Tool and method for forming a thread, in particular an internalthread

A tool for forming a thread with a thread profile, wherein:

• a) the tool is rotatable about a tool axis (A) extending through the tool and is movable axially relative to the tool axis;
• b) the tool comprises at least one thread generating region;
• c) the thread generating region extends along a helical line (G1, G2) with a predefined thread pitch angle (δ) and a predefined thread direction (W) of the thread to be formed and has an active profile which corresponds to the thread profile of the thread to be formed;
• and
• d) the thread generating region has at least one thread and clearing tooth comprising:
• d1) in a front region, when seen in the thread direction, a thread tooth element with a thread tooth profile (GP, GP′) as an active profile for forming or finishing the thread;
• and
• d2) in a rearward region, when seen in the thread direction, a clearing element for clearing the formed thread in a reversing movement, wherein the clearing element has a clearing profile (RP) as the active profile, which corresponds to the thread profile of the formed thread and is substantially identical to the thread tooth profile (GP, GP′) in its front region.

A method for forming an internal thread, with a predefined thread pitch and with a predefined thread profile in a workpiece, comprising:

• a) using a tool for forming a thread, wherein:
• the tool is rotatable about a tool axis (A) extending through the tool and is movable axially relative to the tool axis;
• the tool comprises at least one thread generating region;
• the thread generating region extends along a helical line (G1, G2) with a predefined thread pitch angle (δ) and a predefined thread direction (W) of the thread to be formed and has an active profile which corresponds to the thread profile of the thread to be formed;
• the thread generating region has at least one thread tooth comprising:
• a thread tooth profile (GP) with a front thread tooth profile flank (F1) and a rear thread tooth profile flank (F2);
• a front flank relieved surface, directly adjoining the front thread tooth profile flank (F1), on a front thread tooth flank, and
• a rear flank relieved surface, directly adjoining the rear thread tooth profile flank (F2), on a rear thread tooth flank;
• the front flank relieved surface is isolated or set back to the rear relative to a front thread tooth flank envelope (G1) which extends along or parallel to the helical line and through the front thread tooth profile flank (F1);
• the rear flank relieved surface is displaced or isolated to the front relative to a rear transverse plane (E2) which is oriented perpendicularly to the tool axis (A) and extends through the rearmost point of the thread tooth profile (GP) or the rear thread tooth profile flank (F2);
• and
• the helical line (G1, G2) is inclined to the rear relative to the rear transverse plane (E2) by the thread pitch angle (δ);
• b) moving the tool into the workpiece in a working movement during a first working phase, wherein:
• c) the working movement comprises a rotational movement in a predefined rotational direction about the tool axis of the tool and, synchronized with the rotational movement according to the thread pitch, an axial feed movement of the tool in an axial forwards direction axially relative to the tool axis, in such a manner that a complete revolution of the tool about the tool axis corresponds to an axial feed of the tool by the predefined thread pitch;
• d) during the working movement, the thread generating region forms the thread;
• e) the tool, in a decelerating movement following the working movement, is moved during a second working phase further into the workpiece in the same forwards direction as in the working movement, as far as a reversal point;
• f) the axial feed of the tool, based on a complete revolution, is smaller in terms of amount than the thread pitch at least during part of the decelerating movement and is zero at the reversal point;
• g) the thread tooth, produces at least one, closed or annular, circumferential or peripheral groove in the workpiece during the decelerating movement;
• and
• h) wherein friction of the thread tooth against the workpiece surface both at its front thread tooth relieved surface and at its rear thread tooth relieved surface is avoided or substantially reduced during the working movement and also during the decelerating movement.

A method for forming an internal thread, with a predefined thread pitch and with a predefined thread profile in a workpiece;

• a) using a tool for forming a thread with a thread profile, wherein:
• the tool is rotatable about a tool axis (A) extending through the tool and is movable axially relative to the tool axis;
• the tool comprises at least one thread generating region;
• the thread generating region extends along a helical line (G1, G2) with a predefined thread pitch angle (δ) and a predefined thread direction (W) of the thread to be formed and has an active profile which corresponds to the thread profile of the thread to be formed;
• the thread generating region has at least one thread and clearing tooth comprising:
• in a front region, when seen in the thread direction, a thread tooth element with a thread tooth profile (GP, GP′) as an active profile for forming or finishing the thread;
• and
• in a rearward region, when seen in the thread direction, a clearing element for clearing the formed thread in a reversing movement, wherein the clearing element has a clearing profile (RP) as the active profile, which corresponds to the thread profile of the formed thread and/or to the thread tooth profile (GP, GP′) in its front region;
• b) moving the tool into the workpiece in a working movement during a first working phase, wherein:
• c) the working movement comprises a rotational movement in a predefined rotational direction about the tool axis of the tool and, synchronized with the rotational movement according to the thread pitch, an axial feed movement of the tool in an axial forwards direction axially relative to the tool axis, in such a manner that a complete revolution of the tool about the tool axis corresponds to an axial feed of the tool by the predefined thread pitch;
• d) during the working movement, the thread generating region forms the thread;
• e) the tool, in a decelerating movement following the working movement, is moved during a second working phase further into the workpiece in the same forwards direction as in the working movement, as far as a reversal point;
• f) the axial feed of the tool, based on a complete revolution, is smaller in terms of amount than the thread pitch at least during part of the decelerating movement and is zero at the reversal point;
• g) after the reversal point has been reached, a reversing movement of the tool is initiated, with which the tool is moved out of the workpiece;
• wherein the reversing movement comprises first a first reversing phase, wherein the thread generating region of the tool is guided back into a flight of the formed thread, and, thereafter, a second reversing phase, during which the thread generating region is guided outwards out of the workpiece through the flight;
• and
• h) the thread and clearing tooth, during the reversing movement, clears foreign bodies, in front of or out of the thread with its clearing element and also can smooth the workpiece surface, in the thread, and/or allows no gaps to form with respect to a flight inner wall in the clearing process.