3D Printing - An Overview

What is 3D printing?

3D printing has revolutionised and democratised manufacturing. From complex designs and the bioprinting of human tissues to affordable housing and on-demand manufacturing, the technology is at the forefront of defining what people can build and share.

3D printing, also called additive manufacturing, is a process of making three dimensional solid objects from a Computer-Aided Design (CAD) digital file. It started out in the 1980s as a tool for rapid prototyping, but it has evolved over time to have many applications, such as bioprinting living tissues, speeding up affordable housing, creating custom prosthetics and the decentralised manufacturing of critical and complex components for various industries. This has become possible thanks to increased precision and the availability of a wide range of materials, such as metals, ceramics and various polymers, that can be used in the printing process.

How is a 3D object created?

A 3D printed object is created using additive processes, in which material is deposited, joined or solidified using various techniques. The object is built by laying down successive layers of material under automated control and then solidifying or curing each layer into the required shape using energy sources such as UV light, plasma arcs and heat. Each layer can be thought of as a thinly sliced horizontal cross section of the final object.

The process starts by creating a 3D model and then using slicing software to cut it into layers and individual units called voxels, which are fed into the 3D printer.

The 3D model can be created using CAD software, or by using a simple phone camera together with photogrammetry techniques. The CAD route gives greater precision. Real objects can also be captured using 3D scanners and then corrected for errors such as holes, noise or intersections using CAD software for greater accuracy.

Not all 3D printers use the same technology. There are several ways to print, and all of them are additive. They differ mainly in the way the layers are built to create the final object. Some methods, for example, use melting or softening of material to produce the layers.

The processes of 3D printing

The American Society for Testing and Materials (ASTM) classifies the 3D printing process into the following seven categories.

1. Vat polymerisation

This process involves solidifying a photopolymer resin using an ultraviolet (UV) light source. The following three methods use vat polymerisation:

• Stereolithography (SLA): This method cures photopolymer resin one layer at a time using UV light and galvanometers. The process is repeated on successive layers by moving point to point across the surface of the polymer and fusing it together. It often requires support structures.
• Digital Light Processing (DLP): DLP is the sister technology to stereolithography. It uses arc lamps instead of UV lasers and exposes the whole surface at once. This key difference makes it faster than stereolithography. Its performance is limited by the quality of the lamp, and curved surfaces of the print are often a little boxy, though they can be smoothed out by sanding.
• Continuous Liquid Interface Production (CLIP): This process uses oxygen-permeable optics and heat programmable materials that have a higher Young's Modulus and are truly isotropic. The products formed are engineering grade and not as brittle as those made by other polymerisation methods. The heart of the process is a so-called dead zone, which allows curing of material only above it and maintains a continuous liquid interface, avoiding the peeling step that is built into many resin-based printers.

2. Material jetting

In this process, the material is applied through a nozzle, similar to inkjet print heads, onto a platform and then hardened by UV light.

3. Binder jetting

This process uses a powder base material and a liquid binder, which is applied to the powder using a nozzle to glue it into the required shape. The powder that has not been bound can be reused to print again.

4. Material extrusion

This process is also referred to as Fused Deposition Modelling. A plastic filament is passed through a heated nozzle and extruded into the desired shape using a controlled mechanism. The nozzle can move in 3D space and is not limited to building strictly by flat layering.

5. Powder bed fusion

This technique is similar to binder jetting and uses a powder-based material, with small variations in the way the material is cured, such as:

• Selective Laser Sintering (SLS): The powder material is fused together using a laser, and the bed is lowered step by step to allow curing of the material above.
• Multi Jet Fusion (MJF): This method was developed by Hewlett Packard and uses multiple inkjets that fuse the material selectively. The object is then heated, causing agents to react and creating isotropic, rigid products.
• Direct Metal Laser Sintering (DMLS): This method uses a metal powder instead, and the process is similar to SLS.

6. Sheet lamination

Sheets of materials such as metals, paper or polymer are welded together using ultrasonic waves and then milled into the proper shape using CNC machines.

7. Directed energy deposition

This process uses a multi-axial robotic nozzle that deposits metal powder or wire onto a surface, which is then exposed to an energy source such as a plasma arc or laser beam to melt and then solidify it into the desired shape.

Applications of 3D printing

3D printing has many applications across industries.

Low volume production

It is especially useful for industries where complex parts are produced in low volumes, which reduces the need to invest in expensive tooling. This makes it an ideal choice for original equipment manufacturers (OEMs), particularly in the aerospace and defence industry.

Lightweight parts

3D printing allows the manufacture of hollow designs without compromising structural integrity, so it is useful in the automotive and aerospace industries. Lighter parts help save fuel, which in turn reduces carbon emissions and pollution.

Less waste

Because 3D printing is additive and builds objects layer by layer, it produces less waste of material. Unused material can often be reused and recycled easily.

Complex consolidation

3D printing also allows several components to be integrated into a single functional unit, which simplifies the manufacturing process.

Maintenance and repair

Processes such as Directed Energy Deposition help repair high-end equipment in the military and aerospace sectors by adding material to broken or worn out parts.

Electronics 3D printing

Creating complex circuit boards and antennas is a newer use case that can speed up product development and possibly bring innovation to the nanotechnology industry.

Design flexibility

Testing and making quick design changes gives designers the flexibility to innovate and modify parts in a fraction of the time.

Superior medical devices and personal healthcare

Patients can now have customised and specific medical devices, such as prosthetics and implants, made to fit them exactly.

What is 4D printing?

4D printing is advanced 3D printing that uses programmable materials, such as hydrogels and cellulose composites, and designs that change shape when they interact with conditions such as temperature and humidity. It is also called active origami or a shape morphing system.

It has possible applications in medicine, transport and conductivity, to name a few.

Impact of 3D printing

The points below highlight the larger factors that shape the future of 3D printing, and how the technology affects those same factors in return.

Political: Because 3D printing is an easily accessible and decentralised form of manufacturing, governments around the world will want to regulate its use. 3D printing can be used to make functional weapons without a licence, and it could be used by terrorists and insurgents to design undetectable weapons. It also raises concerns about the unregulated use of intellectual property to make functional products, so governments will need to set legal limits on the use of 3D printing in order to protect patents.

Socio-economic: 3D printing gives a push to the do-it-yourself culture and makes mass personalisation a reality. It will affect the manufacturing and distribution of small products across several industries, leading to the loss of some traditional jobs while at the same time creating new opportunities for 3D designers. It may also change relations in the wage-labour society by de-skilling some work and reducing the bargaining power of labour. On the positive side, it can bring down transport costs and reduce the carbon footprint of production, while promoting decentralisation. Some also worry it could weaken social interaction and cohesion as home ownership of 3D printers becomes common.

Why it still matters

3D printing is no longer just a lab or hobby idea. It is quietly changing how India builds things, and some of the clearest recent examples come from science that students can follow in the news.

On 30 May 2024, an Indian space start-up called Agnikul Cosmos launched a rocket named Agnibaan SOrTeD from Sriharikota. What made it a genuine world first was its engine, Agnilet, the first rocket engine built as a single piece using 3D printing rather than being assembled from many separate parts. Printing the engine in one piece removes hundreds of joints, and fewer joints means fewer places that can leak or fail. Agnikul grew out of IIT Madras, so this is exactly the kind of frontier that young Indian engineers are working on today.

3D printing has also stepped out of the factory and onto the street. In August 2023, India opened its first 3D printed post office in Bengaluru. A construction machine squeezed out layer upon layer of special concrete, much like the material extrusion method described above, and finished the roughly 1,000 square foot building in about 44 days, at around 40 percent less cost than conventional construction. It is the same layer by layer idea from these notes, simply scaled up to the size of a building.

These stories show why the process categories you have just read about matter: the choice of method decides whether you can print a rocket engine, a house or a prosthetic hand. If you want to go deeper into how technologies like this shape the world, explore the Learnacy Hub, browse more Science and Technology notes, or return to all of our study resources.

Sources

1. Space.com: India launches its first 3D printed rocket engine (Agnikul Cosmos, Agnibaan SOrTeD)
2. DD News: India gets its first 3D printed post office in Bengaluru
3. Veritasium: The Surprising Genius of 3D Printed Rockets

Key takeaways

• 3D printing (additive manufacturing) creates three-dimensional solid objects from a CAD digital file by depositing successive layers of material.
• 3D printing began in the 1980s as a tool for rapid prototyping and has evolved to include bioprinting, affordable housing, custom prosthetics, and decentralized manufacturing.
• The ASTM classifies 3D printing into seven categories: vat polymerisation, material jetting, binder jetting, material extrusion, powder bed fusion, sheet lamination, and directed energy deposition.
• Vat polymerisation includes Stereolithography (SLA), Digital Light Processing (DLP), and Continuous Liquid Interface Production (CLIP), each using UV light to cure photopolymer resin.
• 3D printing is especially useful for low-volume production of complex parts and creating lightweight hollow designs without compromising structural integrity.

Test yourself

What is 3D printing?

3D printing, also called additive manufacturing, is a process of making three-dimensional solid objects from a Computer-Aided Design (CAD) digital file.

What are the seven categories of 3D printing processes according to ASTM?

The seven categories are: vat polymerisation, material jetting, binder jetting, material extrusion, powder bed fusion, sheet lamination, and directed energy deposition.

What are three specific applications of 3D printing?

Three specific applications are bioprinting living tissues, speeding up affordable housing, and creating custom prosthetics.