TIPS WITH TONY: Flame-Retardant Thermoplastics and UL Classifications

UL 94 is a plastics flammability standard released by the Underwriters Laboratories (USA). The standard classifies plastics according to how they burn in various orientations and part thicknesses from the lowest flame-retardant to most flame-retardant in six different classifications.

UL 94 Rating

Definition of Rating


                                          Slow burning on a horizontal part.


                                          Burning stops within 30 seconds on a vertical                                             part allowing for drops of flammable plastic.


                                          Burning stops within 30 seconds on a vertical                                             part allowing for drops of plastic that are not                                               inflames.


                                          Burning stops within 10 seconds on a vertical                                             part allowing for drops of plastic that are not                                               inflames.


                                          Burning stops within 60 seconds on a vertical                                             part with no drops of plastic allowed but may                                               burn through the part.


                                          Burning stops within 60 seconds on a vertical                                             part with no drops of plastic allowed and                                                     cannot burn through the part.

Continue reading

TIPS WITH TONY: 3D Printing Living Hinges

Did you know that living hinges are possible with 3D printing? Here are a few things areas to keep in mind when designing hinge functions so your part’s functionality and integrity remain intact.

We offer two processes for 3D printing thermoplastic or thermoplastic-like materials: selective laser sintering (SLS) and stereolithography (SL). But only SLS will produce parts with the functionality required for a living hinge.

An SLS part with living hinge functionality.

Anytime we see the potential for a living hinge in a 3D-printed part, we will strongly guide you to SLS. SLS uses nylon thermoplastic, primarily PA 850 Black, which is a nylon 11 material. PA 850 has an increased EB of 14-51% followed by ALM PA 650 with an EB of 24%.

However, you can’t take a part that was produced in PA 850 or ALM PA 650 and expect it to function as a living hinge without a secondary process first. When you have a living hinge, we need to know what direction or the range of motion in which the hinge may function. This is critical as we anneal the part by heating it to 250-275°F and flex the hinge in the intended range of motion. This extends the life of the living hinge by stretching the material instead of fracturing the links of resin.

SL offers thermoplastic-like materials, but they are not be recommended for living hinge applications. Somos 9120 is our most flexible material of all SL resins with an elongation at break (EB) of 15-25%.

Continue reading

TIPS WITH TONY: Replace Metal with Plastic to Save Weight, Cost

To decrease weight and potentially cost, you can replace metal with plastic on certain parts through 3D printing and injection molding. At Proto Labs, we use industrial 3D printing process stereolithography (SL) to produce thermoplastic-like parts that have a nickel coating on the surface. This offers the increased strength of aluminum die-cast components, without the weight. With injection molding, the introduction of thermally conductive plastics has broken new ground when looking for heat dissipation of expensive heat sinks.

Stereolithography parts built with SLArmor have a metal coating applied over a thermoplastic-like base.

SLArmor involves a ceramic-filled DSM Somos material, which has a metal coating applied to achieve the look, feel and, most importantly, comparable strength of aluminum without added weight. SL is a cost-effective prototyping method for initial parts that mimic metal before moving to higher volumes of die-casted parts.

The material properties of SLArmor are greatly improved in regards to heat deflection, tensile strength, elongation at break and elasticity. The chart below shows exactly how the material relates to die-cast aluminum in three different thicknesses that can be applied based on geometry of SL parts. Note that the thickness of the nickel plating may vary on each part due to the ability to apply the coatings.

Continue reading

TIPS WITH TONY: High-Temperature Thermoplastics

We offer two high-temperature thermoplastics: PEEK and PEI. Both high-performance materials can be machined and injection molded, and produce parts that can withstand extreme temperatures.

PEEK parts contain excellent mechanical and chemical resistance during high-temperature applications. Its mechanical properties consist of tensile modulus strengths of 90-200 MPa and a melting temperature of 662˚F (343˚C). Some grades of PEEK have operating temperatures around 482˚F (250˚C).

Because of its robustness, PEEK is commonly used in applications for mechanical and medical instruments. PEEK is also used widely in the aerospace, automotive and chemical industries due to the insulating properties and creep resistance of any dimensional changes in high-temperature applications.

Like PEEK, PEI (often called by its trade name Ultem) offers outstanding elevated thermal resistance, high strength, stiffness and chemical resistance. PEI consists of tensile modulus strengths of 96-190 MPa and with a melting temperature above 420˚F.

PEI is available in transparent and opaque colors including glass additives for improved mechanical properties. Unlike other thermoplastics, PEI provides optimal strength and resists stress cracking when the material is exposed to hydrocarbons, alcohols and acids that makes them ideal for automotive and aerospace applications.

Which Manufacturing Process is Best?
If you’re in need of small quantities (up to 200) of PEEK and PEI parts, we can machined them in less than 3 days. For increased quantities in the thousands, rapid injection molding can produce parts in 15 days or less.

The physical properties vary little between processes, so please test out one sample using machining before moving to injection molding if you are unsure if your parts design is complete or not.

Contact us if you have any further questions about high-temp plastics and specific questions regarding PEEK or PEI. We have a full staff of customer service engineers who can be reached at or 877-479-3680.

TIPS WITH TONY: The Material Properties of Machined Plastic

If your ultimate product development plan involves a move to injection molding, CNC machining offers a material selection conducive to a transition into increased molded quantities. Proto Labs has more than 30 engineering-grade thermoplastic materials with various benefits.

To illustrate the material properties better (Figure 1), we took four frequently used thermoplastics — ABS, polycarbonate (PC), polypropylene (PP) and nylon polyamide (PA) — and compared the maximum heat deflection, tensile strength and elongation at break that occurs within injection molding, machining and 3D printing.

ABS Molded

ABS Machined

ABS-like SL

Heat Deflection




Tensile Strength

6,091 psi

6,100 psi

7,800 psi

Elongation at Break




PC Molded

PC Machined

PC-like SL

Heat Deflection




Tensile Strength


8,000 psi

11,300 psi

Elongation at Break




PP Molded

PP Machined

PP-like SL

Heat Deflection




Tensile Strength

5,801 psi

4,800 psi

7,250 psi

Elongation at Break




PA Molded

PA Machined


Heat Deflection




Tensile Strength

16,500 psi

10,000 psi

6,946 psi

Elongation at Break




Figure 1: Thermoplastic material properties compared between different manufacturing processes. Properties are dependent on actual material selected, part thickness and geometry. Please review each material data sheet individually as these are estimates.

Translation: CNC machining is ideal for functional prototyping and end-use production parts, and readies your design for an eventual move to injection molding. We have a full staff of technical experts that can answer any machining questions you have at or 877-479-3680. For more information on 3D printing, CNC machining or injection molding at Proto Labs, head over to