Patent Publication Number: US-6212982-B1

Title: Process for manufacturing slot-shaped openings on hollow sections and apparatus for implementing same

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     This application claims the priority of German application 196 47 964.9-14 filed in Germany on Nov. 20, 1996, the disclosure of which is expressly incorporated by reference herein. 
     The invention relates to a process and apparatus for manufacturing slot-shaped openings on hollow sections with the openings being generated without cut outs by the displacement of material using a piercing cutting operation by means of a blade type cutting tool while supporting the hollow sections from the interior during slotting operation. 
     A process and apparatus of this type are known from German Patent Document DE 43 34 203 A1. There, passages are made in a linearly extending collecting pipe of a heat exchanger, in which case several punches, which are arranged in parallel to one another and are fastened on a carrier part and have blades constructed on their free ends, are jointly moved radially onto the hollow section to be worked which forms the collecting pipe. In this case, the punches tear the passages into the wall of the hollow section at the point of application. A rod-shaped tool with support sections is pushed into the hollow section, which support sections, in the appropriate position of the tool, are positioned between the application points of the hollow section for maintaining the shape of the hollow section. With the pushing-through of the hollow section by the punches, the hollow section material is displaced at that point, in which case the edge of the passage to be produced is bent while forming a wall neck projecting into the hollow section. The contact of the wall neck on the support sections ensures a rectangular course of the wall neck so that the hollow section has a defined seat for the flat tubes, which are fitted into the passages, for a later tight soldering. As a result of the bending of the penetration edges and their resting on the support sections of the rod-shaped tool, this tool is blocked with respect to an axial pulling out of the hollow section so that the tool cannot easily be removed from the hollow section to be worked. This is remedied by a bipartition of the tool, in which case first a lower half of the tool can be removed by a simple pushing-out; after which the upper half is rotated until it comes to rest below the bent edges. Then this half can also be pulled out. 
     In another embodiment, the tool, which now consists of one part, only partially fills the cross-section of the hollow section so that a clearance is formed which extends axially along the whole length of the hollow section. In this case, after the machining of the hollow section, the support tool is lowered and is pulled out of the hollow section. 
     In the case of both embodiments, the tool has a high-expenditure construction because of the support sections, in which case, they must have an extremely precisely adjusted distance from one another so that the hollow section can meet the precision requirements for the assembly with the flat tubes. At the same time, the handling of the tool requires high expenditures since it must be positioned in a precisely defined manner relative to the cutting tool. Because of the unavoidable positioning tolerances, the danger exists during the machining on the hollow section that one of the oblong punches will bend because it strikes a point of the hollow section wall which is supported by the support tool or is situated in the edge area of the respective support section, whereby the cutting tool may possibly be irreparably damaged. Likewise, the hollow section may also be damaged such that disadvantageous incisions occur on it which, particularly when the hollow section is used as a liquid-carrying component having sealing problems, will result in an increased reject rate of hollow sections. Furthermore, in the one case, the two-part support tool must be held together during the pushing-in and must be rotated when being removed after the machining, which results in lost production time. In the other case, for an effective support, a high holding force must be applied which is directed against the penetration force of the cutting tool, so that it is avoided that the one-part support tool is pressed into the clearance inside the hollow section under the effect of the cutting tool and, in the process, the support is impaired which is required for maintaining the shape of the hollow section. 
     The thickness of the bent edge at the points of the hollow section acted upon by the punches and the width of the respective support section of the rod-shaped support tool also determine the distance between the passages or openings. However, as a result, very small hollow sections may be too limited in their dimensions in order to be provided with several passages or openings by means of the described device. 
     In addition, the described manufacturing process and the device for its implementation can be used only in the case of linear hollow sections. Other shapes of hollow sections with cross-sectional changes and/or changes of course, such as bent pipes, cannot be provided with openings in this manner. 
     It is an object of the invention to further develop a process and apparatus of the above-mentioned type such that, in a simple manner and while maintaining the shape of the hollow section, slot-shaped openings can be manufactured in a reliable process on arbitrarily constructed hollow sections free of positional tolerances. 
     According to the invention, this object is achieved by a process and apparatus wherein, as a result of interaction between cutting action of the cutting tool integrated in an internal high pressure forming tool and an internal high pressure of a fluid generated within a hollow section disposed in a recess of the internal high pressure forming tool, the hollow section is slotted in a relative movement of the hollow section and of the cutting tool with respect to one another, with continuous, interior-side support of the hollow section by means of the pressure fluid, the support at the point of the piercing of the cutting tool into the hollow section being pushed back and the hollow section material, which is flowable under internal high pressure, flowing off laterally from respective piercing points around the piercing points while forming a wall thickening on the hollow section, and wherein the outer contour of the hollow section being pressed by means of internal high pressure against a contour of a face of a cutting tool carrier which is separate with respect to the cutting tool but is integrated with the cutting tool, which face forms a portion of the forming tool recess which faces the hollow section. 
     Because of the arrangement of the invention, a support tool can be eliminated because the support takes place by the internal high pressure applied inside the hollow section which loads the wall on all sides. In this case, only an internal-high-pressure forming tool is required into whose recess the hollow section is placed, in which case the die of the forming tool has a recess in which the cutting tool together with the support is accommodated. If the hollow section is also calibrated for exact dimensions which are uniform for all hollow sections to be machined, an internal-high-pressure forming tool is required anyhow so that in this case no additional tool—with the exception of the cutting tool—must be used. The recess may be constructed corresponding to the shape of the hollow section with respect to cross-sectional changes and to the axial course so that the device and the process are not subjected to any limitations in this respect. Furthermore, the construction of the slot-type openings takes place in a completely reliable manner with respect to the process because the cutting tool is never in any danger of impacting on a hard support object on which it may be damaged. Because of the recess of the forming tool which is adapted precisely to the hollow section and because of the non-existent requirement of positioning a support tool to be pushed into the hollow section, as well as the integration of the cutting tool into the forming tool in which the cutting tool takes up a defined relative position with respect to the forming tool, the hollow section, the cutting tool and the forming tool, which results in the support within the hollow section, are always positioned precisely with respect to one another in the machining position, in which case no manufacturing tolerances can occur. By means of the simultaneous support of the outer circumference of the hollow section on the recess, no deformations of the original shape of the hollow section will occur so that, as the result, the dimensional accuracy of the hollow section as a whole is maintained. The forming of the hollow section and the providing of the openings on it take place in the same tool and therefore in one operating cycle without the requirement of opening the tool and setting it up again for the cutting operation. 
     Furthermore, by means of the invention, very small-construction hollow sections can also be provided with a large number of openings because a support section of a discussed tool of a finite width and the thickness of the hollow section wall which determines the width of the immersion gap for the blade of the cutting tool, are eliminated. The minimum distance between the openings is therefore determined only by the blade width of the cutting tool, advantageously, also in the case of larger-construction hollow sections, several openings being formable on a partial section. Virtually because of the existing internal pressure, the hollow section material displaced by the blade flows laterally away from the blade and is pressed against the hollow section wall surrounding the respective opening, which, in the case of the finished hollow section, is exhibited in a wall thickening. Because of the displacement of material, the cutting of the hollow section takes place without any occurrence of cuttings and without waste. 
     Finally, openings can be achieved which have sharp-edged margins and thus no bending radii on the exterior side of the section. This maximizes the support surface for add-on pieces to be mounted later so that, during the mounting, the Hertzian stress is distributed as well as possible. 
     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic lateral view of an apparatus constructed according to a preferred embodiment of the invention showing a partial longitudinal sectional view of the top tool of the forming tool assembly; 
     FIG. 2 is an enlarged lateral view of the top tool of FIG. 1; 
     FIG. 3 a  is a horizontal sectional top view of a section of the top tool having cutting tools in the uncut condition of the hollow section inserted in the recess of the forming tool; 
     FIG. 3 b  is a view of the section from FIG. 2 a  showing the cutting tools cutting into the hollow section; 
     FIG. 3 c  is a view of the section from FIG. 3 a  after the penetration of the hollow section by the cutting tools; 
     FIG. 4 a  is a top view of the unmachined hollow section from FIG. 3 a;    
     FIG. 4 b  is a cross-sectional view of the hollow section from FIG. 4 a;    
     FIG. 5 a  is a top view of the machined hollow section from FIG. 3 a;    
     FIG. 5 b  is a cross-sectional view of the hollow section from FIG. 5 a.   
    
    
     DETAILED DESCRIPTION OF DRAWINGS 
     FIG. 1 illustrates an internal-high-pressure forming tool  1  which contains a press slide  2  and a bedplate  3 , the press slide  2  being guided to be liftable and lowerable in strokes and being connected with a hydraulic cylinder, by means of which the press slide  2  in the closed condition of the forming tool  1  can be held on the bedplate  3  against the generated internal high pressure. A top tool  4  is fastened on the bottom side on the press slide, while a bottom tool  5  is mounted opposite on the bedplate  3  on the top side, the faces  13 ,  14  of the bottom tool  5  facing one another having molded-out portions which form a recess  6  in which a hollow section  7  can be placed and which essentially matches it in its molding-out and its cross-sectional measurements. One high pressure cylinder  8  respectively is arranged laterally of the forming tool  1  on both sides, by means of which high pressure cylinder  8  a follow-up punch  9  can be displaced axially with respect to the hollow section  7 . By way of a high pressure duct extending in the follow-up punch  9 , a high-pressure fluid for the high-pressure forming is introduced into the hollow section  7  and the internal high pressure is generated by means of the fluid. Furthermore, the follow-up punch  9  is used, on the one hand, for the axial sealing of the hollow section  7  by way of its faces  10 ,  11  facing the ends of the hollow section  7  and, on the other hand, for the axial follow-up guiding of profile material in the case of a radial widening of the hollow section  7  by means of the internal high pressure for known purposes. 
     Starting from the face  12  of the top tool  4  facing away from the recess  6 , a recess  15  is worked into the top tool  4  and ends close to the other face  13  of the top tool  4 . In the recess  15  a strip-shaped carrier  16  is received on which several blade-type cutting tools  17  are held which are arranged in parallel to one another, as also illustrated particularly in FIG.  2 . The cutting tools  17  are constructed as sharpened slides which, in the sharpened area, have sharp edges which form the blades  25 . Within the recess  15 , the carrier  16  can be displaceably guided radially toward the recess  6  by means of a high-pressure cylinder  19  which is connected with it on the side  18  which is rearward with respect to the recess  6 . In the internal-high-pressure forming process, the high pressure cylinder  19  is used in the same manner as the counterholder for the carrier  16  and for the cutting tools  17 . 
     In this case, the cutting tools  17  are fixedly connected with the carrier  16  and dip into guide gaps  20  which extend inside the forming tool  4  radially toward the recess  6  and connect its face  13  with the recess  15 . The cutting tools  17  may be displaceable inside the gaps  20  in a precisely fitting manner for an optimal sealing of the recess  15  in the direction of the recess  6  or with play with a lubrication for reducing the friction on the gap wall  21 . In the case of an accurate fit, it is conceivable to coat the gap wall  21  with a solid lubrication for reducing the friction, for example, with graphite or molybdenum sulfide. As an alternative, a coating is also contemplated as a wear protection layer consisting of metal nitrides, carbides or carbon nitrides, such as TiN, TiC, TiCN. 
     As an alternative to the fastening of the cutting tools  17  on the carrier  16 , it is contemplated to arrange the carrier  16  stationarily in the recess  15  close to the face  13  of the top tool and to displaceably guide the cutting tools  17  in the carrier  16 . For driving the cutting tools  17 , a transverse duct would then be provided in the carrier  16  which leads to the outside and can be acted upon by a high-pressure fluid and which cuts a blind-hole-type guide bore of the cutting tools  17  on their base and, when acted upon by high pressure, drives the cutting tools  17  toward the recess  6 . The driving of the cutting tools  17  back into their inoperative position can take place by the internal high pressure within the cut-in hollow section  7  while simultaneously removing the pressure inside the transverse duct. In order to hold the cutting tools  17  in this case in the carrier  16  so that they cannot be lost, a stop must be provided on them which finds a counterstop inside the carrier  16  or on the base  22  of the recess  15 . 
     Instead of the construction of a transverse duct, a blind-hole-type bore which points radially to the recess  6  may be constructed in the carrier  16 , in which bore the respective cutting tool  17  is guided. For this purpose, the cutting tool  17  is constructed as a punch whose punch shaft has a tip equipped with the blades  25 . On its face away from the recess  6 , the plate-shaped head of the punch can be acted upon by a high-pressure fluid and, on the opposite face, is in an operative connection with a screw-shaped pressure spring which is supported on the base of the blind-hole bore and drives the punch into the inoperative position of the cutting tool  17 . In this case, the bore is divided into two partial spaces by the punch head. Depending on which acting force (pressure force of the fluid—spring force) is predominant, the punch is pushed back and forth between the operative position and the inoperative position. By means of the arrangement of a ring seal on its circumference in preferred embodiments, the punch seals off the fluid-carrying partial space of the bore from the partial space in which the spring is arranged. 
     As illustrated in FIGS. 5 a, b , for manufacturing slot-shaped openings  23 , the hollow section  7  is placed in the recess  6 , after which the forming tool  1  is closed by lowering the top tool  4  onto the bottom tool  5 . After a high-pressure fluid is introduced into the hollow section  7 , a high pressure is generated in the range of between 800 and 3,000 bar, the hollow section  7  radially widening and placing itself completely onto the recess  6  and as a result being calibrated. During this operation, the cutting tools  17  are in the inoperative position, in which case the slide tip  24  ends flush with the side  13  of the top tool  4  (FIG. 3 a ). After the calibration, while there is still internal high pressure, the carrier  16  is displaced by the high-pressure cylinder  19  in the recess  15  toward the hollow section, in which case the blades  25  of the cutting tools  17  penetrate into the hollow section material in the normal line direction with respect to the impact point on the hollow section  7 . As the result of the internal high pressure directed against the movement of the cutting tools  17 , the hollow section material displaced by them during the penetration is pressed laterally away from the blades  25  onto the interior wall  26  of the hollow section  7  (FIG. 3 b ). During the cutting penetration of the hollow section  7  by the blades  25 , the slot-shaped openings  23  are finally formed. As the blades  25  come through, the penetration operation of the cutting tools  17  is concluded and the displacement movement of the carrier  16  toward the hollow section  7  is finished. Because of the internal high pressure which makes the hollow section material flowable, a toroidal wall thickening  28  on the hollow section  7  (FIG. 3 c ) is formed around the edge  27  of the openings  23 . 
     By means of the permanent contact pressure onto the face  13  of the top tool  4  during the cutting action of the cutting tools  17  in the pushing movement, the exterior wall of the hollow section  7  remains untouched by a possible deformation induced by the penetration so that the dimensional accuracy of the exterior wall is ensured during the machining operation. After the slotting, the internal high pressure is reduced and the cutting tools  17  are withdrawn into the guiding gaps  20  of the top tool  4  by way of a withdrawal movement of the carrier  16  operated by the high pressure cylinder. 
     It is also contemplated according to other preferred embodiments of the invention to provide a passage in the top tool instead of the recess  15 , in which passage the carrier  16  can be displaceably guided, in which case its face  30  pointing to the hollow section  7  forms a portion of the recess  6 . In this case, during the calibration, the face  30  can adjoin the face  13  of the top tool  4  in an aligned manner or it can be in an end position withdrawn into the top tool  4  so that, by means of the face  30  of the carrier  16  and the surrounding walls of the top tool  4 , an expansion trough is formed which is part of the recess  6  and whose base is formed by the face  30 . 
     For this arrangement, the cutting tools  17  together with their carrier  16  can be stationarily connected with the top tool  4  designed as a die, the cutting tools projecting into the expansion trough. For manufacturing the openings  23 , the hollow section  7  is expanded by the effect of the internal high pressure and is pressed onto the oppositely projecting cutting tool  17  protruding into the expansion trough, in which case, after the yield limit of the hollow section material is exceeded, the slot-shaped openings  23  are formed. 
     It is also contemplated to arrange the cutting tools  17  such that they project stationarily and thus non-displaceably into a recess  6  which has no expansion trough. However, in this case, the hollow section  7  to be formed and widened must be dimensioned such that, when it is placed in the recess  6 , it is spaced away from the cutting tools. 
     In both the last two described cases, the slotting and the calibrating or forming of the hollow section  7 , in the interest of an economical process, takes place simultaneously, in which case no movable tool parts are required for the cutting of the openings  23 . This is achieved solely by the internal high pressure. For removing the slotted hollow section  7 , when the forming tool  1  is opened, this forming tool may have to be held so that the cutting tools  17  can be pulled out of the hollow section  7  by way of the stroke of the top tool  4 . In the case of large and heavy hollow sections  7 , the holding measure may be eliminated because of the force of gravity replacing the holding force. 
     The providing of the slot-shaped openings  23  may also take place in that the hollow section  7  is notched at the point of the opening  23  to be formed by a cutting tool  17  guided onto the hollow section  7 . The generating of the opening  23  will then take place by the effect of the internal high pressure onto the notch point. In this case, the cutting tools  17  may again be arranged in the withdrawn inoperative condition so that, merely as the result of the weak point produced by the notching, the internal high pressure will divide it in a material-displacing manner while forming a penetration. 
     It is also contemplated that the blades  25  of the cutting tools  17  remain in the notching position, in which case the internal high pressure, at the notching point along the blades  25 , laterally pushes away the hollow section material it made flowable so that one opening  23  respectively is formed. As the result of the manufacturing process of openings  23  by means of notching in conjunction with internal high pressure, only the essential part of the cutting tool, specifically the blade  25 , comes in physical contact with the hollow section  7  so that, when the cutting tool  17  is withdrawn after the machining operation, the possible danger of a jamming in the hollow section  7  does not occur. 
     The hollow section  7  can be constructed according to the half-shell construction method in two parts or in one part, for example, as an extruded section, the one-part construction resulting in cost and quality advantages during the manufacturing. The hollow section  7  may be formed from an unprofiled blank placed in the internal-high-pressure forming tool, the profiling taking place by internal high pressure before the providing of the openings  23  in the forming tool  1 . Between the profiling and the providing of the openings  23 , the calibration of the hollow section  7  takes place which occurs at a particularly high internal pressure and which, because of the contact pressure on the profile  7 , provides the desired dimensionally accurate, exterior shape of the hollow section  7  which has no manufacturing tolerances. In this case, the two machining steps take place in one operating cycle without opening the tool in-between. 
     Slot-shaped openings  23  on a hollow section  7  are required, for example, when the hollow section  7  is used as a radiator tank of a vehicle radiator in order to insert into them flat tubes which extend transversely to the radiator tank and then establish a connection of the flat tubes, which is water-tight toward the outside, with the radiator tank at the insertion point, for example, by soldering. FIGS. 4 a  and  b  show this radiator tank in the still unslotted condition. The radiator tank has a pipe-shaped construction and, on a circumferential section, has a plane, flat surface  29  which extends axially continuously through the radiator tank. 
     As illustrated in FIGS. 5 a  and  b , the openings  23  are cut into this flat area  29 . Particularly the flat area  29  must be dimensionally accurate since otherwise, because of the resulting different distance between the two opposite radiator tanks of a vehicle radiator, the flat tubes could not be assembled with the radiator tanks to form the radiator. This dimensional accuracy, as the result of the contact pressure of the hollow section  7  onto the correspondingly shaped recess  6 , is first optimized by the calibration and is then maintained during the cutting operation. Advantageously, the high-pressure fluid is introduced by way of the connection to the lines of the cooling circulation system already existing at the radiator tank, and the high pressure is generated. This eliminates the construction of a separate connection which will no longer be required in the use of the finished radiator tank. In this case, the diameter of the connection opening is smaller than the width of the radiator tank. For the later fitting-on of a cooling water hose, a hose taper plug may also be molded out by means of internal high pressure forming on the circumference of the connection opening. 
     Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.