SLA prototype part on the left and investment cast part on the right

Rapid Prototyping Using Additive Manufacturing and Investment Casting

For years, rapid prototypes have been quickly and efficiently produced using additive manufacturing (AM) combined with investment casting. Additive manufacturing allows investment casting foundries to skip the expensive process of machining injection-molding tools for wax patterns. Instead, master patterns are produced using 3D printing, saving time and cost. But, while it began as a way to rapidly produce a part to allow engineers to iterate their designs faster, the 3D printing of patterns has created digital investment casting foundries allowing for much greater freedom in the design of complex metal components.

The so-called “tool-less” pattern creation has opened up various applications and development cycles that were previously too cost-prohibitive. Because of the time and cost savings provided by AM – produced patterns, aerospace companies are adopting faster and more aggressive engineering cycles. Traditionally, the lead time for a CNC-machined, metal injection tool for a wax pattern is up to two weeks; however, with the use of 3D printing the patterns can be done in days or even hours. Not only does this drastic increase in speed allow suppliers to deliver products faster but, it enables engineers to iterate their designs faster – ensuring the final designs will perform more reliably.

Rapid Prototype Investment Casting- How It’s Done

Thanks to advanced software, hardware, and materials, foundries can proceed directly from the CAD to the 3D printed pattern. Highly accurate master patterns are built in a matter of hours or days with Stereolithography (SLA) technology which offers excellent internal structures, thin walls, surface finish.

  1. Patterns are built with a honeycomb, hollow structure and thin walls, creating a durable pattern with complete internal draining and ideal final surface sealing. 
  2. After the SLA pieces are built, complete drainage of uncured liquid material is key to complete pattern burnout and reducing residual ash. Made from photopolymers developed specifically for investment casting, the patterns are expertly sealed and leak-checked for surface cracks that could cause substandard castings. 
  3. After receiving quality approval, the SLA patterns are secured to a central wax bar with gates, called a sprue, and robotically dipped in ceramic slurry and refractory grain silica to form a mold.
  4. After the shell mold dries, it is typically flash-fired in a furnace to sinter the mold and” burn-out” the Investment Casting Pattern from the shell, leaving a negative impression of the casted part.  
  5. The mold is preheated prior to pouring in the molten metal using gravity, pressure, vacuum, or centrifugal force.
  6. The ceramic shell is removed from the solid metal through mechanical vibration, chemical cleaning, or water blasting depending on the particular metal used.
  7. The original parts are now cut from the sprue and gates and ground smooth so that they are ready for additional processes.
  8. Final inspection is performed on each part to assure dimensional accuracy, material density, and other mechanical properties dependent on their final use.

Additive Manufacturing – Produced Patterns Provide Plethora of New Possibilities

Investment casting is a reliable manufacturing process that produces intricate parts and components not achievable with any other metal forming process. In addition, the 3D printing of casting patterns allows for the fast production of prototypes and complex production parts in virtually any metal. No longer limited to the shapes that can be produced using a CNC machine, designers and engineers now create a wide variety of new designs.

Turn expensive fabrications into less costly higher-quality castings.

By using AM – produced casting patterns, engineers can turn fabrications assembled with multiple parts into complex and lightweight one-piece castings. This part consolidation technique significantly reduces cost and lead-times while increasing component strength and quality.

Three Major Rapid Prototyping Processes

There are essentially three main types of 3D rapid prototyping processes. These include Stereolithography (SLA), Fused Deposition Modeling (FDM), and Selective Laser Sintering (SLS).

Stereolithography (SLA)

The SLA process uses a computer-controlled laser to cure resin to build a prototype or part one layer at a time. SLA was the first successful adoption of additive printing (3D printing) on a commercial scale. At the time of its introduction, it was considered the fastest and most affordable option for rapid prototyping. It is still the most preferred process for investment casting because it is friendly to the flash-fire pattern removal process. In addition, SLA patterns are rigid, dimensionally stable and accurate.

Fused Deposition Modeling (FDM)

FDM is a process where thermoplastic filaments are melted within a nozzle and deposited in layers to build a part. While FDM is sometimes associated with the everyday hobbyist, it has several industrial rapid prototype applications that help companies make fast and inexpensive parts.

Selective Laser Melting (SLS)

SLS is highly valued for its ability to make complex geometries out of metals such as aluminum, steel, titanium, tantalum, and cobalt. The process involves fusing the metal powder layer upon layer to build the prototype. The result is a solid and durable prototype.

Selecting a Rapid Prototyping Technique

Selecting a rapid prototype investment casting technique comes down to understanding the advantages and disadvantages of each process.

SLA produces parts with an excellent surface finish at a reasonable price. It’s an established process with a long history of success and multiple materials to choose from.

FDM is the most affordable among the three listed in this article. The process can be used to make complex shapes using plastics such as polycarbonate, acrylonitrile butadiene styrene (ABS), or a combination of the two. However, the surface finish is not as even or clean compared to the other processes, and the parts are nowhere near as strong. FDM provides an excellent visual presentation of the finished part, but is unsuited for strenuous testing.

Finally, SLS produces more durable and robust components than other processes, which means that prototypes can easily endure several tests. Although it’s more expensive than the alternatives, SLS is a highly accurate process. One disadvantage is that parts produced via SLS can sometimes have porosity issues while also being somewhat brittle.

Request Rapid Prototype Investment Castings from Barron Industries

With the right techniques, rapid prototyping can help you reduce product defects, lower production costs, and improve lead time. If you have questions about rapid prototyping or need help finding a solution for your component, reach out to our team at Barron Industries. We’re an AS9100 D and NADCAP™ accredited manufacturer with rapid prototype investment casting capabilities. We can even produce prototypes in as little as 10 days.

Contact us today to schedule a consultation with one of our experts.