Book Description

Casting is one of the oldest manufacturing methods, dating to 5000 B.C. Its influence can still be seen today, accounting for a $110 billion impact on the US economy in 2019. Sand casting, is the most popular casting process due to its ability to produce relatively complex parts with almost any alloy at comparatively low costs, as well as manufacture both large components and small precision castings. Despite its prominence, casting has design limitations such as required draft angles and parting lines due to required tooling and patterns, which has led to the exploration of new manufacturing methods, such as additive manufacturing (AM). AM allows for increased part complexity, reduced material usage, part consolidation, usage of lattices, and decreased lead time between design and production. The rise of this novel technology is reflected in the large influx in publications and patents involving AM within in the past couple decades. However, its limitations in part size, cost, and available alloys prevent it from fully replacing casting. The merger of both sand casting and AM binder jetting into a hybrid manufacturing method is called 3D sand printing (3DSP), and it offers the benefits of both methods. With the advent of 3DSP, more complex geometries and castings are possible, allowing for the redesign and optimization of gating and rigging systems for defect reduction and improvements in casting quality. Despite research having already explored redesigning gating components like pouring basins, sprues, and runners using more complex mold geometries realizable through 3DSP, no research has considered the use of 3DSP for runner extensions. This thesis investigates various runner extension designs for the purpose of defect reduction. Out of the six different runner extension designs, three required 3DSP due to complexity. All designs were evaluated using simulation and experimental validation to ascertain their impact on casting quality. Designs were derived from literature review of gating system concepts. Simulations were completed using Flow-3D Cast v5 CFD software, comparing the resulting entrained air, tracer particles, and void particles present in the casting cavity. Results indicated difference between designs but required additional experimental comparisons to conclude runner extension impact. Designs were tested on manually poured Al319 cast plates, using a hybrid mold making method of both green sand and 3DSP extension molds. A total of eighteen plates were cast, three per design, all of which were scanned with computed tomography (CT) to determine the defect volume fraction present in the final castings. Three-point bending bars were machined from cast plates and tested to compare extension designs impact on mechanical properties. Statistical analysis of both mechanical performance and defect volume fraction showed no differences between runner extension designs. The results obtained in this thesis aid for the further optimization of gating systems and helping foundries reach zero defect casting.