Additive Manufacturing

Definition

Additive Manufacturing (AM) refers to a process by which digital 3D design data is used to build up a component in layers by depositing material.

Key Concept: "What You See is What You Build Process"

• The process of joining materials to make objects from 3D model data, usually layer by layer
• Commonly known as 3D printing
• "Design for manufacturing to manufacturing for design"
• Manufacturing components with virtually no geometric limitations or tools
• Distinguished from traditional subtractive machining techniques

Additive Manufacturing vs 3D Printing

• In the industry, the two terms are used interchangeably
• AM is the broader and more all-inclusive term
• AM is commonly associated with industrial applications, like the fabrication of functional prototypes
• AM also involves end-use applications like the mass production of components
• 3D printing is a process of building an object one thin layer at a time. It is fundamentally additive rather than subtractive in nature

Functional Principle

The AM process follows these steps:

1. System starts by applying a thin layer of powder material to the building platform
2. A powerful heat source (laser beam) then fuses the powder at exactly the points defined by the computer-generated component design data
3. Platform is lowered and another layer of powder is applied
4. Material is fused again to bond with the layer below at the predefined points

Process Flow

3D CAD Model → STL File → Sliced Layers & Tool Path → 3D Printer → 3D Object

Advantages of Additive Manufacturing

1. Complicated geometries which cannot be created by conventional processes can be easily produced with AM
2. Reduces the lead time of manufacturing products
3. Saves on Energy and Costs
4. Can handle various types of materials including metals, polymers, wax and ceramics
5. Ease of material change
6. Capability of manufacturing near net shape components
7. Less material wastage
8. Easy to change or revise versions of a product

Challenges in Additive Manufacturing

1. Availability of suitable materials remains one of the biggest challenges
2. Integrity of prototypes
3. Certification is required to ensure that AM products meet the same standards as traditional methods
4. The most significant barrier to AM adoption is the current skills gap
5. Post processing and post curing challenges
6. Low material strength of the developed components
7. High cost of production and materials

Additive vs Subtractive Manufacturing

Comparison factors:

• Part Complexity: AM excels at complex geometries
• Material: Different material options
• Speed: Varies by process
• Part Quantity: Different optimal ranges
• Cost: Different cost structures

Steps in AM Process

1. CAD - Create 3D model
2. STL convert - Convert to STL format
3. File transfer to machine - Send to AM system
4. Machine setup - Configure parameters
5. Build - Layer-by-layer fabrication
6. Remove - Extract from build platform
7. Post-process - Finishing operations
8. Application - Final use

Evolution of Additive Manufacturing

AM Applications Timeline

• 1988-1994: Rapid prototyping
• 1994: Rapid casting
• 1995: Rapid tooling
• 2001: AM for automotive
• 2004: Aerospace (polymers)
• 2005: Medical (polymer jigs and guides)
• 2009: Medical implants (metals)
• 2011: Aerospace (metals)
• 2013-2016: Nano-manufacturing
• 2013-2017: Architecture
• 2013-2018: Biomedical implants
• 2013-2022: In situ bio-manufacturing
• 2013-2032: Full body organs

Applications of AM Techniques

Current and Potential Industries:

• Aerospace: Complex components, lightweight structures
• Automotive: Prototypes, custom parts
• Medical/Dental: Implants, surgical devices/aids, prosthetics/orthotics
• Jewelry: Custom designs
• Tool/mold making: Manufacturing tooling
• Electronics: Circuit boards, components
• Armaments: Military applications
• Specialty food: Custom food products
• Furniture: Custom designs
• Sports equipment: Performance gear
• Toys/collectables: Custom products
• Textiles: Fabric structures

Future: Home Manufacturing

Potential for customization:

• Bristle hardness
• Colour
• Handle style and shape
• Recycling old products into new ones using home 3D printers

Difference Between Various AM Techniques

AM techniques differ in:

• Techniques used for creating layers
• Techniques of bonding the layers together
• Speed
• Layer thickness
• Range of materials
• Accuracy
• Cost

Classification of Additive Manufacturing

Main Categories:

1. Vat Photopolymerization
2. Powder Based Fusion (PBF)
3. Material Jetting
4. Binder Jetting
5. Material Extrusion
6. Sheet Lamination
7. Direct Energy Deposition

AM Techniques in Detail

1. Vat Photopolymerization/Stereolithography

Process:

• Laser beam traces a cross-section of the part pattern on the surface of liquid resin
• Platform descends
• A resin-filled blade sweeps across the cross section of the part, re-coating it with fresh material
• Immersed in a chemical bath
• Stereolithography requires the use of supporting structures

Key Features:

• Uses photosensitive resin
• UV or laser curing
• High accuracy and surface finish

2. Material Jetting

"Drop on demand method"

Process:

• Print head is positioned above build platform
• Material is deposited from a nozzle which moves horizontally across the build platform
• Material layers are then cured or hardened using ultraviolet (UV) light
• Droplets of material solidify and make up the first layer
• Platform descends
• Good accuracy and surface finishes

Advantages:

• High precision
• Multiple materials possible
• Good surface finish

3. Binder Jetting

Process:

• A glue or binder is jetted from an inkjet style print head
• Roller spreads a new layer of powder on top of the previous layer
• The subsequent layer is then printed and is stitched to the previous layer by the jetted binder
• The remaining loose powder in the bed supports overhanging structures

Key Features:

• No heat required during build
• Fast process
• Supports complex geometries naturally

4. Material Extrusion/FDM

Fuse Deposition Modelling (FDM)

Process:

• Material is drawn through a nozzle, where it is heated and is then deposited layer by layer
• First layer is built as nozzle deposits material where required onto the cross sectional area
• The following layers are added on top of previous layers
• Layers are fused together upon deposition as the material is in a melted state

Key Features:

• Uses thermoplastic filament
• Most common desktop 3D printing method
• Requires support material for overhangs

5. Powder Bed Fusion

Includes:

• Selective Laser Sintering (SLS)
• Selective Laser Melting (SLM)
• Electron Beam Melting (EBM)

No support structures required

Process:

1. A layer, typically 0.1mm thick of material, is spread over the build platform
2. The SLS machine preheats the bulk powder material in the powder bed
3. A laser fuses the first layer
4. A new layer of powder is spread
5. Further layers or cross sections are fused and added
6. The process repeats until the entire model is created

Key Features:

• Powder supports the part during build
• Suitable for metals and polymers
• High strength parts
• Complex geometries possible

6. Sheet Lamination

Process:

1. Metal sheets are used
2. Laser beam cuts the contour of each layer
3. Glue activated by hot rollers
4. The material is positioned in place on the cutting bed
5. The material is bonded in place, over the previous layer, using the adhesive
6. The required shape is then cut from the layer, by laser or knife
7. The next layer is added

Key Features:

• Uses sheet material
• Layer-by-layer bonding
• Laser or knife cutting

7. Directed Energy Deposition

Process:

1. Consists of a nozzle mounted on a multi-axis arm
2. Nozzle can move in multiple directions
3. Material is melted upon deposition with a laser, electron beam or arc
4. A 4 or 5 axis arm with nozzle moves around a fixed object
5. Material is deposited from the nozzle onto existing surfaces of the object
6. Material is either provided in wire or powder form
7. Material is melted using a laser, electron beam or plasma arc upon deposition
8. Further material is added layer by layer and solidifies, creating or repairing new material features on the existing object

Applications:

• Repair of existing parts
• Adding features to existing components
• Hybrid manufacturing

Material Classification for AM

Four Main Categories:

1. Polymers
2. Metals
3. Ceramics
4. Composites

Polymers

• ABS polymer
• Acrylics
• Cellulose
• Nylon
• Polycarbonate
• Thermoplastic polyester
• Polyethylene
• Polypropylene
• Polyvinylchloride

Metals

• Pure metals: Ti, Ni, etc.
• Alloys:
  • Ti-based
  • Ni-based
  • Fe-based
  • Al-based
  • Co-based
  • Cu-based

Ceramics

• Various ceramic materials for high-temperature applications

Composites

• Combination of materials for enhanced properties