A new practical workflow for the laser Powder Bed Fusion (PBF) process, incorporating topological design, mechanical simulation, manufacture, and validation by computed tomography is presented, uniquely applied to a consumer product (crank for a high-performance racing bicycle), an approach that is tangible and adoptable by industry. The lightweight crank design was realised using topology optimisation software, developing an optimal design iteratively from a simple primitive within a design space and with the addition of load boundary conditions (obtained from prior biomechanical crank force–angle models) and constraints. Parametric design modification was necessary to meet the Design for Additive Manufacturing (DfAM) considerations for PBF to reduce build time, material usage, and post-processing labour. Static testing proved performance close to current market leaders with the PBF manufactured crank found to be stiffer than the benchmark design (static load deflection of 7.0 ± 0.5 mm c.f. 7.67 mm for a Shimano crank at a competitive mass (155 g vs. 175 g). Dynamic mechanical performance proved inadequate, with failure at 2495 ± 125 cycles; the failure mechanism was consistent in both its form and location. This research is valuable and novel as it demonstrates a complete workflow from design, manufacture, post-treatment, and validation of a highly loaded PBF manufactured consumer component, offering practitioners a validated approach to the application of PBF for components with application outside of the accepted sectors (aerospace, biomedical, autosports, space, and power generation).
Additive Manufacturing (AM) provides an opportunity to fundamentally redesign components previously limited by conventional manufacturing techniques. A new process for this workflow of design, manufacture by Powder Bed Fusion (PBF) and validation is presented, to which a case study of a crank for a high performance racing bicycle is applied.Topology optimisation generated conceptually ideal geometry from which a functional design was interpreted. Design for AM considerations were employed to reduce build time, material usage and post-processing labour. PBF was employed to manufacture the parts, and the build quality assessed using Computed Tomography (CT). Static and dynamic functional testing was performed and compared to a Finite Element Analysis (FEA). CT confirmed good build quality of tall, complex geometry with no significant geometrical deviation from CAD over 0.5mm. Static testing proved performance close to current market leaders, although failure under fatigue occurred after just 2,495±125 cycles, the failure mechanism was consistent in both its form and location. These physical results were representative of those simulated, thus validating the FEA. This research demonstrates a complete workflow Preprints (www.preprints.org) | NOT PEER-REVIEWED | from design, manufacture, post-treatment and validation of a highly loaded PBF manufactured component, offering practitioners with a validated approach to the application of PBF.A bicycle crankset consists of 2 cranks joined by a bottom bracket (BB), converting pedal force into rotational motion, powering the rear wheel. A typical high performance crank is box-section in form and is machined from aluminium or moulded from Carbon Fibre Reinforced Polymer. As well as low mass, high crank stiffness is also a major consideration in order to cycle more efficiently and effectively.Solutions to achieve maximum stiffness at minimum mass are suited to topology optimisation. In addition, Additive Manufacturing (AM) offers the capability to manufacture such idealised geometry. The build quality of the complex geometry produced by AM, and the results of functional testing can both be verified by using Computed Tomography (CT), comparing a CT generated model with the CAD data e.g [1]. 2: MethodologyThe method developed and followed for the design, manufacture and testing of a high performance crank is given in Figure 1.Preprints (www.preprints.org) | NOT PEER-REVIEWED |
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