One of the benefits of additive manufacturing is the potential to eliminate the need for stored inventory. From end products to replacement parts to tools, 3D printing could make it possible to print what we need, when and where we need it, with the mythical batch size of one and completely custom made with very low lead time.

(Image courtesy of ORNL)

Heavy-duty Cummins cylinder heads wear out after a million miles on the road. Ordinarily, these cast iron parts would have to be replaced with new castings, a costly process in terms of time, energy, and money. Instead, the team ‘scoops out’ the worn section, and uses additive techniques to deposit a high-performance alloy in its place, like a heavy-duty dental filling.

New Process Prints Metal Directly onto Machined Surface

Niyanth Sridharan is an ORNL Post-Doctorate Research Associate working on the project with colleagues Brian Jordan and Ryan Dehoff. Niyanth told me the details of the process:

First, Cummins receives damaged cylinder heads that are out of service, with damage near the site of the fuel injector. Cummins uses conventional milling to machine out the damaged area, and sends it to ORNL.

The researchers then draw a CAD file of the machined section, and preprogram their printer using G-code, so that the filler metal can be deposited directly onto the part, without the need for any other substrate or fabrication.

The G-Code is loaded onto a DM3D direct energy deposition system, a laser powder blown machine, which uses a laser mounted on a 5-axis CNC head. The nozzle sprays a cloud of atomized metal powder right on the area which needs to be repaired and the laser melts the powder to build fully dense parts layer by layer. The advantage of this process is that it can be used to build onto existing parts making the process applicable for repair and hard facing coatings. DM3D is a small business based in Detroit, Michigan.

Oak Ridge has modified DM3D’s device, adding infrared sensors to monitor temperature, and heaters to avoid cracking of the cast iron during the repair/rebuilding process.

Challenges and Next Steps for Engine Repair 3D Printing

Cast iron is extremely difficult to repair, due to its tendency to crack. The researchers are using a high-nickel-containing alloy to avoid cracking and increase thermal efficiency of the part. The deposited alloy bonds to the existing cast iron during the additive process. Microscopic analysis of the bonds shows good adhesion, but the repaired parts have yet to be tested on the road.

Niyanth says next steps for the project include testing how strong the bonds and interfaces are. After that, the team will try out slightly different alloys proposed by Cummins. In-service testing will be the true test, putting the repair through the intense heating/cooling cycles of engine use.

This intriguing research shows the potential of 3D printing: not only replacing parts, but repairing and even upgrading existing parts.

The automotive industry would see obvious benefits from this ability. A dealership or even a third-party repair shop could print the parts needed for a repair instantly, not only eliminating the need for inventories of parts, but also reducing shipping costs and lead times of ordering replacement parts.

Instead of seeing “parts and labor” on your mechanic’s invoice, you may soon see “raw materials and labor.”

Read more about applications of metal additive manufacturing here.