Powder Bed  Fusion

 

In metal Additived Manufacturing there are two types  of powder bed fusion. Laser based Powder Bed Fusion (L-PBF) and Electron beam based Powder Bed Fusion (E-PBF). Most Powder Bed Fusion systems are using one or multiple laser (typically Nd:Yag) as an energy source. L-PBF is the most established industrial metal Additive Manufacturing technology with approximately 9000 systems in the global market by 2020.

 

Laser-based energy deposition 

Process Laser-based energy deposition is also known as Laser Cladding or Laser Metal Deposition (LMD)Most of the systems are powder-fed systems so-called blown powder systems.A nozzle also called head is the core component of the system. This head has multiple jets to supply the build material and a shielding gas. The laser beam is guided via anoptic fibre through into the head and laser window is positioned in the centre of the head. The head is mounted in the chuck of a CNC- multi-axis machine or on an industrial robot.This way the head can be moved with constant distance over the work piece. The angle of deposition can be adjusted according to the geometry of the work piece. Shielding gas is released out of the jets to create locally an inert atmosphere in the work area / the heat-affected zone. When the laser is switched on it heats up the work piece locally, the work piece eventually melts and the build material is added to the gas stream. The powder particles heat up when they are injected into the laser beam. The material fully melts and adds to the melt pool. When the head moves the material solidifies and creates a weld track.Another weld track is placed next to the one created previously until the whole work area is covered with a layer of new material. The next layer is applied on top of the previous layer and the part gains thickness.Depending on the machine setup only the head or also the work piece is moved.
This video
shows a TRUMF TRUCELL 3000 system in operation. Head and workpiece are moved simultaneously to create a thread on a tube.Moving head and workpiece is beneficial as it offers more angles for the deposition.

Resolution

The resolution of laser energy deposition systems varies depending on the nozzle/head. This is set by the focus diameter/ spot size and the jets for the material used resulting in different melt pool sizes. Commonly CNC post machining is applied. MaterialsThe materials for laser-based direct energy deposition processes are usually gas atomised metal powders. All kind of metals can be processed as long they can be gas atomised and be welded by laser. Nickel based super alloys, Stainless steels, Tungsten Carbides are just some of the materials most commonly processed.

 

What are common applications?
 

Applications of Laser based Direct Energy Deposition is preferably used for repair processes.However, it can also be used to create entire parts starting on the build plate or hybrid build-ups starting on a pre-cast or pre-machined work piece.Wear resistant coatings One main application is the deposition of wear resistant coatings.Tungsten carbide can be deposited on tips of drilling equipment.Tubes can be coated on a set-up like lace. The workpiece rotates and the head moves along the work piece creating wear-resistant protective layer.Rebuilding of turbine components of gas turbines are oftentimes made of nickel-based alloys.These components are usually created by casting. The casting process can lead to a geometric deviation of the part compared to the nominal model. During the process, the work piece may deform even further ending upwith a more or less individual shaped. This is why hand welding and brazing techniques are oftentimes applied for repair and refurbishment of this parts.Using Laser based Direct Energy Deposition for reconditioning and repair of such kind of components offers several advantages: It allows a repair with the same or a different material as the base material of the component. It can be integrated in an adaptive-machining process, accommodating the individual shape of the parts which have geometrical deviations through the casting process or operation. It reduces the need for high-skilled labour and as well the chance of human error– The build up, as well the post machining can be performed on one machine Near net shape manufacturing Parts can be additively build up close to their final shape.Substractive machining can be applied in a second step on the same machine.
This video from DMG MORISEIKI shows the benefits of such a hybrid process [LINK]

 

Electron beam based Energy Deposition Systems

 

Electron beam based Energy Deposition Systems are usually wire fed.The machine is in a huge vacuum chamber. A nozzle is moved in gantry system.The nozzle is feeding the material in form of wire. An electron gun is mounted pointing towards the wire outlet. The electron gun heats up and melts the substrate.Material is added in wire form. When the head moves a weld track is created.The next weld track is always placed next to the previous track until the substrateis covered with a layer of new material. The next layer made of weld tracks can beapplied and the part grows.High deposition rates makes this process suitable to build up larger structures.Some machines have machine work areas of several square meters.

 

Applications

Near net shape manufacturing for Aviation industry SCIAKY  is a manufacturer of electron-beam based Energy Deposition Systems.Sciaky is calling its’ technology Electron Beam Additive Manufacturing (EBAM).The material is added as a wire and the electron gun has power of up to 40 kilowatts.See here a video how large scaled components are manufactured near net shape.The process offers great advantages compared to conventional CNC machining of large titanium components for aero industry. According to Sciaky the so-called buy-to-fly ratio is for large components up to 50+% percent better compared to traditional manufacturing methods.2017/01/03 Update: Sciaky recently announced that AIRBUS will utilize one of their EBAM 110 systems https://www.aero-mag.com/sciaky-deliver-large-industrial-scale-metal-3d-printer-airbus/

 

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