ADDITIVE MANUFACTURING is the magazine devoted to industrial applications of 3D printing and digital layering technology. We cover the promise and the challenges of this technology for making functional tooling and end-use production parts.
Issue link: https://am.epubxp.com/i/667993
AM / Knee Surgery's Next Step additivemanufacturing.media 31 makes this fne-tuning easy. DMLS allowed Dr. Piasecki's design changes to be quickly and easily imple- mented. "All he had to do was provide a new model," Self says. DMLS also allowed for left-hand and right-hand versions of the tool to be made, as well as 5.5- and 7-mm ver- sions, without tooling or additional build-setup fees. Stratasys Direct Manufacturing never built the same proto- type twice, but AM allowed them to be built fairly quickly. On average, it took 12 days to build each new design variation, and the company delivered 22 prototypes over 10 months. Additive also allowed for adjustments after the prototyping stage. Because initial test production parts were rejected for dimensional inaccuracies, adjustments were made to compen- sate for dimensional changes that occur as the metal cools. Through design modifcations, Laser Design and Stratasys Direct ultimately achieved a design and process repeatable to within ±0.005 inch. Stratasys Direct also worked with Dr. Piasecki to redesign the handle of the tool to round the sharp edges of grooves intended for grip and stability, a change that reduces the amount of labor needed to remove supports and perform polishing. To date, about 28 Pathfnders in service at approximately 12 hospitals and clinics in the United States have been used to complete more than 500 successful ACL reconstruction surgeries. Improvements are ongoing, as DanaMed continues to receive feedback from surgeons using the device. "Being able to make design changes and 3D print new tools within days was essential in perfecting the Pathfnder's design," Duncan says. "We were able to get feedback from a surgeon, make design adjustments and send an updated Pathfnder within a week. That would not be possible with investment casting or injection molding." It was just one small feature on this surgical tool that made it complicated to produce. By generating that feature, DMLS made this complex design a reality. The tool's difcult-tomanufacture geometry is in the span from the neck of the device to the critical tip. of center. Inconel provided the necessary balance of strength and weight to help the surgeon control the tip when the device is held in his or her hand. A solid handle built as one piece instead of with a replaceable head also helped to provide the desired balance and control. Shape. It was critical that the shape of the tool match the anatomy of the knee. Self describes the organic design: "It features an elongated, slim body section; a slotted groove for capturing and holding the guide pin and for easily disengaging with a simple twist of the tool; and a curvilinear head section to let the surgeon reference inner knee surfaces, turn and manipulate easily within the limited space, and rigidly hold position against bending and drilling forces." Shine. Once the parts are taken out of the DMLS ma- chine, supports are removed and the parts are bead-blasted to remove the surface layer. They are then shined via hand polishing. Polishing also closes of the surface and ensures that the part can withstand staining and cleaning. For the Pathfnder, this cleaning means frequent sterilizing with hot and cold steam, and repeated washing with a strong solution throughout its lifetime. Let the Fine-Tuning Begin Getting to the fnal design of the device required considerable fne-tuning. Compared to other part-making processes, AM The challenges of the complex geometry were met with direct metal laser sintering.