Stainless steel casting with 3D printed sand molds

Sand mold casting is a manufacturing method that has been used for thousands of years. In recent years additive manufacturing has, among other things, enabled production of sand molds with complex geometry resulting in castings with geometry that would have been very hard, if not impossible, to produce with conventional sand mold casting or machining procedures. Since this manufacturing method is relatively new, knowledge gaps exist regarding the benefits and drawbacks of the method as well as when it should be used. The purpose of this study has been to explore casting molds produced by additive manufacturing, how they can be used and what effect they have on the manufactured product. For this purpose, a existing product has been redesigned to be cast in one of these molds instead of traditionally being machined from large aluminium blocks. The design work has been supplemented with calculations on the parts structural integrity, interviews and material sample tests. The redesign was made on behalf of Vattenfall AB and the studied component was a part of a test rig for a hydro power plant called spiral casing. The result of the study is a new design of the spiral casing with a lower weight and volume, made with stainless steel instead of aluminium, and other improvements. Testing of cast samples have shown that the mechanical properties of steel cast in 3D-printed and conventionally manufactured sand molds do not differ significantly. The sample cast in a 3D-printed mold did have a finer surface finish however. Production volume, product complexity, material and lead time are all factors that determine when additive manufacturing should be used in the creation of sand molds. Further studies are required to better determine where the breakeven points are