Ceramic drill for high-speed drilling

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a drill made of a ceramic material. It finds application in particular in the aviation industry for high speed drilling of very hard materials such as refractory materials, in particular superalloys based on nickel and cobalt, such as Inconel 718, which are used in particular for the manufacture of flanged parts in aircraft structures.

BACKGROUND

Currently, ceramics are increasingly used for the manufacture of cutting tools due to its high hardness and ability to withstand high temperatures. As generally known ceramic cutting tools, which were capable of implementing high-speed machining of very hard materials such as those described in EP-V1-0477093 represent milling and turning tools. Unfortunately, the stress that may act on the drill bit (associated with the deep drilling, chip removing, the intensity and the direction of cutting forces) during the drilling operation, exceeds a voltage which could affect the turning tool or a milling cutter during milling operation. These tensions make it difficult to use ceramic drill bits for drilling at very high speeds increased hardness materials.

The catalogs of many manufacturers offer a wide range of ceramic drills. One such drill is disclosed in US-A-5,641,251. Although these drills provide improved performance compared with conventional drills made of high speed steel or tungsten carbide, they can be utilized are limited and do not provide the possibility of drilling at very high speeds such solid materials, such as superalloys. Due to the low viscosity of ceramic materials Ceramic drills have a lower limit of the torsional strength and compression strength than metal drill, for example, made of tungsten carbide with such mechanical characteristics cermet drill exhibit brittleness when drilling hard materials or at high feed rates, or at high speeds. Much has been done to improve the mechanical properties of materials on a ceramic base. In particular, the patent US-A-4789277 describe ceramic materials in which the fibers are introduced (or whiskers), silicon carbide (SiC) for improving their mechanical characteristics. Furthermore, it is known and recommended that the cutting edge of the drill is always performed with a zero or negative angles to protect the cutting edge against wear and thereby increase service life of the ceramic cutter.

The use of such drills is still limited in relation to materials and cutting speeds and feed drills. In cases where the drilled material having a hardness of heat-resistant materials such as base superalloys such as nickel or cobalt (having number Vickers hardness amounts to about 440), and at high cutting speeds and feed, e.g., when the cutting speed exceeding about 400 meters per minute (m / min) and at a feed rate greater than 0.04 mm per revolution, twisting force and axial compressive force, which are generated and act on the drill of the prior art reach values ​​will inevitably lead to destruction of drills . In addition, cutting forces accompanying such drills to workpieces, and the friction between the radially outer surface of the drill and the inner cylindrical surface drilled holes gives rise to thermal stress in the drilled and drilled workpieces, which lead to accelerated deterioration of the drill and the deformation of the workpiece with attempts to drill solids at high speed.

Also, with increasing depth of the drilled hole to torsional forces exerted on the ceramic drill bit becoming more, primarily because of growing larger outer surface area of ​​the drill, the friction of the inner cylindrical surface of the drilled hole, and, secondarily, iz because when drilling at high speeds ceramic drill of the prior art are not capable of effectively removing a large quantity of chips, which leads to the phenomenon of clogging of the drill and thereby to increase the torsional forces applied to the drill bit, and to increase the risk of destruction. These disadvantages generally make it impossible to drill at a high speed to a depth that exceeds the diameter of the drill.

Disclosure of invention

The object of the invention is to eliminate the above drawbacks and to develop a technical solution that would differ simplicity and low cost, and can improve the characteristics of ceramic drills, and provides the ability to drill hard materials with a very high speed.

To solve this problem proposed ceramic drill bit, comprising:

- Cylindrical shank; and

- A working portion extending in the axial direction coaxially with the shank and having a free end forming a cutting tip of the drill, the working part has the shape of a truncated cone whose larger base is situated near the cutting end of the drill,

wherein the cutting tip comprises two major cutting edges and a central edge located between the two main cutting edges, wherein the working portion comprises two cutting teeth and two grooves extending, alternating with each other about the axis of rotation of the drill, the cutting teeth and the grooves extend from the cutting tip towards the shank, each cutting tooth has a ribbon, and each primary groove having a front surface adjacent to the ribbon and the main cutting edge, at least the working part of the drill is made of a ceramic material, wherein

- Rake angle of the drill is positive;

- The rear surface of the drill extending from each main cutting edge at the rear angle of approximately 4 ° to 10 ° relative to a plane perpendicular to the axis of rotation of the bit; and

- Two notches forming two secondary rake faces extend from the central edge of the drill at a positive rake angle is approximately from 1 ° to 7 ° relative to the axis of rotation of the drill.

In an embodiment, the cutting teeth and the grooves are curled helically around the axis of rotation of the drill at an angle of inclination of the helix of approximately 20 ° to 30 °, and preferably from about 20 ° to 25 ° relative to the axis of the drill.

In another embodiment, the angle of taper of the working portion is between about 1 ° to 5 °, and preferably from about 2 ° to 4 °.

In another embodiment, the width of each ribbon is less than one tenth, and preferably equal to or less than one twentieth of the outer diameter of the working part.

The combination of size and geometric characteristics of the drill according to the invention provides several advantages.

One of these advantages is the significant reduction of torsional forces and compression forces, attached to the drill to prevent its destruction or cutting when drilling with a high speed high hard material such as superalloys based on nickel and cobalt. To minimize twisting forces without reducing the strength characteristics of the drill use different solutions, one of which relates to the limited width of facets for reducing the friction torque between the drill and the cylindrical wall of the drilled hole. The taper of the working part of the tool, of approximately from 1 ° to 3 °, also helps to reduce the friction torque between the drill and the wall of the drilled hole, with the ribbons are brought into contact with the inner cylindrical wall of the drilled hole only near the cutting tip of the drill. In contrast to the practice of making ceramic drills prior art rake angles of the drill according to the invention are positive and are from about 4 ° to 10 ° relative to the axis of the drill, whereby the cutting forces are reduced and hence reduce torsional forces on the drill bit. In the prior art rake angles are zero or even negative in order to reduce wear of the cutting edges. Reduction of cutting forces and friction between the drill and the drilled hole walls also gives the opportunity to reduce the heat generated during drilling, which allows for drilling very hard materials at high speed without damaging the bit or the workpiece.

Compressive forces which act on the drill bit when drilling are reduced due to two notches, formed from the central edge of the cermet drill. Conventional central edge cermet drills have a rake angle and, consequently, they have a significant resistance to axial movement of the drill. Having the recesses allows to modify the central edge so that it becomes a cutting edge having a positive rake angle of the two is from about 1 ° to 7 ° relative to the axis of the drill.

According to the invention, and to reduce the risk of breakage or cutting drill cutting teeth and the grooves have a helical configuration enables the drill to better withstand the twisting forces that act on it, without impairing its other strength characteristics. The spiral configuration of the grooves having a helix angle of less than 25 °, allows to provide good chip removal regardless of the cutting speed and depth of drilling, which can exceed the outer diameter of the drill.

Contrary to what one would expect, thermal stress and material damage at the edge of the holes are small and are limited to a depth of several hundred micrometers (microns). Produced chip turns red when it gets out of the hole, which means that its temperature is about 1000 ° C. We can conclude that the energy produced during high-speed drilling, mostly goes into chips and the chips removed. In most cases, drilled workpieces are left unfinished. In contrast, in respect of workpieces that are subjected to severe stresses, such as turbine engines rotors, openings formed in the drilling process, is subsequently subjected to final finish by conventional means. In any case, high-speed drilling using a drill according to the invention beneficial.

According to another feature of the invention the helix angle of the grooves and the cutting teeth is preferably about 20 ° to 25 °, while the working part of the drill has a taper angle of approximately 1 °, each ribbon has a width of less than about one twentieth of the outer diameter drills, extends from the rear surface of each cutting edge at an angle less than 12 ° relative to a plane perpendicular to the axis of the drill, said angle is preferably less than 8 °, in this case may also be formed undercut surface extending in line with each rear surface. Each cutting edge of the drill and the front edge of each ribbon forming the intersection of each ribbon and the front main surface is rounded with a radius of approximately 2 microns to 40 microns. The angles of the cutting edges may also be chamfered approximately 0.5 millimeters (mm) at an angle of about 20 ° relative to the axis of the drill. These additional features are used to reduce the torsional force and compressive force acting on the ceramic drill. They also serve to reduce the amount of energy produced when drilling at high speed, and also to increase the scattering power using said chip.

According to another preferred feature of the drill apex angle corresponding to the angle formed between the two main cutting edges, it is approximately from 140 ° to 155 °. This feature allows self-centering of the drill and, therefore, eliminates the need for a marking operation for centering the drill.

According to other features of the drill according to the invention:

- Each ribbon has a width of 0.2 mm to 0.8 mm, and preferably from 0.4 mm to 0.8 mm;

- The shank portion of the drill and the work is made of a ceramic material;

- Ceramic material is selected based on alumina, zirconia, silicon nitride or a mixture of ceramic materials;

- A ceramic material reinforced with fibers of silicon carbide (SiC); and

a drill adapted for drilling refractory materials, such as the aviation materials based on nickel or cobalt, and optionally, inter alia, on the basis of Inconel 718 having a Vickers hardness number representing about 440.

The problem is also solved by method of drilling using a ceramic drill bit of the type described above, whereby for high speed drilling refractory aviation materials based on cobalt and nickel peripheral cutting speed of the drill is about 400 m / min to 1000 m / min and the feed rate of the drill is between 0.04 to 0.1 millimeters per revolution. These ranges define the conditions in which it is possible to use ceramic drill bit according to the invention, without the risk of rapid wear or destruction of the drill, and which make possible a good chip removal and ensures good heat dissipation by means of chips. For optimum conditions using peripheral cutting speed of the drill is about 400 m / min to 600 m / min.

According to other features of the method according to the invention, drilling is carried out dry, without the use of lubrication, and it does not require pre-marking operations for centering the drill. Use of a lubricant in drilling a drill according to the invention, is not recommended because it deteriorates the characteristics of the drill in relation to cutting parameters and service life.

Depending on the desired final condition of the surface to produce a completed hole may be sufficient to perform a single drilling operation without performing a preliminary marking and without performing subsequent finishing operations. Because the cutting speed is high and since the number of operations is reduced during drilling, the drill according to the invention can significantly reduce the time required for drilling very hard materials. By comparison with drills known from the prior art, which do not allow drilling very hard materials such high speeds, the duration of the drilling operation the drill according to the invention is reduced by at least 5 times.

According to another feature of the invention the method is applicable for drilling refractory materials, in particular, aviation materials based on nickel or cobalt, and possibly on the basis of the material Inconel 718 having a Vickers hardness number representing about 440 and the drilling operation is roughing.

BRIEF DESCRIPTION OF DRAWINGS

The invention is further explained by description of embodiments with reference to the accompanying drawing figures, in which:

1 is a schematic side view of the drill according to the invention;

Figure 2 - a schematic view of the front end of the drill shown in Figure 1;

3 - a side view of part of the tool shown in Figure 1, seen in the direction A in Figure 2; and

Figure 4 - a side view of part of the tool shown in Figure 1, seen in the direction B in Figure 2.

EMBODIMENTS

As shown in Example 1-4 whole ceramic drill bit for high speed drilling of very high strength materials such as refractory aviation materials made of superalloys and, in particular, of Inconel 718.

This ceramic drill 1 comprises (1) a cylindrical shank 2 and the operation portion 3 extending along the axis of the shank 4 of the drill. The shank includes an annular recess 5 for gripping a chuck of a machine tool (not shown). The free end 6 oriented along the axis of the cylindrical shank ends bevelled to facilitate insertion 7 shank in the chuck of the machine tool.

The working part 3 of the drill 1 comprises two cutting teeth 8 and 9 two grooves extending, alternating with one another about the axis 4 from axial end 10 of the drill 1, which is remote from the shank 2 and is called the cutting tip of the drill. Cutting teeth 8 and groove 9 curl helically around the axis 4 at an angle of inclination of the helix 11, which is less than or equal to about 25 °.

Each cutting tooth comprises eight ribbon 12 to slide along the inner wall of the drilled hole and the back surface 13 which have a helical configuration. According to the invention, each ribbon 12 has a width 14 that is less than or equal to about one tenth of the diameter 15 of the working part 3 of the drill 1. Each groove 9 has a main cutting face 16, adjacent to the intersection between the ribbon 12. The ribbon 12 and the surface 16 of the main cutting edge forms, called the leading edge of the ribbon 17, 12.

Each ribbon 12 extends close to the cutting tip 10 of the drill 1 of the main cutting edge 18. The two main cutting edges are separated by a central edge 19. The angle 20 at the apex formed between the two main cutting edges, is approximately from 140 ° to 155 °. Each major cutting edge 18 formed by the intersection of the front surface 16 of the main grooves 9 and rear surface 21 at an angle of less than about 10 ° relative to a plane perpendicular to the axis 4 of the drill. Each rear surface 21 extends from the main cutting edge 18 at the rear angle of approximately 4 ° to 10 °, and preferably from about 6 ° to 8 ° relative to a plane perpendicular to the axis 4 of the drill 1. Positive or negative angle is defined by a front surface 16 oriented 23 relative to the direction of cutting, when the front surface is deflected from the cutting edge 23 in the direction of cutting, the rake angle is negative, on the other hand, when the front surface 16 of the cutting edge is deflected in the direction opposite to the direction of cutting 23, rake angle 22 is a positive.

Each corner drill 24 formed by the intersection between a main cutting edge 18 and front edge 17 of the ribbon 12 includes a chamfer 25 at approximately 0.5 mm and approximately 20 ° relative to the axis 4 of the drill.

The working part 3 of the drill 1 has an overall outer configuration in the form of a truncated cone. The larger base of the truncated cone is located near the cutting tip 10 and the angle of taper 26 of the working part 3 of about 1 ° to 3 °.

Two secondary front surface 28, formed by two recesses 27 (Figures 1, 2 and 4), extend from the center edge 19 of the drill bit at a positive rake angle 29 (Figure 4) of between approximately 1 ° and 7 ° relative to the axis 4 of the drill. Thus, central edge 19 of the invention comprises two secondary cutting edges.

The main and secondary cutting edges 18 and 19 of the drill 1 and the front edge 17 of each ribbon 12 are rounded with a radius of between 2 microns to 40 microns.

The ceramic material constituting the whole drill 1 is formed on an alumina fiber reinforced silicon carbide (SiC).

In an embodiment of the drill according to the invention a ceramic material may be made on the basis of zirconium dioxide, silicon nitride or a mixture of ceramic materials of zirconium dioxide and silicon nitride, possibly fiber-reinforced silicon carbide.

In another embodiment, the working part 3 of the shank 2 and drill 1 are two elements, which are made separately from different materials and connected to each other, eg by brazing. Working part of the drill 3 in this case is made of a ceramic material, while the drill shank 1 is made of a material having greater strength than the ceramic material, to better withstand forces acting on the drill bit 1. For example, the material to perform the drill shank 1 can be 2 be tungsten carbide.

To enhance the performance of the drill 1 according to the present invention, the angle 11 of inclination of the helix is ​​preferably from about 20 ° to 25 °, the working part 3 has an angle 26 of taper of approximately 1 °, each ribbon 12 has a width 14 that is less than about one twentieth outer diameter portion 15 of the working part 3, each clearance surface 21 has an angle of about 8 ° relative to a plane perpendicular to the axis 4 of the drill 1, and each clearance surface 21 may also be extended undercut surface 30.

In one embodiment of the drill according to the invention, the width 14 of each ribbon 12 is approximately 0.5 mm.

Ceramic drill 1 according to the invention is particularly well adapted for drilling refractory materials, such as refractory aviation materials based on nickel or cobalt and generally called "superalloys". For example, it can be drilled with a very high rate of Inconel 718 having a Vickers hardness number representing about 440. According to the invention the peripheral cutting speed of the drill is about 400 m / min to 1000 m / min and a feed rate of from about 0.04 to 0.1 millimeters per revolution when drilling hard materials such as Inconel 718, which makes possible a significant reduction in the stress acting on the drill 1 as a thermally and mechanically in the form of torsional forces and compression forces. At these speeds, thermal stresses are reduced by means of heat dissipation using chips that quickly transfers the heat to the outside of the drilled holes. For optimum conditions using peripheral cutting speed of the drill should be from about 400 m / min to 600 m / min. Using a drill outside the recommended range of speeds leads to accelerated wear of the drill.

According to another feature of the invention dry drilling operate without lubrication and it represents a roughing operation that does not require any pre-marking operations for centering the drill.

Depending on the desired final condition of the surface to perform the completed hole may be sufficient one drilling operation without any preliminary operation markings and without any further finishing operation.