There is often a tendency in media coverage of the AM industry to position additive manufacturing as a game-changing technology that will replace traditional manufacturing processes. Now that the industry has come into its own, it now seems clear that the technology (indeed a game-changer) has been adopted as a complementary process in some key cases. That is, while AM presents its own unique design and direct manufacturing capabilities, it also has extensive integration alongside traditional production methods, such as investment casting, which is proving just as fruitful.
Additive manufacturing pioneer 3D Systems realized the potential of AM in investment casting fairly early on, and it has done well to establish a number of its 3D printing technologies (specifically, Stereolithography and MultiJet Printing) as tools that can offer huge benefits for investment casting production, including making sacrificial patterns with greater design complexity for less time and money and without tooling.
Reinvigorating an ancient manufacturing process
Investment casting, sometimes known as lost wax or shell investment casting, is one of the world’s oldest metal-forming processes. The technique uses a pattern (or master) usually made from wax, which is coated in a ceramic slurry that hardens on top of it. Acting as a sacrificial structure, the original pattern is then melted or burned out of the ceramic shell and molten metal can be poured in to produce a metal part made from any type of metal.
Traditionally, wax casting patterns are made using injection molding, which can not only be time consuming and expensive but can also limit design possibilities. With 3D printing, however, 3D Systems has demonstrated the ability to craft complex patterns in a time- and cost-effective way, significantly streamlining the investment casting process. As an example, the company says that a turbine pattern which could typically take at least five weeks to produce via injection molding and which would incur costs upwards of $20,000 can be 3D printed overnight for only about 10% of the cost.
Primary Value Propositions for 3D Printing in Investment Casting
|Faster turnaround times|
|Geometric design optimization|
|Design flexibility, fast iteration during product development|
|Access to unlimited metal alloys|
QuickCast: printing large, highly accurate investment patterns
Central to AM’s applications for investment casting are two of 3D Systems’ technologies: its SLA-based QuickCast method and its MultiJet Printing. The build style used in QuickCast is mostly hollow and integrates internal hexagonal supports that provide strength to the pattern and facilitate the collapse of the pattern when it undergoes thermal expansion, reducing the risk of the ceramic shell cracking. Developed specifically for investment casting, QuickCast is one of the most popular methods for 3D printing casting patterns and has found applications across the aerospace, medical and defense industries.
Patrick Dunne, Vice President of Advanced Application Development at 3D Systems, tells us how the company’s QuickCast method impacts workflows in these sectors. “The technology is used in production workflows, but primarily for certification workflows,” he says. “In other words, it’s used for parts where you need to certify the functionality of a casting but you don’t want to invest in the tooling to produce the patterns for that casting until you’ve validated and certified your design.”
“It’s mostly 3D printing service bureaus with SLA equipment that supply patterns to investment casting foundries,” he continues. “What we do is we sell our machines to OEMs, to foundries, to service bureaus and we also have our own service bureau that supplies patterns. For very large complex parts, very accurate parts, the go-to is SLA.”
The capacity to 3D print large-scale investment patterns mentioned by Dunne sets 3D Systems apart from other SLA printer manufacturers. For instance, its ProX 950 machine has a build volume of 1500 x 750 x 550 mm (59 x 30 x 22 in). This means that large-scale metal parts—much larger in size than any metal 3D printer currently allows—can be produced using 3D printed sacrificial patterns and investment casting, where segments of the pattern are created and then attached together.
Wax MultiJet Printing for high-resolution quality
3D Systems’ other AM technology for investment casting applications is its Wax MultiJet Printing, which uses an inkjet process to create finely detailed objects from Foundry Wax. Because of higher material and process costs compared to QuickCast and its ability to produce intricate and high-resolution parts, this technique is primarily used for small parts, such as jewelry or dentistry components.
This process enables manufacturers to produce highly detailed and complex parts on a small-scale. Further, the MJP wax systems use a dissolvable support material which makes for an easy, hands-free support removal process, making it possible to prepare a printed pattern for casting without risk of damage.
In one example, Canadian jewelry company Vowsmith—which specializes in customized rings—was able to cut its production and delivery times by 50% by integrating 3D Systems’ ProJet MJP wax 3D printers into its workflow. In a single print, the company was able to produce between 35 and 40 personalized ring patterns, ready for casting.
|Primary 3D Systems Investment Casting Hardware|
|ProX 800 (SLA)||High throughput with highest accuracy and detail|
|ProX 950 (SLA)||Large parts in a single piece|
|ProJet 6000 HD (SLA)||Highest quality in a smaller footprint|
|ProJet MJP 2500W||High-fidelity parts, robust patterns with an office-friendly footprint|
When asked how the emergence of direct metal printing technologies will impact investment casting, Dunne replies that both processes will co-exist, as each presents their own strengths. A particularly notable benefit of investment casting over direct metal printing is material diversity. Specifically, while only a handful of metals are currently suited to metal AM, investment casting offers manufacturers access to almost unlimited alloys, including aluminum, steel, copper, iron, Inconel, titanium and more.
To accommodate this range of casting metals, 3D Systems offers two dedicated QuickCast resins: Accura® CastPro and Accura CastPro AF. The former is well suited for producing patterns that will be replaced with non-reactive metals, such as aluminum, steel, copper. CastPro AF, for its part, is antimony-free, making it suitable for use with reactive metals like titanium. “If you have antinomy in your pattern, it can change the alloy of titanium and can reduce its ductility,” added Dunne. “For titanium casting, there is value in having a version of this material that has the antimony removed.”
For its MJP process, 3D Systems has developed a Wax material which is designed for casting applications. The wax functions as a traditional lost-wax casting material but doesn’t require tooling. Its VisiJet M2 CAST and VisiJet M3 CAST, for example, provide reliable mechanical performance and can be processed quickly and efficiently on 3D System’s MJP Wax 3D printers.
So, while metal AM itself is still better suited for producing parts with complex internal geometries and thin-walled structures, 3D Systems has demonstrated 3D printing’s viability for enhancing even the most traditional manufacturing processes. After thousands of years of investment casting, 3D Systems has suggested that 3D printing might be the key to optimizing the process.
“There are very few production workflows where the 3D printer is the beginning and the end of the story,” said Dunne. “In the vast majority of workflows, the front end consists of traditional steps and the back end is a lot of CNC machining, polishing and traditional techniques as well. 3D printing is a component of the workflow and, from our perspective, it enables very significant capabilities. The primary benefit being speed and the second being the lack of constraints for design optimization.”