I found, and still find, it hard to visualise really small dimensions in a concrete way. To help I made a chart, which you’re free to download if you want.
Archive for October, 2009
Nano-ness
Sunday, October 25th, 2009Roughly speaking
Friday, October 23rd, 2009
Additive fabrication doesn’t necessarily have to be done in 2D layers; a robot arm could possibly deposit material in 3D space in alternative geometrical schemes, maybe following the volumes of individual parts. But in any deposition model, the concept of resolution is critical to the quality and function of the thing being made. With layers, as they get thinner, the surface steps (the layer edges) become smaller; which is to say they become less rough.
In engineering the measurement Ra describes the roughness (or in a more beer glass half-full mood, smoothness) of a surface. Ra is surface Roughness average and is the average difference between peaks and valleys in a given surface region, measured in microns (or micro-inches in US units). A micron is a thousandth of a millimetre. At larger scales roughness is an everyday dimension for us humans — we can feel it and see it — but as Ra gets smaller it can still have a huge impact on the engineering and visual properties of a surface — in bearings, electrodes, mirrors and lenses, and in cosmetic finishes. A rough-turned steel bar or mill finish steel sheet may have an Ra of 25-50 microns, whereas for a hard steel bearing it should be between 0.2 and 0.8 microns. The Ra of window glass is 0.003, at which point it makes sense to give the measurement in nanometres (a thousandth of a micrometer, or a millionth of a millimetre), ie 3.0nm. The super-polished surface of a silicon wafer or hard-drive disk has Ra 0.1nm.
With conventional manufacturing it’s possible to achieve these kinds of surfaces by giving them special attention — grinding, lapping, polishing, and by coating and plating (or by moulding in tools treated these ways). But in an additive process where assemblies are made in-situ (an ambitious goal, we know) these high-function surfaces would ideally need to be made directly, at the ‘print head’. I’ve already described a hypothetical additive car built from 1micron layers, but it’s clear now that a range of resolutions would be needed, from 50 microns for some bulky parts to 1.0 nanometres for electronics (and that’s today’s electronic chips, by the way). One end of this range is 50,000 times courser than the other. You could print the whole car at 1.0nm resolution but that could take not ten years but ten thousand! Exactly. But it’s probable that at these small scales the surface roughness, the RA, is not in fact equivalent to the layer thickness. The droplets of material will merge together to form a wavy rather than ziggurat-stepped surface, so the Ra may be a fraction of the layer thickness, maybe more like a fifth. Perhaps? If true, the layer thickness range required becomes 250 microns down to 5.0 nanometres. A little better.
Julian Vincent — celebrated biomimetics pioneer — has already proposed here in his comment that a car-printing machine should have multiple print heads with a range of resolutions and material ‘specialisations’. Soon I plan to re-visit car printing, an impractical idea most likely, but extreme cases can sometimes help sort out ideas.
But it’s really about Design
Tuesday, October 20th, 2009
It seems to me it’s hard to just launch into a discussion about the effects on design of a whole new way of making things. Maybe I should be talking about how design rules change with the current generation of RM technologies — designing a part for SLS perhaps — and that could be useful. But this blog is about the future, about life in a world where additive manufacture has matured, reached a stage where many of the things that we make today in complex ways out of parts and pieces can instead be zapped out of a single fabrication machine, from scratch. A toaster for example. We know very little about how these machines will work and it’s hard to judge how soon they’ll get that clever, but whereas lots of people are talking about next-generation FDM machines and suchlike, no-one to my knowledge is really trying to get to grips with where it’s all going — and what we can do with it when it gets there.
And that is a conversation worth having, mainly because we can better steer the technology if there’s a long-term vision and Design2.0 is about that vision. But to think about design in an additive world it’s useful to have some ideas about how the technology will work and what it could be able to do. Maybe some structures are beyond the scope of additive — straightforward window glass perhaps — and perhaps a level of assembly will always be advantageous (see previous post).
Anyway, I’ll be talking, speculating about the technology for a while, to set the scene for Design2.0.
Could you… a whole car?
Wednesday, October 14th, 2009
Let’s suppose for a mad moment that you could print a structure by depositing layers of material at nano-scale. Say we’re in the year 2040. The material is deposited by something like an inkjet print head but the inks, instead of having CMYK etc colours, are formulations of raw materials. According to Bill O’Neill, a leading researcher in nano-scale fabrication at Cambridge, if the particles of material in the ‘ink’ are small enough, molecular forces will cause them to bond together into continuous structure, without the need for applied energy. Okay, let’s say you want to print a car. You could print all the parts and then assemble them with screws, fasteners and adhesives; you could print ready-assembled sub-assemblies (power plant, seats, suspension units, electronic packages and so on) — or you could just print the whole car in one lump. Let’s try that, one lump, in layers from the ground up.
The printing machine will have to be pretty big of course. With a car-size-plus build envelope and space for mechanical transport systems, materials tanks, electronics and the rest, it’s probably about the size of a small two-story house. Maybe three stories. So in this machine, an exotic print head is scanning back and forth, progressively moving along the length of the build-space depositing materials, and some kind of support medium we should suppose, layer by layer. And these are thin layers; let’s say each one is only one micron thick, so there are 10,000 layers per cm! There’s already a big problem here, with resolution, because for simpler structures and their materials — a suspension arm for example — it’s most likely too high; for a bearing surface it’s barely acceptable; and for an electronic chip — it’s several orders of magnitude too course. But we’ll ignore this for a while, and proceed anyway (I want to discuss the resolution issue in more detail in a later post).
Of course the resolution in the X direction — the length of the vehicle — will need to be about the same as in the Z. Now, let’s be ambitious and assume the head’s speed and acceleration in traversing the Y axis is about the same as the fastest current generation high-resolution photo-printer — head speed about 250cm/sec — and that the head lays down a strip of dots 2cm wide (that’s 20,000 dots). So the number of material dots printed per second is 20,000*250*10,000 — about 50 billion. Oh well.
If the car is the same size as a 2010 Toyota Prius (X=446cm Y=174.5cm Z=149cm), and if the head takes an ambitious 1sec to traverse a typical Y (including acceleration and deceleration) and with 223 2cm strips in the X, one layer will take 223sec to build. Multiply that by 1,490,000 layers and you get a build time of about 10years!
So that’s not going to work then, not the way I just described it anyway. And even if it did, it’s hard to imagine a satisfactory product with parts so relatively roughly hewn. Anyway, putting all that to one side, what would be a sensible build-time for an all-in-one additive car? In truth, probably no more than an acceptable wait for a factory order car today — say eight to twelve weeks — so consumers can take advantage of the inherent mass-customisation capabilities of the new technology. So they can have not only the colours, trim and accessories choices a new Mini may offer, but also variations in shape and mechanical detail, perhaps. So if we were to aim for a delivery wait of ten weeks, we’d have to speed up the manufacturing build by a factor of about 50.
This mind experiment raises many questions about the scope and capabilities of additive manufacture, many of which I plan to tackle here in the coming weeks. Maybe it’s daft to even consider making a whole car in one go — my own view is that it’s simply a matter of time.