Screwing tool, tool holder, and tool assembly including the screwing tool and the tool holder

A screwing tool includes a tool head and a tool shaft having an external thread. A first support section is disposed between the tool head and the external thread, and a second support section is disposed between the external thread and a free end of the tool shaft. The second support section has radially outwardly projecting supporting elements that are disposed at a distance from each other in the circumferential direction.

FIELD OF THE INVENTION

The present invention relates to a screwing tool, a tool holder and a tool assembly.

BACKGROUND OF THE INVENTION

DE 10 2012 100 976 A1 describes a prior-art generic screwing tool with a tool holder. The screwing tool comprises a tool head, on which cutting edges for metal cutting machining operations are disposed, and a tool shaft having an external thread for connection to the tool holder. In addition, the tool shaft has a first support section between the tool head and the external thread and a second support section disposed adjoining a free end of the tool shaft. Complementary thereto, the tool holder has a receiving opening having an internal thread and a first mounting section disposed between a front face side of the tool holder and the internal thread as well as a second mounting section disposed on an inside end of the receiving opening. The first support section of the screwing tool and the first mounting section of the tool holder as well as the second support section of the screwing tool and the second mounting section of the tool holder are in contact with each other and thereby ensure that the screwing tool is especially effectively supported and centered in the tool holder.

Because of the extremely hard and brittle material, this type of screwing tool invariably runs the risk of breakage, in particular if an excessively high screwing torque is applied when the screwing tool is being installed in the tool holder. It is therefore especially important to ensure that the torque required can be determined as accurately as possible.

SUMMARY OF THE INVENTION

One aspect of the present invention is a screwing tool and a tool holder, which allows them to be securely installed.

A screwing tool, a tool holder and a tool assembly are disclosed herein. Useful embodiments of the present invention are also disclosed.

One special feature of the screwing tool disclosed in the present invention is that the second support section comprises radially outwardly projecting supporting elements that are disposed at a distance from each other in the circumferential direction. These supporting elements have the effect of reducing friction losses due to smaller contact surfaces, which in turn also reduces the torque that is required for installing the screwing tool in the tool holder and that results from the reciprocal contact in the second support section. As a result, the overall torque to be applied corresponds even more closely to the optimum torque calculated for the screw engagement so that excessive stress on the screwing tool can be prevented. In addition, the supporting elements that are disposed a distance from each other cause the vibrations to be more effectively damped due to the higher elasticity of the individual outwardly projecting supporting elements. The damping properties can also be specifically influenced by way of the size and number of the contact surfaces.

In a useful embodiment, the supporting elements are disposed at an equal distance from each other in the circumferential direction. It is, however, also possible to dispose the supporting elements at an unequal distance from each other, but centrosymmetrically with respect to the center line of the screwing tool.

To ensure an especially effective support, the supporting elements can be configured in the form of raised strips that extend in the axial direction of the screwing tool.

In the radially most outward section, the supporting elements can also have a contact surface in the shape of a cylindrical segment, which is preferably configured coaxially with respect to a longitudinal axis of the screwing tool. The contact surfaces in the shape of cylindrical segments allow full-surface contact between the supporting elements and the tool holder and thus ensure stable centering. However, to further reduce friction between the supporting elements and the tool holder, cambered contact surfaces or contact surfaces in the shape of a spherical segment can also be disposed on the supporting elements, the enveloping surface of which contact surfaces is formed using a sphere, the center of which is disposed either on, or radially at a distance from, the center line of the screwing tool. This results, respectively, in a contact point or line between the supporting elements and the tool holder having correspondingly reduced frictional forces.

To facilitate insertion of the supporting elements of the screwing tool into a complementary mounting section of the tool holder and to ensure a uniform elastic deformation of the supporting elements, the supporting elements can have an insertion chamfer on a side facing the free end of the tool shaft.

To stabilize the supporting elements especially during the installation of the screwing tool in the tool holder, transitions between the supporting elements and recesses, which are disposed in the circumferential direction between the supporting elements, can be rounded so as to have smaller outside dimensions.

To ensure that the screwing tool is mounted especially stably and optimally centered in the tool holder, the first support section can be formed using two conical contact surfaces having different angles of taper, which contact surfaces are preferably in contact with each other. Optimum centering can be achieved by tapering both the first conical contact surface and the second conical contact surface in the screwing direction of the screwing tool. Especially in this type of biconical mounting configuration, the screwing torque, because of the absence of a stop surface at right angles relative to the screwing force, must be set especially precisely since the tool holder will otherwise be deformed as the screwing tool is increasingly screwed in.

In addition, the present invention claims a tool holder for a screwing tool. The special feature of this tool holder is that the second mounting section comprises radially inwardly projecting mounting elements that are disposed at a distance from each other. Because of the smaller contact surfaces, these mounting elements have the effect of reducing friction losses, which in turn also reduces the torque required for installing the screwing tool in the tool holder, which torque results from the reciprocal contact in the second support section. As a result, the overall torque to be applied corresponds even more closely to the optimum torque calculated for the screw engagement so that excessive stress on the screwing tool can be prevented. In addition, the mounting elements, which are disposed at a distance from each other, cause the vibrations to be more effectively damped due to the higher elasticity of the individual outwardly projecting mounting elements. The damping properties can also be specifically influenced by the size and number of the contact surfaces.

In a useful embodiment, the mounting elements are disposed at an equal distance from each other in the circumferential direction. It is, however, also possible to dispose the mounting elements at an unequal distance from each other, but centrosymmetrically with respect to the center line of the tool holder.

To ensure an especially effective support, the mounting elements can be configured in the form of raised strips that extend in the axial direction of the tool holder.

In the radially most inward section, the mounting elements can also have a mounting surface in the shape of a cylindrical segment, which is preferably configured coaxially with respect to a longitudinal axis of the tool holder. The mounting surfaces in the shape of cylindrical segments allow full-surface contact between the mounting elements and the screwing tool and thus ensure stable centering of the screwing tool. However, to further reduce friction between the mounting elements and the screwing tool, cambered mounting surfaces or mounting surfaces in the shape of a spherical segment or rotationally symmetrical mounting surfaces that are curved in the cross-section can also be disposed on the mounting elements. This results, respectively, in a contact point or line between the mounting elements and the screwing tool having correspondingly reduced frictional forces.

To facilitate insertion, for example, of a cylindrical mounting section on the screwing tool into the second mounting section and to ensure a uniform elastic deformation of the mounting elements, the mounting elements can have a centering chamfer on a side facing the internal thread of the tool holder.

To stabilize the mounting elements especially during the installation of the screwing tool in the tool holder, transitions between the mounting elements and recesses, which are disposed in the circumferential direction between the mounting elements, can be rounded so as to have smaller outside dimensions.

To ensure that the screwing tool is mounted especially stably and optimally centered in the tool holder, the first mounting section can be formed using two conical mounting surfaces having different angles of taper, which mounting surfaces are preferably in contact with each other. Optimum centering can be achieved by tapering both the first conical mounting surface and the second conical mounting surface in the screwing direction of the screwing tool. Especially in this type of biconical mounting configuration, the screwing torque, because of the absence of a stop surface at right angles relative to the screwing force, must be set especially precisely since the tool holder will otherwise be deformed as the screwing tool is increasingly screwed in.

In addition, the present invention also claims a tool assembly that is characterized in that the screwing tool and/or the tool holder are configured as described above.

Most preferably, both the screwing tool and the tool holder can be configured as described above, wherein the spacing between the supporting elements of the second support section of the screwing tool, which supporting elements project radially outwardly and are disposed at a distance from each other in the circumferential direction, differs from the spacing between the mounting elements of the second mounting section of the tool holder, which mounting elements project radially inwardly and are disposed at a distance from each other in the circumferential direction. This has the effect that, independent of the angular position between the screwing tool and the tool holder when screwed together, at least some of the supporting elements and mounting elements are in contact with each other. However, it is also possible for the spacing between the supporting elements and the spacing between the mounting elements to be identical, in which case these elements are to be disposed on the tool holder and on the screwing tool in such a manner that, when screwed together, the supporting elements and the mounting elements are radially opposite to, and in contact with, each other.

The contact surfaces preferably have the same height. However, if the opposite surfaces coincide, these contact surfaces can also have different heights.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a screwing tool1having a tool head2and a tool shaft3. Disposed on the tool head2are blades (not shown) for machining a workpiece. The tool shaft3comprises an external thread4, a first support section5disposed between the tool head2and the external thread4and a second support section7disposed between a free end6of the tool shaft3and the external thread4. The free end6is formed using a front face side of the tool shaft3.

The second support section7comprises outwardly projecting supporting elements8that are disposed at a distance from each other in the circumferential direction. The configuration of these supporting elements8will be described in greater detail with reference toFIG. 2.

FIG. 2shows the second support section7of the screwing tool1ofFIG. 1in greater detail. As this figure indicates, the supporting elements8are configured in the form of raised strips that extend in the axial direction of the screwing tool1and that are disposed at an equal distance from each other. In the radially most outward section, the supporting elements8each have contact surfaces9in the shape of a cylindrical segment that serve to form a centering and damping contact with a tool holder (not shown). The contact surfaces9in the shape of cylindrical segments are configured coaxially with respect to a longitudinal axis of the screwing tool1so that the contact surfaces9together form a common cylindrical enveloping surface that is concentric with the longitudinal axis of the screwing tool1.

To facilitate insertion of the screwing tool1into a complementary mounting location in a tool holder and to ensure a uniform elastic, radially inwardly directed deformation of the supporting elements8, the supporting elements8have an insertion chamfer10on a side facing the free end6.

Disposed in the circumferential direction between the supporting elements8are recesses11, the outside dimensions of which are radially smaller than those of the supporting elements8, i.e., the recesses11are radially offset inwardly relative to the supporting elements8. These recesses11ensure that the screwing tool1and the tool holder15(not shown inFIG. 2) are not in continuous contact with each other over the entire circumference, but make only intermittent contact in the area of the supporting elements8, so that the friction is reduced by means of the decreased surface contact.

The transitions12between the supporting elements8and the recesses11are rounded so as to ensure that forces, in particular circumferential forces, introduced into the tool shaft3act especially effectively on the supporting elements8.

In addition,FIG. 1shows that the first support section5is formed using two conical contact surfaces13,14that are in direct contact with each other. The diameters of the first conical contact surface13and the second conical contact surface14taper in the screwing direction of the screwing tool1. Particulars relating thereto are explained in greater detail in DE 10 2012 100 976 A1, the contents of which are herein fully incorporated by way of reference.

FIG. 3shows a sectional view of a front section of a tool holder15that is configured to receive the screwing tool1described. The tool holder15has a receiving opening16having an internal thread17. Disposed between a front face side18of the tool holder15facing the screwing tool1(not shown inFIG. 3) and the internal thread17is a first mounting section19. In addition, disposed on an inside end20of the receiving opening16is a second inside mounting section21that comprises radially inwardly projecting mounting elements22that are disposed at a distance from each other.

AsFIG. 3indicates, the mounting elements22are disposed at an equal distance from each other in the circumferential direction and configured in the form of raised strips that extend in the axial direction of the tool holder15. In a radially most inward section, the mounting elements22each have a mounting surface23in the shape of a cylindrical segment that extends coaxially with respect to a longitudinal axis of the tool holder15and serves to form a centering and damping contact with the screwing tool1(not shown).

To facilitate insertion of the screwing tool1and a uniform elastic deformation of the mounting elements22, the mounting elements22have a centering chamfer24on a side facing the internal thread17. In addition, disposed in the circumferential direction between the mounting elements22are recesses25, the outside dimensions of which are larger than those of the mounting elements22, i.e., the recesses25are radially offset outwardly relative to the mounting elements22. These recesses25ensure that the tool holder15and the screwing tool1(not shown inFIG. 3) are not in continuous contact with each other over the entire circumference, but make only intermittent contact in the area of the mounting elements22, so that the friction is reduced because of the decreased surface contact.

The transitions26between the mounting elements22and the recesses25are rounded so as to ensure that forces, in particular circumferential forces, introduced into the tool holder15act especially effectively on the mounting elements22.

The first mounting section19is formed using two conical mounting surfaces27,28having different angles of taper, which mounting surfaces are in direct contact with each other. The diameters of the first conical mounting surface27and of the second conical mounting surface28taper in the direction in which the screwing tool1(not shown) is screwed into the tool holder15, i.e., inFIG. 3, toward the left. Particulars relating thereto are explained in greater detail in DE 10 2012 100 976 A1, the contents of which are herein fully incorporated by reference.

FIG. 4shows a perspective view of the receiving opening16of the tool holder15. As the figure indicates, the first mounting section19is disposed on the front face side18of the tool holder15and comprises the first conical mounting surface27and the second conical mounting surface28. On the end facing the second conical mounting surface28, the first conical mounting surface27, in addition to a cone-shaped segment29, has a rounded profile30as a transition to the second conical mounting surface28. The front face side18is formed by a circumferential edge.

In the inside end20of the receiving opening16following the internal thread17, the second mounting section21is disposed. This mounting section is shown in the detail view ofFIG. 5. As indicated in the figure, the second mounting section21comprises the inwardly projecting mounting elements22that in the circumferential direction are adjoined on both sides by the transitions26and subsequently by the recesses25. In addition, the centering chamfer24is configured on the side of the mounting elements22that faces the internal thread17.

The screwing tool1shown inFIGS. 1 and 2and the tool holder15shown inFIGS. 3 to 5together form a tool assembly, i.e., the external thread4and the internal thread17, the first support section5having the conical contact surfaces13,14, and the first mounting section19having the conical mounting surfaces27,28as well as the second support section7having the supporting elements8and the second mounting section21having the mounting elements22are configured so as to contact each other. The spacing between the radially outwardly projecting supporting elements8that are disposed at an equal distance from each other, i.e., the number of the supporting elements disposed along the entire circumference, can differ from the spacing between the radially inwardly projecting mounting elements22that are disposed at an equal distance from each other, thereby ensuring contact between said elements.

However, it is also possible to configure the second support section7or the second mounting section21in the manner described above only on the screwing tool1or on the tool holder15, respectively, and to correspondingly configure the opposite section of the tool holder15or of the screwing tool1, respectively, so as to have a cylindrical or conical rotationally symmetrical profile.

LIST OF REFERENCE NUMBERS

1Screwing tool2Tool head3Tool shaft4External thread5First support section6Free end of the tool shaft7Second support section8Supporting elements9Contact surface10Insertion chamfer11Recesses12Transition between the supporting elements and the recesses13First conical contact surface14Second conical contact surface15Tool holder16Receiving opening17Internal thread18Front face of the tool holder19First mounting section20Inside end of the receiving opening21Second mounting section22Mounting elements23Mounting surface in the shape of a cylindrical segment24Centering chamfer25Recesses26Transition between the mounting elements and the recess27First conical mounting surface28Second conical mounting surface29Cone-shaped segment2930Rounded profile