This PDF file contains the front matter associated with SPIE Proceedings Volume 11992, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Laser Additive Manufacturing (AM or 3D Printing) is now an accepted method of advanced manufacturing for a variety of industry sectors. The best kept secret of 3D printing, which is a unique innovation, is the deployment of Green Lasers. Using a laser beam with a wavelength in the visible spectrum of 515nm (as opposed to IR at 1063nm), enables laser AM of highly reflective materials like copper, aluminum, gold, silver, platinum and iridium to be more effective and efficient. IR lasers in combination with these reflective materials have a hard time coupling the beam to the metal and can result in reflective losses, with printed parts that have questionable porosity and surface finish. Green Laser technology on the other hand, developed from the “traditional” laser cutting and welding side, when applied to 3D printing, just makes sense in terms of achieving results with better density, lower porosity, better surface finish, less spatter and improved productivity (depending on the part and parameters used, up to ten times faster than IR laser source with pure copper powder). The applications for jewelry, works of art and high value consumer products with precious metals are now limitless in terms of design and imagination. Whereas copper for parts that require electrical conductivity and thermal conductivity can also be printed faster and, for rocket engines for space vehicles that are printed in copper alloys such as C18150, GR Cop 42 or 84, that resultant improved productivity giving a faster print speed with fewer defects, would be another pathway to access space, faster.

Additive Manufacturing technologies such as Laser Powder Bed Fusion (LPBF) provide several advantages compared to conventional manufacturing techniques by being cheaper, faster, more flexible and energy efficient. Therefore, they offer a huge potential for electronics packaging. Direct bonded copper substrates are a commonly used substrate technology for power electronics based on copper and alumina. This paper focuses on reflecting the state of the art in DBCtechnology by investigating the parameters different authors used in their experiments and deriving optimal settings based on these results. Furthermore, works addressing the LPBF of copper or laser-based copper processing on ceramics with and without afterward heat treatments were collected. These works were also studied and potentials, challenges as well as prospects for the LPBF-process of the adaption of the DBC-technology are presented.

A 316L stainless steel [SS316L] plate was fabricated without pores by selective laser melting (SLM) in a vacuum. SS316L has excellent properties such as high corrosion resistance and hardness, but forming complicated structures is challenging due to difficulties working the material. SLM forms a 3D material by building it layer by layer. In SLM process, a denudation zone is caused to form near the laser scan path while laser irradiation. The denudation zone caused to form a layer having an un-uniform thickness and also leads to a decrease accuracy of fabrication. There are many unknown controlling factors about the basis of denudation zone generation. In this study, in order to clarify the mechanism of the denudation zone formation process, SS316L is fabricated by SLM in a vacuum and the width of denudation zone is measured by microscope. The ambient pressure is varied from 10 Pa to 10 ⁵ Pa using a vacuum pump, and argon gas. As the results, at the ambient pressure of 10⁵ Pa, the width of denudation zone is 0.81 mm, and the width of denudation zone at 300 Pa was improved to 0.27 mm. It is clarified that the width of denudation decreases with the decrease of the ambient pressure.

This study analyzes the elevated temperature tensile results of SLM IN718 as a function of strain rate and test temperature in order to better understand the temporal and thermal aspects of environmental sensitivity. Fully heat-treated SLM samples are directly compared to wrought material and corresponding industry standards in order to provide a valuable perspective on the current state of SLM capabilities. It is found that SLM material tested across all conditions have inferior strength and ductility compared to wrought material of the same heat treatment. Strength variation is attributed to different sizes of the primary strengthening phase, γ’’, while ductility variation is caused by environmental sensitivity. SLM samples show evidence of brittle intergranular fracture, crack growth, and oxidized NbC particles on the fracture surface. These features are intensified with decreasing strain rate and increasing temperature. EBSD-generated misorientation maps and strain rate sensitivity calculations demonstrate that the mechanism of plastic deformation is similar between the two processing conditions but wrought material has a greater overall damage tolerance. Premature failure attributed to intergranular crack growth leads to poor ductility in SLM material. Faster strain rates and lower temperatures are shown to improve the ductility in SLM IN718 but despite this recovery it remains susceptible to environmental attack even in the extreme cases of the current study. Sources of environmental sensitivity and the degree to which they affect elevated temperature mechanical properties are discussed.

The need for ever increasing process temperatures during combustion in space engines and gas turbines to increase efficiency requires the use of thermally resistant materials and novel cooling solutions. For the improved cooling of thermally highly stressed components, the technology of transpiration cooling, in which a cooling medium flows through a porous structure, has been known for a long time. Additive manufacturing and, in particular, laser powder bed fusion (LPBF) offers great potential for the near-net-shape production of porous structures compared to complex conventional manufacturing. In this contribution, porous structures were manufactured and the process parameters were optimized to increase the quality of the pores. The study discloses an adapted exposure parameter set for the improved fabrication of cylindrical pores in an INCONEL® 718 material and the associated mechanical properties of porous and dense components.

Diffractive optical elements (DOEs) have a number of advantages over refractive or reflective optical elements, including improved dispersion, wider profile tolerances, and greater design freedom. A critical DOE, the Fresnel zone plate (FZP) is widely used in a variety of optical systems, including nano/micro focusing lenses, X-ray imaging, and beam shaping. Optics research on tunable functional devices has a long history of being an enticing field, having a significant impact on the evolution of optical information technology and photonic integrated circuits. The active-spiral Fresnel zone plate (ASFZP), the nanoscale polymer-dispersed liquid crystals (LC) tunable Fresnel lens, and the tunable spiralized Fresnel zone plate are all examples of tunable zone plates. All previously described tunable zone plates achieve tunability by modifying their properties or shape in two dimensions along the lateral plane. In this study, we demonstrate an active flexible three-dimensional tunable spiral plate (3DSP). Rather than alternating bright and dark zones, these zone plates have a spiral pattern in three dimensions. These zone plates enable tunability in both wavelength and depth of focus by actively modifying the lateral and vertical planes. These zone plates achieve a combination of selective wavelength transmission and predefined depth of focus by activating the 3DSP to predefined settings.

Femtosecond laser direct write (fs-LDW) is a promising technique of 3D printing of biomaterials such as protein due to nonlinear multiphoton absorption processes facilitating microfabrication along a designated laser light path. To use protein as precursor material for fs-LDW is attractive because the fabricated structures retain their native function as demonstrated by several reports. These reports range over a select variety of protein and photoactivators, but pure protein can also be utilized as precursor. The resulting proteinaceous microstructures with retained native function and submicron feature sizes might offer diverse biomedical or biochip applications. Based on the review of previous publications, it seems that both MHz and kHz range have been used to fabricate microstructures. In our body of work, we considered so far fluence and total accumulated fluence to be the key parameter to control fabrication success and fine-tune feature sizes. Here, we aim to explore whether repetition rate is a significantly contributing parameter to the process of proteinaceous microfabrication by fs-LDW. We fabricate microstructure arrays from the protein bovine serum albumin for repetition rates between 10kHz and 1MHz with constant pulse width and pulse energies from 20 to 100 nJ. We find that 100kHz is the optimal repetition rate for our protein precursor.

The layer-by-layer manufacturing approach utilized in additive manufacturing (AM) allows access to layers offering opportunities to embed technologies at each layer leading to 3D electronics, for example. Achieving this goal requires the coupling of multiple technologies including material extrusion 3D printing, machining, and robotic component placement & soldering. When exploited synergistically in this hybrid manufacturing (HM) approach, additional functionalities can be integrated in parts to produce multifunctional parts, or parts containing any additional functionality beyond rendering of basic shape. By combining additively manufactured dielectrics and nonconductive materials with conductors (wiring and electronics) via mechatronic equipment/tooling, the 3D printing process can be interrupted to embed and enclose sophisticated electronics within materials to produce electrically functional, end-use devices for custom and embedded sensing capability. To embed and connect electrical circuits, we developed methods for ultrasonic wire embedding and laser soldering. Laser soldering was studied to create joints on wire-wire and wirecomponent junctions. Of particular importance was the placement, spacing, and fixturing of 1608 components (1.6 × 0.8 mm) relative to adjacent wires in a butt joint configuration. Additionally, resistor-capacitor circuits were fabricated (i.e., embedded within printed polycarbonate material) in series and parallel. Both circuit variants were characterized via visual observations and impedance spectroscopy. The electrical test results demonstrated feasibility of the manufacturing approach, however, elevated failure rates of encapsulated circuitry warrant further investigation into process improvement.

Laser Metal Deposition (LMD) is an additive manufacturing process that reaches high deposition rates. Its applications are mainly found in repair, cladding and manufacturing. The two commonly used LMD processes are powder-based (LMDp) and wire-based (LMD-w). Despite the fact that wire-based LMD uses material more efficiently, its process stability is a major concern. One approach to increase the process stability is superposing a pulsed laser (pw) beam with the conventionally used continuous laser (cw). Previous studies have shown that the metal vapor caused by pulsed laserinduced evaporation in the process zone significantly improves energy absorption. Furthermore, a direct relation between vapor pressure and melt pool form has been demonstrated. In this contribution, we correlate the pw-controlled melt pool geometry to process stability. High-speed camera imaging is employed to evaluate the dynamic melt pool behavior as a function of pw frequency and power. It is shown that irregular melt pool oscillations impairing process stability in conventional LMD-w are reduced if the pulsed laser is added. The melt front is shaped depending on the acting pw-induced pressure. This leads to a more stable interaction between wire and melt pool. Furthermore, the pw pressure changes the welding bead height and width. This cross-sectional geometry has an impact on the resulting waviness in 3D build-up. We also investigate how the waviness influences process stability during multilayer LMD-w. The results demonstrate that the dual beam technology is a promising way to develop more reliable and resource-efficient AM processes.

Metal Additive Manufacturing has been recognized as a technology of the future providing numerous benefits such as the production of complex shape and lightweight parts, easy customization, design freedom, etc. However, there are many areas where metal additive manufacturing cannot be applied since the quality of produced parts still does not satisfy the requirements of high-demanding industries for the production of their critical parts. Recently, Laser Shock Peening (LSP) has been investigated as a post-processing technique in metal additive manufacturing, primarily for the improvement of fatigue behavior. Here we will present improvements in fatigue life, the analysis of microstructure, and all the benefits LSP can bring to Metal Additive Manufacturing, for two types of material; stainless steel AISI 304L and titanium alloy Ti6Al4V.

Current strategies for closed loop control of the temperature sensitive selective laser sintering (SLS) process are often based on slow thermal cameras. Another method is single scanner pyrometry. In that case the pyrometer uses the same scanner as the laser. The pyrometer measuring spot and the laser spot are always in the same position. It is not possible to measure temperature outside of the laser spot. In a novel approach, a highly dynamic double scanner system is used to position the measuring beam of a high speed pyrometer. With this approach it is possible to position the laser and measurement spot independently on the powder bed surface (e.g. leading or trailing measurement relative to the laser spot). A very fast pyrometer which outputs measurement data up to 50 kilohertz and FPGA (Field Programmable Gate Array) technology will be used for real time processing of the measured temperature. With this it is possible to process temperature fluctuations on the surface and respond to them very quickly. This technique should be applied to make the SLS process more stable and to get the best results out of the entire build volume. For this purpose, the measured temperature is used to dynamically control the power of the laser.