A Contrast to Convention
Conventional manufacturing won’t be wholly replaced by Additive Manufacturing, certainly not in the foreseeable future, but there are some types of products which benefit from this new technology in a number of different ways.
Additive Manufacturing is a far more effective way of working, requiring less intervention from machinists and delivering far greater degrees of precision, being printed digitally directly from a CAD model rather than subject to interpretation.
Increased precision is achieved with 3D printing from a CAD model
However, it’s the method of creation which is so markedly different to any kind of existing technology, including CNC (computer numerical controlled) machining to which it is often compared. Most conventional types of manufacturing production, including CNC, use subtractive methods; material is removed to create the final result. This can mean there’s a lot of wastage with the material used typically being scrapped.
Additive Manufacturing – as the name suggests – is an additive method, this means that material is added to create the product. By using an additive method rather than subtractive, the process is far more economical and also eco-friendly, and there’s a much greater scope for designs
An Overview of the Process
There’s a variety of different types of Additive Manufacturing methods which can be utilised to achieve the final result, but each broadly goes through the same steps in the process.
The design is first created using CAD software on computer; this is what the final design will be created from, a digital blueprint, so every detail needs to be right. This software can help engineers predict how the final structure will behave and how strong it will be so it’s a vital part of the design process.
An innovative use of Additive Manufacturing technology with these face models
Once complete the CAD design is converted to a .stl file (standard tesselation language) which is what’s needed for the printer to be able to interpret the instructions. This file type was first created in 1987 when it was used by stereolithography, a forerunner to the modern Additive Manufacturing technology.
Before the object starts to be created, the orientation of the design and the printer need to be set up, in the same way as a 2D printer would be. This mean configuring the size and orientation, just how you might select between landscape and portrait prints, and filling up the cartridges with the right powder or binders to complete the job.
You’re now ready to let the printer create the product, gradually building up the design one microscopic layer at a time. A typical layer is around 0.1mm in thickness but bigger or smaller layers can also be created, depending on the structure being printed.
During this time, there’s no intervention required; the printer will simply keep layering the levels until the product is complete. Periodic checks to make sure no errors have occurred is all that’s needed. The item could take anything from several hours to days to complete, depending on the size and complexity of the design.
Direct and Binder 3D Printing
There are different types of Additive Manufacturing and arguably one of the simplest is the use of direct or binder 3D printing.
Direct 3D printing makes use of common inkjet technology, but rather than moving back and forth, the nozzles move up and down dispensing polymers and wax, rather than ink. These polymers and waxes come out as a liquid but quickly solidify, creating a sturdy base for each level of the cross section. This type of Additive Manufacturing was very popular with Rapid Prototyping and even today, Multi-jet Modelling (MJM) is often used, where large numbers of nozzles work simultaneously to create plastic or wax designs.
Binder 3D printing is not vastly dissimilar, also relying on inkjet technology, but instead using two separate materials to create each layer. The printer releases both a fine powder and then separately, a liquid binder, and it’s the combination of these two substances that creates each layer. The advantages of this method are that different materials can be combined during the same printing design.
Sintering and photopolymerisation
When plastics are being used in Additive Manufacturing a process known as photopolymerisation can be used to create a strong and sturdy design. This involves small drops of the liquid plastic being exposed to ultraviolet light, delivered via lasers. This laser transforms the liquid into a solid material, thus creating the product one layer at a time.
This photopolymerisation formed the basis of the first types of 3D printing, stereolithography. The process, referred to as SLA, used a vat of plastic photopolymers held in liquid form, and a laser beam. The laser repeatedly passes over the photopolymers, layer by layer, until the final product is complete.
Stereolithography model of the Royal Palace of Venaria
Sintering is a modern type of Additive Manufacturing which is used to great effect on both plastics and also metals. The process involves lasers heating up the raw materials to just below full melting point; this allows them to liquify and then set as a hard, solid design. This mechanism is not vastly dissimilar to 2D printing where the toner is melted to stick to the paper and create the image. Just like other methods, sintering uses a painstaking layer by layer approach, carefully heating and merging the particles in each level before moving on to the next.
Sintering is useful for alloys but when pure metals are being used, melting rather than sintering may be used to create the final product. The advantage of melting the metal is that a less porous finish can be attained. Both sintering and melting are incredibly precise methods of Additive Manufacturing engineering and are widely used in a variety of applications today.
We hope you have enjoyed this introduction to how additive manufacturing works. If you have any questions around how our Lasers can improve your AM processes then call us on+44(0)1489 779696 or complete our online contact form instead.