Drill Tapered Portion Chamfer Geometry Fracture Resistance
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Solution Overview
Problem
Existing drills used for machining through holes in metal aluminum, such as for aircraft components, face challenges in maintaining fracture resistance and stable chip discharge, particularly due to the susceptibility of tapered cutting edges to fracture and improper chip guidance, leading to potential damage to the machined surface.
Innovation Solution
A drill design featuring a tapered portion with a second helical flute, a chamfered part, and a connection part with a curved surface, where the width of the chamfered part gradually decreases toward the first end side, enhancing fracture resistance and guiding chips into the second helical flute for stable discharge, while the first helical flute and first cutting edge facilitate initial drilling and burr removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a tapered portion with second cutting edge is added to machine through holes, then the ability to form tapered surfaces and remove burrs is improved, but the fracture resistance of the tapered cutting edge deteriorates
Solution Approach 1:
The patent applies local quality by creating a chamfered part with gradually decreasing width along the second cutting edge, where the width w at the outer peripheral end satisfies w/L ≤ 0.5. This local geometric modification strengthens the tapered cutting edge at critical locations while preserving the overall tapered surface formation capability. The chamfered part acts as a stress distribution feature that prevents fracture initiation.
Solution Approach 2:
The patent changes the geometric parameters of the tapered portion by defining specific relationships: the width w of the chamfered part's outer peripheral end relative to the length L of the second cutting edge (w/L ≤ 0.5), and the gradual decrease of width along the cutting edge. These parameter changes optimize both fracture resistance and tapered surface formation without compromising either function.
2Strength
If the chamfered part width is increased to enhance fracture resistance, then the strength is improved, but the chip discharge stability deteriorates due to improper chip guidance
Solution Approach 1:
The chamfered part with gradually decreasing width creates local geometric features that serve dual purposes: the reduced width at the outer peripheral end (w/L ≤ 0.5) strengthens the cutting edge while the gradual taper provides a smooth transition path for chip discharge. This local quality variation simultaneously addresses both strength and chip flow requirements.
Solution Approach 2:
The gradual decrease in chamfered part width creates a curved, tapered surface that guides chips smoothly into the second helical flute. This curved geometry prevents abrupt chip deflection and ensures stable chip discharge while maintaining the structural integrity of the tapered cutting edge.
3Manufacturing precision
If the second cutting edge is made longer to improve tapered surface quality, then the manufacturing precision is improved, but the fracture susceptibility increases
Solution Approach 1:
The patent changes the geometric parameters by defining the relationship w/L ≤ 0.5, where L is the length of the second cutting edge and w is the width of the chamfered part's outer peripheral end. This parameter control allows the second cutting edge to be sufficiently long for quality tapered surfaces while the chamfered part provides localized reinforcement to prevent fracture.
Data Source
AI summary
In an embodiment, a drill has an elongated shape and a rotation axis. The drill includes a drilling portion, a shank portion, and a tapered portion. The shank portion includes a first helical flute and a first cutting edge. The tapered portion is located between the drilling portion and the shank portion. The tapered portion includes a second helical flute, a second cutting edge, a chamfered part, and a connection part. The chamfered part is getting smaller gradually as moving toward the first end side. The connection part has a curved surface and connects the second cutting edge and the drilling portion. A ratio of w/L is 0.0015-0.5 where L is a length of the second cutting edge in a front view of the first end, and w is a width of an outer peripheral end of the chamfered part in a direction parallel to the rotation axis.