2.5 Molten Material-Addition Processes

EBM wire process architecture

The Electron Beam Melting wire process is used to melt metal wire feedstock with an EBM gun that discharges directly in the melt weld pool. This entire process takes place inside of a vacuum chamber. The resultant weld pool is approximately 3/8” wide and must be machined after being fabricating. Gross deposition rates range from 7 to 25 lbs. of metal per hour depending on the specific metal selected. The EBM wire process machines are quite large, existing machines scaling to 19ft x 4ft x 4ft, and the process is not size constrained. After feature deposition on the build plate substrate, the resulting structure is stress relieved and machined to the final shape.

Relative to traditional hog-out machined parts, the advantage of using EBM wire to construct parts includes:

• Less material wasted during fabrication
• Less processing time incurred during fabrication

The typical machine architecture consists of the following:

• Wire Feed
• Electron Beam Gun
• 3 Axis Gantry
• Vacuum Chamber
• Build Plate Substrate
• Melt Pool Closed Loop Control Optical Feedback System
• Computer / HMI

DED blown powder process architecture

DED blown powder process architecture is defined as an additive manufacturing process in which a laser source, attached to a gantry, melts a weld pool from a feedstock of free-flowing powder typically being discharged from a coaxial deposition head. In addition to constructing freeform geometry, DED blown powder is often used as a weld repair cladding process to efficiently laser weld cracked surfaces on various metallic structures. This entire process takes place inside of an Argon filled low pressure chamber. The resultant weld pool can range from .065” - .100” wide and exhibits a rough surface similar to a casting. The DED blown powder process machines can range in scale and capability. Some of the larger machines commercially available displays a build volume of up to 5ft x 5ft x 7ft. Hybrid DED blown powder machines are also commercially available. These machines have the ability to build layer by layer similar to a traditional AM machine, but also include the ability to stop between deposition and machine away the previously deposited surface, thereby leaving a very smooth surface finish.

The basic machine architecture consists of the following:

• Powder Feed Mechanism
• Deposition Head
• Laser
• 3 Axis or 5 Axis Gantry System with Articulating Table
• Argon chamber
• Baseplate Substrate
• Optional Mill Cutting System for Hybrid Machines
• Computer / HMI

DED wire fed process architecture

DED wire fed process architecture is defined as an additive manufacturing process in which a plasma arc discharging from a deposition head is attached to a gantry. This melts a weld pool from a feedstock of welding wire typically being fed from the side of the deposition head. This entire process takes place inside of an argon filled low pressure chamber or alternatively, shielded gas provides the appropriate environment to retard oxidization. The resultant weld pool can range from .125”-.250” wide and exhibits a rough surface similar to the EBM wire fed process. The DED wire fed process machines can range in scale and capability. Some of the larger machines commercially available exhibit a build volume of up to 6ft x 1.25ft x 2ft.

The basic machine architecture consists of the following:

• Wire Feed Mechanism
• Deposition Head
• Optional Pre-heat head
• 3 Axis or Gantry System
• Argon chamber or gas shielded deposition head
• Baseplate Substrate
• Optional Mill Cutting System for Hybrid Machines
• Computer / HMI

Material Delivery System

Metallic welding wire is fed through a series of pinch rollers to a deposition head, where a plasma arc flows the molten metal onto the surface of the workpiece. As with all AM systems, layers of newly deposited material are placed on top of previously deposited layers, thereby building up structure.

Energy Source

Similar to traditional welding, DED wire fed processes use a plasma arc energy source to deposit the material. Specifications for each plasma deposition head may vary between 50 to 350 amps and voltage from 27 to 31 volts. On some systems two multiple plasma arc heads are used. One head for preheating the baseplate substrate, while the other head is used for material deposition. This approach limits the amount of distortion of the baseplate during part fabrication. Similar to DED blown powder, the DED wire fed process is easily capable to scaling to much larger sizes and the amount of plasma arc heads will scale in relation to the machine sizing.

Metal Welding Wire Feedstock

Much more cost effective than powder based additive manufacturing technologies, the welding wire used in DED wire fed processes reduces production costs substantially. Commercial grade off the shelf welding wire may be used which can vary in diameter from .025”-.120” and price based on the material type.

Typical materials used in DED wire fed machines include:

• Steel
• Titanium

Small scale polymer material extrusion process architecture

One of the most common desktop AM technologies, small scale polymer material extrusion machines are available in very small scale for hobbyists (4” x 4” x 6”), and larger scale (39” x 39” x 39”) for industrial applications, and a range of sizes in between. Also known as Fused Deposition Modeling (FDM), this technology uses amorphous polymer filament as a feedstock. The feedstock is liquified in a deposition head which moves in the x-y plane, depositing the polymer material. The part is built upon a table that moves in a z direction. Variant machines also exist that allow for the build plate to move in y axis and the deposition head to move in the x and z axis.

The basic machine architecture consists of the following:

• Material Feeder
• Heated Head/Nozzle
• Build Platform and Motion System
• Build Plate
• Computer / HMI

Large scale polymer material extrusion process architecture

Large scale polymer material extrusion machines are available exclusively for industrial applications. Also known as big area additive manufacturing, these machines represent a very scaled up version of the small-scale polymer extrusion machines. These are enormous systems had originally been designed for laser/plasma cutting applications and retrofitted with a deposition head to create large AM machines. This technology uses polymer injection molding pellets as a feedstock as it is less expensive to scale to larger sizes relative to filament. The feedstock is liquified by a heated screw in a deposition head which moves in the x-y plane, depositing the polymer material. The part is built upon a table that moves in a z direction. Deposition rates of 80 pounds of material per hour are attained on a build workpieces as large as 240” x 90” x 72”.