David M. Keicher

The laser forming of metallic components using particulate materials

Direct fabrication technology, which utilizes computer-aided design solid models to automatically control the manufacture of functional piece parts, is rapidly gaining popularity as a means to significantly reduce the time to market of new concepts. Since the introduction of stereolithography in 1982, several different rapid prototyping technologies have evolved using surrogate rather than actual materials of construction. Most recently, researchers have begun to develop laser-based methods to obtain fully dense metallic components directly from a computer-aided design solid model. Each of these methods is unique, but possesses aspects that are similar to the others. Many of these methods hold a great deal of promise for applications; however, none have been developed into a commercial product.

Using the laser engineered net shaping (LENS) process to produce complex components from a CAD solid model

The laser engineered net shaping (LENSTM) process, currently under development, has demonstrated the capability to produce near-net shape, fully dense metallic parts with reasonably complex geometrical features directly from a CAD solid model. Results to date show that excellent mechanical properties can be achieved in alloys such as 316 stainless steel and Inconel 625. In fact, due to the highly localized nature of the laser heating, a fine grain structure will occur resulting in a significant increase in yield strength at no expense of ductility. The current approach lends itself to produce components with a dimensional accuracy of plus or minus .002 inches in the deposition plane and plus or minus .0.015 inches in the growth direction. These results suggest that this process will provide a viable mens for direct fabrication of metallic hardware directly from the CAD solid model.

Laser beam characterization results for a high power CW Nd:YAG laser

In an effort to understand multimode laser beam propagation characteristics for better development of laser material processing applications, beam diagnostic experiments were performed on a 1800 watt cw Nd:YAG laser. Beam diameter data were acquired at approximately 12 positions along the beam optical axis about the minimum waist created by a long focal length single element lens at several power levels. These data were then used to evaluate the laser output beam characteristics using two differing techniques. For the ISO technique, two data points from the beam diameter data were used in determining the output laser beam characteristics. These points were the beam minimum waist diameter and the diameter at a point along the beam optical axis where the beam diameter had increased to approximately 0.7 times that of the beam minimum waist diameter. The second analysis technique involved fitting the entire data set to theoretical equations used to describe the multimode laser beam propagation and points from the fitted curve fit were then used to determine the output beam characteristics from the laser. For all power levels evaluated, calculated results predicting the laser beam minimum waist location were in agreement with measured values and more consistent using the curve-fit technique than the two-point evaluation technique.

Selective evaporation of focusing fluid in two-fluid hydrodynamic print head.

The work performed in this project has demonstrated the feasibility to use hydrodynamic focusing of two fluid steams to create a novel micro printing technology for electronics and other high performance applications. Initial efforts focused solely on selective evaporation of the sheath fluid from print stream provided insight in developing a unique print head geometry allowing excess sheath fluid to be separated from the print flow stream for recycling/reuse. Fluid flow models suggest that more than 81 percent of the sheath fluid can be removed without affecting the print stream. Further development and optimization is required to demonstrate this capability in operation. Print results using two-fluid hydrodynamic focusing yielded a 30 micrometers wide by 0.5 micrometers tall line that suggests that the cross-section of the printed feature from the print head was approximately 2 micrometers in diameter. Printing results also demonstrated that complete removal of the sheath fluid is not necessary for all material systems. The two-fluid printing technology could enable printing of insulated conductors and clad optical interconnects. Further development of this concept should be pursued.