When I was at university in 1985, we had an HP 7475A plotter in the computer room. It was the coolest thing I had ever seen. It is like watching an artist draw right in front of you. To get it to draw, you had to write code. You could get color if you swapped pens. I still find plotters fascinating.
When I interviewed at HP, my interviewing manager told me the ThinkJet printer would change the world. He was right.
The ThinkJet printer could print 120 characters per minute at a resolution of 96x96 dots per inch. It could not do color, it could not do graphics. In fact, it only had one font. “Fonts will come,” he said.
I was amazed. HP did not just see a future, it invented the future.
It is truly incredible how much has changed. Today, the HP T200 InkJet press is able to print at 19 pages per second and the Niagara T3500 Poster printer can print 32 x 48 inch posters in 3–4 seconds. The performance of InkJet in drops per second has doubled approximately every 18 months since 1985. If you do the math, this is going from approximately 6,000 drops per second in 1985 to almost 10 billion drops per second today.
As I look back, I realize that where we are in 3D is exactly where we were in 2D nearly 30 years ago.
HP 3D printing builds on 2D InkJet
The HP 3D printer just won the 2017 Invention of the Year award. It is fun to watch, too. You only see one layer at a time, however, and each layer is printed nearly instantaneously. It is like seeing sheets of paper, each with an image, all stacked together. Where the image is printed, the powder melts or fuses together causing a 3D object to be created layer by layer.
HP Jet Fusion printers handle powder in very inventive ways. The powder is spread so it looks like a blank sheet of paper and the print heads can then add the design of the next layer by placing very small drops of liquid onto the powder bed.
We refer to the liquids as “functional agents” because they are not exactly ink. One is black and we call this a fusing agent. Another is clear and we call it a detailing agent. The job of the liquids is not to color the part, but rather to change the thermal characteristics of the underlying powder. When energy is applied, the black powder gets hot and melts, whereas the white powder stays cool. A part is built up by printing each layer, fusing, and then repeating. HP has exceptional speed because the drops can be placed down in parallel at 30 million drops per second.
From pixels to voxels
Just like in 1985, we had to convert digital picture elements, or pixels, into dots per inch and adjust color tables to give reflective color that matched expected color. In 3D, we have to convert designs intended for injected moulded plastic into slices and those slices into volume elements, or voxels. We are working on matching color, but we still have to figure out what Gamut means for objects that are not quite smooth. How do we describe surfaces and textures?
From paper handling to powder handling
In 1985, HP had to worry about how deep ink would penetrate into paper, and whether we needed to have custom paper or could use easily available paper. We had to worry about whether the ink was dry before advancing a page. There are amazing parallels in 3D. In 3D, surface texture and part features depend on the accuracy of placing a drop, the penetration rate of the drop, the size of the underlying plastic powder, the ability to control the fusing of the plastic powder, and numerous other parameters.
In 1985, Microsoft Word and Excel did not exist yet. We were just learning languages to describe circles, shading, and splines. There was early work on fonts and treating edges of objects so they looked crisp. There was work on compression, color accuracy, and color perception.
Creating the new language for 3D parts
HP created the Printer Control Language to define how to control printers. In parallel, Adobe created Postscript. These were two different approaches to describing mixed text and graphics. We are in the same place again with 3D. We can match the capability of analog tools where all the material is the same—but we do not yet have the language for describing digital parts. We do not know how to describe parts that have texture, parts where a sphere is partially filled, and parts that have conductive traces. Almost all computer-aided design (CAD) tools reference geometries but not about these digital/voxel material properties.
Just as pixels in print allowed us to manipulate color, in 3D we can manipulate other things. We are working on technology that allows us to manipulate translucency, conductivity, surface finish, texture, and pliability at the voxel layer. Each voxel can be different. We now have parts that we can build, but cannot describe. There is no CAD tool yet for describing a part that feels like leather or how to make a part the color of a snake.
New design tools will come
Just like in 2D, it will be a few years until the design tools catch up to digital manufacturing, but the future is clear. Everything that can go digital will go digital. Just as LaserJet transformed the office printing market, InkJet transformed home print, and Indigo transformed the commercial print and photo market, voxels and Multi Jet Fusion will transform manufacturing. Thirty years from now we will look back to this time as the start of something big that is built one voxel at a time. 3D printing is three decades of InkJet.
By Keith Moore, HP Fellow, Head of the Print Adjacencies and 3D Lab, HP Labs
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