Operating the 3D Systems Projet 660
The Projet 660 requires a dedicated 120V/20A circuit. It is also advisable to operate the printer in low humidity environments and to keep the temperature in the room stable through the printing process to increase print consistency. The printer is advertised as safe for office use but, the maintenance of the printer and the post-processing of the models can be messy, so unless you are only running a few 3D prints a month, it is best to operate the printer in a warehouse type setting. It is also sometimes difficult to come by 20A circuits in office spaces and the printer has a vacuum cycle that runs every few minutes that produces a fair amount of noise.
The 3D printer is controlled by software that comes packaged with the 3D printer called ZPrint. ZPrint allows you to import models, position them in the build and start prints. The quality of the final 3D print is affected by the orientation of the model inside the 3D printer. It is usually recommended to print the 3D models laying on their side as this orients the 3D printing build lines straight up and down the model which helps hide them.
Consumables for the printer you need to keep on hand include: the powder (zp151), yellow, cyan, magenta, clear and black binder cartridges, HP11 print heads, zbond cyanoacrylate (super glue) and waste disposal trays, along with choice maintenance materials including alcohol swabs and distilled water. It is advisable to maintain a service agreement on the printer for around $9,000 annually. The consumables are quite expensive as many of them are proprietary to 3D Systems so 3D Systems charges as much as they can. For example, a 14kg container of powder (pictured on the left below) costs $1,100.
The Projet 660 is a fast 3D printer with the ability to print up to 1.1 inches in height per hour, however, relative to other manufacturing processes, the printer is still extraordinarily slow. At a print speed of 1.1 inches per hour, an average 6 inch (15cm) print takes approximately 3 hours to print. The time to print does not increase linearly with the number of models you print at a single time, so it usually makes sense to print multiple models at once if you can keep the total height of the build minimized. For example, printing nine 6 inch models at the same time would take approximately 12 hours for an average of 1.33 hours/ model versus the 3 hours/model if you print them alone. This time savings is achieved because the printer has a preparation sequence that runs at the beginning of a print and a drying period that must run regardless of the number of prints in a single build. In addition to this, the printer is faster at moving in the X and Y dimensions, so if increasing the number of models does not increase the height of the build (Z dimension), then the printer can do the extra work quickly. It is not advisable to fit as many prints as possible in the printer because a single printer error usually ruins the entire build and the longer the printer runs, the more likely it is to fail in one way or another, so a careful balance has to be struck between packing enough prints in a build to speed up the printing process and not packing so many in that you lose a lot of time and money when the printer fails.
Once the 3D printer has completed a build the models must sit inside the bed of powder for an additional 90 minutes to “dry.” The drying process helps the binders set so that the models are more robust for the post-processing step. When the models have finished “drying” in the printer bed, they are ready to be pulled from the printer bed and post-processed.
Pulling the models from the printer bed is achieved using the vacuum built into the 3D printer. The models are buried in the powder so the vacuum is used to suck up the powder surrounding the models until enough of the model is exposed to very carefully move it into the attached de-powdering station. At this stage the 3D prints are very fragile and would easily crush in your hand if you applied force. The prints, especially if there are small features, can collapse under the weight of the excess powder if a thorough enough vacuuming isn’t performed.
Once the prints are carefully excavated, the powder remaining in the printer bed is vacuumed up and recycled for future builds.
The de-powdering chamber contains a small stylus attached to an integrated air compressor to blow off the remainder of the excess powder from the models. This step requires as much careful attention as pulling the models from the printer as the models are still very fragile and any powder that is not blown off the model will become a permanent fixture of the model during the next step.
Once the fine de-powdering of the models is complete they are removed from the de-powdering chamber and moved to an area properly equipped to deal with large amounts of cyanoacrylate (super glue). This typically means a workstation with an exhaust hood, disposable gloves, an apron or other protective clothing, airtight lab goggles and a chemical mask. The models are then doused in cyanoacrylate either by submersion, by having it poured over top or having it sprayed on. The cyanoacrylate permeates the models to give them additional strength and also burns off the top layer of powder increasing the vibrancy of the colors on the prints. Cyanoacrylate emits very strong fumes that can cause serious harm to your lungs and eyes. Skin contact with large quantities of cyanoacrylate can cause chemical burns.
It is possible to substitute cyanoacrylate with a saline solution or a wax with very low viscosity but the final print quality is worse than using cyanoacrylate.
The models must sit and dry for 1- 4 hours following the application of cyanoacrylate. Cyanoacrylate bonds very strongly, so special drying racks must be assembled to prevent the models from becoming permanently fixed to a surface, or the models must be routinely moved.
A few companies have developed additional post-processing steps following the application of cyanoacrylate to either change the surface quality of the 3D print such as applying an epoxy (pictured above) to give the prints a glassy sheen or to fix or hide 3D printing defects such as applying a very thin layer of wax to fill in “build lines.”
The 3D printer must be cleaned and prepared after every build to ensure quality and the longevity of the printer as the powder is abrasive and rapidly wears parts down. We have 3 levels of maintenance which we perform on our 3D printers. A basic clean that takes 30 minutes before every build. A thorough clean which takes ~1 hour and requires disassembly and assembly of parts as well as spare parts in order to perform preemptive maintenance, which we perform every 2 weeks and a ground up clean, repair and recalibration that takes a few hours that we perform every month. It is critical to properly clean and service the printer because the tiniest hiccup during a 12 hour build will ruin the entire build.