FDM or SLS: when filament printing is not enough

FDM and SLS are available in our workshop. Selection starts with the part's function: its loads, mounting, environment and quantity. The same model may need different design changes for each process.

Two different physics

FDM deposits paths of molten filament. In SLS, a laser sinters powder while the surrounding unsintered material supports the part. Both processes build layers. FDM support needs depend on overhangs, bridges and orientation; SLS removes separate support structures but still requires powder removal.

What does this change in design

• —
  An integrated mechanism needs clearances and cleaning access. Motion is checked after powder removal.
• —
  Channels and cavities need a way to remove powder. Trapped powder changes the result.
• —
  Orientation affects surfaces, fits and properties. SLS can also differ between test axes.
• —
  For a critical feature, agree a drawing, inspection and trial before the series.

What the numbers on material data sheets say

PA12: tensile strength 50 MPa, modulus 1,850 MPa and elongation 11% X/Y and 6% Z (ASTM D638 Type 1). Notched Izod is 32 J/m (ASTM D256-10). PA11 has an Izod result of 71 J/m and 40% X/Y elongation; its sheet does not give a separate Z elongation. These are specimen results, not part fatigue life. The sheets describe seven days of conditioning at 50% relative humidity and 23 °C.

Full results with test methods and availability conditions are on the PA12 and PA11 sheets.

When FDM is truly sufficient

Consider FDM for a review model, simple geometry, accessible support surfaces or a single-part budget. It can also make functional parts: suitability depends on filament, toolpaths, orientation and loading. The process alone does not set a service life of a few weeks. Dimensions are checked for the specific machine.

When filament printing is not enough

SLS is a candidate when separate supports obstruct the geometry and channels or moving assemblies can be cleaned. Compare a series by its full scope: material, inspection, finishing and number of builds. Oil or solvent contact needs the medium, concentration, temperature and duration; a cube's mass gain in a 24-hour test does not establish part durability or leak tightness.

Cost: why SLS has a threshold while FDM does not

FDM pricing depends on material, geometry and settings; several parts can share a build plate. SLS depends on chamber use, but printing and cleaning time are not fixed for every layout. Our FDM estimate has no minimum order or file-preparation fee. SLS B2B has a PLN 299.00 net minimum and a PLN 150.00 net fee for a new file, paid once at its first production run. Quantity discounts start at 100 parts. Terms: pricing and quotation. Export terms require individual confirmation.

How to check this on your own file

Add quantity, mounting, force and duration, temperature and critical dimensions to your model brief. The calculator shows an indicative price for supported options; a technologist confirms the scope after reviewing the file. Quote your model. Without a file, send photos and a description.

Sources: Nylon 12 TDS (PDF), Nylon 11 TDS (PDF), Fuse Series SLS Design Guide.