Hi
I am trying to model a cutting problem with a blade and comparing the results with and without ultrasonic vibration. From experimental results in our group, the use of ultrasound can significantly reduce the cutting force required, although Im not sure that the current model can show this. Has anyone got any general advice for incorporating such a high-speed boundary condition to the model?
I have added an image showing the damage model (top two images) and a comparison of reaction force on the blade with and without ultrasound
The results without vibration seem to be sensible, although when I apply the vibration, the cutting tool experiences a high reaction force which I don’t believe represents the true scenario. For the work-piece I have implemented Johnson-Cook plastic and damage criteria. Any general advice foe this type of problem would also be greatly appreciated!
The unusually high reaction forces observed in your cutting model with ultrasonic vibration may be due to improper implementation of the high-speed boundary conditions associated with the ultrasonic excitation. Ensure that the time step in your simulation is sufficiently small to capture the high-frequency vibrations accurately. Also, check the coupling between the blade and the work-piece to ensure it realistically represents the interaction under ultrasonic conditions. Verify that the ultrasonic frequency and amplitude applied are within the realistic range of your experimental setup. Additionally, the material model, including the Johnson-Cook plasticity and damage criteria, should be validated for high-strain-rate conditions typical of ultrasonic cutting. Consider consulting literature or experts on ultrasonic cutting to ensure that all parameters and boundary conditions in your model are correctly applied.
Alexander Hamilton You're right, a well-implemented vibration model in cutting simulations should show a decrease in cutting force compared to a static model. The high reaction force you're seeing with vibration suggests there might be an issue with how the vibration is implemented. Double-check the amplitude of the vibration you're applying. An excessively large vibration can lead to unrealistic forces. Ensure the vibration amplitude aligns with the expected values for your ultrasonic system. Verify that the vibration is applied in the correct direction relative to the cutting motion. It should likely be perpendicular to the cutting direction (normal to the blade surface). Also, When simulating vibration, it's important to use non-reflective boundary conditions at the edges of your model to prevent reflections that can cause unrealistic forces. These conditions absorb the outgoing waves, mimicking an infinite space. For some materials, the material properties like stiffness and damping can be frequency dependent. Including frequency-dependent material properties in your model might be necessary to capture the effect of vibration accurately. The friction model used can significantly impact the cutting forces. Consider using a friction model that accounts for the relative velocity between the tool and workpiece due to vibration. Some models account for adhesion and separation effects during contact which might be relevant for ultrasonic cutting.
- The high reaction forces observed when adding vibration to your cutting model likely indicate an issue with the implementation of the vibration. Several factors could be contributing to this anomaly. Firstly, check the amplitude of the vibration being applied; an excessively large amplitude can lead to unrealistic forces. Ensure that the amplitude aligns with the expected values for your ultrasonic cutting system. Secondly, verify that the vibration is applied in the correct direction relative to the cutting motion. Typically, in ultrasonic cutting, the vibration should be perpendicular to the cutting direction, normal to the blade surface. If the direction is incorrect, it could result in abnormally high reaction forces.
- Additionally, the boundary conditions in your simulation might be contributing to the problem. When simulating vibration, it’s crucial to use non-reflective boundary conditions at the edges of your model. These conditions absorb outgoing waves and prevent reflections that can cause unrealistic force spikes. For accurate simulation, consider whether the material properties in your model are frequency-dependent. Some materials exhibit different stiffness and damping characteristics at varying frequencies, and including these properties can help capture the effects of vibration more accurately.
- Lastly, the friction model used in your simulation can significantly impact the cutting forces. It’s advisable to use a friction model that accounts for the relative velocity between the tool and workpiece due to vibration. Advanced friction models that consider adhesion and separation effects during contact might be necessary for accurately modeling ultrasonic cutting. By carefully examining and adjusting these factors—vibration amplitude and direction, boundary conditions, frequency-dependent material properties, and the friction model—you should be able to reduce the excessive reaction forces and achieve a more realistic simulation of the cutting process.
To incorporate high-speed boundary conditions like ultrasonic vibration into a cutting model, consider dynamic analysis, suitable material models, fine mesh density, accurate boundary conditions, proper contact modeling, experimental validation, and sensitivity analysis. Adjust parameters to reflect the behavior under ultrasonic vibration for accurate results.
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