3D printing with metal: The final frontier of additive manufacturing

Few areas of technology have seen as much development in one year as that of 3D printing. Undoubtedly, the most dramatic and challenging has been printing with metal. For your enjoyment, we have assembled a few incredible videos that showcase the power and flexibility of 3D printing with metal — to not be amazed is to be numb to the technology of our day.

The first attempts to print with metal can be traced back to the 1880s when the first welders used carbon electrode arcs to fuse two pieces of metal. It was later found that if a third sacrificial stick of material was used a metal bead could be laid down. When Humphry Davy first discovered the electric arc in 1800, he chose to call it an arc since the evaporating gases buoyed it up into an erratic but generally rounded shape. It was not until the advent of electron beams and vacuum chambers that precise metal printing would first be made possible.

The real breakthrough that has enabled 3D printing for the masses has been the laser. Spray welding is a technique that has been used for decades to build up worn motor shafts, but it is far too crude for controlled additive printing. Spray welding uses a gravity-fed powdered metal dispenser integrated into a special oxygen-acetylene torch head which melts the powder as it is dispensed. Swapping the torch for a laser gave us the powerful construction tool we have today. A powdered metal feedstream, confined and protected against oxidation with a surrounding jet of inert shielding gas, fused by a laser piped through a central bore in the head is now the state of the art technology. Trumpf makes one such device, as shown in the video below.

NASA recently used a technique called selective metal melting (SLM) with great success tobuild rocket motor components out of steel. NASA’s engineers have been able to produce parts with complex geometry only previously imagined, and with dimensional accuracy beyond that possible with traditional fabrication methods.

To compete with modern manufacturing methods, perhaps the fastest method of metal printing is to deposit a powder metal matrix that contains binders. After each layer is deposited, the binder is melted and the metal is temporarily held together until it is fused in a final bake in an oven. The part can be printed entirely in this way, or just a shell can be printed which can then be used to mold metals of a lower melting point.

One of the premier organizations to capture public attention is Shapeways, which has streamlined the process to be able to provide a (metal or plastic) printed part in the shortest time possible. It has a variety of metal materials to choose from, and even offers precious metal printing in silver. Nowadays you can do a lot with a thousand dollars in the world of 3D printing — and what you can do with few hundred thousand is a whole lot more incredible.

When Apple was selling bare-bones phone cases for exorbitant prices, many people decided that it was time to take matters into their own hands — they began to design their own cases with the help of Shapeway’s tools. A price of $8.00 per cubic centimeter for stainless steel, $6.00 handling fee, and optional gold plating of $9.00 made it a no-brainer for the artistically inclined. As long as your part fit inside a bounding box of 750x380x380mm and had walls at least 3mm thick, Shapeways could probably make it. The only drawback you might find is that the stainless steel used is similar to the common 400 series steel — sufficiently magnetic to be undesirable when those properties are not wanted, but too weakly magnetic when magnetic properties might be of use. Likely that too will soon change.

The future of 3D printing with metal

Two technologies on the horizon will offer us even higher resolution parts. Two-photon laser curing permits extreme precision by using laser absorbers in the binders which are only activated by simultaneous absorption of two photons. If the laser beam is then strongly focused with a high degree of convergence, it will pass through most of the material without reaction, achieving sufficient density for curing only within a localized volume. Similar techniques have already been used to etch features inside the center of a piece of glass.

The other tool increasingly at our disposal is the femtosecond laser. Initially the province of high-end systems for micromachining or corrective eye surgery, they are now finding application in 3D printing. Femtosecond lasers are still prohibitive in cost, in part due to the sapphire crystal at their heart. They use pulse compression to squeeze a huge amount of optical energy into an extremely short pulse and give a lower power laser the ability to fuse metal. Aluminum oxide, which chemically is identical to sapphire, structurally lacks the clarity one normally associates with it. Aluminum oxide can be printed and fused — printed sapphire, now that would be something else.

Fuente: http://www.extremetech.com/extreme/143552-3d-printing-with-metal-the-final-frontier-of-additive-manufacturing