The concept of a part taking shape as it reacts to its environment may be new to engineers, but nature has been doing this for a long time. Take for instance the evolution of bones—long skeletal bones will grow and change shape as they are subjected to loads and boundary conditions.
Altair’s solidThinking has programmed this bone-like behaviour into Inspire, a concept modeling application for mechanical design. Essentially, Inspire uses a bone growth algorithm to create the shape of a part from little more than loads, boundary conditions and a space that represents a maximum build volume.
Inspire is an interesting example of early concept CAE design. Instead of bringing simulation into the initial CAD design, Inspire works backwards. It will “grow” a near optimal concept using FEA simulations.
“Inspire is based on human bone growth algorithms developed at the University of Michigan in the mid ‘80s,” said Kroeger. “We mimic what nature would do. We took this high-end engineering technology, OptiStruct from Altair, and made it simple and easy to use for designers. That technology was put together with FEA solvers which essentially allowed you to figure out what the best structure is.”
Analysis During Conceptual Design
Keeping initial concept CAE tools simple is important in the design engineering world. Products can benefit a lot from simulation-based insights to ensure concepts are already near optimal in the early stages based on reduced mass, maximum stiffness, or frequency.
“Companies get more value from engineering tools the earlier they are used in the design process,” said Shaun Kroeger, Director of Partner Sales at solidThinking. “Inspire takes engineering tools and puts them in the very front, in the concept design phase.”
Maximizing the Concept Creation Potential of Inspire
“If the user uses CAD then Inspire is a cake walk,” joked Jaideep Bangal, Senior Application Engineer at solidThinking. “The most difficult part is thinking outside the box when designing a part with the tool.”
For example, Bangal told the story of a customer who designed an engine mount the same way for 10 years. When they input their standard packaging space and loads, the customer was confused to find a similar design to the original part.
“They used the same packaging space that the old part occupied as their starting point. The idea is to start with the biggest possible packaging space you have,” said Bangal. “If you force the packaging of your current optimized part you will not get the most out of Inspire. You need to think outside the box of your current packaging.”
Essentially, Inspire will mesh a part based on the packaging space. If an area of the mesh experiences a load, Inspire will keep or remove material based on that load distribution and natural bone-growth algorithms.
Seeing an optimization tool like this build a concept design out of thin air might make some engineers worry about job security. However, Bangal assures that this isn’t the case. “The main role is to create a design that works with all the parameters and is still manufacturable. All we give an engineer is a starting point. Before, engineers started with a block. We say the starting point should be our results so they don’t have to go through the iterative process.”
“Can a design engineer come up with these design[s]?” He added, “Maybe, but the easy route is an I-beam. Our results are stronger and lighter, but they also allow design engineers to come out of their I-beam cocoons. It allows them to come up with the most efficient and organic design.”
Besides, anyone can design an I-beam, and with the help of Inspire engineers can be more creative—even artistic.
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How to Use Inspire to Create a Near Optimal Concept
The Inspire workflow is designed to be simple and intuitive for use in the early design cycles.
The workflow leads engineers to move through the ribbon tool icons from left to right.
“You don’t have to be an expert to use the tool,” says Bangal. “It takes about 4 hours in our training class to become productive. We have even had a few customers watch YouTube videos to start using it … And if you do make a mistake, you can hit ‘ctrl-z’ any number of times to undo the last action.”
Though Inspire isn’t a CAD package it does have some sketching abilities. This allows users to start from scratch by building a packaging space. Alternatively, users can import a design or revisit an old part by importing a CAD geometry. However, Bangal reminded users to “not constrain yourself to the existing geometry pockets. Remove fillets, holes, and increase the packaging space as much as you can.”
It takes a detailed eye to create a CAE tool focused on usability. For instance, take the mouse pointer icons within Inspire. The pointer icon will change based on the part feature you are hovering over. This helps engineers to determine what they will select when they click the mouse. There is a different mouse pointer for points, curvatures, faces and edges.
The tools in Inspire work in a similar fashion. This means if you learn the workflow of one tool you should be able to use the others. “The load and support definition is common to the contact definition. The program also doesn’t default to pull down menus or model trees unless the user prefers to use them,” clarified Bangal.
With the geometry built, users can then set displacement constraints, boundary conditions, materials, and loads onto a part. When defining a mass loading, for instance, “you don’t need to draw an engine in CAD,” said Bangal, “all you need is a center of mass, where it is mounted, and how much it weighs.” As for the material definition, users can choose from a library or create their own. Users can also define multiple load cases to ensure the part is optimized for all use cases. When inputting these values, users don’t have to worry about keeping their units. Inspire will keep track of units.
For most CAE software the next step is to build a mesh based on your geometry. Given the role that the mesh plays in Inspire’s optimization of the part, it is surprising that users have little control over mesh generation. To ensure simple usability and quick turnaround, Inspire builds the mesh automatically.
For instance, localized mesh constraints would be useful to engineers that are concerned about the force distribution involved at a certain section of a part. However, the current control of the mesh is limited to the definition of the following global parameters: minimal part thickness, minimal element size and average element size.
Therefore, once the boundary conditions, loads, and packaging space are defined the user determines the goal of the study. They can optimize the concept part based on maximum stiffness, minimal mass and resonant frequency.
“The maximum stiffness is based on the given loads while the minimization of mass is based on a given factor of safety,” clarified Bangal. “Frequency optimization ensures that the part is designed to avoid a frequency.”
Once the concept part is created, users can run FEA analysis within the Inspire platform to assess the geometry. This will help the engineer to determine which concept designs to pursue with their CAD programs.
Bangal explains that Inspire will make designs that are organic and mathematically correct to handle the given loads and boundary conditions within the current packaging space.
However, due to the organic nature of these shapes, there may be no means to fabricate the design using traditional manufacturing practices. As such, the concept parts are often constructed first via 3D printing.
However, “We realize that not everyone has 3D printers yet and there’s a lot of traditional manufacturing,” said Kroeger. “So we have shape controls in our solver that force the answers to be something that could be cut out of sheet metal, or something that could be cast. That really allows any user to benefit from Inspire.”
Once satisfied with the geometry, engineers can send it to CAD to finalize the design.
“Inspire uses Parasolid as a communication mechanism,” said Kroeger. “So we can actually read in CAD files directly and we write out Parasolid of these ideal shapes. Then you can bring that into your preferred CAD software, and use that to start your designs.”
This model transferability stresses the point that “the result from Inspire is still a concept part,” said Bangal. “Engineers will have a better idea of the final changes the part will need. But with Inspire, many of our customers were able to experience massive savings for their part, some almost halved the weight.”