EP0372360A2 - Method of making tubular construction parts - Google Patents

Abstract

The invention relates to a method of making tubular construction parts, a tube being formed starting from a sheet and the two ends being welded to one another and the tube thus obtained being subjected to an expanding process. The object of the invention is to provide a method of making tubular construction parts with which high-quality tubular construction parts, for example for baking tubes, can be made in a cost-effective and operationally reliable manner. The invention essentially consists in the tube being mechanically pre-expanded before the expanding process and in the pre-expanded tube, with its two ends sealed, being subjected in a closed manner to a hydroforming expanding process. The advantages achieved consist in particular in the fact that, when the method is used, there is a considerable saving of material with regard to the body to be made and virtually no scrap arises in the course of the manufacturing process. Furthermore, low tool costs result for the changeover if various types of tubular construction parts are made. There is also no problem in using sheets of the most varied quality, e.g. normal deep-drawing steel as well as austenitic and ferritic stainless steel. Different sheet thicknesses can also be readily processed. <IMAGE>

Description

The invention relates to a method for producing tubular components, a tube being formed from a sheet and the two ends being welded to one another, and the tube thus obtained being subjected to an expansion process.

Various methods are known for the production of tubular components, for example inner containers for dishwashers, oven tubes and tubes for microwave ovens. It is common practice to press the required recesses out of a sheet and to bend this deformed sheet into a rectangular tube, the ends of which are then welded together. This process is cumbersome and difficult to use.

Another known method for the production of tubular components consists in forming a tube by means of bending rounds starting from a sheet metal and then welding the two ends together. The tube thus obtained is then mechanically expanded in a suitable device in order to obtain the bulges which are necessary in the finished baking oven, for example. Following this process, further shaping can take place in different stations in order to achieve the final shape. This method has certain advantages over the first one described method, but it can not be used for many purposes because the manufacturing costs associated with this method are relatively high.

The invention has for its object to provide a method for producing tubular components with which inexpensive and reliable high-quality tubular components for example, baking ovens can be produced.

This object is achieved in that the tube is mechanically pre-expanded prior to the expanding process and that the pre-expanded tube is sealed and subjected to a hydroform expanding process while sealing its two ends.

According to a further embodiment of the invention, it is provided that a tube-like component close to the final shape is already produced during the pre-expansion.

Another embodiment of the invention is that a circumferential sealing ring is formed in the pipe to be expanded to seal the two pipe ends.

According to the invention it is also provided that the two circumferential sealing rings are formed like a labyrinth.

According to the invention it can also be provided that the pressure required in the hydroforming expansion process is applied in stages up to the maximum pressure.

It is particularly advantageous if, according to the invention, the pressure is applied in a pulsating manner up to the maximum pressure.

In the method according to the invention it can also be provided that the pressurized water system provided for the hydroform expanding process is designed as a closed circuit in which the hydraulic pressure is changed with the aid of a separate oil circuit coupled to the pressurized water system.

It is also within the scope of the invention that the hydroform expansion process is carried out with the aid of a core carrying the pressurized water and without the interposition of a rubber sack or a membrane that can be placed on the core.

According to the invention, it is further provided that a mechanical deformation is superimposed on the hydroform expanding process.

Said mechanical deformation according to the invention can take place simultaneously with the hydroform expanding process, but it can also take place after or before the hydroform expanding process.

The advantages achieved by the invention are, in particular, that when the method is used there is considerable material savings with regard to the body to be produced and practically no waste is produced in the course of the production process. Furthermore, there are low tool costs for the changeover when different types of tubular components are manufactured. There is also no problem in using sheets of the most varied quality, for example normal deep-drawing steel and austenitic and ferritic stainless steel. Different sheet thicknesses can also be processed without any problems.

The invention is described in more detail with reference to the drawings.

• Fig. 1 die wesentlichen Elemente einer Linie zum Herstellen von rohrartigen Bauteilen nach der Erfindung,
• Fig. 2, Fig. 3 und Fig. 4 eine schematische Darstellung der drei wesentlichen Schritte des neuen Verfahrens,
• Fig. 5 die Einzelheit X aus Fig. 3,
• Fig. 6 und Fig. 7 die Station der Linie nach Fig. 1 für den Hydroform-Expandierprozeß in zwei Ansichten,
• Fig. 8 den erfindungsgemäßen Verlauf des Druckaufbaus beim Hydroform-Expandierprozeß,
• Fig. 9 schematisch das Hydraulik-System für den Hydroform-Expandierprozeß,
• Fig. 10 ein vorteilhaft mit dem neuen Verfahren herstellbares rohrartiges Bauteil und
• Fig. 11 schematisch eine Vorrichtung zur Überlagerung einer mechanischen Verformung bei dem Hydroform-Expandierprozeß.

Show it

• 1 shows the essential elements of a line for the production of tubular components according to the invention,
• 2, 3 and 4 show a schematic representation of the three essential steps of the new method,
• 5 shows the detail X from FIG. 3,
• 6 and FIG. 7 the station of the line of FIG. 1 for the hydroform expanding process in two views,
• 8 shows the course of the pressure build-up according to the invention in the hydroform expansion process,
• 9 schematically shows the hydraulic system for the hydroform expanding process,
• 10 shows a tubular component which can advantageously be produced using the new method
• 11 schematically shows a device for superimposing a mechanical deformation in the hydroform expanding process.

The production line shown in Fig. 1 for the production of tubular components shows only the essential elements necessary for understanding the invention. For example, it is not shown that, starting from a sheet metal plate or from a bundle, a tube is produced by bending rounds. Incidentally, this tube, which serves as a preform for the tubular component to be produced, can have any shape in cross section. In the example shown, the tube 1 is circular in cross section, but it can also be square or rectangular, for example. In Fig. 1 is also not shown that the tube is welded together at its two ends after the bending round. The tubular components 2 to be produced with a line according to FIG. 1 serve in particular as inner containers for dishwashers, oven tubes or, for. B. Tubes for microwave ovens.

1 shows various stations 3 to 10, on which the tube 2 is made into the final tubular component 2 in different steps. The preformed and welded tube arrives in station 3, in order then to be subjected to the mechanical expansion process according to the invention in station 4. This pre-expansion preferably takes place in such a way that a tube-like component close to the final shape is already produced, as shown in FIG. 2. In this case, a tube with a rectangular cross-section was produced from the circular tube, which already has approximately the shape as shown by the tubular component 2 in FIG. 4. The weld seam between the two pipe ends is designated 11. This important step of pre-expanding before the expansion process to be described has essentially two effects: on the one hand, this results in a substantial saving in material and, on the other hand, the pipe 1 to be expanded already receives considerable rigidity in this production phase.

With the aid of the handling device 12 movable over the various stations 3 to 10, the pre-expanded pipe 1 is fed to station 5, in which the hydroform expansion process according to the invention takes place.

The station 5 is shown in somewhat more detail in FIGS. 6 and 7 in two views. The first important step of the method according to the invention in station 5 is that the two ends 13 and 14 have a circumferential sealing ring 15. Preferably, the sealing rings to be molded at the two ends 13 and 14 are labyrinthine, as shown in FIG. 5. This shaping of the circumferential sealing rings 15, in which the material remains undamaged in contrast to known methods, takes place with the aid of the matrices 16 (FIG. 6, FIG. 7) which can be adjusted in the direction of the core 17. This first step in the hydroforming expansion process in station 5 is illustrated with reference to FIGS. 3 and 5, where the circumferential sealing rings 15 are shown at the ends 13 and 14. After pressing the matrices 16 and the resulting molding of the circumferential sealing rings 15, a lock 18 engages so that the space 19 between the core 17 and the matrices 16, in which the component 1 to be expanded is located, is hermetically sealed. The matrices 16 have corresponding depressions corresponding to the bulges to be attached to the tube 1. If water or a water-based emulsion is now supplied to the core 17 under high pressure via the line 20, the tube 1 is inserted into the depressions in the tube Matrices 16 expanded. This hydroform expanding process gives the tube 1 its essential shape as prescribed by the tubular component 2. In stations 6 to 10 in FIG. 1, the tubular component 1 is further processed until it can be removed as a finished component at the last station 21.

According to an advantageous embodiment of the invention, the pressure required in the hydroform expansion process in station 5 is applied in stages up to the maximum pressure, in particular in a pulsating manner, as is shown in FIG. 8. This procedure brings excellent results in terms of dimensional accuracy and the formation of the bulge to be attached to the pipe 1; the pulsation of the pressure in the region 22 in FIG. 8 until the maximum pressure 23 is reached prevents the tube 1 from bulging out suddenly in the direction of the dies 16. Rather, the tube 1 is advantageously deformed step by step until it is finally shaped, the full contact of the tube 1 on the depressions in the matrices 16.

A special feature of the invention is that, contrary to the usual procedure in the hydroforming process, no rubber bag or membrane is provided between the core 17, the tube 1 to be deformed or the matrices 16. In the method according to the invention, the pressurized water reaches the pipe 1 to be deformed directly via the core 17 and presses the pipe 1 against the dies 16.

The high level of operational safety and the low maintenance costs when using the new method are also due to the fact that the pressurized water system 24 is designed as a closed circuit. The hydraulic pressure to be changed in this system 24 is varied with the aid of a separate oil circuit 25 coupled to the pressurized water system 24 (FIG. 9). For this purpose, an expansion cylinder 26 is connected between the two systems 24 and 25, each having a cylinder / piston system 27 and 28 for the water side and oil side. In this way, two separate hydraulic circuits are available, which has great advantages: The critical water side is limited to a minimum, so that you can get by with two water valves. With regard to the costs for maintenance, there are also essential positive aspects for the new method according to the invention.

10 shows a tubular component which has been produced with the aid of the method according to the invention. It is characterized by the fact that practically two tube-like components have been produced in one work step without waste being produced. After the hydroform expansion process or the subsequent operations in stations 6 to 10, the two tubular components are separated from one another. This example underlines the high cost-effectiveness that results from the method according to the invention when manufacturing tubular components.

The described pre-expansion can be omitted if the properties of the material (sheet) to be shaped require it. For example, so much deformation may be necessary in the hydroform expansion process that pre-expansion is prohibited.

Further considerations have shown that it may be expedient not to leave the hydroform expansion process alone to realize all the radii and profiles that occur. This applies above all to tight radii and sharp-edged profiles in the tubular component to be manufactured.

This object is achieved according to the invention in a method of the type specified in the introduction in that a mechanical deformation is superimposed on the hydroform expanding process.

The additional mechanical deformation according to the invention can take place simultaneously with the hydroform expanding process, but it can also, always in the hydroform expanding station, take place after or before the hydroform expanding process.

The advantages achieved in this way are, in particular, that even complicated molded parts made of sheet metal can be produced to the final shape in one operation, that is to say, even in the presence of, for example, narrow radii, no post-forming is required - in a further work station. In addition, there is an improvement in the product because all occurring deformations, whether in wide arches or in narrow radii or in sharp-edged sections, can be optimally produced; All deformations are carried out in one work step, with each deformation being assigned its working method. The less problematic deformations are applied via the hydroform expansion process, while tight radii etc. are realized by additional, superimposed mechanical deformation. If this is done in accordance with the invention, the deformation pressure for the hydroform expansion process can be reduced, which has great advantages for the water hydraulics. In addition, the water pressure of the hydroform expansion process can take on a holding function as far as the pipe to be deformed is concerned.

According to the method according to the invention described in the introduction, all bulges or depressions are made exclusively with the aid of the hydroform expanding process. If tight radii etc. occur, then very high pressures are required in the water hydraulics, which has considerable disadvantages. Narrow radii can of course also be achieved by post-forming in a separate work station downstream of the hydroforming station. This method of working is cumbersome and involves relatively high costs.

In contrast, the invention exists inter alia. in a combined process, a process with a hydroform expanding process and a mechanical deformation superimposed on this process.

11 schematically shows, starting from FIGS. 6 and 7, an apparatus for carrying out the method according to the invention. The hydroforming expansion process has already been described, which consists essentially in that high pressure water is supplied to the core 17, as a result of which the tube 1 is expanded into the depressions 51 in the dies 16. the direction of action of the water coming from the core 17 is indicated by the arrows 52.

According to the invention, a mechanism can additionally be provided, which can consist, for example, of plungers 53. With the help of this plunger 53, for example sharp-edged profiles 54 and very narrow radii 55 realized. The plungers 53 move in the direction of the double arrows 56.

With the aid of the arrangement shown, it is possible, for example, to proceed in such a way that, in the manner described above, the hydroform expanding process for less problematic depressions first takes place, with the pressure from the hydroform expanding process the tube 1 is held on the dies 16 and then the plunger 53 are operated to produce sharp-edged depressions and, for example, narrow radii in this way. The water pressure required here can be significantly lower than in the process specified at the outset.

Claims (12)

1. A method for producing tubular components, a tube being formed from a sheet and the two ends being welded to one another and the tube thus obtained being subjected to an exploding process, characterized in that the tube is mechanically pre-expanded before the expanding process and that the pre-expanded tube sealed under its two ends is subjected to a hydroform expansion process. 2. The method according to claim 1, characterized in that a tube-like component close to the final shape is already produced during the pre-expansion. 3. The method according to claim 1, characterized in that a circumferential sealing ring is formed in the pipe to be expanded to seal the two pipe ends. 4. The method according to claim 3, characterized in that the two circumferential sealing rings are formed like a labyrinth. 5. The method according to claim 1, characterized in that the pressure required in the hydroform expansion process is applied in stages up to the maximum pressure. 6. The method according to claim 5, characterized in that the pressure is applied pulsating up to the maximum pressure. 7. The method according to claim 1, 5 or 6, characterized in that the pressure water system provided for the hydroform expansion process is designed as a closed circuit in which the hydraulic pressure is changed with the aid of a separate oil circuit coupled to the pressure water system. 8. The method according to one or more of the preceding claims, characterized in that the hydroform expansion process is carried out with the aid of a core carrying the pressurized water and, without the interposition of a rubber bag or a membrane, matrices which can be employed on the core. 9. The method according to one or more of the preceding claims, characterized in that a mechanical deformation is superimposed on the hydroform expanding process. 10. The method according to claim 9, characterized in that the mechanical deformation takes place simultaneously with the hydroform expanding process. 11. The method according to claim 9, characterized in that the mechanical deformation takes place after the hydroform expansion process. 12. The method according to claim 9, characterized in that the mechanical deformation takes place before the hydroform expanding process.

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