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Advanced Manufacturing 40 MoldMaking Technology —— AUGUST 2016 tools might take between three and four weeks to produce, and medium-sized molds average six to eight weeks in lead time, depending on their complexity. Average cycle times for wax molds can vary a great deal due to the range of complexities, he says, but usually fall between three and five minutes, including one to two minutes of curing time. Batch Programming The company's batch approach to machining of mold inserts also results in time savings. Rather than machining custom inserts individually, the shop's toolmakers routinely cut mul- tiple, differing inserts in the same program cycle. The lead toolmaker on a job will conduct pre-production planning and scheduling based on a customer's specifications, then batch several programs together to run as one continuous program on one of the 12 CNC machines. Novak says the toolmakers calculate the maximum number of inserts that can be cut from one piece of raw material stock with minimal waste. For some smaller tools, top and bottom plates are machined from the same stock in the same setup, saving even more time. "While the programming takes slightly longer, machining multiple inserts in the same setup saves us over 50 percent in machining time versus machining each insert individually," he says. This approach also makes more efficient use of an operator's time, enabling him to manage two to three CNC machines simultaneously, Novak says. It also allows the com- pany to increase its lights-out machining time. The Investment Casting Process Just what is investment casting? Basically, it is a process for making complex, detailed alloy parts using a wax model, or pattern, that is molded using the aluminum molds that companies like South Coast Mold build. Here's how it works: A foundry injects molten wax into the aluminum molds, much like in- jection molders inject plastic into steel molds. After a cycle time of two to three minutes, plus two minutes for curing, foundry workers manu- ally remove the wax patterns from the molds. The wax models are then placed on a wax "tree" and dipped into a thick, cold, liquid ceramic-like mixture called "slurry." Sand is poured over the models, and they are then allowed to dry completely. This dipping is repeated six or seven times to ultimately create a uniform, hard ceramic shell about 3/8-inch thick. This entire process is often done by hand, although some compa- nies have automated it. Either way, it could take five days to complete. Next, the ceramic-covered wax assembly is placed into a hot steam chamber called an autoclave so that the wax can be melted out of the shell, usually to be reused. The ceramic mold with its complex contours then is heated to about 1,600°F so that it does not crack when it is next filled with a molten metal like titanium, steel, brass or bronze, which can reach temperatures as high as 2,200°F. Once the metal part is cast, it is allowed to cool at room temperature, which takes approximately three to five hours depending on the type of metal. Once cooled, a vibrating hammer is used to break off the ceramic shell from the cast metal. The gate through which the metal entered the ceramic mold is cut off, and the cast part's surface is ground smooth. Parts are checked for dimen- sional accuracy using a coordinate measuring machine or by scanning the castings. Because the wax is so smooth, the finish on the castings is some- where between a sand-casted surface, which is bumpy or rough to the touch, and a surface that has been finish-machined or ground. For most applications this is enough, says Paul Novak, South Coast Mold presi- dent. Any critical surfaces can be machined to tolerances. The investment casting process begins with an aluminum mold with complex details machined into it, like the one shown here, made by South Coast Mold. LEARN MORE Organizers of the International Manufacturing Technology Show (IMTS) interviewed Paul Novak and wrote a short feature about South Coast Mold and how IMTS helps even small companies plan future growth based on the people and technologies they meet at the event. short.moldmakingtechnology.com/scoast Extended Lights-Out Machining Fully equipped with Unigraphics CAD/CAM software for mold design and for programming tool paths, South Coast Mold builds and inspects molds from solid models, and routinely runs lights-out machining every evening and, when necessary, during entire weekends. "Just this week, we ran a CNC cut- ting program for over 72 hours. That three-day program is not even a record for us; it's just routine, unattended machining," Novak says. In fact, South Coast has been running lights-out machining for 20 years, and daytime hours are regularly spent preparing for those long, overnight and weekend runs. The network of Mori Seiki machines makes this possible. The CNC machines can run for hours unattended and then power down at the end of a programmed cycle, Novak says. Because they all are networked using distributive numerical VIDEO