FDM vs SLA 3D Printers: A Complete Comparison Guide

3D printing technology has revolutionized product design and manufacturing processes. The two most common technologies used in desktop 3D printing are Fused Deposition Modeling (FDM) and Stereolithography (SLA). Both offer distinct advantages and disadvantages for different applications. This guide provides a comprehensive comparison of FDM vs SLA to help you select the right 3D printing technology for your needs.

How Do FDM and SLA 3D Printers Work?

Understanding how FDM and SLA 3D printers work provides great insight into their key differences.

Fused Deposition Modeling (FDM)

FDM printers create objects by heating and extruding thermoplastic filament layer by layer. The print head moves in the X and Y axes, depositing material onto the print bed or platform. After a layer is completed, the platform lowers along the Z-axis, and a new layer is built on top of the previous one.

Common FDM thermoplastics are ABS and PLA. The filament is fed from a spool through a heated print head (extruder) that melts it and deposits it onto the print bed. The extruder head typically moves along the X and Y axes, while the print bed lowers along the Z-axis.

Key components of an FDM 3D printer include:

• Print head extruder: Heats and melts the thermoplastic filament
• Print bed: Holds the object being printed with a “raft” to prevent warping
• Filament spool: Provides the raw plastic material
• Stepper motors: Control motion of print head and print bed
• Hot ends: Nozzles where heated plastic is extruded

FDM printing is considered an additive manufacturing process because objects are built by depositing material layer-by-layer.

Stereolithography (SLA)

SLA 3D printers work by using a UV laser to cure and solidify liquid photopolymer resin layer by layer. An SLA printer starts with an upside-down build platform submerged in a vat of liquid resin.

A laser beam traces each layer, hardening the resin. Once a layer is finished, the build platform lifts slightly, allowing new liquid resin to flow under the object. The laser then traces and hardens the next layer on top of the previous one. This process repeats until the full object is formed.

Key components of an SLA 3D printer include:

• VAT of liquid photopolymer resin
• Build platform
• UV laser
• Optics and mirrors to guide laser
• Controller software

SLA is considered a vat photopolymerization process because each layer is cured by light in a vat of resin.

Key Differences Between FDM vs SLA

Now that you understand the basic operation of FDM and SLA printers, let’s compare some of the key differences between the two technologies.

1. Materials Used

The materials used in FDM vs SLA processes create significant differences in applications and properties of final parts.

FDM: Filament thermoplastics like ABS, PLA, PETG, TPU, NYLON. Materials come on spools as a solid filament.

SLA: Liquid photopolymer resins. The resin vats contain a liquid material with properties that change when exposed to light.

FDM thermoplastics produce functional parts focused on mechanical properties like strength, flexibility, durability. SLA photopolymers produce highly detailed parts focused on accuracy and surface finish.

2. Accuracy and Resolution

FDM: Print resolution ranges from 100 to 200 microns on consumer printers. Thicker layers and extrusion width result in visible layer lines on curved or sloped surfaces.

SLA: Offers superior accuracy of 25-100 microns in the XY axis. Thinner layers produce extremely smooth surfaces without visible layer lines.

SLA printers have much higher X-Y resolution but lower Z axis resolution than FDM. This makes them ideal for cosmetic and decorative objects with fine details.

3. Print Speed

FDM: Print speeds range from 30-200 mm/s. Faster than SLA overall, especially for larger layers. Minimal post-processing.

SLA: Typical speeds of 10-100 mm/s. Constrained by the need to pause between layers for resin to cure. Additional post-processing adds time.

FDM can produce parts much faster than SLA since it does not require stopping between layers. Simple designs with thicker layers can be printed very quickly with FDM.

4. Part Strength

FDM: Good layer adhesion plus solid thermoplastics produce strong, durable parts. Suitable for mechanical applications.

SLA: Photopolymer resin is brittle when cured. Parts can break under high stress or impact. Excellent for precision parts like jewelry.

The layered thermoplastic extrusion in FDM generally produces much stronger parts than SLA photopolymers. Great for functional components.

5. Supported Geometries

FDM: Dual extruder heads allow dissolvable supports. This enables complex geometries like overhangs.

SLA: Resin bath provides inherent support so all geometries can be printed without dedicated support structures.

SLA printers have fewer constraints on part geometries since the liquid resin vat supports overhangs. But FDM dual extruders have broadened capabilities.

6. Post-Processing

FDM: Minimal post-processing needed. Remove part from bed, break away supports, sand if needed.

SLA: Washing, drying, and UV curing of parts is required after printing is complete. More labor intensive.

SLA’s liquid resin requires more post-processing once printing is done. FDM prints can typically be used with minimal cleanup.

7. Applications

FDM: Functional prototypes, end-use parts, tooling, fixtures, mechanical components. Durable and practical prints.

SLA: Concept models, precision castings, jewelry, miniatures, cosmetic prototypes. Excellent fine detail and smoothness.

FDM is ideal for strong functional parts while SLA excels at smooth surface finish and micro-precision details.

8. Operating Costs

FDM: Thermoplastic filament is inexpensive. Lower maintenance costs overall.

SLA: Photopolymer resin is more expensive. Requires cleaning and replacing resin vats.

The material costs of FDM filament is generally much lower than proprietary SLA resins over the long term.

9. Print Bed Size

FDM: Range from 4.7″ x 4.7″ up to 14″ x 14″ for desktop printers. Larger industrial FDM printers reach 6 feet square.

SLA: Typical build volumes of 4.5″ x 2.5″ x 6″ up to 10″ x 10″ x 12″. Size limited by laser power.

FDM machines can accommodate very large build areas by using a moving gantry over a stationary print bed. SLA printers are limited by laser power needed to cure each layer.

10. Supported Materials

FDM: Wide range of thermoplastic materials from various suppliers. Common materials like ABS, PLA, PETG work on most printers.

SLA: Photopolymer resins are proprietary blends. Limited material options optimized for each printer manufacturer.

FDM printers have an open supply chain allowing many filament options. SLA requires using proprietary resins matched specifically to each printer model.

How to Choose Between FDM vs SLA

When selecting an FDM or SLA 3D printer, consider your application requirements, budget, speed needs, material properties, and more.

When to Choose FDM

• Designing functional parts like machine components, tools, fixtures, or enclosures
• Applications requiring durability, impact or heat resistance
• Larger build volumes over 12″ in any dimension
• Printing very large objects over 2 feet square
• Fast print speeds are needed for production
• Prototyping mechanical parts with detailed dimensions

When to Choose SLA

• Highly detailed miniatures, jewelry, cosplay props
• Smooth surface finish and fine features are critical
• Accuracy below 0.05mm is required
• Casting molds for manufacturing
• Biocompatible dental and medical applications
• Price is less of a concern than quality

For most hobbyists and small businesses, an FDM printer like the Prusa i3 offers excellent capabilities at a great value. SLA printers excel with micro-detail at the cost of higher resin expenses and post-processing time.

Key Takeaways: FDM vs SLA 3D Printers

• FDM printers extrude heated thermoplastic filament in layers to build strong, durable parts good for functional prototypes and end-use components.
• SLA printers use a UV laser to selectively cure liquid photopolymer resin layer-by-layer to achieve extremely smooth details down to 25 microns.
• FDM advantages include strength, larger build volumes, reliability, material choice, fast speeds, and lower costs. Better for mechanical parts.
• SLA advantages include precision detail, smooth surface finish, intricate geometries without supports, and micro-accuracy. Better for miniatures.
• Consider requirements for accuracy, speed, cost, build size, and applications when choosing between the two technologies.

Both FDM and SLA offer great opportunities for additive manufacturing. Evaluate your specific needs to determine if FDM or SLA is the right 3D printing process for your next project.