Over the last two years, Metallum3D has been developing a new type of microwave heating process that uses non-resonant, cross-polarized slotted waveguides and a granular susceptor material to evenly distribute microwave energy during processing. Until now, microwave energy has not been successfully used in additive manufacturing applications due to the uneven microwave energy distributions of the current multi-mode resonant technology. Recently, Metallum3D completed the construction of a second-generation microwave furnace that implements non-resonant, cross-polarized slotted waveguides as a microwave energy feeding system. A picture of the microwave furnace is shown below in Figure 1.
Figure 1
The performance of the non-resonant, cross-polarized slotted waveguides used in this microwave furnace has been simulated using the electromagnetic simulation software CST Microwave Studio. The simulations showed that the non-resonant, cross-polarized waveguides generate an electric field with uniform microwave energy distribution. Figure 2 shows a 3D CAD model of the non-resonant, cross-polarized waveguide pair and a simulation of the electric field being generated in free space. The uniform color distribution within the electric field cross-section is indicative of uniform microwave energy distribution.
Figure 2
A separate simulation was conducted to evaluate the performance of the non-resonant, cross-polarized slotted waveguides as mounted in the microwave cavity. Figure 3 shows the simulation of the electric field generated by the non-resonant, cross-polarized waveguides at the mid-section of the microwave cavity. The uniform color distribution within the electric field cross-section is indicative of uniform microwave energy distribution.
Figure 3
A recent validation study completed by Metallum3D utilized cast gypsum plates saturated in a cobalt chloride solution and thermal imaging to map the actual microwave energy distribution of the non-resonant, cross-polarized waveguides under operating conditions. After exposing the plates to a microwave field, the heating of the plates causes a color change in the cobalt chloride that forms a color map of the microwave energy distribution. The visual color map results were cross-validated with thermal imaging.
The Metallum3D microwave furnace uses two sets of waveguides, with each waveguide being directly fed by 1.5 kW magnetrons for a total of 6kW. Figure 4 shows the internal and external waveguide arrangement.
Figure 4
For validation testing, 6 casted plates were vertically loaded into the microwave with the aid of a PVC fixture as shown in Figure 5.
Figure 5
Microwave heating of the plates resulted in a uniform color change of all the plate surfaces from a pinkish-grey color to a bluish-gray color. There was no color banding in any of the plate surfaces indicating homogenous microwave heating throughout the entire microwave cavity volume. The visual results obtained were then cross-validated through thermal imaging, which also showed uniform microwave heating throughout the surfaces of all the plates. The actual microwave energy distribution of the non-resonant, cross-polarized slotted waveguides is in good agreement with the predicted microwave energy distribution previously obtained through electromagnetic simulation. A technical white paper detailing the validation testing and results is available for download at the following link:
Metallum3D Technical White Paper Download
The successful validation of this new type of microwave heating process by Metallum3D is creating new opportunities for processing additively manufactured parts. Our Microwave Furnace is configured for both microwave sintering and microwave digital casting. For microwave sintering, parts are embedded in a granular susceptor material within a microwave transparent and thermally insulating box for rapid microwave sintering, which is up to 90% faster than conventional sintering. A schematic representation of the Metallum3D microwave sintering process is shown in Figure 6.
Figure 6
Microwave Digital Casting is a process that combines additive manufacturing and microwave heating to create a new agile and cost-effective casting process that bypasses the need to pour molten metal into a mold. The first step in the microwave digital casting process is to 3D print a sacrificial ceramic shell mold. The second step is to fill the ceramic shell mold with a metal powder and embed it in our granular susceptor material. The third step is to place the embedded mold in our microwave furnace to melt the metal powder within the mold to form a cast part. Figure 7 shows the basic steps of the Metallum3D Microwave Digital Casting process.
Figure 7
As a result of the successful validation of our new microwave heating process, Metallum3D in conjunction with P3 Additive is launching a Beta Customer Program. Under this program, we are looking to identify 10 customers that have applications that could benefit from implementing our Microwave Sintering or Microwave Digital Casting process. Use the link below to apply to the Beta Customer Program.