Material Selection for Rapid Prototyping: A Guide to Common Plastics

Choosing the right material is a critical step in rapid prototyping. The ideal choice depends on your prototype's purpose: Is it for a visual model, a functional test, or a master pattern for molding? Each material offers a unique balance of strength, heat resistance, durability, and aesthetics.

Here’s a breakdown of the key characteristics for ABS, PC, PA, POM, and PMMA.

1. ABS (Acrylonitrile Butadiene Styrene)

ABS is one of the most popular and versatile prototyping materials, often considered a great "all-rounder."

• Key Properties: Good impact strength, decent rigidity, and good machinability. It's easy to sand, paint, and glue.

• Strengths:

• Toughness: Offers a good balance of strength and flexibility, resistant to chipping.

• Surface Finish: Can be easily post-processed to a very smooth, high-quality finish.

• Cost-Effective: Generally inexpensive and widely available.

• Weaknesses:

• Poor UV Resistance: Long-term exposure to sunlight can cause it to yellow and become brittle.

• Low Heat Resistance: Softens and deforms at relatively low temperatures (~80-100°C).

• Poor Chemical Resistance: Can be attacked by solvents like acetone and certain oils.

• Best For:

• Concept Models: General-purpose prototypes to check form, fit, and assembly.

• Functional Testing: Parts that require moderate toughness and durability.

• Pre-production Visuals: Models that need to be painted or finished to look like a final product.

• Common Prototyping Processes: FDM (Fused Deposition Modeling), CNC Machining.

2. PC (Polycarbonate)

PC is the go-to material when you need high strength, durability, and exceptional heat resistance.

• Key Properties: Excellent impact strength (virtually unbreakable), very high heat deflection temperature, and good clarity.

• Strengths:

• Extreme Toughness: One of the toughest thermoplastics available.

• High Heat Resistance: Can withstand temperatures up to ~125-135°C, making it suitable for under-hood automotive applications or hot environments.

• Transparency: Naturally transparent, ideal for clear prototypes like lenses or covers.

• Weaknesses:

• Prone to Scratching: The surface is relatively soft and can scratch easily.

• Requires High-Temperature Printing: Printing with FDM can be challenging due to warping; often requires a heated chamber.

• More Expensive: Typically costs more than ABS.

• Best For:

• High-Stress Functional Parts: Gears, brackets, and tools that undergo significant load.

• Heat-Resistant Components: Prototypes for engines, electrical housings, or medical devices that require sterilization.

• Clear Applications: Transparent covers, light diffusers, and lenses.

• Common Prototyping Processes: FDM, CNC Machining, SLS (Selective Laser Sintering) in PC-blends.

3. PA (Nylon)

Nylon, or Polyamide, is known for its excellent wear resistance, toughness, and semi-flexible nature.

• Key Properties: High strength, good fatigue resistance, excellent abrasion and wear resistance, and some grades are flexible.

• Strengths:

• Durability: Very resistant to wear, making it ideal for moving parts.

• Tough & Slightly Flexible: Can absorb impact and return to its original shape.

• Chemical Resistance: Resistant to many oils, fuels, and solvents.

• Weaknesses:

• Hygroscopic: Absorbs moisture from the air, which can affect dimensions and properties. Often requires drying before processing and sealing afterward.

• Can Warp: Prone to warping during printing if not properly controlled.

• Poor UV Resistance: Similar to ABS, it degrades in sunlight unless stabilized.

• Best For:

• Wear-Resistant Parts: Functional prototypes like gears, bearings, bushings, and hinges.

• Tough, Living Hinges: Parts that need to flex repeatedly.

• Complex, Strong Components: Often used in SLS to create intricate, durable parts without support structures.

• Common Prototyping Processes: SLS (most common), FDM, CNC Machining.

4. POM (Polyoxymethylene / Acetal)

Commonly known by the brand name Delrin, POM is an engineering powerhouse valued for its stiffness, low friction, and excellent machinability.

• Key Properties: High stiffness and strength, very low friction, excellent dimensional stability, and high resistance to creep.

• Strengths:

• "The Steel of Plastics": Excellent long-term load-bearing capability.

• Low Friction: Self-lubricating, making it ideal for sliding parts.

• Superb Machinability: Produces clean, sharp edges and has a very smooth surface finish when machined.

• Weaknesses:

• Not Suitable for FDM/3D Printing: It has a strong tendency to warp and crack during layer-by-layer deposition. It is almost exclusively used in CNC Machining for prototyping.

• Poor Adhesion: Difficult to glue or paint.

• Sensitive to Acid Attack: Degrades in strong acids.

• Best For:

• Precision Mechanical Parts: High-accuracy prototypes for gears, slides, locks, and fasteners.

• Low-Friction Applications: Bushings, rollers, and conveyor parts.

• Common Prototyping Processes: CNC Machining (primary method).

5. PMMA (Polymethyl Methacrylate / Acrylic)

PMMA, often called acrylic, is the best choice when optical clarity and aesthetics are the top priority.

• Key Properties: Crystal-clear transparency, high gloss surface, good UV resistance, and stiff but brittle nature.

• Strengths:

• Optical Clarity: Offers the best transparency and light transmission of the common prototyping plastics.

• Excellent Aesthetics: Has a high-gloss, "finished" look.

• UV Stable: Resists yellowing and degradation from sunlight.

• Weaknesses:

• Brittle: Low impact strength; it can crack or shatter under stress.

• Scratches Easily: The surface is relatively soft.

• Poor Chemical Resistance: Can be cracked by many solvents.

• Best For:

• Transparent Models: Light pipes, lenses, display covers, and windows.

• Aesthetic & Visual Prototypes: Models where appearance is more important than function.

• Common Prototyping Processes: CNC Machining (best for clarity), SLA (Stereolithography - for good clarity but less than machined PMMA), Laser Cutting.

Quick Selection Guide Summary

Final Tip: Always discuss your prototype's specific requirements (mechanical stress, temperature exposure, chemical environment, and required tolerances) with your prototyping service provider. They can help you select the optimal material and manufacturing process for your project.