In 1983, Chuck Hull worked for a small California-based company that used ultraviolet light to turn liquid polymers into hardened, or cured, coatings. Inside the firm’s lab on his nights and weekends, Hull found a way to make UV-curable materials the basis for his Stereolithography Apparatus, patented the following year.

Tech Briefs spoke with Hull about the future of his invention, the 3D printer.

Thirty-two years later, Hull is the co-founder, executive vice president, and chief technology officer of 3D Systems, headquartered in Rock Hill, South Carolina. The company, established in 1986, sells and designs 3D printing technology based on Hull’s pioneering work.

When you were developing the first 3D printer, what was the need being served?

Chuck Hull: Back in the early 1980s, I was trying to come up with a way to more rapidly prototype plastic parts that were going to be injection-molded. The process was very time-consuming between when you had an idea for a plastic part and when you had the first article in your hand. We’d even use blueprints back then, not computer design, to design a part. Then, the part went to a tool designer who would design a tool so that it could be molded; then, a toolmaker made the tool; then, finally an injection molder ran a few samples for you.

How long would it take to create a part?

Hull: This could take 6 weeks, even longer, before you saw the first part. And if you found problems with it, you had to start the cycle over again. It was very tedious. I had seen UV curable materials in thin layers for coatings and inks and so forth, and I thought, “Maybe we can figure out some way to prototype plastic parts with it.”

In basic terms, what is the Stereolithography Apparatus (SLA)?

Hull: The concept of 3D printing is to additively build up thin layers in the material, and to have the data that’s driving those thin layers. So, you take the data, build the layer, and build the next layer, adhering it to the one before it. When you finally get done adding up the layers, you have the part that you’re building. Almost all 3D printing is based on that, even today. That was the principle I worked on back then: drawing thin layers, with a light pen, of a UV curable material, one on top of the other, using digital data to decide what that cross-section was like.

What were your biggest challenges in putting together the technology?

Hull: As I was trying to learn how to work with these UV curable materials, the challenge was getting materials that had good adhesive properties, because each layer had to adhere to the layer below. And then [I had to think of] what we now call the cure depth: how far does the light penetrate, let’s say, a vat of this material? It can’t get too far, or else you won’t get any detail, but it has to go far enough to create the layer and get the adhesion.

How did you imagine it being used, and did it exceed your expectations?

Hull: Oh, for sure, it exceeded the expectations. The application was the prototyping of plastic parts. Right away, as people worked with the technology, they started to envision other applications well beyond what I had initially thought of. These days, there are hundreds of applications in really diverse fields. There was no way to anticipate that back then.

What is most exciting to you about the possibilities of 3D printing?

Hull: There are two areas I get excited about. One is all the healthcare applications that have been developed. The other is using 3D printing not for prototyping, but more and more for product applications. 3D printing can replace, supplement, and improve a lot of our current production methods. There is a lot of work going on again around the country and world, setting this trend.

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