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Layer by Layer: the wonderful world of additive manufacturing

A close up of a lazer cutter

Additive manufacturing, (3D printing) is a construction technique that can change the world. Saving time, money and resources by simply ‘printing’ much needed components, one layer at a time. Here we explore the theory, advantages and challenges of the most creative and innovative manufacturing processes.

Not so long ago, I used to spend hours with my Lego. The simple brick was transformed (in my mind) into a spaceship one day or a Formula 1 race track on another. The reason why I loved Lego and indeed why it’s famous, is because of its simplicity and universality! Imagine building “real life” parts by adding one layer of material on top of another. Like attaching individual blocks of Lego.

This is the principle of additive manufacturing (or 3D printing). We build a component, layer by layer, according to the required shape and size. In this process, a component is designed in a computer and a robot then follows the instructions. Creating a 3D structure not dissimilar to us following the instructions sheet within a Lego set.

Just as we need different elements to build our Lego spaceship. Additive manufacturing also requires various components to work together. The first thing we need to build any structure, is the material out of which our part is going to be built. This is quite literally our “building block”.

This can be anything from the Aluminium used in aircraft, to the plastics in your 3D printed Darth Vader toy. Examples include implants made out of magnesium alloys that can be absorbed by the body, or polymers used to print coral reefs in the oceans. The choice of material depends on the required properties for the part. And, it could be used in different forms for the build. Researchers across the world are working on using the required material in the form of wires or powders for additive manufacturing (AM). Each can have pros and cons.

Once we decide on a material, the next challenge is to find a way of “sticking” the new material to the part being built. This can be done by selectively melting or by injecting a binder into the areas we want to stick. If the former is chosen, we would use a heat source to melt the raw wire or powder on top of the build. As the deposited material cools down and solidifies, it becomes a new layer. The process repeats until the part is complete. It is similar to the process of welding. The selection of the heat source influences the micro structure and the resultant properties of the part. Nevertheless, parts have been additively manufactured successfully using Lasers, electron beams or an electric arc like plasma as heat sources.

Additive manufacturing is being used around the world to produce parts for cars, aircrafts, architectural features and even medical devices.

A formula 1 car, then an aeroplane, then a building, then a scanner

Next, we need to figure out a way to deposit the material in different places to build more complex shapes. The simplest method is to use our hands and guide the heat source and the raw material. But, this method isn’t practical for additive manufacture because of the heat source and speed needed for efficient production. So, we use computers and robots to move the heat source or bed where the part is fixed. This way we can choose where we want to deposit the next layer and give our part more complex and intricate geometries.

The different ways of combining the raw material and heat source can seem confusing but the decision is based on why and for whom the part is being built. It is a balancing act between how detailed we want our part to be and how fast we want it built. If we want a detailed part with complex contours, then each new layer has to be very small to capture these features. Small layers means we have to deposit more times and it can seem like it takes forever to build!

For example, a complex aerospace component would use a slow but more detailed process. Alternatively, a simple box or a prototype of an actual component would trade accuracy for speed. Some less detailed parts can be machined afterwards, to give them their final shape. Thereby gaining the speed of deposition and the detailed finish. But, allowances must be made for the time, delay and other challenges associated with the machining process. As a rule of thumb, powders are used to capture more details and wires are used for parts that require greater deposition rate.

When we get it right, additive manufacturing offers unique advantages that make it worthwhile! The cost of production is less due to a decrease in raw materials used. Precision application reduces waste materials. Greater customisation becomes possible as each part is built individually. We could for example, create custom-made soles for our shoes. Ensuring a perfect and more comfortable fit at a reduced cost.

Researchers and companies around the world are using additive manufacture to produce parts for cars, aircrafts, architectural features and even medical devices! But that’s not all. As technology matures, industries ranging from biomedicine (where AM can be used to build custom implants) to aerospace (where AM is used to build parts of an aircraft and/or rocket) are constantly adopting AM into their manufacturing capabilities.

A 3d printer behind an example of a 3D printed bone

Despite its advantages, there are challenges that await the current and next generation of researchers. There is always the need to reduce cost and increase the speed of production. Either through research in robotics or quality control, as that would enable us to get what we need cheaper and quicker. One of the main research areas is to monitor the part, looking for cracks and defects as we are building rather than at the end. That would allow us to identify and rectify defects almost immediately, saving time, resources and unwanted surprises that could render the whole part invalid. Research into new compounds and materials to use in additive manufacturing will allow us to build even more objects with different properties.

So when you see a 3D printer, imagine the wonderful world of AM and what we can design and create. But also think about how we can make this technology even better; consider how the material, heat source and computer are working together. Ask yourself how you would improve them and join us if you are intrigued as well!

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Surya Krishnaswamy
Research Fellow, Cranfield University

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