protoTYPING: More than a Machine, an Ode to our SLA 3D Printer

protoTYPING: More than a Machine, an Ode to our SLA 3D Printer

Just how much do we love our SLA 3D Printer? Let us count the ways.

One of my favorite tools in the shop is the SLA 3D printer. It is one of our 3D printers from 3D Systems, and it is the workhorse of the bunch. For the 3D printer geeks or industry professionals reading this, it is a Projet 6000. It prints in high resolution with layer height of just .05mm, has a 10” cubed build volume, and is reliable. I can put parts in it on a Friday afternoon, let it run all weekend while I am out enjoying my free time, and come in on Monday morning with a platform full of perfectly formed parts. 

Projet 6000

The ProJet 6000 with a batch of parts drying inside the build chamber.

Shorthand for stereolithography, the SLA machine is so reliable that I often forget how remarkable it is.

 

Our 3D Systems support engineer, Jordan, came to the shop for a preventative maintenance service call on the machine, and while curiously watching him give it a tune-up, I had an epiphany about how interesting the technology is. It was the same sort of moment you have sometimes while flying when you realize how the plane that you are in is such a great piece of engineering, or when you stop to think of how magical the guts of a TV are. Despite using the technology all of the time, I realized how little I knew about it. So I did a little bit of research to share some details about how the machines work and how they were invented.

Stereolithography is a resin-based type of 3D printing that uses ultraviolet light to cure the resin into the desired shape. It makes parts by tracing the geometry of each layer with concentrated UV light produced by a laser. The build platform is lowered into the resin bath after each layer to make fresh resin available for the next. Depending on the geometry of the part, a wiper blade will skim the resin every couple of layers to keep it building smoothly. The software calculates where the overhangs are and it prints a spider web like matrix of support structure to keep the part stable. Once the build is finished, the parts are scraped off of the build platform, and the supports are torn off by hand. Then the parts are scrubbed and rinsed in an alcohol bath to remove the excess resin. The finished parts are dried off and set into a UV light box for about half an hour to cure to their finally toughness.

Cleaning parts in an alcohol bath.

Cleaning parts in an alcohol bath.

3D Systems has been at the forefront of stereolithography technology since its inception.

 

Charles Hull built the first SLA machine in 1983 and filed his patent for the technology in 1986. He then went on to found 3D Systems, and the first commercially available SLA machine called the SLA-250 was sold in 1989. 3D printers and CAD software were not easily compatible at the time, so Hull developed the STL file format, .stl, which was a graphics file that was easy for the CAD software of the time to generate, and easy for the SLA machines to process into layers to create build files. This same format is still used today for SLA machines and many other types of 3D printers, too.

Example of an .stl file

A virtual build platform of parts populated with .stl files. The weblike supports are shown in green.

One of the big technical hurdles to overcome was power consumption of the laser system.

 

Generating laser light in the UV spectrum required a lot of power and the use of massive power supplies that were water cooled. The advent of solid state lasers brought the form factor and cooling requirements down. This also lowered the bar for customers as the printers now had a smaller footprint and a less complicated installation. However, the SLA material had to be tweaked to account for the differences in the laser types. The first solid state SLA system was launched in 1996 and is still the core technology found in current machines.

The resolution and strength of SLA parts make them useful for prototyping. The photo curable SLA material is more brittle than an engineered plastic. However bendable features, like snap fits can be prototyped if you are careful about handling them and do not cycle them too many times. It will also hold plastic screw without stripping, so it is really good for making functional models. The high resolution makes for fully-resolved models that can be used for one-to-one validation of part geometry and test fitting.

Printed parts from the SLA machine

Wine Shark parts printed on the SLA machine with snap fits and screw bosses.

Sometimes there are part geometries that are fine for the final molded product, but are too small or would take too much force and break in SLA. In these instances we will increase the wall thickness or thicken certain areas of the part to make sure that it will live through the rigors of testing the prototype. There is no magic formula when deciding when to beef up certain areas. However, it is usually easier to remove excess material than it is to fix a broken feature. If the model does break, the material is easy to fix. Cyanoacrylate glue, often referred to as super glue or CA glue, bonds it together. Another trick to repair an SLA part is to lay strips of fiberglass over the inside of the broken area, and use off-the-shelf two-part epoxy to wet out the fiberglass and adhere it to the part.

Another great feature of SLA is that is easy to sand and paint. When the parts come off of the machine, they have steps in them from the layered build process. These smooth out very easily with sandpaper. Some engineered plastics, like HDPE and polypropylene, have a high surface energy which makes the surface slick and resists adhering to paint. However, SLA material bonds to paint easily, and prototypes can be made to look like production samples easily.

SLA Machine printed production sample

The same SLA shells from above painted to look like a production sample.

SLA parts can also be used to make molded parts.

 

One way is to make an SLA print of the finished part and pour silicone over it. When the silicone hardens, the SLA part is removed and a cavity is left to make a mold. Liquid urethane cane be injected into the mold to make rubber parts. Alternatively, a mold can be designed and made directly with SLA material. Then room temperature curing material like silicone or urethane can be poured into the mold to form the part.

A mold made on the SLA machine used to make urethane rubber parts.

A mold made on the SLA machine used to make urethane rubber parts.

While SLA machines have been primarily used by professional product developers, it is becoming more accessible to casual inventors.

 

The life cycle of many of the SLA patents has run its course, and the technology is now in the public domain. This has led to a multitude of companies developing desktop SLA machines. The Formlabs Form 1 and Form 2 and the XYZPrinting Nobel 1.0 are just a few of the options. Both have about 5” square build platforms with prices ranging from $1,500-3,700 to get started.

Alternatively, 3D printing services like Quickparts and Protolabs offer SLA parts that are shipped in just a few days. The prices are based on the size and geometry of the part, and are a good option for inventors who do not have the capital or expertise to have a printer at home.

There are numerous types of 3D printing technology, but SLA is one of the best. SLA machine made parts are fast to build, high resolution, strong, and easy to paint and repair. They can be used to make tough working prototypes, or can be used to make molds for rubber parts. Due to the speed and versatility, there have been very few prototypes made in the 520 Elliot shop that did not have the help of the SLA machine.


 

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3 Comments protoTYPING: More than a Machine, an Ode to our SLA 3D Printer

  1. Jacob Downey

    Reminds me of the puzzle cells we printed for composite type electrochemical current collector testing.

  2. Mary Dickson

    Hi Gary,

    This in from Jeremy…

    Short answer: Yes

    Longer answer: Yes, but how well it works will depend on the material. Most 3D-printed plastics are stiff and slightly brittle and they would crack before the end of the zip tie got into the receiver. It looks like softer materials like PLA that are available for consumer grade 3DPs have been used with good results.

    Here is a link that includes a downloadable file.

    https://blog.adafruit.com/2016/08/18/3d-print-your-own-zip-ties/

    Hope this helps!!

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