Laser Shock Peening Pressure Impulse Determination via Empirical Data-Matching with Optimization Software

Laser shock peening (LSP) is a form of work hardening by means of laser induced pressure impulse. LSP imparts compressive residual stresses which can improve fatigue life of metallic alloys for structural use. The finite element modeling (FEM) of LSP is typically done by applying an assumed pressure impulse, as useful experimental measurement of this pressure impulse has not been adequately accomplished. This shortfall in the field is a current limitation to the accuracy of FE modeling, and was addressed in the current work. A novel method was tested to determine the pressure impulse shape in time and space by optimization driven data-matching. FE model development and material model verification was completed in Abaqus. A 2D and 3D model type study was conducted. A proof of concept data-matching optimization tool was developed and verified. This data-matching optimization tool, using the Hooke-Jeeves optimization algorithm, was then applied to match experimentally collected residual stress measurements from single LSP treated spots in 2024-T351 aluminum specimens. Validation of this “best-fit” pressure impulse was attempted in a 6Al-4V titanium material model for the same LSP treatment process. A combination Johnson-Cook viscoplasticity and Mie-Grüneisen equation of state (EOS) material model was shown to be amply sufficient for modeling the highly dynamic LSP event. A 2D axisymmetric FE model was shown to adequately represent a square LSP treatment process, in terms of residual stress field results with the use of a linear adjustment factor. The Hooke-Jeeves optimization algorithm proved highly successful at working through a FE model “black box” to match a target residual stress outcome. Further, this method was successful in matching the residual stress field of experimentally collected data. The validation of the best-fit pressure impulse in titanium was not a perfect match, but exhibited enough accuracy to be useful to design engineers in certain cases, and further shows potential for improvement and implementation toward this impulse matching goal

Micromachining

To present their work in the field of micromachining, researchers from distant parts of the world have joined their efforts and contributed their ideas according to their interest and engagement. Their articles will give you the opportunity to understand the concepts of micromachining of advanced materials. Surface texturing using pico- and femto-second laser micromachining is presented, as well as the silicon-based micromachining process for flexible electronics. You can learn about the CMOS compatible wet bulk micromachining process for MEMS applications and the physical process and plasma parameters in a radio frequency hybrid plasma system for thin-film production with ion assistance. Last but not least, study on the specific coefficient in the micromachining process and multiscale simulation of influence of surface defects on nanoindentation using quasi-continuum method provides us with an insight in modelling and the simulation of micromachining processes. The editors hope that this book will allow both professionals and readers not involved in the immediate field to understand and enjoy the topic

Elucidation of dross formation in laser powder bed fusion at down-facing surfaces : Phenomenon-oriented multiphysics simulation and experimental validation

Dross formation is a phenomenon that is observed while printing metallic components using Laser Powder Bed Fusion (L-PBF) and occurring primarily at down-facing surfaces that are unsupported and suffer inadequate heat removal. Naturally, dross formation causes dimensional inaccuracy, high surface roughness and also adversely affects the mechanical properties of printed components. Through simulation and experimentation, this study fundamentally elucidates the driving phenomenon behind dross formation. The simulation results, in terms of the degree of generated dross domain, well agree with the ones observed in the printed samples and the behaviour of the melt pool while moving from bulk material to the powder domain is clearly depicted in this study. The simulations show that due to the low thermal conductivity of loose powder and the inability to conduct heat away, the quasi steady state melt pool collapses while entering the powder domain and transitions to a keyhole-like melt mode which causes a pronounced drilling effect. This causes excessive melting known as dross that is seen both in the simulation and the experimental parts. This work also shows through simulation and experimentation the reasoning behind the production of larger and smaller dross domains while printing with high and low laser energy densities respectively. Additionally, through SEM imagery this study also explains the observed deep internal grooves and near-surface porosity that are present within this dross domain which can further affect mechanical properties such as density, fatigue strength etc

Laser processing of materials

Light amplification by stimulated emission of radiation (laser) is a coherent and monochromatic beam of electromagnetic radiation that can propagate in a straight line with negligible divergence and occur in a wide range of wave-length, energy/power and beam-modes/configurations. As a result, lasers find wide applications in the mundane to the most sophisticated devices, in commercial to purely scientific purposes, and in life-saving as well as life-threatening causes. In the present contribution, we provide an overview of the application of lasers for material processing. The processes covered are broadly divided into four major categories; namely, laser-assisted forming, joining, machining and surface engineering. Apart from briefly introducing the fundamentals of these operations, we present an updated review of the relevant literature to highlight the recent advances and open questions. We begin our discussion with the general applications of lasers, fundamentals of laser-matter interaction and classification of laser material processing. A major part of the discussion focuses on laser surface engineering that has attracted a good deal of attention from the scientific community for its technological significance and scientific challenges. In this regard, a special mention is made about laser surface vitrification or amorphization that remains a very attractive but unaccomplished proposition

Special Issue of the Manufacturing Engineering Society (MES)

This book derives from the Special Issue of the Manufacturing Engineering Society (MES) that was launched as a Special Issue of the journal Materials. The 48 contributions, published in this book, explore the evolution of traditional manufacturing models toward the new requirements of the Manufacturing Industry 4.0 and present cutting-edge advances in the field of Manufacturing Engineering focusing on additive manufacturing and 3D printing, advances and innovations in manufacturing processes, sustainable and green manufacturing, manufacturing systems (machines, equipment and tooling), metrology and quality in manufacturing, Industry 4.0, product lifecycle management (PLM) technologies, and production planning and risks

Selective laser melting of Inconel 601 alloy using nanosecond fibre laser

The paper describes the impact of selective laser melting factors including using a nanosecond fibre laser, including laser powers, scanning speed, and thickness of layer, on the relative density and micro hardness Vickers of IN 601 samples was studied. Selective laser melting (SLM) is a commonly used powder bed fusion metal additive manufacturing (AM). Recent advances in additive manufacturing have attracted significant industrial interest, especially for producing metallic parts. Scanning electron microscopy (SEM), EDX and other techniques were utilized for studying the effect of speed of scanning and power of laser on densification behaviour, microstructural evolution and micro hardness of Inconel v alloy that was processed by SLM. With a VED of 3200 J/mm3, a scan speed of 250 mm/s with a 80 W, micro cracks of about 79-93 µm and voids of about (4.5 µm – 5.7) µm in diameter were realised. Moreover, the best hardness of 394 HV was attained with 80 W laser power. However, increasing the energy to more than the required values increased the porosity and decreased hardness. Using microsecond laser in SLM leads to the achievement of full density (almost 99.5%), whereas using nanosecond laser allows the achievement of less density (75-95%), which will be very useful for functions that require a porous structure and less weight, such as those in the aerospace applications, automotive industry and so on

Finite-element simulation of residual stresses induced by laser shock peening in TC4 samples structurally similar to a turbine blade

This study is devoted to the investigation of residual stresses distribution (RSD) in a TC4 sample treated with laser shock peening. The study placed special emphasis on analyzing the RSD at the part of the samples structurally similar to a turbine blade, which is more frequently subjected to damage during service according to the aircraft statistics. Results of simulation showed that low power density of 1.11 GWt/cm2 could not induce compressive residual stress on the surface of a treated object. Furthermore, increasing the overlapping of laser spots does not improve the situation and still fail to induce surface compressive residual stress at a laser intensity of 1.11 GWt/cm2. The compressive stresses occur only with the rise in power density. Reducing the spot size from 3 mm to 1 mm for the power density of 10 GWt/cm2 results in a 20% increase in the magnitude of compressive residual stress in the area of interest. Moreover, applying 35% overlapping further enhances this value. In addition to increasing the magnitude of residual stress, this approach also leads to a more homogeneous RSD of the treated material

Evaluation of Thermal Mechanisms to Predict the Transient Electroplastic Effect in Aluminum and an Investigation of Electrically Assisted Drilling

The objective of this research is twofold: first, to evaluate if the microscale Joule heating theory can predict the transient electroplastic effect in 7075-T6 aluminum. Second, to determine if electrical application can have a significant impact on drilling of 1500MPa steel, and if the operation is predictable using a modified Merchant’s machining model. Both 7075-T6 and 1500 MPa steel are of interest to the automotive industry due to their high strength-to-weight ratios. These metals are important to aid in lightweighting to meet increasingly strict governmental fuel economy standards. However, the strength of the steel makes it difficult to machine in post-forming operations. The ductility of the aluminum makes it impossible to form using conventional methods, especially for deep parts such as a body side outer. A potential fix to these problems is electrical augmentation to locally or globally soften the metal. It has been shown that electricity can increase ductility/formability in metals while also decreasing the forming loads and stresses required (this group of phenomena is termed the electroplastic effect). While the effects of electricity are well known, the underlying mechanisms are not, resulting in four key theories, two of which have already been disproven. This research examines one of the remaining two theories to predict the transient electroplastic effect. The microscale Joule heating theory suggests that microscale hot spots develop inside of the metal in areas of high electrical resistivity, such as grain boundaries where dislocations pile up during deformation. A coupled mechanical-thermal-electrical model was partitioned with grains, grain boundaries, and precipitates. Temperature and dislocation density-dependent electrical resistivity was used in order to evaluate the microscale Joule heating theory. It was found that this theory cannot fully explain the resultant stress drop caused during the transient phase of electrically-assisted pulsed tension. During model testing it was discovered that electricity changes the strain hardening behavior of aluminum. To further investigate, the effect of electricity on precipitates was explored through measurement of precipitate size and distribution in specimens treated with different electrical treatments. An electrically-assisted drilling experiment was designed, fabricated, and tested to determine the effect of electricity on a drilling process. A design of experiments study was conducted on 1008 steel to determine if electric current had a significant effect on process temperature, axial force, and tool wear compared to inputs of feedrate and spindle RPM. It was found that current was dominant and that tool wear and cutting forces could be decreased with electric current. The first electrically-assisted drilling model was created by modifying Merchant’s machining model. This model was found to have shortcomings due to knowledge limitations on friction and equipment limitations on temperature measurement. The knowledge generated from the 1008 experiments was used to further the constraining limits of the drilling process, leading to 1000% tool life improvement on drilling of 1500 MPa steel while increasing the achievable feedrate for cutting by 200%

Laser Shock Processing and Related Phenomena

Laser shock processing (LSP) is a continuously developing effective technology used to improve surface and mechanical properties for metallic alloys. LSP is in direct competition with other established technologies, such as shot peening, both in preventive manufacturing treatments and maintenance/repair operations. The level of LSP maturity has increased in recent years and several thematic international conferences have been organized (i.e., the 7th ICLPRP held in Singapore, June 17–22, 2018) to discuss different developments of a number of key aspects. These aspects include: fundamental laser interaction phenomena; material behavior at high deformation rates/under intense shock waves; laser sources and experimental process implementation; induced microstructural/surface/stress effects; mechanical and surface properties with experimental characterization and testing; numerical process simulation; development and validation of applications; comparison of LSP to competing technologies; and novel related processes. All of these aspects have been recursively treated by well-renowned specialists, providing a firm basis for the further development of the technology in its path to industrial penetration. However, the application of LSP (and related technologies) on different types of materials with different applications (such as the always demanding aeronautical/aerospatial field or the energy generation, automotive, and biomedical fields) still requires extensive effort to elucidate and master different critical aspects. Thus, LSP deserves a great research effort as a necessary step prior to its industrial readiness level. The present Special Issue of Metals in the field of “Laser Shock Processing and Related Phenomena” aims, from its initial launching date, to collect (especially for the use of LSP application developers in different target sectors) a number of high-quality and relevant papers representing state-of-the-art technology that is useful to newcomers in realizing its wide and relevant prospects as a key manufacturing technology. Consequently, in an additional and complementary way, papers were presented at the thematic ICLPRP conferences, and a call was made to authors willing to prepare high-quality and relevant papers to the journal, with the confidence that their work would become part of a fundamental reference collection regarding the present state-of-the-art LSP technology. The Special Issue includes two reviews and nine research papers. Each contribution adds to the reference knowledge of LSP technology and covers the practical totality of open issues, which will lead to present-day research at worldwide universities, research centers, and industrial companies

Laser welding of titanium and tin plate

Imperial Users onl