Topology Optimization is key if you are looking for a better way to design a model that meets all goals efficiently, looks aesthetically pleasing and comes in under budget. In this second installment of our series on this topic, we will be studying how the simulation stage, where we create a topology optimization study, plays a critical role in creating successful modeling results.
Creating a New Topology Optimization Study
The topology optimization study is capable of applying all of the same loads, fixtures and interactions used in an original baseline static study. Since it is recommended that this study is completed first, an analyst can simply copy (using ctrl+c, or right mouse click) the simulation features directly from the static study, into the topology optimization study.
As with all studies, the first step is ensuring that the 3D model contains no errors and has the required reference material. Planes, axes, and split faces are incredibly useful to orient forces and fixtures to truly capture the real world effects the application may endure.
Model faces and edges that have fixtures or loads applied to them will not be reduced or optimized by default since the face is required to define the simulation feature. If you would like to optimize the load-bearing elements, splitting these faces or edges may be required to help with this effort.
The Load Case Manager is compatible with topology studies and can be used to evaluate combinations of forces to determine which load case produces the maximum stresses. The topology optimization study will then return a single optimized shape capable of withstanding the various load cases.
Here are some recommended suggestions when beginning a new topology study:
- Run an initial static or frequency study to determine baseline capability.
- Create a new topology study and ensure the proper models and components are being analyzed.
- Copy loads/fixtures from the initial study to ensure optimized shape is analyzing the same variables.
- Mesh the model at an appropriate resolution. Remember, we should see a minimum of two high-quality elements through any given thickness of the part.
Goals and Constraints
Topology Studies are broken down into 3 major considerations for the overall goal of the optimized shape.
Best Stiffness to Weight Ratio
The optimization algorithm yields the shape of a component with the largest stiffness considering the given amount of mass that will be removed from the initial maximum design space.
Minimize Maximum Displacement
The optimization algorithm yields a shape that minimizes the maximum displacement on a single node (calculated from a static study). Optimization yields the stiffest design that weighs less than the initial design and minimizes the maximum displacement.
The optimization algorithm yields a shape that weighs less than the maximum size model and does not violate the given target for the displacement constraint. The algorithm seeks to reduce the mass of a component while restricting the displacement (max observed value of component or user-defined at a single node) under a certain limit.
Beyond that, there are additional secondary considerations that can be made to further control the strength capability of the final component. Combining these requirements will increase analysis time, but is the fastest way to consider several design requirements in a single optimized shape.
Control displacement of optimized shape as a specific value or factor of maximum displacement.
Reduce mass of optimized shape by specific value or percentage of original value.
Control natural frequency value of first mode shape of optimized shape.
Stress/ Factor of Safety Constraints
Limit maximum stress in new part with specific value or percentage of material yield strength.
Specify maximum or minimum factor of safety of optimized part.
As we discussed earlier, a primary reason topology optimization is not more widely used at the moment, is the manufacturing considerations. The unique organic shapes produced may be optimized for stress and aesthetically pleasing, but they pose entirely new challenges for manufacturing.
What good is an optimized shape if it can never be produced? Each process has critical limitations that must be considered in the final shape. SOLIDWORKS can help us accomplish this using several tools.
Allows users to select specific faces of the original design space and exclude them from optimization. Users can even prescribe a uniform wall thickness on the selected faces to ensure manufacturability.
Analysts can specify a minimum or maximum thickness of the structural members of the resulting optimized shape. This will ensure that the individual features are still within scope for the selected process.
De-mold controls ensure that the optimized design is manufacturable and can be extracted from a mold.
By specifying a de-mold direction, analyst can ensure that all areas of the resulting shape are accessible to the selected direction of pull.
Due to the finite element approach, the resulting shape is dependent on the simulation mesh, and may not be symmetrical. While symmetrical shapes are not required, asymmetrical shapes can pose additional manufacturing challenges.
Running the Study
At this point you are ready to run your study. As we mentioned earlier, the more constraints and manufacturing controls you include in your study, the longer the solve time will be. To help manage the overall time, we recommend the following considerations:
- Run a simple static or frequency study on the full-size model to ensure the mathematical model can be built with no errors.
- Determine critical manufacturing controls to ensure the final part can still be produced using the desired process. Any result is meaningless if it cannot be made!
- Select a primary study goal and run an initial optimization study to determine if additional constraints are required.
- Copy your study and slowly add in secondary constraints, one at a time, in each subsequent copy. This will allow you to evaluate the results and determine if a pattern arises, if so, you can save the need for creating more complex studies by creating an aggregate shape based on each of the simpler studies.
Material Mass Plot first displays the mesh elements that can be removed based on the stress results. The slider can be used to add or remove material relative to the stress results.
Topology result plots to verify stress in optimized part. Precise detailed plots will need a secondary analysis after the part has been rebuilt and parameterized.
If the results are undesirable, a second-round may be needed. That’s ok! The primary use case of this tool is to determine a more general framework for how a part can be optimized. Users can tweak the manufacturing controls, loads, or goals to create a new shape. These changes can also be made at a later stage using SOLIDWORKS features.
Read our in-depth white paper on using these dynamic tools available in SOLIDWORKS so that you can use topology optimization to design components with manufacturability in mind right from the start, regardless of industry!