Patent Description:
Drilling is one of the most common machining operations in modern manufacturing and provides a reliable and cost effective method to make holes with high precision. During the drilling operation it is important to use a coolant to cool the drill and the work piece and thus prolong the lifetime of the drill and to improve the quality of the hole. The coolant passes through coolant channels in the drill which terminate at the front end of the drill. The coolant also evacuates chips produced in the drilling operation from the drill area via chip flutes in the envelope surface of the drill. <CIT> discloses such a drill.

A problem that may occur during drilling, especially when drilling difficult to machine materials, such as, for example, Titanium alloys, is a phenomenon called chip jamming. Chip jamming is when machined chips gets stuck in a chip flute, between the surface of the chip flute and the wall of the drilled hole, thus to some extent or completely blocking the chip flute. Chip jamming is detrimental to the drilling process and may lead to a damaged drill tool and to an impaired quality of the drilled hole.

Therefore, it is a need for improvements in a drill for metal cutting machining such that chip jamming can be prevented or, if chip jamming has occurred, loosen the jammed chips to again achieve an unhindered flow in the chip flutes.

It is therefore an object of the present invention to present an improved drill for metal cutting machining with a decreased risk of chip jamming.

According to the present invention, the above mentioned object is achieved by means of a drill for metal cutting machining having the features defined in claim <NUM>.

The drill for metal cutting machining according to the present invention comprises: a central rotation axis defining a longitudinal direction of the drill and around which the drill is rotatable, an axially front end, an axially rear end, an envelope surface extending between the front end and the rear end, a shaft extending axially rearward from the front end, a shank extending axially forward from the rear end, at least one cutting insert releasably mounted at the front end, a first and a second chip flute in the envelope surface of the shaft, a coolant chamber inside the shank, a first and second coolant channel extending from the front end of the coolant chamber and terminating at the front end of the drill. The first coolant channel is associated with the first chip flute and the second coolant channel is associated with the second chip flute. The coolant chamber comprises a flow control element, which is movable between a neutral position, in which coolant flow is distributed substantially equally to the first and second coolant channels, and an active position, in which the flow control element directs the coolant flow at least mainly to one of said coolant channels, and that the flow control element is arranged to move from said neutral position to said active position in response to a flow restriction in one of the chip flutes, such that the coolant is directed at least mainly to said one coolant channel associated with the chip flute having a flow restriction.

The present inventors have realized that this configuration alleviates the problem with chip jamming. When chip jamming occurs in the first chip flute the flow of coolant in the first chip flute will be restricted. This flow restriction will lead to an increase in the coolant pressure in the first coolant channel associated with the first chip flute. This creates a pressure difference between the first coolant channel and the second coolant channel. The pressure difference moves the flow control element from a neutral position to an active position in which the flow in the second coolant channel is restricted. This disrupts, or drastically reduces, the coolant flow in the second channel and in the second chip flute. The reduced flow in the second coolant channel implies that the pressure of the coolant in the first coolant channel and first chip flute increases. The increased pressure in the first chip flute results in that the jammed chips in the first chip flute are flushed away thus removing the chip jam from the first chip flute. Preferably, the flow in the restricted coolant channel is reduced at least <NUM> % when the flow control element is in an active position, more preferably at least <NUM> % of the flow is restricted, even more preferably at least <NUM> % of the flow is restricted, even more preferably at least <NUM> % of the flow is restricted, and most preferably approximately <NUM> % of the flow is restricted.

Associated with here means that a majority of the coolant flow from the first coolant channel reaches the first chip flute and the majority of the coolant flow from the second coolant channel reaches the second chip flute. The reason for this may be due to different design alternatives. That the first coolant channel terminates close to or in the first chip flute, that the outlet of the first coolant channel is directed towards the first chip flute or that the rotation of the drill implies that most of the coolant from the first coolant channel reaches the first chip flute. The same applies for the second coolant channel and the second chip flute.

Many different types of coolant can be used, for example a water-based coolant or an oil-based coolant.

According to one preferable embodiment, the flow control element automatically moves from the neutral position to an active position when there is a pressure difference in the coolant between the first and the second coolant channel. This configuration ensures that the flow control element moves from the neutral position to an active position, without any outside assistance or actuators, when there is a chip jam in one of the chip flutes since a chip jam in one of the chip flutes will lead to an increased pressure in the coolant channel associated with the affected chip flute.

According to one preferable embodiment, the flow control element moves back to the neutral position when the flow restriction in one of the chip flutes is removed. This configuration implies that the flow of coolant will again be evenly distributed between the first and second coolant channel when the chip jam has been removed. This ensures even distribution between the first and second chip flute to obtain best possible cooling and continuous evacuation of chips.

According to one preferable embodiment, the flow control element is entirely mechanical. This configuration is suitable and durable for the harsh conditions encountered when drilling in metallic materials. Flow control elements comprising electrical parts would be more susceptible to failure during the drilling operation.

According to one preferable embodiment, the flow control element is positioned between the rearward axial extensions of the first and second coolant channel when the flow control element is in the neutral position.

With this configuration the flow control element is suitably positioned to be able to move to restrict the flow in either the first coolant channel or the second coolant channel.

According to one preferable embodiment, the flow control element is a pendulum rotatable around an axle.

This configuration is cost effective and having the flow control element in the form of a pendulum rotatable around an axle ensures that the flow control element automatically moves from a neutral position to an active position when there is a pressure difference between the first and second coolant channel.

According to one preferable embodiment, the pendulum is hinged to the axle by a hole at the rear end of the pendulum and that the axle is partially threaded and fastened to the shank by a threaded hole in the shank.

This configuration is cost effective and ensures simple installation and replacement of the pendulum.

According to one preferable embodiment, the hole in the shank is positioned on the rotation axis, perpendicular to the rotation axis and perpendicular to a line passing through the center of the first coolant channel and the center of the second coolant channel at the rear ends of the first and second coolant channel.

This configuration ensures that the pendulum can swing in directions to cover either the first or the second coolant channel to restrict the flow in respective channel.

According to one preferable embodiment, the coolant chamber, in a cross-section perpendicular to the rotation axis, has a width approximately equal to the distance between the radially outermost parts of the rear ends of the first and second coolant channels.

According to one preferable embodiment, the coolant chamber, in a cross-section perpendicular to the rotation axis, has a thickness approximately equal to the diameter of the first and second coolant channels at the rear ends of the first and second coolant channels.

This configuration ensures that the pendulum at its end points of its swing plane cover either the first or the second coolant channel to restrict the flow in respective channel.

The width of the coolant chamber may also be larger than the diameter of the first and second coolant channels at the rear ends of the first and second coolant channels.

According to one preferable embodiment, the pendulum has its front end approximately at the front end of the coolant chamber.

According to one preferable embodiment, the cross-sectional area of the front end of the pendulum is larger than the cross-sectional area of either of the first and the second coolant channel at the rear ends of the first and the second coolant channel. With this configuration the coolant flow in the first or the second coolant channel is effectively restricted when the pendulum is in an active position.

According to one preferable embodiment, the pendulum has a thickness that is approximately equal to the thickness of the coolant chamber.

This configuration further improves the restriction of coolant flow when the pendulum is in an active position.

According to one preferable embodiment, the drill has two axially extending arms at its front end, the arms spaced apart about the rotation axis to define a jaw, the cutting insert releasably mounted within the jaw between the arms.

With this configuration a single drill body can hold a variety of cutting inserts with varying geometries, allowing greater flexibility for optimum performance across multiple materials and applications.

According to one preferable embodiment, the drill has a central cutting insert releasably mounted in an insert seat at the front end of the drill and a peripheral cutting insert releasably mounted in an insert seat at the front end of the drill.

This configuration ensures efficient drilling and allows the usage of indexable cutting inserts which improves the economy of the drill operation.

Further advantages of the present invention will appear from the description following below.

Embodiments of the invention will now be described in detail with regard to the annexed drawings, in which:.

Reference is made to <FIG>, which show a drill according to an embodiment of the invention. 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.

The drill, generally designated <NUM>, has a central rotation axis (C) around which the drill is rotatable. The drill further has a front end <NUM>, a rear end <NUM> and an envelope surface <NUM> that extends between the front end <NUM> and the rear end <NUM>.

In the following description the front end of an element refers to the parts of the element that is closest to the front end <NUM> of the drill <NUM> when the element is mounted in the drill. Correspondingly, the rear end of an element refers to the parts of an element that is closest to the rear end <NUM> of the drill <NUM> when the element is mounted in the drill. Further, an axial direction refers to a direction parallel to the rotation axis (C) and a radial direction refers to a direction perpendicular to the rotation axis (C).

The drill <NUM> further has a shaft <NUM> extending axially rearward from the front end <NUM> of the drill <NUM> to a collar <NUM>. A shank <NUM> extending axially forward from the rear end <NUM> of the drill <NUM> to the collar <NUM>. The shank <NUM> is for attaching the drill <NUM> to a rotatable tool holder (not shown). The shaft <NUM> includes first <NUM> and second chip flutes <NUM> for transporting coolant and chips away from the bottom of a drilled hole. The first <NUM> and second chip flutes <NUM> preferably extends all the way to the collar <NUM> which directs coolant and chips away from the hole. The first <NUM> and second chip flutes <NUM> are helically shaped around the shaft <NUM> for efficient cooling and transportation of chips. The front of the collar <NUM> has a generally conical shape and has a diameter that is larger than the diameter of the shaft <NUM> and larger than the diameter of the shank <NUM>, to efficiently direct chips away from the hole and away from the rotatable tool holder. The rear side of the collar is perpendicular to the rotation axis to act as a stop when inserting the shank <NUM> in the rotatable tool holder.

Axially extending arms <NUM>, forming a jaw <NUM> between them, are positioned at the front end <NUM> of the drill. A cutting insert <NUM> is mounted in the jaw <NUM> by threaded screws (not shown). The cutting insert <NUM> extends across the whole diameter of the drill <NUM> and comprises cutting edges that meet at the center of the front end of the cutting insert <NUM> at the rotation axis (C) of the drill <NUM>. The cutting insert <NUM> further comprises chip channels that connect to the chip flutes <NUM>, <NUM> of the drill <NUM>. The drill <NUM> is thus what is usually called an exchangeable head drill.

A coolant chamber <NUM> is positioned at the rear end <NUM> of the drill. The rear end of the coolant chamber <NUM> is connected to a coolant inlet (not shown). A flow control element <NUM>, here in the form of a pendulum <NUM>, can be fastened in the coolant chamber by an axle <NUM> through a hole <NUM> at the rear end of the pendulum <NUM>. The axle <NUM> is inserted into a threaded hole <NUM> in the shank <NUM> and through the hole <NUM> in the pendulum. A threaded end <NUM> of the axle <NUM> engages the threaded hole <NUM> in the shank <NUM> to ensure that the axle is secured.

Referring now to <FIG> showing some of the features inside the drill <NUM>. A first <NUM> and second coolant channel <NUM> starts at the front end of the coolant chamber <NUM> and terminates at, or close to, the front end <NUM> of the drill <NUM>. Terminates in here means that the first and second coolant channels have their outlets at, or close to, the front end <NUM>. Coolant will pass through the first and second coolant channels <NUM>, <NUM> to cool the drill <NUM>, the cutting insert <NUM> and the work piece that is being drilled. The coolant will further flush drilled chips away from the bottom of the drilled hole through the first and second chip flute <NUM>, <NUM>. The first and second coolant channels <NUM>, <NUM> are preferably twisted in the drill <NUM>.

The first coolant channel <NUM> is said to be associated with the first chip flute <NUM>. That means that the first coolant channel has its outlet close to or in the first chip flute <NUM> and/or has its outlet directed towards the first chip flute <NUM>. A majority of the coolant that flows in the first coolant channel <NUM> will pass through the first chip flute <NUM>. The same applies for the second coolant channel <NUM> and the second chip flute <NUM>.

The coolant chamber occupies approximately <NUM> % of the length of the shank <NUM> and the width W of the coolant chamber <NUM> is approximately <NUM> % of the diameter of the shank <NUM>.

In the coolant chamber <NUM> the mounted pendulum <NUM> is seen hinged on the axle <NUM>. The axle <NUM> is positioned perpendicular to the rotation axis (C) and perpendicular to a line passing through the center of the first coolant channel <NUM> and the center of the second coolant channel <NUM> at the rear ends of the first and second coolant channels <NUM>, <NUM>. By this configuration the pendulum <NUM> will have a swing plane that reaches the rear ends of the first and second coolant channels <NUM>, <NUM>. <FIG> shows the pendulum in a neutral position positioned along the rotation axis (C) between rearward axial extensions of the first and second coolant channel <NUM>, <NUM>. Fig. 2b shows the pendulum in an active position where it restricts the flow in the first coolant channel <NUM>.

The axle <NUM> is positioned at a distance from the rear end <NUM> of the drill <NUM> that is approximately equal to <NUM> % of the length of the coolant chamber. The length of the pendulum <NUM> is such that the front end of the pendulum <NUM> extends approximately to, or very close to, the front end of the coolant chamber <NUM>.

During drilling machined chips transported from the bottom of the drilled hole through the first and second chip flutes <NUM>, <NUM> may get stuck, or jammed, between a chip flute and the wall of the drilled hole. If a chip gets jammed in the second chip flute <NUM> the flow of coolant will be restricted in that chip flute. This leads to an increased pressure of the coolant in the second coolant channel <NUM> associated with the second chip flute <NUM>. An increased pressure in the second coolant channel <NUM> leads to a pressure difference between the first coolant channel <NUM> and the second coolant channel <NUM>. The pressure difference moves the pendulum from a neutral position to an active position where it restricts the flow in the first coolant channel <NUM>. The restriction of flow in the first coolant channel leads to an increased flow and pressure in the second coolant channel <NUM> and the associated second chip flute <NUM> which will help alleviate the problem of the jammed chips in the second chip flute <NUM>. When the chip jam in the second chip flute <NUM> is removed the pressure difference between the first <NUM> and second coolant channel <NUM> will disappear and the pendulum will again move to a neutral position thus creating an even distribution of coolant flow to the first <NUM> and second coolant channel <NUM> and to the first <NUM> and second chip flute <NUM>.

The forces arising from the pressure of the coolant acting on the pendulum is much larger than the forces that arises on the pendulum due to the rotation of the drill <NUM>. The pendulum <NUM> can therefore restrict the flow in either of the first <NUM> or second coolant channel <NUM> when there is a pressure difference between them and return to a neutral position when the pressure difference between the first <NUM> and second coolant channel <NUM> ceases. The pressure of the coolant when entering the coolant chamber <NUM> from the coolant inlet is between <NUM> to <NUM> bar. Most often pressures between <NUM> to <NUM> bar are used.

Referring now to <FIG> which shows the drill <NUM> from its rear end <NUM> with the pendulum <NUM> and axle <NUM> removed. The coolant chamber <NUM> is positioned at the radial centre of the drill and the first <NUM> and second coolant channels <NUM> are positioned equidistant from the rotation axis (C). The coolant chamber <NUM> has the shape of a slot in a cross-section perpendicular to the rotation axis (C), with semi-circles at its short ends. The coolant chamber <NUM> has a width W that is approximately the same, or slightly larger, than the distance between the radially outermost points of the first and second coolant channels <NUM>, <NUM>. The coolant chamber <NUM> has a thickness T that is approximately the same, or slightly larger, than the diameter of the first and second coolant channels <NUM>, <NUM>. This configuration ensures that the pendulum <NUM> effectively restricts the flow in the first <NUM> or the second coolant channel <NUM> when the pendulum is at one of its end points in its swing plane in an active position.

Referring now to <FIG> which shows the pendulum <NUM>. The pendulum <NUM> is elongated and has a longer length in an axial direction than it is wide in a radial direction. The pendulum <NUM> is slightly wider close to its rear end than at its front end. Close to the rear end of the pendulum <NUM> a hole <NUM> for hinging the pendulum <NUM> to axle <NUM> is seen. The front end <NUM> of the pendulum <NUM> has a flat elliptical surface with an area that is larger than the area of either of the areas of the first <NUM> or the second coolant channel <NUM> at the rear end of the coolant channels. This ensures efficient restriction of flow in either of the first <NUM> or second coolant channel <NUM> when the pendulum <NUM> is in an active position. The pendulum <NUM> has a thickness t that is approximately the same size or slightly smaller than the thickness T of the coolant chamber <NUM> to ensure that the pendulum <NUM> swings within the coolant chamber <NUM> with ease and that it efficiently restricts the flow in the first <NUM> or second coolant channel <NUM> when the pendulum <NUM> is in an active position.

The rear end <NUM> of the pendulum <NUM> is curved to ensure a smooth flow of coolant around the pendulum <NUM> and to decrease stress in the pendulum <NUM>. For the same reasons the sides of the pendulum <NUM> may be curved or beveled.

Referring now to <FIG> which shows another embodiment of the present invention. Same reference numerals designate the same features, as for the embodiments described above with reference to <FIG>. The drill <NUM> in <FIG> differs from the embodiment in <FIG> substantially only in the arrangement of cutting insert(s) at the front end of the drill. More specifically, at the front end of drill <NUM> two insert seats are positioned to accommodate a central insert 118c and a peripheral insert 118p where the central insert 118c is positioned closer to the rotation axis (C) than the peripheral insert 118p. These inserts 118c, 118p are usually indexable meaning that several different cutting edges can be used on the same insert 118c, 118p.

Claim 1:
A drill (<NUM>, <NUM>) for metal cutting machining having a central rotation axis (C) defining a longitudinal direction of the drill (<NUM>, <NUM>) and around which the drill is rotatable, comprising:
- an axially front end (<NUM>),
- an axially rear end (<NUM>),
- an envelope surface (<NUM>) extending between the front end (<NUM>) and the rear end (<NUM>),
- a shaft (<NUM>) extending axially rearward from the front end (<NUM>),
- a shank (<NUM>) extending axially forward from the rear end (<NUM>)
- at least one cutting insert (<NUM>, 118c, 118p) releasably mounted at the front end (<NUM>),
- a first (<NUM>) and a second chip flute (<NUM>) in the envelope surface (<NUM>) of the shaft (<NUM>),
- a coolant chamber (<NUM>) inside the shank (<NUM>),
- a first (<NUM>) and second coolant channel (<NUM>) extending from the front end of the coolant chamber (<NUM>) and terminating at the front end (<NUM>) of the drill, the first coolant channel (<NUM>) is associated with the first chip flute (<NUM>) and the second coolant channel (<NUM>) is associated with the second chip flute (<NUM>),
characterized in that the coolant chamber (<NUM>) comprises a flow control element (<NUM>), which is movable between a neutral position, in which coolant flow is distributed substantially equally to the first (<NUM>) and second coolant channels (<NUM>), and an active position, in which the flow control element (<NUM>) directs the coolant flow at least mainly to one of said coolant channels (<NUM>, <NUM>), and that the flow control element (<NUM>) is arranged to move from said neutral position to said active position in response to a flow restriction in one of the chip flutes (<NUM>, <NUM>), such that the coolant is directed at least mainly to said one coolant channel (<NUM>, <NUM>) associated with the chip flute (<NUM>, <NUM>) having a flow restriction.