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14 August 2017 17:08
Understanding the two fundamental types of SLS material
Selective laser sintering (SLS) creates solid objects by fusing together fine powders via the use of a laser, in order to build up solid structures, layer by layer. For the vast majority of SLS printing, the powders used are based on a fine, nylon-based plastic material. In this context, ‘nylon’ refers to a specific type of polyamide, i.e. a synthetic polymer. While there are a wide range of such materials available nowadays (silk being the most well-known), when it comes to industrial 3D printing, we’re only interested in the two polyamides that form the basis of all SLS materials: PA11 and PA12.
The vast majority of the SLS powders currently available today are based on one of these two material types (we’ll look at some of the less common options in a future blog post) Both offer distinctive advantages when it comes to creating 3D printed parts, so material specification sheets will often list one of these types as a high-level indicator of a material’s qualities. It’s therefore good to understand the differences between the two material categories, as this will help you make an informed decision about which powder is right for your next SLS print.
Let’s look at each of them in detail…
PA11 is a fine bioplastic, created using materials derived from different vegetable oils. As it requires very few non-renewable materials to produce, it has minimal environmental impact. As a result of its elasticity, it has excellent impact resistance, although it has less heat resistance than other polyamides. It also has very strong UV resistance.
PA11-based materials are widely used for functional, mechanical parts, where there is likely to be some load-bearing requirement, or in designs that incorporate moving parts. It is especially good at capturing the fine details of 3D models, including thin walls and lattice structures. In particular, it is a popular choice in the automotive sector for creating interior parts for cars.
PA12 is derived from petroleum sources and produces an end result similar to injection-moulded plastics. Its primary characteristic is its material strength. It is extremely strong and stiff, even with extreme temperatures, and is highly resistant to cracking and abrasion. It is also highly resistant to moisture and chemicals (including solvents). This behaviour is extremely consistent over time.
All this means that PA12-based materials are often the first choice for SLS parts where durability and strength are essential. It is also widely used for parts that need to meet specific regulations when it comes to material qualities (functional aerospace parts, for instance). It also accepts more finishing options than PA11, which can be useful if a specific look is required for a display piece, or to enhance a particular aspect of its mechanical qualities.
So what does this mean for your next SLS print?
When choosing a material for your next SLS print, the first detail you check on a specification sheet should be whether the powder in question is a PA11 or PA12 type. With this as your benchmark, you can then drill down to the specific qualities of each material, to choose the one that is absolutely right for your applications.
Bear in mind that there are a number of composite materials available nowadays that blend PA11 and PA12 with materials like glass (DuraForm GF), carbon fibre (DuraForm ProX HST), or aluminium (Alumide®) to provide specific mechanical properties. We’d therefore strongly recommend that you consider all the available options before making your decision, and consult your materials supplier if you are looking to achieve a specific result, as you may be surprised at what can be achieved with the right material and some strategic post-processing.