6. Conclusion
In this paper, the minimum void length scale control is well addressed under the level set framework. Innovatively, two lower bounds are concurrently applied which correspond to the different machining tool radii of the rough-to-finish machining process. The derived optimal design demonstrates the outstanding characteristics that, both rough and finish machining operations can be effectively performed, through which both the machining efficiency and quality can be guaranteed. As for the side effects, the applied double lower bounds slightly sacrifice the design optimality. Especially for the rough machining lower bound, if a large value is applied, the optimal structural topology may not be achievable. For further work, we intent to extend the developed minimum void length scale control method to address stress-constrained problems, which is even more challenging because the stress level is not simply monotonic to the material volume fraction.