Tapping Tool Reboring Edge for Defect-Free Internal Threads
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Solution Overview
Problem
Existing tapping tools often result in material weaknesses and defects in the formed internal thread due to plastic deformation, particularly at the radially inner thread crest, which can impair the setting behavior of screw elements.
Innovation Solution
A tapping tool with a reaming cutting edge that completes the internal thread by drilling it out to the core diameter in a reversing stroke, and a thread-forming section with a radially outer tooth crest and inner tooth base, along with a displacement chamber for plastic deformation, ensures stress-free chip removal and deburring of cut surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a non-cutting thread-forming section is used to create the internal thread, then chip removal is simplified, but material weaknesses and defects form at the radially inner thread crest due to plastic deformation
Solution Approach 1:
The thread-forming section is divided into multiple forming teeth (at least two, preferably three) distributed around the circumference, each responsible for a portion of the thread formation. This segmentation distributes the plastic deformation load and prevents concentrated stress that causes defects at the radially inner thread crest.
Solution Approach 2:
The forming teeth are designed with a specific geometry where the tooth crest radius is larger than the tooth base radius, creating a progressive deformation zone. This preliminary geometric configuration ensures that material is gradually displaced from the core region outward, preventing defects before they form.
2Manufacturing precision
If the thread-forming profile creates the internal thread with reduced core diameter, then the thread raw profile is formed, but defects impair the setting behavior of screw elements
Solution Approach 1:
Different regions of the forming tooth are given different radii: the tooth crest has a larger radius than the tooth base. This local quality variation creates an optimized stress distribution during deformation, ensuring that the radially inner thread crest area receives adequate material flow without excessive stress concentration.
Solution Approach 2:
The forming tooth geometry parameters (radii ratios, tooth height, tooth spacing) are specifically optimized to control the plastic deformation process. By adjusting these parameters, the material flow is controlled to fill the thread root region properly, eliminating voids and defects that would compromise screw element setting behavior.
3Strength
If the forming tooth is moved out of the threaded bore during reversing stroke, then stress is avoided, but the reaming cutting edge must complete the internal thread to core diameter
Solution Approach 1:
The reaming cutting edge is integrated into the drill bit structure, merging the thread completion function with the existing drill bit geometry. This eliminates the need for separate reaming operations or additional complex mechanisms, while still achieving the goal of stress-free tool withdrawal during reversing stroke.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution guarantees a reliable screw connection by reducing mechanical stress on the tool and preventing defects in the internal thread, ensuring proper screw element setting behavior.
Implementation Method 1
a drill bit (25) having a front-side pre-drilling cutting edge (27) for producing a pre-drilled hole (30)
Implementation Method 2
with at least one drill web (35) a thread-forming section (29) is formed with at least, in particular precisely one forming tooth (41, 42, 43), with which an internal thread raw profile (8) can be produced in a pre-drilled wall (30)
Implementation Method 3
viewed in the tool axial direction, an additional reaming cutting edge (51) is formed between the pre-drilling cutting edge (27) and the thread-forming section (29), with which in the reversing stroke (R) the inside diameter of the thread can be drilled out down to the core diameter (dK) of the thread
Implementation Method 4
the tapping tool is operated in the tapping stroke with a tapping feed with a tapping speed synchronized thereto
Implementation Method 5
In the subsequent reversing stroke in the opposite direction, the tapping tool is guided out of the tapped hole in a reversing direction, specifically with the opposite reversing feed rate and the reversing speed synchronized therewith. This ensures that the forming tooth of the thread-forming section is moved out of the threaded bore in the thread turn of the internal thread without any stress.
Data Source
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AI summary
The invention relates to a tapping tool for producing a workpiece tapped hole (1), the internal thread (9) of which has a thread external diameter (dA) and a thread core diameter (dx). The tapping tool (23) can be driven in a tapping stroke (G) into the not pre-drilled workpiece (5), and, in a reverse stroke (R), the tapping tool (23) can be brought out of the tapped hole (1) in a rotational movement in the opposite direction, wherein an end-face pre-drilling cutting edge (27) for producing a pre-drilled hole (30) is formed on a drill tip (25) of the tapping tool (23), and wherein, on at least one drill web (35), a thread forming portion (29) having at least one, in particular exactly one, forming tooth (41, 42, 43) is formed, by means of which an internal thread rough profile (8) can be produced in a pre-drilled hole wall in the tapping stroke (G), which profile has the thread external diameter (dA) and, in comparison with the thread core diameter (dK), has a reduced thread internal diameter (dI). According to the invention, a reboring cutting edge (51) is provided in the tool axial direction between the pre-drilling cutting edge (27) formed on the drill tip (25) and the thread forming portion (29), by means of which reboring cutting edge, in the reverse stroke (R), the thread internal diameter (di) can be enlarged to the thread core diameter (dk), specifically to form the finished internal thread (9).