Building parts using additive processes depends on selecting the right material for the additive process, the design, and the end-use application.
Additive manufacturing differs significantly from classic processes such as injection molding, and therefore requires specialized resins and compounds tailored to provide the desired properties.
Polymer suppliers are developing materials that align with the characteristics of specific printing processes and can meet the higher performance demands of production parts in the end-use environment.
But here are few tips for the main additive processes:
Fused deposition modeling:
Currently, fused deposition modeling has the widest choice of commercially available engineering thermoplastics that can meet different functional properties.
This process involves heating a thermoplastic filament to its melting point and then extruding it, layer by layer, to create a three-dimensional object. Amorphous resins are well suited for this widely used process, as they typically shrink less than semi-crystalline resins. While amorphous resins exhibit good consolidation and uniform shrinkage, layers of a semi-crystalline material tend to shrink non-uniformly and to a greater extent, which can cause warpage, leading to dimensional issues with the part.
Polylactic acid (PLA) and acrylonitrile-butadiene-styrene (ABS) are commonly used for desktop printing, while low/mid-temperature resins such as polycarbonate (PC) and PC/ABS, and high-temperature polyetherimide (PEI) and polyphenylsulfone (PPSU) resins, are often chosen for industrial use. Newer materials for industrial printing include high-temperature plastics like polyether ether ketone (PEEK) and Stratasys’ ESD PEKK (polyether ketone ketone), and resins with fillers like carbon fiber for enhanced strength and stiffness.
Selective laser sintering:
In this method, powdered thermoplastics are sintered into a solid object with a computer-controlled laser. After each cross-section is scanned, the powder bed is lowered by one layer of thickness, a new layer of material is applied on top, and the process repeats until the part is completed.
Semi-crystalline materials typically used for SLS are polyamides (nylons) such as PA12 and PA11 because they offer a good “sintering window,” a moment calculated as the difference between the melting onset temperature and the crystallization onset temperature of a polymer. Polyamides’ discrete melting point and sharp drop in viscosity enable effective coalescence between layers, resulting in good part properties. In contrast, amorphous materials soften gradually, leading to incomplete layer consolidation and parts with lower density, dimensional inconsistencies and sub-optimal physical properties.
However, polyamides may not meet the performance specifications of certain applications, limiting the usefulness of SLS in some production applications. Thus, some materials developers have focused on proprietary technologies to overcome some of the drawbacks of amorphous resins.
SLS and stereolithography techniques provide greater isotropic properties as well as better print resolution, leading to better surface quality.
This technology relies on photopolymerization; the cross-linking of polymer molecules that occurs under exposure to ultraviolet (UV) light. A UV laser draws a design on the surface of a vat of photosensitive liquid resin, solidifying the resin and forming a single layer of the part. The print bed is lowered incrementally, and a resin filled-blade recoats the surface of the vat so that a new layer of uncured resin is exposed to the laser. The process is repeated until the part is completed.
Although photo-initiated epoxy and acrylate resins are commonly used for stereolithography, some materials lack long-term light stability and can become brittle over time. Material innovation to provide more-robust long-term performance can expand the number of applications for which this technology is suited.