Thursday, 3 January 2013

3D printing, more!

3D printing is, arguably, at the stage of development that television was in the 1930’s. Technically primitive but with a huge development potential ahead. Today’s 3D printers can be considered the mechanical scan televisions of that early video era. There’s just enough utility to make them worthwhile, but, if you can believe the metaphor, the technology is at the start of the growth curve.

The 20th Century was the age of the 2D image. The invention of chemical photography meant that mastery of image had changed, from being the sole province of the artist, to being within the range of anyone with the money and skills to equip themselves. Whole new art forms grew from this new technology, and quickly. The first moving images were hugely popular, and a constant stream  of innovation kept on improving the quality and taking the technology, radically, from chemistry into electronics. Finally, in the first quarter of the 21st century, we seem to be entering the 3D era. 

And, while the first televisions of the 1920s were poor, expensive and unreliable the technology has now been so refined that electronic image systems are so ubiquitous that they are added as an almost free feature to phones and cars and hardly rate a mention.

Now some technology looks blindingly obvious in retrospect. If painting was superceded by photography, shouldn’t 3D art, sculpture, eventually also get replaced by technology? But, if it’s so important, and not just a technological novelty, why wasn’t it done years ago?

Sidestepping, for now, the question, does everyone need the ability to produce electronic sculptures? (In 1850 you might well have asked the same sort of question regarding photography of portraits.) Of course, the concept can only be realized once the prerequisits are in place. So what were the prerequisits of 3D printing?

Firstly, we needed  a whole generations worth of development of 3D image tools. These, came out of engineering and entertainment. 

Automatic manufacturing.  Cam controlled lathes, for instance, have existed for over a hundred years but numerically controlled machine tools, with a significant electronic content,  came in for serious development in the 1940s and the huge, war funded, investment in volume manufacturing. The analogue control systems and analogue computing techniques that had been developed for gun laying, bomb aiming and aircraft automatic pilots were borrowed and these made possible the first automatic machine tools.  These machines gave manufacturers new levels of accuracy and repeatability.

With the rise of the digital computer these analogue machine tools went digital.  It became cost effective to get the engineering information they needed straight onto the computer where it could generate other benefits. Through the 1970s and 80s huge strides were made in CAD/CAM (computer aided design and manufacture) which saw mechanical and electronic design bypassing the draughting board and going straight onto the computer. 

The mechanical engineers were able to ‘model’ a part on the computer screen as never before. In the old days 3 views on paper had to be drawn first and often physical models made from these.  3D computer models of mechanical components then needed to be translated into instructions that numerically controlled machine tools could work with. The machine tool industry devised a protocol, ‘G Code’ which defined the path a milling machine tool head must follow in order to machine a chunk of metal into a useful part.

And, as computers became cheaper and faster, more software tools were developed for manipulating 3D images. Video game and movie animators were also working with 3D images. Eventually, 3D modeling software changed from being eye-wateringly expensive to freeware, and much easier to use.

The digital control of small motors developed. This development enabled cheap inkjet printers and small plotters. These didn’t need the complex analogue servo systems.  This new technology could achieve equivelant precision and was much cheaper.

Finally, came the Internet. (By now established as a piece of infrastructure as vital as the electricity power grid.) With the internet came filesharing sites that allow anyone to upload, download and, equally important, find all manner of information.

Finally, all the prerequisites for 3D printing were in place.  So how do we go about using it?

First a 3D model must be made or found. The filesharing site Thingiverse is the Facebook of 3D printing. You can, of course, create or modify your own 3D file. Tools such as Sketchup, Meshlab and Blender are freeware and are all useful modeling tools. 

The chosen 3D model file must then be prepared for printing. It is sliced into horizontal sections by a special program. These sections are then broken down into G code commands. These define how the extrusion head will move to ‘print’ the model. G code is the DNA of a printed object. It is an expression of the objects shape, layer by layer, as it must be built up on the bed of the 3D printer.

3d printing is an additive process. Parts are built up in layers using extruded plastic. The technology allows plastic down to 0.1 mm thick to be used. My printer can build a part within its build volume of 200 mm by 200 mm by 100 mm. The machine has 3 axis of motion and the stepper motors move the plastic extruder head within the build volume. But parts are built, like a house, from the bottom, Z=0, up.

The additive process is the big difference to conventional, numerically controlled machine tools. These are subtractive, mills and lathes start with a hunk of material and grind bits off until the desired part remains. 3D printers build the part up. 

The part is extruded/printed onto a heated, ‘build plate.’ The extruder head heats the feed plastic to about 200C and the plastic filament is extruded. The build plate is heated to ensure that the freshly extruded plastic sticks firmly to it. Additive machines have a special problem. Those numerically controlled mills simply hold the base of what will eventually be the part. But how can you secure a piece of liquidized plastic? The answer is to extrude the plastic onto a heated base covered in plastic film.  As soon as the plastic touches down it hardens and sticks to the film. The first layer of the part is put down slowly to give it time to harden and then it sticks firmly in place.   

And then the part is built up. The layers in the Z direction are the defining characteristic of this form of 3D printing.  The shallower the layers, the less apparent they will be, but the longer the print takes. 

Overhang parts, bridges and arches, where the printer is printing on thin air, can be made.  Sometimes support structures must be made. The slicing software will generate this. Support material is cut away later.  

And that’s it. Do that and you’ve printed a part. 

“Did you make this?” I’ve been asked about the various Raspberry Pi boxes that my printer has produced. Well no, not really. I made the printer, (bolted it together) but I no more made the parts than I painted the photographs from my digital camera. The act of creation is in the generation of the 3D model.

3D scanning systems are also developing rapidly. At a recent British computer show they were making 3D models of people, scanning them and quickly producing a 3D minature. The, instant, 3D sculpture had arrived.  

But where will all this 3D printing go? Some people think that simple shells of plastic are just the beginning and that in a few years we will be printing electronic circuitry, maybe even living tissue. See 

Our 2D technology has provided a means of studying images as never before. But to examine a 3D structure, aside from walking around it, we need a 3D computer model or a physical model. Years ago I stuck about a million plastic model airplanes together. I loved the shape of the aeroplane. No picture could allow me to internalise the beautiful physical forms of aircraft as those models did. Perhaps, in the same way that the various techniques of 2D imaging have allowed us to examine the fleeting images of the visual world, 3D printing will allow us a new access to the forms of the physical world.  

No comments:

Post a Comment