DESIGN GUIDELINES for FDM (Fused Deposition Modeling) components.
ABS (Acrylonitrile Butadiene Styrene) is an industrial plastic, widely used in thousands of applications. ABS+ thermoplastic used in our 3D printer is tough enough for prototyping, functional testing or producing manufacturing tools and end-use parts. ABS thermoplastics are stable and have no appreciable warpage, shrinkage, or moisture absorption. Parts produced are accurate and durable.
FDM begins with a software process, which processes an STL file (Stereo Lithography File format) mathematically slicing and orienting the model for the build process. The machine dispenses two materials – one for the model and one for a disposable support structure. Support structures are automatically generated.
FDM is accomplished by extruding thin layers of molten thermoplastic layer by layer until a part is produced. TWO LAYER THICKNESSES can be used to choose whether to print 30% faster at resolution .330 mm (.013”) or at a finer resolution .254 mm (.010”).
MAXIMUM PART SIZE X (width) × Y (length) × Z (height) is: 203×203×152 mm (8×8×6”). In orientation should be noted that extruded plastic has its strongest strength in the tensile mode along the X-Y plane. The lowest strength is in the Z-direction for both tensile and shear modes.
Recommended minimum WALL THICKNESS (to eliminate brittleness) varies depending upon the slice thickness that will be used to build the part, being about 1 mm (.040”) with higher resolution and about 1.30 mm (.050”) with lower resolution.
Minimum SIZE OF FEATURE is a function of part orientation and selected resolution. Usually smallest size can be figured out roughly: X-Y (width-length) 4× resolution, and Z (height) 2× resolution.
WARP is not a common problem. However, to avoid potential warping (deformation of vertical walls) when building thin-walled sections of a model, usually ribs are added.
When designing built-in THREADS, avoid sharp edges and include a radius on the root. Also, use a “dog point” head of at least 0.8 mm, this makes starting the thread much easier. Small threads, smaller than 8…10 mm, are not recommended and hand-tapping probably required to smooth threads and correct clearances. Easy alternative is to make holes smaller than required for the thread, and drill and tap thread, or use self-tapping threaded inserts. Lock nuts, embedded nuts, or metal inserts are stronger fastening options than adding threads to the FDM plastic.
UNDERCUTS for design features such as O-ring grooves are easily handled without causing manufacturing issues.
FILLETS are not necessary, but they can be used to increase the overall strength of the part. Design fillets with an outer radius equal to the inner radius plus the wall thickness to maintain consistent thickness.
Exterior dimension SHRINKAGE is usually to about 99.7% of their modelled size. Interior dimensions, such as holes, shrink to about 98.5% of their modelled size. Thereby, a pin printed the exact same size as a hole will not fit in the hole once it’s printed. When tight tolerances are required, holes will be drilled or reamed to ensure accurate diameter.
OVERHANGING NON-SUPPORTED FEATURES require a foundation of support material to be built, which increases build time and material usage. For example, half of a box-shaped casing will be usually built with the main exterior facing down, so that no internal support is needed.