Industrial Materials and Methods - Materials - Make: 3D Printing (2014)

Make: 3D Printing (2014)

Part IV. Materials

Chapter 9. Industrial Materials and Methods

A materials guide for 3D printing services.

Stuart Deutsch

There has never been a better time to purchase a desktop 3D printer. Nonetheless, they are still too expensive for many users. If you can’t justify the cost of a personal printer, you may be able to access one at a local hackerspace, and there are many online 3D printing services to choose from, including Ponoko, Shapeways, and i.materialise. These companies use a variety of printing technologies to create physical objects from your digital designs and can print in many other materials besides extruded thermoplastic.

Composites and Ceramics

Powder bed and inkjet printers use inkjet-type print heads to deposit tiny droplets of liquid binder on top of a thin layer of powder. Once the build platform lowers, a roller spreads and compacts a fresh layer of powder across the surface. The final object is essentially a stack of powder layers finely glued together. Dyed binders can be used in certain machines to produce full-color display models (Figure 9-1). Treatment with super glue and UV protectants can improve model strength and reduce color fading.

Bowie the Bunny in fine mineral power, with color binders, via power bed/inkjet process

Figure 9-1. Bowie the Bunny in fine mineral power, with color binders, via power bed/inkjet process

The powder bed/inkjet system can also be used to create food-safe ceramic models (Figure 9-2). The use of ceramic powder has become quite popular with online printers who now offer a rainbow of single-color options. After removal from the powder bed, raw ceramic parts undergo a series of heat treatments to dry, fire, and glaze the model, improving both strength and appearance.

Food-safe ceramic, via powder bed/inkjet process, followed by heat treatment

Figure 9-2. Food-safe ceramic, via powder bed/inkjet process, followed by heat treatment


Stereolithography (SLA)

Stereolithography is the original 3D printing process, in which a liquid plastic resin is selectively hardened by exposure to high-intensity light, often from a laser. After the laser has drawn a 2D path along the surface, the freshly polymerized model layer is lowered into the surrounding resin bath. The laser traces over the fresh surface, curing and joining the resin to the previous layer. SLA produces prints of exceptional smoothness.

Selective Laser Sintering (SLS)

Selective laser sintering uses a high-power laser to melt and fuse particles of very fine plastic powder, often nylon (Figure 9-3). The laser scans across a leveled and compacted powder surface, and when each layer is completed, the entire bed is lowered and fresh powder is spread on top. As the laser works its way across the new layer, molten powder particles in the top surface fuse to each other and to the layer below. The unfused powder acts as support material, so SLS fabrication works well for models that have thin sections, overhangs, or complex geometries.

Fused nylon powder, via selective laser sintering

Figure 9-3. Fused nylon powder, via selective laser sintering

SLS is one of the most economical 3D printing methods and is forgiving in terms of design guidelines. Most vendors charge by volume of powder consumed, so you can often save money by “hollowing out” solid models and printing them as shells. Most vendors also charge for “trapped” powder, however, so models printed as shells will usually need to include at least one small hole so that the powder can be recovered when the print is done.

Photopolymer Jetting

Photopolymer jetting uses movable heads, like an inkjet printer, to deposit droplets of resin onto a build platform through a number of very small jets. Once the droplets are in position, a UV lamp moves across the platform to harden the resin. A support material may be printed surrounding the droplets and can be removed, manually or by washing, once the print is complete. Photopolymer jetting can create very finely detailed models with smooth surfaces and multiple materials—tinted, clear, rigid, flexible, etc.—in a single print (Figure 9-4). It is not widely available from 3D printing services, yet.

UV-curing acrylic, via photopolymer jetting

Figure 9-4. UV-curing acrylic, via photopolymer jetting


Direct Metal Laser Sintering (DMLS)

Direct metal laser sintering uses a laser to directly fuse certain metal powders, such as titanium, in a fashion very similar to SLS in plastics. Other specialty alloys can be printed via DMLS, but high costs and stricter design guidelines make the process less accessible to beginners.

Direct Metal Printing

Direct metal printing uses a multistep method to create powder-based metallic models, mainly from stainless steel. First, the object is printed into a bed of very fine stainless steel powder using the inkjet-binder process.

A carefully controlled heat treatment then burns out the plastic binder and fuses the steel particles together. Finally, the porous sintered model is infused with molten bronze, which wicks into the empty spaces and fills them (Figure 9-5). The finished model is a kind of stainless steel sponge filled with bronze, and can be given a variety of surface treatments, including plating with gold or other metals.

Bronze-infused stainless steel, via direct metal printing

Figure 9-5. Bronze-infused stainless steel, via direct metal printing

Indirect Printing Methods

Indirect printing methods create positive or negative models that can be used with conventional casting processes to create metal parts. For instance, a sacrificial model of a part can be 3D printed in a wax-like resin using stereolithography, and then duplicated in metal using the traditional lost-wax process. Alternately, the powder bed/inkjet process can be used to print molds in silica sand or other traditional foundry media, which are then used to cast metal parts in the normal way.

Dr. Stuart Deutsch is a materials consultant in the NYC area and executive editor at