Learning Objectives
By the end of this section, students will be able to:
- Understand EBM wire technology.
- Comprehend DED blown powder technology.
- Grasp the concept of DED wire fed technology.
- Realize both large and small scale polymer material extrusion.
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
Material Delivery System
The material delivery system consists of a mechanism that feeds common welding wire feedstock through a feeding system. Similar to traditional welding systems, the feed system is installed at an angle to provide the optimum material fusion upon electron beam welding
Energy Source
An electron beam gun is used to provide the energy to the workpiece. The electron beam gun used in this process uses a high powered laser, ranging up to 42kW. Coupled with the feedstock, this energy creates a weld pool on the surface of the workpiece.
Metal Wire Feedstock
Example wire materials that are used in this process include:
- Titanium
- Inconel
- Tantalum
- Tungsten
- Stainless Steel
- 4340 Steel
- Aluminum
- Zircalloy
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
Material Delivery System
Metallic powder is pressurized through a series of tubes to a coaxial deposition head, where a stream of powder is evenly distributed onto the surface of the workpiece. Only about 25% of the feedstock is melted during the deposition process, with the remaining 75% of material being recycled.
A unique aspect of the DED blown powder process is the ability to include multiple powder feedstocks at different rates into the deposition head, thereby creating a functionally gradient weld system within a part.
Energy Source
DED blown powder processes use a solid state IPG laser system. Smaller systems contain 2-3kW lasers, where some of the larger machines can showcase up to 4kW laser systems. The DED blown powder process are easily capable to scaling to much larger sizes and laser wattages will scale in relation to the machine sizing.
Metal Powder Feedstock
Like all powder based additive manufacturing technologies, the particle size distribution, morphology and flowability are key variables in maintaining a quality powder. Compared to laser powder bed material and EBM, the optimum particle size distribution range for DED blown powder is much coarser and is typically between 20-200μm.
Typical materials used in DED blown powder machines include:
- Nickel Alloys
- Cobalt Chrome
- Stainless Steel
- Titanium
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
Delivery Systems
Polymer filament is pulled from a spool of material through a series of pinch rollers and pushed into a liquefier head, where it is melted. Material oozes out of the tip of the head and belted stepper motors drive a linear x-y motion, thereby depositing a small contour of material in a selective manner.
Energy Sources
Electrical resistance in heating elements provide the energy to melt the polymer filament. The heating elements are embedded in the deposition head around the liquification tip. Before the process begins, the deposition tip must warm to a temperature just above the melting temperature of the filament, but not too high that it burns the filament leaving behind carbon buildup deposits.
Material
A wide variety of polymers are available to be processed using small scale polymer extrusion. Typically, because of the relatively large melt range, amorphous polymers tend to be more compatible with small scale polymer extrusion than semi-crystalline. Though semi-crystalline Nylon and PEKK materials have started to become available recently. The following list provides an idea of the type of polymers compatible with small scale extrusion technology:
- PLA
- ABS
- PC
- PEI
- PPSF
- PEKK
- PA
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”.
Delivery Systems
Polymer pellets are stored in an air dryer system to ensure little humidity effect on the pelletized polymers. The pellets are sourced from injection molding polymer suppliers. Once dried to a desired relative humidity level, the pelletized resin is transferred through air handler lines to the injection screw. Material oozes out of the tip of the screw head and linear motors drive the large gantry up and down the part build area, thereby depositing a large contour of material in a selective manner. Various extrusion die nozzle diameters are available from .200”, .300” and .400” to adjust to specific part application feature sizes.
Energy Sources
The screw head is heated and spins to create a compressive shearing effect on the pelletized polymer resin which liquifies the material for deposition. The spin rate, shape and pitch of the screw threads are adjusted depending on the material being extruded. For example, it is not uncommon to have an optimized screw for use with ABS and a different screw shape for PPS.
Material
Most common injection molding materials are used for large scale polymer extrusion. These would include:
- PEI
- PPS
- PC
- PLA
- ABS
- Carbon filled ABS
- TPU