A primer on 3-D printing technology

By Shawna Kulpa

These days, with technology evolving seemingly overnight, it can feel overwhelming to buy just about anything. And in our industry, nowhere is that sentiment felt more than when it comes to 3-D printing.

To determine which 3-D printer is best suited to meet your needs, you first need to understand the technology behind the different options on the market. Although there are about a dozen types of 3-D printers out there, most of them are limited to more industrial applications and can’t achieve the model size or resolution requirements needed in the jewelry industry. This narrows the field considerably to three types of 3-D printers suitable for use in the industry.

To help you find the technology that will best meet your needs, we’ve compiled a basic primer on the three types of printers and highlighted some of the pros and cons of each. While there’s no one 3-D printer that may be the exact fit for everyone, we hope this will help you narrow down the field to find the technology (and printer) that will work best for you.

Stereolithography

One of the oldest 3-D printing technologies, stereolithography (SLA) printers use a liquid photopolymer resin that hardens and forms into solid objects when it is exposed to ultraviolet light (UV). In these printers, that UV light is produced through a laser that uses two motors (known as galvos) positioned on the X (horizontal) and Y (vertical) axes of the printer. While some SLA printers have a build platform that slowly lowers down into a resin vat, the majority of the printers being used in the jewelry industry feature build platforms that rise up from the bottom of the vat.

To begin, the build platform is lowered into the vat until it reaches the bottom, which is covered by a thin film to protect the vat as well as prevent any of the resin from leaking into the machine. The laser is then directed toward the build platform, shining light through the bottom of the vat to trace the shape of the first layer of the model being built.

Once that layer is complete, the platform is raised to peel the newly formed layer that now resides on the build platform away from the bottom of the vat. Some printers have a tilt feature that allows the bottom of the vat to tilt away from the build platform, helping to separate the model from the film. Other printers have a bar that slides across to separate the part from the film. Still others just allow the platform to tear away. While the peeling method doesn’t affect the price of the printer, it will affect the printing time. Tilt platforms and those with sliders will require more build time than those models that simply tear away from the vat. However, the trade-off is that the tear-away process can cause more stress on the part being built, which could affect the integrity of the model.

Once it is free, the build platform continues to rise to allow for a new layer of resin to flow under it before it lowers back down to the bottom of the vat for the next layer to be created. This process continues as the object is slowly built from the bottom up, layer by layer.

One of the advantages that SLA printers offer over some of the other types of printers suitable for use in the jewelry industry is the build envelope. Because the laser can travel a far distance within the printer, it allows for a fairly large build envelope. However, the shape of the beam can change as it travels. “Laser SLA machines can have a larger build envelope, [but] the downside of that is the galvo that moves the beam around the envelope shapes the beam into an oval instead of [a round shape] as it travels farther from the center,” warns Tyler Teague of Proto Products in Nashville, Tennessee. “[That oval] can make rough surfaces and inaccurate parts.”

The laser also means that the resolution of models produced on SLA printers isn’t typically as fine as can be produced with other types. Because the layer is being formed by the UV light emitted from the laser, the XY resolution of the model is tied to the spot size of the laser beam. Generally speaking, the larger the spot size of the laser beam, the rougher the surface.

Another disadvantage to this type of printer is the time needed to grow models. Because the laser beam has to trace the entire cross-section of an object at whatever beam spot size it has, it can take much longer to build a model compared to other types of printers, where each layer is solidified at one time. (Teague notes that while it is possible to set the machine to print at a faster speed, the resolution of the models produced will be much poorer.) Print time is also dependent on the layer thickness you select. The more layers you print, the more time the printer spends not only creating them, but also having to cycle the build platform up and down between layers.

One final concern to consider is the cost of maintaining SLA printers over time. The laser in the machines “burn up the trays really quickly,” says Teague. He estimates that users should expect to get about two to three builds per area on the tray before it will need to be replaced, though some trays can be rotated to get more life out of them. The cost of the trays will depend on the machine, with some trays priced around $70 while others can run into the thousands.

Digital Light Processing

Similar to SLA printers, Digital Light Processing (DLP) printers feature a vat of photopolymer resin. However, instead of a laser beam to solidify the material, DLP printers use a digital light projector to project a single image of each layer. The UV light is projected onto the resin usually using either a light-emitting diode from a digital light engine or a modified home projector. “New and very low-priced machines have come on the market recently that use LED screens like you have on your cell phone that emit visible light directly under the vat, but the resolution that can be achieved is limited,” says Teague.

The light is directed through the bottom of the resin vat to the build platform surface. When each layer is finished, the build platform moves up and the next layer is created. Since they expose an entire layer at one time, DLP printers generally offer faster print times compared to SLA machines. “With DLP, it doesn’t matter how many parts per build, it exposes the whole layer at once,” says Teague.

The accuracy of this type of printer is determined by the size of the pixel that is being projected from the light source. The smaller the pixel size of the light being projected, the better the surface resolution of the model being built. Since pixels can be and often are smaller than a laser beam, DLP printers generally produce finer surfaces than SLA printers. However, it’s worth noting that the smaller the pixel size, the smaller the printer’s build envelope becomes. “You can either get the same resolution [as with SLA] with a bigger build envelope, or a super high resolution with a decent build envelope,” says Teague.

According to Brett Northcutt, model department director at Stuller Inc. in Lafayette, Louisiana, a decent size build platform for jewelers would be 80 mm by 40 mm. “When you get smaller, you get better resolution, but you may be able to fit only two to three parts per build,” he says.

One advantage that DLP printers have over other types of 3-D printers is the speed they offer users. Because layers are exposed all at one time, they’re generally formed faster than they are with SLA printers, which rely on the laser beam to trace the outline of the model.

A recent development in technology may help to speed up the printing process even more. There’s a new type of film for the bottom of the resin vat that is permeable to oxygen, which inhibits the resin-curing process. These no-adhesion printers pressurize oxygen under the platform, allowing oxygen (but not resin) to permeate through the film and prevent the material from sticking to it. This results in quicker build times as well as reduced stress on the objects being built.

Another advantage that some DLP printers offer is that they give users the option to move the light projector in and out to increase or decrease the build envelope, thereby changing the XY resolution. “If you needed a bigger build envelope, this gives you the flexibility to do it,” says Northcutt.

Material Jetting

Material jetting printers are similar to inkjet printers—they hold containers of liquid that they then selectively deposit droplets of onto a build plate. These printers can deposit only one droplet at a time, which makes them operate on the slower side, although printers can have multiple jets to help speed up the printing process. It’s important to note, however, that the more jets a printer has, the more issues a user can face because jets can get clogged, and the more moving parts mean more things can go wrong. If considering this type of printer, be sure to factor in the costs for replacement parts because jets can be expensive to replace. Teague estimates replacement jets to be around $1,000. “The price of these machines is typically far higher than DLP printers,” he says.

One of the major advantages that these printers offer users is in the build material that must be used with them. Although some material jetting printers can be run with photopolymer resin, they mainly run using a wax/starch material, making them easier for those who may struggle with or just want to avoid casting resin models. In addition, these printers require a separate material they use to build the support structures at the same time as the model is being built. Once the print build is complete, the models can be placed in a solution and the support material dissolves away, leaving the wax model ready for casting. This is a definite advantage over SLA and DLP printers, where the supports have to be removed manually from the models.

Another advantage that this type of printer offers is a large build plate, as the print head can move in the X and Y axes. This allows users to build more parts per session. However, it’s worth noting that the more parts being created means the more time the job will take to complete. Since the printer operates by depositing one drop of material at a time, it’s already slower than both SLA and DLP printers.

One downside to these printers’ ability to print in wax is that the models created tend to be more fragile than those printed in photopolymer resin. The wax models can be easily broken and will not stand up to the same abuse that resin models can withstand. 

Another disadvantage that’s often cited about this type of printer is the surface quality of the printed models. There’s a limit to how small the droplets that are deposited can get, and these printers can’t achieve the same small size as a laser beam or the pixels created with DLP printers.

Unfortunately there’s no one technology that can currently do it all—offer fast print times, a large build platform, perfect surface resolution, and problem-free casting. Each type of printer offers its own advantages and disadvantages. Before making the investment in one type of technology, sit down and figure out what you want and need from a 3-D printer. Do you want the best resolution possible? Are you more concerned with avoiding casting problems? Or is print speed your primary consideration? Once you’ve determined your needs, you can narrow your focus down to the technology best suited to meet them.

But it’s also important to remember that regardless of the printer technology you choose, there will be a learning curve.

“You can’t get into printing with the assumption that you’ll have success every time,” says Northcutt. “It can be difficult to get these things up and running, and you’re going to have fails. You have to be willing to learn along the way.”