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.