Design, Manufacturing and Development of Hybrid Manufacturing System for Rapid Investment Casting
Creators: Arora, Piyush
Publisher: name: University of Alberta Library
Year: 2024

<p>Direct rapid investment casting integrates additive manufacturing (AM) technology into conventional investment casting. This approach addresses the challenges of high lead time and cost but is effective only on a small scale (up to a cube of 0.3 m side). It utilizes thermoplastics such as Acrylonitrile Butadiene Styrene (ABS) as a sacrificial pattern material, but after burnout, thermoplastics can lead to defects such as shell cracking and residual ash. The layer-by-layer printing process in AM introduces stair-stepping defects, significantly impacting surface quality. Additionally, the conventional investment shell fabrication method, involving submerging the pattern in a ceramic tank, results in uncontrolled shell thickness, leading to shell cracking due to the formation of local hotspots while pouring molten metal.<br>
A novel hybrid additive-subtractive manufacturing chain is proposed to address these issues. This approach incorporates 3D printing for large-scale pattern fabrication and post-processing to improve surface quality and dimensional precision. Another additive module fabricates the investment shell around the processed pattern. This methodology eliminates the need for complex tooling in conventional investment casting, resulting in saving lead time and costs.<br>
A three-axis cartesian large-scale hybrid manufacturing system was designed and manufactured in-house to validate the proposed hybrid chain. This system is capable of producing metal castings up to one cubic meter in size and incorporates additive and subtractive modules selected based on literature review. Fused Granulated Fabrication-Additive Manufacturing (FGF-AM), a large-scale extrusion technology was employed in the study for printing sacrificial patterns using wax, a material preferred in foundries for producing defect-free metal castings. The methodology involved the development of a systematic approach to optimize and validate critical printing parameters using a design of experiments (DoE). An in-situ CNC machining facility was integrated to address stair-stepping issues, improving surface quality and dimensional tolerance to meet investment casting (IC) standards. After post-processing patterns, the subsequent step involved fabricating the investment shell using Direct Ink Writing additive manufacturing (DIW-AM), employing a large-scale extrusion process with red earthenware clay as the feedstock material. Influential printing parameters were optimized using DoE to achieve fully dense investment shells.<br>
The utilization of the hybrid system yielded positive outcomes where FGF-AM achieved an optimal throughput of 0.5 kg/hour, and in-situ machining ensured an average dimensional accuracy of ±40 μm, precision of ±170 μm, and a surface roughness of 3 ± 0.5 μm Ra, all within the prescribed investment casting (IC) norms. Additionally, the sacrificial pattern printed at optimal parameters exhibited 0.5% porosity, affirming the print quality and the system&#39;s capability to generate dense patterns. The Direct Ink Writing (DIW) technique for printing investment shells attained the maximum mass flow rate of 2.2 kg/hr. It achieved objects with a relative density of 99.5% under optimal printing parameters.<br>
The system&#39;s capability and conformity to investment casting standards were demonstrated through case studies, which included the fabrication of an ASME wax slip-on flange and several intricate clay artifacts. The research findings suggest that the developed system exhibits substantial potential for industrial scalability, delivering 10–20 times higher productivity than alternative 3D printing methods and reducing the total cycle time for investment casting applications by 50–60%.</p>