Plasma-Driven Projectile Surface Strengthening for Deep Residual Stress
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Solution Overview
Problem
Current methods for enhancing the mechanical properties of workpieces, such as shot peening and high-power laser technology, are limited by high costs and accessibility issues, and fail to achieve significant residual stresses and depth penetration effectively.
Innovation Solution
A method involving a polymeric projectile strip with a metal foil, where an electric current pulse evaporates the metal foil into plasma, accelerating the projectile to impact the workpiece surface, generating high compressive forces and residual stresses through shock waves, and using a device with a nozzle and electromagnetic Lorentz force to enhance surface treatment efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If shot peening is used to strengthen surface layers, then compressive residual stress is introduced, but the achievable stress values and affected depth are limited
Solution Approach 1:
The invention changes the parameters of the strengthening process by using laser irradiation to generate shock waves in a liquid medium, which transmit much higher stresses to the workpiece surface compared to traditional shot peening. The laser power, pulse duration, and liquid medium properties are optimized to achieve deeper penetration and higher compressive residual stresses.
Solution Approach 2:
The invention replaces the mechanical shot peening system with an optical field (laser) that generates shock waves in a liquid medium. This substitution allows for more efficient energy transfer and deeper stress penetration into the workpiece surface without the limitations of mechanical projectile impact.
2Area of stationary object
If high-power laser technology is used for surface strengthening, then deep residual stresses and large treatment areas are achieved, but investment and operating costs become very high
Solution Approach 1:
The invention introduces a liquid medium as an intermediary between the laser source and the workpiece surface. The laser generates shock waves in the liquid, which then transmit the stress to the workpiece. This intermediary approach allows for more efficient energy utilization and reduces the required laser power compared to direct laser irradiation methods.
Solution Approach 2:
The invention uses pulsed laser irradiation with optimized pulse durations and repetition rates. The periodic action allows for heat dissipation between pulses, reducing overall energy consumption and operating costs while still achieving the desired deep residual stresses and large treatment areas.
3Reliability
If laser surface reinforcement is applied, then service life of critically stressed parts is extended, but direct optical access and liquid coverage are required
Solution Approach 1:
The invention uses a liquid medium (hydraulic approach) to transmit the laser-generated shock waves to the workpiece surface. The liquid can flow over complex geometries and provide uniform coverage, eliminating the need for direct optical access to the treatment area while still achieving effective surface strengthening.
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 approach effectively introduces deep residual compressive stresses into the workpiece surface, improving mechanical, cavitation, and corrosion resistance without the contamination risks and cost constraints of existing technologies, enabling efficient treatment of larger areas with rapid cycle repetition.
Implementation Method 1
an electric current pulse is introduced by the discharge of the capacitor, and the pulse is large enough that it melts the metal foil, evaporates it and subsequently turns it into an expanding plasma
Implementation Method 2
the plasma generated by the electric current pulse, in addition to the expansion pressure, is also accelerated by the electromagnetic Lorentz force caused by the passage of an electric current through this plasma in the generated magnetic field
Implementation Method 3
The impact of the projectile induces plastic deformations in the surface layer of the workpiece which introduce residual mechanical stresses
Data Source
AI summary
A method and a device for strengthening the surface of workpieces, in particular of metal ones, by mechanical effects accompanying the impact of small projectiles or by mechanical effects accompanied by the impact of a shockwave induced by plasma created by electric evaporation of a metal foil are described.