Patent Publication Number: US-6038901-A

Title: Method and device for producing press-rolled pipes with inner wall thickenings at the ends

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method and a device for producing press-rolled pipes. 
     Rotationally symmetrical parts (for example tubes) are required in the structural design of loaded parts in the construction of vehicles (for example bicycle/motorcycle construction) which should be as light as possible, but must have the necessary resistance torques at the loaded positions. For this purpose, with tubular structural parts, for example, the ends are reinforced on the inside, the wall thicknesses in the middle are reinforced on the inside, longitudinal ribs are applied to the inside or combinations of these measures are carried out. Because the outer dimensions of these tubular structural parts cannot be changed for structural reasons, these even being standardized in part (for example in the case of bicycles), these measures are basically applied advantageously to the inside of the tubular workpieces. 
     These measures for modification of the inner region of the rotationally symmetrical parts have already been known for a long time and are prior art. However, the measures necessary for this purpose are very costly and even today to some extent cannot represent, in practice, justifiable costs. In this way, a tubular structural part for bicycles with inner thickening of the tube ends on both sides can already be produced today. However, for this purpose several costly pulling procedures are required, and on every individual structural part. Because of the method-dependent tolerances dependent upon the method in the conventional production of these parts, any advantage in terms of weight cannot be used in full because of the large tolerance zone of, for example, the uneven walls (differences in wall thickness), because the smallest wall thickness must be considered in the structural calculation. 
     The generic DE-P 44 46 919 describes a method for flow turning internally geared parts, wherein a workpiece is arranged on a press mandrel, which workpiece is plastically deformed by means of the force loading of pressure rollers. The co-pressing method and the counter-pressing method are described in detail. 
     In this respect, press-rolling technology allows maximized use of weight advantages as a result of the very small wall thicknesses due to the very high highest levels of hardening of the materials used (steel, steel alloys, aluminium and aluminium alloys, titanium and titanium alloys, copper and copper alloys, special steels etc.) which are attainable and the extremely even thickness of the parts produced. In particular the method allows excellent surfaces to be obtained in the interior of the workpieces, i.e. there is very little roughness. This low surface roughness guarantees special protection against cracks which can start from internal notches in the event of, for example, overstressing. In addition, the method allows high reproducible levels of accuracy. Fluctuations within the workpieces are minimal. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to create a method and an associated device with which it is possible to produce tubes which are press-rolled in a cost-favourable manner and with accurate tolerance and which have inner wall thickenings at the ends. 
     In accordance with the invention the object is achieved by using, in a first working operation, a first press mandrel with a tailstock-end shoulder, by the pressure rollers beginning their transforming work at the tailstock-end shoulder and working in the direction of the machine spindle, by the half-finished tube subsequently being taken from the first press mandrel, by the half-finished tube at the end with the wall thickening which has already been produced being clamped in a second working operation into a lathe chuck (tensioning spindle or similar) mounted in the press-rolling machine, and a second press mandrel, fastened on the tailstock end and having an outer diameter which corresponds to the inner diameter of the wall thickening, being pushed into the half-finished tube, and by the pressure rollers subsequently forming the second wall thickening from the tailstock-end in the direction of the machine-spindle side. 
     By means of this method, it is possible to produce a tube with inner wall thickenings at the ends using simple means. In the press-rolling machine, only a second press mandrel fastened on the tailstock end is required. 
     In accordance with the invention the external diameter of the first press mandrel corresponds to the desired internal diameter of the non-thickened middle region of the finished tube, and the external diameter of the shoulder corresponds to the desired internal diameter of the wall thickenings. 
     In a preferred embodiment, the press mandrel and/or the shoulder is provided on its outside with a profile. The profile can also only be applied to certain sections and advantageously comprises ribs and grooves. However, any other conceivable profile is possible. 
     In a specific embodiment, the press mandrel and/or the shoulder is at least partially polygonal in cross section, being for example a hexagon. Here the press mandrel is of course understood to mean the first or the second press mandrel or both. 
     In accordance with the invention this method and this device are particularly suitable for producing structural parts for bicycles/motorcycles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features of the invention are evident from the figures which are described in detail in the following: 
     FIG. 1 shows diagrammatically the first working operation for producing a tube with end wall thickenings; 
     FIG. 2 shows in section the half-finished tube after the first working operation; 
     FIG. 3 shows diagrammatically the second working operation; 
     FIG. 4 shows the finished tube with end wall thickenings; 
     FIG. 5 shows working operation of a tube on a hexagonal press mandrel and the finished tube after the working; 
     FIG. 6 shows different pipes with different internal profiles; and 
     FIG. 7 shows a press mandrel with a profile comprising ribs and grooves. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows diagrammatically the first working operation on a press-rolling machine for producing a tube 3 with end wall wall thickenings. The tube 3 is arranged on a first press mandrel 1a and is plastically deformed by the force loading of the pressure rollers 2. The outer diameter of the first press mandrel 1a corresponds in this respect to the desired internal diameter of the middle region of the finished pipe 3 which is not thickened later. 
     On the first press mandrel la is arranged a tailstock-end shoulder 4, the outer diameter d 1  of which corresponds to the desired internal diameter of the end wall wall thickenings of the finished tube 3. 
     As a first working operation the pressure rollers 2 begin their transforming work at the tailstock-end shoulder 4 and work in the direction of the machine spindle which is not shown. The advance of the pressure rollers 2 is indicated by the reference symbol 8. 
     FIG. 2 shows the half-finished tube 3a produced by means of this working operation with the one-end wall thickening 5 produced on one end. The end of the processing by the pressure rollers 2 is indicated by the reference symbol 9. 
     After the half-finished tube 3a is taken from the first press mandrel 1a, in a second working operation (see FIG. 3) the half-finished tube 3a is clamped into a lathe chuck 6 (tensioning spindle or similar), mounted in the press-rolling machine at the end with the wall thickening 5 which is already produced. Moreover, a press mandrel 1b fastened on the tailstock end is pushed into the half-finished tube 3a. In this respect, the second press mandrel 1b has an external diameter d 2  which corresponds to the internal diameter of the wall thickening. Subsequently, the pressure rollers 2 form the second wall thickening from the tailstock-end in the direction of the machine spindle. The end of the processing by the pressure rollers 2 is indicated by the reference symbol 12. 
     FIG. 4 shows the finished tube 3 with the end wall thickenings. 
     FIG. 5a shows a press mandrel 1 having a hexagonal cross section, with a tube 3 being processed by pressure rollers 2. In FIG. 5b the finished tube 3 is shown. This press mandrel 1 can be manufactured in the most varied modifications. Always meant by pressure rollers 2 are flow turn rollers. 
     FIGS. 6 a,b,c show three different tubes 3 each with a different internal contour. FIG. 6a shows a tube 3 with a hexagonal cross section like FIG. 5b. FIGS. 6b,c show a tube with ribs 10 and grooves 11. 
     FIG. 7 shows a pressing mandrel 1 with ribs 10 and grooves 11. A multiplicity of variations of these press mandrels 1 and shoulders, not all of which can be shown here, 4 is possible. 
     Cold-press-rolled parts can be manufactured with the different tool arrangements described above to modify the interior of these workpieces. To some extent, the desired modifications in the interior of these components can be produced with justifiable costs only with the tool arrangements described. With respect to the bicycle industry this means that high-strength and thin-walled parts can be manufactured with the press-rolling method which have a good chance on the market in the field of racing cycles and racing sport cycles, as well as against aluminium cycles. As a result of good wall evenness, smooth internal surfaces and very high levels of strength with elongation values which are still adequate, it is possible to have thin-walled components which are therefore lighter than components which are customary today. Furthermore, the devices described allow high levels of reproducible accuracy. In this way any one part is like an other because the deviations in values are minimal. By way of variations in the degree of transformation and naturally by way of the modifications in the interior of the parts. The methods allow resistance torques and strengths which are different in part. That is to say, there is the possibility of individually allocating the place with the highest strain to the appropriate resistance torques and strengths. For example, very high strengths at one position and very high elongation values at another position can be combined. Finally, the devices allow the production of conical parts, partially conical parts, perhaps combined with wall thicknesses which in part have different sizes, and with ribs or grooves applied on the inside, in one working operation. 
     All of these advantages lead to savings in cost in the production of tubular parts as a result of the described modifications in the interior of these workpieces.