DE10303853A1 - Method of manufacturing high pressure fuel line e.g. for diesel engines, heating of outer tube is achieved during welding of outer tube part - Google Patents

Abstract

A method for manufacturing a compound metal line/rail (1,2) for high pressure fuel, in which a first inner tube part (1) is inserted into the boring of a second outer tube part (2) which is then heated and subsequently cooled and then joined to the inner tube part (1) in the shrink seating. The heating of the outer tube part (2) is effected by welding at the outer tube part (2). Independent claims are also included for the following: (I) A compound metal line for high pressure fuel. (II) A metal-line or rail.

Description

The invention relates to a method for the production of a composite metal pipe for under High-pressure fuel, with a first inner pipe part in the bore of a second outer tube part is inserted, which is then heated and then cooled is shrink-fitted to the inner tube part. Further The invention relates to a composite metal line for under High-pressure fuel, with a first, inner pipe part with press fit inserted into the bore of a second, outer tube part is.

Out DE-U-1 954 706 a pipe for lines with high internal pressure, in particular for injection lines of diesel engines, is known. The tube consists of a tubular outer jacket (outer tube) and a thin-walled lining (inner tube). The wall thickness of the inner tube is calculated so that the operating pressure can plastically deform the inner tube to bring about a press fit in the bore of the thick-walled outer tube. The inner tube undergoes strain hardening, which is said to significantly increase its resistance to cracks.

Out DE-A-25 01 156 For the production of a multilayer pressure tube, it is known to first insert the metallic tube parts telescopically into one another, then to pull them and then to compress them radially until the individual tube parts are firmly connected to one another. A cold drawing process for the production of the multilayer pressure tube is therefore proposed.

Out DE-A-30 39 802 a composite metal pipe is known, which is manufactured by inserting a special steel pipe into an outer pipe with a press fit. Previously, the steel lines were coated on the interlocking surfaces with copper films, and subsequent heating of the copper films leads to the formation of a welded connection of the nested pipes with a press fit. Alternatively, in DE-A-30 39 802 proposed to push a thick-walled, outer tube part and an inner tube part with a wall thickness of 1.5-8.5% of the outer total diameter of the assembled tube into one another. By using a special steel pipe as an inner pipe part, the need for welding after insertion with a press fit should be eliminated.

In DE-C-36 24 403 describes a thick-walled, composite steel tube together with the manufacturing process. A small diameter steel tube is then inserted into a large diameter carbon steel tube. The two tubes are then subjected to a press fit by means of a drawing process, the diameter being reduced and an interference fit between the inner and the outer tubular part being achieved. The press-fit tube thus obtained is then heat-treated in a furnace with a non-oxidizing atmosphere without solder and diffusion-welded. This creates a bond between the mating surfaces of the inner and outer tubular parts.

In DE-C-197 16 659 describes a high pressure fuel injection pipe for a diesel engine with a double pipe structure. The inner tube is welded and positioned in a press fit within the outer tube.

According to DE-C-198 08 807 In a double pipe structure, the press fit is generated in the radial direction by an external pressure system, for which purpose a punching tool is proposed.

In DE-A-29 26 447 is a durable metal composite piece together with manufacturing process about the type mentioned as a sealing ring with instrument connection devices for use as a connector of high pressure lines disclosed. Two concentric and thick-walled pieces of pipe are pushed into each other to form a shrink fit and fit together. The shrink fit is formed by inserting and inserting the smaller inner tube piece into the heated, larger outer tube piece, and cooling the outer tube piece in such a way that it forms a shrink fit with the outer jacket of the smaller inner tube. Before shrinking, a fit with an oversize is provided between the outer jacket of the inner tube and the inner jacket of the outer tube, so that both jackets can be connected and inserted into one another by a shrink fit. To further improve the fatigue strength, a cold stretching treatment by applying an internal pressure is also proposed. The outer tube piece is stretched by the action of heat in such a way that the inner tube piece can be pushed into the interior of the outer tube piece by a sliding movement. Then the outer tube piece shrinks, and a shrink fit is created with a surface pressure between the outer jacket of the inner cylinder and the inner jacket of the outer cylinder. However, nothing has been said about the problem of how the effect of heat should be carried out.

So the object of the invention based on a composite high-pressure metal pipe with a shrink fit to create the high reliability and precision as well through a simple, easy to handle and inexpensive to manufacture with low tolerance requirements and without the need for one Honors fine machining. In particular, the shrink fit also for those for High-pressure rails occurring workpiece lengths practical and with minimal effort be producible. To the solution this task is based on the independent claims 1 and 16 referenced. Advantageous further developments result from the Dependent claims.

According to the invention the heating of the outer tube part necessary for the shrink fit is therefore made use of a heat welding process which is known per se from manufacturing technology as a joining process. For example, with a welding torch, the material of the outer pipe part is melted locally to a limited extent, whereby at least this area heats up. After the welding action has ended, the metallic material of the outer pipe part cools down in the welded area, with a volume reduction (shrinkage) in the welding area of the outer tube part occurs. This results in a reduction in circumference and diameter and, above all, a non-positive connection between the inner and the outer tube part. Furthermore, the shrinking of the outer tube part results in tensile stresses in the circumferential direction of the outer tube part and compressive stresses in the circumferential direction in the inner tube part. In fuel distributor operation under high, pulsating pressures, the compressive stresses generated by the shrink-fit preload overlap with the tensile stresses generated by internal pressure in the inner tube. This means that the tensile stresses are reduced by the proportion of the stored compressive stresses, which has a positive effect on the fatigue strength and service life of the assembled metal line.

According to a preferred training The invention is called a welding process fusion welding used, in particular the outer tube part on the outer jacket or based locally on one place, one area or a section of the entire pipe jacket is melted. This is useful for Formation of a so-called (longitudinal) Welded.

By in the course of fusion welding through Heat input pipe part material is brought into the liquid state, there is a trace, in particular a weld, which is caused by the remelting has been generated. This trace or seam created by welding has shrunk when cooling and looks like one Screw clamp at the welding point. As a result, the entire circumference of the outer tube part is contracted from the outside, which results in the desired shrinkage effect.

However, is within the scope of the invention also the use of other welding processes as fusion welding, for example pressure welding is conceivable.

It is within the scope of the invention at the same time with the welding warming of the outer tube part Third items add with. According to a preferred embodiment however, so-called "blind welding" is carried out, i.e. i.e., welding takes place on the outer tube part, without joining or a connection with a third-party object. This remains unaffected the option to support of welding to use known, special welding filler materials, the present not as third-party items respectively third parts are viewed. Leave with or without filler materials expediently on the outer jacket of the outer tube part Make blind welds. These are useful with a course in the pipe part or pipe longitudinal direction designed to Cool one if possible full and even shrinkage of the total volume of the outer tube part to reach. End-of-life training, according to which, also serves this purpose at least two blind welds with respect to the Line center axis are formed diametrically opposite one another.

When tight shrinking using blind welding, the to be added Semi-finished products have standard tolerances such as IT 9, such as they can be produced during cold drawing. The number of blind welds is freely selectable, so that a secure shrinkage with pretension can be achieved.

For adequate and uniform remelting of the local welding area or weld seam volume of the outer tube part, it is further provided according to an inventive design that the welding is carried out with a penetration depth of 70-95% of the wall thickness of the outer tube part. This idea is also supported by a method training according to which an outer tube part with a wall thickness that is relatively small compared to the inner tube part is used. This makes it easier to implement the penetration depth of 70–95%. In addition, welding processes with a good depth effect are known, such as plasma welding, plasmatron welding or CO ₂ laser welding. If a V-groove, joint, notch or other recess is previously worked into the pipe part jacket, welding processes with filler materials such as MAG (= metal active gas) welding processes can be used. The recess is filled with the filler material.

To facilitate postponement of the outer tube part on the inner pipe part, it is appropriate to both pipe parts to each other corresponding to a pair of fits to be measured with play. For example, there is a pairing of passports Proven in practice by H9 / h9.

Welding is promoted if, after training in inventions, unalloyed structural steel is selected as the material for the outer tube part. Unalloyed structural steel is characterized by good weldability. On the other hand, in the context of the manufacturing method according to the invention, welding on the inner tube part can be excluded, so that for this a material with particularly high strength, such as B. cold drawn round steel St52 can be drilled deep hole. The inner tube part does not experience any heat, unlike the outer tube part action, so that the strength state from the cold forming is retained.

More details, features and Advantages based on the invention result from the following Description of preferred embodiments the invention and from the drawings. These show in:

1 a metal line composed according to the invention as a fuel distributor for a diesel engine (common rail), suitable for pressures of 2000 bar, in a schematic longitudinal section;

2 a cross-sectional view along line AA in 1

3 a 2 corresponding cross-sectional view of a modified version,

4 a 2 corresponding cross-sectional view of a further modified version

The high-pressure fuel rail or common rail is in accordance with 1 realized with a composite metal pipe, consisting of the inner tube part 1 and the outer tube part shrunk onto it 2 , Both are made from steel. Furthermore, connecting pieces are known in a conventional manner 3 with preload screw connection and upsetting head as well as holding sleeves 4 about welds 5 welded. The inner tube 1 can be deep-drilled from drawn round steel or made from tube cold-forged over mandrel. For the inner tube 1 materials such as St52, C35, C45 or the like as well as suitable stainless steels come into question. As a result of the cold forming mentioned, the strength of the respective material is in the upper range (eg with St52 at 600–800 N / mm ² ). For example, the inner tube 1 manufactured with a DA tolerance of h9. The outer tube piece 2 is first on the inner tube piece 1 postponed with a fitting pairing of, for example, H9 / h9.

According to in 2 The example shown is about the local melting and cooling of the outer tube piece 2 and the resulting shrinkage on the inner tube piece 1 trigger, two diametrically opposed blind welds 6 melted axially parallel. The penetration depth is designed so that approx. 80–90% of the wall thickness of the outer pipe section 2 be remelted (see also 3 ). This is the outer tube piece 2 dimensioned with its wall thickness relatively thin, so that the wall thickness of the inner tube piece 1 is a multiple of this. Due to the depth of penetration mentioned, there is sufficient local melting of the material of the outer tube piece 2 , so that subsequently cooling can take place there with a sufficient temperature difference in order to achieve a tight shrink effect of the outer tube piece 2 on the inner tube piece 1 by reducing the volume of the outer pipe section 2 to effect. In the context of the invention, the local melting and cooling can be carried out solely via the blind weld seams 6 or - both alternatively and additionally via the welding points 5 for the connecting piece 3 and holding sleeves 4 respectively. The weld seams or spots 6 . 5 can act like volume-reducing straps.

The inner tube piece 1 is preferably made from round steel with a fixed length, which is subjected to deep hole drilling, optionally internal smooth rolling and turning at the ends. Before the outer tube piece 2 over the inner tube piece 1 is pushed, it is appropriate to the outer tube 2 Cut to length, stamping contact surfaces, punching holes and the holding sleeves 4 to weld. Only then is the outer tube piece particularly advantageous 2 over the inner tube piece 1 pushed and positioned. Then there is the melting of the blind welds 6 for example by means of plasmatron welding or laser welding for heating the outer tube piece 1 appropriate. After shrinking in the course of cooling the outer tube piece 2 , which consists for example of easily weldable, unalloyed structural steel, the connection piece 3 can be added via capacitor discharge welding.

According to 3 is the outer tube 2 with four blind welds 6 , two diametrically opposite each other, provided. These can be produced without filler material using CO ₂ laser welding. With this welding process, a good depth effect can be achieved in the full material with the aforementioned penetration depth of the blind weld seams 6 80-90% of the wall thickness of the outer tube 2 achieve. In other words, it will be according to 3 locally limited to four to 80-90% of the wall thickness of the outer tube 2 remelted. In the course of the subsequent cooling with the solidification of the melt, the circumference of the outer tube is reduced 2 what the desired "solid shrink" effect on the inner tube 1 results.

According to 4 is a welding area by means of a welding joint before local melting 11 in the outer jacket of the outer tube 2 been incorporated. The joint 11 is V-shaped in cross-section with an angle of approximately 90 °. The known MAG welding with filler material, with which the joint is used, is useful here 11 is replenished. Here, too, the shrinkage is due to remelting or melting in the weld joint area, ie the circumference of the outer tube is shortened by solidification and cooling of the melt 2 with resulting shrinking onto the inner tube 1 ,

The weld joint is in accordance with the preceding exemplary embodiments 11 also with a penetration depth of 80–90% of the wall thickness of the outer tube 2 made so that a remaining thickness I remains for the unmelted remaining wall.

1

inner tube

2

outer tube

3

connecting branch

4

holding sleeve

5

weld

6

blind weld

7

outer sheath

8th

Line central axis

9

Wall thickness of the outer tube part

10

wall thickness inner tube part

11

Welding seam

I

residual thickness

Claims (19)

Method of making a composite metal pipe ( 1 . 2 ) for fuel under high pressure, a first, inner pipe part ( 1 ) in the bore of a second, outer tube part ( 2 ) is inserted, which is then shrunk-fit with the inner tube part by heating and subsequent cooling ( 1 ) is connected, characterized in that the heating of the outer tube part ( 2 ) by welding on the outer tube part ( 2 ) is effected. A method according to claim 1, characterized in that used as a welding process fusion welding becomes A method according to claim 1 or 2, characterized in that the heating locally limited to a location, area or section of the outer tube part ( 2 ) is carried out. Method according to one of the preceding claims, characterized in that the welding on the outer tube part ( 2 ) with or without welding filler metal and in any case without connecting it to a third part ("blind welding"). A method according to claim 4, characterized in that the heating by making one or more blind welds ( 6 ) takes place, which in the outer tube part ( 2 ) from its outer jacket ( 7 ) are attached starting. A method according to claim 5, characterized in that at least one blind weld ( 6 ) is attached in the pipe part or pipe longitudinal direction. Method according to Claim 5 or 6, characterized by the application of at least two blind weld seams ( 6 ) with respect to the central line ( 8th ) are diametrically opposed to each other. Method according to one of the preceding claims, characterized in that the welding with a penetration depth of 70 to 95% of the wall thickness ( 9 ) of the outer tube part ( 2 ) is carried out. Method according to one of the preceding claims, characterized by the use of an inner tube part ( 1 ), the wall thickness ( 10 ) a multiple of the wall thickness ( 9 ) of the outer tube part ( 2 ) is. Method according to one of the preceding claims, characterized by the use of plasma welding, plasma welding or CO ₂ laser welding without filler material. Method according to one of the preceding claims, characterized by the use of MAG welding with filler material, wherein previously in the outer jacket of the outer tube part ( 2 ) at least one fugue ( 11 ), Notch or other recess has been incorporated, in which the MAG welding then takes place. Method according to one of the preceding claims, characterized in that the outer diameter of the inner tube part ( 1 ) and the inner diameter of the outer tube part ( 2 ) are dimensioned relative to each other in accordance with a pass pairing with play, for example H9 / h9. Method according to one of the preceding claims, characterized by the use of unalloyed structural steel as the material for the outer tube part ( 2 ). Method according to one of the preceding claims, characterized in that for the inner tube part ( 1 ) a material with higher strength than for the outer pipe part ( 2 ) is selected. Method according to one of the preceding claims, characterized in that the outer tubular part ( 2 ) is produced by cold working, in particular cold drawing. Compound metal pipe ( 1 . 2 ) for high-pressure fuel, in particular produced by a method according to claim 4 and possibly one of the other preceding claims, with a first, inner tube part ( 1 ) with a press fit in the bore of a second, outer tube part ( 2 ) is arranged, characterized by one or more weld seams ( 6 ) or other welding areas on the outer jacket of the outer pipe part ( 2 ) with or without welding filler material and in any case without connection to a third part ("blind welding seams" or "blind welding areas"). Metal line according to claim 16, characterized in that the blind welds ( 6 ) or areas from the outside into the interior of the wall of the outer tube part ( 2 ) extend. Metal line according to claim 16 or 17, characterized in that the blind welds ( 6 ) or areas extend in the longitudinal direction of the pipe ("longitudinal blind welds"). Metal line according to one of the preceding claims, characterized by at least one in its outer jacket ( 7 ) attached joint ( 11 ), Notch or other recess, which is processed by means of welding, in particular MAG welding with welding filler material.