Speaker
Description
Additive manufacturing is a transformative technology and manufacturing process that offers significant advantages over traditional manufacturing techniques, including greater design flexibility, higher material efficiency, reduced reliance on costly tooling, and shorter production lead times. Wire-based Direct Energy Deposition (w-DED) can produce large components on a scale of metres at high deposition rates, and the plasma transferred arc (PTA) power source offers stable deposition with a high level of control. Crucial issues in the PTA w-DED process include stabilising metal transfer and avoiding defects, affected by the torch-to-workpiece distance and deposition parameters. However, low torch height and wire position result in low manufacturing tolerance to layer height variation, leading to higher collision risk and more complex control systems. In addition, large-part deposition requires local shielding protection, which makes it more difficult to accommodate sensors for in-situ process monitoring. A proposed solution is to increase the torch height while ensuring arc stiffness, metal transfer stability, and avoiding defects or exposure. This work investigates the feasibility of the extended-torch-height PTA w-DED process for increasing its manufacturing tolerance. An experimental method was first developed to quantify the PTA arc pressure, and the effects of current, torch height, and PGFR were systematically examined at a conventional low torch height (~6 to 8 mm). Single-pass melting experiments were then performed at torch heights of 6-20 mm using PGFRs of 0.4-2.5 L/min, and the results reveal a distance-dependent role of PGFR. Excessive PGFR increased arc pressure impingement, leading to keyhole defects at lower torch heights. In contrast, higher PGFR became beneficial to the elongated plasma arc stiffness at an extended torch height of 20 mm. Energy distribution measurements showed that extended torch height broadened the effective heating area, increasing melt pool size and reducing remelting depth. At extended torch height, wire-based deposition tests showed that the droplet trajectory deviated from the vertical centreline by 30–35°, indicating challenges with material feeding accuracy, but the arc pressure contributed more for metal transferring when the wire melting point is in front of the centre of the plasma arc. A local shielding device was used to protect the deposition process with extended torch height, and in-situ measurements demonstrated that the oxygen level around the melt pool dropped below 1000 ppm after 20 seconds of purging with pure Ar gas, satisfying the oxidation-mitigation requirement during deposition for most alloys. Therefore, manufacturing tolerance in w-DED additive manufacturing can be improved by increasing the torch and wire height, enabling a stable deposition process with suitable arc pressure, wire-feeding strategy, and local shielding, providing a foundation for more flexible additive manufacturing of large-scale components and for the development of in-situ process monitoring sensors.
| Speaker Country | UK |
|---|---|
| Would you like to publish your paper in the special issue of BHM "Berg- und Hüttenmännische Monatshefte" | No |