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 filled and Carbon fibre filled.

MULTI JET FUSION (MJF)

Multi Jet Fusion is a relatively new technology that is designed to provide cost-effective solutions from prototype to production. MJF is a powder based technology but rather than a laser sintering the parts, a combination of a fusing agent (binder ink) and a strong infra-red heat lamp binds the particles together, creating strong accurate parts. 

Parts are unsupported allowing design freedom. 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.

 

SLS V MJF

  • 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 25-30% using SLS
  • MJF is 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 cycle takes approximately 20-25 hours to warm up, sinter and break out the parts from the build cake. An average MJF build takes 16 hours, however this does not include cool down. Whilst there is a ‘Fast Cool’ option available with MJF, parts can be more susceptible to warping, a natural cool has become the norm and adds another 10-12 hours to the cycle. 
  • Due to the faster speeds of the MJF platform it has the edge over SLS with low to mid volume production runs. Cost savings over SLS for multiple part orders tend to be around 30% more cost-effective and with some geometries even more so
  • Typical SLS lead times are 5-7 working days and MJF 3-5 working days. I-2 day lead times can be available on both technologies at a premium. 
  • The surface finish of SLS parts are similar to MJF parts, the main difference being the colour. Unfilled Nylon parts are white and can be dyed in a multitude of colours (see images below), filled Nylons such as our Graphite and Carbon filled SLS materials are naturally dark grey / black in appearance. MJF parts have a light grey appearance but parts can be dyed black. 
  • Parts printed in both technologies have a textured finish after a light media blast to remove excess powder but can be post-processed to a high standard. As the layers of powder are drawn at around 80 microns in MJF the details and resolution tends to better than SLS equivalents, SLS tends to draw powder at 100 microns. With such a wide range of SLS powders now available, part quality and finish does vary considerably between powders and bureaus. 
  • The accuracy of SLS and MJF is similar, some geometries will be better suited to SLS and others to MJF, see the reference chart below

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 our own powders with enhanced mechanical properties. With the freedom to change base powders and ‘filler’ ingredients, SLS offers far more flexibility than MJF currently but this is set to change with the new powder development programme launched by Hp. As the speed and size of SLS machines increases, SLS is set to solve more low to mid volume production solutions. 

Hp have invited selected partners to start developing powders to run on the new MJF platform. The next few years are set to see a number of new materials being released for this platform. There is a flexible TPU material being released later this year which looks really interesting and several more powders being launched in 2020. 

The two technologies should be considered as complimentary technologies and both have a role to play in Prototype and Production.

 

To receive the latest SLS or MJF datasheets, please email sales@graphite-am.co.uk or call 01296 482673.

 

To find out which technology is the best fit for your application, please contact Graphite AM on 01296 482673 or send an email to sales@graphite-am.co.uk.

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