Redesigning a bicycle crank arm for metal additive manufacturing by applying DFMAM guidelines to the topology optimization process

Metal additive manufacturing has transformed the conventional design process. With the assistance of additive manufacturing, complex and novel geometries that were previously unfeasible to construct using convention methods, can now be fabricated. Traditionally manufactured parts can be improved upon by employing topology optimization and Design for Metal Additive Manufacturing (DFMAM) guidelines. This research optimizes a commercially manufactured bicycle crank arm for the metal additive manufacturing process. The initial three-dimensional CAD model was obtained by using a white light scanner. Loading conditions obtained from cycling loads found in published literature, were applied to an ANSYS Finite Element Analysis (FEA) model. The FEA model was used to determine the von-mises stress, strain, and deflection that occurred throughout the part. These results were transferred to ANSYS’s Topology Optimization module, which uses an iterative process to remove areas of material that experience low amounts of stress. After each iteration, the solver recalculates the maximum stress and removes additional material until the solution converges on a target maximum stress value. DFMAM principles were applied to the resulting optimized geometry to increase the part’s printability. The optimized design was calculated to weigh 41.5% less than the original crank arm. The FEA results showed that the maximum stress increased from 41.2% of the material’s yield strength to 61.5% of the material’s yield strength, which is greater than the target optimization stress value of 50% of the material’s yield strength. The simulation results were confirmed by a physical experiment. Both the original crank arm and the DFMAM optimized crank arm were printed using a metal additive manufacturing machine. A testing apparatus was designed and fabricated to enable the testing of each crank arm by a universal tensile testing machine. Testing was conducted throughout the range of motion at 15-degree intervals. Strain gauges and dial indicators were used to measure strain and deflection for each test. The resulting experimental data closely resembled the results from the FEA model, thus validating the theoretical simulations. The topology optimization software was proven to be a suitable and useful design tool for optimizing parts for metal additive manufacturing. However, DFMAM principles must still be applied to the resulting optimized geometry to achieve a highly manufacturable design. In conclusion, this research has shown, by using a bicycle crank arm as an example, that topology optimization in conjunction with DFMAM principles can reduce the weight of an existing product without exceeding a targeted maximum stress level