Hard Material Insert Chamfer Design for Percussion Drill Stress
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Solution Overview
Problem
Rotary percussion drills experience failure due to high internal stresses in the brazing material caused by temperature differences and varying expansion coefficients between the hard material insert and the shank, leading to reduced service life when drilling reinforced concrete.
Innovation Solution
A hard material insert with a design featuring a first chamfer on the attachment surface and a wider second chamfer forming a wedge-shaped radial edge area, optimized for hard soldering, which balances stress distribution and accommodates tolerances, and an X-shaped configuration for enhanced cutting and stress management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a chisel-shaped hard metal plate is hard-soldered to the shank end, then the drill can effectively cut reinforced concrete, but high internal stresses occur in the brazing material due to temperature differences and expansion coefficient variations, leading to failure
Solution Approach 1:
The patent applies different chamfer geometries at different locations on the hard material insert. The first chamfer is located at the fastening surfaces for material-locking attachment, while the second, wider chamfer is located at the free surfaces. This local differentiation optimizes stress distribution specifically at the solder joints without compromising the overall cutting performance of the insert.
Solution Approach 2:
The patent introduces asymmetry in the chamfer design by making the second chamfer wider than the first chamfer. This asymmetric configuration creates a wedge-shaped radial edge area that balances stress distribution during hard soldering, preventing extreme stress concentrations that would otherwise occur at the solder edges due to thermal expansion differences between the hard material and shank.
2Ease of manufacture
If the hard material insert has a uniform design, then manufacturing is simpler, but stress distribution during hard soldering is unbalanced, causing extreme stress values at the solder edge
Solution Approach 1:
Instead of a uniform chamfer design, the patent implements local quality by specifying different chamfer widths at different locations. The first chamfer at the fastening surfaces has a standard width, while the second chamfer at the free surfaces is explicitly designed to be wider. This local differentiation addresses the stress distribution problem without significantly complicating the manufacturing process.
3Manufacturing precision
If the first chamfer width is increased to accommodate tolerances, then stress distribution improves, but the wedge-shaped radial edge area for balancing stress is insufficient
Solution Approach 1:
The patent resolves this contradiction by introducing asymmetry in the chamfer design. Rather than uniformly increasing all chamfer widths, it specifically makes the second chamfer at the free surfaces wider than the first chamfer at the fastening surfaces. This asymmetric approach creates the necessary wedge-shaped radial edge area for effective stress balancing while maintaining appropriate tolerance accommodation at the fastening surfaces.
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
The design significantly reduces extreme stress values at the solder edge, preventing crack initiation and extending the service life of the percussion drill by effectively managing stress and tolerances during the hard soldering process.
Implementation Method 1
a bottom surface 6 opposite the cutting edges 3, which is designed for material-locking attachment (hard soldering) to a shank end 5 of the percussion drill
Implementation Method 2
Due to the high temperature differences that occur during joining and percussion drilling, high internal stresses occur in the brazing material connecting the hard solder, mediated by the different temperature expansion coefficients of the hard material insert and the end of the shank
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The insert has a cutting edge (3), two bevel (9a,9b) and a base surface opposite the cutting edge and formed for the firmly bonded attachment on a shaft end (5) of the percussion drilling tool (2). The base surface forms the former bevel circulating piecewise to an attachment surface arranged transverse to the base surface. The later bevel, that is broader than former bevel and circulating piece-wise, is designed at open surface (10) and arranged crosswise to bottom surface (6).