SLA (Stereolithography ) is often compared to the FFF (Fused Filament Fabrication) / FDM (Fused Deposition Modelling) process of 3D printing and always shows very impressive results. The detail level is far superior for SLA but there are a lot of complications to the process. Due to the huge numbers of dentists, dental labs and orthodontists contacting us recently I thought I would share some of what I have learned.
The most common comparison is the strength of the parts created from resin vs those created with fused filament which always comes out on top. Next are the many resin handling issues which make filament printers much easier and safer to use.
It is easy to discount FFF/FDM completely by just looking at pictures of the excellent smoothness of an SLA print vs an FDM print. The SLA process can create a smoother and more detailed surface finish and and can create a fully solid, partially transparent part which is difficult to achieve on FFF /FDM machines without post processing. This makes it harder for those of us demonstrating fused filament fabrication printers to keep a viewers attention.
To someone viewing the printed results of 2 models side by side it would be hard to choose the FFF / FDM print if visual quality or surface detail was the goal. In a comparison of useability which requires strength, the FFF /FDM print is far more likely to come out on top particularly due to the huge selection of material types available. The SLA materials tend to be closely linked to specific printers, it is unlikely a 3rd party resin will be allowed or compatible. This limits the SLA user to the resins developed by that manufacturer. In a comparison of workflow the SLA process is quite scary, warning labels and notes on resin handling and cleanup dominate but the consumption of core components of the SLA printer along with litres at a time of IPA (Isopropyl alcohol) and the expensive resin is certainly worth exploring before any decision is made to exclude filament printing. The accuracy of the two methods should theoretically be the same but I have yet to see an SLA print which has been perfectly dimensionally accurate while my Robox is within 0.01mm in all axes without my input all day every day. Cost comparisons are far further apart than the price of the printers would suggest. SLA resin cost is high, plastic filament cost is low. This expensive resin is wasted with every print, plastic filament is only extruded as required. This cost in particular is not shown in “part cost comparisons”, nor is the very wasteful rinsing in IPA to remove excess resin following a print or the cost of the consumable resin carrying and curing parts, or the disposal and storage as well as low shelf life for expensive SLA resins. Oh and the space required for SLA printing is rarely mentioned, you really need a spare room and some strict policies to control the spread of sticky resin the smell and the harm to the environment.
Click the image to make it bigger.
In the chart below I’ve listed some positives and negatives of each method along with typical usage and costs. Blue indicates the best in my opinion for each row. I obviously support filament printers in this, perhaps your comments can sway my opinion?
| FDM | SLA |
| Limited detail, high accuracy, layer lines visible | High detail and accuracy, layer lines hard to see in some cases |
| Parts and excess material can be disposed of in regular waste | Resin waste and printed parts require special disposal. H413: May cause long-lasting harmful effects to aquatic life |
| No material wasted except with support creation, no mess | Wasted resin is washed away in IPA and disposed of regularly in build tank, sticky residue from resin spreads around work area and is hard to clean. Disposal of cleaning products restricted |
| No use by date on filament with low cost | 12 month shelf life and high cost |
| Material is inert and harmless before and after printing | Requires special handling equipment |
| Can be used in any work area | Requires special work area |
| Materials are widely available and cross compatible | Only specified resins can be used with most SLA printers |
| Minimal requirements for storage of material | Requires special storage conditions for resins and required cleaning chemicals in large quantities |
| No additional equipment | Cleaning baths, UV Light booth, safety, storage and disposal equipment |
| Minimal space required to function | Considerable space requirement to keep several large pieces of equipment away from other equipment and work areas |
| Range of materials in many colours and with a huge range of mechanical properties | Very limited range of materials, locked to manufacturer |
| Opaque parts unless post processed | Optical clarity in some materials |
| Material dependant useable indefinitely | Low shelf life of parts due to UV exposure |
| Low cost of consumable parts | High cost of consumable parts |
| Material cost is low $25 per kg | Material cost is high $99 per kg + processing and waste! |
| Medium flexural strength (material relevant to medical use) | Low flexural strength (material relevant to medical use) |
| Low upfront equipment cost | High upfront equipment cost, printer and additional equipment |
| Potential for dual material with dissolvable or peel away support | Single material with mechanical removal of support |
| System allows dual material for overmolded parts and pause features for inserting captive objects | No system for inserted or overmolded parts |
| No training required for use or handling | High level of materials handling trainingrequired |
My conclusion is this:
SLA is not a threat to FFF / FDM printing, if anything the 2 methods can work side by side as their benefits do not overlap. Personally I would not let the resin (or the smell of it) near my home or my family but if I had a dedicated space within a business and the training and staff to run this then I would consider SLA as an addition to several far lower priced FFF /FDM printers. I could print many iterations of a design on the filament printers and perhaps a surface model on the SLA machine once the design was final, actually it might be best to just outsource that part…
