Additive Manufactured Branched Column Connection

Abstract

An investigation into the application of additive manufacturing to the production of structural joints was conducted for this thesis. The main goal was to determine all necessary aspects that someone needs to consider when designing a structural part that is intended to be printed with additive manufacturing. As an example, the branched column connection was selected due to its inherent limitations, which can be effectively addressed through the integration of additive manufacturing techniques.
Within the construction realm, wire arc additive manufacturing (WAAM) stands out as particularly advantageous due to its ability to yield high mechanical properties comparable to conventionally manufactured materials, coupled with a high deposition rate. As with any manufacturing process, WAAM operates within certain constraints dictating the types of objects feasible for production.
To ensure compatibility with WAAM while achieving desired structural and aesthetic benchmarks, three laboratory tests were conducted. These tests scrutinized the impact of input process parameters, overhang, and overlapping on the quality of the build. Factors such as travel speed, wire feed speed, voltage, and current were examined for their influence on welding bead dimensions and quality. Additionally, an investigation into how the percentage of overlap affected print quality was done. Among the constraints, the most pivotal one was the overhang limitation, determining the minimum allowed overhang angle in perpendicular and parallel directions depending on the direction of the print.
The primary objective in designing the connection was to reduce the necessary material for the branched column connection’s manufacture. Topology optimization (TO) played a crucial role in achieving this goal. Various models were constructed, each differing in TO input parameters to find the model with the lowest required mass while maintaining adequate structural performance. These models varied based on TO objectives (equivalent von Mises stress, compliance, mass, and volume) and TO constraints (either mass retain percentage or maximum stress), while also integrating manufacturing constraints obtained from lab tests. Ultimately, the model that offered the lowest mass and satisfactory structural performance focused on compliance as its objective, while retaining 15% of its initial mass.
Based on the above explained research a design guideline could be proposed and includes all necessary steps and considerations that someone needs to take into account when designing a connection manufactured with WAAM. The steps of the guideline include: 1. Selection of additive manufacturing process; 2. Material selection; 3. Determination of additive manufacturing process manufacturing limitations; 4. Design phase including TO with the proposed input parameters.
In illustrating the advantages and limitations of WAAM in the construction industry and proposed design guideline, a case study involving a comparative analysis between a steel plate and a WAAM branch column connection was done. This study centered on the real life project, 6 Bevis Marks in London. The findings showcased a notable reduction in the required material. However, the limitations of this approach were apparent in the increased manufacturing time and costs.