Abstract
High-performance machinery components, such as robot links, are mostly made of iron, its alloys, and a variety of other metallic alloys. Precision machinery structures achieve both stiffness and damping by using large castings of these conventional materials. However, this can limit the dynamic performance and induce thermal errors. Manufacturing robot links from conventional materials is less sustainable, typically requires high energy and potentially several post-casting operations, and also increases actuation running cost due to the higher mass. This research addresses these issues by developing a lightweight structural member that can be manufactured without bespoke, resource-intensive processes, instead utilising standard commercially available resources and is suitable for replication in small industries.Due to their high strength-to-weight ratio and excellent mechanical properties, carbon fibre tubes have become a preferred choice for the link after the literature review. However, challenges such as porosity, delamination, and other defects make thicker tubes commercially uncommon. To address this, the novel design incorporates commercially available carbon fibre tubes arranged in a honeycomb-inspired configuration, optimised using a custom analytical design tool. This configuration requires a substrate solution, without which the tubes may shift, leading to asymmetry. Moreover, simple bonding between the tubes is not feasible due to the low surface area. An analytical model was developed for determining the stiffness of the robot link design. Based on the ANOVA results, it was revealed that tube thickness contributed most to the stiffness. Also, as the number of filler tubes increases, the stiffness increases. The substrate material was found to be contributing the least towards the stiffness. This analytical model was then used to develop the optimised design. The optimisation suggested that incorporating the maximum number of filler tubes is desirable and provides improved stiffness. However, the improvement in stiffness was not significant enough to outweigh the benefits of simpler manufacturing, highlighting a trade-off between structural performance and manufacturability
Research on existing materials revealed that chopped carbon fibre epoxy composites can be prepared using a ‘cold forging’ method, which requires no heat energy during manufacturing. Composite samples were manufactured using this technique with two different mixing processes, and the elastic modulus was determined. The porosity analysis on the baseline samples revealed that the first crack load is inversely proportional to porosity at the midsection, i.e., as porosity decreases, the first crack load increases. The clustering of pores and their positions, along with the overall porosity, affect the flexural strength and contribute to scatter in the data. The XCT result suggested that the porosity of the bulk mixed samples was higher, leading to a reduction of 32.40% in Young's modulus compared to the baseline mixing procedure. Because of the gradual mixing of the carbon fibre and epoxy inside the mould cavity (baseline sample), there was a preferential fibre alignment, which resulted in an increase in flexural strength. However, the bulk-mixed samples demonstrated no preference in terms of fibre orientation (near isotropy), which, along with porosity, reduced the flexural strength. The Poisson’s ratio and the coefficient of thermal expansion were also determined. The same bulk mixing was carried out in the prototype manufacturing, and similar porosity was expected; however, the variations in flexural strength due to porosity are expected to have a negligible effect, as found from the ANOVA.
Based on the insights from a pre-elementary prototype, a robot link was manufactured from commercially available CFRP tubes using the cold forging technique and then experimentally validated. The prototype exhibited a static stiffness, which was 91% of the FEA-predicted value and matched that of an equal-weight structural steel tube. Dynamically, the prototype's natural frequency matched with FEA value and its 1% damping ratio was comparable to conventional materials. In addition, the coefficient of thermal expansion was reduced by about 71% compared to structural steel. The developed prototype matched the static and dynamic properties of steel-based links while providing superior thermal stability. The prototype’s manufacturing was simple and resource-efficient compared to bespoke methods. The proposed robot link can be used in low to medium-capacity industrial robots with the design methodology applicable to other high-dynamic machine structures.
| Date of Award | 22 Apr 2026 |
|---|---|
| Original language | English |
| Sponsors | Engineering and Physical Sciences Research Council |
| Supervisor | Simon Fletcher (Main Supervisor) & Andrew Longstaff (Co-Supervisor) |