Product Review: AMT PostPro SFX Vapour Smoothing Machine
Our review of the AMT PostPro SFX Vapour Smoothing Machine shows how this system delivers consistent, injection-moulded finishes on 3D…
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Selecting between SLA and FDM 3D printing can determine whether a prototype meets its performance expectations, visual requirements, and production timeline. For engineers and designers, the choice affects surface finish, strength, cost, accuracy, and how quickly you can iterate. This guide breaks down each process in depth, highlighting practical trade-offs and use cases to help you choose the right fit for your prototyping needs.
Stereolithography (SLA) is a vat photopolymerisation process. It works by curing liquid resin layer by layer using a UV light source, either laser-based or using digital projection. The result is a part with highly accurate detail, tight tolerances, and a smooth, injection-moulded-like surface finish.
The SLA process begins with a build platform submerged in a tank of photopolymer resin. A laser or projector then selectively cures each cross-section of the model, solidifying the resin. After each layer is cured, the platform moves incrementally, allowing the next layer to be formed on top. This continues until the complete part is formed.
There are three main types of SLA systems:
Laser-based SLA: Uses a laser beam to trace each layer.
DLP (Digital Light Processing): Projects the entire layer at once using a digital projector.
LCD (Masked SLA): Uses an LCD screen as a light mask, offering fast and cost-efficient printing.
SLA is especially useful for visual prototypes, dental and medical applications, intricate assemblies, and cosmetic parts where fine detail matters. Formlabs offers a complete guide on SLA 3D printing that covers workflow, materials, and accuracy benchmarks.
Fused Deposition Modelling (FDM) is the most common extrusion-based 3D printing process. It builds parts by melting and depositing layers of thermoplastic filament. The filament is fed through a heated nozzle, which moves in the X-Y plane to create each layer. Once a layer is complete, the build platform lowers and the process repeats.
FDM relies on thermoplastics, which solidify as they cool. This makes it ideal for printing durable and functional prototypes using engineering-grade materials. A wide range of polymers are available including:
PLA (Polylactic Acid): Easy to print, suitable for visual models.
ABS (Acrylonitrile Butadiene Styrene): Durable and heat-resistant.
PETG (Polyethylene Terephthalate Glycol): Combines strength and chemical resistance.
TPU (Thermoplastic Polyurethane): Flexible and elastic.
Nylon and CF composites: High strength and wear resistance for engineering use.
FDM is particularly suitable for larger parts, functional prototypes, mechanical testing, and fit-and-assembly trials where surface finish is less critical. Learn more about our FDM 3D printing service and how it supports functional prototyping across sectors. Print settings like infill density, wall thickness, and layer height allow you to balance speed, strength, and material use depending on your goals.
SLA provides smoother surfaces and finer resolution. Its layer heights can go as low as 25 microns, making it ideal for aesthetic models or detailed prototypes like casings and connectors.
FDM prints typically show visible layer lines. Post-processing such as sanding or vapor smoothing (for ABS) may be needed to achieve a smoother finish, but even then, it won’t match SLA’s clarity or surface quality.
FDM has the advantage for strength and durability. It prints with real thermoplastics used in end-use parts, giving prototypes realistic mechanical behaviour. ABS and nylon are commonly used in prototypes subjected to impact or load testing. For example, ABS has a tensile strength of around 40 MPa and heat deflection temperature of about 95°C, making it suitable for fixtures and housings.
SLA parts, unless printed with engineering-grade resins, tend to be more brittle. Standard resins have a tensile strength in the range of 25–50 MPa and are best suited for cosmetic or lightly loaded parts. Tough SLA resins can improve impact resistance and flexibility but still lag behind the performance of standard FDM materials.
SLA is capable of tight tolerances, often achieving dimensional accuracy of ±0.05 mm. It’s well-suited for snap-fit assemblies or precision housings. SLA printing offers finer resolution and tighter tolerances (complete SLA tolerances breakdown) than most FDM printers.
FDM has good repeatability but may need calibration and compensation for material shrinkage. It can produce dimensionally accurate parts with tolerances in the ±0.1–0.2 mm range depending on geometry.
FDM can print much larger parts economically. Desktop machines can build parts up to 300 mm or more in any axis, with industrial FDM extending beyond 1 metre. For example, a typical prototype housing measuring 350 × 200 × 100 mm could be printed on an industrial FDM machine in one go, reducing the need for segmentation.
SLA systems are usually limited by resin vat size. While large-format SLA exists, it is significantly more expensive and slow compared to FDM. A resin printer with a 200 × 120 × 150 mm build volume is common, which may restrict larger conceptual models or functional prototypes.
FDM prints faster for bulky parts due to higher layer heights and infill tuning. It is ideal when quick iterations are needed.
SLA’s print speed depends on the resin and layer height but is generally slower due to the curing process. However, it excels in small, detailed parts and offers predictable print times regardless of part density.
FDM materials are cheaper and more abundant. A 1 kg spool of PLA or ABS might cost £20–£35. This affordability makes FDM ideal for repeated design iterations.
SLA resins cost more (typically £80–£150 per litre), and post-processing equipment (wash and cure stations) adds operational cost. However, the visual quality and precision may justify the investment for the right applications. With SLA, you can choose from a wide range of engineering resins (industrial SLA resin comparison guide) to match specific mechanical or thermal needs.
SLA requires isopropyl alcohol cleaning and UV curing post-print. Supports are also typically harder to remove cleanly, and parts must be handled with gloves during finishing.
FDM prints need only basic support removal and trimming. Optional finishing includes sanding, filler priming, or chemical smoothing depending on the polymer.
For a deeper technical comparison between FDM, SLA, and SLS technologies, Formlabs provides a detailed breakdown of strengths, applications, and costs.
Both SLA and FDM require attention to safety and environmental impact, especially in enclosed office or workshop settings.
ABS emits ultrafine particles (UFPs) and VOCs when heated. Ventilation or enclosed machines with HEPA filters are recommended.
PLA is safer and biodegradable, making it suitable for office environments.
Minimal PPE is needed beyond basic machine safety.
Uncured resin is a skin irritant and must be handled with gloves.
Isopropyl alcohol is flammable and requires proper storage.
Disposal of resin waste must follow hazardous materials guidelines.
In both cases, keeping equipment clean and well-ventilated reduces health risks and improves part quality.
Visual models for client presentations
Prototypes where fine features or fit are critical
Transparent or cosmetic housings
Medical and dental models
Miniatures or highly detailed assemblies
Rapid functional prototypes
Structural or load-bearing test parts
Large-format models
Fixtures and jigs
Low-cost iteration during early development
A product design agency was developing a new consumer electronics enclosure. They initially used SLA to produce high-resolution prototypes for user testing and visual approval. The smooth finish helped stakeholders visualise the final product.
Once the exterior was approved, the engineering team switched to FDM to test bracket placement, structural rigidity, and tolerance to repeated assembly. They used ABS to produce mounting brackets and PLA for iterative design shells. The feedback loop was fast, and the functional testing revealed key ergonomic changes that would not have been discovered using visual models alone.
Combining SLA and FDM allowed the team to reduce design cycle time by 40% and saved over £3,000 in tooling revisions. The final design was signed off after just three prototype rounds.
Need high detail or cosmetic appeal? Use SLA
Need durable parts for load or impact? Use FDM
Printing large prototypes? Use FDM
Tight tolerance assembly fit? Use SLA
Low budget iterative testing? Use FDM
Medical/dental model accuracy? Use SLA
Basic fit checks or mockups? Use FDM
Clear/translucent materials? Use SLA
FDM prints are mechanically stronger because they use real thermoplastics. SLA resins are more brittle, although specialised resins can close the gap.
Yes. SLA can print features and tolerances at much finer resolution than FDM, which is why it’s often used for small precision parts.
Only if the resin is designed for mechanical use. Standard resins are better for visual prototypes. Tough or high-temperature resins are better suited for functional use.
Yes. FDM filament is much cheaper, and post-processing is minimal. SLA carries higher material and finishing costs.
FDM is usually faster for larger or basic parts. SLA is more time-consuming due to post-processing, though it can be efficient for high-detail small runs.
The choice between SLA and FDM comes down to the purpose of your prototype. If you’re demonstrating form, surface finish, or fine detail, SLA is the clear winner. If your focus is function, mechanical fit, or rapid iteration, FDM is often more suitable.
In many workflows, the best approach is to use both: start with SLA to validate aesthetics, then switch to FDM for rugged functional testing. This hybrid method helps you move faster through development while maintaining high design integrity.
Our SLA 3D printing service supports applications across product design, dental, and engineering sectors with industry-grade resolution and resin performance.
Looking for expert guidance on choosing the right 3D printing process for your prototype? Explore our 3D Printing Services or Get a Quote today.
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