Investment Cast parts beside 3D-printed patterns. (Image courtesy of Aleph Objects.)

As the technology matures, it’s becoming clear that the biggest benefits of 3D printing often come about indirectly. This is illustrated most immediately by its applications in prototyping; the ability to iterate designs quickly or produce sample parts for customers has led to better products, even though most of those products are not themselves 3D printed. Additive manufacturing (AM)—3D printing in production—is coming along, but some of the best examples of its use are still indirect.

Take investment casting, for example.

The Investment Casting Bottleneck

Based on lost-wax casting, investment casting is a positively ancient manufacturing technique. Dating back approximately 5,000 years, the process involves multiple steps but the idea is simple: a hollow cast is made from a mould based on a master pattern; that cast is then covered with a fire-proof mould, which is heated and processed to remove it. The investment mould is then filled with molten metal, resulting in a final product.

In modern manufacturing, the investment casting process is often supported by injection molding, as Eric Beardslee, product marketing manager at Aleph Objects explained.

“If you have a model and you want an injection mold made of it, which is expensive—it might be $10,000 -- depending on what you’re doing, you send it off and they make a wax pattern. Then you take it to your foundry, they attach the sprues, and then give it at least six coats of a ceramic slurry, alternated with layers of fine zircon sand. The number of layers depends on the thickness of the part: for one with more delicate features, they’ll typically go nine or even twelve layers. Then they bake it in a kiln— at 1,000 degrees Celsius or more —for a couple of hours.”

One of the major bottlenecks in this process is the initial tooling phase, as Beardslee noted: “Typically, if you have to send a design off to create a die, that could take two to three weeks and cost thousands of dollars,” he said. “The process as it is now is prohibitive for people that might not have as much capital, or have short deadlines to deliver prototypes.”

That’s where 3D printing comes in.

Additive Manufacturing & Investment Casting

3D printing has had an edge on injection molding in the prototyping space for some time, and it can compete in investment casting for many of the same reasons. Unlike an injection molded part, which takes considerable time and capital to produce, a 3Dprinted part can be created directly from a CAD file.

Of course, you might initially get some odd looks when taking a 3D printed pattern to a foundry.

3D-printed patterns for jewellery. (Image courtesy of Aleph Objects.)

“They were dubious at first,” said Beardslee. “When we came in with these printed pattern, the guy at the desk who had been there a long time was not very excited, because his prior experience with plastic filament was that it didn’t burn out very well. But the Polycast filament by Polymaker that we’re using leaves less than .003 percent ash. After they were finished, he said it was one of the cleanest burnouts they’d ever seen.”

In other words, although some foundries may be skeptical due to their initial forays into working with patterns made from filaments, 3D printing technology has advanced to the point where those early experiences may no longer reflect the state of the industry. In order to appreciate how far additive manufacturing has come, it helps to look at some practical applications.

Aleph Objects, Inc., makers of the LulzBot 3D Printers, put Polycast to the test by printing patterns for various automotive parts, including ring and pinion gears and even a complete turbocharger assembly.

“It prints just like PLA, so it’s super-easy to work with,” Beardslee commented. “Plus, with our 3D printers, users have the option to customize the 3D printer for different qualities and print times. We can go all the way from near-SLA-quality prints with a 0.25-millimeter nozzle up to large and fast prototypes with a 1.2-millimeter nozzle. This is the broadest range in terms of print capabilities—or, at least, print qualities—for any desktop 3D printer available right now. For our test, we used a 0.25 millimeter nozzle and printed a ring designed as jewelry, and it turned out fantastic—it was almost flawless.”

Cast metal parts based on 3D-printed patterns. (Image courtesy of Aleph Objects.)

Post-processing for the 3D-printed patterns involved an X-ACTO knife, 800-grit sandpaper and isopropyl alcohol. A bath in the last ingredient smooths the surface of the part by dissolving some of the filament, in addition to sealing any cavities that could potentially corrupt the casting process. Aleph Objects took their 3D printed patterns to Art Castings of Colorado, where they certainly made an impression. As one employee noted, there was significantly less debris left in the moulds after burnout.

Getting Started with 3D Printing for Investment Casting

Polymaker’s Polycast is the latest addition to Aleph’s filament offerings, adding yet another option to the company’s already diverse repertoire. The roughly three dozen tested filaments have pre-configured profiles available within the Cura software, making it very easy to get fast results.

“We have a comprehensive offering of printers with ways to customize for specific applications,” Beardslee explained. “That enables you to go from high-quality jewelry—rings and earrings—up to large printed patterns, since we have almost a square foot of build volume to work with.” Aleph Objects manufactures two LulzBot 3D Printers: The Mini 2, which has a 160 x 160 x 180 mm (6.3” x 6.3” x 7.1”) build volume; and the TAZ 6, which has a 280 x 280 x 250 mm (11" x 11" x 9.8") build volume.

In regards to investment casting, Beardslee added, “We have created bundles that have everything you need to create 3D printed patterns for metal casting.” Beardslee noted that, in some cases, LulzBot 3D Printers are being used for prototyping cast parts, but there are also users making final 3D-printed products.

“Whether you need parts in steel, stainless steel, aluminum alloy, platinum, gold, silver, or bronze, there’s no limit to that,” he said.

Close-up on cast stainless steel parts based on 3D-printed patterns. (Image courtesy of Aleph Objects.)

While prototyping is the obvious application for 3D printing in investment casting, Beardslee commented that some of Aleph’s customers use the technology as a stopgap, enabling them to begin low-volume manufacturing immediately until they receive the dies for larger production runs. “Whether it be automotive or aerospace or any number of industries—any place that they're currently using cast metal—this shortens that initial ramp to final cast parts for prototype or low volume,” Beardslee said.

One other advantage of this approach that’s worth noting is the relatively low risk involved in trying it. Unlike industrial metal 3D printers, which are easily into the six figures, professional desktop 3D printer bundles such as those from LulzBot range from $1,800 to $3,800, depending on accessories and options. Moreover, the LulzBot bundles are preconfigured to simplify the ease-of-use process.

Ready to take the next step?

Check out this tutorial on how to 3D Print Patterns for Investment Casting.

Aleph Objects Inc. has sponsored this post. All opinions are mine. --Ian Wright