SLA vs FFF / FDM workflow and space requirements

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spacecomparison_featured

SLA vs FFF / FDM workflow and space requirements

By | Education, Healthcare, Materials, News | No Comments

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…

SLA should remain in the hands of professional labs or dedicated service providers, FFF /FDM is for everyone. In fact with the low cost of filament printers, every designer should have one on their desk.

Spiral Printing on Robox

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Robox_spiral_cup_side

Spiral Printing on Robox

By | Chris Elsworthy Design Blog, Design, Printables, Software Updates, Stuff and Things | 4 Comments

If you’ve downloaded the latest version of AutoMaker then you may have noticed that we’ve activated Spiral Printing for you to play with. Robox is particularly good at spiral printing as it offers the highest ranges of wall thickness without having to remove and replace the nozzle.

Below is a quick guide on how to best use this new feature.
There are a number of things that you should be aware of when trying this feature.

  1. Only place one object on the bed at any time.
    Because of the nature of spiral printing the flow of material from the nozzles does not stop and start. Placing more than one object on the bed means that the models would be impossible to print in one continuous extrusion.
  2. Ensure that your print has only one continuous island from bottom to top.
    This is for the same reason – multiple islands on any layer means that the flow of material has to stop and start. Spiral printing is designed to avoid this.
  3. Consider how thick you want the base to be
    This is one of the few controls Automaker has for spiral printing, the number of layers you choose and the layer thickness will equate to your base thickness before spiral printing starts. The first layer is always 0.3mm and as a guide I would ensure that this is the minimum filament width to ensure good adhesion to the bed. The sequence layers heights are controlled by, yes you’ve guessed it, ‘layer height’. So for example if you’ve chosen a layer height of 0.2mm and 5 base layers your spiral print with have a 1.1mm thick base. (0.3mm + (4 x 0.2mm))
  4. Think about what wall thickness you want
    After the base of your part is completed the system moves to the spiral printed section, continuously moving up as it orbits the perimeter of your design laying down a single line of filament. The wall thickness is controlled by the perimeter width and because its only going to be done in one pass you may want to increase it and use the larger 0.8mm nozzle to create wall thickness of up to 1.2mm. As a guide I’ve found that the ratio between layer height and wall thickness should be between 2:1 – 5:1, the thicker the wall and the smaller the layer height the more likely overhangs will be printed perfectly.
  5. The part must be solid, not hollowed out with a wall thickness
    Because we are using ‘Solid layers at Bottom’ and perimeter thickness to control the thickness of your part the part needs to be a solid to start with. If you want an inner and outer shell, and don’t mind a hollow centre you can use an idea I had when designing the is thermal mug: add a very thin cut down through the part to make each layer a single perimeter again. On the photo below, you can see that the sequence of printing is outside surface of the bowl -> half the handle -> inside surface of the bowl -> half the handle -> outside surface of the bowl… and so on…Thermal MugSpiral Mug Section Small
    6 . Your design is less than 99mm tall
    Robox has a 100mm Z-build height, but because of the way Cura adds the Z move to every move on the layer sometimes the sliced part will come out slightly above 100mm. The post processor will throw this out as impossible print, so to avoid this scale your part to ensure it is less than 99mm high.

Robox_spiral_cup_iso

You can download the cup above from this link. robox_spiral_mug.stl

Robox_spiral_lee_hand

Or the Vase with Support engineer Lee’s face on it by clicking the image above. LeeVase_Mk2.stl

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