A recently developed technology uses both additive and subtractive processes to make complex 3D parts. The developer says the special method, initially developed for prototyping and production tooling, shows great promise in making “smart“ medical implants. These are solid devices embedded with sensors or integrated circuits that can wirelessly transmit information to healthcare personnel.

The proprietary technology from Solidica Inc., Ann Arbor, Mich. (solidica.com), uses what the company calls “ultrasonic consolidation“ to build-up thin layers of metal to aluminum base plates that are rigidly fixed to its special machine tools. After the machine welds a certain number of layers to the plate, a CNC-controlled cutting tool removes unwanted material and the welding and cutting process repeats until the 3D part is complete. The method eliminates fixturing and setup time.

Vice president of strategic development Ken Johnson says ultrasonic consolidation is actually a form of ultrasonic welding. But ultrasonic welding only bonds two components together. Ultrasonic consolidation, on the other hand, involves bonding many thin layers of material, typically about 0.006-in. thick, on top of each other to form the solid object. Both processes are solid-state welding methods, meaning metal is joined without fusion, or melting.

“Most additive metal processes are quite inaccurate or rough,“ says Johnson. “One, for example, uses a laser deposit to melt powdered metal. But our process immediately machines parts without waiting for them to cool. Better yet, parts contain no residual stresses. And the CNC-controlled removal of material lets us hold tight tolerances,“ he adds.

The company initially joined 3000 and 6000 series aluminum layers to manufacture molds for wax patterns in investment casting. The company has also made tools by joining dissimilar metals such as aluminum to titanium and silver to copper. Titanium implants with embedded sensors are currently in developmental stages.

“You can't cast titanium around electronics. But our cold-deposition process lets us locate sensors and integrated circuits in the part as it is built. We end up with what appears to be a solid piece of metal, but is, in fact, a self-diagnosing device,“ says Johnson.

In one application, the company is making a titanium hip implant with a strain gage inside that uses an RF stream to transmit information such as stress on the part. This lets a doctor run a diagnostic on the implanted joint, pulling down all the data saved from the patient's last visit.