additive manufacture

1. Additive Manufacturing (AM) – Definition

Additive Manufacturing is a process of creating three-dimensional (3D) objects by adding material layer by layer, based on digital 3D models (usually CAD).

It is often called 3D printing and contrasts with traditional subtractive manufacturing, where material is removed from a solid block (e.g., milling, turning).

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2. Classification of Additive Manufacturing

According to ISO/ASTM 52900, AM processes are classified into seven main categories:

No Category Example Process

1 Material Extrusion FDM (Fused Deposition Modeling)

2 Vat Photopolymerization SLA (Stereolithography)

3 Binder Jetting Jet Binder Printing

4 Material Jetting PolyJet

5 Powder Bed Fusion SLS (Selective Laser Sintering), SLM

6 Sheet Lamination LOM (Laminated Object Manufacturing)

7 Directed Energy Deposition DED, Laser Metal Deposition

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3. Pre-Processing, Processing, and Post-Processing

Let’s discuss each process:

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A. FDM (Fused Deposition Modeling)

Category: Material Extrusion

a. Pre-Processing

Create 3D model (CAD)

Convert to STL file

Slice the model into layers

Set print parameters (temperature, layer height, infill, speed)

b. Processing

Thermoplastic filament (e.g., PLA, ABS) is heated and extruded through a nozzle

Material is deposited layer by layer on the build platform

c. Post-Processing

Support removal

Sanding, polishing, or acetone vapor smoothing

Painting or coating

🧩 Illustration: 

Advantages

Low cost

Easy operation

Good for prototypes

Disadvantages

Low surface finish

Lower strength (anisotropic layers)

Limited material types

Defects/Problems

Warping

Layer delamination

Stringing

Poor adhesion between layers

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B. SLA (Stereolithography)

Category: Vat Photopolymerization

a. Pre-Processing

CAD modeling and STL conversion

Slicing

Add supports and set laser parameters

b. Processing

UV laser cures liquid photopolymer resin layer by layer

c. Post-Processing

Wash in alcohol to remove uncured resin

UV curing for final hardness

Support removal and surface finishing

🧩 Illustration: 

Advantages

High precision

Excellent surface finish

Good for complex geometries

Disadvantages

Expensive resin

Brittle parts

Limited to photopolymers

Defects/Problems

Overcuring or undercuring

Resin contamination

Curling and shrinkage

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C. Binder Jetting

Category: Binder Jetting

a. Pre-Processing

Create CAD model and slice

Define layer thickness and binder saturation

b. Processing

Powder material (metal, sand, or ceramic) is spread layer by layer

Liquid binder is jetted to join powder particles selectively

c. Post-Processing

Curing or sintering to strengthen parts

Infiltration (e.g., with bronze for metal parts)

Surface finishing

🧩 Illustration: 

Advantages

Fast printing

No heat distortion

Multi-material printing possible

Disadvantages

Weak green parts (before sintering)

Low mechanical strength

Requires post-processing

Defects/Problems

Binder saturation issues

Warping during sintering

Powder spreading inconsistency

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D. Sheet Lamination

Category: Sheet Lamination (e.g., LOM)

a. Pre-Processing

CAD modeling and slicing

Define sheet size and bonding pattern

b. Processing

Sheets (paper, plastic, or metal) are cut and bonded layer by layer

Cutting done by laser or blade

c. Post-Processing

Trimming edges

Surface finishing or coating

🧩 Illustration: 

Advantages

High build speed

Low material cost

Suitable for large parts

Disadvantages

Limited material selection

Rough surface finish

Weak interlayer bonding

Defects/Problems

Delamination

Wrinkling of sheets

Misalignment between layers

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Summary Table

Process Category Material Type Advantages Disadvantages Common Defects

FDM Material Extrusion Thermoplastic filament Low cost, easy to use Low strength, rough surface Warping, delamination

SLA Vat Photopolymerization Liquid resin High accuracy, smooth finish Brittle, costly Shrinkage, overcuring

Binder Jetting Binder Jetting Powder (metal/ceramic/sand) Fast, no heat Weak before sintering Binder unevenness, warping

Sheet Lamination Sheet Lamination Paper/plastic/metal sheets Fast, low cost Poor surface finish Delamination, misalignment

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