Reverse Tilt Pour Process Saves Costs on Custom Castings
LAWRENCEBURG, Ind.--Since its founding in 1945, Batesville Products, Inc. (BPI), of Lawrenceburg, Indiana, has used the permanent mold casting process to manufacture custom components and assemblies for a wide variety of industries. In recent years, the company has manufactured permanent mold castings using reverse tilt pour molding, a process that allows Batesville to create parts more economically by increasing metal yields and offering more repeatability. According to Batesville Vice President Tim Weber, the technology enables BPI to produce shapes that normally would require low pressure permanent mold casting, but with greater cost savings. Parts ranging from wind turbine hubs to large high-volume fan blades for factories, and enclosures for U.S. Army tanks, have been produced using the process.
"The way we've adapted reverse tilt pouring technology is what's important," says Weber. "Not only is it cheaper for us to do this, but we can get into production a lot quicker. So it's a win-win for everyone involved. We can get a better part out of this process and do it more economically than what's typically out there right now. I would say that we can get the tooling costs down about 25%, and we can cut lead times down from eight weeks to five or six weeks. And we can get more properties out of the process and more quality."
The reverse tilt pour process requires the molten metal, usually aluminum or zinc, to be delivered through gravity to the center of the cavity in a controlled manner while the whole mold is rotated 90 degrees, according to Tony Stenger, the company's engineering manager. "The rotation speed is controlled to maintain exact metal delivery into the cavity," he explains. "This process lends itself, on certain part designs, to ideal progressive solidification." The method is said to reduce the amount of metal that needs to be put into the process to get a quality part. "It increases the yield quite a bit, since it's a controlled process," Stenger insists. "If you have a wheel, for example, instead of having the metal feed from around the perimeter, you have it feed directly from the center. The process allows us to control the rate of material that goes into the cavity, so you get good repeatability. Unlike low pressure molding, it doesn't require being attached to a melting furnace down below the mold.
"Our adaptation to the process is how we actually orchestrate our tooling to keep the tooling inexpensive," Stenger continues. "What we do with our tooling is make it with less of a footprint, so it requires less steel. Our tooling has less active parts in it, so it cuts down on the tooling costs."
Batesville has built a few presses specifically for the reverse tilt pour process, using multiple slides on the tooling to put more complexity into the part. "Maybe the customer wants holes in the side of the casting," says Stenger, "so we'll put a slide on there. If we were casting a square box, and we wanted to put ribs on the side of it, we can't orchestrate that with molding because you have to get the metal part out of the metal mold. If you put a slide on it, you can actually pull that part of the mold away, so the casting can be ejected from the tooling."
During the past few years, Batesville has served the alternative energy industry by making parts and components for wind turbines. Generally, these parts are castings--primarily hubs for the massive blades at the top of the wind turbine. "We use the reverse tilt pour process for these turbine parts," says Terry McCarthy, the firm's vice president of sales. "It's a controlled casting process, and it allows the casting to come out with a fine grain structure, which yields very good mechanical properties. There's a lot of stress and strain on these components, so the mechanical properties are very critical."
McCarthy says the reverse tilt pour method is excellent for making sure the company gets the most out of materials that are specified in the original design. After molding, the company machines all of the critical dimensions on the parts, so that it can supply the customer with totally finished parts. "We do all of this in-house, which is somewhat unique for a casting company," McCarthy insists. "So we're a one-stop-shop for these parts. We also make other wind turbine castings that help align the turbines to the direction of the wind."
The wind turbine parts are all made out of A356 aluminum, and range in size from 5 pounds to 50 pounds of material. "There are only a few casting companies that can make castings that are that large and require tight tolerances as well," says McCarthy. "The reverse tilt pour lends itself to round shapes. In some cases, we'll do the assembly of the bearings and other parts, such as assembling shafts into gear mechanisms."
Another casting that BPI produces is a large fan blade hub for moving air within large manufacturing plants. "The blades move a high volume of air with low speed," says McCarthy. "We also make this part with our reverse tilt pour process and perform all secondary machining on this casting."
Batesville also makes a part that's used for energy conservation. It's basically a box-like enclosure that holds electronic parts inside its interior. "This part takes a lot of machining," says Weber. "The part turns electrical energy into a useable state, from DC current into AC current. It also has to keep everything cool, so it has cooling fins and other features to it that will take heat out of the inside of the box."
The parts that Batesville manufactures vary greatly in form, fit, and function, necessitating the use of several different molding processes. Besides reverse tilt pour, the company uses conventional tilt pour and horizontal and vertical gating methodologies. "The part specifications drive the process," says Stenger. "Take, for example, the wind turbine hubs; they have a strength requirement that necessitates using the reverse tilt pour method. These parts are a challenge because the center section is relatively thick compared to the perimeter of the part, so the part geometry also lends itself to using reverse tilt pour. Our engineers work closely with our customers' design engineers. The solidification analysis allows us to feed back information to our customers for part design to allow them to modify the part while it's still being designed."
The traditional casting method for round parts--low pressure tilt pour--yields a good casting, but it has a limit on how many parts can be poured before operators have to shut down the process. For example, on the large ceiling fan blade, only about ten castings can be poured before shutting down the process. In reverse tilt pour, the center of the part has a riser. A machine operator fills the pour cup by hand, and the pour cup fills up the mold automatically. The key is filling the cavity in a predetermined manner.
"With low pressure, you're filling the mold up from the bottom using low pressure to push it into the cavity," says Stenger. "All of this has to be sealed up in a crucible that operates at 1300 degrees, and you can only fill the crucible with 500 to 1000 pounds of molten metal. In reverse tilt pour, you're not limited to that aspect. Once you start production, you can run continuously."
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