As a bonus, the silkworms also naturally applied a protective coating to the spider silk, resembling that produced by spiders themselves. This is likely to result in the fibres being more durable than artificially created spider silk, says Mi. “This makes silkworms an all-in-one station for spider silk fibre production,” he says.

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Another thing Utley mentioned is part stress. The 3D printing process generates tremendous temperature differentials as the powdered metal melts and rapidly cools, layer by layer, until the workpiece is complete. That’s why Proto Labs heat-treats nearly all 3D-printed metal parts. Without this secondary stress-relief process, it’s possible the part would curl up like a potato chip during machining.

The resulting silkworms produced silk that was 100 per cent spider silk and could withstand a stretching force of 1299 megapascals without breaking, making it 1.3 times stronger than nylon. Its toughness – the energy it could absorb under impact – was 319 megajoules per cubic metre, making it six times tougher than Kevlar.

Substances having metallic properties and being composed of two or more chemical elements of which at least one is a metal.

Bonding of adjacent surfaces in a mass of particles by molecular or atomic attraction on heating at high temperatures below the melting temperature of any constituent in the material. Sintering strengthens and increases the density of a powder mass and recrystallizes powder metals.

According to industry experts—such as the additive-manufacturing consulting firm Wohlers Associates, Fort Collins, Colo., and simulation and product development experts Phoenix Analysis and Design Technologies (PADT)—3D-printed metal from laser-based powder-bed fusion systems cuts no differently than a billet of 17-4 PH stainless steel, titanium, Inconel or one of the many other alloys available today.

Now, Junpeng Mi at Donghua University in China and his colleagues have used a more advanced genetic engineering technique – CRISPR – to insert the genes responsible for making spider silk proteins into silkworms.

Spider silk has been seen as a greener alternative to artificial fibres like nylon and Kevlar, but spiders are notoriously hard to farm. Now researchers have used CRISPR to genetically engineer silkworms that produce pure spider silk

Silkworms have been genetically engineered with CRISPR to produce pure spider silk for the first time. The worms could offer a scalable way to create things like surgical thread or bulletproof vests from spider silk, which is prized for its strength, flexibility and lightness.

Kip Hanson is a contributing editor for Cutting Tool Engineering magazine. Contact him by phone at (520) 548-7328 or via e-mail at kip@kahmco.net.

“In general, for parts printed using powder-bed laser melting processes, we recommend the standard speeds, feed rates and cutting tools found in the Machinery’s Handbook,” said Rey Chu, principal of PADT, Tempe, Ariz.

This titanium hip implant looks like tough stuff, but the most-difficult thing about machining parts like these is fixturing them. Image courtesy of McClay Tooling.

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“The sintering process creates some pretty extreme internal stresses,” Utley said. “Even without machining, it’s important to remove them if you’re going to produce a stable part.”

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Eric Utley, applications engineer at Minneapolis-based Proto Labs’ Morrisville, N.C., location, said 3D-printed metals are “like machining a sand-casted part” and agreed that fixturing is probably the biggest struggle. “You have to wrap your head around how to hold these parts, where you’re going to touch off and make sure you’re machining what actually needs machining. That said, one of the beauties of 3D printing is that it’s usually easy to design in part-locating surfaces, provided you think about it in advance.”

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Are you being asked to quote secondary machining operations on a handful of 3D-printed metal parts? If so, how do you cut these parts?

The engineered silkworms could enable cheap mass production of spider silk, which may be used as surgical suturing thread or in bulletproof vests, says Mi. The team has already experimented with using the spider silk as a suturing thread for stitching up incisions in rats and found that their wounds healed better than when traditional nylon threads were used, he says.

But not so fast. Mark Fisher, workshop manager at Christchurch, New Zealand, machine shop McClay Tooling Ltd., agreed that the 3D-printed titanium hip implants the company machines are virtually indistinguishable from titanium bar stock, except for their “slightly harder skin.” For these parts, McClay designed proprietary cutters that it operates at feeds and speeds Fisher is unable to discuss. He is, however, willing to point out the difficulties faced in fixturing these parts due to their complex, organic shapes, a factor that also presents challenges during 5-axis machining operations.

Spider silk has been eyed as a greener alternative to synthetic fibres, which are derived from fossil fuels and leach harmful microplastics into the environment. Farming silk from spiders themselves is difficult, however, because they tend to eat each other and only produce a small amount of silk fibre to make their webs. A 4-square-metre spider silk shawl that was displayed at the Victoria and Albert Museum in London, for example, had to be created from the silk of over 1 million golden orb-weaver spiders.

As a result, several groups have tried to genetically engineer silkworms so that they make spider silk instead of their own silk, since silkworms are easier to farm and spin much larger quantities of fibre. But until now, the silk produced by these modified silkworms has been less than 36 per cent spider silk.

A quick Google search returns images of some cool-looking components, but what’s with all the curvy geometries and gnarly surface finishes that, at first glance, appear rougher than corn cobs? 3D-printed parts must be tough to machine, right?