WO2005113927A1

WO2005113927A1 - Method and device for the drilling of partially overlapping bores

Info

Publication number: WO2005113927A1
Application number: PCT/EP2005/052337
Authority: WO
Inventors: Stefano Lambertini
Original assignee: Officine O.F.P. S.R.L.
Priority date: 2004-05-21
Filing date: 2005-05-20
Publication date: 2005-12-01
Also published as: TW200607589A; ITMI20041014A1

Abstract

A method for drilling partially overlapping bores (80, 82), is characterised in that it comprises the steps of carrying out a longitudinal slot (81) within a first bore (80); inserting in said first bore (80) a guide member (6) comprising a drilling head (1) with a pre-set eccentricity with respect to said guide member (6) and means (7) for engaging said slot (81); and drilling a second partially overlapping bore (82) by sliding said guide member (6) within said first bore (80), and said means (7) within said slot (81). The invention also provides a device for carrying out such method.

Description

METHOD AND DEVICE FOR THE DRILLING OF PARTIALLY OVERLAPPING

BORES

Field of the invention

This invention relates to an device and to a method for the drilling of bores which partially overlap each to the other. The method and the device according to the present invention are particularly advantageous for the drilling of deep bores in metal bodies. Prior art In some mechanical applications it is necessary to drill very deep bores through metal bodies or masses, the cross section of these bores may even have dimensions of about ten times smaller than the length of the bores itself. In some cases, the depth of the bore may even be 150-200 times the size of the bore cross section (150-200 times the diameter, in the case of circular cross section bores). Further, in certain circumstances may be requested to have non-circular cross section for the drills, i.e. bores with lobe sections.

In these circumstances, it is known that in order to drill bores having a cross section with the shape of an "eight", it is necessary to drill two partially overlapping circular bores with a deep drilling rotary head, for example of the type described in patent applications WO 95/34397 or WO 00/78489, in the name of SANDVIK AB. According to the above described method, an initial single circular cross section bore is drilled, and a bar having approximate the same diameter of the bore is fitted therein. Then, a second bore is drilled by removing part of the material of the so inserted bar, and lastly the bar is removed. However, the above method has some disadvantages. Because of the inevitable structural differences between the material of the inserted bar and the main body to be drilled, and at the same time the structural discontinuity between the inserted bar and the bore due to the tolerance required for the insertion of the bar, this method leads to strong deviations on the axis of the second bore with respect to the first bore. Moreover, with the abovementioned method, along the two intersecting lines of the two circular bores, it will not be possible to obtain sharp edges which, in some applications, may be desirable (for example, to give structural resistance to the drilled bore when it has to contain a fluid with very high pressures).

Such parallelism errors, being emphasized by the hardness of the materials to be drilled, i.e. alloy steels, produce bores having axis that considerably diverge one from the other. Thus, with the present chip removal rotary heads, it is only possible to drill "eight-shaped" bores no longer than 1-2 meters.

Therefore, object of the present invention is to avoid the abovementioned disadvantages of the method and device of the prior art, by providing a method for the drilling of partially overlapping bores, i.e. made up of two or more partially overiapping bores with a relatively considerable depth with respect the dimension of the cross section thereof, and an device to carry out such method.

Summary of the invention

Such object is achieved, according to a first aspect of the present invention, with a method and device for the drilling of partially overlapping bores having the features of claim 1.

According to a second aspect of the present invention, such object is achieved with an device for the drilling of partially overlapping bores according to claim 5.

The advantages and features of the present invention will be more apparent to those skilled in the art through the following non-limitative detailed description of a preferred embodiment, with reference to the following figures.

List of figures

Figure 1 schematically shows a side view, partially in section, of an device for drilling lobed deep bores in a functional phase, according to the present invention,;

Figure 2 schematically shows a front view of a drilling rotary head of the device in Figure 1 ;

Figure 3 schematically shows a side sectional view of a guide support of the device in Figure 1 ;

Figure 4 schematically shows a front view of a part of the guide support of Figure

3; Figures 5 and 6 schematically show the cross sectional views, respectively, according to section planes C-C and B-B of the support in Figure 3;

Figure 6A schematically shows a detailed part of the view of Figure 6; Figures 7, 8 and 9 schematically show cross sectional views of a deep bore obtained by the deep drilling method of the present invention, respectively taken at three subsequent time periods. Detailed description of the invention With reference to Figure 1 , the device for drilling bores with partially overlapping cross sections according to the present invention is shown. The device comprises a chip removal rotary drilling head 1 which is suitable designed for the drilling of deep bores. The rotary head 1 is provided with a first series of cutting blades or front tools 2 (as already known in the art, e.g. made of ceramic material) which are mounted closer to the axis of rotation of the head 1 , and a second series of cutting blades or peripheral tools 3, e.g. made of ceramic material, which are mounted away from the axis of rotation of the head 1. It has to be specified herewith that according to other embodiments of the above described head 1 and not shown herewith, there may be a different kinds and settings for the cutting tools 2 and 3, respectively.

With reference to figure 2, the head 1 is also provided with three groups of double centring shoes 4 (better shown in the following) which are arranged in order to abμt against the walls of the bore, for the centring and guiding of the head 1 when drilling. With reference now to figure 3, according to the present invention the drilling head 1 is installed within a guide support 5 which comprises a front guide member 6 having basically a cylindrical shape and having its axis within a preset eccentric position with respect to the axis of the head 1. As better shown in figure 4, the front guide member 6 is provided with a longitudinal projecting part 7 having the shape of a parallelepiped and arranged parallel and along the axis of rotation of the head 1, the function thereof will be more apparent in the following. With particular reference to figures 5, 6 and 6A, the guide support 5 has two longitudinal protrusions 50 projecting from the external surface of the support 5, the function thereof is for the guiding and sliding of the support member 5 inside the second circular bore 82. More precisely, the longitudinal protrusions 50 allow the part of the support 5 located behind the head 1 to abut the walls of the second bore 82, thereby guiding the head 1. On the other hand, at the in area A as shown in Figure 6 there is more clearance between the surface of the support member 5 and the inner wall of the second bore 82, for example about 0.3-1 mm of clearance.

Further, as shown in Figures 3 and 5, at a region which corresponds to a region behind the cutting end of the head 1 , the member 5 has a part 54 which is shaped in order to slide and engage inside the first bore 80, thereby guiding the head 1 during the drilling operation.

Furthermore, as shown in figure 5 the guide support 5 has two grooves 51 at opposite sides. The grooves 51 correspond to edges 83 resulting in the drilled bore (Figure 9), thereby surrounding the latter during the drilling operation, so as to avoid damaging of said edges 83 after their formation.

According to the present invention, and with particular reference to figure 6A, in case of the edges 83 need to be sharp edges, the guide support 5 is provided with two cutting edges 53 extending longitudinally onto said support member 5. As can be understood from the figures, the position and arrangement of the cutting edges 53 is preset and the same are located beside the head 1 and arranged in order to slit and cut the material M at the edges 83 during the rotation of the head 1. Preferably, the cutting edges 53 are basically set at a preset height, according to the plane DC (shown in Figure 6), which contains the two axis of the cross sections of the first 80 and second bore 82. Furthermore, a reduction of the radial tolerances between the surface 54 of the guide support 5 and the first bore 80 allows achieving cleaner and sharper edges 83, with respect to the method of the state of the art. In the present embodiment, the cutting edges 53 are integrally obtained from the support 5, but in another different embodiment they can be realised as added inserts made of suitably hard material.

On the other hand, with reference to figures 5 and 6, the part 54 has two bores 55 for the passage of oil or different fluid for the lubrication and the cooling during operation. More precisely, when drilling the second bore 82, the cooling and lubricating fluid flows out of the support 5 towards said head 1 and is discharged along with removed chips. With particular reference to figure 2 and according to the present embodiment, in the head 1 the front tools 2 and peripheral tools 3 are grouped two by two, i.e. one front tool 2 and one radial tool 3. Further, the tools of each group are aligned according to the radial direction with respect to the axis of rotation of the head 1 , and equally spaced between each other. Advantageously, each group of front tools 2 and the peripheral tools 3 is aligned and spaced each from the other of an angle α equal to 120°. With this arrangement, during the drilling operation of the second circular bore 82, two radial groups of tools 2, 3 contact the walls of the bore 82, thereby reducing drilling vibrations. However, it has to be herewith specified that depending on the specific structure of the bore to be drilled, it is also possible to set up more than three groups of cutting tools 2 and 3 for the head 1 , e.g. there can be set four, five, or seven groups of tools 2 and 3 equally spaced on the head 1. Preferably, in order to further reduce vibrations during the drilling operation, the tools 2 and 3 of each group are set up so that their cutting edges 20 and 30 lie in the same plane within each group, respectively and according to the direction of rotation of the head 1 shown by the arrow DR in figure 2.

Preferably, in order to facilitate the construction and assembling of the head 1 , each group of front tools 2 and peripheral tools 3 is installed on the same supporting surface 8. The same applies to the centring shoes 4 which are mounted equally spaced from each other. More preferably, the arrangement of the centring shoes 4 shall be staggered of α/2 with respect to the arrangement of the radial groups of tools 2 and 3, respectively and in order to keep each shoe or group of shoes away from a group of tools 2 and 3. This arrangement onto the head 1 reduce vibrations during the drilling operation.

Now, a detailed explanation of the method according to the present invention will be given with reference to the annexed figures.

According the invention and with particular reference to figure 7 to 9, to drill deep bores having a cross section partially overlapping , i.e. "8" shaped in a metal piece, first a drilling operation for a first bore 80 has to be carried out, up to a final depth as the final overlapping bore. Consequently, as shown in figure 8 a guiding slot 81 is realised, the slot 81 extends along the entire length of the first bore 80, for example with a rectangular profile and by a broaching tool operation or similar.

On the other hand, the cylindrical part 6 of the guide support 5 is inserted in the first bore 80. It must be herewith specified that the diameter of the cylindrical part 6 has to be chosen slightly smaller than the diameter of the first bore 80, so as to limit the clearance between the two parts, thereby allowing the cylindrical part 6 to slide into the bore 80.

After fitting the part 6 of the support 5 into the bore 80 it is possible to carry out a second bore 82 which overlaps partially the first bore 80, as shown in figure 9. More precisely, when carrying out the second bore 82, the extension 6 and the guide member 7 guides the head 1 in a preset position with respect to the first bore 80 which is established by the eccentricity between the axis of the support 5 and the axis of the head 1 , which coincides with the axis of the two bores 80 and 82, respectively. The device and the method of the present invention has several advantages.

A first advantage consists in that the use of the support member 5 prevents or considerably limits deviations between the axis of the first bore 80 and the axis of the second bore 82. A second advantage consists in that the projecting part 7 after engaging in the slot 81 prevents or considerably limits the axial flexure of the head 1 during operation especially for deep bores, thus allowing to carry out a second bore 82 with smaller parallelism tolerances with respect to the method of the state of the art. For example, the applicant found that using the present invention a parallelism error between the axes of bores 80 and 82 was metered no bigger than + 0.02 mm per meter of length of the bore, up to bores having a depth/length of 150-200 times the diameter of the first bore 80 or the second bore 82.

A third advantage consists in that the use of the cylindrical part 6 reduces the linearity error of the axis of the second bore 82 with respect to the axis of the first bore 80. A fourth advantage consists in that the above drilling device and drilling method are liable to many modifications and variations, though without departing from the scope of the present invention. For example, the male/female mating between the longitudinal projecting part 7 onto the part 6 and the slot 81 in the first bore 80 can be reversed by mating a radially protruding longitudinal rib obtained from the walls of the bore 80 with a suitable longitudinal slot or groove obtained onto the part 6 of the support member 5.

Claims

1. A method for drilling partially overiapping bores (80,82), comprising the step of drilling a first bore (80), characterised in that it comprises the following steps: carrying out a guiding slot (81) within said first bore (80) along the whole length of the latter; inserting within said first bore (80) a guide member (6) of a supporting member (5) which comprises a drilling head (1 ) with a pre-set eccentricity with respect to said guide member (6) and means (7) for engaging said slot (81 ); and - drilling a second bore (82) which partially overlaps said first bore (80) by means of said drilling head (1) by sliding said guide member (6) within said first bore (80), and said means (7) within said slot (81).

2) The method according to claim 1 , wherein said preset eccentricity between said guide member (6) and said support member (5) substantially corresponds to the distance between the axes of said first bore (80) and said second bore (82).

3) The method according to claim 1 or 2, wherein said means for engaging said slot (81) comprises a projecting part or shoe (7) arranged in a parallel manner with respect to the axis of said first bore (80) and for engaging said slot (81) along the whole length during the drilling operation. 4) The method according to claim 1 or 2 or 3, wherein said guide part (6) has an outside diameter which substantially coincides with the diameter of said first bore (80).

5) The method according to one or more of the preceding claims, wherein during the drilling operation said second bore (82) overlaps and takes away said slot (81). 6) The method according to one or more of the preceding claims, wherein during the drilling operation the guide support (5) slides within said first bore (80). 7) A device (1) for drilling a partially overlapping second bore (82) to a first bore (80) within a piece of metal (M), characterised in that it comprises: a drilling head (1); a guiding support member (5) wherein said drilling head (1) is rotatably mounted; and a guiding means (6,7) integral to said support member (5) and for cooperating with said first bore (80) during the drilling of said second bore (82). 8) The device according to claim 7, wherein the said guiding means comprises a front guide member (6) consisting of a tubular body of substantially same diameter of said first bore (80) and arranged in a fixed manner onto said support member (5) with a pre-set eccentricity, said eccentricity corresponding to the distance between the axis of said partially overlapping first bore (80) and said second bore (82). 9) The device according to claim 7 or 8, wherein said guiding means further comprises at least one longitudinal projecting shoe or part (7) mounted onto said guide member (6) with its axis parallel to the axis of said guide member (6) and for co-operating with a respective longitudinal slot (81) within said first bore (80).

10) The device according to one or more claims from 7 to 9, wherein said support member (5) comprises at least two longitudinal protrusions (50) onto its outer surface for co-operating with the inner surface of said first bore (80).

11 ) The device according to one or more claims from 7 to 10, wherein said support member (5) further comprises two longitudinal grooves (51) which correspond to respective edges (83) at the intersection of said first bore (80) and said second bore (82).

12) The device according to one or more claims from 7 to 11 , wherein said support member (5) further comprises two cutting edges (53) extending longitudinally onto said support member (5), said cutting edges (53) corresponding to respective edges (83) at the intersection of said first bore (80) and said second bore (82). 13) The device according to the preceding claim, wherein said cutting edges (53) are integrally obtained from the support member (5).

14) The device according to one or more claims from 7 to 12, wherein said cutting edges (53) are added inserts made of suitably hard material.

15) The device according to the preceding claim 7-14, wherein said drilling head (1) comprises at least three groups of cutting tools (2,3) each group being arranged in a radial direction on the head (1 ) and equally spaced from the others.

16) The device according to the preceding claim, wherein each group of tools (2,3) is aligned and spaced each from the other of an angle (α).

17) The device according to the preceding claim, wherein each group of tools (2,3) is spaced from the other of an angle equal to 120°

18) The device according to claim 15 or 16 or 17, wherein the tools (2,3) of each group of cutting tools onto said head (1) have respective cutting edges (20,30), the arrangement being such that said cutting edges (20,30) lie in the same plane for each group of tools (2,3).

19) The device according to one or more claim from 15 to 18, wherein said drilling head (1) further comprises at least three centring shoes (4) mounted equally spaced from each other onto said head (1) for co-operating with the inner surface of said second bore (82).

20) The device according to the preceding claim, wherein the arrangement of said centring shoes (4) is staggered of a pre-set angle (α/2) with respect to the arrangement of said radial groups of tools (2,3). 21) The device according to the preceding claim, wherein said stagger angle is pre-set half of said angle between each group of tools (2,3).