SELECTIVE LASER SINTERING (SLS)
The SLS process uses a bed of powdered material, which is fused one layer at a time by a high power CO2 laser. SLS is used to build strong functional parts and can provide cost-effective solutions from prototype to production. The laser ‘draws’ a single layer cross-section of the required part on the surface of the powder bed, accurately creating the part layer and joining it to the layer below.
During construction, an object being built by SLS is supported by the surrounding powder – it is possible therefore to build very complex geometries without any need for interfering support structures. In this way the SLS process allows previously impossible shapes to be built.
Functional parts can be built cost-effectively allowing designers and engineers the freedom to design without the constraints of traditional manufacturing.
At Graphite AM we have developed two market leading SLS powders – Graphite reinforced and Carbon fibre reinforced.
MULTI JET FUSION (MJF)
Multi Jet Fusion is a relatively new technology that is designed to provide cost-effective alternative to SLS. MJF is a powder based technology but rather than using a laser, a combination of a fusing agent and a strong infrared heat lamp sinters the particles together, creating fully dense parts.
Materials are still fairly limited with PA12 and PA11 being the most common powders. There is also a Glass Bead filled PA12 and a TPU material being released later in 2019.
Key points
- SLS is a well-established technology therefore offering a wider range of materials to the current MJF materials available (these include; Flame Retardant, Glass Filled, Carbon Filled, Conductive Materials, Polypropylene and Anti-Static Nylons)
- MJF offers greater recyclability of the powder, up to 85% compared to only typically 20-30% on SLS
- Due to the different material usage, SLS has the price advantage on parts only with a high volume to bounding box ratio. MJF has the advantage on all other parts. MJF is typically 30% cheaper than SLS on average
- MJF has a more automated at post-processing than SLS, allowing the reloading of the powder to be quicker
- MJF offers cost-effective solutions from prototype to mid volume production runs and is aimed to be an alternative to Injection Moulding for the right geometries
- A typical SLS build takes 30 hours to warm up, sinter and cool before removal from the machine. An average MJF build takes 16 hours and can be cooled down out of the machine due to a removable build cartridge
- Typical SLS lead times are 5-7 working days and MJF 4-6 working days. 2-3 day lead times can be available on both technologies with our Express service
- The surface finish of SLS parts are similar to MJF parts, with MJF having a slight advantage on detail and definition
- Unfilled SLS Nylon parts are white and can be dyed in a multitude of colours. Our Graphite and Carbon reinforced SLS materials are naturally dark grey / black throughout. MJF parts in their natural ‘basic’ finish have a patchy grey appearance. They can be dyed black, but we offer a blasted ‘cosmetic’ finish as standard which gives a darker uniform finish
- Shrinkage of MJF is slightly higher than that of SLS. This is measured and adjusted for as standard, but any geometry prone to warping or distortion is at greater risk with MJF. We’d normally recommend larger parts that require high accuracy are built in SLS
| MJF | SLS | |
| Dimensional Accuracy (typical) | + 0.2mm up to 66mm + 0.3% over 66mm | + 0.25mm up to 100mm + 0.25% over 100mm |
| Usable Build Envelope | 360 x 264 x 360mm | 320 x 280 x 400mm |
| Layer Thickness | 0.08mm | 0.1mm |
| Minimum Wall Thickness | 0.5mm | 0.7mm |
WHAT’S NEXT
Both technologies are here to stay and the speed of development over the next few years is sure to be exciting. With the open source nature of SLS, there is a wide range of materials currently available with many more coming to market. SLS allows companies like Graphite AM to develop its own powders with enhanced mechanical properties. MJF has a part price advantage and the range of materials is set to grow in the future new powder development programme launched by HP.
The two technologies should be considered as complimentary technologies, and both have a role to play in Prototype and Production.
To find out which technology is the best fit for your application, please contact us.
