PPSF Finishing Techniques
PPSF (polyphenylsulfone) is a high-temperature, high-strength and chemically resistant FDM
material. While ideal for demanding applications, the durability and chemical resistance make it
difficult, and time consuming, to finish PPSF parts with sandpaper or solvents.
When smooth surfaces are needed, the two options most often used have been hand sanding
or milling. Resistant to abrasion, PPSF makes hand sanding a laborious task that can consume
hours of time. While a finishing pass with a CNC mill can make short work of surface smoothing,
it negates many of the advantages of the FDM process. To prepare for machining, time is needed
for CAM programming and machine set-ups. Machining also requires that an operator oversees
If PPSF is used to make tools or molds,
there is a new and faster alternative
for surface smoothing, thermoforming.
A thin sheet of plastic is drawn onto
the surface of the PPSF part. While
it conforms to the part’s shape, the
plastic sheet does not transfer the layer
lines to the outer surface. To preserve
the mechanical, thermal and chemical
advantages of PPSF, the thermoforming
process uses sheets of plastic made from
PEEK resin. Versus hand sanding, PEEK
thermoforming can reduce lead time by
75 percent and cost by 90 percent.
Smoothing a PPSF part with an outer skin of PEEK is a relatively simple process that requires few
modifications to a standard thermoforming operation. The key differences are that PEEK is the
thermoformed material and the FDM part serves as the thermoforming mold.
Following are highlights of the process. For a detailed, comprehensive description of
thermoforming with FDM, see Stratasys’ “Thermoforming for Prototype and Short-Run
- Part Construction:
Select the desired thickness of the PEEK sheet that will be thermoformed. The recommended
thickness range is 0.003 to 0.005 inch (0.08 to 0.13 mm), but sheets as thick as 0.010 inch (0.25
mm) may be used. Note that thicker sheets of PEEK will require more vacuum pressure during
thermoforming and may resist drawing into small features.
To compensate for the thermoformed sheet’s thickness, adjust the CAD model of the PPSF part
by offsetting all external surfaces. Optionally, the CAD model may be modifi ed to include a 0.050-
inch (1.27 mm) deep ring around the perimeter of the mold. This ring will aid in bonding the
PEEK fi lm to the part.
To simplify and expedite the thermoforming process, modify the FDM build parameters to make
the PPSF part more porous. This allows the vacuum in the thermoforming machine to be pulled
through the part without having to manually drill vent holes around its periphery. Do this in
Insight by adjusting the raster air gaps of the two outermost surfaces to 0.001 inch (0.03 mm).
Also, change the model’s body raster air gaps to 0.010 inch (0.25 mm) to promote air flow
through the part.
Next, build the PPSF part an Fortus system. After the build is complete, remove the supports in
preparation for thermoforming.
Mount the PPSF part on a base plate cut to a size that fi ts on the thermoforming machine’s
platen. The base plate can be made from any rigid material that will withstand the heat of the
Load the PPSF part in the vacuum forming machine and insert a sheet of PEEK material. To ensure that there is a strong mechanical bond between the PPSF part and PEEK film,
adhesive-backed materials are suggested. Testing has shown that Victrex P500S, an APTIV PEEK
film backed with silicone adhesive, works well for this application.
Heat the sheet to 284-320 °F (140-160 °C) and draw it onto the PPSF part as soon as it reaches
its forming point. Typically, this cycle should be completed in less than 20 seconds. Extended
cycle times will cause the PEEK film to crystallize, which causes it to become stiff and opaque. To
avoid crystallization, observe the PEEK sheet. As heat is applied, it will relax and then become
taut. Once the PEEK sheet draws tight, quickly apply the vacuum and hold it until the
PEEK film cools.
Following the vacuum forming operation, trim the PEEK sheet to the size of the PPSF part. The
PPSF/PEEK part is now ready to be put into service.
Time and cost comparison of hand sanding and PEEK Thermoforming FDM mold model of a rear tire blower nozzle.
3 hours (75%)