Additive Manufacturing Breathes New Life into Legacy Equipment

Broken gear for a German Knapp rack mill. (Image courtesy of Hansford Parts and Products.)

Do a little snooping on the floor of any machine shop and you’re likely to find a piece of legacy equipment older than company’s youngest employee. It’s no secret; it’s the logical outcome of adhering to a variation on that old adage, “If it ain’t broke, don’t replace it.”

Of course, the risk of keeping old machines around for too long is that you end up struggling to maintain them. Maintenance, repair and overhaul (MRO) operations depend on readily available supplies of spare parts. So, what happens when your equipment supplier no longer makes the parts you need?

You could try to track down whatever spare parts are still floating around out there, but that only delays the inevitable. No one wants to scramble to find a whole new machine because their spare parts ran out at a crucial junction in production. Fortunately, there is an alternative.

Remanufacturing Broken Gear Teeth

Hansford Parts and Products, a New York-based machine shop, recently was confronted with just this problem. The company purchased a German Knapp rack mill in 1966 to make keyway broach cutters. It’s been in operation ever since, until a bearing failure led to broken teeth on a gear, one that’s no longer in production.

Gear shaft after the broken teeth were removed and the base diameter undercut. (Image courtesy of Hansford Parts and Products.)

Rather than scrap the machine, Hansford partnered with engineers from the Rochester Institute of Technology’s Golisano Institute for Sustainability (RIT-GIS) to find a better solution.

“The first steps involved analyzing the original material and properties using x-ray analysis and micro-hardness testing,” said Mark Walluk, RIT-GIS mechanical design and analysis engineer. “Next, we used an optical measuring machine to capture the existing tooth profile.”

That profile was translated into a CAD model. The broken teeth were then removed, and the base diameter undercut.

It’s at this point that 3D printing enters the picture in the form of an Optomec LENS 3D Metal Hybrid VMC operated by RIT-GIS. The LENS system was initially used to add material at the base diameter to strengthen the interface with the existing material. This new surface was then milled flat using the subtractive side of the hybrid system to ensure the new teeth would be straight.

The gear shaft with a new 3D-printed near net shape tooth profile. (Image courtesy of Hansford Parts and Products.)

Using CAM software to output G-code from the CAD model for the LENS system, the Hansford and RIT team was able to print a near net shape of the missing teeth on the gear.

“The near net shaped tooth resembled a trapezoid after fabrication with the LENS system and was roughly machined to the profile we captured,” Walluk said.

After checking the micro-hardness of the new teeth—which appeared similar to the originals—the team 3D surface machined the final tooth profile and returned the gear to the rack mill, which is once again up and running.

Remanufacturing Challenges

As heartening as it is to see a venerable piece of equipment revitalized with current technology, the process wasn’t quite as smooth as suggested by the description above.

“The complex geometry created by the shoulders on the gear shaft affected the shield gas and powder flows, making material deposition difficult at first,” Walluk said. “The initial methodology we borrowed from other applications had to be adapted to meet the nuances of building between teeth and next to the shoulder.”

The gear shaft with a new 3D-printed near net shape tooth profile. (Image courtesy of Hansford Parts and Products.)

At least the compatibility between the 3D-printed metal and the original metal of the gear shaft proved not to be a problem.

“Due to the limited loading and wear in this application, we did not match the original material, but substituted another alloy that we had experience with and was known to provide similar mechanical properties,” Walluk said.

Additive Manufacturing & The Future of MRO

It’s difficult to make a direct comparison between this method of repair and more traditional approaches—like shaft machining—since the project’s goal was simply to find a method for fixing the teeth. However, Walluk did comment that, “In the future, similar repairs could be performed in a fraction of the time it would take to fabricate an entire gear shaft.”

The previously broken gear shaft, repaired with 3D printing. (Image courtesy of RIT-GIS.)

On the question of whether manufacturers are more likely to keep 3D printers in house for their MRO needs or contract out their additive work, Walluk responded that, “In the near term, I think smaller companies are likely to outsource this type of one-off repair work to external fabrication houses. Once experience with these additive processes grows, then I envision more companies bringing the technology in-house. Large remanufacturing companies have already adopted technologies similar to this process and are using them to repair components.”

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