Patent Description:
The present invention is related to a drilling tool according to the preamble of claim <NUM>. Such a drilling tool is known from <CIT>.

The drilling tool according to the present invention is particularly designed for chip forming machining of metallic work pieces and for drilling composite materials.

Such a drilling tool comprises a tool body having a center axis defining a longitudinal direction of the drilling tool, the tool body having an axially forward end and an axially rearward end, the distance in the longitudinal direction between the forward end and the rearward end defining a length of the drilling tool, and at least two indexable cutting inserts, which are arranged at the axially forward end, a first indexable cutting insert being arranged at a radially inner position and a second indexable cutting insert being arranged at a radially outer position, the tool body comprising a first flute portion extending axially rearward from the first indexable cutting insert, and a second flute portion extending axially rearward from the second indexable cutting insert.

Prior art drilling tools of this kind are suffering from a number of inherent problems which are difficult to overcome as will be discussed in the following.

For a cutting insert arranged at a radially inner position, i.e. close to the center, and with a given number of rotations per minute (rpm), the cutting speed is rather low due to its location at a small radius while the cutting speed is much higher for a cutting insert at a radially outer position, i.e. located at a larger radius. The different cutting parameters which are strongly varying from the radially inner cutting insert to the radially outer cutting insert cause the formation of different types and sizes of chips, which have different chip transportation requirements.

Further, the forces acting on the chips lead to a repeated deformation of chips, which in turn results in the generation of additional heat and unbalanced and varying cutting forces. This in turn causes an unstable behavior of the drilling tool during a cutting operation and may even cause breaking of the drilling tool, in particular of small diameter drilling tools which are less stable and may not withstand unbalanced and varying cutting forces. Even for drilling tools having a larger diameter, the unbalanced and varying cutting forces may result in vibrations and may cause an increase of wear.

A main object of the present invention is to provide a drilling tool having increased stability and torsional rigidity in order to obviate or at least minimize some or all of the afore-mentioned problems. A further object is to provide a drilling tool having improved chip transport characteristics. A still further object is to provide a drilling tool which can be manufactured in an economical way.

At least the main object is achieved by means of a drilling tool having features defined in claim <NUM>.

The first flute portion of the drilling tool according to claim <NUM> transitions into the second flute portion at an axially forward transition area of the tool body, thereby forming only one flute of the drilling tool.

In this way, a more stable and torsional rigid drilling tool is provided, especially in relation to conventional drilling tools having two separate flute portions, which run separately along the length of the drilling tool.

Furthermore, the chip transport of the drilling tool is improved. Surprisingly, it has been established that during drilling operations the larger chips produced by the radially outer cutting insert promote transportation of the smaller chips produced by the radially inner cutting insert in an advantageous way. By having said transition area at an axially forward location, the positive effect on the smaller chips is achieved close to the formation of these smaller chips.

The transition area is located at an axial distance from the forward end amounting to no more than L/<NUM>.

According to another embodiment the transition area is located at an axial distance from the forward end amounting to no more than L/<NUM>.

In a further embodiment the first flute portion runs internally through the tool body forming a through hole from a front end surface to the second flute portion. In this way, the chips generated by the first, i.e. the radial inner, cutting insert are transported internally through the tool body to the second flute portion. Hereby, these chips do not come in contact with the hole wall being generated during this transport and the surface finish of the hole wall is improved.

According to another embodiment the first flute portion opens into a front end surface of the tool body via a first opening.

According to the invention, the second flute portion opens into a peripheral surface of the tool body, which improves chip transport as well as enables production of the drilling tool in an economical manner.

Specifically, the second flute portion is open to the peripheral surface along the entire extent thereof in the longitudinal direction. This further improves chip transport and further simplifies production of the drilling tool.

According to another embodiment the first opening intersects a first plane being perpendicular to the center axis, thereby defining a first area, which is no more than <NUM>% of the area of the front end surface. This relationship provides for a rigid drilling tool, while enabling good chip transport.

According to a further embodiment the first opening intersects a first plane being perpendicular to the center axis, thereby defining a first area, which is no more than <NUM>% of the area of the front end surface. In this way, an even more rigid drilling tool is provided, while still securing an efficient chip transport.

In another embodiment a cross-section of the first flute portion in a second plane perpendicular to the center axis is smaller than a cross-section of the second flute portion in a third plane perpendicular to the center axis. In this way, the size of the respective flute portions is adapted to the different sizes and shapes of the chips generated by the different cutting inserts. At the same time, the rigidity of the tool body is improved.

According to another embodiment the second flute portion is helical.

In a further embodiment the first flute portion as well as the second flute portion are helical. Thereby, a smooth transition between the first and second flute portions is established. At the same time, chip transport is improved.

According to another embodiment the pitch of the first flute portion is substantially the same as the pitch of the second flute portion, which further improves chip transport. Also, this enables production of the drilling tool in an economical way.

According to a further embodiment the tool body is a single-piece body made from one piece of material. Firstly, this enables production of the drilling tool in an economical way, since there is no need for connecting a plurality of different tool body parts. Secondly, a more rigid tool body is provided, without any connections between different tool body parts. Such connections are typically more prone to breakage at heavy loads.

According to the invention, said second flute portion has a radial depth, which is larger than a radius of the tool body along at least a first longitudinal segment of the second flute portion. In this way a larger second flute portion is provided, which enables transport of larger quantities of chips and decreases problems with chip congestion.

In a further embodiment the tool body comprises a coolant channel, which opens into the front end surface of the tool body via a coolant channel opening, which is adjacent to the first indexable cutting insert. In this way, coolant may be provided close to first indexable cutting insert, thereby improving performance of the drilling tool.

According to yet another embodiment the second flute portion has a partly circular cross-section, a first intersection of the second flute portion and the peripheral surface and a second intersection of the second flute portion and the peripheral surface together forming an angle of no more than <NUM>°. In other words, the second flute portion is somewhat closed, i.e. in cross-section the second flute portion is larger or wider towards the center of the drilling tool, than at its intersection with the peripheral surface. In this way, the chips are better contained within the flute portion during chip transport, thereby improving surface quality of the hole wall being generated by the drilling tool. Also, a more rigid drilling tool is obtained in this way.

According to a further embodiment a cross-section of the first flute portion gradually increases from the front end surface to the second flute portion. In this way a more rigid drilling tool towards the front end surface is obtained.

The present invention will now be explained in more detail by a description of different embodiments of the invention and by reference to the accompanying drawings.

Reference is made to <FIG>, which show a drilling tool according to a first embodiment. Such a drilling tool is a device which is adapted for use in metal or composite cutting operations, primarily drilling operations, but the drilling tool can also be used for helical interpolation, boring, plunging and turning operations. The drilling tool is arranged to be mounted or connected to a machine tool (not shown), such as a CNC machine, either directly or indirectly by one or more tool holders, to a tool spindle of the machine tool.

As can be seen from <FIG>, the drilling tool <NUM> comprises a tool body <NUM>, which has a center axis A defining a longitudinal direction of the drilling tool <NUM>. The drilling tool <NUM> is rotatable around the center axis A in a rotational direction <NUM>, see <FIG>. The tool body <NUM> has an axially forward end <NUM> and an axially rearward end <NUM>. The distance in the longitudinal direction between the forward end <NUM> and the rearward end <NUM> defines a total length L of the drilling tool <NUM>. Rearward from the forward end <NUM>, a peripheral surface <NUM> extends on a front cylindrical portion <NUM> of the tool body. Said front cylindrical portion, i.e. having shank-like form, ends in a collar portion <NUM> having generally conical shape, which in turn transforms into a rear mounting portion <NUM>, which is arranged to be mounted in a machine tool (not shown). The mounting portion <NUM> has a generally cylindrical form. The front cylindrical portion <NUM> extends between a first plane P1, which is perpendicular to the center axis A, and a seventh plane P7, which is parallel with the plane P1, but is located axially behind or lower than the first plane P1, as illustrated in <FIG>. Thus, the seventh plane P7 indicates the transition between the front cylindrical portion <NUM> and the collar portion <NUM>. The axial distance between the first plane P1 and the seventh plane P7 defines a maximum cutting length Lc of the drilling tool, i.e. how deep a hole can be machined with the drilling tool without interfering with the collar portion <NUM>.

The drilling tool further comprises at least two indexable cutting inserts <NUM>, <NUM>, which are arranged at the axially forward end. A first indexable cutting insert <NUM> is arranged at a radially inner position <NUM> and a second indexable cutting insert <NUM> is arranged at a radially outer position <NUM>. More specifically, the tool body <NUM> comprises a radially inner pocket <NUM> for receiving the first indexable cutting insert <NUM> and a radially outer pocket <NUM> for receiving the second indexable cutting insert <NUM>. The cutting inserts <NUM>, <NUM> are secured in their respective pockets <NUM>, <NUM> by means of a suitable clamping arrangement, such as by a screw <NUM>.

The tool body <NUM> of the drilling tool is a single-piece body made from one piece of material, preferably tool steel, whereas the cutting inserts <NUM>, <NUM> preferably are made of a hard metal such as cemented carbide.

The indexable cutting inserts <NUM>,<NUM> include a front insert end surface <NUM>, <NUM>', a back insert end surface <NUM>, <NUM>' and an insert side surface <NUM>,<NUM>'. The cutting inserts <NUM>,<NUM> further include at least one cutting edge <NUM>, <NUM>' defined by the intersection of a front insert end surface <NUM>, <NUM>' and an insert side surface <NUM>, <NUM>'. The exact shape and cutting geometry of the first indexable cutting insert <NUM> and the second indexable cutting insert <NUM> may vary based on user requirements. The cutting inserts <NUM>, <NUM> as illustrated have a generally rectangular or square configuration, but also other shapes, such as triangular inserts, are conceivable. Thus, in the illustrated embodiment the cutting inserts <NUM>,<NUM> have an insert side surface <NUM>,<NUM>' defining four sides, which meet in four corner surface portions <NUM>, <NUM>'. These corner surface portions <NUM>, <NUM>' are curved. For each side, said cutting edge <NUM>, <NUM>' includes a straight cutting edge portion <NUM>, <NUM>', formed by the intersection of the front insert end surface <NUM>, <NUM>' and the insert side surface <NUM>, <NUM>'. Further, for each corner, said cutting edge <NUM>, <NUM>' includes one or more radiused or curved cutting edge portions <NUM>, <NUM>' formed by the intersection of the front insert end surface <NUM>, <NUM>' and the corner surface portions <NUM>, <NUM>' of the insert side surface <NUM>, <NUM>'.

In the illustrated embodiment the cutting inserts <NUM>, <NUM> are indexable, i.e. rotatable around the axis defined by the screw <NUM>, into four different active positions. Also other configurations, such as cutting inserts having two or three different active positions are conceivable.

Furthermore, based on user requirements the first indexable cutting insert <NUM> and the second indexable cutting insert <NUM> may be of identical or different configuration. In the illustrated embodiment the first, radially inner, indexable cutting insert <NUM> is different from the second, radially outer, indexable cutting insert <NUM>. This is best illustrated in <FIG>, where each of the four sides of the radially inner cutting insert <NUM> includes more surface portions, than corresponding four sides of the radially outer cutting insert <NUM>. Accordingly, the cutting edge <NUM> of the radially inner cutting insert <NUM> includes more cutting edge portions, of different configuration, than the cutting edge <NUM>' of the radially outer cutting insert <NUM>.

The first, radially inner, indexable cutting insert <NUM> and the second, radially outer, indexable cutting insert <NUM> have radially overlapping working or active portions of their respective cutting edges <NUM>, <NUM>'. In other words, as apparent from <FIG>, the forwardmost portions of the cutting edge <NUM>, <NUM>' of the cutting inserts <NUM>,<NUM>, together cover a distance being at least equal to a radius R of the tool body, i.e. the radial distance from the center axis A to the periphery of the tool body <NUM>. Thus, during drilling operation and rotation of the drilling tool the radially overlapping working or active portions of the cutting edges <NUM>, <NUM>' together machine the full diameter 2R of the drilling tool.

As apparent from <FIG> the first radially inner cutting insert <NUM> and the second radially outer cutting insert <NUM> are not mounted exactly <NUM>° in relation to each other. Rather, in top view of the drilling tool, a fourth plane P4 being tangent to the front insert end surface <NUM> of the radially inner cutting insert <NUM> and parallel with the center axis A, and a fifth plane P5 being tangent to the front insert end surface <NUM>' of the radially outer cutting insert <NUM> and parallel with the center axis A, together form an angle α amounting to <NUM>°. Thus, the first radially inner cutting insert <NUM> and the second radially outer cutting insert <NUM> are slightly rotationally offset, i.e. offset in the rotational direction <NUM>. Consequently, in top view of the drilling tool, the axially forwardmost portions of the cutting edges <NUM>, <NUM>' of the cutting inserts <NUM>,<NUM> do not form a straight line, but together these forwardmost portions of the cutting edges <NUM>, <NUM>' also form an angle α amounting to <NUM>°.

The tool body <NUM> comprises a first flute portion <NUM> extending axially rearward from the first indexable cutting insert <NUM>, and a second flute portion <NUM> extending axially rearward from the second indexable cutting insert <NUM>. The first flute portion <NUM> transitions into the second flute portion <NUM> at an axially forward transition area <NUM> of the tool body <NUM>, thereby forming only one flute <NUM> of the drilling tool <NUM>.

According to the present invention the transition area <NUM> is located at an axial distance <NUM> from the forward end <NUM> amounting to no more than L/<NUM>. In the illustrated embodiment in <FIG>, the transition area <NUM> is located at an axial distance <NUM> from the forward end <NUM>, which is smaller than L/<NUM>. As illustrated in <FIG>, the axial distance <NUM> is the distance between a first plane P1, which is perpendicular to the center axis A, and a sixth plane P6, which is parallel with said first plane P1, but located axially behind or lower than the first plane P1. As can be seen from <FIG> the first flute portion <NUM> runs internally through the tool body <NUM> forming a through hole from a front end surface <NUM> of the tool body to the second flute portion <NUM>. As a result, the peripheral surface <NUM> is continuous and not interrupted by the first flute portion <NUM>. The first flute portion <NUM> opens into the front end surface <NUM> of the tool body <NUM> via a first opening <NUM>. In top view, the first opening <NUM> has a generally round shape. In the emobodiment illustrated in <FIG>, the first opening <NUM> includes a large arc <NUM>, roughly having the form of a half-circle, which is connected to two smaller arcs <NUM>, <NUM>, which each is connected to the radially inner insert pocket <NUM>. Thus, the generally round shape of the first opening <NUM> is formed by said three arcs <NUM>, <NUM>, <NUM> together with the radially inner insert pocket <NUM>. As apparent from <FIG>, the area covered by said first opening <NUM> is smaller than the area of the front end surface <NUM>.

As can be seen in <FIG>, according to this embodiment the front end surface <NUM> is perpendicular to the center axis A in a first plane P1. With reference to <FIG>, in top view of only the tool body <NUM> of the drilling tool <NUM>, the first opening <NUM> intersects the first plane P1, which is perpendicular to the center axis A, thereby defining a first area <NUM>. In other words, according to the illustrated embodiment, the first opening <NUM> intersects the front end surface <NUM>, thereby defining the area <NUM> being delimited by the radially inner insert pocket <NUM> and the three arcs <NUM>, <NUM>, <NUM>. According to one embodiment, the first area <NUM> is no more than <NUM>% of the area of the front end surface <NUM>. In the embodiment of <FIG>, the first area <NUM> is no more than <NUM>% of the area of the front end surface <NUM>.

Further, the second flute portion <NUM> opens into the peripheral surface <NUM> of the tool body <NUM>. According to the present invention and as illustrated in <FIG>, the second flute portion <NUM> is open to the peripheral surface <NUM> along the entire extent thereof in the longitudinal direction. Thus, the second flute portion <NUM> is open to the peripheral surface <NUM> along the front cylindrical portion <NUM> of the tool body. As can be seen in <FIG> the second flute portion <NUM> continues from the front cylindrical portion <NUM> into the collar portion <NUM> and ends in the conical envelope surface of the collar portion <NUM>.

In the embodiment illustrated in <FIG>, the first flute portion <NUM> has a generally smaller cross-section than the cross-section of second flute portion <NUM>. More specifically, the cross-section of the first flute portion <NUM> in a second plane P2 perpendicular to the center axis A is smaller than a cross-section of the second flute portion <NUM> in a third plane P3 perpendicular to the center axis A. The first plane P1 is tangent with the forward end <NUM> of the drilling tool, and is also tangent with the front end surface <NUM>. The plane P2 is parallel with the plane P1, but is located axially behind or lower than the plane P1, as illustrated in <FIG>. The plane P3 is parallel with the planes P1 and P2, but is located axially behind or lower than the plane P2, which is also apparent from <FIG>.

Based on user requirements the first flute portion <NUM> may have varying or substantially constant cross-section along the axial extent of the first flute portion <NUM>. In other words, the size of the first flute portion <NUM> may vary or be substantially constant along the axial extent thereof. In the embodiment illustrated in <FIG> the first flute portion <NUM> has a substantially constant cross-section. According to another embodiment, the cross-section of the first flute portion <NUM> increases gradually from the front end surface <NUM> to the second flute portion <NUM>. In other words, the first flute portion <NUM> becomes gradually larger or has a generally conical configuration along its extent in the longitudinal direction from the front end surface <NUM> to the second flute portion <NUM>.

Preferably, the first flute portion <NUM> as well as the second flute portion <NUM> are helical. In other words, the first flute portion <NUM> and the second flute portion <NUM> run in a helical manner in the longitudinal direction of the drilling tool. Further, the pitch of the first flute portion <NUM> is substantially the same as the pitch of the second flute portion <NUM>, so as to form one continuous, helical flute <NUM> having one and the same pitch. As illustrated in <FIG> the second flute portion <NUM> comprises a curved inner surface <NUM>. In the illustrated embodiment, for a more economical production of the drilling tool, the tool body <NUM> comprises a first flat surface <NUM> extending from the front end surface <NUM> and the radially outer insert pocket <NUM> to the curved inner surface <NUM>. The first flat surface <NUM> intersects the peripheral surface <NUM> and is substantially parallel with the plane P5, i.e. substantially parallel with the front insert end surface <NUM>' of the radially outer cutting insert <NUM>. For a more economical production of the drilling tool, the tool body <NUM> further comprises a second flat surface <NUM> extending from the front end surface <NUM> to the curved inner surface <NUM>. The second flat surface <NUM> intersects the peripheral surface <NUM> and is oriented in parallel with the center axis A and substantially at right angle with the first flat surface <NUM>. Further, the first flute portion comprises a curved inner surface <NUM>, which adjoins the arc <NUM> at the front end surface <NUM>.

As illustrated in <FIG>, the second flute portion <NUM> has a radial depth RD, which is larger than a radius R of the tool body <NUM>. In other words, a radial distance RD from an intersection between the second flute portion <NUM> and the peripheral surface <NUM> is larger than a radius of the tool body <NUM>, i.e. the radial distance from the peripheral surface <NUM> to the center axis A. As illustrated in <FIG>, a first intersection <NUM> is formed between the second flute portion <NUM>, more specifically, the curved surface <NUM> thereof, and the peripheral surface <NUM>. A first radial distance RD<NUM> larger than the the radius R is formed between the first intersection <NUM> and the curved surface <NUM> of the second flute portion. Further, a second intersection <NUM> is formed between the second flute portion <NUM>, more specifically, the curved surface <NUM> thereof, and the peripheral surface <NUM>. A second radial distance RD<NUM> larger than the the radius R is formed between the second intersection <NUM> and the curved surface <NUM> of the second flute portion <NUM>. According to different embodiments the first radial distance RD<NUM> may be equal to or different from the second radial distance RD<NUM>. The second flute portion <NUM> has a radial depth RD, which is larger than a radius R of the tool body <NUM>, along at least a first longitudinal segment <NUM> of the second flute portion <NUM>. In the embodiment illustrated in <FIG>, the first longitudinal segment <NUM> extends the between the sixth plane P6 and the seventh plane P7. In other words, the first longitudinal segment <NUM> extends between the transition area <NUM>, i.e. where the first flute portion <NUM> transitions into the second flute portion <NUM>, and the transition between the front cylindrical portion <NUM> and the collar portion <NUM>. Thus, the first longitdunal segment <NUM> extends a major part of the maximum cutting length Lc of the drilling tool. According to another embodiment, the first longitdunal segment <NUM> is shorter, for example such that it extends from the sixth plane P6 but ends before, or above, the seventh plane P7.

Further, as can be seen in <FIG>, the tool body <NUM> comprises a coolant channel <NUM>, which opens into the front end surface <NUM> of the tool body <NUM> via a coolant channel opening <NUM>, which is adjacent to the first indexable cutting insert <NUM>. In other words, the coolant channel opening is located close to the first indexable cutting insert <NUM>, but more distant in relation to the second indexable cutting insert <NUM>. The coolant channel opening <NUM> is substantially circular. The tool body <NUM> further comprises a first groove <NUM>, which is arranged in the front end surface <NUM> and connects the coolant channel with the first flute portion <NUM>. Also, the tool body <NUM> comprises a second groove <NUM>, which is arranged in the front end surface <NUM> and connects the coolant channel with the second flute portion <NUM>. As best seen in <FIG>, in this embodiment the tool body comprises an elongate recess <NUM>, extending from the front end surface <NUM> in the longitudinal direction of the drilling tool and extending from the peripheral surface <NUM> to the first flute portion <NUM> in the radial direction. This recess <NUM> enables the insertion of a fastening tool, such as a screwdriver, from outside the drilling tool through this recess <NUM> into the first flute portion <NUM> reaching the screw <NUM> for fastening the radially inner cutting insert <NUM> in the radially inner insert pocket <NUM>.

As illustrated more in detail in <FIG>, the second flute portion <NUM> has a partly circular cross-section, i.e. a cross section of the curved surface <NUM> of the helical flute <NUM> will generate a curve being at least partly circular. Further, the first intersection <NUM> of the second flute portion <NUM> and the peripheral surface <NUM> and the second intersection <NUM> of the second flute portion <NUM> and the peripheral surface <NUM> together form an angle β of no more than <NUM>°. Thus, the the first radial distance RD, and the second radial distance RD<NUM> together enclose the angle β being no more than <NUM>°. In other words, the second flute portion <NUM> is somewhat closed. As apparent from <FIG>, the second flute portion <NUM> is larger or wider towards the center axis A of the drilling tool, than at its intersection with the peripheral surface.

The dimensions of the drilling tool as described above can be configured based on user requirements. For example, the total cutting length Lc of the drilling tool <NUM> may be <NUM> or larger, but normally not larger than <NUM>. Examples of diameters 2R of the drilling tool include diameters from <NUM> to <NUM>. Further, the relationship between drilling tool diameter 2R and maximum cutting length Lc is preferably configured such that Lc/2R is at least <NUM> but not more than <NUM>.

The invention is not limited to the embodiments disclosed, but may be varied and modified within the scope of the following claims.

Claim 1:
A drilling tool (<NUM>) comprising
a tool body (<NUM>) having a center axis (A) defining a longitudinal direction of the drilling tool (<NUM>),
the tool body having an axially forward end (<NUM>) and an axially rearward end (<NUM>), the distance in the longitudinal direction between the forward end (<NUM>) and the rearward end (<NUM>) defining a length (L) of the drilling tool (<NUM>), and
at least two indexable cutting inserts (<NUM>, <NUM>), which are arranged at the axially forward end (<NUM>), a first indexable cutting insert (<NUM>) being arranged at a radially inner position (<NUM>) and a second indexable cutting insert (<NUM>) being arranged at a radially outer position (<NUM>),
the tool body (<NUM>) comprising
a first flute portion (<NUM>) extending axially rearward from the first indexable cutting insert (<NUM>), and
a second flute portion (<NUM>) extending axially rearward from the second indexable cutting insert (<NUM>),
wherein
the first flute portion (<NUM>) transitions into the second flute portion (<NUM>) at an axially forward transition area (<NUM>) of the tool body (<NUM>), thereby forming only one flute (<NUM>) of the drilling tool (<NUM>),
the transition area (<NUM>) is located at an axial distance (<NUM>) from the forward end (<NUM>) amounting to no more than L/<NUM>, and
the second flute portion (<NUM>) is open to a peripheral surface (<NUM>) along the entire extent thereof in the longitudinal direction, and in characterized in that
said second flute portion (<NUM>) has a radial depth (RD), which is larger than a radius (R) of the tool body (<NUM>) along at least a first longitudinal segment (<NUM>) of the second flute portion (<NUM>).