Contribution 2

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Overview

Additive manufacturing (AM) refers to the application of 3D printing to create functional, industrial components including prototypes, tooling and end-use production parts. AM’s advantages include the freedom to produce small batches of intricate parts cost-effectively, as well as the freedom to realize part designs that would not be manufacturable in any other way, and in some cases to use materials that otherwise would be impractical to apply [1].

The 7 Categories of Additive Manufacturing [2]

VAT Photopolymerisation

Vat polymerisation uses a vat of liquid photopolymer resin, out of which the model is constructed layer by layer. An ultraviolet (UV) light is used to cure or harden the resin where required, whilst a platform moves the object being made downwards after each new layer is cured. As the process uses liquid to form objects, there is no structural support from the material during the build phase., unlike powder based methods, where support is given from the unbound material. In this case, support structures will often need to be added. Resins are cured using a process of photo polymerisation (Gibson et al., 2010) or UV light, where the light is directed across the surface of the resin with the use of motor controlled mirrors (Grenda, 2009). Where the resin comes in contact with the light, it cures or hardens.

Material Jetting

Material jetting creates objects in a similar method to a two dimensional ink jet printer. Material is jetted onto a build platform using either a continuous or Drop on Demand (DOD) approach. Material is jetted onto the build surface or platform, where it solidifies and the model is built layer by layer. Material is deposited from a nozzle which moves horizontally across the build platform. Machines vary in complexity and in their methods of controlling the deposition of material. The material layers are then cured or hardened using ultraviolet (UV) light. As material must be deposited in drops, the number of materials available to use is limited. Polymers and waxes are suitable and commonly used materials, due to their viscous nature and ability to form drops.

Binder Jetting

The binder jetting process uses two materials; a powder based material and a binder. The binder acts as an adhesive between powder layers. The binder is usually in liquid form and the build material in powder form. A print head moves horizontally along the x and y axes of the machine and deposits alternating layers of the build material and the binding material. After each layer, the object being printed is lowered on its build platform. Due to the method of binding, the material characteristics are not always suitable for structural parts and despite the relative speed of printing, additional post processing (see below) can add significant time to the overall process. As with other powder based manufacturing methods, the object being printed is self-supported within the powder bed and is removed from the unbound powder once completed. The technology is often referred to as 3DP technology and is copyrighted under this name.

Material Extrusion

Fuse deposition modelling (FDM) is a common material extrusion process and is trademarked by the company Stratasys. Material is drawn through a nozzle, where it is heated and is then deposited layer by layer. The nozzle can move horizontally and a platform moves up and down vertically after each new layer is deposited. It is a commonly used technique used on many inexpensive, domestic and hobby 3D printers. The process has many factors that influence the final model quality but has great potential and viability when these factors are controlled successfully. Whilst FDM is similar to all other 3D printing processes, as it builds layer by layer, it varies in the fact that material is added through a nozzle under constant pressure and in a continuous stream. This pressure must be kept steady and at a constant speed to enable accurate results (Gibson et al., 2010). Material layers can be bonded by temperature control or through the use of chemical agents. Material is often added to the machine in spool form as shown in the diagram.

Powder Bed Fusion

The Powder Bed Fusion process includes the following commonly used printing techniques: Direct metal laser sintering (DMLS), Electron beam melting (EBM), Selective heat sintering (SHS), Selective laser melting (SLM) and Selective laser sintering (SLS). Powder bed fusion (PBF) methods use either a laser or electron beam to melt and fuse material powder together. Electron beam melting (EBM), methods require a vacuum but can be used with metals and alloys in the creation of functional parts. All PBF processes involve the spreading of the powder material over previous layers. There are different mechanisms to enable this, including a roller or a blade. A hopper or a reservoir below of aside the bed provides fresh material supply. Direct metal laser sintering (DMLS) is the same as SLS, but with the use of metals and not plastics. The process sinters the powder, layer by layer. Selective Heat Sintering differs from other processes by way of using a heated thermal print head to fuse powder material together. As before, layers are added with a roller in between fusion of layers. A platform lowers the model accordingly.

Sheet Lamination

Sheet lamination processes include ultrasonic additive manufacturing (UAM) and laminated object manufacturing (LOM). The Ultrasonic Additive Manufacturing process uses sheets or ribbons of metal, which are bound together using ultrasonic welding. The process does require additional cnc machining and removal of the unbound metal, often during the welding process. Laminated object manufacturing (LOM) uses a similar layer by layer approach but uses paper as material and adhesive instead of welding. The LOM process uses a cross hatching method during the printing process to allow for easy removal post build. Laminated objects are often used for aesthetic and visual models and are not suitable for structural use. UAM uses metals and includes aluminium, copper, stainless steel and titanium (Ultrasonic Additive Manufacturing Overview, 2014). The process is low temperature and allows for internal geometries to be created. The process can bond different materials and requires relatively little energy, as the metal is not melted.

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 commonly used to repair or add additional material to existing components (Gibson et al., 2010). A typical DED machine consists of a nozzle mounted on a multi axis arm, which deposits melted material onto the specified surface, where it solidifies. The process is similar in principle to material extrusion, but the nozzle can move in multiple directions and is not fixed to a specific axis. The material, which can be deposited from any angle due to 4 and 5 axis machines, is melted upon deposition with a laser or electron beam. The process can be used with polymers, ceramics but is typically used with metals, in the form of either powder or wire.

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: Stainless 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, Aluminium, 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 that uses blown powder and in situ laser. The LENS can also be used for cladding and repair of precious 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 features an external powder hopper with valve interlocks to allow additional material to be added whilst the process is running. It is possible to remove the hopper for cleaning or to exchange with a secondary hopper for materials change, using the universal silo lift. This means that multiple material types can be interchanged on the AM250 platform with relative ease. The powder overflow containers are outside the chamber and have isolation valves so that unused materials can be sieved and reintroduced to the process via the hopper while the system is 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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