Method of forming a tubular member

Information

  • Patent Grant
  • 6447399
  • Patent Number
    6,447,399
  • Date Filed
    Wednesday, December 20, 2000
    24 years ago
  • Date Issued
    Tuesday, September 10, 2002
    22 years ago
Abstract
A method of forming a tubular member with longitudinal slots along part of its wall, comprising the steps of: firstly, forming longitudinal zones of weakness along part of the wall of the tubular member, and secondly, expanding the said part of the tubular member radially to cause fracture of the wall of the member along the longitudinal zones, thereby to form longitudinal slots.
Description




The invention relates to a method of forming a tubular member with longitudinal slots in its wall. By way of example, one such tubular member is the tubular shell of a blind breakstem rivet, of the type which is provided with multiple longitudinal slots so that, when the rivet is set by axially compressing part of the shell, the shell deforms into a number of outwardly projecting legs which provide a blind head having a relatively large radial dimension of engagement with the workpiece. Examples of such blind rivets with slotted shells are commercially available under the Registered Trade Marks BULBEX and TLR. However such longitudinally slotted members can be used for many other purposes.




The term ‘slot’ is intended to include both constructions in which there is a gap between the edges or walls of the parts of the material of the tubular member separated by the slot, and also constructions in which the two edges or walls of the slot are in contact with each other, there being a mechanical discontinuity in the material.




Such slotted members are usually of metal. With a relatively soft metal, such as aluminium, forming the slots in a tubular blank is commonly done by driving through the bore of the blank a close-fitting tool of much harder material, such as steel, which carries a number of radially projecting longitudinal ribs, each having a radial height equal to at least the wall thickness of the tubular blank. Each rib forms a corresponding longitudinal slot in the blank. However, if this method is applied to tubular blanks of steel, it is found that rapid and excessive wear to the tool, particularly to the leading ends of the ribs, occurs.




The present invention aims to provide a new method of forming a tubular member with longitudinal slots in its wall, which overcomes this problem.




Accordingly, the present invention provides, in one of its aspects, a method of forming a tubular member with slots along part of its wall, which method is set out in the accompanying claim


1


.




Further features of the invention are set out in the accompanying claims


2


to


16


. The invention includes a tubular member which has been formed by a method according to the invention, as set out in claim


16


.











Some specific examples of the invention will now be described by way of example and with reference to the accompanying drawings, in which:





FIGS. 1



a


to


1




i


show successive configurations of a blank during one example method;





FIGS. 2



d


to


2




h


correspond to

FIGS. 1



d


to


1




h


respectively and illustrate a second example method which is a modification of the first example;





FIGS. 3



d


to


3




h


correspond to

FIGS. 1



d


to


1




h


respectively and illustrate a third example method which is a different modification of the first example;





FIG. 4

illustrates a blind rivet assembly incorporating a tubular shell made according to the invention; and





FIGS. 5



a


and


5




b


show the rivet of

FIG. 4

in the placed condition.











The term ‘blank’ is used to refer to the tubular member in all these successive configurations, apart from the finished product.




In

FIGS. 1

,


2


and


3


the blank is shown at least in longitudinal axial section, and in some Figures in cross-section as well, the cross-section being taken on the arrowed section line on the longitudinal section. In some Figures, the die in which the blank is contained, and a punch and/or ejector, is also shown.




In the examples, the blank is typically of low carbon steel and is designed to be used in the manufacture of a rivet shell of about 5 mm external diameter. Punches and dies used in the manufacturing processes are made of tool steel. The manufacturing methods are performed using a progressive cold-heading machine, of the type commonly used to make such rivet shells and other items, and well known and understood by those skilled in the art.




Thus, referring first to

FIG. 1



a,


a blank


11


has been formed from a cylindrical slug cut from wire and has been formed with a head


12


and a tapering axial depression


13


at the head end. It is offered up to a die


14


which has a cylindrical in shape with four longitudinal ribs


15


spaced at 90° apart around the die. As illustrated in

FIG. 1



a,


the ribs are triangular in section with an included apex angle of 90° and a fairly sharp crest.




A punch is then driven into the depression


13


of the blank. The punch


16


is co-axial with a spring-loaded tool


17


which has an annular recess


18


on its leading end, to fit around the head of the blank. The punch and tool drive the blank into the die, as shown in

FIG. 1



b,


until the leading end of the blank contacts the bottom of the die (which is provided by the end face of an ejector pin


21


), and the underside of the head of the blank contacts the face of the die. As illustrated in

FIGS. 1



b


and


1




c


the diameter of the punch


16


is rather less than the diametrical distance between opposed crests of ribs


15


. Continued movement of the punch


16


into the die


14


causes backwards extrusion of the material of the blank upwardly around the punch


16


, the co-axial tool


17


rising against its spring-loading. The ribs


15


in the die


14


have formed longitudinal grooves


19


in the exterior face of the rearwardly extruded blank, as shown in

FIG. 1



c.


These grooves extend from near the underhead face of the blank to the remote end of the blank. The punch


16


is driven into the die only far enough that its leading end is spaced from the end wall of the die by a distance which leaves a thick web


22


at the end of the blank, as shown in

FIGS. 1



c


and


1




d.






The punch


16


and tool


17


are now withdrawn and the blank ejected from the die by the ejector


21


. The blank is in the form shown in

FIG. 1



d,


and will now be referred to by the numeral


23


. Most of the length of the blank comprises four full-thickness longitudinal zones


34


, joined each to the next by a thin longitudinal web


35


, indicated in

FIG. 1



d.


The blank


23


is now inserted in the next die


24


, as shown in

FIG. 1



e


(which also shows a punch


25


entering the blank


23


). The die


24


has its lower end provided by the top face of an ejector pin


26


. The inner end portion


27


of the die, adjacent the ejector


26


, and the outer end portion


28


of the die


24


, are of appropriate diameter to fit the exterior diameter of the blank


23


. However, a lengthy intermediate portion


29


of the die is of larger diameter than the blank


23


. This enlarged portion


29


merges to each of the smaller diameter end portions


27


,


28


by a tapering portion


31


,


32


.




When the blank


23


has been fully inserted into the die


24


so that its bottom end contacts the ejector pin


26


and its underhead surface abuts the outer face of the die, the web


22


of the blank is contained within the inner end portion


27


of the die which is of a reduced diameter. A cylindrical punch


25


is driven into the blank.

FIG. 1



e


illustrates the start of this process. The punch has a main diameter greater than that of the bore of the blank


23


, and has a chamfered leading edge


33


to facilitate its entry into the blank's bore. As the punch


25


progressively enters the die, it radially expands the blank


23


. This has the effect of bursting apart the four full-thickness longitudinal zones


34


by breaking the four thin webs


35


, at least over the majority of their lengths, to give four gaps


36


shown in

FIG. 1



f.


The material in the thin webs


35


is work hardened to a much greater extent than the other parts of the blank. This, together with the stress concentration in the webs, assists in their breaking.

FIG. 1



f


shows the fullest penetration of the punch


25


into the blank. The bottom end face of the punch is opposite the lower tapering portion


31


of the die, and is spaced slightly apart from the web portion


22


of the blank. The gaps do not extend to the web portion at the end of the blank. The ends of each gap


36


taper in width due to the effect of the tapering portions


31


,


32


of the die.




The punch


25


is now withdrawn, and the ejector pin


26


is actuated to force the blank back out of the die


24


.

FIG. 1



g


shows an intermediate stage in this action. As the major part of the blank, in the form of the four longitudinal zones


34


, is pushed through and past the tapered portion


32


and the reduced diameter outer portion


28


of the die, the four zones


34


are forced radially inwards, thus closing up the four longitudinal gaps


36


.

FIG. 1



h


shows the form of the blank after this process has been completed. The edges of each adjacent pair of longitudinal zones


34


are in contact with each other adjacent the inner wall of the tubular member, with a slot


37


of effectively zero thickness (i.e. a physical discontinuity) between them, and a groove down the outside of the member.




The blank in the form shown in

FIG. 1



h


is then inserted in another die (not shown) where the web portion


22


at the end of the blank is removed by a suitable tool (not shown), as indicated schematically in

FIG. 1



i.


This leaves the fully manufactured tubular slotted member as illustrated at


38


in

FIG. 1



i.






The man skilled in the art of progressive cold-heading will appreciate that, allowing for two dies to head and form the depression in the initial blank


11


in

FIG. 1



a,


the two dies


14


and


24


, and the further die for removing the end web, this example manufacturing process can be carried out on a 5-station progressive cold header.





FIG. 2

illustrates a modification of the example method described with reference to FIG.


1


. In

FIG. 2

,

FIGS. 2



d


to


2




h


respectively correspond to

FIGS. 1



d


to


1




h.


For ease of comparison and understanding, identical parts are indicated by identical reference numerals, and corresponding parts are indicated by similar reference numerals with 100 added to the number.




The only difference of substance in this modification is that the die


124


has a slightly larger diameter mouth. This is apparent from

FIGS. 2



e


&


2




f,


which show an annular gap


41


between the blank


23


and the outer portion


128


of the die adjacent its mouth. The effect of this is that, when the blank is ejected, its radially enlarged part is reduced to a diameter slightly larger than its original size. Consequently, the four longitudinal parts


134


are not in edge-to-edge contact with each other, but are separated by narrow gaps


137


, as shown in

FIG. 2



h.






A further example is illustrated in

FIGS. 3



d


to


3




h,


which also correspond respectively to

FIGS. 1



d


to


1




h.


Again, identical parts are given identical reference numerals, and corresponding parts by similar reference numerals with 200 added. This is also a modification of that first example method, but is a greater modification than the one just described.




In this example, the tubular blank


223


before radial expansion has, effectively, four equally spaced longitudinal grooves


219


along its inner face. The bore of the blank is in fact square in section as illustrated in

FIG. 3



d.


This is achieved by using a die and punch which are a modification of those illustrated in FIG.


1


. The die will be cylindrical in section, and the punch square in section. The man skilled in the art of cold forming will readily understand how to design such a die and punch, which are the inverse of those of FIG.


1


. The other difference is that the blank made in this form has a bore extending completely through it, with no web across the end, although the corresponding tail end portion may be thickened as at


222


in

FIG. 3



d.






The radial expansion of the blank is by means of a die


224


and punch


225


. The punch


225


has its end part


44


of reduced diameter, which fits inside the far end part of the blank bore where, in

FIGS. 1 & 2

, the web portion


22


was. This radial expansion of the blank, and its subsequent reduction in diameter on ejection from the die, are substantially identical to those described in the first example method with reference to FIG.


1


. The only substantial difference in the finished manufactured tubular member


238


is that it has its four longitudinal parts


234


separated by longitudinal internal grooves each of which leads to a zero-thickness slot


237


adjacent the outside of the tubular member. There is no web at the end of the tubular member to be removed. Thus this manufacturing process can be carried out on a 4-station header.





FIG. 4

illustrates how a tubular member such as


38


,


138


or


238


is used in a blind rivet, assembled on a stem


41


having a stem head


42


. When the rivet is placed, by axially compressing the shell


38


,


138


or


238


, the shell parts at the four slots


37


,


137


or


237


, to form four outwardly folded legs


43


, as shown in FIG.


5


.




The configuration of the tubular member


138


illustrated in

FIG. 2



h


is particularly advantageous for use as a blind rivet shell. The fact that an intermediate length of the shell has its outer surface radially outwardly offset with respect to its ends promotes initial buckling of the shell under axial compression.




The invention is not restricted to the details of the foregoing examples. A slotted tubular member may be utilised for any convenient purpose, other than a blind rivet shell.




A combination of both internal and external grooves could be used.



Claims
  • 1. A method of forming a tubular member with longitudinal slots along part of its wall, comprising the steps of:firstly, forming longitudinal zones of weakness along part of the wall of the tubular member, each comprising a longitudinal zone of reduced wall thickness; secondly, expanding the said part of the tubular member radially to cause fracture of the wall of the member along the longitudinal zones, thereby to form longitudinal slots, each bounded by opposed edges or walls; and thirdly, radially compressing at least the said part of the tubular member so that the edges or walls of at least part of each slot move nearer each other.
  • 2. A method as claimed in claimed in claim 1, in which the third step comprises radially compressing the tubular member until the edges or walls of at least part of the length of each slot are in contact with each other.
  • 3. A method as claimed in claim 1, in which the third step comprises compressing the tubular member so that edges or walls of at least part of each slot move nearer to each other but do not contact each other.
  • 4. A method as claimed in claim 1, in which radial expansion of the tubular member is achieved by driving axially into its bore a pin of larger diameter than the bore.
  • 5. A method as claimed in claim 1, in which radial expansion of the tubular member is achieved by locating it within a die cavity having part of its length, corresponding to the aforesaid part of the tubular member, of a diameter corresponding to the desired enlarged diameter of the tubular member, and driving axially into the bore of the tubular member a pin of larger diameter than the bore, and in which the die is provided with at least one other part of its length of reduced diameter.
  • 6. A method as claimed in claim 5, in which radial compression of the thus radially expanded tubular member is achieved by axially forcing the expanded part of the tubular member through a part of the die of reduced diameter.
  • 7. A method as claimed in claim 1, in which the longitudinal zones of weakness are provided by longitudinal grooves along the inner surface of the wall of the tubular member.
  • 8. A method as claimed in claim 1, in which the longitudinal zones of weakness are provided by longitudinal grooves along the outer surface of the wall of the tubular member.
  • 9. A method as claimed in claim 1, in which the longitudinal zones of weakness are provided by longitudinal grooves along the inner surface, and longitudinal grooves along the outer surface, of the tubular member.
  • 10. A method as claimed in claim 7 or claim 8, in which the forming of the aforesaid longitudinal grooves takes place in the same operation as the forming of the bore of the tubular member.
  • 11. A method as claimed in claim 10, in which the forming of the grooves is achieved by backwards extrusion.
  • 12. A method as claimed in claim 9, in which the forming of the aforesaid longitudinal grooves takes place in the same operation as the forming of the bore of the tubular member.
  • 13. A method as claimed in claim 12, in which the forming of the grooves is achieved by backwards extrusion.
  • 14. A method as claimed in claim 1, in which the tubular member is initially formed with its bore stopping short of one end of the member, the bore being opened at that end of the member in a subsequent operation.
  • 15. A method as claimed in claim 1, in which the tubular member is initially formed with its bore extending completely throughout its length.
  • 16. A tubular member with longitudinal slots along part of its wall which has been formed by forming longitudinal zones of weakness along part of the wall of the tubular member, each comprising a longitudinal zone of reduced wall thickness, and expanding the said part of the tubular member radially to cause fracture of the wall of the member along the longitudinal zones, thereby to form longitudinal slots.
Priority Claims (1)
Number Date Country Kind
9812093 Jun 1998 GB
Parent Case Info

This application is a 35 USC 371 of PCT/GB99/01776 filed Jun. 4, 1999.

PCT Information
Filing Document Filing Date Country Kind
PCT/GB99/01776 WO 00
Publishing Document Publishing Date Country Kind
WO99/64751 12/16/1999 WO A
US Referenced Citations (9)
Number Name Date Kind
2843861 Gandy Jul 1958 A
3009177 Carusi et al. Nov 1961 A
3114921 Carusi Dec 1963 A
3247698 Baldwin et al. Apr 1966 A
3292414 Goeke Dec 1966 A
3638259 Eibes Feb 1972 A
4520521 Miyake Jun 1985 A
4580936 Francis et al. Apr 1986 A
4708553 Braychak et al. Nov 1987 A
Foreign Referenced Citations (3)
Number Date Country
0162647 Nov 1985 EP
0328314 Aug 1989 EP
0631831 Jan 1995 EP