Drilling Tip Convex-Concave Geometry for Stress Relaxation
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Solution Overview
Problem
Drilling tips with a cemented carbide tip main body coated with a polycrystalline diamond sintered hard layer face issues of residual stress-induced cracking and shortened lifespan due to differences in thermal expansion coefficients, leading to premature exposure of the tip main body during drilling in hard rock conditions.
Innovation Solution
A drilling tip design featuring a cemented carbide tip main body with a distal end portion having a convex and concave arc shape, where the diameter of the posterior end portion is between 8 to 20 mm, and the ratios of the radii of these arcs are optimized to relax residual stress, preventing crack formation and enhancing wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an intermediate layer is interposed between the hard layer and tip main body to relax residual stress, then crack resistance is improved, but the thickness of the outermost layer cannot be secured and wear resistance deteriorates
Solution Approach 1:
The invention applies curvature by forming a convex portion with a convex arc shape at the distal end of the tip main body. This curved geometry eliminates angular corners that concentrate stress, thereby relaxing residual stress without requiring an intermediate layer that would reduce the hard layer thickness. The convex arc shape directly addresses both stress relaxation and maintains full hard layer coverage.
Solution Approach 2:
The invention changes the geometric parameters of the tip main body by defining specific ratios: the radius of the convex arc (r1) relative to the posterior end diameter (D) should be 0.05 < r1/D ≤ 0.5, and the radius of the concave arc (r2) should be 0.05 < r2/D ≤ 3.0. These parameter changes optimize the stress distribution while maintaining structural integrity and full hard layer coverage.
2Duration of action of stationary object
If the hard layer is made thicker to prevent tip main body exposure, then life is extended, but residual stress increases and crack generation becomes more likely
Solution Approach 1:
By forming convex and concave portions with specific arc radii ratios, the invention creates a stress-distributing geometry that allows thicker hard layer application without proportionally increasing residual stress. The curved surfaces prevent stress concentration that would otherwise occur at sharp transitions, enabling the hard layer to be sufficiently thick for durability while maintaining crack resistance.
3Strength
If an intermediate portion with smaller outer diameter is formed to secure hard layer thickness, then wear resistance is improved, but stress concentration occurs at corner parts and crack resistance deteriorates
Solution Approach 1:
The invention eliminates the problematic corner parts by using convex and concave arc shapes with controlled radii. The transition between different diameter sections is made through curved surfaces rather than sharp corners, preventing stress concentration while maintaining the reduced outer diameter configuration that ensures adequate hard layer thickness.
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 optimized design extends the lifespan of the drilling tip and drill bit by reducing residual stress, improving impact resistance, and preventing premature exposure of the tip main body during drilling, allowing for efficient drilling operations.
Implementation Method 1
a distal end portion of a tip main body made of a cemented carbide is coated with a hard layer made of a polycrystalline diamond sintered body, is manufactured by integrally sintering the cemented carbide of the tip main body and the polycrystalline diamond sintered body of the hard layer
Implementation Method 2
the distal end portion of the tip main body has a convex portion having a convex arc shape of which a surface is convex toward the distal end side in a cross section taken along the tip center line, and a concave portion having a concave arc shape
Data Source
AI summary
A drilling tip includes a tip main body that has a posterior end portion having a columnar or disk shape centered on a tip center line and a distal end portion and is made of a cemented carbide and a hard layer that coats the distal end portion and is made of a polycrystalline diamond sintered body. The distal end portion has a convex portion, and a concave portion. A diameter D of the posterior end portion is 8 mm to 20 mm. A ratio r1/D of a radius r1 of the convex portion is 0.1 to 0.65, and a ratio r2/D of a radius r2 of the concave portion is 0.05 to 3.0. An angle formed by a straight line that connects a tangent point which the convex portion tangents to the concave portion and a center of the convex portion to each other is 20° to 90°.