Stereolithography & the Future of Aftermarket By Peter Skipp

An Overview

Stereolithography is a rapid prototyping technology that has emerged over the past two decades. Instead of hand-making a prototype, you now design it in a computer and "print" it out in "geographic contour" layers of photosensitive resin. An extension of rapid prototyping is rapid manufacturing, where the computer-designed prototype is "printed" as many times as needed for a small number of clients.

The Subject

Zvezda's lovely Il-86 reached the bourgeois West in mid-May. While it was well up to standard, its engine fans let it down (one wag suggested they had been made with the fine nozzle of a cake decorating kit!). In late May, Laurent announced in modeling forums that he had designed an aftermarket stator and fan assembly. Since the item was so tiny and complex, however, he had no option but to offer it as a rapid manufacturing part: straight from the 3D printer.

The Parts

I immediately ordered one set (six were on offer at 15 euro/18 dollars each). Yet, others had great objections. A professional modelmaker experienced in stereolithography stated that, however fine the computer model, "stair-stepping" (resulting from the layers in which resin is applied) and general crudity would need much hand finishing. Another stated that the resins used were prone to expansion and contraction with temperature and humidity changes.

The package on my doorstep contained a nice 5 x 1cm (2 x 1/2 in) "frame" with four extremely fine fan and inlet stator vane assemblies to complete an Il-86. Weight was about 1/6 ounce. Feel was midway between polystyrene and nylon. Appearance was like semitranslucent nylon (off-white to yellowish cream), with the silky-smooth surface of extra-finely ground Venetian glass. A thumbnail drawn across the surface leaved a glistening mark.

Looking at the parts, you could not tell by what process they were made; more than anything, they appeared organic in their elegant fragility -- the product of intelligent bees.

There was not the slightest evidence of "stair-stepping," even under a magnifying glass (in truth, I would not have expected much stair-stepping in what was essentially a cylinder). Laurent did not smooth out the outside facets of the cyllindrical part in his computer model (this would have been unnecessary), and each facet was faithfully reproduced!

As to expansion and contraction, I did not have the opportunity to monitor the parts under different temperature and humidity conditions. The parts fitted the IL-86 nacelles superbly, though a tiny allowance was evident, possibly to take expansion into account. I spot-glued them into my Il-86, allowing for this.

Comprising a fan and fan disc (spinner), plus a set of 12 stator vane blades each, the parts could not have been injection molded. The fan blades actually overlap (!), and the miniature gap between them and the vanes (1/16th inch-ish) is so small, any combination of injection molded parts would have been compromised (wall thickness and fitting flanges all eating into shape fidelity). Moreover, due to the different injection pressures neede, it is doubtful whether the extremely thin spoke-like stators could have been put on the same mold as other items, or if they had been, whether results would be uniform each shot.

The future will undoubtedly bring us more and more rapid manufacturing parts. Personally, I feel that within a decade and a half, the aftermarket cottage industry will switch to rapid manufacturing as its mainstream medium for small parts. Cost remains an issue; Laurent has not covered his costs at the experimental rate he charged.

All of which leaves me with one big problem: how to paint such exqusitely complex inlets with my bear's paws...