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Large Format FDM Printing - What to expect?

We use Builder Extreme FDM (Fused Deposition Modelling) machines to print parts that are too large for our MJF (Multi Jet Fusion) machines to print.

There are a number of factors to consider regarding part quality, price & mechanical properties when using FDM:


  • Resolution

  • Support Material & Down Faces

  • Material & Colour

  • Splitting Parts

  • Infill & Walls

  • Burn Marks & Minor Surface Defects

  • Hand Finishing

  • Tolerance





Resolution (Nozzle Ø & Layer Height)

We will use one of 3 different nozzle sizes depending on the nature of your project:

0.4mm (High)

0.8mm (Standard)

1.2mm (Experimental)


Larger nozzles are typically used with greater layer heights, which usually reduces print time & cost. Larger nozzles do, however, result in more prominent layer lines.

Layer lines become most apparent on faces that have a small angle to the horizontal.


In this example the layer lines are very noticeable as the face has a shallow angle to the horizontal & these parts are much smaller than we would typically print on our FDM machines.


Layer lines can be sanded away by hand, which is a service that we offer (See hand finishing section).




Support Material & Down Faces


During FDM printing parts are built layer by layer starting off the bed of the machine.


We usually choose a large flat face on the part to act as the ‘bottom face’. If the part doesn’t have a useful flat face to print off we often split the part up before printing (see splitting parts section).


This bottom face will have a slightly different appearance to the side & top faces.



Any part of the geometry that is overhanging must be connected to the bed of the machine via printed support material. This support material will be removed after printing.


Typically anything less than 45 ° to horizontal needs support material, in some cases additional supports are added for stability.



Any part of the geometry that is overhanging must be connected to the bed of the machine via printed support material. This support material will be removed after printing.


Typically anything less than 45 ° to horizontal needs support material, in some cases additional supports are added for stability.



Anywhere that is less than 45 ° will also have a rougher surface finish, which is worse with larger nozzles / layer heights.


Support material helps reduce this effect but doesn’t eliminate it. Again, this is something that can be filled & sanded back, which is a service we offer (See hand finishing).


Material & Colour Options


As standard we use Ultrafuse ® Pro1 PLA by BASF in either black or white colour. This material is higher performance than most standard PLA options, the data sheet can be found on the BASF website:



If you require other colours we can source it but this will add time & cost to your project. We also offer painting as a service (See hand finishing section).





Splitting parts


Sometimes parts are too big to fit even on our large FDM machines.

In these cases we usually split the part into multiple pieces for printing. For no extra cost we can join them back together before sending them, or keep them separate if you prefer.



This image shows a typical join-line around the neck with no hand finishing applied. If your part needs the join lines to be removed we can do this as part of our hand finishing services.


We will choose the most suitable type of joint for the given part to optimise for printing, joint strength & ease of assembly. Some of these include lap joints, tongue & groove joints & pins.




Infill & Walls


FDM parts with thick sections are rarely printed ‘solid’. To maintain print quality as well as manage cost & print time we usually print with a standard rectilinear infill pattern set to 20% infill. For the vast majority of projects this provides ample strength.


We adjust the number of wall extrusions depending on the geometry of your part, typically it will be somewhere between 3-10 extrusions thick.



For parts made up of thin walls we recommend a minimum thickness of 5mm to ensure a strong bond between layers, particularly on large parts.




Burn Marks & Minor Surface Defects


With large format FDM prints can take up to 10 days & during that time a lot of material is extruded. Additionally the large volume means that there is a lot of heat energy within the print. Sometimes this results in burn marks appearing in the material. This can be masked by choosing a darker material or painting over the part (Hand finishing).



Hand Finishing


While FDM machines leave noticeable layer lines they can be filled & sanded back to a high quality finish. Join lines can also be hidden with the same technique. If you require this please ask as we quote it as an additional service.


Additionally we can paint the part to almost any finish & colour, but we will need to know what RAL paint-code you require before we can quote this. More information on RAL paint-codes can be found here:









Tolerance


Expected tolerance for large parts is 3-5%. We can reduce this tolerance by first running a test print of your part, taking measurements, & then adjusting the scaling to account for shrinkage. We can also offer 3D scanning & deviation analysis. Every geometry shrinks differently hence the need to print a test of your specific part. If this is required please let us know as it will need to be quoted for as an additional service.




Any part that has been split & re-assembled cant have its tolerance controlled as closely without creating specific jigging for the part. Again this is an additional service that we can quote for.




Conclusion


If you follow our guidelines & considerations large format FDM 3D Printing is an excellent method for creating large objects quickly. While sometimes the raw print might be the wrong colour or texture there is always room to change that with hand finishing processes that we offer.



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