A high-frequency non-resonant elliptical vibration-assisted cutting device for diamond turning microstructured surfaces
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-01-15 |
| Journal | The International Journal of Advanced Manufacturing Technology |
| Authors | Zhengjian Wang, Xichun Luo, Haitao Liu, Fei Ding, Wenlong Chang |
| Institutions | University of Strathclyde, Harbin Institute of Technology |
| Citations | 18 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis focuses on the development and validation of a high-frequency non-resonant Elliptical Vibration-assisted Cutting (EVC) device designed for diamond turning microstructured surfaces.
- High Operational Frequency: The device achieves a stable operational frequency of up to 5 kHz, significantly higher than most existing non-resonant EVC devices for diamond turning, thereby improving machining efficiency.
- Novel Flexure Design: Structural rigidity and performance are enhanced by combining a Leaf Spring Flexure Hinge (LSFH) and a Notch Hinge Prismatic Joint (NHPJ), mitigating cross-axis coupling.
- Low Coupling and Thermal Load: Experimental cross-axis coupling ratios (4.71% to 9.76%) are acceptable, and maximum heat generation is low (2.74 W at 132 V), allowing for air-cooled, long-term operation.
- Tunable Trajectory: The device successfully generates regular elliptical trajectories with variable amplitudes (up to >2 ”m) by tuning the input frequency, voltage, and phase lag.
- High Precision Machining: Demonstrated ability to generate complex microstructures (micro-dimple arrays, two-tier structures) on pure copper with high accuracy.
- Dimensional Accuracy: Machining errors were confirmed to be low: less than 1.26% for wavelength and less than 10.67% for height, validating the design consistency.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Max Operational Frequency | 5 | kHz | Non-resonant working mode |
| First Natural Frequency (Cutting Direction) | 5.2 | kHz | Experimental result |
| First Natural Frequency (DOC Direction) | 8.5 | kHz | Experimental result |
| Max Input Voltage (Tested) | 132 | V | Limit set to protect piezo stacks |
| Max Heat Generation Power | 2.74 | W | At 132 V input, suitable for air cooling |
| Max Vibration Amplitude | >2 | ”m | Achieved in cutting and DOC directions |
| Equivalent Stiffness (Cutting Direction) | 50.9 | N/”m | Experimental/FEA result |
| Equivalent Stiffness (DOC Direction) | 52.1 | N/”m | Experimental/FEA result |
| Cross-Axis Coupling Ratio (C1, DOC) | 4.71 | % | Experimental result |
| Cross-Axis Coupling Ratio (C2, Cutting) | 9.76 | % | Experimental result |
| Wavelength Machining Error | <1.26 | % | Demonstrated on microstructures |
| Height Machining Error | <10.67 | % | Demonstrated on microstructures |
| Device Material | 65Mn | High carbon spring steel | Chosen for high yield strength |
| LSFH Thickness (l) | 1.3 | mm | Optimized for modal characteristics |
| NHPJ Neck Thickness (t) | 0.2 | mm | Optimized for coupling ratio |
| Surface Roughness (Ra) | 46 to 66 | nm | Machined copper surfaces |
Key Methodologies
Section titled âKey MethodologiesâThe development and validation of the non-resonant EVC device followed a structured process combining modeling, optimization, and rigorous experimental testing.
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Mechanical Design and Material Selection:
- The device structure integrated a Leaf Spring Flexure Hinge (LSFH) and a Notch Hinge Prismatic Joint (NHPJ) to achieve two perpendicular reciprocating motions and high structural stiffness.
- High carbon spring steel (65Mn) was selected for its high yield strength required for cyclic loading.
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Static Modeling and Optimization:
- Both mathematical static modeling (based on virtual work and flexure hinge equations) and Finite Element Analysis (FEA) were used.
- FEA employed the mapped meshing method (regular hexahedron meshes) to increase modeling accuracy, particularly around the flexure hinges.
- LSFH Thickness Optimization: Thickness (1.3 mm) was determined to ensure the desired translational modes (Mode I and II) were the first two natural frequencies, maximizing the operational frequency limit.
- NHPJ Neck Thickness Optimization: Neck thickness (0.2 mm) was determined to minimize the cross-axis coupling ratio, ensuring accurate elliptical tool trajectory.
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Experimental Setup and Thermal Analysis:
- A prototype was manufactured and tested using piezo actuators (PSt150) driven by a power amplifier (E01.A2).
- Thermal tests confirmed that the maximum heat generation (2.74 W at 132 V) was acceptable for continuous operation under air-cooled conditions.
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Dynamic and Coupling Tests:
- Modal Testing: Impact hammer tests and frequency sweep tests (0 to 10 kHz) were conducted, confirming the first natural frequency in the cutting direction was 5.2 kHz, setting the operational limit.
- Coupling Evaluation: Sinusoidal input signals (500 Hz, 132 V) were applied to one piezo actuator at a time. Displacements were measured using capacitive sensors (Lion Precision CPL190) to calculate the cross-axis coupling ratios (C1 and C2).
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Elliptical Trajectory Generation:
- Two sinusoidal input signals with varying phase lags (0° to 180°) and voltages (24 V to 132 V) were applied simultaneously.
- The tests confirmed that regular elliptical trajectories could be generated across the full operational frequency range (up to 5 kHz) by adjusting input parameters.
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On-Machine Machining Trials:
- Diamond turning was performed on pure copper workpieces.
- Cutting Parameters: Tool feed (5 mm/min), DOC (3 ”m), Spindle speed (30 rev/min).
- Microstructures Generated: Micro-dimple arrays (500 Hz operation) and two-tier sawtooth structures (1000 Hz operation).
- Measurement: Machined surfaces were measured using a white light interferometer (Zygo CP300) to verify wavelength and height accuracy.
Commercial Applications
Section titled âCommercial ApplicationsâThis high-frequency non-resonant EVC technology is critical for industries requiring high-throughput, high-precision manufacturing of functional surfaces.
- Tribology and Lubrication: Manufacturing of microstructured surfaces (e.g., micro-dimples, grooves) on engine components and bearings to reduce friction, improve lubrication retention, and extend component lifetime.
- Automotive and Aerospace: Production of tailored surfaces for high-performance mechanical parts requiring specific physical or chemical properties.
- Optics Manufacturing: Generation of complex, periodic microstructures (e.g., diffractive optical elements, micro-lens arrays) with high dimensional accuracy using diamond turning.
- Tooling and Molds: Creation of micro-structured molds and inserts for replication processes, enabling the mass production of functional surfaces.
- Advanced Materials Processing: Potential application in machining hard-to-machine materials (e.g., stainless steel, silicon, optical glasses) where conventional diamond turning is limited by tool wear or chemical reaction.
View Original Abstract
Abstract In recent years, research has begun to focus on the development of non-resonant elliptical vibration-assisted cutting (EVC) devices, because this technique offers good flexibility in manufacturing a wide range of periodic microstructures with different wavelengths and heights. However, existing non-resonant EVC devices for diamond turning can only operate at relatively low frequencies, which limits their machining efficiencies and attainable microstructures. This paper concerns the design and performance analysis of a non-resonant EVC device to overcome the challenge of low operational frequency. The structural design of the non-resonant EVC device was proposed, adopting the leaf spring flexure hinge (LSFH) and notch hinge prismatic joint (NHPJ) to mitigate the cross-axis coupling of the reciprocating displacements of the diamond tool and to combine them into an elliptical trajectory. Finite element analysis (FEA) using the mapped meshing method was performed to assist the determination of the key dimensional parameters of the flexure hinges in achieving high operational frequency while considering the cross-axis coupling and modal characteristics. The impact of the thickness of the LSFH on the sequence of the vibrational mode shape for the non-resonant EVC device was also quantitatively revealed in this study. Moreover, a reduction in the thickness of the LSFH can reduce the natural frequency of the non-resonant EVC device, thereby influencing the upper limit of its operational frequency. It was also found that a decrease in the neck thickness of the NHPJ can reduce the coupling ratio. Experimental tests were conducted to systematically evaluate the heat generation, cross-axis coupling, modal characteristics and diamond toolâs elliptical trajectory of a prototype of the designed device. The test results showed that it could operate at a high frequency of up to 5 kHz. The cross-axis coupling ratio and heat generation of the prototype are both at an acceptable level. The machining flexibility and accuracy of the device in generating microstructures of different wavelengths and heights through tuning operational frequency and input voltage have also been demonstrated via manufacturing the micro-dimple arrays and two-tier microstructured surfaces. High-precision microstructures were obtained with 1.26% and 10.67% machining errors in wavelength and height, respectively.