How does FDM 3D printing differ from SLA and SLS?

How does FDM 3D printing differ from SLA and SLS?

FDM deposits and fuses a filament bead by bead; SLA cures liquid resin with a laser or projected light; SLS fuses polymer powder without the same support structure; MJF uses fusing and detailing agents over a powder bed. Their parts differ in anisotropy, surface, material state, and post-processing.

What does FDM change?

FDM parts are affected by layer direction, bead width, bonding, cooling, and infill or wall design. The critical load should be oriented through the stronger direction where possible, and moisture or thermal conditioning should be controlled for hygroscopic materials.

See FDM process guidance as a process family reference, then qualify the actual material and geometry.

What do powder-bed routes change?

SLS and MJF can make complex nylon forms with less support, but powder refresh, thermal history, packing, surface finish, and powder removal still affect the result. Fit and fatigue-critical surfaces may need finishing or a larger design margin.

A powder-bed part should be quoted with material, machine, orientation or nesting, and final finish.

When is resin appropriate?

SLA or DLP is useful for fine details, smooth surfaces, and certain molds or visual models. The cured resin can be sensitive to UV, heat, moisture, and sustained load. Do not use a resin prototype as a thermoplastic production proxy without a test.

FDM provides an accessible thermoplastic route and can be economical for prototypes, fixtures, and short runs. The build direction determines how bead interfaces carry load, and cooling can affect warpage and bonding. SLS and MJF can create nested nylon parts without the same support burden, but powder handling, thermal history, surface, and finishing remain part of the result.

SLA and DLP provide fine detail and smooth surfaces with photopolymers, but the cured material ages differently from a thermoplastic. They are useful for visual models, patterns, and selected functional parts, not as an automatic substitute for nylon or PC. Process selection must include the final material state and service environment.

The quote should specify machine family, polymer grade, orientation or nesting, wall strategy, support or powder removal, surface finish, and post-processing. If a tolerance is critical, state the datum and whether it is measured before or after conditioning. If the part is hollow, state cleaning and residue limits.

A first article can reveal fit and finish problems before a batch is released. Use the first article to confirm the geometry, conditioning, and functional test, not merely to approve the color or appearance.

Process selection should include support, powder, or resin removal. A part that can be printed but cannot be cleaned or measured is not complete.

Ask for an inspection method that reaches the critical feature and for a finishing allowance that does not consume the required wall or datum.

Process comparison should include post-processing and inspection access. A powder-bed part can avoid supports but still need cleaning; an FDM part can be inexpensive but need a careful orientation; a resin part can be detailed but need a strict cure route. The best process is a complete route, not a printer label.

FDM, SLS, MJF, SLA, and DLP differ in bonding, powder or resin state, supports, surface, and aging. Ask for the actual machine, polymer, orientation or nesting, post-processing, and measurement condition. A process with fine detail is not automatically a process with the required fatigue or heat performance.

A representative first article should confirm a feature that matters: a clip, boss, seal, hole, thread, or duct, not only a flat coupon.

FDM, SLS, MJF, SLA, and DLP should be compared as complete production routes. Include material lot, orientation or nesting, supports or powder removal, surface, conditioning or cure, and inspection. FDM may offer an economical thermoplastic route but needs a load-direction decision. Powder-bed processes may reduce support work but need cleaning and thermal control. Resin may reproduce fine detail but age differently.

A first article should contain the feature that controls the part: a clip, boss, seal, thread, duct, or mating hole. A flat coupon alone may not show the risk in the actual geometry.

The route review should ask how supports, powder, or uncured resin leave the part. A trapped support, powder, or resin defect can affect mass, fit, odor, cleanliness, or later strength. If the part has a cavity, define drain and inspection access before the geometry is approved.

The material brief should be attached to the drawing or purchase order so the service condition is not lost when the part is reproduced. State whether the target is dry, conditioned, cured, coated, or assembled. If the material is hygroscopic or the load is sustained, include the conditioning time and temperature. This makes a later dimensional or functional comparison meaningful.

The purchase record should name the conditioning and measurement state beside each critical dimension. This is especially important for hygroscopic polymers and for parts whose fit changes after cure or environmental exposure.

Process comparison and first article

FDM lays down beads, so orientation, cooling, and interlayer bonding control the load path and warpage. SLS and MJF fuse powder without the same support burden, but powder refresh, thermal history, nesting, surface, and conditioning affect the delivered part. SLA and DLP cure photopolymer and therefore require a separate wash and cure record. plastics service

Choose by geometry, quantity, material state, and the feature that must be accepted. A thin FDM clip needs a cycle test after conditioning; a nylon housing needs dimensional and assembly checks after humidity exposure; a cured resin detail needs final-cure and aging boundaries. and material extrusion should explain the selected route, not replace the first-article evidence.