Selecting a Material for Stereolithography (SLA) 3D Printing
Comparing injection-molded thermoplastics to ‘thermoplastic-like’ materials in stereolithography
Many factors come into play when comparing the material properties of thermoplastics found in injection molding versus “thermoplastic-like” materials used in an industrial-grade 3D printing technology like stereolithlography (SLA).
SLA uses a thermoset liquid, not a thermoplastic, which is UV-cured in layers to form final parts. Because of this major difference in fabrication methods, material properties like tensile strength, heat deflection and flexure modulus may differ from SLA’s more traditional counterpart. Furthermore, SLA produces anisotropic properties where the values for X, Y and Z axis may differ depending on the orientation of the build—a consideration unique to 3D printing processes.
At Protolabs, a thorough selection of thermoplastic-like materials are offered through SLA, but what may surprise you is the versatility and range of potential applications for SLA parts. We’ll take you through each material and its properties, and compare them with one another (as well as with molded plastics) to help you decide how to best implement SLA.
Accura 5530 material is transparent in color, temperature tolerant and water resistant. It also is resistant to automotive fluids making it suitable for under-the-hood and electrical applications. Note that secondary operations are required to achieve transparency and the final part will still retain a slight amber hue.
Accura 60 offers the ability for fine detail while providing good stiffness in parts. Common applications include durable prototypes for automotive, consumer electronics and lighting components, as well as medical instruments. Accura 60 has a high tensile strength and modulus making this a good choice to replace polycarbonate (PC) when heat resistance is not critical. However, Accura 60 has the highest moisture absorption rate of the SLA materials, which may impact dimensional stability overtime.
Somos NanoTool has an added ceramic filler that increases stiffness and brittleness over other SLA materials. Along with stiffness, Nanotool touts the highest temperature resistance compared to most materials offered in SLA. It’s regularly used in aerospace and automotive applications that often require greater strength and temperature resistances.
|Accura 5530||Accura 60||Somos NanoTool||PC (Molded)|
|Hardness, Shore D||88||86||93-94||118-120(R-Scale)|
|Tensile Modulus||3,585 - 3758 MPa||2690-3100 MPa||10,400-11,400 MPa||2,400 MPa|
|Tensile Strength||47-61 MPa||58-68 MPa||66-80 MPa||50-72 MPa|
|Flexural Modulus||3,496 - 3634 MPa||2700-3000 MPa||9,960 - 10,200 MPa||2,200 - 2,400 MPa|
|Flexural Strength||96-108 MPa||87-101 MPa||103-149 MPa||82-93 MPa|
Chart 1: Three PC-like materials and one molded PC thermoplastic are compared across six material property categories. Notice how the heat deflection in the PC-like parts are be much lower or have a wider range than the molded PC due to the anisotropic properties discussed earlier. *Heat deflection was measured at 66 psi.
RenShape SLA 7820 has high strength and good dimensional stability, even in high humidity. The material is black and commonly used in automotive parts, consumer packaging, electrical housings and toys due to its impact resistance and ease of secondary finishing that provides the appearance of production quality.
MicroFine Green™ is a proprietary material at Protolabs, offering an extremely high resolution and build accuracy. MicroFine™ has a unique opaque green color distinguishing it from other materials. Layer thicknesses of 0.001 in. and feature sizes of 0.002 in. are possible with MicroFine Green™ to accommodate application that require very small parts.
Somos Watershed XC 11122 is strong, durable, water-resistant ABS-like material. It’s nearly colorless and mimics a clear engineered-grade plastic. Watershed’s high clarity makes it a perfect material for prototyping lenses, flow-visualization models and microfluidics. Note that secondary operations will be required to get the material completely clear. Watershed will also retain a very light blue hue afterward.
|Accura ABS Black||MicroFine Green™||Somos Watershed||ABS (Molded)|
|Hardness, Shore D||87||85||--||109 (R-Scale)|
|Tensile Modulus||2,000 - 2,500 MPa||2,100 MPa||2,650 - 2,880 MPa||2,200 - 2,500 MPa|
|Tensile Strength||39-51 MPa||45 MPa||47-54 MPa||32-42 MPa|
|Flexural Modulus||2,100 - 2,500 MPa||2,200 MPa||2,040 - 2,370 MPa||1,800 - 2,600 MPa|
|Flexural Strength||62-80 MPa||74 MPa||63-74 MPa||60-72 MPa|
Chart 2: Three ABS-like materials and one molded ABS thermoplastic are compared across six material property categories.
Accura Xtreme White 200 is comparable to both a polypropylene (PP) and ABS thermoplastic in that it offers strength and durability, lending itself well to application that require snap-fit features. Note that Xtreme White 200 has the lowest heat deflection of the SLA materials offered at Protolabs.
Somos 9120 is translucent in appearance, providing excellent resolution and fine detail. You may want to consider Somos 9120 for parts with thin walls or small holes. The PC-like material is also the most flexible SLA material at Protolabs, while maintaining its durability. Potential applications include automotive components, electrical housings and medical devices.
|Accura Xtreme White||Somos 9120||PP (Molded)|
|Hardness, Shore D||78-80||80-82||80-100 (R-Scale)|
|Tensile Modulus||2,300-2,630 MPa||1,227-1,462 MPa||1,720 MPa|
|Tensile Strength||45-50 MPa||30-32 MPa||27-40 MPa|
|Flexural Modulus||2,350-2550 MPa||1,310-1,455 MPa||1,000-1,400 MPa|
|Flexural Strength||75-79 MPa||44-46 MPa||41 MPa|
Chart 3: Two PP-like materials and one molded PP thermoplastic are compared across six material property categories. Notice that properties are fairly similar between each.
FineLine SLArmor uses DSM Somos NanoTool as a base material for 3D printing and has a secondary process that adds a thin metal coating that provides the look, feel and strength of a metal part without any added weight. SLArmor’s nickel plating adds strength and temperature resistance to SLA parts that previously was not achievable. Note that we typically layer either 0.002 in. or 0.004 in. of plating thickness on parts.
|SLAmor||Die Cast Aluminum|
|10% metal volume||20% metal volume||30% metal volume|
|Tensile Strength||100 MPa||145 MPa||200 MPa||300 MPa|
|Elongation at Break||0.9%||1.04%||1%||2-5%|
|Mod. Of Elasticity||21,000 MPa||31,000 MPa||42,000 MPa||70,000 MPa|
Chart 4: Three grades of nickel-plated SLArmor and die-cast aluminum compared across four material property categories. Protolabs tests to ASTM D638M standards.
Unlike thermoplastics, long-term exposure to UV light and moisture will alter the appearance and mechanical properties of SLA materials if they are not protected by plating or painting. Over time, you may experience part warpage, yellowing and brittleness in some parts. SLA parts are not intended for long-term use in many instances, but understanding the short-term benefits of having highly cosmetic and functional parts to use during early prototyping can greatly benefit you.
Remember to work closely with the 3D printing experts to ensure that build orientation, anisotropism and material properties are optimized. Adjusting the direction in which the part is built can often improve the material properties and clarity of the part.
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