Additive Manufacturing

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Overview

Additive Manufacturing (AM) is a new 3D printing technology utilized to create functional, industrial complex components such as prototypes, tooling and final products. AM’s advantages include the geometrical freedom in design, cost efficiency in production, and ability to use materials that otherwise would be impractical to apply [1].

The 7 Categories of Additive Manufacturing [2]

VAT Photopolymerisation

In Vat polymerisation technique a chamber of liquid photopolymer resin exists, which is used to construct the model layer by layer. To cure or harden the resin, ultraviolet (UV) light is used, after hardening each new layer, the objects are moved downwards. Unlike powder based methods in which the unbound material acts as a support for model, in this process, no structural support is available during the build phase, because the material used is in liquid form. In this case, support structures can be added. In the process of photo polymerisation (Gibson et al., 2010) or UV light treatment, mirrors are used to direct the light across the surface of the resin (Grenda, 2009) and in those spots that resin comes in contact with the light, it cures or hardens.

Material Jetting

Material jetting technique acts like a two-dimensional ink jet printer. In this method material is jetted onto a build platform through a nozzle which moves horizontally across the platform and deposits the material with a continuous or Drop on Demand (DOD) approach. The model is built layer by layer through solidification of deposited material applying ultraviolet (UV) light. Polymers and waxes are appropriate and commonly used materials for this technique because they are viscous materials in nature and can be deposited in drops.

Binder Jetting

In binder jetting technique two materials are used; a powder based material and a binder which acts as a glue between powder layers. So, the binder usually exists in liquid form and the build material in powder form. As print head moves horizontally across the x and y axes of the machine, layers of the build material and the binding material are deposited alternatively. As new layers are added, the printed object goes lower in the platform. This technology is often referred to as 3DP technology. All materials are not suitable for this method and despite the relative speed of printing, additional post processing is time consuming. Unlike this method in other powder based manufacturing methods, the printed object is supported within the powder bed and once completed is easily removable from unbound powder.

Material Extrusion

Fuse deposition modelling (FDM) is a common material extrusion process and is commercialized by the company Stratasys. Material is heated in a nozzle and then deposited layer by layer. The nozzle moves horizontally and after deposition of each new layer the platform moves up and down. It is the main technique used in domestic and hobby 3D printers. Multiple factors in this process determine the quality of final model and this process has great potential as long as these factors are controlled successfully. FDM process likewise all other 3D printing processes uses a similar layer by layer approach, but in this process the material is deposited through a nozzle in a continuous stream with a constant pressure and speed which is necessary to get the accurate results (Gibson et al., 2010). As shown in the diagram material is often added to the machine in spool form.

Powder Bed Fusion

The Powder Bed Fusion (PBF) process includes Direct metal laser sintering (DMLS), Electron beam melting (EBM), Selective heat sintering (SHS), Selective laser melting (SLM) and Selective laser sintering (SLS). In powder bed fusion (PBF) methods laser or electron beam is utilized for melting and fusion of material powder together. Electron beam melting (EBM), methods require a vacuum but is applicable on metals and alloys. In all PBF processes, the powder material is spread over previous layers using either a roller or a blade. In Direct metal laser sintering (DMLS) unlike SLS which uses plastics as raw material, metals are used. The main difference of Selective Heat Sintering with other processes is the way it utilizes the heated thermal print head to fuse powder material together. As before, layers are added with a roller in between fusion of layers.

Sheet Lamination

Sheet lamination processes comprised of ultrasonic additive manufacturing (UAM) and laminated object manufacturing (LOM). In Ultrasonic Additive Manufacturing process, ultrasonic welding is utilized for binding of sheets or ribbons of metal together, however, additional machining is often required after the welding process. Laminated object manufacturing (LOM) constructs models using a similar layer by layer approach, however, in this process paper is used as material and adhesive instead of welding. LOM process utilizes cross hatching method, so the printed object once completed is easily removable. Laminated objects are often used as visual models and are not appropriate for structural use. The metals used in UAM include aluminium, copper, stainless steel and Titanium (Ultrasonic Additive Manufacturing Overview, 2014). The process is low temperature, so internal geometries can be created. The process can attach different materials and since the metal used is not melted, it requires relatively little energy.

Directed Energy Deposition

Directed Energy Deposition (DED) covers a range of terminology: ‘Laser engineered net shaping, directed light fabrication, direct metal deposition, 3D laser cladding’ It is a more complex printing process utilized to repair or add additional material to existing components (Gibson et al., 2010). A typical DED process is similar in principle to material extrusion, but the nozzle is mounted on a multi axis arm and moves in multiple directions. The material is melted upon deposition using laser or electron beam, then it is deposited from any angle. Either polymers or ceramics can be used in this process but it is typically used with metals powder or wires.

Materials Used In 3D Printing and Additive Manufacturing

VAT Photopolymerisation

The Vat polymerisation process uses Plastics and Polymers.

Polymers: UV-curable Photopolymer resin

Resins: Visijet range (3D systems)

Material Jetting

The material jetting process uses polymers and plastics.

Polymers: Polypropylene, HDPE, PS, PMMA, PC, ABS, HIPS, EDP

Binder Jetting

Metals: Steel

Polymers: ABS, PA, PC

Ceramics: Glass

All three types of materials can be used with the binder jetting process.

Material Extrusion

The Material Extrusion process uses polyers and plastics.

Polymers: ABS, Nylon, PC, PC, AB

Powder Bed Fusion

The Powder bed fusion process uses any powder based materials, but common metals and polymers used are:

SHS: Nylon DMLS, SLS, SLM: Stainless Steel, Titainium, Aluminum, Cobalt Chrome, Steel EBM: titanum, Cobalt Chrome, ss, al and Copper (Materials Arcam, 2014).

Sheet Lamination

Effectively any sheet material capable of being rolled. Paper, plastic and some sheet metals.

The most commonly used material is A4 paper.

Directed Energy Deposition

The Electron Beam Melting process uses metals and not polymers or ceramics.

Metals: Cobalt Chrome, Titanium (EBM - Built Materials, 2014).

Available at CAVS

LENS 750

OPTOMEC Laser Engineered Net Shaping (LENS): a Direct Laser Deposition (DLD) additive manufacturing process for metals utilizing blown powder and in situ laser. The LENS has application in cladding and repairing valuable components.

Key Features

• Dual-Camera Monitoring and Control System • 500W, 1kW laser power (Nd:YAG)

• Stratonics ThermaViz® melt pool pyrometer and in-chamber infrared camera

• Stratonics ThermaViz® process control capabilities

• 12in x 12in x 12in build envelope (300mm x 300mm x 300mm)

Fig. 1. Laser Engineered net shaping (LENS)[3].

YouTube [6]

SLM

The AM250 is an external powder reservoir with valve interlocks which allows additional material to be added while the process is running. The reservoir can easily be removed for cleaning purposes or for materials change, utilizing universal silo lift. So, on the AM250 platform, multiple material types can be interchanged conveniently. The powder overflow reservoirs are placed outside the chamber and contain isolation valves which is useful for saving the unused materials which can then be reintroduced to the process via the hopper during the running. The system has a build volume of 250 mm × 250 mm × 300 mm [4].

Fig. N. Selective Laser Melting (SLM)[5].

YouTube [7]

References

  1. [1]
  2. [2]
  3. [3]
  4. [4]
  5. [5]
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