Watch: Metal 3D printing process promises faster production at lower cost

A new metal 3D printing process promises faster production speeds and lower costs than competing metal additive manufacturing processes. The technology, known as joule printing, uses a process similar to resistance welding. A wire is positioned and melted by resistive heating to enable rapid metal deposition.

Joule printing is ideal for fabricating small parts that range in size from a baseball to a beach ball and works with any metal, including difficult-to-cut metals like titanium, H13 tool steel and P20 tool steel.

Figure 1: Joule printing enables rapid metal 3D printing by positioning and melting a wire in one step through resistive heating. Source: Digital Alloys

Figure 1: Joule printing enables rapid metal 3D printing by positioning and melting a wire in one step through resistive heating. Source: Digital Alloys

With no post-processing, the technology produces fully dense parts with almost no porosity (e.g., greater than 99.5% dense), with tensile strengths equivalent to wrought metal and stronger than castings. The first joule printing system delivers material at a rate of 5 to 10 kg/h (11 to 22 lb/h) to while consuming less than 1 kWh/kg.

Process

The joule printing process involves the continuous feeding of a wire with a tip placed in contact with the targeted printing location. Melting of the wire tip and fusion between adjacent metal is accomplished — much like in resistance welding — by resistive heating caused by current sent through a circuit consisting of the wire, part and print bed. As the wire melts, the print head moves along a programmed path, depositing a continuous bead of metal that fuses with neighboring material to build the part layer-by-layer.

The wire is melted by joule heating, also known as resistive heating or ohmic heating, a process by which heat is generated due to the resistance of a conductor to electric current; it is the same heating process used in electric water heaters and toasters. Joule heating occurs within the wire as a result of the energy transfer that occurs as conduction electrons collide with the wire’s metal atoms. These resistive losses quickly produce heat, which melts the wire rapidly allowing fast print head movement.

Advantages

The simultaneous placement and melting of the wire reduces processing time and variability and lowers production costs compared to other metal additive manufacturing processes like binder jetting and laser or electron-beam powder bed fusion. Joule printing’s advantages over these alternatives include the elimination of multiple process steps such as powder spreading, binder deposition and post-process sintering.

The joule printer’s precision wire feed, positioning and electrical system is managed by a closed-loop control system that receives real-time voxel-level process data feedback. The system measures and controls the volume of metal delivered to the melt pool as well as the supplied current and voltage. The voxel-level process data is also recorded for later use in machine learning analysis for non-destructive quality assurance.

Digital Alloys

Joule printing is a development of 3D printing company Digital Alloys based in Burlington, Massachusetts. The startup has received funding via investments from welding equipment manufacturer Lincoln Electric and aerospace giant Boeing through its HorizonX Ventures funding program.

The company currently provides a parts manufacturing service to the aerospace, automotive, consumer and oil and gas industries and expects to begin delivery of printers to customers by the end of 2020.