A PRODUCT AND A METHOD OF MANUFACTURING TUBULAR PRODUCTS BY EXPOSING A TUBULAR BLANK TO INNER PRESSURE

Abstract: The invention relates to a method of manufacturing products, wherein a blank is produced in the shape of a closed profile and having an at least partially profiled wall and is then deformed to its final shape by applying pressure to the wall of the blank. In accordance with the invention a piece of material (M1) is provided with longitudinal indentations (8) through roll-forming, the profile piece of material is formed to a substantially closed generally tubular profile in a pipe mill and the profile is closed by firmly connecting adjacent side edges thereof, whereupon the profile is deformed by applying pressure to the wall of the closed profile in a manner that is known in itself. The invention also relates to a blank for use in hydroforming operations.

Description: A product and a method of manufacturing tubular products by exposing a tubular blank to inner pressure . TECHNICAL FIELD The present invention relates generally to methods of manufacturing products of metal and other materials having similar properties of material, by which methods a blank is formed having the shape of a closed profile and by which the blank is then deformed into the final shape of the product. BACKGROUND Generally, within different areas tubular metal blanks or work pieces are employed as semimanufactures for the manufacture of finished products having a specific shape. Thereby, the finished product is normally given its final shape by being expanded by means of mechanical or hydraulic pressure that is applied at the inner side of the blank. A very cuπent example of such manufacture that employs semi-manufactures in the shape of tubular blanks or work pieces is the method of manufacturing that is generally known as "hydroforming", and especially the variant thereof that may be refeπed to as "internal hydro- forming". By this manufacture, a tubular blank is positioned in a tool having an internal cavity being formed so that it coπesponds to the final shape of the product. The ends of the blank are sealed and a fluid of a very high pressure is introduced therein so that the blank is forced out into engagement with the tool and is given its final shape. The expansion of the blank causes tensioning of the material and thereby a change of its properties that is in most case undesirable. The outer dimension of the blank should therefor be well adapted to the shape of the tool in order to minimize tensioning of the material. This in turn means that it may be necessary to produce a great number of tubular blanks of different diameters and to keep them in stock for future manufacturing. The production of tubular blanks of many different diameters involves high costs, predominantly in short series production, whether they are produced for instance through drawing, rolling or extrusion. When it comes to hot forming of metals there are also general limitations with regard to the smallest thickness of the material that can be produced. U.S. Patent No. 2 707 820 discloses a method of manufacturing tubular members, and specifically a method of producing metal tanks or vessels of larger dimensions. An extrusion of tank blanks is considered in accordance with this document. The costs of the extrusion method increase dramatically with increasing tube diameter, partly since the cost of the actual press tools increases but primarily due to the size of the press that has to be employed for generating the required pressure. In the above mentioned U.S. Patent it is suggested that the costs for producing a specific tank size is reduced by extruding the tubular member with a significantly smaller outer diameter than that of the finished tank but with a coπugated wall. The tubular member is expanded to its final dimensions by applying inner hydraulic pressure to it, whereby the expansion is obtained by "unfolding" the coπugations. Thereby, the material is also subjected to minimal tensioning during the final shaping or forming thereof. Under certain conditions, extrusion may well be employed for producing tubes or pipes or other closed profiles of steel. However, this method is normally restricted to the manufacture of profiles of a non-feπous metal. Moreover, a change of tool, i.e. the die as well as the core, is required as soon as there is a slight change of the profile, such as a change of the outer diameter as well as of the shape, size and/or mutual positions of the coπugations. In summary, it may therefore be established that the conventional methods of manufacturing that are traditionally being used for the above discussed purposes have required a relatively troublesome and expensive rigging and adjustment work for the production of different profiles. In other words, there is an apparent need for finding a method of manufacturing that offers a solution to said problems and that permits quick and simple adjustment between different profiles. SUMMARY OF THE INVENTION The invention overcomes the above problems in an efficient and satisfactory manner. A general object of the invention is to provide a solution to the problem of being able to quickly and conveniently manufacture generally tubular profiles such as blanks or semimanufactures intended for a final forming of products having different dimensions and shape. A basic object of the invention is therefore to provide a simple and appropriate method of manufacturing generally tubular basic profiles or blanks that are intended to form final products having different dimensions and different cross section shapes after being subjected to a final deformation thereof. Thus, the invention provides a method of manufacturing products by producing a blank having a closed profile and an at least partially corrugated wall and by deforming said blank into the final shape of the product. In accordance with the invention the blank is produced by roll-forming a generally sheet-like piece of material, on the one hand for profiling or shaping the blank and on the other hand for closing the profile of the blank, and by subsequently firmly connecting the sides of the blank. The final shape of the product is then obtained by deforming the blank in a manner that is in itself previously known. In this manner, a comparatively simple adjustment is obtained for manufacturing blanks having different profiles adapted to the final product in question and/or to the final forming thereof through deformation. This in turn leads to significantly reduced job times and costs when compared to the conventional methods. In accordance with embodiments of the invention the blank is provided with indentations or corrugations during the roll-forming, said indentations being distributed uniformly or alternatively non-uniformly around the circumferential surface of the blank. By employing the roll-forming it is possible to provide a comparatively quick and simple adjustment between manufacturing blanks suitable for symmetrical and unsymmetrical deformation, respectively. In accordance with other embodiments of the invention, a blank is provided with indentations during the roll-forming, said indentations having the same or alternatively different depth. Hereby is offered a further possibility of providing the adjustment between manufacturing blanks suitable for symmetrical and unsymmetrical deformation, respectively in a comparatively quick, simple and flexible manner. In accordance with further embodiments of the invention the deformation of the blank is caπied out by applying mechanical or alternatively hydraulic pressure to the inner or outer surfaces, respectively of the entire blank or alternatively only to portions of said inner or outer surfaces, respectively. With such embodiments a very extensive flexibility is obtained with simple means, said flexibility concerning the final shape of the products that may be produced in accordance with the invention. Yet another embodiment of the invention relates specifically to the manufacturing of products that are given their final shape by hydroforming, specifically "internal" hydroforming. In accordance therewith, blanks are formed through the roll-forming operation so that they have different contents of material, in the form of indentations of different depth and/or width, but have the same outer diameter. This means that the manufacturing may be rationalized further since only one outer diameter of the profiles has to be produced in the pipe mill, although the profiles shall be deformed into final products having different shapes and sizes. In accordance with another embodiment, the blanks are also provided with a varying number of indentations having different mutual positions in dependence upon the deformed final shape of each blank. Thereby, the manufacturing may be rationalized even further and simultaneously cold tensioning may be avoided. Further embodiments of this first aspect of the invention are specified in the coπesponding dependent claims. A further object of the invention is to provide a work piece or blank for hydroforming, said blank having a profiled or contoured surface so that the material of the blank will be subjected to a minimum amount of tensioning during the hydroforming operation. These and further objects of the invention are met by the invention as defined in the appended patent claims. In summary, the present invention provides the following advantages: - A comparatively quick and simple adjustment for manufacturing blanks adapted to different final products; - The shape of the blank may relatively easily be "tailored" to the shape of the final product; The shape of the blank may with a smaller amount of adjustment work be adjusted so that the material is subjected to a minimum amount of tensioning during the deformation, such as by hydroforming; For hydroforming, blanks may be manufactured in a pipe mill to have a uniform outer diameter but different contents of material. Thereby blanks having the same outer diameter may be employed for the deformation into final products having a large difference in dimensions; - By hydroforming, tube blanks of high-strength materials may also be employed, without any danger of changing the material properties through cold tensioning. Further objects, features and advantages of the invention as well as further embodiments thereof will appear from the dependent patent claims and from the following description of exemplifying embodiments. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in detail below, in connection with the enclosed drawings, in which: Fig. 1 A is a partial schematic end view of a station in a roll-forming machine, as viewed in the forming direction; Fig. IB is a partial schematic end view of a station in a pipe mill, illustrating the principles of closing a blank profile; Fig. 2A-B illustrate an example of an embodiment of a blank profile according to the invention shown in three different stages of the production; Fig. 3A-B illustrate an example of an alternative embodiment of a blank profile according to the invention shown in three different stages of the production; Fig.4A-B illustrate a further example of an alternative embodiment of a blank profile according to the invention shown in three different stages of the production; Fig, 5A-B illustrate an alternative design and an alternative distribution, respectively, of the longitudinal indentations of the blank; Fig. 6A-D illustrate examples of further embodiments of a final product according to the invention; and Fig. 7A-B illustrate an example of a further embodiment of the invention, for manufacturing a final product in the form of a composite product. DESCRIPTION OF EMBODIMENTS With reference primarily to figures l-2A : the basic principles of the. invention shall now be described with the aid of a first embodiment thereof that is illustrated in said figures. At the same time, the differences in comparison with previously known methods shall be explained. In accordance with the invention it is basically suggested that for the manufacture of a finished product 9 (see fig.2B) apiece of material Ml;'in the form of a sheet of an appropriate material is in a first step provided with longitudinal parallel indentations 8. A characteristic feature of the invention is that the indentations or corrugations are formed through roll-forming. Drawing figure 1A very schematically illustrates an example of a roll-forming machine 1 of a conventional design. Conventionally, such a machine consists of a number of stations 2, only one is illustrated in fig 1 A, that are positioned after one another in the forming direction. Each station comprises a pair of upper and lower shafts 3 and 4, respectively, on which upper and lower forming rolls 5 and 6 respectively, are supported, Said upper and lower forming rolls cooperate in pairs and between them form indentations 8 in the piece of material Ml. Normally, some of the rolls simultaneously serve to advance the material Ml. The depth of the indentations 8 in the piece of material Ml is gradually increased in the subsequent stations 2 and the indentations reach their final shape in the last station. Regarding further details of the general design of a conventional roll-formmg machine, reference may be made for instance to Swedish Patent No, 348 955. However, the invention is in no way restricted to the design of the roll- foπning machine illustrated in principle herein or to the design thereof described in said patent On the contrary, any appropriate roll-forming machine may be employed when practicing the present invention. The same applies to the pipe mill 7 illustrated in fig. IB, where the piece of material Ml that has been indented in the forming stations 2 in a second step is formed to a substantially closed profile PI (see fig. 2 A) having a generally tubular shape. The pipe mill 7 is included as a final station in or connects to the roll-forming machine 1 and consists of a number of sub-stations 7A of which only one is illustrated in fig. IB, each comprising a lower roll 7B and an upper roll 7C. This forming operation is caπied out in such a manner that the indented or profiled piece of material Ml is gradually closed to the desired profile shape by the pipe mill 7, by means of the roll sets being positioned one after the other. Said roll sets and are provided with rolls 7B, 7C having a shape that is gradually changed for forming a profile the radius of which is reduced more and more until its final shape is obtained. This is schematically illustrated in figure IB by means of the intermediate shapes Ml ', Ml 'of the piece of material being drawn with dashed lines. The general design of such pipe mills is part of the prior art and does not form any part of the present invention. The major difference compared to the conventional pipe mills is that the gap between the upper and lower rolls has to be increased coπesponding to the height or depth of the indentations in the piece of material, so that the indentations are not deformed at this stage. Thus, in accordance with the first embodiment of the present invention illustrated in figs. 1 and 2A-B, the piece of material Ml is formed with longitudinal indentations 8 in the roll-forming machine 1. In this embodiment said longitudinal indentations 8 are formed with the same depth and pitch and in this first step they will be given the shape that is illustrated in figure. 2A. In this example, the indentations 8 have a generally trapezoidal shape and are uniformly distributed across the piece of material Ml. In the second step, the piece of material is formed to a generally cylindrical profiled tubular shape PI in the pipe mill 7, i.e. in the final station of the roll-forming machine. Said tubular shape PI is illustrated with solid lines in fig. 2B. In a third step, not illustrated, the facing edges of the piece of material are then connected to each other by means of conventional methods, such as welding or cold welding for metals and adhesive bonding or welding for other materials. Thereby, the blank is ready for the final foπning through deformation. In fig. 2B the form of the final product 9 is illustrated with dashed lines, and in this case it is a matter of an expansion of all available material in the indentations 8, so that the final product 9 is given the shape of a smooth cylinder. The expansion of the profile PI to the shape of the final product may be caπied out mechanically, for instance by means of a mandrel, but in a presently prefeπed application the expansion is perfonned by means of a fluid under high pressure, i.e. through hydroforming. By the hydroforming, that is in itself known, the expansion is generally performed in such a way that by applying high hydraulic inner pressure thereto the blank PI is formed against the inner surface of a tool that has the intended final shape and that is not illustrated here. It was stated in the introduction that the basic object of the invention is to provide a method that eliminates the disadvantages of the conventional technique and to specifically achieve this by providing a very flexible method of manufacturing that permits quick and simple adaptation or adjustment to the final product in question. An example of this great flexibility shall now be described with specific reference to figs. 3A-B and 4A-B. Fig. 3 A illustrates an embodiment where in a roll-forming machine a piece of material M2 has been provided with the same number of longitudinal indentations 18 as the piece of material Ml according to fig. 2A. However, in this case the indentations 18 are formed having a much greater depth than the indentations 8 according to fig. 2 A. In spite thereof, the piece of material M2 may in the same final station be formed to a blank P2 having the same outer diameter as the profile PI . This means that much more material is available for an expansion without cold tensioning to the shape of the final product 19. The final product 19 has a significantly larger diameter than the final product 9 according to fig. 2B. Accordingly, such a solution provides a possibility of accomplishing a very rational manufacture since the same pipe mill may be employed to produce blank profiles for final products of very varying dimensions. This is very useful for instance for the hydroforming process. In order to obtain the same outer shape for blanks intended for different final products it is thus possible to vary different parameters such as the depth, width, form, distribution and/or mutual distance of the indentations, and to thereby cover a very large area of final shapes after deformation. Fig. 4A-B illustrates a further example of a variation that is possible to produce in a relatively simple manner through the roll-forming. This variant may likewise be made with one and the same pipe mill, i.e. in the form of a blank profile P3 having the same outer diameter as those of the previous embodiments. This variant is specifically suited for the expansion through hydro- forming of other final shapes 29 than absolutely cylindrical shapes since different amounts of material for the expansion without cold tensioning is concentrated in different parts of the profile P3. As is best illustrated in fig. 4A this is achieved by forming indentations 28, 28' having different depth in different parts of the plate M3 coπesponding to the different portions of the circumference of the final product 29. In figures 2A-B, 3A-B and 4A-B all of the indentations are illustrated having a generally trapezoidal shape and being positioned with the same spacing. However, the invention is not restricted to such designs. To exemplify this, figs. 5A and 5B illustrate designs having generally sinusoidal indentations 38 and. 38', respectively, that in fig. 5 A are uniformly distributed over the piece of material M4 and that in fig. 5B are non-uniformly distributed in the piece of material M5, coπesponding to the intended final shape (not illustrated) after deformation. It should be obvious that the shape of the indentations 38, 38' as well as the distribution thereof may be varied freely within the scope of the invention. Finally, figs. 6A-C illustrate examples of other final products 39, 49, 50 that may be produced within the scope of the invention. For the sake of simplicity, the illustrated designs of said examples are all based on the blank profile PI that is illustrated in fig. 6 A and that coπesponds to the profile according to fig. 2A. Fig. 6B illustrates a design where the blank profile PI according to fig. 6 A has been expanded to a tapered or conical final product 39 by being expanded gradually more and more towards one end 39 A, whereas it has been maintained in its original shape in the other end 39B. The conical shape is obtained by means of said expansion and at the same time the indentations become more and more shallow towards the expanded end 39 A. Alternatively, said end 39A may be expanded to a cylindrical shape in those cases where, for a specific application, the indentations do not need to be continuous. In figs. 6C and 6D is illustrated a further variant where the blank profile PI according to fig. 6A is expanded so to say linearly. This is done by applying inner pressure, preferably mechanically, for instance along two diametrically opposite lines at the inner surface of the blank PI. Supplementing this inner pressure by an outer pressure that strives to flatten the blank will form a product 49 according to fig. 6C having inner and outer channels. Like in the embodiment according to fig. 6B the blank has here been expanded gradually more and more towards an end 49A thereof, whereas the indentations in the other end 49B have on the whole maintained their original shape. In fig. 6O is illustrated a further variant where the product 49 has been divided so that two generally fan shaped halves 50 are formed, of which only one is illustrated in the figure and which are in this case the final product. The final products illustrated in the drawings have not been shown bearing any specific use or application thereof in mind, but for the purpose of demonstrating the possibilities that are afforded by the use of the principles of the invention. Furthermore, it shall be emphasized that although all of the examples that have been illustrated and described herein refer to a deformation for obtaining the shape of the final product substantially through expansion of the blank, the invention shall not be restricted thereby. Thus, the invention also comprises a deformation of blanks by applying pressure to their outer surface, i.e. by forcing the entire outer surface or portions thereof inwardly, or by a combination of expansion and such inward forcing. As was mentioned earlier, the invention is presently regarded as having one of its most important applications within the hydroforming technique. By using the invention, it is thereby above all possible to employ also tubular blank of high-strength materials, and to do so without running the risk of changing the material properties. When employing the conventional techniques such a risk of changing the material properties will exist as a result of the cold tensioning that occurs by the deformation of a cylindrical tubular blank. In this connection, it is further suggested in accordance with the invention to heat the plate in connection with the roll-forming of the indentations. Specifically, the plate is heated locally in the area of the indentations or (for indentations having sharp corners) alternatively very locally, only in the area of the corners or edges of the indentations. Such a local heating may advantageously be performed by means of laser and serves the purpose of eliminating, as far as possible, cold tensioning of the material also during the roll-forming. For the same reason the generally sinusoidal indentations illustrated in fig. 5A-B - or other indentations having coπesponding rounded comers - are presently regarded to be most advantageous, especially when employing high strength materials. In accordance with a further embodiment of the invention illustrated in figs. 7A, 7B a blank PI as described above may be arranged inside a tubular second product P4 and may then be expanded into engagement with the second tubular product P4. Said method may be used for instance for repairing a broken conduit. In a variant thereof the blank may be formed of a material having properties that differ from those of the material of the second tubular product, to thereby obtain a composite product 59 having different internal and external properties of material. This embodiment may for instance be used for lining an existing pipe with a nobler metal. According to the invention it is presently normal to start with a piece of material in the form of a metal plate, but the invention also comprises manufacturing blanks and products from other materials having similar properties, that is materials that are possible and suitable to roll-form and to deform to their final shape, for instance synthetic materials. The basic material is preferably a substantially flat sheet or plate of the material in question, but other sheets or plates may naturally also be used, for instance sheets or plates having a certain preformed structure. By employing the roll-forming to form the closed profile it will also be possible to use many different material qualities or grades, even such qualities that are not at all suitable for e.g. extrusion. In the same manner, the wall thickness of the blank may thereby be varied in a way that is not possible by extrusion. It will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departure from the scope thereof, which is defined by the appended claims.

Claims: CLAIMS 1. A method of manufacturing products (9; 19; 29; 39; 49; 50), whereby a blank is manufactured having a shape of a closed profile (PI; P2; P3) and having a wall that is at least partially profiled and whereby said profile is deformed to its final shape by applying pressure to the wall of the blank, characterized in that in a first step a piece of material (Ml; M2: M3; M4; M5) is provided with longitudinal indentations (8; 18; 28; 28'; 38; 38') through roll- forming, and in that in a second step the piece of material that is in itself profiled is formed, likewise through roll-forming in a pipe mill (7), into an essentially closed, generally tubular profile (PI; P2; P3) and in that in a third step the profile is closed by firmly interconnecting adjacent side edges thereof, whereupon the profile is deformed by applying a pressure, in a manner known per se, to the wall of the closed profile. 2. The method according to claim 1, characterized in that through the roll-foπning the piece of material (Ml; M2; M4) is provided with longitudinal indentations (8; 18; 38) that are uniformly distributed over the surface of the piece of material or over portions of its surface. 3. The method according to claim 1, characterized in that through the roll-forming the piece of material (M3; M5) is provided with longitudinal indentations (28, 28'; 38') that are non- uniformly distributed over the surface of the piece of material or over portions of its surface. 4. The method according to claim 1, 2 or 3, characterized in that the longitudinal indentations (8; 18; 38; 38') of one and the same piece of material (Ml; M2; M4; M5) are formed having essentially the same depth. 5. The method according to claim 1, 2 or 3, characterized in that the longitudinal indentations (28, 28') of one and the same piece of material (M3) are formed having mutually different depth. 6. The method according to any of claims 1-5, characterized in that when deforming the blank (PI) pressure is applied locally to portions of the wall of the closed profile (PI) in order to modify the general tubular shape. 7. The method according to any of claims 1-5, characterized in that when deforming the blank (PI; P2; P3) pressure is applied to the entire wall of the closed profile (PI; P2; P3) in order to modify the generally tubular shape. 8. The method according to any of claims 1-7, characterized in that mechanical pressure is applied to the wall of the closed profile (PI; P2; P3). 9. The method according to any of claims 1-7, characterized in that hydraulic pressure is applied to the wall of the closed profile (PI; P2; P3). 10. The method according to claim 9, for manufacturing products (9; 19; 29; 39; 49; 50) through hydroforming, characterized in that through the roll-forming operation blanks (PI; P2; P3) are produced having different contents of material, in the form of longitudinal indentations (8; 18; 28; 28'; 38; 38') having different depth and/or width, and/or in the fonn of a different number of and/or a different distribution of said indentations, and in one and the same pipe mill said blanks are formed having a specified common outer diameter. 11. The method according to claim 10, characterized in that the depth of the indentations (8; 18; 28; 28'; 38; 38') of the blanks (PI; P2; P3) is determined based upon the size of the deformation of the respective closed profile that shall be provided by means of the hydrofonning. 12. The method according to claim 10 or 11, characterized in that the depth, the width, the number of or the positioning of the indentations (8; 18; 28; 28'; 38; 38') around the circumference of the blanks (PI; P2; P3) are determined based upon the deformed final shape (9; 19; 29; 39; 49; 50) of the respective blank that shall be provided by means of the hydroforming. 13. The method according to any of claims 1-12, characterized in that the blanks (PI; P2; P3) are formed of a metal. 14. The method according to any of claims 1-13, characterized in that the blanks (PI; P2; P3) are formed of a high-strength material. 15. The method according to any of claims 1-14, characterized in that in connection with the roll-forming of the indentations (8; 18; 28; 28'; 38; 38') the piece of material (Ml; M2; M3) is heated in the area of the indentations. 16. The method according to any of claims 1-15, characterized in that the indentations (38; 38') are formed having a generally sinusoidal shape. 17. The method according to any of claims 1-15, characterized in the indentations (8; 18; 28; 28') are formed having a generally trapezoidal shape. 18. The method according to any of claims 1-17, characterized in that the blank (PI) is positioned in a tubular second product (P4) and is then expanded into engagement with the second tubular product. 19. The method according to claim 18, characterized in that the blank (PI; P2; P3) is foπned from a material the properties of which differ from the properties of the material of the second tubular product, to obtain a composite product (59) having different inner and outer material properties. 20. A blank for hydroforming consisting of a closed generally tubular profile (PI; P2; P3) having a profiled peripheral surface with longitudinal indentations (8; 18; 28; 28'; 38; 38'), characterized in that the longitudinal indentations (28; 28') have different depth, as seen in a radial direction of the tubular profile (P2). 21. A blank according to claim 20, characterized in that the longitudinal indentations (8; 18; 28, 28'; 38) are uniformly distributed over the peripheral surface of the blank or over portions of said peripheral surface. 22. A blank according to claim 20, characterized in that the longitudinal indentations (38') are non-uniformly distributed over the peripheral surface of the blank or over portions of said peripheral surface. 23. A blank according to any of claims 20-22, characterized in that the longitudinal indentations (38; 38') are fonned having a generally sinusoidal shape. 24. A blank according to any of claims 20-22, characterized in that the longitudinal indentations (8; 18; 28; 28') are formed having a generally trapezoidal shape. 25. A blan according to any of claims 20-24, characterized in that it consists of metal. 26. A blank according to any of claims 20-25, characterized in that it consists of high- strength material.

Inventors: LUNDGREN CLAES-HAAKAN, LUNDGREN, CLAES-HAAKAN
Applicants: LUNDGREN CLAES HAAKAN, PLAATFORM CLAES HAAKAN LUNDGRE, LUNDGREN, CLAES-HAAKAN, PLAATFORM CLAES-HAAKAN LUNDGREN
Application year: 2001
Main classification: B21D26
IPC codes: B21C37, B21D26