Thread Forming Tap With Segmented Back Taper To Reduce Torque
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Solution Overview
Problem
Thread forming taps experience high rotational torque and accelerated wear due to the large load on protruding portions at the extreme leading end, leading to reduced service life, especially when reversing after tapping, as existing solutions either increase torque or fail to disperse load effectively.
Innovation Solution
The thread forming tap is designed with a complete thread portion divided into a front thread portion with a short axial length and a rear thread portion, where the front thread portion has a fixed or gradually decreasing radial size with a small gradient, and the rear thread portion has a larger gradient, dispersing load and reducing torque and wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a back taper is provided on the complete thread portion to reduce rotational torque, then rotational torque during tapping work is reduced, but the protruding portions at the extreme leading end bear large load and wear is accelerated
Solution Approach 1:
The complete thread portion is divided into a front thread portion (with axial length 5 times or less the thread pitch) and a rear thread portion. The front thread portion has a fixed radial size or back taper with small gradient, while the rear thread portion has back taper with larger gradient. This segmentation allows the front portion to disperse load across multiple protruding portions, reducing wear on individual protrusions, while the rear portion provides overall torque reduction through larger back taper.
Solution Approach 2:
Different regions of the complete thread portion are given different back taper gradients. The front thread portion has either zero gradient (fixed radial size) or small gradient, while the rear thread portion has larger gradient. This local differentiation optimizes each region's function: the front region protects against wear by load dispersion, while the rear region reduces overall rotational torque.
2Reliability
If a large diameter thread portion with multiple threads is provided to disperse load, then load is dispersed across multiple threads, but rotational torque during tapping work increases
Solution Approach 1:
The thread portion is segmented into front and rear sections with different functional characteristics. The front thread portion (length ≤ 5P) provides load dispersion across multiple protruding portions to extend service life, while the rear thread portion provides larger back taper to reduce rotational torque. This segmentation resolves the contradiction by assigning different functions to different segments.
Solution Approach 2:
The axial length of the front thread portion is controlled to be 5 times or less the thread pitch, and the radial size gradient is controlled to be small or zero. These parameter optimizations allow sufficient load dispersion while limiting the increase in rotational torque, achieving a balance between service life and power consumption.
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 reduces rotational torque and wear by dispersing load across multiple protruding portions, improving the service life of the tool by up to 1.4 to 2 times compared to existing technologies, while maintaining effective internal thread formation and reducing springback.
Implementation Method 1
Screwing the tap into a prepared hole of a workpiece at the chamfered thread portion allows the protruding portions to cut into a surface layer portion of an internal wall of the prepared hole. Then resultant plastic deformation at the surface layer portion of the internal wall of the prepared hole such that the internal thread is formed.
Data Source
AI summary
A thread forming tap having a complete thread portion, formed with a predetermined back taper with that decreases rotational torque during tapping work, which reduces load acting on first complete protruding portions, formed at an extreme leading end of the complete thread portion, and thereby suppressing degradation in service life of the tool due to wear.