CAT 988K Tilt Arm
CAT 988K Tilt Arm
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The project was to create a bottom-up model of a product of our choice and perform shape optimization on the geometry for the MECH 465 class. For this project, I selected a tilt link from a CAT 988 K, with the objective of minimizing volume, which translates to minimizing mass. The load was 130 kN, acting at 45 degrees on the bucket end of the arm. In reality, this arm typically experiences nonlinear loading across a range of angles; however, that is out of the scope of this course.
Note that this project was done in ANSYS APDL. While it was helpful to understand the backbone of ANSYS Workbench, using APDL is obsolete; Workbench should have been used.
Model Simplifications
Model Simplifications
Notably, the course requirement was to make this a bottom-up model; otherwise, the model had to be simplified, or the project would not be completed within the course timeline. All fillets, chamfers and rounds where the hydraulic cylinders attach were removed.
Volume Mesh - Total 136 elements,
"Laptop" Mesh - 424 Elements
Optimization Mesh - 78 684 Elements
Mesh
Mesh
Above, you can see the volumes created from the model. Note that this part is symmetric and was constrained for all nodes on the back face. The mesh on my laptop used only 424 elements; however, it was parametrized to scale to 78,684 elements, which were used for analysis and optimization.
Results
Results
As seen in Model Simplification, I started with a simplified CAD model and created 23 unique design vectors to test and iterate the optimization and determine the best result. It should be noted that each optimization run typically ran only 9 iterations before being caught in a local minima, even with a 1% tolerance.
von Misses Stress
von Misses Stress
Deflection
Deflection
Errors
Errors
It should be noted that an error was made: the position of the inner side of the lug relative to the symmetric face was not defined; thus, the part became skinnier without consideration for the hydraulic cylinder that would normally sit there. This is an inaccuracy, however, due to the course structure and timeline, this change was not possible before the course completion.
On the top face of the part, there is a stress riser due to a sharp incline. This error results from that point not being considered a design variable. In the future, this can be elevated by making it a design variable or by adding a fillet for the final design.
Again, outside the scope of the project, a mesh convergence test would be beneficial for determining the optimal number of elements to reduce computational time.
Moving forward
Moving forward
On this project, overall I was able to achieve 95%. However it would be interesting to perform a topology study with the proper loading in the future.
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