Every additive process builds a part layer by layer from a digital model, but the way each layer forms decides resolution, strength, material choice, and cost. Choosing the wrong process wastes weeks of iteration. This guide compares the five processes engineering teams use most.

How the layer forms decides everything

Fused deposition modeling extrudes molten thermoplastic. Stereolithography and digital light processing cure liquid photopolymer with ultraviolet light. Selective laser sintering fuses polymer powder with a laser. PolyJet jets and UV-cures droplets of photopolymer. That single mechanical difference drives every downstream trade-off, from surface finish to the anisotropy of the finished part.

Fused deposition modeling

• Strengths: low machine and material cost, wide thermoplastic range including PLA, ABS, PETG, nylon, and filled composites, simple workflow
• Limits: visible layer lines, 100 to 300 micron typical layer height, weak Z-axis strength, support removal on overhangs
• Best for: early form-and-fit prototypes, jigs and fixtures, large low-detail parts

Stereolithography and digital light processing

• Strengths: 25 to 100 micron layers, smooth surfaces, fine feature reproduction, growing resin range covering rigid, tough, flexible, and high-temperature grades
• Limits: photopolymers are more brittle and less UV-stable than engineering thermoplastics, parts need washing and a UV post-cure, resin handling requires gloves and ventilation
• Best for: master patterns for casting, enclosures with tight tolerances, optical and lens prototypes, consumer-product appearance models

DLP projects a full layer image at once, so build time depends on part height rather than cross-sectional area. That makes it faster than laser-scanned SLA for trays of small parts. Both processes depend on a controlled post-cure to reach final mechanical properties, which is where a dedicated lamp or chamber matters more than the printer itself. See the best UV lamp for resin curing for matching output to resin chemistry.

Selective laser sintering

• Strengths: no support structures, near-isotropic strength, functional nylon parts, nested builds for volume
• Limits: grainy matte surface, powder handling and sieving, higher machine cost, 0.3 mm minimum wall
• Best for: functional end-use components, ducting and manifolds, low-volume production bridge parts, aerospace and industrial brackets

PolyJet

• Strengths: multi-material and multi-color in one build, 16 to 30 micron layers, rigid and rubber-like zones in the same part
• Limits: high consumable cost, smaller build volume, photopolymer aging under UV
• Best for: overmold and gasket prototypes, tactile design review models, complex assemblies printed as one piece

Email Us to discuss adhesives and coatings that bond or protect printed photopolymer parts.

Matching the process to the project

Four questions narrow the field quickly:

1. Does the part carry load, or only communicate geometry? Load-bearing points to SLS or filled FDM.
2. How fine are the smallest features and how smooth must the surface be? Sub-millimeter detail points to SLA, DLP, or PolyJet.
3. What is the service temperature and UV exposure? Photopolymers soften and yellow sooner than sintered nylon or ABS.
4. How many units, and how fast? Nested SLS or DLP trays beat single-head FDM for batches.

Tolerances and material properties by process

Dimensional accuracy and mechanical behavior vary widely:

• FDM holds roughly plus or minus 0.2 to 0.5 mm and shows 40 to 60 percent of injection-molded tensile strength in the Z direction
• SLA and DLP hold plus or minus 0.05 to 0.15 mm with near-isotropic properties once fully post-cured, though impact resistance trails engineering thermoplastics
• SLS holds plus or minus 0.1 to 0.3 mm with 80 to 95 percent of molded nylon strength and good fatigue behavior
• PolyJet holds plus or minus 0.02 to 0.1 mm but the softest photopolymers creep under sustained load

Design rules follow from these numbers. FDM needs generous fillets and wall thicknesses of 1.2 mm or more. Resin processes tolerate 0.4 mm walls but need drain holes in enclosed volumes. SLS needs 0.5 mm minimum walls and escape holes so unfused powder can be removed.

Cost drivers

Machine cost is only part of the picture. FDM filament is inexpensive, but slow print speeds add labor. Resin cost per part is moderate, and a wash-and-cure station is a required add-on. SLS carries high machine and powder cost but amortizes it across densely nested builds, which is why service bureaus favor it for low-volume production. PolyJet has the highest consumable cost of the group. For a run of a few hundred functional parts, SLS or a DLP tray usually beats single-head FDM on total cost despite the higher entry price.

Finishing and bonding printed parts

Printed parts rarely leave the machine ready to use. FDM parts often need vapor smoothing or epoxy coating to seal porosity. Resin parts need a full post-cure to consume residual monomer and stabilize dimensions. Multi-part designs that exceed a build volume are printed in sections and joined, and the adhesive has to tolerate the base polymer plus any coating. UV-curable adhesives bond clear photopolymer without clouding, while structural epoxies handle nylon and filled composites. A practical comparison is in UV glue vs epoxy: which is better for transparent bonding, and controlled post-cure of assembled resin parts is covered in matching a UV cure chamber to lamp and part size.

Closing

No single process wins. FDM iterates cheaply, SLA and DLP deliver detail and finish, SLS produces functional nylon without supports, and PolyJet combines materials in one build. Define the part’s mechanical, thermal, and cosmetic requirements first, then pick the process that meets them at the volume you need. Contact Our Team for guidance on curing, bonding, and coating additive-manufactured parts.

Visit www.incurelab.com for more information.