FDM, SLA and SLS all produce three-dimensional objects, but build them differently. That changes material choices, surfaces, geometry, finishing and cost. No process wins every comparison: start with function, critical dimensions, appearance, quantity and use.
A quick starting point
- FDM often suits accessible prototypes, larger shapes, fixtures and functional parts where visible layers are acceptable.
- SLA is worth investigating for fine details, small geometry, a smoother surface or a particular resin property.
- SLS can suit complex functional parts, several copies and shapes that benefit from a powder bed.
These are starting points. A small FDM part may be accurate enough, a technical resin may serve a functional purpose, and a complex shape does not automatically make SLS economical. Ask how the proposed process fits your design.
How the processes build a part
FDM: depositing heated filament
A nozzle lays down heated thermoplastic filament in successive paths and layers. Path direction and bonding between layers affect both appearance and mechanical behaviour.
The design assessment should cover bed orientation, support locations, visible and critical surfaces, thin walls, bridges, overhangs and the relationship between load and layer direction. Available materials and sizes depend on the actual printer, nozzle, environment and process control.
SLA: curing liquid resin with light
SLA selectively cures photopolymer resin layer by layer. It can produce fine detail and a different surface character from filament printing. Cleaning and further curing are part of production, not optional details to ignore when comparing quotes. Supports and orientation affect visible surfaces and finishing work.
Resin is a family of formulations. Choose an exact variant for detail, stiffness, toughness, temperature, use and any additional requirements.
SLS: selectively fusing powder
SLS fuses selected areas of powder. The surrounding powder supports the part during production, allowing many shapes without separate printed supports.
Parts still need unpacking, powder removal and possibly further finishing. Build-chamber placement, wall thickness, powder escape from cavities and clearances between features remain design constraints. Functional nylon parts and small batches can be relevant applications, depending on grade, size, tolerance and supplier.
For a detailed display model, read how to assess resin for small features. For a functional powder-based part, compare nylon and its process requirements. These guides help specify the request; they do not confirm availability of a process from OmniTechs.
Compare surface, strength, fit and size
Surface
FDM generally shows paths and layer structure. SLA can offer finer detail and a smoother visual result, while still requiring attention to supports and finishing. SLS has a characteristic powder-based surface.
Do not choose only by which photograph looks smoothest. A rougher surface may be functionally acceptable; a visible consumer object may need additional finishing with any process. Agree the finished surface before production.
Mechanical behaviour
Performance depends on the exact material, geometry, orientation, settings and loading. “SLS is stronger” or “resin is brittle” is too broad without a specific variant and application.
Discuss stiffness, toughness, load direction, repeated loading, impact, wear, temperature, environment and fixing method. The requirement might be low deflection rather than resistance to a single impact, for example.
Fit and dimensions
Every process has tolerances and design rules. Sliding, interference, snap and threaded connections require different clearances. Use a trial or calibration feature where the fit is critical.
Mark critical dimensions on a drawing. Overall model size does not show which diameter, hole spacing or flatness determines whether the part works. The tolerances and clearance guide helps distinguish those requirements.
Size
FDM may be practical for larger parts, but long print times, distortion and joints need assessment. SLA and SLS have their own build-volume and cost constraints. Splitting and assembling the model may help; another manufacturing method may sometimes be more suitable.
Compare total cost and delivered condition
Material volume is only one cost factor. Consider machine time and capacity, preparation, orientation, supports or powder use, failure risk, cleaning, support removal, curing, blasting, sanding, painting or coating, quality checks, quantity, nesting and documentation.
One simple FDM part can be efficient, while a long print with extensive support and finishing may not be cheap. SLA's fine detail still involves washing, curing and removing supports. SLS can combine several parts in a build, but preparation and powder handling still cost time.
Ask for a price at the same delivered condition. A raw part and a display-ready finished object are different orders.
Examples of useful comparisons
Shape and size prototype
Purpose: check dimensions and ergonomics quickly. FDM is often a useful candidate unless fine detail or a particular surface determines the test.
Small detailed model
Purpose: fine text, miniature forms or visual presentation. Assess SLA, including the exact resin and finishing.
Functional clip or enclosure
Purpose: assembly, bending or repeated use. Compare a suitable FDM material, technical resin or SLS nylon against the geometry and load.
Internal channel or complex assembled geometry
Purpose: produce features difficult to reach with supports. SLS may help, but powder removal, wall thickness and inspectability must be checked.
Larger fixture or mould-like tool
Purpose: positioning, dimensions or production support. FDM, possibly split into parts, may be practical depending on stiffness and environment.
Small batch
Purpose: repeat identical functional parts. Compare total cost and quality across suitable printing processes and other manufacturing methods. The best prototype process is not automatically the best batch process.
Information that changes the process choice
Supply the model and original CAD where available, overall dimensions, quantity, critical fit, function, loading, required material behaviour, environment, visible faces, finish, colour, permitted design changes, trial purpose and consequences of failure.
| Priority | Investigate FDM | Investigate SLA | Investigate SLS |
|---|---|---|---|
| Accessible shape trial | Often a strong starting point | Possible | Less obvious as a first choice |
| Large part | Often relevant | Build-volume dependent | Build-volume and cost dependent |
| Fine visual detail | More limited | Often relevant | Depends on detail and surface |
| Complex geometry without separate supports | Orientation dependent | Supports still matter | Powder support can help |
| Functional nylon | Possible with filament processing | Not the main route | Often relevant |
| Smooth visible surface | Finishing may be needed | Often relevant | Finishing may be needed |
| Several small parts | Assess each part | Assess build and supports | Nesting may be useful |
Let the main requirement guide the request
Identify what you need to assess: a visible finish, a mating connection or a specific movement. For a first shape or fit trial, discuss a prototype with that test purpose. If you have an existing model and know the construction and quantity, prepare a printing request.
Ask which process, material grade and finishing the proposal actually includes. This comparison is not a list of machines or processes operated by OmniTechs. Compare total printing costs only after matching the delivered condition.