Tool for machining a wall of a workpiece, in particular made from a composite material

Abstract

A tool for machining a wall of a workpiece, made from a composite material, that can cut a groove in the wall, the tool including a head mounted integrally with a rod having a longitudinal axis and capable of being driven in rotation about the longitudinal axis. The head includes at least one main protruding annular rib with an outer surface covered with abrasive grains of predetermined particle size and with a radial height corresponding to the depth of the groove to be cut, and at least one auxiliary protruding annular rib with an outer surface covered with abrasive grains of predetermined particle size and with a radial height less than the radial height of a main rib. The auxiliary rib includes two circular ridges separated by a ring band that is flat and that can be conical in shape.

Claims

1. A tool for machining a wall of a workpiece, or a workpiece made from a composite material, configured to cut a furrow in the wall, the tool comprising: a head securely mounted on a stem of a longitudinal axis that can be driven in rotation about the longitudinal axis, the head comprising main projecting annular ribs including an outer surface is covered with abrasive grains of predetermined grain size and a radial height of the main projecting annular ribs corresponds to a depth of the furrow to be cut, and at least a plurality of mutually parallel auxiliary projecting annular ribs that define grooves including an outer surface is covered with abrasive grains of predetermined grain size and a radial height of the auxiliary projecting annular ribs is less than the radial height of the main projecting annular ribs, wherein the auxiliary projecting annular ribs comprise two circular edges separated by an annular band that is flat, a separation between the two circular edges of a single auxiliary rib increasing on approaching a longitudinal end of the head, wherein the auxiliary projecting annular ribs form a frustoconical portion, wherein the main projecting annular ribs are closer to a free longitudinal end of the head than the auxiliary projecting annular ribs, wherein the frustoconical portion increases towards the free longitudinal end of the head, and wherein the radial height of the two ribs closest to the free longitudinal end of the head is a maximum value of the radial heights of the ribs.

2. The machining tool as claimed in claim 1, comprising between two and six mutually parallel main projecting annular ribs, which define grooves therebetween.

3. The machining tool as claimed in claim 2, for cutting a furrow of a given pitch, wherein the main ribs are regularly spaced from one another, such that a pitch of the main ribs is equal to a pitch of the furrow.

4. The machining tool as claimed in claim 1, wherein the radial height decreases regularly from a main projecting annular rib closest to the free longitudinal end of the head, such that radial ends of the auxiliary ribs and of an adjacent main rib are aligned along a straight line that is inclined with respect to the longitudinal axis and belongs to an axial plane passing through the longitudinal axis.

5. The machining tool as claimed in claim 4, wherein the annular band is aligned with the straight line.

6. The machining tool as claimed in claim 4, for cutting a furrow of a given pitch, wherein the main ribs and the auxiliary ribs are regularly spaced from one another, such that a pitch of the ribs is equal to a pitch of the furrow.

7. The machining tool as claimed in claim 4, wherein the abrasive grains associated with a main annular rib have a grain size, or a grain size between 46 m and 91 m, which is smaller than the grain size of the abrasive grains associated with an auxiliary rib, or between 107 m and 427 m.

8. The machining tool as claimed in claim 1, wherein the abrasive grains are made of diamond, natural or synthetic, or of cubic boron nitride.

9. The machining tool as claimed in claim 1, wherein the head comprises at least one internal duct for supplying fluid which opens laterally via discharge openings.

10. A method for tapping a workpiece made from a composite material comprising at least one cylindrical hole, the method comprising: providing the workpiece made from the composite material comprising the cylindrical hole; providing a tool, the tool including a head securely mounted on a stem of a longitudinal axis that can be driven in rotation about the longitudinal axis, the head comprising main projecting annular ribs including an outer surface is covered with abrasive grains of predetermined grain size and a radial height of the main projecting annular ribs corresponds to a depth of a furrow to be cut, and at least a plurality of mutually parallel auxiliary projecting annular ribs that define grooves including an outer surface is covered with abrasive grains of predetermined grain size and a radial height of the auxiliary projecting annular ribs is less than the radial height of the main projecting annular ribs, wherein the auxiliary projecting annular ribs comprise two circular edges separated by an annular band that is flat, a separation between the two circular edges of a single auxiliary rib increasing on approaching a longitudinal end of the head, wherein the main projecting annular ribs is closer to an end of the head than the auxiliary projecting annular ribs, and wherein the head is tapered such that a diameter of the head increases towards the end of the head and the radial height of the two ribs closest to the end of the head is a maximum value of the radial heights of the ribs; and tapping the hole of the workpiece using the tool to cut a furrow in the hole, the tool carrying out a helical interpolation by simultaneously moving circularly in a transverse plane orthogonal to an axis of the hole and moving in translation along an axis parallel to the axis of the hole, wherein the auxiliary projecting annular ribs are inserted into the hole before the main projecting annular rib.

11. A tool for machining a wall of a workpiece, or a workpiece made from a composite material, configured to cut a furrow in the wall, the tool comprising: a head securely mounted on a stem of a longitudinal axis that can be driven in rotation about the longitudinal axis, the head comprising main projecting annular ribs including an outer surface is covered with abrasive grains of predetermined grain size and a radial height of the main projecting annular ribs corresponds to a depth of the furrow to be cut, and a plurality of mutually parallel auxiliary projecting annular ribs that define grooves including an outer surface is covered with abrasive grains of predetermined grain size and a radial height of the auxiliary projecting annular ribs is less than the radial height of the main projecting annular ribs, wherein the auxiliary projecting annular ribs comprise two circular edges separated by an annular band that is flat, a separation between the two circular edges of a single auxiliary rib increasing on approaching a longitudinal end of the head, wherein the auxiliary projecting annular ribs form a frustoconical portion, wherein the main projecting annular ribs are closer to a longitudinal end of the head opposite a free longitudinal end than the auxiliary projecting annular ribs, wherein the frustoconical portion is tapered towards said free longitudinal end of the head, wherein the radial height of the two ribs closest to said end of the head is a maximum value of the radial heights of the ribs, and wherein a spacing between the main annular projecting ribs is regular and a width of each of the main projecting ribs is the same.

12. The machining tool as claimed in claim 11, wherein the abrasive grains are made of diamond, natural or synthetic, or of cubic boron nitride.

13. The machining tool as claimed in claim 11, wherein the head comprises at least one internal duct for supplying fluid which opens laterally via discharge openings.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The figures of the appended drawing will make clear how the invention may be realized. In these figures, identical references designate similar elements.

(2) FIG. 1 represents schematically, in a profile view, a first exemplary embodiment of a machining tool in accordance with the present invention.

(3) FIG. 2 is a schematic perspective view of the tool of FIG. 1.

(4) FIG. 3 shows an example of a trajectory associated with a helical interpolation followed by the longitudinal axis of the tool of FIG. 1, during an operation of tapping a hole.

(5) FIG. 4 shows, in a schematic perspective view, a second exemplary embodiment of a machining tool in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIGS. 1 and 2 show a first exemplary embodiment of a machining tool 1, in accordance with the present invention, which is used to tap a cylindrical hole O (partially represented)of longitudinal axis Z-Z drilled in a workpiece made from an OMC materialby cutting a helical furrow S of a given pitch a in the wall P of the hole O.

(7) Although it is particularly suited to machining a workpiece made from a composite material (and in particular made from an OMC material), it will be understood that the machining tool 1 may equally serve to machine workpieces formed from any other material (metal, plastic, etc.).

(8) As shown in FIGS. 1 and 2, the machining tool 1 comprises: a stem 2 of longitudinal axis L-L which is designed to be attached, at one of its longitudinal ends, to a numerically controlled machine tool (not shown in the figures) which is able to rotate the stem about its axis L-L (this rotational movement being symbolized by the arrow F1); and a head 3 which is formed from a cylindrical body 4 and which is secured to the free longitudinal end of the stem 2. It will be noted that the stem 2 and the head 3 may be distinct or, on the contrary, form a single part.

(9) According to this first example, the head 3 comprises ten projecting annular ribs 5 and 6the outer surface of which is covered with abrasive grains deposited by electroplatingwhich each belong to a plane orthogonal to the axis L-L. The ribs 5 and 6 are mutually parallel and independent from one another.

(10) The projecting ribs 5 and 6, defining, two by two, grooves 7, are regularly spaced from one another such that the associated pitch a is equal to the pitch of the helical furrow S to be cut in order to tap the hole O.

(11) Among the ten projecting ribs 5 and 6, there are: five adjacent main ribs 5, whose radial height h corresponds to the depth of the helical furrow S; and five adjacent auxiliary ribs 6, whose radial height h is less than the radial height of a main rib 5. In other words, the radial height of an auxiliary rib 6 is less than the depth of the helical furrow S.

(12) In addition, the main ribs 5 are arranged on the side of the free longitudinal end 3A of the head 3, whereas the auxiliary ribs 6 are next to the main ribs 5 and are positioned on the side of the longitudinal end 3B of the head 3, which is secured to the stem 2.

(13) As shown in FIGS. 1 and 2, the radial height h of the auxiliary ribs 6 decreases regularly from the maximum radial height associated with the main rib 5 which is adjacent to the first auxiliary rib 6.

(14) Thus, the radial ends 6E and 5E of the auxiliary ribs 6 and of the adjacent first main rib 5 are aligned along a straight line D-D which is inclined with respect to the axis L-L and which belongs to an axial plane passing through this axis L-L. The auxiliary ribs 6 and the first main rib 5 which is adjacent thereto then define a frustum, one generatrix of which is formed by the straight line D-D. In other words, by virtue of the main ribs 5 and the auxiliary ribs 6, the head 3 has a cylindrical portion (the main ribs 5) and a frustoconical portion (the auxiliary ribs 6).

(15) While the main ribs 5 comprise just a single circular projecting edge at the radial end 5E, which is at a height h from the base of the corresponding rib, the auxiliary ribs 6 comprise two circular edges (one of which corresponds to the radial end 6E) each belonging to a generatrix D-D defining the frustum. The separation between two circular edges of a given auxiliary rib 6 is larger as one approaches the longitudinal end 3B of the head 3.

(16) For each auxiliary rib 6, an annular band 8, whose corresponding lateral surface coincides with the surface of the frustum defined by the generatrix D-D, is defined between the two associated circular edges. This annular band having a flat outer surface (that is to say a revolved shape having a straight generatrix) therefore has a large surface area, covered with abrasive grains, which comes into contact with the composite material. This large surface area in contact with the wall of the hole to be tapped makes it possible, in comparison with the prior art, to remove large volumes of shavings on each pass of the tool and therefore to produce, more quickly, a first stage of the tapping threads by means of the secondary ribs. By virtue of the action of this surface, the number of passes necessary for the creation is then reduced and, in practice, a single pass is generally sufficient for tapping a hole in composite material.

(17) In this example, the abrasive grains covering the outer surface of the main ribs 5 are smaller than the abrasive grains covering the outer surface of the auxiliary ribs 6.

(18) By way of non-limiting numerical example, the grain size of the abrasive grains of the main ribs 5 may be between 46 m and 91 m and that of the abrasive grains of the auxiliary ribs 6 may be between 107 m and 427 m.

(19) Thus, the auxiliary ribs 6 having large grains cut a first stage of the furrow S in the wall P of the hole O, which is then finished by means of the main ribs 5 having fine grains in order to obtain the definitive shape of the furrow S.

(20) It will be noted that the abrasive grains of the main ribs 5 and those of the auxiliary ribs 6 are either of the same type or of different types.

(21) Advantageously, the abrasive grains used within the scope of the invention may be made of diamond, either natural or synthetic, or made of cubic boron nitride. The coating binder which agglomerates these grains is, for example, metallic, made of resin or also of electroplated nickel.

(22) Furthermore, the machining tool 1 may comprise one or more internal ducts (not shown) for the supply of fluid, either lubricant or coolant, which are created in the head 3 and open laterally via discharge openings 9.

(23) In accordance with the invention, as shown in FIGS. 1 and 3, the operation of tapping, by means of the machining tool 1, the cylindrical hole Oformed in the wall P made from OMC materialmay be carried out automatically with the aid of the numerically controlled machine which is capable of guiding the tool along a helical trajectory T. In this manner, the machining tool 1 carries out a helical interpolation.

(24) A helical interpolation of this type is obtained by combining a circular movement (symbolized by the arrow F2) in a transverse plane which is orthogonal to the axis Z-Z with a simultaneous movement in translation (symbolized by the arrow F3) along an axis parallel to the axis Z-Z of the hole O.

(25) In order to tap the hole O, the numerically controlled machine sets the tool 1 in rotation about itself (arrow F1), lowers the tool 1 along the axis Z-Z, offsets the axis L-L of the tool 1 with respect to the axis Z-Z of the hole O following a spiral motion in a plane which is transverse to the axis L-L, so as to bring the tool 1 against the inner wall P of the hole O which is to be tapped, and begins moving the tool 1 along the helical trajectory T (arrows F2 and F3).

(26) When the axis L-L of the tool 1 completes a full rotation (i.e. 360, the head 3 of the tool 1 carries out a movement, parallel to the axis Z-Z, equal to the length of the pitch of the furrow S to be cut and thus of the pitch of the ribs.

(27) In the second exemplary embodiment of the machining tool in accordance with the invention, the auxiliary ribs 6 are now arranged at the longitudinal end 3A of the head 3 of the tool 1, such that the shortest auxiliary rib 6 is positioned at this longitudinal end 3A.

(28) Thus, if the machining tool 1 of the first example of FIGS. 1 and 2 is suited to tapping the through hole O by means of an operation of helical interpolation with raising of the machining tool 1 along the wall P of the hole O (symbolized by the arrow F3), the machining tool 1 of the second example of FIG. 4 is, for its part, suited to tapping a blind hole or a through hole O, employing a helical interpolation with lowering of the machining tool 1 along the wall P of said hole O.

(29) Furthermore, although in the examples described the machining tool is used as a tapping tool, it will be understood from the above that it is equally suited for threading an outer wall of a workpiece or, in addition and more generally, for creating a helical furrow or multiple parallel furrows in a workpiece.