Howmet Executive Tracks Improvements In Titanium Investment Casting Process By Michael C. Gabriele
B
oyd Mueller, the vice president and general manager of technology and metals for the Engines Business Segment of Howmet Aerospace Inc., has seen steady, significant improvements in the field of titanium investment casting during the last five years—at his Boyd Mueller company and throughout the titanium industry at large. It’s a trend that will continue to gain momentum during the next five years. Titanium investment casting produces parts through the metallic replication of wax models. The resulting titanium parts have a very smooth surface that requires little finishing after the process. Because a wax model is created in the exact size and shape as the part, investment casting allows for high dimensional accuracy. Investment casting, or “lost-wax” casting, is a fundamental manufacturing technology for producing precision titanium parts for the aerospace industry, industrial markets, and oil and gas business sectors. Investment casting begins with the production of an exact wax model or pattern of the final product. This pattern is typically produced by injection molding, but it also can be produced by Additive Manufacturing (AM) printing. The pattern is then coated in a ceramic material to create a “shell” or mold. The mold is placed
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into a furnace where the wax is melted and drained from the shell, leaving behind an empty cavity in the shape of the final casting. The shell is then placed into a vacuum chamber to remove contaminants and ensure casting quality. Molten titanium is then poured into the ceramic mold, which fills the shell cavity. The titanium is allowed to solidify and cool. The ceramic mold is destroyed and removed from the component casting, revealing the final cast titanium part. Investment cast titanium is light weight, has high strength up to 1000°F and is corrosion resistant, which makes it ideal for many aerospace, defense, and subsea applications.
Aerospace Titanium Investment Casting
Mueller identified process management as a major area of
improvement for titanium casting, which he’s witnessed during the last five years. The thrust, he said, is to be pro-active to define potential problems on the front end of the casting process, rather than try to make adjustments on the back end. “Process management for casting has become much more engineering driven. It involves understanding the process and eliminating defects and rework. The goal is to improve casting integrity and have more consistent properties and quality in the cast parts.” Another advance cited by Mueller is the utilization of additive manufacturing (AM) in the investment casting process. As he explained it, an AM model or prototype is produced, rather than a wax pattern, for the lost-wax casting process. “We take a different approach for using additive manufacturing,” he said. “Using additive manufacturing, rather than a tooled wax pattern, cuts out time and expense to produce a cast part. We replace a traditional wax pattern with a printed, additive manufacturing pattern.” He added that using AM, rather than wax, has other advantages, as AM is suited to support the increasing complexity of cast parts, especially those where the geometry is difficult or impossible to tool. A third area of recent innovations for the casting process is the specification of higher-performance titanium alloys. Much of this is driven by demands from the aerospace industry to produce titanium parts
