Rotary cutting tools such as drill bits or reamers

Abstract

The present invention relates to a rotary cutting tool (1), such as a drill bit (2) or a reamer (3), which extends longitudinally along an axis (4) and includes at least one main cutting edge (5), such that when the tool (1) rotates about the axis (4), the tool (1) moves axially forward to perform a cutting operation on a material. According to the present invention, the tool (1) includes braking means (7) for braking the axial forward movement of the tool (1) during the cutting operation.

Description

Technical Field

[0001] The present invention relates to the technical field of rotary cutting tools, such as helical tools, for performing drilling, boring, reaming, countersinking or chamfering operations by rotation.

[0002] The present invention specifically relates to drill bits, right-hand spiral reamers, reaming drill bits, countersink drills or chamfer mills (milling cutters), and has found advantageous applications in the aviation field, where the assembly of aircraft structures requires drilling and reaming a significant number of holes in parts that can consist of stacks of multiple layers (sometimes of different materials). Background Art

[0003] Helical drilling tools, such as drill bits or right-hand spiral reamers, are known in the prior art, which include at least one main cutting edge and extend longitudinally along an axis. These tools are intended to rotate about the axis and advance axially to perform a drilling operation on a material.

[0004] When it is necessary to drill large diameters in particularly hard materials such as steel or titanium, or when it is necessary to achieve tight hole tolerances, or when a pilot hole is required during the assembly process of the part to be drilled, this type of tool can also be stepped or driven.

[0005] The problem with this type of rotary drilling tool lies in the effect of the engagement of the tool with the material during drilling, which can be relatively high, leading to a risk of tool jamming or breaking.

[0006] This problem is even more serious when the drilling operation is manual. In fact, it is difficult for the operator to control the feed of the tool into the material to be drilled and must hold the tool to counteract the engagement force of the tool.

[0007] In addition, when the tool is stepped, there is also the problem of chatter in the tool steps hitting the material, which further increases the risk of jamming or breaking.

[0008] To avoid the risk of jamming or breaking, it is known to produce tools with an inherently low engagement force in the material in this case by reducing the helix angle and / or by reducing the clearance angle of the cutting edge. This has the disadvantage of increasing the thrust, which makes these manual operations time-consuming and tedious, resulting in a reduced tool life. Summary of the Invention

[0009] Therefore, an object of the present invention is to remedy the above disadvantages by providing a rotary cutting tool, such as a helical one, such as a drill bit, a reamer, a right-hand spiral reamer, or having a cutting angle generated by a ramp, such as a grinding or chamfering tool, which avoids the risk of jamming or breaking during the cutting operation and especially during manual drilling.

[0010] Another object of the present invention is to provide a tool which allows an optimal drilling rate by reducing the cycle time of the drilling operation.

[0011] Another object of the present invention is to provide a tool which allows a reduction in thrust, an increase in the life of these tools, and an improvement in drilling comfort and hole quality.

[0012] To this end, a rotary cutting tool has been developed which, according to the prior art, extends longitudinally along an axis and has at least one main cutting edge such that when the tool rotates about the axis, the tool advances axially to perform a cutting operation on the material.

[0013] According to the present invention, the tool comprises means for braking the axial advance of the tool during the cutting operation.

[0014] Thus, the braking means included in the rotary tool make it possible to limit the effect of the significant engagement of this type of tool in the material being drilled, enabling the user to better control the feed of the tool during manual drilling. As a result, the risk of jamming or breakage is avoided.

[0015] Furthermore, a tool geometry with a greater inherent engagement can be used in combination with these braking means, thereby reducing thrust and cycle time while avoiding the risk of jamming.

[0016] According to a particular embodiment, the braking means are axially retracted relative to the main cutting edge and are intended to come into contact with the material being drilled during the drilling operation in order to slow down the axial advance of the tool.

[0017] According to a particular embodiment, the braking means are in the form of an additional cutting edge which is located downstream of the main cutting edge relative to the rotation of the tool and has a lower cutting power than the main cutting edge.

[0018] To this end, the additional cutting edge has:

[0019] - an axial cutting angle smaller than the axial cutting angle of the main cutting edge;

[0020] and / or

[0021] - a clearance angle smaller than the clearance angle of the main cutting edge.

[0022] Other techniques are possible. For example, the additional cutting edge includes an edge preparation, such as a so-called honing radius, i.e., the additional cutting edge is rounded and has a circular cross-section or a faceted surface.

[0023] In this way, the additional cutting edge has a lower cutting power than the main cutting edge, thus limiting the penetration of the additional cutting edge into the material, which enables control of the feed of the tool during manual drilling or even during automatic or semi-automatic drilling with a column drill, semi-automatic machine tool, automatic drilling unit, or even under numerical control.

[0024] The present invention also allows for an increase in the axial cutting angle and clearance angle of the main cutting edge, thereby enhancing the cutting power and efficiency of the tool.

[0025] According to another specific embodiment, the braking device is in the form of a braking surface or braking edge, which is positioned downstream of the main cutting edge with respect to the rotation of the tool.

[0026] The braking surface is constituted, for example, by a secondary clearance extending the main clearance of the main cutting edge, and the angle of the secondary clearance is smaller than the angle of the main clearance.

[0027] The braking edge is constituted, for example, by the trailing edge of the clearance of the main cutting edge, which recedes from the main cutting edge and does not lie in the generatrix of the clearance.

[0028] According to a specific embodiment, the braking device is positioned at an axial distance of between 5 μm and 250 μm and preferably between 5 μm and 200 μm from the main cutting edge.

[0029] The rotary cutting tool according to the present invention can be in the form of a drill bit, reamer, right-hand spiral reamer, grooving or chamfering tool, and preferably includes a braking device at the tip or entrance chamfer, or in the case of a stepped tool, includes a braking device on at least one step, so as to eliminate the chattering effect during manual drilling. Description of the Drawings

[0030] Other advantages and features of the present invention will become more apparent from the following description given by way of non-limiting examples with reference to the drawings, in which:

[0031] Figure 1 is a view showing a stepped or guided drill bit according to the present invention;

[0032] Figure 2 is a view showing a right-hand spiral reamer or reaming drill bit of stepped or guided type according to the present invention;

[0033] Figure 3 is a view showing the main cutting edge and the additional cutting edge of the same drill bit, the additional cutting edge being axially recessed and having a smaller axial cutting angle than the main cutting edge;

[0034] Figure 4A diagram showing the main cutting edge and the additional cutting edge of the same drill bit, where the additional cutting edge is axially retracted and has a clearance angle smaller than that of the main cutting edge;

[0035] Figure 5 A diagram showing the main cutting edge and the additional cutting edge of the same two-flute drill bit, where the additional cutting edge is axially retracted and has a clearance angle smaller than that of the main cutting edge;

[0036] Figure 6 A diagram showing the main cutting edge of a drill bit with a secondary clearance having an extended main clearance, where the angle of the secondary clearance is smaller than that of the main clearance and is axially retracted;

[0037] Figure 7 A diagram showing the trailing edge of the clearance of the main cutting edge, where the trailing edge is retracted from the main cutting edge to form a braking edge;

[0038] Figure 8 A diagram of the additional cutting edge of a drill bit having a honing radius; and

[0039] Figure 9 A diagram showing the additional cutting edge of a drill bit having a faceted surface. Detailed Description

[0040] With reference to Figures 1 to 9 , the present invention relates to a rotary tool (1) for performing drilling or reaming operations, and more particularly to a rotary cutting tool (1), such as a drill bit (2), a right-hand spiral reamer (3), a grinding wheel, or a chamfering tool, etc.

[0041] In a known manner, and with reference to Figure 1 and Figure 2 , the tool (1) extends longitudinally along an axis (4) and has at least one main cutting edge (5), and preferably has at least one additional cutting edge (6), which may or may not be opposite, such that when the tool (1) rotates around the axis (4), the tool (1) advances axially to perform the actual drilling operation.

[0042] Depending on the application, especially depending on the hardness of the material to be drilled, the drill bit (2) or the reamer (3) can be stepped or guided and can have a single flute or a double flute, see Figure 5 .

[0043] In fact, the tool (1) according to the present invention has found particularly advantageous applications in the aviation field, where a relatively large number of holes must be drilled to assemble parts together, which sometimes requires drilling multi-layer parts that may have different materials.

[0044] Thus, in order to facilitate the operation of drilling a relatively large-diameter hole, a drill bit (2) or a reamer (3) with a right-hand helix has a number of steps with diameters increasing in sequence.

[0045] In this application, right-hand helix drill bits (2) or reamers (3) are used extensively, and in the case of the high torque required for drilling hard materials such as steel or titanium and a relatively large diameter, the right-hand helix drill bit (2) or reamer (3) tends to have a very high engagement effect generated by the cutting angle of the tool (1) or the slope of the helix shape.

[0046] When it comes to manual drilling, this engagement effect is restrictive because it is difficult for the operator to control the feed of the tool (1), which leads to a risk of breakage or jamming of the tool (1). In addition, when the tool (1) is stepped, these risks increase because the tool (1) vibrates against the material being drilled at each step.

[0047] Therefore, the tool (1) according to the present invention includes means (7) for braking the axial advancement of the tool (1) during the drilling operation.

[0048] For this purpose, according to a specific embodiment, the braking means (7) are axially retracted relative to the main cutting edge (5) and are intended to contact the material being drilled during the drilling operation in order to slow down the axial advancement of the tool (1).

[0049] These braking means (7) can be, for example, in the form of an additional cutting edge (6), or in the form of a braking surface (8), or in the form of a braking edge (9).

[0050] Referring to Figures 3 to 5 、 Figure 8 and Figure 9 ,in the case of the additional cutting edge (6), the additional cutting edge is located downstream of the main cutting edge (5) relative to the rotation of the tool (1), and in order to contact the material being drilled and slow down the feed, the additional cutting edge has a lower cutting power than the main cutting edge (5).

[0051] The fact that the additional cutting edge (6) has a lower cutting power limits the penetration of the additional cutting edge (6) into the material, which makes it possible to control the feed rate during drilling, especially manual drilling.

[0052] In order to reduce the cutting power of the additional cutting edge (6), several techniques are possible.

[0053] For example, referring to Figure 3, the additional cutting edge (6) has an axial cutting angle (9a) that is smaller than the axial cutting angle (10) of the main cutting edge (5). For example, for a drill bit having a main cutting edge (5) and a single opposing cutting edge, the axial cutting angle (10) of the main cutting edge (5) can be 30°, while the axial cutting angle (9a) of the additional cutting edge (6) can be 20° or even negative.

[0054] According to another embodiment, and referring to Figure 4 and Figure 5 , the additional cutting edge (6) has a clearance angle (11) that is smaller than the clearance angle (12) of the main cutting edge (5). As an example, the clearance angle (12) of the main cutting edge (5) is, for example, between 8° and 12°, while the clearance angle (11) of the additional cutting edge (6) is, for example, 1°.

[0055] Other ways to reduce the cutting power of the additional cutting edge (6) are to form a so-called honing radius (13) with a radius greater than 8 μm (e.g., 10 μm) at the additional cutting edge (6), see Figure 8 , or to form a facet (14) or chamfer the additional cutting edge (6), see Figure 9 . The facet (14) can have a width greater than 10 μm, for example. In the latter configuration, in addition to the size reduction, the result is similar to the arrangement of an additional cutting edge (6) having a smaller cutting angle and / or clearance than the main cutting edge (5).

[0056] Referring to Figure 6 , when the braking device is the braking surface (8), it is formed, for example, by a secondary clearance that extends the main clearance (15) of the main cutting edge (5). The angle (16) of the secondary clearance is smaller than the angle (17) of the main clearance (15), such that the braking surface (8) formed by the secondary clearance contacts the material being drilled to slow down the advancement of the tool (1). For example, the angle (17) of the main clearance (15) is between 8° and 12°, while the angle (16) of the secondary clearance is 1° or even negative. In the case where the secondary clearance has a negative angle, braking is achieved by a braking edge (9) formed by the trailing edge of the secondary clearance, see Figure 7 .

[0057] Referring to Figure 7 , when the braking device is the braking edge (9), it is actually formed by the trailing edge of the clearance of the main cutting edge (5), which is recessed relative to the main cutting edge (5) and does not lie in the generatrix of the clearance.

[0058] The braking device (7) is preferably axially retracted from the main cutting edge (5) by a distance between 5 μm and 250 μm, and preferably between 5 μm and 200 μm, depending on the spacing between the main cutting edge (5) and the braking device (7) in the rotational path (1) of the tool. For a drill bit having a main cutting edge (5) and a braking device (7) positioned on an opposing additional cutting edge (6), an axial distance of less than 5 μm will tend to lengthen the cycle time of the tool (1) and shorten its lifespan, while an axial distance greater than 250 μm will result in a risk of jamming or breaking the tool (1) during the drilling operation.

[0059] The braking device (7) can be located directly on the tip of the drill bit, on the entrance chamfer of the tool, or, if necessary, on one or each stage.

[0060] Another way of presenting the tool according to the invention is to consider that the braking device is retracted from the main cutting edge (5) and includes clearances (11, 16) that have an angle smaller than the clearance angle (12, 17) of the main cutting edge (5), or even a negative angle, in order to generate an edge that cuts or does not cut depending on its position relative to the flute, intended to come into contact with the material being drilled during the cutting operation in order to slow down the axial advance of the tool (1).

[0061] The geometry of the tool thus obtained has inherently contradictory characteristics, since the main cutting edge helps the tool to advance in the material with its axial cutting and clearance values, while the axially retracting edge generated by a clearance angle smaller than that of the main cutting edge will limit the advance. The maximum feed rate of the tool (1) will be determined by the angle and axial position (i.e., helical offset) at which this edge comes into contact with the material.

[0062] According to one embodiment, the clearance for generating an axially retracting edge intended to come into contact with the material being drilled during the cutting operation in order to slow down the axial advance of the tool is the clearance (11) of the additional cutting edge (6), which is located downstream of the main cutting edge (5) relative to the rotation of the tool (1) and has a lower cutting power than the main cutting edge (5).

[0063] According to another example, the clearance that allows the generation of an axially retracting edge and is intended to come into contact with the material being drilled during the cutting operation in order to slow down the axial advance of the tool is a secondary clearance (16) in an extension of the main clearance (15) of the main cutting edge (5), so as to constitute a braking surface (8) located downstream of the main cutting edge (5) relative to the rotation of the tool (1) in the case where the angle of the secondary clearance (16) is smaller than the angle (17) of the main clearance (15), or a braking edge (9) constituted by the trailing edge of the secondary clearance (16) in the case where the angle of the secondary clearance (16) is smaller than the angle (17) of the main clearance (15) and is negative.

[0064] As can be clearly seen from the above, the present invention provides a rotary cutting tool (1), in which the risk of jamming or breakage during drilling, and particularly during manual drilling, is avoided, while allowing an optimal drilling rate by reducing the cycle time of the drilling operation, and allowing a reduction in the thrust force, increasing the lifespan of these tools, and improving the drilling comfort and the quality of the holes.

Claims

1. A rotary cutting tool (1) that extends longitudinally along an axis (4) and includes at least one main cutting edge (5) such that when the rotary cutting tool (1) is driven to rotate about the axis (4), the rotary cutting tool (1) advances axially to perform a cutting operation on a material. The rotary cutting tool (1) includes a braking device (7) for braking the axial advance of the rotary cutting tool (1) during the cutting operation. The braking device (7) includes gaps (11, 16) that have an angle smaller than the clearance angles (12, 17) of the main cutting edge (5), or a negative angle, in order to generate an edge that cuts or does not cut depending on its position relative to the flute of the rotary cutting tool (1). The gaps (11, 16) that generate the axially retreating edge are intended to contact the material being drilled during a drilling operation in order to slow down the axial advance of the rotary cutting tool (1). The gaps (11, 16) are the gaps of an additional cutting edge (6) that is located downstream of the main cutting edge (5) relative to the rotation of the rotary cutting tool (1) and has a lower cutting power than the main cutting edge (5).

2. The rotary cutting tool (1) according to claim 1, characterized in that, The additional cutting edge (6) has an axial cutting angle (9a) that is smaller than the axial cutting angle (10) of the main cutting edge (5).

3. The rotary cutting tool (1) according to claim 1, characterized in that, The braking device (7) is positioned at an axial distance between 5 μm and 200 μm of retreat.

4. The rotary cutting tool (1) according to claim 1, characterized in that, The rotary cutting tool is in the form of a drill bit (2), a reamer, a grinding wheel, or a chamfering tool.

5. The rotary cutting tool (1) according to claim 1, characterized in that, The rotary cutting tool includes a braking device (7) located at the tip or the entrance chamfer, or in the case of a stepped tool, at at least one step.

6. The rotary cutting tool (1) according to claim 1, characterized in that, The rotary cutting tool is a reamer (3) with a right-hand helix.

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