Munition Casing Microhole Patterning for Controlled Fragmentation
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Solution Overview
Problem
Natural fragmentation of cylindrical munition casings results in poor performance due to the production of long strips, and existing methods for controlled fragmentation either alter the surface significantly or increase manufacturing costs, while laser microdrilling faces challenges in achieving high aspect ratios and is prone to cracks and long drill times.
Innovation Solution
Electrical discharge machining (EDM) is used to drill micron-sized holes in the casing of munitions, creating a modified microstructure that controls fragmentation without altering the outer surface, allowing for improved fragmentation performance without reducing mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If laser microdrilling is used to drill deep holes in thick casing, then fragmentation performance is improved, but aspect ratio requirements become extremely high and drill times increase
Solution Approach 1:
The patent replaces laser microdrilling with electrical discharge machining (EDM) to drill microholes in the casing. EDM uses electrical discharges instead of laser energy to erode material, achieving the required deep microholes with much shorter processing times while maintaining the same fragmentation control function.
Solution Approach 2:
The patent changes the machining method from laser-based to EDM-based, fundamentally altering the physical parameter of energy delivery (from photothermal to electrical discharge) to achieve the same structural modification with improved efficiency and reduced processing time.
2Manufacturing precision
If laser microdrilling is used to create microholes, then fragmentation performance is improved, but cracks in microstructure occur making material susceptible to fatigue failure
Solution Approach 1:
The patent substitutes laser microdrilling with EDM to create microholes. EDM produces cleaner holes without the thermal stress and microcracks that laser drilling introduces, thereby maintaining fragmentation control while improving fatigue resistance and overall reliability of the casing.
Solution Approach 2:
The patent converts the potential harm of microcracking from laser drilling into a benefit by using EDM, which inherently avoids the thermal damage and microcrack formation that compromise fatigue life, thus turning the reliability issue into a strength of the new method.
3Manufacturing precision
If traditional notch or groove methods are used for controlled fragmentation, then fragment size distribution is controlled, but surface of casing is significantly altered
Solution Approach 1:
The patent applies local quality by drilling microholes only in specific patterns on the outer surface of the casing, creating stress concentrations at localized points that control fragmentation without requiring large-scale surface modifications like traditional notches or grooves.
Solution Approach 2:
The patent transitions from two-dimensional surface features (notches and grooves) to three-dimensional microhole structures that extend through the casing thickness, controlling fragmentation through subsurface geometry rather than surface profile alteration.
4Manufacturing precision
If double wall construction with scored walls is used, then fragmentation performance is improved, but tooling requirements double leading to high manufacturing costs
Solution Approach 1:
The patent extracts the fragmentation control function from the complex double-wall construction with scored walls and implements it through a simpler single-wall design with EDM-drilled microholes, eliminating the need for additional tooling while achieving the same performance.
Solution Approach 2:
The patent creates the necessary stress concentrations and fragmentation patterns directly in the single wall through EDM microholes, copying the functional effect of the double-wall construction without requiring the additional wall and its associated tooling complexity.
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
EDM drilling enhances fragmentation by creating desired fracture lines and fragment sizes, maintaining the casing's strength and allowing for mass production without the limitations of laser microdrilling, resulting in effective and efficient munition performance.
Implementation Method 1
forming holes in the casing using electrical discharge machining (EDM)
Data Source
AI summary
A method for forming a fragmentation explosive munition includes providing a casing, and forming holes in the casing using electrical discharge machining (EDM), thereby forming a modified casing.