|Molds made using maskless photopolymerization technology and airfoil components produced using this technique could be applied to manufacturing medical device parts. (Georgia Tech photo by Gary Meek)|
Developed by researchers at the Georgia Institute of Technology (Georgia Tech; Atlanta), an all-digital method for casting metal components that allows manufacturers to make parts directly from computer-aided design (CAD) could change manufacturing practices, including in the medical device industry. The new method speeds prototype development times and improves the efficiency and cost-effectiveness of manufacturing procedures after a part moves to mass production.
Developed by Suman Das, a professor in the George W. Woodruff School of Mechanical Engineering, the new approach relies on a technique known as investment casting, or lost-wax casting. Dating back thousands of years, this process is performed by pouring molten metal into an expendable ceramic mold to form a part. The mold itself is made by creating a wax replica of the part to be cast, surrounding or 'investing' the replica with a ceramic slurry and then drying the slurry and hardening it to form the mold. The wax is then melted out--or lost--to form a mold cavity into which metal can be poured and solidified to produce the casting.
While Das's efforts are focused on manufacturing turbine-engine airfoils for the aeronautics industry, investment casting is also used in a range of other industries, including medical device manufacturing. Most precision metal castings today are designed on computers, using computer-aided design software, Das remarks. However, the next step--creating the ceramic mold--involves a sequence of six major operations requiring expensive precision-machined dies and hundreds of tooling pieces.
In contrast, the new method involves a device that builds ceramic molds directly from a CAD design. Called large-area maskless photopolymerization (LAMP), this high-resolution digital process accretes the mold layer by layer by projecting bitmaps of ultraviolet light onto a mixture of photosensitive resin and ceramic particles. It then selectively cures the mixture to form a solid.
The technique places one 100-µm layer on top of another until the mold is complete. After the mold is formed, the cured resin is removed through binder burnout, and the remaining ceramic is sintered in a furnace. The result is a fully ceramic structure into which molten metal, including nickel-based superalloys and titanium-based alloys, are poured. "The LAMP process lowers the time required to turn a CAD design into a test-worthy part from a year to about a week," Das notes. "We eliminate the scrap and the tooling, and each digitally manufactured mold is identical to the others."
The new process not only creates testable prototypes but could also be used in the actual manufacturing process, Das states. That would allow more-rapid production of complex metal parts in both low and high volumes and at lower costs in a variety of industries. "When you can produce desired volumes in a short period without tooling," he adds, "you have gone beyond rapid prototyping to true rapid manufacturing."