Rapid Manufacturing by Laser

   RCAM has created and developed a variety of technologies to realize the potential of rapid manufacturing and repair by three-dimensional laser powder deposition. The Laser-Based Additive Manufacturing system (LBAM) has made it possible to precisely deposit metal, ceramic, and composite powder materials, creating fine geometric features and excellent material properties. Shown below are some of the features of the LBAM system and several examples of parts created with this technology.

The LBAM system currently relies on a six-axis welding robot for laser head motion. A multi-axis CNC machine is used for subtractive operations. Here, the robotic arm can be seen with a laser head designed and built at RCAM. This system includes the powder delivery nozzle as well as a coaxial vision system used to provide feedback for control of the molten pool size during powder deposition.

Successful laser powder deposition requires a precise and responsive powder feeder. RCAM has applied for a patent on the design of a novel powder feeder which meets these needs. Two prototype examples are shown here. These machines feature feeding rates below one gram per minute (and up to 20 grams per minute if needed), with a repeatability of less than one gram per minute. Here they are shown placed on precision weight scales, which provide feedback to the powder feeder controller for more precise powder delivery.

This diagram shows how the feedback control of the molten pool size is calibrated. A second high-shutter speed camera, assisted by two pulsating nitrogen lasers, provides a strongly contrasted image of the molten pool. A computer algorithm determines the edge of the molten pool and compares this data to the gray scale infrared image obtained by the coaxial camera. The specific gray scale number which corresponds to the edge of the molten pool is then determined, and the coaxial camera can then be used as a feedback sensor to control the molten pool size.

The LBAM system is capable of depositing material in any direction - not just vertically. Here, a thin wall approximately 1mm thick has been deposited in the horizontal direction.

This system is also capable of creating parts with internal cavities. Here, a laser-deposited part has been cut in two to reveal the complex geometry within.

This part displays the uniform deposition possible with the LBAM system, along with the capability to combine thick and very thin sections at any point within the part.

Because the LBAM system includes multiple powder feeders which can be independently controlled, it is possible to change the mix of materials being deposited on the fly, both within a single layer and from layer to layer. This makes it possible to create alloys and composites with functional gradience, so that the material properties at any point within the part match the needs. For instance, an erosion-resistant carbide composite with a high carbide content can be deposited at the surface of the part, with the carbide content gradually decreasing towards the center of the part. This creates a part with a hard, erosion-resistant exterior and a tough core, without the abrupt transitions typical of hardface coatings. The sample shown here has a 100% tool steel base, which gradually blends into a 100 percent tungsten carbide/NiSiB binder mixture at the top.

This picture shows a novel approach to building parts with LBAM technology. Rather than building the part layer by layer, it is possible in some cases to create the geometry in a continuous fashion. Here, a helical spring is created in one pass using tool steel as the deposited material.

The finished spring, the first created at RCAM, is shown. Creating the spring in this way is far more efficient than the layer-by-layer method. This spring can be compressed without yielding or fracturing.