FR2502034A1 - METHOD FOR FIXING TOGETHER A PLURALITY OF PARTS USING A RIVET - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A PROCESS FOR ASSEMBLING TOGETHER A PLURALITY OF PARTS BY RIVETING. ACCORDING TO THE PROCEDURE, THE RIVET HEAD 15 IS PREFORMED. THE RIVET ROD 25 IS SIZED UNTIL THE DIMENSIONS OF THE OPENINGS RECEIVING THIS ROD 25 IN THE PARTS 55, 60 IS REFORMED AND THE GEOMETRY OF THE CONNECTION OF THE RIVET HEAD 15 IS REFORMED AND ROD 25 TO MINIMIZE CLEARANCE IN THE FINAL ASSEMBLY.

Description

The present invention relates to a method for fixing together a

  plurality of pieces by means of a rivet,

  and more precisely such a process where the game in the direc-

  both longitudinal and cross-sectional

  at the rivet rod is substantially eliminated.

  When manufacturing precision equipment such as engine fuel control devices

  gas turbine, riveted connections of parts relating to

  actively mobile are required. In the arrangements for

  gas turbine engine fuel, such parts include levers, rods, etc. which pivot in response to operator demand and engine operating conditions, and the accuracy of fuel flow to the engine by the adjuster is largely dependent on the accuracy of the motion

such pivotable elements.

  Typically, the commercially available rivets used for such connections comprise a first enlarged first head having a flat inner surface and a generally straight shank extending perpendicular to the inner surface, the junction between the first head and the shank comprising a round. The connection is made by inserting the rivet rod through aligned openings in the pieces and by deforming the end of the rod to form a second enlarged head, the pieces being trapped between the two rivet heads. . The quality of the riveted connection, (the absence of play in it) is a function of the

  the precision with which the openings of the

  with the rod they receive and the precision with which the rivet heads abut the surfaces

  external parts. It has been determined that non-uniform

  the diameters of the commercially available rivet rods, as well as the shape of the head, and the geometry rounded at the head junction, and

  the eccentricity head-rod, make the obtaining of

  pivotable, uniform, without unwanted play, difficult to say impossible with techniques

known riveting.

  Another problem associated with riveted connections using known techniques is that, when the connection is heated where the adhesive materials used in the apparatus are fired, or when the connection is used in a warm environment, a relaxation and a permanent elongation of the rivet may result

  contributing more to creating a game in the connection.

  It is an object of the present invention to implement a method for assembling a plurality of parts by riveting or reducing the clearance in the riveted assembly so that the operation of the assembly under varying thermal conditions does not result. in one

exaggerated play in the connection.

  According to the present invention, the manufactured rivet head is first shaped so that the inner surface thereof is concave and the cross-sectional area of the rounded portion is reduced to facilitate adjustment between the head and the adjacent room. The rivet rod is then inserted through aligned openings in the parts and the parts are pressed against the manufactured head, thereby flattening the

  inner surface of the head against the adjacent piece.

  While the pieces are held pressed against the first head, a second enlarged head is formed to

  the free end of the rod in a counter-bore

  in one of the openings so that the required length of the rivet is minimized to decrease the expansion of the rivet under temperature conditions

high.

  So that the invention can be better understood, reference is made to the following figures: Figure 1 is a view, partially in section, of the first step of the method according to the invention during which the inner surface of the manufactured head of the rivet is shaped to have a shape allowing

  a riveted connection with a minimum of play.

  FIG. 2 is a sectional view showing the head of the riveted rivet during the step shown in FIG.

Figure 1.

  FIG. 3 is a partially sectional view of the third step of the method according to the invention where parts are pressed against the manufactured head of the rivet for the reduction of the clearance between the parts and a precise conformation of the geometry. head with the coin

adjacent to it.

  Figure 4 shows the final stage of the process

  according to the invention, a second head is formed at the end.

free mite of the rivet rod.

  In Figure 1, a typical, commercially available rivet is shown at 10, including a first manufactured head or head having an inner surface

  generally flat and a rod 25 extending perpendicularly

  the junction between the head and the stem being defined by a rounding 30. It can be seen that if such a rivet was inserted into an opening of a

  piece having a flat outer surface, the rounding 30

  The inner surface 20 of the head of the outer surface of the part will be tilted, which would result in a clearance parallel to the longitudinal axis of the rivet. Without changing the geometry of the rivet, the only way to accurately fix the inner surface on an adjacent piece would be to achieve

  a part opening to receive the rod, sufficient

  width in cross-section to take account of the

  rounding. However, this would result in a trans-

  excessive versal in the resulting connection, which is

also undesirable.-

  According to the present invention, the manufactured head

  15 is preformed to reduce the cross-sectional area

  2. In FIG. 1, the rivet is inserted into a bore 35 created in a die 40 comprising a surface 45 of convex form. (conical) and is comprised between the die 40 and a fixed support member 47 including a generally conical recess 50. The conical shape of the recess 50 ensures that the preforming force is uniformly distributed around the rivet head to achieve uniform preforming around the periphery of the rivet.

the head.

  The compression of the rivet head between the fixed part 47 and the die results in a rivet shape shown in FIG. 2. In FIG. 2, it can be seen that the cross-sectional area of the rounding is substantially reduced by In this way, in cross-section, the inner surface 20 and the outer surface define a generally acute angle. In addition, it can be seen that the internal surface, after preforming, is no longer flat but

takes a concave (conical) shape.

  According to FIG. 3, once the rivet head has been preformed according to the method described above, the rivet rod is inserted into the aligned openings intended to receive this rod, in the parts 55 and 60. opening in the part 60 comprises a counterbore at 65 and a countersink at 70, the counter-bore allowing the rod to be substantially shorter than the combined thickness of the parts. It has been found that the longitudinal expansion of the rivet due to thermal cycling at the connection and because of the elastic elongation of the rivet can be substantially reduced by minimizing the

  length of the rivet as permitted by the counter

  Boring 65. The countersink 70 facilitates the passage of

  re of the rod or its movement when the end of the rod is deformed into a second head. To eliminate

  spaces between the rooms and between room 55 and the first

  15, the parts are pressed against the inner surface of the head between the fixed tool 47 and a hollow punch or pylon 75. In addition to reducing such gaps, this pressing flattened the concave inner surface 20, subjecting the parts radially. outer of the rivet head at a pretension so that when the end of the rod

  is distorted into a second head, the parts are closed

  caught by the rivet between the heads of the latter.

  While the pieces remain pressed against the first head 15 by means of the hollow pestle 75, the end of the rod 25 is formed in a second enlarged part by compression of the rivet along the longitudinal axis thereof between the fixed tool 47 and a solid punch 85, _5-

  thus completing the riveted connection. (Figure 4).

  As described above, the manufacturing tolerances of commercially available rivets are such that the diameter of the rod and the geometry of the manufactured head and the rounding vary significantly as well as the head-to-stem eccentricity. To accommodate rods of varying diameter, the openings in the parts 55 and 60 for receiving the rod must be slightly larger than the maximum diameter

  of the rod that would be found in the rivets available

  commercially available with particular characteristics.

  Thus, it can be seen in FIG. 3 that the rod and the openings for receiving the rod define a game between them which, if left as it is, would cause a substantial play in the finished assembly. If it were not the counterbore of the part 60 which allows the reduction of the length of the rivet to a minimum, with the formation of a second head by the known techniques, there would be a risk of a deformation of the rod by creating a warping in the openings to receive the rod. However, compression of a rod of minimum length for head formation 80 prevents this warping described above associated with head formation in methods known in the art. Moreover, the formation of the head 80 results in a "sizing" or expansion (enlargement) of the cross-section of the rod to precisely adjust it to the dimensions of the openings for receiving the rod in the pieces, further reducing the

game in the assembly.

  Therefore, it can be seen that the method of the present invention substantially eliminates any play in the riveted connection thus formed. The sizing or widening of the stem part guarantees an adjustment

  almost perfect between the rod and the openings of the pieces.

  Preforming the rivet head minimizes backlash. i and adjusts the inner surface of the head for firm retention of parts between rivet heads. Maintaining the pressing of the pieces against the first head while the second head is formed minimizes the risk of a space between

  the parts themselves or the parts and the first head.

  The milling of the rivet heads minimizes the thermal expansion of the rivet and the clearance at the connection

that can result.

-7-

Claims (6)

claims:   A method of fastening together a plurality of pieces by means of a rivet comprising a first enlarged head having a generally planar inner surface and a rod extending perpendicularly from said interstage surface, the connection between said head and said rod being defined by a rounding, which process consists in creating aligned openings in these parts to receive this rivet rod, inserting this rod into these openings and deforming the free end of this rod to form a second enlarged head,   characterized in that prior to this formation of the second   of enlarged head (80): a) this inner surface (20) is simultaneously reformed into a concave shape and the cross-sectional area of this round (30) is reduced by compression of this head (15) to this inner surface (20). against a first die (40) having a convex forming surface (45), and then b) pressing said pieces (55,60) against said enlarged first head (15) to eliminate gaps between the pieces (55,60 ) and between this first enlarged head (15)   and the piece (55) adjacent thereto.   2. Method according to claim 1, characterized in that the pressing of these parts (55,60) against this first head (20) is maintained for training of this second head (80).   3. A method according to claim 1 further characterized by said first head (20) on the outer surface thereof being received in a recess (50) of a stationary piece (47) extending said enlargement thereof. stem (25) peidant this pressing of these parts (55,60) against this first head (15) and during the formation of this second head (80).   4. Method according to claim 3, characterized in that the hollow (50) of the fixed part (47) is generally conical shape.   The method of claim 1, further characterized in that a countersink (70) is made at the opening of the workpiece (55) adjacent to the forming location of this second head (80).   The method of claim 1, further characterized in that a counterbore (65) is made at the opening of the workpiece (55) adjacent to the location of the formation of that second head (80). ), said second head (80) being formed within said counter-bore (65) so that the required length of the rivet (20) is minimized to decrease the longitudinal extent of said rivet both because of thermal expansion and elongation elastic of it.