the joint sites of the two pipes 1, 2 is the same, and the diameters of the steps also have the same dimensions. Thus, FIG. 5a and FIG. 5b show two pipes 1, 2 to be connected by means of friction welding, the outside diameters of which are the same, so that they are flush at the outer circumference, and FIG. 6a and FIG. 6b show pipes, the inside diameters of which are the same, so that a flush inner circumference occurs. Although the first pipe 1 has an inner step, the second pipe has a congruent outer step. The undercut 7 is introduced into the step of the pipe 1, 2 that has the thinner wall, in each instance, in other words into the inner step of the pipe 1 in the case of the outer flush embodiment of FIG. 5, and into the outer step of the pipe 2 in the case of the inner flush embodiment according to FIG. 6.

[0076] When the number of steps in the joining region of the pipes 1, 2 is the same, however, at least two outer face surfaces 3.1 and 3.2 (FIG. 5) or two inner face surfaces 5.1 and 5.2 (FIG. 6) always still lie opposite one another, between which surfaces, as described above, a sufficiently wide outer axial ring gap 11 or a sufficiently wide inner axial ring gap 12 must be present at the beginning of the friction-welding process, for the reasons stated, in addition to the joining surfaces 4.1 and 4.2, which form the joint site of the friction-weld connection. Likewise, here the overlap 13, in other words the radial overlap of the face-side friction surfaces 4.1 and 4.2, must have a minimal size for a sufficient cross-section of the weld seam and for force transfer. For an overlap 13 having at least 20% of the wall thickness s.sub.1 of the pipes 1 and 2, as well as for optimal action of the heat throttle and easy introduction of the pipes 1 and 2 into one another, the following dependencies occur for the joint-site structure shown in FIG. 5a to FIG. 6b:

0.1s.sub.1≦b≦0.3s.sub.1

b≦c≦0.8s.sub.1

a.sub.2≧s.sub.1−c

[0077] The indices 1 and 2 were assigned to the respective pipe 1 and 2.

[0078] All of the characteristics presented here can be essential to the invention both individually and in any desired combination with one another.

[0079] Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.