Patent Publication Number: US-9897131-B2

Title: Method and a connecting system for the joining of moulded parts

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional application 61/610,501 filed Mar. 14, 2013 and German patent application No. 10 2012 204 015.3 filed Mar. 14, 2013, the entire disclosures of which are incorporated herein by way of reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention concerns a method and a connecting system for the joining of moulded parts. 
     A method of known art for the joining of moulded parts is so-called punch riveting with a solid rivet. Punch riveting often finds application in automotive construction and more generally in the sheet metal processing industry on thin sheets of a very wide variety of metallic materials. Suitable materials are, for example, light metals such as aluminium and magnesium, or ferrous metals such as steel. However, punch riveting also allows the joining of a metallic moulded part to a plastic-based moulded part and thus the manufacture of hybrid joints. By virtue of the relatively low strength of the joint under tensile head loading in comparison to the shear strength, a punch rivet joint is often used only at locations that are subjected to shear loading. 
     Punch riveting with a solid rivet is based on a combined perforation and pressure forming of the moulded parts, in which a rigid solid rivet generates a force and a form fit point joint. For purposes of manufacturing the joint the moulded parts are fixed on a die by means of a hold-down device. The punch rivet is then driven by means of a riveting header through the moulded parts and in this manner the latter are perforated. As a result of the contour of the die and the pressure force applied via the riveting header and the hold-down device the material of the moulded part on the die flows into a peripheral groove on the shank of the punch rivet. The flow of material is thereby opposed to, or transverse to, the punching direction. At the same time the head of the punch rivet is pressed against the riveting header-side moulded part, or if it is a countersunk head, it is impressed into the riveting header-side moulded part. The main component of the strength of the joint under tensile head loading is found in the form fit, which is generated from the undercut on the head of the punch rivet and the filling of the groove on the shank of the punch rivet. In order to increase the form fit component for higher load-bearing capacities, so-called multi-region rivets can be deployed. The multi-region rivets have a plurality of parallel shank grooves, which increase the form fit when the rivet is in the set state. Examples of multi-region rivets are described in the U.S. Pat. Nos. 6,527,490 B1 and 4,978,270. However, in general it has been shown that the filling of the shank grooves is strongly dependent on the respective material of the moulded parts. In DE 10 2010 000 500 A1 it is therefore proposed that for purposes of applying punch rivets to all punchable materials, the punch rivet should be locked outside the moulded parts. For this purpose a locking collar is set in place on a shank section led out through the punched hole, and is pressed together with a shank groove by means of an axial upsetting force. 
     An alternative joining method for purposes of connecting sheet metal-type moulded parts is joining by means of a locking collar pin. In this method a hole is introduced into the moulded parts before the actual riveting operation, through which hole the locking collar pin is then led out and subsequently locked with a locking collar squeezed onto the locking collar pin. The result is a joint with a high load-bearing capacity, which by virtue of parallel locking grooves has a high tensile head strength and also has high reliability in the locked state. However, by virtue of the separate perforation operation before the riveting process, this method is more labour-intensive than the punch rivet method. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to create a method and a connecting system for the joining of moulded parts, which removes the disadvantages cited above and enables a joint that has a high load-bearing capacity. 
     In an inventive method for the joining of moulded parts a locking collar pin with locking grooves, or with an external thread, is punched through the moulded parts, and subsequently a locking collar is locked with at least two locking grooves or with two threaded sections (two threads) by the application of radial pressure, or by means of a screwing or threading operation. 
     The inventive method enables the implementation of a joint with a higher strength compared with that of a conventional punch rivet process, since the locking collar pin is simultaneous engaged with a plurality of locking grooves, or threaded sections. In that the locking collar is locked together with the locking collar pin by means of radial pressure or a screwing force, and not by means of an axial, or essentially axial, upsetting force, as in the case of the above-cited DE 10 2010 000 500 A1, the locking collar in the locking operation is not upset, or is virtually not upset, and its height before the application of pressure corresponds, or virtually corresponds, to its height after the application of pressure. Since the locking collar pin is itself driven through the moulded parts and the punched hole that accommodates it is thus formed automatically, there is no initial perforation operation. Thus in the inventive method the advantages of a locking collar pin—high strength—are combined with the advantages of punch riveting—no initial perforation operation. Here the term “radial” means not only exclusively, but also primarily, or essentially, in the radial direction. 
     An inventive connecting system for the joining of moulded parts, in particular for purposes of executing the inventive method, has a locking collar pin for purposes of punching the moulded parts, and a locking collar for purposes of locking the locking collar pin, wherein the locking collar extends over at least two adjacent locking grooves in the axial direction, or over at least two adjacent threaded sections in the axial direction. 
     The punching section enables execution of a high-quality punching operation, that is to say, the formation of a precise punched hole, and the avoidance of any unwanted deformation of the moulded parts in the edge region of the punched hole. Moreover the punching section enables execution of the punching operation with a minimal punching force. The fact that the locking collar extends over at least two adjacent locking grooves in the axial direction, or over at least two adjacent threaded sections in the axial direction, allows the formation of a multiplicity of undercuts, and thus a high strength for the joint. Here, in contrast to the locking grooves, the external thread enables the locking collar to be unscrewed. In particular when opening the joint the locking action can be quickly and easily released by unscrewing the locking collar. 
     In order to be able to screw on the locking collar for purposes of the locking operation, the latter can have an internal thread corresponding to the external thread of the locking collar pin. Here it is particularly advantageous if the punching section of the locking collar pin has, for example, a lead-in chamfer for purposes of guiding on the locking collar, or is formed with a small axial extent and is therefore narrow. However, the form of the punching section need not be taken into account during screwing operations, if the punching section can be, and is, removed before the locking collar is screwed on, and before it is screwed off. 
     For purposes of reducing the complexity of the device the locking collar in one example of an embodiment has a cutting edge. Such a locking collar can be used as a cutting die and immediately after the punching operation can be squeezed onto the locking collar pin by the application of radial pressure, or screwed onto the latter. A tool change for the application of radial pressure by the locking collar is therefore not necessary. 
     In an alternative example of an embodiment, the cutting edge is formed on a shaping projection on the periphery of the end face of the locking collar. The shaping projection allows the use of the locking collar as a shaping die and the latter can likewise, immediately after the punching operation, be radially squeezed, or screwed, onto the locking collar pin. A tool change for the application of radial pressure by the locking collar is therefore also not necessary in this example of an embodiment. The shaping of the locking collar-side moulded part thereby causes strain hardening of the same in the region of the punched hole, and thus leads to an increase in the strength of the joint. 
     In an alternative example of an embodiment, a cutting ring manufactured discretely from the locking collar is provided with a cutting edge. By this means the two functions of punching and locking are separated, whereby the cutting ring undertakes the punching function and the locking collar undertakes the locking function. In this manner the cutting ring and the locking collar can be optimally matched to their respective functions. 
     In a further alternative example of an embodiment a shaping ring manufactured discretely from the locking collar is provided with a cutting edge. By this means the shaping ring acts as a shaping die and by virtue of the separation of functions the shaping ring and the locking collar can be optimally matched to their respective punching and locking functions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In what follows preferred examples of embodiments of the invention are elucidated in more detail with the aid of very simplified schematic representations. Here: 
         FIG. 1  shows a section through a joint using a first example of an embodiment of an inventive connecting system, 
         FIG. 2  shows a section through a joint using a second example of an embodiment of the inventive connecting system, 
         FIG. 3  shows a section through a joint using a third example of an embodiment of the inventive connecting system, 
         FIG. 4  shows a section through a joint using a fourth example of an embodiment of the inventive connecting system, and 
         FIG. 5  shows a section through a joint using a fifth example of an embodiment of the inventive connecting system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a joint  1  between two moulded parts  2 ,  4  with a first example of an embodiment of an inventive connecting system. Needless to say, more than two moulded parts  2 ,  4  can also be joined with the inventive connecting system. The moulded parts  2 ,  4  are designed in the form of plates in the region of the joint  1 , and in each case preferably are made of a material that can be cold formed such as aluminium, magnesium, steel, or an appropriate metal alloy. However, the moulded parts  2 ,  4  can also be manufactured from non-metallic materials that are suitable for punching operations such as wood, or a fibre composite material, which for example has a multiplicity of plastic, natural, or metal fibres embedded in a plastic matrix, or a metal matrix. The connecting system has a locking collar pin  6  and a locking collar  8 . The locking collar pin  6  is sectionally led out through a punched hole  10  extending through the moulded parts  2 ,  4 , and at its end is locked with the locking collar  8 . 
     The locking collar pin  6  includes a metallic material such as steel, or a non-metallic material such as an oxide ceramic. It has a head  14  and a shank  16 . 
     In this example of an embodiment the head  14  is designed as a universal head with a planar seating face  18  for purposes of a real seating on the upper, i.e., head-side moulded part  2  in accordance with the representation in  FIG. 2 . Alternatively the head  14  is designed, for example, as a countersunk head. 
     The shank  16  has a cylindrical shape with a central shank section  20 , a locking section  22 , and also a punching section  24 . However, it can also have another shape, and can be elliptical, for example. 
     The central shank section  20  extends orthogonally from the head  14  and has a smooth peripheral wall. However, it can also be enlarged conically, i.e., in the form of a cone, in the direction of the head  14 , so that during the punching operation strain hardening of the moulded parts  2 ,  4  occurs in the punched hole region of the central shank section  20 , as a result of radial enlargement of the punched hole  10  in certain regions. 
     The locking section  22  serves to lock the joint  1  with the locking collar  8 . It has a multiplicity of locking grooves  26  located parallel and adjacent to one another in the axial direction, i.e., the punching direction; these grooves have a uniform core diameter d, and in this example of an embodiment are in each case evenly spaced apart from one another in the axial direction. The locking grooves  26  can, however, also have a variable spacing relative to one another. Alternatively the locking grooves  26  are designed as an external thread. 
     The punching section  24  is formed at the end of the shank  16  as an extension of the locking section  22 . It serves to form the punched hole  10 , and in the example of an embodiment shown here has a cylindrical shape. Alternatively, however, it can taper radially in the direction of the head  14 , for example in the form of a cone. However, it can also be enlarged radially in the direction of the head  14 , so that during the punching operation strain hardening of the moulded parts  2 ,  4  occurs over the whole of the punched hole region as a result of radial enlargement of the punched hole  10 . The punching section  24  is preferably hardened by means of local heat treatment. 
     The locking collar  8  serves to lock the locking collar pin  6 , i.e., to lock the joint  1 . It is made preferably of a metallic material that is easy to deform, and a through hole  28  passes through the collar. In order to enable locking of the locking collar  8  with at least some of the locking grooves  26 , or threaded sections, of the locking collar pin  6 , the locking collar  8  has a height h, which enables locking with at least two of the locking grooves adjacent to one another in the axial direction, or with two threaded sections adjacent to one another in the axial direction. The locking collar  8  preferably has a height h, which is somewhat less than a length  1  of a shank region of the locking collar pin  6  projecting out of the punched hole  10 , so that an active engagement takes place with as large a number of locking grooves  26  as possible, and so that the end face of the locking collar  8  does not protrude beyond the punching section  24  after the locking operation. For purposes of seating on what is, in accordance with  FIG. 1 , the lower moulded part  4 , the locking collar  8  has an end face contact surface  30  which is free of steps, i.e., is planar. For purposes of achieving an optimal locking operation with at least some of the locking grooves  26  while subjecting these to minimal radial compressive force the locking collar  8  is preferably not hardened. 
     The through hole  28  has an internal diameter such that, on the one hand, a punched billet can fall freely out through the through hole  28 , and on the other hand, only a minimum radial deformation of the locking collar  8  is necessary for purposes of radial compression together with the locking section  22 . However, if the locking section  22  has an external thread instead of the locking grooves  26 , the through hole  28  can also be provided with an internal thread corresponding with the external thread. 
     The first example of an embodiment of the inventive connecting system described above enables the execution of a two-stage joining method. “Two-stage” means that the joining operation does not take place in a single stroke, but rather that a tool change is necessary. The moulded parts  2 ,  4  are clamped together between a hold-down device and a die. The punching section  24  of the locking collar pin  6  is then pressed against the moulded parts  2 ,  4  by means of a riveting header. The locking collar pin  6  penetrates into the moulded parts  2 ,  4  to the extent that the head  14  of the pin is seated on the upper moulded part  2 . If the head  14  is designed as a countersunk head it is impressed into the upper moulded part  2  in a manner appropriate to the depression in the latter. A punched billet is ejected through the die. After the formation of the punched hole  10  the die is removed and the locking collar  8  is positioned on the locking section  22  of the locking collar pin  6 , and is subjected to a radial compressive force such that it is squeezed together with at least two of the locking grooves  26 . 
       FIG. 2  shows a second example of an embodiment of a joint  1  between two moulded parts  2 ,  4  that are connected with one another using a second example of an embodiment of the inventive connecting system. In contrast to the first example of an embodiment in  FIG. 1 , in this example of an embodiment a die is integrated into a locking collar  8 . Thus the locking collar  8  in this example of an embodiment also undertakes the punching function and for purposes of forming the die has an integral die section  32  and also a deformation section  34 , through both of which passes a through hole  28 . 
     The die section  32  has a radially internal cutting edge  36 , which in the outlet region of the through hole  28  is provided with an end face contact surface  30  that is free of steps, i.e., is planar. The cutting edge  36  allows the use of the locking collar  8  as a cutting die, wherein for purposes of stabilizing the shape of the locking collar  8  during the punching operation, and for purposes of achieving a high quality punching operation, the die section  32  and in particular the cutting edge  36  can be hardened by means of local heat treatment, 
     The deformation section  34  serves to provide radial squeezing of the locking collar  8  together with at least some of the locking grooves  26  of the locking collar pin  6 . For purposes of achieving an optimal locking operation with at least some of the locking grooves  26 , whilst subjecting the latter to minimal radial compression force, the deformation section  34  is preferably not hardened. 
     The locking collar pin  6  corresponds to that in the first example of an embodiment in  FIG. 1 , and has a central shank section  20 , a locking section  22  and a punching section  24 . 
     The second example of an embodiment of the inventive connecting system enables the execution of a single-stage joining method. “Single-stage” means that the locking collar  8  acts as a die and thus the joining operation takes place in one stroke, and therefore no tool change is required after the punching operation in order to apply pressure with the locking collar  8 . The moulded parts  2 ,  4  are clamped together between a hold-down device and the locking collar  8  acting as a cutting die. For purposes of forming the punched hole  10  the locking collar pin  6  with its punching section  24  is then pressed against the moulded parts  2 ,  4  by means of a riveting header. The locking collar pin  6  penetrates the moulded parts  2 ,  4  to the extent that its head  14  is located seated on the upper moulded part  2 . A punched billet is ejected through the through hole  28  of the locking collar  8  and the punching section  24  is sectionally led out of the through hole  28 . If the head  14  is designed as a countersunk head it is impressed into the upper moulded part  2  in a manner appropriate to the depression in the latter. By the application of radial pressure force the locking collar  8  is then deformed such that the locking collar  8  is squeezed together with at least two of the locking grooves  26 . The moulded parts  2 ,  4  are now securely locked between the head  14  of the locking collar pin  6  and the locking collar  8 . Here a high level of strength is achieved in the joint  1  as a result of the engagement of the locking collar  8  with a plurality of locking grooves  26 . The height h of the locking collar  8  has thereby not been altered, or has virtually not been altered, as a result of the application of radial pressure. 
       FIG. 3  shows a joint  1  between two moulded parts  2 ,  4  that are connected with one another using a third example of an embodiment of the inventive connecting system. In contrast to the second example of an embodiment in  FIG. 2 , in this example of an embodiment a cutting die is not integrated into a locking collar  8 , but instead is formed as a separately, i.e., discretely, manufactured cutting ring  38 , which after the punching operation remains on the locking section  22 . Consequently the locking collar  8  in this example of an embodiment has just a deformation section  34 , with what is preferably a low hardness. The locking collar  8  can therefore be a locking collar  8  in accordance with the first example of an embodiment in  FIG. 1 . 
     The cutting die  38  has a radially internal cutting edge  36  and in comparison to the locking collar  8  has a higher level of hardness, i.e., strength. It is aligned flush with the locking collar  8  and is preferably connected on its end face with the locking collar  8  in a material bond, or a force fit, or a form fit. It is, for example, pressed onto the locking collar  8 , or is adhesively bonded or welded to the latter. 
     The locking collar pin  6  corresponds to that in the above examples of an embodiment in  FIGS. 1 and 2 , and has a central shank section  20 , a locking section  22  and a punching section  24 . 
     The third example of an embodiment of the inventive connecting system enables the execution of a single-stage joining method in accordance with  FIG. 2 . However, in contrast to the example of an embodiment in  FIG. 2 , during the punching operation an axial counter-support does not need to make contact directly with the locking collar  8 , but rather can be positioned on the cutting ring  38 . For purposes of locating the counter-support, the cutting ring  38 , as shown in  FIG. 3 , can have a larger external diameter than the locking collar  8 . Alternatively, however, the locking collar  8  can also have, for example, openings on its periphery, through which the counter-support can be led, so that the external diameter of the cutting ring  38  can be the same as, or even smaller than, the external diameter of the locking collar  8 . 
     The execution of the single-stage joining method is then possible even if the cutting ring  38  is not connected with the locking collar  8 . However, the cutting ring  38  and the locking collar  8  must then be secured against any alteration of location relative to one another during the punching operation. 
       FIG. 4  shows a joint  1  between two moulded parts  2 ,  4  that are connected with one another using a fourth example of an embodiment of the inventive connecting system. In contrast to the second example of an embodiment in  FIG. 2 , in this example of an embodiment a locking collar  8  has an axial shaping projection  40  extending around its periphery in the region of its integral die section  32 , and thus has a step-type contact surface  30 . By virtue of the integrated die section  32  the locking collar  8  in this example of an embodiment undertakes the two functions of punching and locking, in an analogous manner to the second example of an embodiment in  FIG. 2 . 
     The shaping projection  40  has a radially internal integrated cutting-edge  36  and enables the use of the locking collar  8  as a shaping die, as a result of which during the punching operation the lower moulded part  4  is strain hardened in the outlet region of the punched hole  10 . The die section  32 , and in particular the shaping projection  40 , are preferably hardened. A deformation section  34  of the locking collar  8  is preferably unhardened. 
     Since the locking collar  8  is not radially pressed together with the locking collar pin  6  in the region of the shaping projection  40 , the shaping projection  40  is not taken into account in the height h of the locking collar  8 . Thus the locking collar  8 , in this example of an embodiment also, preferably has a height h that is somewhat smaller than a length of a shank region of the locking collar pin  6  projecting out of the punched hole  10 . 
     The locking collar pin  6  corresponds to that in the above examples of embodiments in  FIGS. 1, 2 and 3 , and has a central shank section  20 , a locking section  22  and a punching section  24 . 
     The above-described fourth example of an embodiment of the inventive connecting system enables the execution of a single-stage joining method in accordance with  FIGS. 2 and 3 . Additionally, however, the shaping projection  40  is axially impressed into the lower moulded part  4  during the punching operation of the punched hole  10 , so that the lower moulded part  4  is strain hardened in the outlet region of the punched hole  10 . Here however, as can be discerned in  FIG. 4 , the shaping projection  40  is not impressed into the locking grooves  26  encompassed by the former on the internal periphery, and is not subjected to any plastic deformation. The shaping projection  40  is thus dimensionally stable. 
     In the joint  1  shown in  FIG. 5  between two moulded parts  2 ,  4  that are connected with one another using a fifth example of an embodiment of the inventive connecting system, the shaping die is not integrated into a locking collar  8 , but rather is formed as a separately, i.e., discretely, manufactured shaping ring  42 . The locking collar  8  has just a deformation section  34 , and can be a locking collar  8  in accordance with the first and third examples of embodiments in  FIGS. 1 and 3 . 
     The shaping ring  42  has a shaping projection  40  with a radially internal cutting edge  36  and in comparison to the locking collar  8  has a higher level of hardness, i.e., strength. It is aligned flush with the locking collar  8  and is preferably connected on its end face with the locking collar  8  in a material bond, or a force fit, or a form fit. 
     The locking collar pin  6  corresponds to that in the above examples of embodiments in  FIGS. 1, 2, 3 and 4 , and has accordingly a central shank section  20 , a locking section  22  and a punching section  24 . 
     The fifth example of an embodiment of the inventive connecting system enables the execution of a single-stage joining method, wherein by means of the shaping projection  40  the lower moulded part  4  is strain hardened in the outlet region of the punched hole  10 . As can be discerned in  FIG. 5 , the shaping projection  42  is not, however, impressed into the locking grooves  26  encompassed by the former on the internal periphery. The locking of the joint  1  is undertaken exclusively by the application of radial pressure by the locking collar  8  onto the locking grooves  26 . The shaping ring  42  is thus dimensionally stable. In an analogous manner to the example of an embodiment in  FIG. 3  an axial counter-support does not need to make contact directly with the locking collar  8  during the punching operation, but rather can be located on the shaping ring  42 . For purposes of locating the counter-support, the shaping ring  42 , as shown in  FIG. 5 , can have a larger external diameter than the locking collar  8 . Alternatively, however, the locking collar  8  can also have, for example, openings on its periphery, through which the counter-support can be led, so that the external diameter of the shaping ring  42  can be the same as, or even smaller than, the external diameter of the locking collar  8 . 
     The execution of the single-stage joining method is then possible even if the shaping ring  42  is not connected with the locking collar  8 . However, the shaping ring  42  and the locking collar  8  must then be secured against any alteration of location relative to one another during the punching operation. 
     Insofar as in all the above described examples of embodiments the locking section  22  is provided with an external thread instead of the locking grooves  26 , and the locking collar  8  is provided with an internal thread, the locking collar  8  can also be screwed onto the locking section  22  for purposes of locking. 
     The single-stage method in accordance with  FIGS. 2, 3, 4 and 5  can in principle also be executed as a two-stage joining method. However, in this case a die, or cutting ring  38 , or shaping ring  42 , is to be removed after the punching operation in accordance with  FIG. 1 . 
     Since in the case of the first, second and third examples of embodiments in accordance with  FIGS. 1, 2 and 3 , no shaping projection  40  is provided, in these three examples of embodiments the locking collar-side, i.e., lower, moulded part  4  can be made of a material that can be punched, such as plastic, that cannot be strain hardened, or cannot be plastically strain hardened. The inventive connecting system in accordance with these examples of embodiments, when using a locking collar pin  6 , can thus be used with a universal head, i.e., with no countersunk head, independently of the material of the moulded parts  2 ,  4 . 
     Since in the fourth and fifth examples of embodiments in accordance with  FIGS. 4 and 5  a shaping projection  40  is provided, the lower moulded part  4  must be made of a material that can be strain hardened. The punchable material of the upper, i.e., head-side, moulded part  2  can be freely selected, if a locking collar pin  6  with a universal head is selected. However, if the locking collar pin  6  has a countersunk head, then the upper moulded part  4  must also be capable of being strain hardened. 
     Disclosed is a method for the connection of moulded parts, wherein a locking collar pin with locking grooves or with an external thread, is driven through the moulded parts and subsequently a locking collar is locked together with at least some of the locking grooves, or with threaded sections of the locking collar pin, by the application of radial pressure, or by means of a screwing operation; also disclosed is a connecting system with a locking collar pin, which has a punching section for purposes of punching through the moulded parts, and also locking grooves for purposes of active engagement with a locking collar; the latter extends over at least two adjacent locking grooves in the axial direction, or over at least two adjacent thread sections in the axial direction. 
     As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art. 
     REFERENCE SYMBOL LIST 
       1  Joint 
       2  Head-side, i.e., upper, moulded part 
       4  Locking collar-side, i.e., lower, moulded part 
       6  Locking collar pin 
       8  Locking collar 
       10  Punched hole 
       12  Hole wall 
       14  Head 
       16  Shank 
       18  Seating surface 
       20  Central shank section 
       22  Locking section 
       24  Punching section 
       26  Locking grooves 
       28  Through hole 
       30  Contact surface 
       32  Die section 
       34  Deformation section 
       36  Cutting edge 
       38  Cutting ring 
       40  Shaping projection 
       42  Shaping ring 
     d Core diameter 
     h Height 
     l Length