FR2480644A1 - METHOD FOR DRILLING HOLES OF A PREDETERMINED DIAMETER IN A SET OF SUPERIMPOSED SHEETS COMPRISING AT LEAST ONE SHEET OF MATERIAL REINFORCED WITH GLASS FIBERS OR CARBON FIBERS, A STEEL SHEET AND A TITANIUM SHEET - Google Patents

Abstract

THE PROCESS INCLUDES A FIRST DRILLING OPERATION USING A MANUALLY CONTROLLED DRILL EQUIPPED WITH A ROTATING DRILL, A SECOND HOLE ENLARGEMENT OPERATION OBTAINED IN THE FIRST OPERATION, PERFORMED WITH AN AUTOMATIC DRILL EQUIPPED WITH A 7-TURNING DRILL OF DIFFERENT DIAMETERS 8, 9, A THIRD HOLE BALLING OPERATION OBTAINED IN THE SECOND OPERATION, THE BALLING OPERATION BEING CARRIED OUT WITH AN AUTOMATIC DRILL EQUIPPED WITH A BALLING TOOL INCLUDING TWO PARTS HAVING DIFFERENT DIAMETERS, OF WHICH A GUIDE TO.

Description

The present invention relates to a method for drilling diameter holes

  predetermined in a set of superimposed sheets comprising at least one sheet of a material reinforced with glass fibers or carbon fibers, a steel sheet and a titanium sheet. Composite sheets of this type are used in aircraft construction to form structures having

  very high mechanical resistance and very low weight.

  In order to rigidly connect the three sheets of the assembly and / or to connect the various elements of a structure, the sheets are connected by means of members inserted in

  corresponding holes made in them.

  The subject of the present invention is a method of drilling such holes in composite sheets of the type

indicated above.

  Usually holes like this are drilled

  with a manually operated drill or by means of a machine

  appropriate piercing china provided with a mobile head at a predetermined advance speed on guides; in both cases, the tool used is a carbide-tipped forest

of tunastene.

  Holes drilled using the indicated method

  above have serious drawbacks which make them

  tooth unsuitable for aircraft construction in which 2.

  the elements must be completely free of

  faults. Indeed, the holes obtained in the manner indicated above generally have many defects, because their shape and their dimensions do not correspond to the expected shapes and dimensions and above all, because

  that the surface of the holes and the areas in the vicinity

  swims are damaged, which compromises the resistance

  this mechanics of the bonds obtained, bonds which must

  sister, as is well known, to work tensions

very high.

  In such holes, small cracks and pieces of broken fibers are sometimes encountered near the edge of the hole formed in the sheet of fiber-reinforced material.

  glass or carbon fiber, or damage to the over-

  face due to steel drilling chips; the roughness of the surfaces of the holes thus obtained is always very large. In addition, only very large tolerances can be obtained.

  on the diameter of the holes, and the holes have fairly frequent

  only undesirable ovalization or taper.

  Finally, the tools undergo significant wear, this being due above all to the action produced on the cutting edges by the carbon fibers; tools must

  therefore be replaced very often.

  The object of the present invention is to provide a-

  method of the type indicated above which makes it possible to eliminate the drawbacks listed above so that flawless holes can be formed economically with shapes and dimensions corresponding to the shapes and dimensions expected, with very strict tolerances and

  a high finish of the surfaces concerned.

  According to the present invention, there is provided a method of drilling holes of a predetermined final diameter in a set of superimposed sheets comprising at least one sheet of material reinforced with glass fibers or carbon fibers, a steel sheet and a sheet. made of titanium, the thickness of the sheets being respectively between 3.2 and 10 mm, between 0 and 1.5 mm and between 2 and 5 mm, characterized

  in that, for each hole, a first operation is carried out

  drilling with a manually operated drill equipped with a rotating forest having a first diameter less than the predetermined final diameter so as to obtain, at the end

  from the first operation, a hole with a substantial diameter-

  ment equal to the first diameter; a second widening operation

  sliding of the hole obtained at the end of the first operation performed with an automatic drill equipped with a forest

  turning comprising two parts having different diameters

  annuities, an upper part with a diameter equal to the diameter

  predetermined final decreased by 0.8 mm, and a lower part

  re of a diameter equal to that of the upper part reduced by 0.8 mm so as to obtain at the end of the operation a hole having a diameter substantially equal to that of the final diameter reduced by 0.8 mm; a third operation of boring the hole obtained at the end of the second operation carried out with a portable automatic drilling machine comprising a tool

  bore made up of two parts with different diameters

  ferent, an upper part with a diameter equal to the final diameter and a lower part with a diameter equal to the diameter obtained at the end of the second operation, so as to guide

  the boring tool by means of the lower part of the

  til itself during the boring phase.

  The present invention will be well understood during the

  following description made in conjunction with the drawings below

  joints in which: FIGS. 1 and 2 schematically represent 1 the set of sheets at the start and at the end, respectively, of a first operation; FIGS. 3 and 4 schematically represent the set of sheets, respectively, at the start and at the end of a second operation; and Figures 5 and 6 schematically show the set of sheets, respectively, at the beginning and at the end

  of a third operation which ends the process.

  The method of the present invention is used 4. for drilling a set of superimposed sheets, such as the set shown in FIG. 1, consisting of at least a first sheet 1 of material reinforced with glass fibers or fibers carbon, a second sheet 2 of steel, a third sheet 3 of titanium; the sheet 2 is made of a steel of a type that can be rolled, that is to say capable of reaching a thickness allowing its positioning between the two other sheets. Composite sheets of

  this type are widely used in aeronautical construction

  nautical to constitute structural elements having a very high mechanical resistance and a very low weight; the

  bond between the sheets of the whole or between the different

  rents structural elements is obtained by means of connecting members inserted in holes which can be formed in

  according to the process of the present invention.

  The best results of the process are obtained

  when the thickness of the sheets 1, 2, 3 is included,

  pectively, between 2 and 10 mm, between 0 and 1.5 mm and between 2 and 5 mm. The hole diameter is conveniently understood

between 2.5 and 9 mm.

  To obtain each of the holes, a

  first drilling operation using a compact drilling machine

  manual control (not shown) equipped with a rotating tungsten carbide forest 4; the relative position of the forest in relation to the composite sheet to be drilled, at the start of the

  first operation, is shown in Figure 1.

  The forest is a normal forest on the right of the type uti-

  used in normal drilling operations, for example

  with a helical groove forming an angle of 30 relative to

  port to its axis; the angle of the point, represented at a in the

  figure 1, must be 1350. The diameter da of the forest is com-

  taken between 1/2 and 2/3 of the predetermined final diameter of the hole you wish to form, while the speed of rotation of the forest itself, which is constant for the duration of the first operation, must be between 450 and 550

Rotations per minute.

  The operation is carried out by inserting the forest 4 into a guide ring 5, which is suitably supported, for example by means of a plate 6pet having a height h of between 25 and 30 mm, in such a way that the forest itself -self is securely guided during its penetration into the composite sheet 1, 2, 3. For this purpose, a small diametric play

  tral is left between the forest and the surface of the hole of the ba

  gue, play which can be of the order of 0.01 mm.

  To execute this operation, the operator, after positioning the ring 5 so that its axis coincides

  with the axis of the hole to be formed, introduces the forest into the base

  gue, applying sufficient manual force to it

cause it to advance.

  During this operation, the central core of the hole to be drilled is substantially removed, which makes it possible to obtain, with a notable speed, as can be seen in FIG. 2, a hole having a diameter substantially equal to d even if it does not is not very regular both in terms of dimensions

than the surface finish.

  If the diameter of the final hole must be very small,

  the first operation described above can be omitted.

  The second operation of the process consists in enlarging

  the hole thus obtained: in Figure 3 there is shown schematically-

  only the tool then constituted by a rotating forest 7, po-

  positioned relative to the set of plates 1, 2, 3 at the start

of the operation.

  Forest 7 has two parts, a lower part

  upper 9 and upper part 8, having different diameters

  famous; the diameter of the upper part, represented in dC of FIG. 3, is linked to the predetermined final diameter df

  of the hole to be obtained (Figure 6) by the following relation

  te: dc = df - 0.8 mm, (1) the diameter of the lower part, shown in dd, is linked to the diameter dc (and therefore on the basis of equation (1) to the diameter df) by the following relation: dd = dC - 0.8 mm = df - 1.6 mm (2)

  Apart from the presence of two parts of diameter

  be different, forest 7 is a normal forest on the right in

24 O644

  6. tungsten carbide comprising, for example, helical grooves inclined by 30 relative to its axis. The angle P3 of the tip (FIG. 3) which is the same as the angle of the connection zone between the upper part 9 and the lower part 8 is 1350.

  Forest 7 is mounted on the movable head of a person.

  portable type with automatic feed

(not shown).

  The speed of rotation of the forest 7 must be chosen

  between 250 and 350 revolutions per minute, while the advance

should be 2/10 mm per rotation.

  During the drilling carried out in this operation, the forest 7 is guided by a ring 10 suitably supported, for example by means of a plate 11; in this case, too, a diametral clearance of 0.01 mm is left between the forest and the inner surface of the ring, and the height

  h of the ring is between 25 and 30 mm.

  During the operation, the diameter hole of

  naked at the end of the previous operation is enlarged, first

  at the lower part, then at the upper part 8 of the form

  rêt, which allows to obtain at the end of the operation, as we can see in figure 4, a hole of diameter d which on the c basis of the relation (1) is slightly less than the diameter

final df that we want to obtain.

  In the third operation of the pre-

  invention, the hole thus obtained is bored so as to bring it to the desired final diameter and to cooperate on the surface

a very high quality finish.

  The boring tool 15 used during this operation

  tion is shown in Figure 5, in the relative position it occupies with respect to the set of plates 1, 2, 3 at

start of the reaming operation.

  This tool which is a normal hole boring tool

  made of tungsten carbide, comprises two parts having diameters

  very different, a lower part 16 and an upper part

  upper 17, having diameters d and df. The bond angle y and the angle of the point a (Figure 5) are respectively

  1350 and 900. This tool is mounted as in the previous operation.

  7.Tooth on a drill or boring machine with a tool holder

  having an automatic advance and during the operation is

  thimble by a ring 18 of a height h. from 25-30 mm; between the

  the surface of the ring hole there is a clearance

  0.01 mm tral. The speed of rotation of the boring tool must be between 250 and 350 revolutions per minute and the feed

  must be equal to 2/10 mm per rotation.

  During the third operation, the lower part

  re 16 of tool 15 is inserted into the hole, the diameter of which

  tre is equal to that of the part itself, so that

  the outer part 18 is guided in a very strict manner

  te by coupling, and therefore during its advance is able to perform a perfect bore of the hole of diameter dc

  bringing it to the final diameter df (Figure 6).

  The holes obtained with the process of the present invention are perfectly cylindrical and the tolerance of the diameter with respect to the nominal diameter is of the order of 0.05 mm; the surface finish is also better and is

  almost specular; the average roughness obtained with the pro-

  yield of the present invention is equal to or less than 80 RHR. There is no damage to the edge of the holes of the top sheet 1 and the bottom sheet 3, and these

  edges are free of delamination or other defects.

  If holes must be formed with the same characteristics as described above, with larger tolerances of the diameter, but remaining between the values indicated first (i.e. 0.05 mm and 0.076 mm ), the speed of rotation of the forest in the second operation and of the reaming tool in the third operation must be increased compared to the values indicated first, which has the advantage of reducing the time necessary for the formation of holes. If the hole diameter tolerance is within the range shown above, the speed should be between 450 and 550 rpm. These operations can, under these conditions, be executed with

a manually operated drill.

  8. The appreciation of some of the measurement values

  above should take into account that they pro-

  come from the conversion of Anglo-Saxon units into metric units. The present invention is not limited to the exemplary embodiments which have just been described, it is on the contrary susceptible of variants and modifications which

will appear to those skilled in the art.

9.

Claims (6)

  1 - Method of drilling holes with a diameter fi-   predetermined nal in a set of superimposed sheets comprising at least one sheet of material reinforced with glass fibers or carbon fibers, steel sheet and a   titanium sheet, the thickness of the three sheets remaining   pectively between 2 and 10 mm, between 0 and 1.5 mm and between 2 and 5 mm, characterized in that for each hole a first drilling operation is carried out by means of a manually operated drill comprising a rotating forest   having a first diameter less than the predetermined final diameter-   finished so as to obtain at the end of the first operation   a hole having a diameter substantially equal to the first diameter   tre, a second enlargement operation of the hole obtained   at the end of the first operation performed with a collection   automatic with a rotating forest comprising two parts   ties having different diameters, an upper part having a diameter equal to the predetermined final diameter reduced by 0.8 mm, and a lower part having a diameter equal to   that of the upper part reduced by 0.8 mm, so as to   hold, at the end of the operation, a hole having a diameter substantially equal to that of the final diameter reduced by 0.8 mm; a third hole reaming operation obtained at the end of the second operation, performed with a portable automatic drilling machine provided with a reaming tool comprising two parts having different diameters, an upper part having a diameter equal to the final diameter and a lower part   having a diameter equal to the diameter obtained at the end of the se-   second operation, so as to guide the boring tool by means   of the lower part of the boring tool during pha- of bore.   2 - Method according to claim 1, characterized in that during the operations, the 'rotating forests and the boring tool are guided by means of a guide ring in which the tools are inserted with a diametral play   minimum of the order of 0.01 mm, the axial length of the base   gue being between 25 and 30 mm.   3 - Method according to one of claims 1 or 2,   10. characterized in that in the first operation the speed of rotation of the rotating forest is chosen between 450 and 550 revolutions per minute and in the second and the third operation   the speed of rotation of the rotating forest and the random tool   wise is chosen between 250 and 350 revolutions per minute, when one wishes to obtain a first tolerance of the final diameter   predetermined hole of 0.05 mm or less.   4 - Method according to claim 3, characterized   in that the advance of the rotating forest and the boring tool.   1D in the second and third operations, respectively, is chosen at 0.2 mm per revolution.   - Method according to one of claims 1 to 4,   characterized in that in operations the rotational speed   tion of the rotating forest and the boring tool is included   between 450 and 550 revolutions per minute when one wishes to obtain   nir a second tolerance of the predetermined final diameter of the hole greater than the first tolerance and less than   0.075 mm, the operations being carried out by means of a manually operated eraser.   6 - Method according to one of claims 1 to 5,   characterized in that the angle of the tip of the rotating forest   used in the first recce is 1350.   7 - Method according to one of claims 1 to 6,   characterized in that the angle of the connection between the parts   lower and upper boring tool is 135.