An Evaluation of Ultrasonic Shot Peening and Abrasive Flow Machining As Surface Finishing Processes for Selective Laser Melted 316L

Additive Manufacturing, and specifically powder bed fusion processes, have advanced rapidly in recent years. Selective Laser Melting in particular has been adopted in a variety of industries from biomedical to aerospace because of its capability to produce complex components with numerous alloys, including stainless steels, nickel superalloys, and titanium alloys. Post-processing is required to treat or solve metallurgical issues such as porosity, residual stresses, and surface roughness. Because of the geometric complexity of SLM produced parts, the reduction of surface roughness with conventional processing has proven especially challenging. In this Thesis, two processes, abrasive flow machining and ultrasonic shot peening, are evaluated as surface finishing processes for selective laser melted 316L. Results of these experiments indicate that AFM can reliably polish as-built internal passages to 1 µm Ra or better but is unsuitable for passages with rapidly expanding or contracting cross-sections. AFM can also polish relatively small passages, but lattice components may prove too complex for effective processing. USP cannot achieve such low surface roughness, but it is a versatile process with multiple advantages. Exterior surfaces were consistently processed to 1.7 to 2.5 µm Ra. Interior surfaces experienced only partial processing and demonstrated high geometric dependence. USP significantly hardened the surface, but steel media hardened the surface better than ceramic media did. Both AFM and USP are recommended processes for the surface finishing of SLM manufactured parts. Good engineering judgement is necessary to determine when to use these processes and how to design for post-processing

The effects of submerged laser peening, cavitation peening, and shot peening on the improvement of the torsional fatigue strength of powder bed fused Ti6Al4V produced through laser sintering

This study demonstrates the improvement in the fatigue strength of additive manufacturing (AM) metals such as laser-based powder bed fusion of metals by post-processing. Titanium alloy samples manufactured by powder bed fused (PBF) Ti6Al4V produced through laser sintering (LS), treated by submerged laser peening (SLP), cavitation peening (CP), and shot peening accelerated via a water jet (SPwj), were subjected to torsional fatigue testing and compared with the as-built specimen. At SLP, the samples were treated by laser ablation (LA) and laser cavitation (LC) which was developed following LA. A cavitating jet was used for CP. For comparison, conventional post-processing using SPwj was also performed. To characterize the microstructural modification caused by the three post-processing methods, the cross-section of the treated surface was observed by electron backscatter diffraction. The fatigue strengths at 107 cycles were found to be 217, 361, 313, and 285 MPa for the as-built, SLP, CP, and SPwj specimens, respectively. The primary factors contributing to fatigue strength improvement by post-processing were surface smoothing and the introduction of compressive residual stress. The experimental observations were used to derive correlation formulas to estimate the fatigue life improvement due to post-processing as the function of the surface roughness and surface residual stress

Simulation of shot peening: From process parameters to residual stress fields in a structure

Manufacturing industries perform mechanical surface treatments like shot peening at the end of the manufacturing chain to protect important working parts. This treatment modifies the near surface of the treated part with the introduction of compressive residual stresses due to the repeated impacts of the shot. Then, the treated part exhibits, not only a longer life, but also a better fretting behavior, an improved resistance to corrosion… The objective of the present paper is first to study the relation between the process parameters and the material state (residual stress and plastic variables…) for a complex geometry. Next, a numerical tool is proposed, able to predict this material state in a time frame that is consistent with industrial constraints. The originality of the proposed approach thus consists in the chaining of the different steps. The first step is to choose the process parameters for the shot peening process considering conventional or ultrasonic shot peening and model the shot dynamics for a complex geometry. Once the impact velocity field is known, the objective is to compute the local incompatible plastic deformation field due to the repeated impacts using analytical methods. Then, a finite element model is used to compute the residual and deformation fields in the considered mechanical part. The complete method has been performed on the model of a gear, a mechanical part that is most often shot peened and exhibits a complex geometry

Improvement to the surface finish of additive laser manufactured parts made by selective laser melting

The Selective Laser Melting (SLM) process has been used since the end of last decade for different applications in the industrial sector. The priority of the technique is to produce fully dense and functional metallic parts of very complex design, but it is limited by a few issues such as quality of surface finish and porosity. The current study focuses on improving the surface finish of parts built on an SLM machine through two different approaches of post processing technique, laser re-melting followed by electropolishing. In this investigation Renishaw’s SLM 125 was employed to produce 3Dimensional (3D) parts by using stainless steel 316L material with powder particle size ranges from 15 to 45 microns. Samples with different inclinations were constructed in order to generate samples with different surface roughness; the parts were measured and inspected for surface finish by measuring Ra. The initial surface roughness ranges from 10 to 20μm Ra. Due to the poor surface quality, laser re-melting was implemented as a first stage in order to eliminate the initial surface roughness. Laser re-melting as a post-processing technique was employed for re-melting procedure employing the RECLAIM machine at Manufacturing Technology Centre (MTC) Coventry. Different setups of process were analysed to optimize the parameters for re-melting. The results proved that the best results are conducted with laser energy density ranges between 2160 to 2700 J/cm2 to give exceptional results of surface roughness of about 1.4 μm±15% Ra. In such case it’s possible to say that laser re-melting has the capacity to improve surface finish by about 80% compared to the initial surface roughness created by SLM. In the second stage, improvement was carried out by implementing green process to reduce the waste, pollution and high toxicity using a suitable room temperature ionic liquid (RTLs) as a solution in order to eliminate the secondary surface roughness that comes after re-melting. Physical properties such as shininess and reflectivity were significantly improved, due to the capacity of the process to improve the surface roughness and remove the oxide film created during re-melting. The method proved that the best results were obtained when the specimens were anodically kept at current densities associated with potential ranges between (4 to 5.5 volt), maintained at (40 C°) to give roughness (Ra) less than 0, 5μm. These levels of voltage can be facilitated to operate and avoid any passivation of material dissolving, which can lead to pitting of the surface.Libyan Governmen

Powder-based laser hybrid additive manufacturing of metals:a review

Recent advances in additive manufacturing (AM) have attracted significant industrial interest. Initially, AM was mainly associated with the fabrication of prototypes, but the AM advances together with the broadening range of available materials, especially for producing metallic parts, have broaden the application areas and now the technology can be used for manufacturing functional parts, too. Especially, the AM technologies enable the creation of complex and topologically optimised geometries with internal cavities that were impossible to produce with traditional manufacturing processes. However, the tight geometrical tolerances along with the strict surface integrity requirements in aerospace, biomedical and automotive industries are not achievable in most cases with standalone AM technologies. Therefore, AM parts need extensive post-processing to ensure that their surface and dimensional requirements together with their respective mechanical properties are met. In this context, it is not surprising that the integration of AM with post-processing technologies into single and multi set-up processing solutions, commonly referred to as hybrid AM, has emerged as a very attractive proposition for industry while attracting a significant R&D interest. This paper reviews the current research and technology advances associated with the hybrid AM solutions. The special focus is on hybrid AM solutions that combine the capabilities of laser-based AM for processing powders with the necessary post-process technologies for producing metal parts with required accuracy, surface integrity and material properties. Commercially available hybrid AM systems that integrate laser-based AM with post-processing technologies are also reviewed together with their key application areas. Finally, the main challenges and open issues in broadening the industrial use of hybrid AM solutions are discussed. 2021, The Author(s).The authors would acknowledge the support received from the ESIF/ERDF Smart Factory Hub (SmartFub) programme in West Midlands. The authors also acknowledge the support received from Yamazaki Mazak, DMG MORI, LASEA and Systems 3R for establishing the hybrid AM facilities at the University of Birmingham.Scopu

Additive Manufacturing of Al Alloys and Aluminium Matrix Composites (AMCs)

In this chapter a large description of additive manufacturing techniques for obtaining Al alloys and Al matrix composites is given. Results on mechanical properties, roughness and microstructure achievable with such fabrication route on Al alloys are reported

Novel approaches for the chemical, mechanical, and thermal post-processing of polymer components obtained by fused filament fabrication

La creixent demanda de productes de baix cost i fets a mida impulsada per les necessitats del sector industrial contemporani ha promogut el desenvolupament i el perfeccionament de diverses tècniques de processat de materials. En aquest panorama de fabricació en constant canvi, la fabricació per filament fos (FFF), un dels mètodes de fabricació additiva (AM) més estesos per la seva simplicitat tecnològica, posseeix el potencial per a proporcionar respostes a moltes de les necessitats que revela el mercat actual. No obstant, la naturalesa de la construcció capa a capa dels objectes fabricats que permet una flexibilitat geomètrica tan elevada és, tanmateix, una barrera important per a l’ús dels components finals en certes àrees crítiques de la realitat industrial. Aquestes limitacions, com la necessitat d’eliminar les estructures que suporten en la seva construcció a voladissos i forats interns, l’anisotropia mecànica dels components i l’acabat superficial pobre en comparació amb les tècniques de fabricació convencionals, formen part dels grans reptes que ha d’abordar la comunitat AM. A més, la diversitat de materials i equips d’impressió desenvolupats en els últims anys per a ampliar les capacitats de la FFF exigeix l’adaptació dels mètodes de postprocessament existents i la creació d’altres de nous capaços d’aportar solucions efectives a aquestes necessitats. Per conseqüent, aquesta tesi doctoral considera el postprocessat químic, mecànic i tèrmic de components fabricats amb el termoplàstic de grau enginyeril Ultem™ 9085 per mitjà de FFF amb l’objectiu d’aconseguir millores en la seva usabilitat i rendiment mecànic. La investigació que sustenta aquest estudi està basada en un rigorós disseny d’experiments, que inclou una matriu ortogonal de Taguchi i una metodologia de superfície de resposta, acompanyats de les campanyes experimentals suficients per a validar les propostes abordades. De tots els anàlisis que conformen el conjunt d’aquesta tesi, de la que han derivat cinc publicacions científiques en revistes indexades, és possible extreure un bon nombre d’aportacions que s’estimen de gran importància per al progrés de la investigació en AM. D’entre ells, destaquen la validació d’un tractament químic capaç de dissoldre el material de suport de l’Ultem™ 9085 amb un impacte mínim en les prestacions mecàniques del material model, un postprocessat mecànic basat en el brunyit amb bola que ha demostrat produir una reducció significativa de la rugositat de la superfície i una duplicació de la vida a fatiga per flexió de les peces tractades, i una recuita tèrmica combinada amb pressió isostàtica capaç de densificar els components tractats al mateix temps que en millora el seu acabat superficial i redueix les diferències en les propietats mecàniques de peces fabricades utilitzant diferents orientacions d’impressió. Cadascun dels enfocs abordats, així com els procediments que s’han utilitzat per a la seva validació, apareixen meticulosament documentats en aquesta memòria, juntament amb totes les recomanacions pràctiques necessàries per a aplicar les metodologies proposades a altres materials.La creciente demanda de productos de bajo coste y hechos a medida impulsada por las necesidades del sector industrial contemporáneo ha promovido el desarrollo y el perfeccionamiento de múltiples técnicas de procesamiento de materiales. En este panorama de fabricación en constante cambio, la fabricación por filamento fundido (FFF), uno de los métodos de fabricación aditiva (AM) más extendidos por su simplicidad tecnológica, posee el potencial de proporcionar respuestas a muchas de las necesidades que revela el mercado actual. Sin embargo, la naturaleza de la construcción capa a capa de los objetos fabricados que permite una flexibilidad geométrica tan elevada es, al mismo tiempo, una barrera importante para el uso de los componentes finales en ciertas áreas críticas de la realidad industrial. Tales limitaciones, como la necesidad de eliminar las estructuras que soportan en su construcción a salientes y agujeros interiores, la anisotropía mecánica de los componentes y el acabado superficial pobre en comparación con las técnicas de fabricación convencionales, forman parte de los grandes desafíos que debe abordar la comunidad AM. Además, la diversidad de materiales y equipos de impresión desarrollados en los últimos años para ampliar las capacidades de la FFF exige la adaptación de los métodos de postprocesamiento existentes y la creación de otros novedosos, capaces todos de aportar soluciones efectivas a estas necesidades. En consecuencia, esta tesis doctoral aborda el postprocesado químico, mecánico y térmico de componentes fabricados con el termoplástico de grado de ingenieril Ultem™ 9085 mediante FFF con el propósito de conseguir mejoras en su usabilidad y rendimiento mecánico. La investigación que sustenta este estudio está basada en un riguroso diseño de experimentos, que incluye una matriz ortogonal de Taguchi y una metodología de superficie de respuesta, acompañados de las campañas experimentales suficientes para validar las propuestas abordadas. De todos los análisis que conforman el conjunto de esta tesis, de la que han derivado cinco publicaciones científicas en revistas indexadas, es posible extraer un buen número de aportaciones que se estiman de gran importancia para el progreso de la investigación en AM. Entre ellos, destacan la validación de un tratamiento químico capaz de disolver eficazmente el material de soporte del Ultem™ 9085 con un impacto mínimo en las prestaciones mecánicas del material modelo, un postprocesado mecánico basado en el bruñido con bola que ha demostrado producir una reducción significativa de la rugosidad de la superficie y una duplicación de la vida a fatiga por flexión de las piezas tratadas, y un recocido térmico combinado con presión isostática capaz de densificar los componentes tratados al tiempo que mejora su acabado superficial y reduce las diferencias en las propiedades mecánicas de piezas fabricadas utilizando diferentes orientaciones de impresión. Cada uno de los enfoques abordados, así como los procedimientos que se han utilizado para su validación, aparecen minuciosamente documentados en esta memoria, junto con todas las recomendaciones prácticas necesarias para aplicar las metodologías propuestas a otros materiales.The increasing demand for low-cost, custom-made products driven by the needs of the contemporary industrial sector has propelled the development and refinement of multiple material processing techniques. In this ever-changing manufacturing landscape, fused filament fabrication (FFF), one of the most popular additive manufacturing (AM) methods due to its technological simplicity, possesses the potential to provide the required answers to many of today’s marketplace requirements. However, the layered nature of the fabricated objects that enables such high shape flexibility is also a major barrier to implementation in critical application areas. This is attributed to the need to eliminate the supporting structures in overhanging parts and inner holes, the components’ mechanical anisotropy, and the inferior surface finish compared to conventional manufacturing techniques. In addition, the diversity of materials and printing equipment developed in recent years to expand FFF’s capabilities demands the adaptation of existing and novel post-processing methods to address the mentioned issues. Accordingly, this doctoral thesis addresses the chemical, mechanical, and thermal post-processing of components made of the engineering-grade thermoplastic Ultem™ 9085 by FFF to improve their usability and mechanical performance. The research is based on rigorous designs of experiments, which include a Taguchi orthogonal array and a response surface methodology, as well as additional tests to validate the proposed strategies. From the analyses that make the whole of this thesis, out of which five scientific articles published in peer-reviewed journals have been derived, it is possible to extract a substantial number of scientific contributions of great importance for the progress of research in the field of AM. Among them, a solvent-based chemical treatment that effectively dissolves Ultem™ 9085’s support material with minimal impact on the model material’s mechanical performance; the use of ball burnishing as a finishing technique that has proven to produce a significant reduction in surface roughness, and a minimum two-fold increase in the flexural fatigue life of the treated parts; and a thermal annealing treatment combined with isostatic pressing capable of inducing densification and reducing the surface roughness while homogenizing the mechanical properties of parts fabricated using different printing orientations. The considered approaches and the procedures used for their validation are thoroughly documented in this doctoral thesis, together with practical recommendations to apply the proposed methodologies in other materials

Effects of laser shock peening on the mechanisms of fatigue short crack initiation and propagation of AA7075-T651

A laser shock peening (LSP) treatment was performed on AA7075-T651 for maximum fatigue improvement. Surface and microstructural characterisation techniques (micro-hardness, SEM-EBSD, contact-profilometry) showed LSP surface modification was limited, and LSP generated deep compressive residual stresses above -300MPa. Fatigue testing showed a two-order magnitude increase in overall life, due to the mechanism of crack initiation changing from surface second-phase particles to subsurface crack initiation dependent on the local stress field. Modelling highlights the sensitive balance between surface roughness (including LSP-induced pits) and residual stress on the micro-mechanism of crack initiation, and how this can be used to maximise fatigue life extension