In this work we investigate the performance of a novel ultrashort laser cavity design that incorporates an intracavity deformable mirror as a versatile phase-control element. With this cavity it is possible to induce user- defined phase changes into the pulse directly from the laser oscillator, as depicted in Fig. 1 thereby eliminating the need for an additional external pulse shaper.

Sandia National Laboratories is developing a technology called Laser Engineered Net ShapingTM (LENSTM). This process allows complex 3-dimensional solid metallic objects to be directly fabricated from a CAD solid model. Experiments performed demonstrate that complex alloys such as Inconelm 625 and ANSI stainless steel alloy 3 16 can be used in the LENSTM process to produce solid metallic shapes. In fact, the fabricated structures exhibit grain growth across the deposition layer boundaries. Mechanical testing data of deposited 3 16 stainless steel material indicates that the deposited material strength and elongation are greater than that reported for annealed 3 16 stainless steel. Electron microprobe analysis of the deposited InconelTM 625 material shows no compositional degradation of the 625 alloy and that 100% dense structures can be obtained using this technique. High speed imaging used to acquire process data during experimentation shows that the powder particle size range can significantly affect the stability, and subsequently, the performance of the powder deposition process. Finally, dimensional studies suggest that dimensional accuracy to kO.002” ( in the horizontal direction) can be maintained.

Rapid prototyping (RP) has revolutionized the approach to fabricating geometrically complex hardware from a CAD solid model . The various RP techniques allow component designers to directly fabricate conceptual models in plastics and polymer coated metals; however, each of the techniques requires additional processes, e.g. investment casting, to allow the fabrication of functional metallic hardware. This limitation has provided the impetus for further development of solid freeform fabrication technologies which enable fabrication of functional metallic hardware directly from the CAD solid model. The Laser Engineered Net Shaping (LENSm) process holds promise in satisfying this need. This newly emerging technology possesses the capability to fabricate fully dense components with good dimensional accuracy and with unique material properties. Relatively complex geometrical shapes have been fabricated using this technology. In continuing to develop the LENSTM process, further advancements are required. The functional dependence of the component surface finish and microstructural characteristics on process parameters including powder size and size distribution are being evaluated. A set of statistically designed experiments is being used to sort through the various process parameters and identify significant process variables for improving surface finish and achieving optimum material microstructural properties.

During manufacturing of components by laser engineered net shaping (LENS®), a solid freeform fabrication process, the introduction of residual stresses causes deformation or in the worst case, cracking. The origin is attributed to thermal transients encountered during solidification. In the absence of reliable predictive models for the residual stresses, measurements are necessary. Residual stresses were measured in LENS® samples of 316 stainless steel and Inconel 718 having simple geometrical shapes by both neutron diffraction and the contour methods. The results by the two methods are compared and discussed in the context of the growth direction during the LENS® process. Surprisingly, the residual stresses are practically uni-axial, with high stresses in the growth direction.

The Laser Engineered Net Shaping (LENS®) system at Sandia National Laboratories, a laser-based direct metal deposition process, was recently used for the fabrication of a complex prototype. The LENS process involved the challenges of adjacent areas of thick and thin cross section, overhanging unsupported features, high aspect ratios, and a hemispherical substrate. These challenges were overcome through the use of closed-loop weld pool control, height monitoring, a strong understanding of build parameters, and unique process planning strategies. The near-net shape LENS part was completed with annealing and conventional machining to produce the complex components in a reduced timeframe.

The residual stress distributions in two laser-engineered net shaping (LENS®) samples were mapped by neutron diffraction. The samples took the form of a thin wall and a pillar of square cross-section. Stresses were measured in the three orthogonal symmetry directions of the parts, parallel and perpendicular to the growth direction. Surprisingly, over most of the bulk of the samples the stress was uniaxial and directed along the growth axis, with compression in the centre of the samples and tension at the edges. The magnitudes of the maximum residual stresses were significant fractions (50 and 80 per cent for the thin wall and pillar respectively) of the 0.2 per cent yield point. The origin of the residual stress distributions is discussed qualitatively in terms of the thermal histories of the samples.

Femtosecond laser processing is a promising new technology for the fabrication of micro-scale components from engineering materials, such as metals. In the femtosecond time regime, the ablation process is nearly a solid to vapor transition, thereby providing access to cut smaller features. Sandia National Laboratories has constructed a femtosecond laser microfabrication system to study the ability to produce microscale components in metals and glasses. In this paper, we will report on our initial studies to understand the metal ablation process with respect to manufacturing process parameters. With this understanding, we will show that femtosecond laser processing can fabricate complex components with fine feature detail and clean surfaces. A key finding in this work is the substantial effect of layer decrement on resulting recast material deposition when processing in air.

Laser Engineered Net Shaping (LENS) is a novel manufacturing process for fabricating metal parts directly from Computer Aided Design (CAD) solid models. The process is similar to rapid prototyping technologies in its approach to fabricate a solid component by layer additive methods. However, the LENS technology is unique in that fully dense metal components with material properties similar to wrought materials can be fabricated. The LENS process has the potential to dramatically reduce the time and cost required realizing functional metal parts. In addition, the process can fabricate complex internal features not possible using existing manufacturing processes. The real promise of the technology is the potential to manipulate the material fabrication and properties through precision deposition of the material, which includes thermal behavior control, layered or graded deposition of multi-materials, and process parameter selection.

The primary purpose of this LDRD project was to characterize the laser deposition process and determine the feasibility of fabricating complex near-net shapes directly from a CAD solid model. Process characterization provided direction in developing a system to fabricate complex shapes directly from a CAD solid model. Our goal for this LDRD was to develop a system that is robust and provides a significant advancement to existing technologies (e.g., polymeric-based rapid prototyping, laser welding). Development of the process will allow design engineers to produce functional models of their designs directly from CAD files. The turnaround time for complex geometrical shaped parts will be hours instead of days and days instead of months. With reduced turnaround time, more time can be spent on the product-design phase to ensure that the best component design is achieved. Maturation of this technology will revolutionize the way the world produces structural components.

In solid freeform fabrication (SFF) processes involving thermal deposition, thermal control of the process is critical for obtaining consistent deposition conditions and in limiting residual stress-induced warping of parts. In this research, nondimensionalized plots (termed process maps) are developed from numerical models of laser-based material deposition of thin-walled structures that map out the effects of changes in laser power, deposition speed and part preheating on process parameters. The principal application of this work is to the Laser Engineered Net Shaping (LENS) process under development at Sandia Laboratories; however, the approach taken is applicable to any solid freeform fabrication process involving a moving heat source. Similarly, although thin-walled structures are treated in the current work, the same approach could be applied to other commonly fabricated geometries. A process map for predicting and controlling melt pool size is presented and numerically determined results are compared against experimentally measured melt pool lengths for stainless steel deposition in the LENS process.

In direct laser metal deposition technologies, such as the laser engineered net shaping (LENS) process, it is important to understand and control the thermal behavior during fabrication. With this control, components can be reliably fabricated with desired material properties. This paper will describe the use of contact and imaging techniques to monitor the thermal signature during LENS processing. Development of an understanding of solidification behavior, residual stress, and microstructural evolution with respect to thermal behavior will be discussed.

Direct metal deposition technologies produce complex, near net shape components from CAD solid models. Most of these techniques fabricate a component by melting powder in a laser weld pool, rastering this weld bead to form a layer, and additively constructing subsequent layers. This talk describes a new direct metal deposition process, known as WireFeed, whereby a small diameter wire is used instead of powder as the feed material to fabricate components. Currently, parts are being fabricated from stainless steel. Microscopy studies show the WireFeed parts to be fully dense with fine microstructural features. Initial mechanical tests show stainless steel parts to have good strength values with retained ductility.