Additive Layer Manufacturing:

Current & Future Trends

L.N. Carter, M. M. Attallah, Advanced Materials & Processing Group

Interdisciplinary Research Centre, School of Metallurgy and Materials

Additive Layer Manufacturing?

Three-dimensional

CAD file

Sequence of two-dimensional

slices

Each slice is formed and

bonded to the previous layer

The three-dimensional shape is constructed from

the two-dimensional slices

ALM Refers to a group of techniques where 3-dimensional shapes are constructed by combining 2-dimensional slices of a specific thickness

Additive Layer Manufacturing

Rapid Prototyping Rapid Manufacturing Production of demonstration

components, typically polymers or porous metals

Production of fully dense and functional components

Techniques include:

• Stereolithography

• Selective Laser Sintering (SLS) of Plastics

• 3D Printing

• SLS of metals (with binder: eg. ‘rapidsteel’)

Techniques include:

• Selective Laser Melting (SLM) of metals

• Blown Powder (DLF)

• Electron Beam Deposition (Arcam)

Stereolithography (SLA)

• Developed in the 1980’s • Utilises a vat of UV curable resin and a lowering platform • With each layer the platform is lowered and a layer of resin is spread over the build area • A UV laser selectively cures that ‘slice’ and bonds it to the layer below • The process is repeating, building up a three dimensional shape

Courtesy of Wikipedia

Selective Laser Sintering (SLS) of Plastics • Can produce parts in various materials (typically a Nylon or Wax) • Utilises a bed of powder heated to a temperature below the melting point of the material • A low power IR laser selectively heats and sinters each 2-dimensional slice • A roller lays down each successive layer of powder to build up the shape

Courtesy of Wikipedia

3D Printing • Covers a wide range of technologies where material is delivered via a ‘print head’ • Plastics can be melted and deposited in liquid form, or cured by UV (similar to stereolithography) • Does not require a bed or reservoir of material • Durable acrylic materials can produce functional parts • Easily removed support material allows for mechanisms to be constructed ‘in-situ’

SLM Powder-Bed Fabrication • Selective Laser Melting (SLM) Powder-Bed: An Additive Layer Manufacturing (ALM) Technology for the production of fully dense metallic components - this is achieved through selective melting of each layer and the remelting of the previous layer to ensure good bonding.

Concept Laser M2 • 250mm x 250mm Build Plates • 300mm Max. Build Height • Typical 20µm slice thickness • Variable 200W Fibre Laser • Max. 7000mm/s scan speed • Fixed 150µm dia. Spot Size • Uses metal powder in the size range +15-53µm • Powder handing and processing carried out under argon atmosphere

Argon Gas Atomised Powder

Advantages

•  Eliminates expensive tooling •  Ideal for low-volume batch

•  Reduces the ‘Design to component’ time

•  Promotes ‘Design for functionality’ rather than ‘Design for manufacture’

•  Potential to reduce material waste & material efficiency

•  Produces complex ‘netshape/near-netshape’ components

Limitations •  High capital investment for

equipment (~€ 400k).

•  Potentially high component cost, due to the low deposition rates (10–20 mm3/hour).

•  Requires research for the qualification of specific alloys.

•  Overhanging sections require support structures

•  Current commercial use limited to steels and Ti

SLM Powder-Bed Fabrication

Resources Availability

Support Structures • Overhangs – surfaces overhanging more than 45o generally require supporting

• Offsetting – Typically all components are offset by 5mm of supports from the build plate to allow for poor initial build layers and reduce the build plate heat-sink effect

Why are they needed? • Heat Transfer Route – Building overhangs onto loose powder leaves poor underside surface finish/dimensional accuracy due to large melt pool formation

With Support Without Support

• To Anchor – Thin overhang sections may tend to deform during fabrication, supports hold these in place to avoid build failure

Support Structures

• Lattice like structure made up if single laser-scan walls

• Easily removed as they are attached to the main component by teeth

• Automatically generated by software, although typically require modification to make them appropriate

SLM Projects & Examples

Lightweight & Porous Structures

Aerospace

Biomedical and Dental

Leverhulme Project

A.M.& P. SLM Aims and Activites Establish a manufacturing route for netshape/near-netshape components via the SLM powder-bed route to producing results comparable to traditional methods.

- Mechanical Testing

-Microstructural Characterisation

.. And the variation of these with the process parameters...

- Dimensional accuracy

Direct Laser Fabrication (Blown Powder) • Similar to 3D printing as material is deposited from a nozzle • Metal powder is blown into the focal point of a high power laser • The nozzle is positioned so that the powder can be deposited on a substrate or previously built layers • The process has very high deposition rates and has the ability to repair damaged components • Surface and dimensional accuracy are poor compared with SLM

Trumpf DLF system • 6.5 axis CNC head • 4KW YAG laser • Spot Size 0.2 mm – 6 mm • Glove Box: 1.5mx1mx3m

The Future for SLM • Faster build times, Larger components, Lower residual stresses through:

• Larger build platforms (500mm x 500mm) • Higher power lasers with variable focus (or multiple lasers) • In-situ monitoring and feedback • Heated beds to reduce thermal gradients

The Future for A.M.& P. • Process understanding through:

• Microstructure study • Tomography • Synchrotron examination of residual stresses • Process Modelling

Thank-You for Listening

Mr. Luke Carter – Doctoral Researcher Tel: 0121 414 7882 Email: LNC943@bham.ac.uk