Phill Dickens of the University of Nottingham and Added Scientific Ltd. was recently invited to review the latest machines from HP at their development centre in Barcelona, Spain. This was a 2 day event occurring on the 3rd and 4th of May but information from this was embargoed until 08:30 EST on 17th May 2016.
The first day started with a presentation from Stephen Nigro, President of the HP 3D Printing Business. He explained that in October 2014 they set their ambition to develop a process that was 10x faster, used an open platform, and produced parts with precision and quality. He claimed that their Multi Jet Fusion (MJF) technology featured speed, cost, quality and reliability.
MJF uses a combination of a powder bed and Thermal Inkjet Technology. The machine looks similar to laser sintering equipment in that it uses nylon powder which is held just below the melting point; additional energy is used to then fully melt each cross section. However, the energy is not supplied by a laser but by infra-red lamps.
The machine undergoes pre-heating for 1 hour prior to first powder layer being spread across a heated platform (this can happen outside of the printer to not impact productivity). A ‘fusing agent’ is then printed into the powder at the cross section of the part. This is generally used at a ratio of 1:20 with the nylon powder. A ‘detailing agent’ is printed just outside the boundary of the part (20 – 30 microns wide) to inhibit sintering past the part boundary whilst an infra-red lamp simultaneously passes over the part. Wherever the fusing agent has been printed, the powder preferentially absorbs the infra-red energy and melts. This process is repeated until the full build is generated. Once the build is complete the build chamber is rolled out of the machine and replaced, ready for the next job.
The hot build chamber with the part cake inside can either be left to cool on its own or it can be placed in a dedicated processing station which will both predict and monitor the powder cake temperature. The processing station can use forced cooling to greatly reduce the time before parts can be removed. HP claim that full build times are around 10 hours whereas cooling times with forced cooling are similarly 10 hours. All unused powder from the part cake is reused in the next build at a ratio of 4:1 with virgin powder. When the parts are removed from the powder cake they retain a thin layer of residual powder on the surface which is held together by the detailing agent. This is removed by bead blasting (as is normally done with laser sintered parts) however, the surface roughness of parts shown appeared to be superior to that achieved with selective laser sintering (SLS).
HP will initially provide two different machines with a build envelope of 406x305x406 mm (16x12x16 inches): one for prototyping (3200) and one for manufacturing (4200). The manufacturing model will print 25% faster (about 16 seconds per layer), will have custom print modes and more operator control of the process parameters and lower cost per part. The cost of the printers will start at $130,000 and complete solutions with the processing station will come in at $155,000. Mention was made of an office printer but I do not see this process working in that environment; there is too much heat loss and inevitably some powder will escape making it inappropriate for the office environment (although it is much more controlled than Laser Sintering).
An example of build times and costs were given for the production of a 5 gram gear. On the HP machine 2500 gears were built in 11 hours, whereas only 250 were built by SLS in same time frame and only 50 were built on an FDM machine. The production rate on the HP machine may be even higher, after some quizzing it transpired that a spacing of 5mm between gears was used. It should be possible to get them much closer than this! For comparison, the break-even volume with injection moulding was around 58,000 parts.
The software that comes with the machine is called 3D Build Manager; it fixes files, undertakes auto packing, and provides machine status and material supply information. Importantly, for manufacturing it also provides heat map recording. It supports both stl and 3MF formats. There is also a 3D Command Centre for multiple installations and machines will be linked to HP for machine performance monitoring.
The powder materials will be purchased either from HP or from third party suppliers (if they have been HP certified). HP is today partnering with Evonik, BASF, Arkema, Lehmann & Voss & Co. as the first companies to join the HP open platform to deliver Certified materials powder. The powders will initially be PA12 and PA11 but they plan to introduce PA12 with glass beads (as a fire retardant version PA12) and also an elastomer and also additional high performance thermo-plastics in line with those available for Laser Sintering.
Ramon Pastor, the General Manager of 3D Printing, explained that the Thermal Inkjet Heads have a nozzle density of 1200 per inch which generate 10 picolitre drops at a total rate of 300 million drops per second across the width of the bed. Apparently they chose Thermal Inkjet Heads rather than piezo driven heads because they have a lot of experience from their 2D printing business and with these heads they can achieve higher density of nozzles at a lower cost.
At the moment the detailing agent only affects the thermal conductivity of voxels at the boundary of the part but in future the detailing agent will control colour, roughness, electrical conductivity, mechanical properties and transparency.
It is interesting that the machine does not need a nitrogen atmosphere and HP claim that this is because peak temp is lower and the molecular structure is slightly different to nylon for Laser Sintering.
There are many details yet to be released (or learned) such as:
The take-home message is this is a very exciting development where a machine has been designed which has much more potential for manufacturing than its competitors. It will be very interesting to see how other machine manufacturers respond to this challenge. I am hopeful that we can now start looking at Additive Manufacturing for volumes of hundreds of thousands, if not more.