In part 1 of our blog we covered the business value of driving our design with simulation. In this post it’s time to “get into the weeds” a bit. When setting up simulation studies and specifically optimization, we often think back to setting up proofs or “showing your work” in an exam. If you wanted any partial credit at all before you start trying to solve the problem you need to lay out your: “Givens, Assumptions and Unknowns”.
We were supposed do it to promote good problem-solving skills but it did not hurt that you could get a few points just for defining them at the start of your solution. Setting up an optimization problem forces you to think about all aspects of the design, so you can take them into account at the onset of the project.
Inspire: Your Pre-Design Checklist:
✅ Packaging Needs
Inspires start with defining simple design spaces and any features to include/retain. Here we work out our basic packaging and concepts.
✅ Define and Understand Loading
What types of abuse will our design see in normal cases, worst case? Static or dynamic? Should we start with a motion model to generate loads?
✅ Manufacturing Constraints
Cast or stamped? Printed or fabricated? Each process will have its own needs that can drive the design. For example, “How deep can we make a bead? Where’s the split line going to be so we can cast it? How can we print this part so we aren't printing more support material than part material?
The Inspire Design Process Example: Convertible Linkage and Brackets
As an example of the “Inspired” design process let’s look at a convertible design from start to finish:
- Package and concept geometry
- Motion simulation
- Structural optimization
There was a time when the only way to accomplish tasks 1-3 would take you in and out of 3 or 4 different pieces of software. There would also be a fair number of intermediate text files being shared between codes with lots of room for error and frustration. It required a true FEA/CAE geek team to accomplish this series of analysis.
Phase One – Package Space
We start with a simple design that encompasses our packaging needs. Note that all the linkage and bracket shapes are basically blocks and holes for pivots with a few chamfers thrown in. Ideally, we would start with a blank slate in Inspire and import added geometry for packaging background and connecting parts.
Phase 2 – Evaluate Loading and/or Kinematics
If the design is a static structure we might start by defining sets of loads and supports (known as "load cases") directly to the geometry.
Inspire Structures Toolbar for Defining Static Load Cases in Structures
In this case, we are dealing with a mechanism so we will use motion studies first. Motion studies are used to verify the kinematic and dynamic behavior of our model. These studies will calculate loads and forces in joints, motors and actuators as well as displacements, velocities and accelerations.
Inspire creates motion joints based on geometry relationships and are shared between motion analysis and FEA analysis.
When using Inspire, creation of the joints and transfer of the loads to FEA require minimal user interaction. The joints in our model are derived from the part geometry and we can apply motors, actuators and forces to drive the model using expression builders.
Profile Editor for Actuators and Motors
By moving our geometry our analysis joints will update along with our model. CAD Mates are NOT needed to create a motion model. In addition, you can work from a multi-body part which can be very handy. If your current tool forces you into assembly modeling just to run a simple motion simulation you will really appreciate this aspect of Inspire. Sketch out your model and Inspire recommends your connection selections for simulation.
Video of Top Motion and Expression Builder along with Joint Forces
Once we are happy with the top motion and the cylinder drive forces we can begin optimizing the structure using our motion loads as our inputs. In this case we needed to move the pivots on the front panel a bit to get the top to collapse further. You can see from our force plots the downside of that change are large force spikes as we collapse the top. In addition, we looked at the effect of adding joint friction to the model to better understand the potential loads in the system.
Example drive force plots with and without friction included.
Phase 3 – Optimization: Constraints, Goals and Manufacturing Needs
At this point we want to think about our manufacturing process as well as the performance criteria. For casting we can choose a single or split draw. If we want a constant section we can use extrusion constraints.
VIDEO of Shape Constraints, Optimization Load Transfer dialog and Shape Explorer
If the part is intended for printing, Inspire can consider print direction and overhang constraints to ensure the design is self-supporting during printing. In addition to lattice fill optimization. Inspire will size each beam optimally in your lattice within a specified size range.
Additional Tools for Additive Manufacturing
Now that we have defined forces “manually” or set up motion runs to derive our loads we are ready to launch our optimization(s). At run time we can choose if we are more concerned with strength or stiffness along with the size of the features in the design space(s). If the system is dynamic we could also include frequency constraints to avoid resonance issues.
Optimization Run Dialog, What’s important to you?
Once the optimization run is completed you can review the results within the Shape Explorer. To help you find the ideal optimized design you can compare optimization results based on stiffness and mass.
Shape Explorer for reviewing optimization results. For a less conservative design slide left for more material slide right.
Single Draw Constraint Result Versus Extrusion Constraints on the Right
Phase 4 – Optimization Results and Design Direction
In the old “design then analyze” paradigm we may have already started detailing our parts. Then we might have set up some preliminary studies using our design embedded FEA or created a work order for the CAE group or called our consultant/brother-in-law to do an FEA on our CAD model. After getting our FEA results back we would be interpreting contour plots of stress or deflection and trying to understand what does it all mean? Red means bad, right?
A contour plot tells us the result of our design change. An Inspire topography result tells us where to put the material based on our optimization parameters and constraints. It is a more direct path to success than the "old" paradigm where we make a design change, re-analyze and repeat if we did not hit our performance targets.
Optimization Output (left)/Contour Plot of Stress on The Design Space (right)
We can work with these optimized shapes in multiple ways:
- Immediately evaluate stress and deflection on the optimized geometry to get the "warm and fuzzies" on our actual deflection and stress levels of the optimized design.
- Export an stl mesh representation of the optimization as a template to "draw over" in CAD.
- Smoothed geometry to CAD or printer or Analysis.
- Remaster with Inspire using geometry tools such as PolyNurbs.
Now that I’ve had the opportunity to walk you through the typical design phases you experience when using Inspire, in part 3 of this series we will investigate the different ways to work with our optimization output to drive our CAD or remaster within Inspire for a “final” validation.
By the way, you really don’t have to wait for part 3 to experience Inspire 2018. Download now and use it FREE for the next 15 days or if you’d like a benchmark, talk to someone on the Alignex team. They’ll be happy to help!
Written by Guest Author - solidThinking Team
solidThinking employs a relentless focus on delivering innovative technology with a streamlined user experience. Its tools empower users and organizations to make informed decisions and design, engineer, manufacture, and deliver amazing products to market faster than ever before. solidThinking’s tools are sold and supported through a global network of industry and domain experts.