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Pulsed Laser Deposition for 3D Printed Parts Repair

Wes Wheeler
By Wes Wheeler Sales Manager, Alpha Laser US

Laser welding is a superior technology for repairing defects in tooling, plastic injection molds, stamping dies, blow molds, turbine blades, and nearly any tooling component made of stainless steel, aluminum, copper alloy, cast iron, and all tool steels. Now, pulsed laser welding is being used to repair 3D printed parts as well.

The use of 3D printing, or additive manufacturing, is growing rapidly in the tooling industry. In the plastic injection mold industry, the speed of cooling is a critical factor in mold cycle time. With 3D printed parts, engineers can move water lines closer to the molding surfaces to cool the plastic faster so the molded part can be ejected faster. This innovation has reduced cycle times significantly and has increased the output of each mold.

New tooling made via additive manufacturing is printed layer by layer and designed with conformal cooling. Unfortunately, the thin sections and hollow areas of these 3D parts are more prone to warping, cracking, and other damage when traditional welders are used for repair. As a result, laser welding has become the go-to repair method for these tooling parts due to its low heat input.

A pulsed laser beam can precisely control how much heat is introduced into the workpiece. A laser welded heat-affected zone (HAZ) is only 0.004-0.010″ (0.102-0.254-mm) deep and the workpiece is softened in that shallow HAZ by 2-4 points on the Rockwell scale. With a conventional welder, the HAZ would be 0.100″ (2.54-mm) deep or more and the workpiece would be softened by 15-22 Rockwell.

Physics 101 tells us that heat drives grain growth and when grain size grows it becomes weaker. Therefore, heat is not your friend when welding tool steels. The pulsed laser welder introduces so little heat into the workpiece that you can lay your bare hand on the workpiece when finished welding. The color of the workpiece never changes during pulse laser welding and the part can be finished machined immediately.

Additionally, a TIG welder may have difficulty reaching certain areas on the part, especially at the delicate edges. Unlike the torch of a TIG welder, the beam of a laser welder shoots straight out from the machine and doesn’t obstruct the technician’s view—as long as he can see the area to be welded, it will be welded. A TIG welder simply doesn’t have that flexibility or precision.

Laser Speeds Catching Up With TIG

The newest laser welders are significantly faster than just a few years ago and are approaching the speeds of TIG welding. Yet compared with TIG, heat input into the part is managed much more efficiently with laser—controlling for thermal growth, distortion, warping, and annealing. Laser welding more accurately applies metal to the defect area, but stays off adjacent surfaces, greatly reducing rework times.

The cost of 3D printed parts is considerably higher than parts manufactured by traditional methods. That makes laser welding a cost-effective choice for repairing a damaged 3D part. Instead of scrapping a damaged or misprinted part, the pulsed laser welder can repair it with little damage, regardless of the materials the part is made from. Pulsed laser welding creates extremely low dilution, so the base metal and the welded materials are bonded but not forced to dilute, eliminating porosity or cracking.

Laser welding is a flexible solution as well. For example, most of the lasers sold by Alpha Laser are capable of welding 3D printed parts. The process can be used to join many uncommon alloys, can be deployed in areas of parts with delicate details and features, and causes very little damage or change in the base substrate. As a result, laser welding is an outstanding solution to many of the manufacturing problems confronting the additive manufacturing industry.

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