AU611748B2

AU611748B2 - Method and tooling for manufacturing die forged rivets and the rivet obtained

Info

Publication number: AU611748B2
Application number: AU27781/89A
Authority: AU
Inventors: Bernard Albert Marie Colin; Michel Antoine Claudius Cortey
Original assignee: Airbus Group SAS
Current assignee: Airbus Group SAS
Priority date: 1988-01-08
Filing date: 1989-01-06
Publication date: 1991-06-20
Anticipated expiration: 2009-01-06
Also published as: EP0323931A1; FR2625697B1; DE68901647T2; AU2778189A; DE68901647D1; ES2033100T3; FR2625697A1; EP0323931B1

Description

Association, L s on .1....Regi-starxe d -P-a nt tore TiHE COMMISSIONER or PATENTS.

Sda d. Watlers Sc at, MelboSune.

I COMMONWEALTH OF AUSTRALI PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification L.Jdkied: it Ar cepted: Published: Priority: Related Art: Name of Applicant: Address of Applicant: Actl Inventor: Address for Service: AEROSPATIALE SOCIETE NATIONALE INDUSTRIELLE 37, Boulevard de Montmorency, Paris l6eme, France BERNARD ALBERT MARIE COLIN and MICHEL ANTOINE CLAUDUIS

CORTEY

EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Complete Specification for the invention entitled: METHOD AND TOOLING FOR MANUFACTURING DIE FORGED RIVETS AND THE RIVET OBTAINED The following statement is a full description of this invention, including -the best method of performing It known to US 1 rrespect of the invention the subject ot the application.

SDECLARED hio 2.9.t. day 8 Signature. To: THE COMMISSIONER OF PATENTS.

.1 1 r METHOD AND TOOLING FOR MANUFACTURING DIE FORGED RIVETS AND THE RIVET OBTAINED The present invention relates generally to mechanical riveted assemblies and more particularly relates to a novel industrial method for manufacturing rivets by die forging.

The presently employed method for manufacturing rivets by die forging has drawbacks in that, following on this operation and owing to the fact that the rivet is expelled from the impression of the die by an ejectorexertinga 10 pressure on a part of the end of the rivet, the latter is deformed and causes disturbances capable of giving rise to cracks or splits when this end of the rivet is crushed in the course of the riveting operation, which markedly decreases the mechanical properties and has a serious adverse effect on the resistance to corrosion of the

S

riveting obtained.

An object of the invention is to overcome these drawbacks by providing an industrial method and tooling for manufacturing rivets by die forging which avoid the appearance of these disturbances and the resulting defects.

The invention provides for this purpose an industrial method for manufacturing rivets by die forging a cylindrical blank in an impression of a die, in which one end of said blank is placed against a hollow surface having a shape which is quasi complementary to the shape of the rivet to be obtained, said hollow surface being formed at the end of a cylindrical member constituting an ejector which is disposed A j h.i -2 within the impression and whose geometry of the hollow surface varies under the force exerted by the die forging pressure applied to the other end of the blank so as to obtain a self-sealing effect of the active end of the ejector against the walls of the impression of the die throughout the duration of the die forging and the ejection of the rivet obtained.

The invention also provides tooling for carrying out the method defined hereinbefore, comprising a die having an impression, a punch and an ejector, said impression being a 0. 10 cylindrical bore having a diameter which is constant throughout the extent thereof which receives the blank and ejector, said ejector having an end which has a hollow shape defined by a solid of revolution whose shape is quasi complementary to the shape of the end of the rivet to be obtained, and this solid of revolution being of uniform bending strength, and therefore deformable under the action of the pressure exerted by the end of the blank when die forging said blank and when ejecting the rivet obtained, so as to be applied in such manner as to obtain a self-sealing effect against the walls of the impression, said ejector having a diameter which is roughly equal to the diameter of the bore and being slidably mounted and adjustable in said bore.

The following description, with reference to the I accompanying drawings given by way of non-limitative examples, will explain how the invention can be carried out.

In the drawings: 3 Fig. 1 is a side elevational view of rivet.

Figs. 2 and 3 show the different stages of the die forging operation for a blank of a rivet shown in Fig. 1, in accordance with the conventional method employed heretofore Fig. 4 shows the rivet obtained in this way.

Fig. 5 shows a riveted assembly obtained by means of a rivet manufactured in accordance with the prior art illustrated in Figs. 2 to 4.

Figs. 6 to 8 show how the method according to the invention is carried out and the shape of the die and the S shape of the ejector according to the invention.

In the various figures, similar parts or elements are designated by the same reference characters followed by the index for distinguishing the invention from the prior art.

.The rivet R shown in Fig. 1 is conventional. It has a head 1 and a ,tem 2 whose end 3, termed the front end, as opposed to the head 1 has a frustoconical shape to facilitate the introduction of the rivet in the holes of assemblies to be riveted in automated industrial assembly methods.

The blank of the rivet R is forged in an impression 4 of a die 5 in which the rivet is forged by means of a striking punch 6 with the end 3 of the rivet bearing against the end of the impression which has a frustoconical shape complementary to that of the rivet to be obtained.

.A bore 4a is provided in the die 5 and extends coaxially -4 in the extension of the impression 4, but has a diameter which is smaller than the diameter of the impression, and an ejector 7 is slidably meunted in this bore.

Under the action of the punch 6, the stem 2 of the rivet expands and is applied closely against the wall of the impression, against which it exerts a pressure indicated by the arrows f in Fig. 3.

0 At the same time, the material of the rivet subjected to the pressure of the punch 6 flows around the end of the ejector 7 in the interstice 8 between the latter and the :R bore 4a in which it is slidable, which constittes its normal operational clearance, thereoy forming an annular projecting ring 9.

When the striking punch 6 has been moved away from the head 1 of the rivet, the ejector 7 is actuated so as to expel the rivet from the die by exerting on the end of the rivet sufficient axial force to overcome the friction or fee* resistance due to the sum of the forces f.

The pressure required, which is applied by a surface area as small as that of the ejector 7, inevitably results in an indentation of the material of the rivet at the center of the ring 9 (Fig. 4).

The high forces to which the material at the end 3 of the rivet is subjected results in disturbances of its internal structure. Indeed, when the rivet is placed on an assembly 10 to be riveted, the ring 9 which pertains to the disturbed region is crushed and bent inwardly as shown at 11 5 (Fig. which might result in micro-cracks in this region.

These micro-cracks are harmful to the mechanical behavior of the assembly achieved and constitute, with the bent-in part, recipients for corrosive elements.

Furthermore, with this conventional method and tooling, dies of different lengths are required to obtain a range of rivets of different stem lengths.

0 According to the invention, there is employed a die whose impression 4' and coaxial bore 4'a in which the 10 ejector 7' is slidable, have a cylindrical shape of constant common diameter. In other words, the impression 4' does not have an end having a shoulder of frustoconical shape which is complementary to that of the front end 3' of the stem of the rivet.

.15 Furthermore, the end of the ejector 7' in contact with the end of the rivet has a hollow shape defined by a solid of revolution constituting an even cavity 12 of a shape which is quasi complementary to that of the end 3' of the rivet to be obtained, andthis solid of revolution being of uniform bending strength and therefore deformable under the action of the pressure exerted by the end of the blank when die forging said blank and when ejecting the rivet obtained, so as to be applied in such manner as to obtain the selfsealing effect against the walls of the impression, the intersection of the cylindrical volume of the injector 7' with said hollow surface 12 forming a sharp and circular edge 13 contained in a plane perpendicular to the axis X-X

I

6 of the impression 4' in which the ejector 7' is slidable, as shown in Fig. 6.

The ejector 7' is slidably mounted in the impression 4', but is adapted to be adjusted at the desired position in the impression by known means which are not part of the invention.

With this arrangement, it is sufficient to adjust the a axial position of the ejector 7' in the bore therefor to be capable of die forging blanks of rivets which bear against 10 the end of the ejector, it being possible for these rivets to have any desired stem length L with the use of one and the same tool. It will be understood that, not only is a single tool sufficient, which replaces the entire range of tools employed heretofore, but it is possible to produce 15 rivets having all the desired different stem lengths.

In practice, it is advisable to maintain and guide the ejector 7' in a minimum safety length G. It has been found that this length G must be about 3.5 times the diameter of the impression 4' (Fig. 6).

In the course of the die forging operation, the material at the frustoconical end 3' of the rivet is enclosed and compressed under the action of the punch 6' in the cavity 12 of the ejector 7' which constitutes an abutment at a point of the impression 4' which is chosen in accordance with the desired length of the rivet.

Under the effect of the pressure applied by the punch this material is subjected to forces f which cause it to 7 be applied closely against the walls of the impression 4' and against the walls of the cavity 12 of the ejector 7' with the forces f.

Consequently, the geometry of the hollow surface of the ejector is deformable in a variable manner under the force exerted by the die forging pressure applied to the ether end S of the blank.

S

This is achieved by the shape of the end of the ejector which defines the cavity 12 which is a solid of revolution 0 "'of uniform bending strength" and, under the increasing die 10 forging pressure, there is established, by a harmonious bending of this solid, a self-sealing effect of the latter against the wall of the impression first of all by its *55*5 circular edge 13 and then by a more sustained bending of the 15 sections sl, s2, s3. .sn of the solid of revolution 15 located immediately below the edge 13 (Fig. 8) which constitutes a sealing "wedge" between the end 3' and the wall of the impression whose self-sealing effect increases with the pressure; this bending being allowed by the normal clearance between the ejector and the impression 4'.

When the rivet is ejected under the pressure exerted by the ejector this "self-sealing" effect is the same, and the whole of the surface of the cavity 12 is applied against the corresponding surface of the end 3' of the rivet whose material cannot flow around the ejector 7'.

As this surface of the end 3' is completely subjected to the pressure, it consequently has no localized partial i

-I

8 deformation liable to disturb the internal structure and no undesired projection as in the prior art.

The hollow surface of revolution is a frustoconical surface having a straight or concave curved generatrix including a flat or curved or complex inner end.

The rivets obtained by the method and tooling according to the invention have a constant shape and surface quality t000 and are devoid of the defects of the rivets of the prior *0 art.

a

S

0 0 400 04 0 *0 9* 09 0 0

Claims

1. Industrial method for manufacturing rivets by die forging a cylindrical blank in an impression of a die, comprising the steps of placing one end of said blank against a hollow surface having a shape which is partially complementary to that of the rivet to be obtained, and forming said hollow surface at the end of a cylindrical member constituting an injector in the impression, the geometry of the hollow surface being variable under the force exerted by the pressure of the forging applied to the other end of the blank so as to obtain a self-sealing effect of the end of the ejector against the walls of the impression of the die throughout the duration of the die forging and the ejection of the rivet obtained. 0 00 B 0

2. Tooling for carrying out the method defined in S. claim 1, comprising a die having an impression, a punch and an ejector, said impression being a cylindrical bore having a constant diameter throughout the extent thereof which receives the blank and the ejector, said ejector havinbg an end having a hollow shape defined by a solid of revolution whose shape is partially complementary to that of the end of the rivet to be obtained, and this solid of revolution being of "uniform bending strength" and therefore deformable under the action of the pressure exerted by the end of the blank when die forging said blank and upon the ejection of the rivet obtained, so as to be applied in such manner as to o• achieve a self-sealing against the walls of the impression, e LJD:JJC (5/13) I i l n. said ejector having a diameter roughly equal to the diameter of the bore and being slidably mounted and adjustable in said bore.

3. Tooling according to claim 2, wherein said hollow surface of said ejector is of revolution and frustoconical and has a straight, curved or complex generatrix, the inner end of said surface being flat or having a concave curved shape. 6

4. Tooling according to claim 3, wherein the 10 intersection of the cylindrical volume of the ejector with said hollow surface forms a sharp and circular edge contained in a plane pe:pendicular to the axis of the S. impression.

5. Tooling according to claim 4, wherein the minimum length of the injector engaged in said bore when die forging is about 3.5 times the diameter of said bore.

6. A die-forged rivet obtained by the amthod and tooling '0 as defined in any one of the claims 1 to DATED this 5th day of January 1989. AEROSPATIALE SOCIETE NATIONALE INDUSTRIELLE EDWD. WATERS SONS PATENT ATTORNEYS QUEEN STREET MELBOURNE. VIC. 3000.