Partial-Thread Forming Tap Geometry to Prevent Crest Chipping

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Solution Overview

Problem

Thread forming taps with incomplete threads are prone to chipping and machining defects due to friction with the inner surface of pilot holes, caused by the crest of the incomplete thread making contact with the pilot hole during rotation.

Innovation Solution

The thread forming tap features an incomplete thread portion with lobes protruding in radial directions and inclined surfaces, which engage with the pilot hole surface to prevent friction and chipping, while the manufacturing method includes beveling to form these features, preserving the original lobes and reliefs to enhance deformation and reduce contact with the pilot hole.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the incomplete thread is beveled along the circumference direction to remove crests, then the thread forming tap can be manufactured, but the crest of the incomplete thread is pressed against the inner circumferential surface of the pilot hole creating friction and causing chipping

Engineering Contradiction:

Improveease of manufactureVSAvoidreliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The invention applies local quality by creating lobes with protruding crests at specific locations on the incomplete thread portion. These lobes are positioned to engage with the pilot hole inner circumferential surface, transforming the uniform beveled structure into a localized feature distribution that prevents continuous frictional contact while maintaining manufacturability through standard beveling processes.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention utilizes curvature by forming rounded lobe shapes on the incomplete thread portion instead of sharp crests. The lobes have curved surfaces that facilitate smooth engagement with the pilot hole, reducing stress concentration and preventing chipping while maintaining the beneficial friction-reducing effects of the beveled incomplete thread structure.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Productivity

If the incomplete thread makes contact with the pilot hole during rotation, then thread formation can proceed, but chips are generated and caught between the pilot hole surface and threads causing machining defects

Engineering Contradiction:

ImproveproductivityVSAvoidmanufacturing precision

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The invention converts the harmful frictional contact into a beneficial engagement mechanism. The lobes on the incomplete thread are designed to actively engage with the pilot hole inner circumferential surface, using the contact that previously caused chipping and defects to instead deform and smooth the pilot hole surface, thereby eliminating chip generation while maintaining productive thread formation.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The invention applies parameter changes by modifying the geometric parameters of the incomplete thread portion. The lobes are formed with specific radius ratios (R1/R2 between 0.5-2.0) and height ratios (h1/h2 between 0.3-1.5) relative to the complete thread, transforming the contact characteristics from harmful friction to beneficial deformation while maintaining manufacturing efficiency.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If the crest of the incomplete thread has constant height around the axis, then the structure is simple, but the crest is susceptible to chipping due to friction with the pilot hole

Engineering Contradiction:

Improvedevice complexityVSAvoidstrength

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The invention introduces asymmetry by creating lobes with varying heights and positions around the axis of the incomplete thread portion. This asymmetric lobe distribution prevents uniform frictional contact with the pilot hole, reducing stress concentration on any single crest and preventing chipping while maintaining relatively simple manufacturing through conventional beveling processes.

Inventive Principle:

Principle #4Asymmetry

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 design effectively reduces machining defects by preventing the incomplete thread from being pressed against the pilot hole, thereby minimizing chipping and ensuring smooth thread formation.

Implementation Method 1

the lobes can deform the inner circumferential surface of the pilot hole

Methodology Applied

Scientific EffectDeformation: Deformation

Data Source

PatentUS11007590B2Thread forming tap and manufacturing method for thread forming tap

Publication Date: 2021.05.18 OSG

AI summary

A thread forming tap includes a partial thread. The partial thread is provided, in the axis direction view, with a protrusion formed so as to protrude in the radial direction and a clearance section formed so as to have a smaller diameter than the protrusion, and as a result of the foregoing, if a thread forming tap rotates in a state where the inner circumferential surface of a pilot hole and the partial thread come into contact, the protrusion of the partial thread can be caused to engage with the inner circumferential surface of the pilot hole. Due to this configuration, rubbing in a state where the partial thread is pressed against the inner circumferential surface of the pilot hole can be suppressed, and as a result, chipping of the partial thread can be prevented.