Pro/ENGINEER has some very powerful capabilities to help us understand the real form, fit and function of a design. Any time you have a design where you have fast-moving parts, that design will generate high acceleration values which mean large forces. Remember what our friend Sir Isaac Newton taught us – F = m * a.
And remember going to college for your engineering degree and spending a lot of time waiting outside your professor’s office to get help calculating the very complex formulas found in your Dynamics text book? Things got a lot more complicated when going from “statics” (not moving) to “dynamics,” which can really make your head spin.
If you are Pro/ENGINEER Wildfire 2.0 (or beyond) user you will most likely have the ability to run a kinematic range of motion on your design with the Mechanism Design functionality that is part of the basic Pro/ENGINEER Foundation XE package. However, this capability is greatly extended in Pro/ENGINEER Mechanism Dynamics. With Pro/ENGINEER Mechanism Dynamics you can set up and find critical dynamic forces. You can also find exactly where peak forces occur within a range of motion and use these forces as key input values to run an FEA analysis in Pro/ENGINEER Mechanica.
Boy, imagine having this capability when taking that Dynamics class. But more importantly, this capability will allow you to fully simulate how a moving part will be stressed and find out ways to optimize your design for the best performance with no failures.
So how can you set up and run a dynamics study on your Pro/ENGINEER models today? It’s actually pretty simple. Here is a 10-step process to run a dynamic/FEA analysis along with key figures for each step.
1. In Pro/ENGINEER Mechanism Dynamics you’ll need to assemble your design using Mechanism joint connections. This will allow the assembly to move throughout its range of motion. You can create these joints in Assembly mode or go to Applications/Mechanism.
Figure 1: Mechanism connection joints
2. You’ll need to define the dynamic bodies and forces like spring, dampers, cams, friction, and gravity. It’s easy to create these items from the Mechanism Model tree located in the lower left corner of window. For instance, just select Gravity/RMB/New or Edit Definition from the Model Tree to get access to the menu.
Figure 2: Dynamic entities like springs, dampers, gravity, friction, etc.
3. You need to define a driver, which is basically like a motor that starts your mechanism motion.
Figure 3: Driver motors
4. You want to define an initial condition that defines exactly what that driver is doing at time=0. You can setup a snapshot for the position of the start and include that with the initial condition.
Figure 4: Initial conditions
5. You’ll need to define a dynamic analysis where you define how long you want the driver to run, start the initial condition, and turn on gravity and friction. Now run this analysis. This is required for the next step to calculate the forces.
Figure 5: Creating a dynamic analysis
6. Create connection force measures at each key location on the model. These measures can be a graph for the entire time range. Just select the force measures and the dynamic analysis and hit the graph icon. Also, you typically want to play back the analysis and show the force magnitude arrows to graphically see where the peak forces occur.
Figure 6a: Force measures with graph
Figure 6b: Force measures arrows
7. Pick File/Use in the structure and select the component of interest, and apply all the peak loads which occur at a single time location or max all loads across the time range. Typically, you want to just select the forces, and deselect the rest (moments, accelerations, etc). The graph should help you validate when the max load occur.
Figure 7: Calculating peak loads
8. Now that the loads have been transferred to the Pro/ENGINEER model, you can open the model by itself in another window. Go right into Pro/ENGINEER Mechanica. With any Pro/ENGINEER Mechanica analysis you typically need to define three things 1) material properties 2) loading and 3) constraints. With a moving body, the constraints will be handled as inertia relief during the analysis set up. Assign the material properties for the part.
Figure 8: Material properties
9. Insert/Mechanism Loads to bring in the loads into the model. Now, just click the force that currently is applied at a point and apply/distribute the force across the appropriate model surface.
Figure 9: Mechanism loads applied to model surfaces
10. Set up a static analysis where you use the loading you just defined and set it to inertia relief. Run the analysis and post process the results for stresses and displacements.
Figure 10a: Inertial relief static analysis
Figure 10b: Post processing of stress and displacement results
For more details around Pro/ENGINEER Mechanism Dynamics and Pro/ENGINEER Mechanica you can look for PTC University courses on mechanism design and simulation. Instructor lead training and web-based training is available.
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