Additive manufacturing, or 3D printing, lowers costs, saves time, and transcends the limits of fabrication processes for product development. From concept models and functional prototypes in rapid prototyping to jigs, fixtures, or even end-use parts in manufacturing, 3D printing technologies offer versatile solutions in a wide variety of applications.
Over the last few years, high-resolution 3D printers have become more affordable, easier to use, and more reliable. As a result, 3D printing technology is now accessible to more businesses, but choosing between the various competing 3D printing solutions can be difficult.
Which technology is suitable for your particular application? What materials are available? What equipment and training do you need to get started? How about costs and return on investment?
In this article, we’ll take a closer look at the three most established plastic 3D printing processes today: fused deposition modeling (FDM), stereolithography (SLA), and selective laser sintering (SLS).
Fused Deposition Modeling (FDM)
Fused deposition modeling (FDM), also known as fused filament fabrication (FFF), is the most widely used form of 3D printing at the consumer level, fueled by the emergence of hobbyist 3D printers. FDM 3D printers build parts by melting and extruding thermoplastic filament, which a printer nozzle deposits layer by layer in the build area.
FDM works with a range of standard thermoplastics, such as ABS, PLA, and their various blends. The technique is well-suited for basic proof-of-concept models, as well as quick and low-cost prototyping of simple parts, such as parts that might typically be machined.
FDM parts tend to have visible layer lines and might show inaccuracies around complex features. This example was printed on a Stratasys uPrint industrial FDM 3D printer with soluble supports (machine starting at $15,900).
FDM has the lowest resolution and accuracy when compared to SLA or SLS and is not the best option for printing complex designs or parts with intricate features. Higher-quality finishes may be obtained through chemical and mechanical polishing processes. Industrial FDM 3D printers use soluble supports to mitigate some of these issues and offer a wider range of engineering thermoplastics, but they also come at a steep price.
FDM printers struggle with complex designs or parts with intricate features (left), compared to SLA printers (right).
Stereolithography (SLA)
Stereolithography was the world’s first 3D printing technology, invented in the 1980s, and is still one of the most popular technologies for professionals. SLA resin 3D printers use a laser to cure liquid resin into hardened plastic in a process called photopolymerization.
See how stereolithography works.
SLA parts have the highest resolution and accuracy, the clearest details, and the smoothest surface finish of all plastic 3D printing technologies, but the main benefit of SLA lies in its versatility. Material manufacturers have created innovative SLA photopolymer resin formulations with a wide range of optical, mechanical, and thermal properties to match those of standard, engineering, and industrial thermoplastics.
SLA parts have sharp edges, a smooth surface finish, and minimal visible layer lines. This example part was printed on a Formlabs Form 3 desktop SLA 3D printer (machine starting at $3,499).
SLA is a great option for highly detailed prototypes requiring tight tolerances and smooth surfaces, such as molds, patterns, and functional parts. SLA is widely used in a range of industries from engineering and product design to manufacturing, dentistry, jewelry, model making, and education.
Selective Laser Sintering (SLS)
Selective laser sintering is the most common additive manufacturing technology for industrial applications.
SLS 3D printers use a high-powered laser to fuse small particles of polymer powder. The unfused powder supports the part during printing and eliminates the need for dedicated support structures. This makes SLS ideal for complex geometries, including interior features, undercuts, thin walls, and negative features. Parts produced with SLS printing have excellent mechanical characteristics, with strength resembling that of injection-molded parts.
SLS parts have a slightly rough surface finish, but almost no visible layer lines. This example part was printed on a Formlabs Fuse 1 benchtop SLS 3D printer (machine starting at $9,999).
The most common material for selective laser sintering is nylon, a popular engineering thermoplastic with excellent mechanical properties. Nylon is lightweight, strong, and flexible, as well as stable against impact, chemicals, heat, UV light, water, and dirt.
The combination of low cost per part, high productivity, and established materials make SLS a popular choice among engineers for functional prototyping, and a cost-effective alternative to injection molding for limited-run or bridge manufacturing.
Compare FDM, SLA, and SLS 3D Printing Technologies
Each 3D printing technology has its own strengths, weaknesses, and requirements, and is suitable for different applications and businesses. The following table summarizes some key characteristics and considerations.
| FUSED DEPOSITION MODELING (FDM) | STEREOLITHOGRAPHY (SLA) | SELECTIVE LASER SINTERING (SLS) | |
|---|---|---|---|
| Resolution | ★★☆☆☆ | ★★★★★ | ★★★★☆ |
| Accuracy | ★★★★☆ | ★★★★★ | ★★★★★ |
| Surface Finish | ★★☆☆☆ | ★★★★★ | ★★★★☆ |
| Throughput | ★★★★☆ | ★★★★☆ | ★★★★★ |
| Complex Designs | ★★★☆☆ | ★★★★☆ | ★★★★★ |
| Ease of Use | ★★★★★ | ★★★★★ | ★★★★☆ |
| Pros | Fast Low-cost consumer machines and materials |
Great value High accuracy Smooth surface finish Range of functional applications |
Strong functional parts Design freedomNo need for support structures |
| Cons | Low accuracy Low details Limited design compatibility |
Sensitive to long exposure to UV light | Rough surface finish Limited material options |
| Applications | Low-cost rapid prototyping Basic proof-of-concept models |
Functional prototyping Patterns, molds, and tooling Dental applications Jewelry prototyping and casting Modelmaking |
Functional prototyping Short-run, bridge, or custom manufacturing |
| Print Volume | Up to ~200 x 200 x 300 mm (desktop 3D printers) | Up to 300 x 335 x 200 mm (desktop and benchtop 3D printers) | Up to 165 x 165 x 320 mm (benchtop 3D printers) |
| Materials | Standard thermoplastics, such as ABS, PLA, and their various blends. | Varieties of resin (thermosetting plastics). Standard, engineering (ABS-like, PP-like, flexible, heat-resistant), castable, dental, and medical (biocompatible). | Engineering thermoplastics. Nylon 11, Nylon 12, and their composites. |
| Training | Minor training on build setup, machine operation, and finishing; moderate training on maintenance. | Plug and play. Minor training on build setup, maintenance, machine operation, and finishing. | Moderate training on build setup, maintenance, machine operation, and finishing. |
| Facility Requirements | Air-conditioned environment or preferably custom ventilation for desktop machines. | Desktop machines are suitable for an office environment. | Workshop environment with moderate space requirements for benchtop systems. |
| Ancillary Equipment | Support removal system for machines with soluble supports (optionally automated), finishing tools. | Post-curing station, washing station (optionally automated), finishing tools. | Post-processing station for part cleaning and material recovery. |
3D Printing Costs and Return on Investment With FDM, SLA, and SLS Technologies
Ultimately, you should choose the technology that makes the most sense for your business. Prices have dropped significantly in recent years, and today, all three technologies are available in compact, affordable systems.
Calculating 3D printing costs does not end with upfront equipment costs. Material and labor costs have a significant influence on cost per part, depending on the application and your production needs.
Here’s a detailed breakdown by technology:
| FUSED DEPOSITION MODELING (FDM) | STEREOLITHOGRAPHY (SLA) | SELECTIVE LASER SINTERING (SLS) | |
|---|---|---|---|
| Equipment Costs | Budget printers and 3D printer kits start at a few hundred dollars. Higher quality mid-range desktop printers start around $2,000, and industrial systems are available from $15,000. | Professional desktop printers start at $3,500, large-format benchtop printers at $10,000, and large-scale industrial machines are available from $80,000. | Benchtop systems start at $10,000, and industrial printers are available from $100,000. |
| Material Costs | $50-$150/kg for most standard and engineering filaments, and $100-200/kg for support materials. | $149-$200/L for most standard and engineering resins. | $100/kg for nylon. SLS requires no support structures, and unfused powder can be reused, which lowers material costs. |
| Labor Needs | Manual support removal (can be mostly automated for industrial systems with soluble supports). Lengthy post-processing is required for a high-quality finish. |