Stress-Assisted Machining of Thin-Walled Workpieces
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Solution Overview
Problem
Machining of slender or thin-walled workpieces, particularly those made of materials like cast iron, nickel or titanium-based alloys, is challenging due to deformations from residual stresses, vibrations, and complex geometries, leading to poor surface finish and fatigue issues.
Innovation Solution
A stress assisted machining method that applies controlled stress states, including tensile, compressive, bending, or torsional stresses during machining to stabilize the workpiece, reducing deformations and vibrations, and inducing compressive residual stresses on the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If machining is performed on slender or thin-walled workpieces without stress control, then the workpiece can be processed, but deformations occur due to residual stresses and the workpiece lacks sufficient rigidity
Solution Approach 1:
A controlled stress state is applied to the workpiece before machining begins. This preliminary stress application stabilizes the workpiece structure, increases its rigidity, and prevents deformations that would otherwise occur during the machining process due to residual stresses and material removal.
Solution Approach 2:
The stress state parameters (magnitude and direction) are carefully controlled and adjusted during machining. By changing the stress parameters dynamically, the workpiece maintains optimal rigidity throughout the machining process, allowing precise dimensional control even on slender geometries.
2Productivity
If machining is performed on slender workpieces, then the workpiece can be processed, but vibrations occur due to low natural frequencies
Solution Approach 1:
The workpiece is pre-stressed before machining to shift its natural frequencies away from the excitation frequencies generated during machining. This preliminary frequency adjustment prevents resonance and chatter vibrations, enabling stable machining of slender workpieces that would otherwise be too flexible.
Solution Approach 2:
The applied stress creates counteracting forces that balance the vibratory forces generated during machining. This stress-induced stiffening effect acts as a mechanical counterweight to the destabilizing vibrations, allowing higher productivity without excessive chatter.
3Shape
If material is removed during machining, then the desired geometry is achieved, but residual tensile stresses are generated on the machined surface
Solution Approach 1:
A controlled compressive stress state is applied during machining to counteract the tensile residual stresses that would naturally form on the machined surface. This preliminary anti-action prevents the formation of harmful tensile stresses, improving the fatigue life and reliability of the finished component.
Solution Approach 2:
The stress application process, which initially seems to add complexity, actually converts the harmful tensile residual stresses into beneficial compressive residual stresses on the machined surface. This stress transformation improves surface integrity and fatigue resistance while achieving the desired geometry.
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 method improves surface finish, increases rigidity, and reduces vibrations, enabling the machining of complex geometries with higher precision and fatigue resistance.
Implementation Method 1
the natural frequencies (rate at which an oscillatory system tends to oscillate in the absence of disturbance) of these workpieces are relatively low, enough to be excited during machining, producing vibrations of considerable magnitude
Implementation Method 2
it is essential to verify that the machining operation generates compressive residual stresses on the final surface of the workpiece
Implementation Method 3
applying a stress state to the workpiece... an increase in the rigidity of the workpiece
Data Source
Figure 1
Figure 2A)~2D)
Figure 3
AI summary
Stress assisted machining method for the machining of workpieces (4), for example slender, or thin-floored or thin-walled workpieces (4), based on the application of a controlled stress state to the workpiece (4) during machining. The method comprises the steps of placing (20) a workpiece (4) in a machining machine; applying (30) a stress state to the workpiece (4), the stress state being selected from tensile, compression, bending, torsion and a combination of two or more of them; performing (40) a machining operation while maintaining the stress state on the workpiece (4) and releasing (50) the applied stress state from the workpiece (4).