Manufacturing Of Metal Parts Research Articles

Review of quality issues and mitigation strategies for metal powder bed fusion

PurposeSelective laser melting and electron beam melting processes are well-known for the additive manufacturing of metal parts. Metal powder bed fusion (MPBF) is a common term for them. The MPBF process can empower the manufacturing of intricate shapes by reducing the use of special tools, shortening the supply chain and allowing small batches. However, the MPBF process suffers from many quality issues. In literature, several works are recorded for qualification of the MPBF part. The purpose of this study is to recollect those works done for quality control and report their helpful findings for further research and development.Design/methodology/approachA systematic literature review was conducted to highlight the major quality issues in the MPBF process and its root causes. Further, the works reported in the literature for mitigation of these issues are classified and discussed in five categories: experimental investigation, finite element method-based numerical models, physics-based analytical models, in-situ control using artificial intelligence (AI) and machine learning (ML) methods and statistical approaches. A comparison is also prepared among these strategies based on their suitability and limitations. Additionally, improvements in MPBF printers are pointed out to enhance the part quality.FindingsAnalytical models require less computational time to simulate the MPBF process and need a smaller number of experiments to confirm the results. They can be used as an efficient process parameter planning tool to print metal parts for noncritical applications. The AI-ML based quality control is also suitable for MPBF processes as it can control many processing parameters that may affect the quality of the MPBF part. Moreover, capabilities of MPBF printers like thinner layer thickness, smaller beam diameter, multiple lasers and high build temperature range can help in quality control.Research limitations/implicationsThis study converts the piecemeal data on MPBF part qualification methods into interesting information and presents it in tabular form under each strategy. This tabular information provides the basis for further quality improvement efforts in the MPBF process.Originality/valueThis study references researchers and practitioners on recent quality control efforts and their significant findings for a better quality of MPBF part.

Research progress on heteromorphic structure parts fabricated by additive manufacturing based on inside-laser coaxial powder feeding

Inside-laser material feeding laser cladding deposition (IMF-LCD) is a directed energy deposition technology featuring “hollow beam, annular spot, centered powder, and coaxial powder feeding.” IMF-LCD offers distinct advantages over traditional outside laser material feeding laser cladding deposition (OMF-LCD), such as a good laser-powder coupling effect, high powder utilization, high forming flexibility, uniform thermal field distribution in molten pools, and excellent forming surface quality. IMF-LCD would significantly improve forming efficiency and surface quality while it was applied to rapid direct manufacturing and repair of complex metallic parts compared to OMF-LCD. In this manuscript, the working principle of IMF-LCD technology is briefly introduced. Mostly, the research progress on heteromorphic structure parts fabricated by IMF-LCD was summarized, focusing on layered design, posture change, forming strategy optimization, and process parameter adjustment. The heteromorphic structure included a twisted thin-walled structure, variant height/width structure, overhanging structure, and closed structure. Based on the excellent characteristics of this technology, the exploration of high forming quality heteromorphic structural parts is carried out by changing the process parameters and forming processes such as the variable attitude stacking method, the conformal discrete layering method and the normal layering method, and the surface roughness is as low as 1.323 μm, the dimensional accuracy is as high as 1.6%. Simultaneously, the powder utilization rate of IMF-LCD reached 60%–80% on average, in accordance with the advantages of the laser-powder coupling effect. Finally, the remarkable research and application of IMF-LCD technology in high flexibility, high precision, high surface quality, and high material utilization would further promote the development of additive manufacturing with higher performance, higher quality, and lower cost in the future.

Development of Carbon Nanotube‐Reinforced Nickel‐Based Nanocomposites Using Laser Powder Bed Fusion

Modern aerospace applications demand the development of high‐performance components with advanced materials. The development of nanomaterial‐reinforced metal matrix composites is a practical approach to improve properties. Laser powder bed fusion (LPBF) is one of the popular additive manufacturing approaches to fabricating metal parts with complex geometric structures. This research investigates multiwalled carbon nanotube (CNT)‐reinforced nickel‐based alloy (Haynes 230) nanocomposite for property improvement. Three volumetric concentrations (0%, 2.5%, and 5%) of CNTs in the metal matrix are investigated with different printing parameters. Different characterizations are conducted on the test specimens. Results show that LPBF‐printed Haynes 230 with 2.5 vol% CNTs has higher relative density (99.36%) and less porosity compared to those printed with 5 vol% CNTs. Mechanical test results show that LPBF‐printed Haynes 230 with 2.5 vol% CNTs has the highest hardness, modulus of elasticity, yield strength, and ultimate strength than those printed with as‐received Haynes 230 powder (with 0 vol% CNTs), Haynes 230 with 5 vol% CNTs, and commercial Haynes 230 plates. The strengthening behavior of the CNTs in the metal matrix composites is discussed in this paper. The potential of CNT‐reinforced nickel‐based nanocomposites for applications requiring materials with outstanding mechanical properties, such as aerospace and defense, is demonstrated.

Laser melting modes in metal powder bed fusion additive manufacturing

Additive manufacturing, called 3D printing, has become ubiquitous in classrooms, laboratories, and research centers. While printing with plastics has revolutionized prototyping and modeling, it is now possible to fabricate metal parts and devices directly from computer models by fusing metal particles together with high-intensity lasers. This review focusses on the flow of heat and material in the high temperature environment, the instabilities that arise, and the tools to control them.

Smart System for Additive Manufacture of Metal Parts

Smart System for Additive Manufacture of Metal Parts

Investigation of the Mechanical Properties of Additively Manufactured Metal Parts with Different Relative Densities

Currently, metal additive manufacturing (MAM) has been receiving more attention in many sectors for its production of metal parts because MAM effortlessly enables the fabrication of complex metal parts and provides faster and more sustainable manufacturing than conventional processes. Recently, a MAM-using bound metal deposition (BMD) has been proposed as a user-friendly manufacturing method that can provide low-volume production, economical metal parts, and operation safety. Since the BMD technique is new, information on the mechanical properties of MAM parts using this technique has not been sufficiently provided. This paper aims to study the mechanical properties of MAM parts manufactured by the BMD technique, examining the elastic modulus, yield strength, ultimate strength, and fatigue behavior of the parts with different relative densities. The MAM parts made from 316L and 17-4PH stainless steel were investigated using tensile and fatigue tests. Some mechanical properties of the infill parts in this study were validated with formulas from the literature. The weight efficiency is used as an index to assess the efficiency of the infill parts with different densities by examining the relationship between the mechanical properties and the weight of the MAM parts. The experimental results and a discussion of the weight efficiency assessment are presented as a novel information report on MAM products fabricated by BMD technology.

Resonances and mode shape imaging for characterizing the microstructure of complex metals

Resonant Ultrasound Spectroscopy (RUS) is a mature and reliable technique for measuring the elastic stiffness constants of anisotropic materials. In highly processed materials such as additively manufactured metal parts, the anisotropic stiffnesses arrive from microstructures that contain grains with preferred orientations, which can result from directionally dependent thermal or mechanical processes. The connection between elastic stiffnesses and microstructure suggest the potential for RUS being used as a tool to characterize microstructure. This presentation will highlight modeling and experimental measurements in this direction. The RUS model is developed from a micromechanical foundation and includes structure-property linkages between the microstructure’s orientation distribution function and the macroscopic elastic constitutive behavior. The micromechanical basis allows efficient creation of a complete catalog containing all possible resonant behavior (resonant frequencies and mode shapes) of polycrystalline samples as a function of the possible textures. The second part of the presentation will focus on connecting experimentally measured resonances and mode shapes to a particular catalog entry. The inclusion of mode shape imaging in the analysis is expected to offer additional detail and potential for expanded characterization beyond texture and elastic stiffnesses.

Metallurgical Characteristics of Low Carbon Steel Cylindrical Components Made by Wire Arc Additive Manufacturing (WAAM) Technique

Fabrication of metal parts by wire and Arc Additive Manufacturing (WAAM) has received an increased interest in recent years, as it allows high design flexibility and reduction of material wastage compared to other traditional manufacturing routes. This article compares the effect of heat input on metallurgical characteristics of wire arc additive manufactured low carbon steel cylindrical components fabricated by Gas Metal Arc Welding (GMAW) and Cold Metal Transferred Arc Welding (CMTAW) processes. Firstly, the influence of heat input on the grain size was analyzed. Subsequently, the effect of heat input on the metallurgical characteristics of the cylindrical components was studied along the building direction. The microstructure of the built cylindrical-walled component varies from the top to the bottom regions and can be distinguished into two regions: lamellar structures (widmanstatten ferrite and grain boundary ferrite) in the top regions; and equated grains of fully ferrite in the bottom region in GMAW. In the CMT-WAAM cylindrical component samples have been noted two different regions: the bottom region characterized by a ferritic structure with thin strips of pearlite and the top region characterized by a lamellar structure typically bainite with acicular ferrite.

Symmetry and Its Application in Metal Additive Manufacturing (MAM)

Additive manufacturing (AM) is proving to be a promising new and economical technique for the manufacture of metal parts. This technique basically consists of depositing material in a more or less precise way until a solid is built. This stage of material deposition allows the acquisition of a part with a quasi-final geometry (considered a Near Net Shape process) with a very high raw material utilization rate. There is a wide variety of different manufacturing techniques for the production of components in metallic materials. Although significant research work has been carried out in recent years, resulting in the wide dissemination of results and presentation of reviews on the subject, this paper seeks to cover the applications of symmetry, and its techniques and principles, to the additive manufacturing of metals.

A Feasibility Study on Directed Energy Deposition of SS 316L with Coaxial Wire-powder Feeding

Compared to single wire/powder feeding, the directed energy deposition (DED) technique with coincident wire-powder feeding enables the fabrication of metallic parts with high deposition efficiency and performance. The existing investigations on DED process with wire-powder feeding utilized the combination of lateral wire feeding and coaxial/lateral powder feeding. In addition, they found that the deposition efficiency and final performance can be improved by increasing the wire injection angle in a vertical plane. However, the DED of metallic parts with coaxial wire-powder feeding remains unexplored due to the machine limitation. In this paper, we studied the effects of powder feed rates on the surface quality, defects, and microstructure of as-built SS 316L parts with coaxial wire-powder feeding. The results found that the surface finish of wire-deposited samples is much better than as-built samples fabricated with high powder feeding rates. In addition, the dual feedstock DED process has a higher susceptibility to porosity than pure wire deposition due to the entrapped gas in powder particles, and the porosity increases with the powder feed rate. Moreover, the wire-deposited samples present more distinct melt pool boundaries than those fabricated with wire-powder feeding. With an increase in powder feed rate, the grain size and grain boundary thickness in the fusion areas experience a decrease first and subsequent increase. This paper will provide guidelines for the efficient production of high-performance metallic alloy/composites with coaxial wire-powder feeding.

Influence of laser polishing on fatigue life of conventionally machined and laser powder bed fusion 316L stainless steel

One of the main factors keeping additive manufactured metal parts from being used in industry is the relatively low fatigue life of the as-printed parts when compared to their conventionally manufactured counterparts. In addition, certain areas on additively manufactured parts need finishing operations in order to make them functional. While laser polishing has demonstrated the ability to reduce the roughness of various metal surfaces, including additive manufactured ones, it is necessary to study the influence of this process to ensure the surface roughness improvements are not gained at the detriment of fatigue life. The objective of this work is to determine the influence of laser polishing on the fatigue life of both conventionally and additively manufactured metal parts. Fatigue samples were generated from 316L stainless steel using conventional machining and additive manufacturing through laser powder bed fusion. A single set of laser polishing parameters was used to determine the influence of laser polishing on samples manufactured from both methods. This work has shown that surface roughness of both machined and additive manufactured parts can be reduced without sacrificing fatigue life under certain polishing conditions. This demonstrates that laser polishing is a practical method for addressing additively manufactured surface roughness challenges while not negatively impacting fatigue performance.

Benchmark Test Artifacts for Selective Laser Melting - A Critical Review

Background: Selective laser melting is a best-established additive manufacturing technology for high-quality metal part manufacturing. However, the technology is yet to be accepted widely, especially in critical applications, due to the absence of a thorough understanding of the technology although several benchmark test artifacts have been developed to characterize the performance of selective laser melting machines. Objective: The objective of this paper is to inspire new designs of benchmark test artifacts to better understand the selective laser melting process, and to promote the acceptance of the selective laser melting technology. Method: The existing benchmark test artifacts for selective laser melting are analyzed comparatively, and the design guidelines are discussed. Results: The modular approach should still be adopted in designing new benchmark test artifacts in the future, and task-specific test artifacts may also need to be considered furtherly to validate machine performance for critical applications. The inclusion of the design model in the manufactured artifact, instead of the conformance to the design specifications, should be evaluated after the artifact is measured for the applications requiring high-dimensional accuracy and high surface quality. Conclusion: The benchmark test artifact for selective laser melting is still under development, and a breakthrough of the measuring technology for internal and/or inaccessible features will be beneficial for understanding the technology.

Development of the design and technology of extrusion of metal-polymer mixtures for the production of feedstocks

The paper is devoted to the development of new equipment for the production of metal-polymer thread. 3D printing with metal-polymer thread is one of the advanced directions in the technology of manufacturing metal parts of complex shape. The proposed technology is an alternative to the currently existing metal injection molding (MIM) technology and selective laser melting printing technology. An important step in this work was to conduct computational experiments to determine the effect of screw rotation on the process pressure parameter and the design of the main assembly of the screw extruder. As a result of the research, the pressures on the metal-polymer composition were determined depending on the rotation speed of the screw. With a rotation of 30 rpm, the pressure reached 0.05 Pa and the maximum pressure was 0.18 MPa. The experiments were carried out in the CradelSFlow program. The computer calculation showed a margin of the screw strength coefficient k=1.8, and a maximum deflection of 2.8∙10–4 m, which meets the condition of static rigidity. To determine the correct value of the gap δ between the screw ridge and the extruder walls, an analysis of the rotor dynamics was carried out. The result of this study is the critical extruder rotation speed of 60 rpm at which the phenomenon of precession may occur. Amplitude-frequency characteristics ydin=7∙10–4 m. According to the results of the dynamic calculation, the screw dimensions were adjusted, the geometry was reduced by ∆=0.5 mm. The experiments made it possible to verify the optimal parameters of the technological process of metal-polymer mixture extrusion. The data obtained are important for the improvement and development of 3D printing technology for metal parts of complex geometric shape.

Metal FFF sintering shrinkage rate measurements by X-ray computed tomography

ABSTRACT Fused filament fabrication (FFF), also known under the brand name fused deposition modelling, has recently emerged as a more straightforward and economic alternative to established 3D printing or additive manufacturing technologies such as powder bed fusion for metal part manufacturing. In this work, we report on possible approaches to the measurements of FFF sintering shrinkage rates from X-ray computed tomography (XCT) data, with particular focus on those that use greyscale data, and are thus independent of any errors introduced by segmentation. Metallic parts were produced using FFF technology, which relies on an isotropic scaling factor applied to the STL model of the part to be produced to compensate for the shrinkage happening during the sintering of the printed (green) part. We report that for the stainless-steel parts produced, the shrinkage rates were not isotropic and the one along the build direction was the largest, the other two being similar to one another. Overall, the shrinkage rate measured by the different methodologies all fell between 15 % and 16 %. XCT data also clearly showed the typical defects encountered with this technology, such as voids resulting from insufficient overlap or caused by print head blockages, are not mitigated by the sintering process. Autocorrelation was introduced as a way of characterising the 3D structure of the sample before and after sintering, and thus the sintering shrinkage rates.

Saturation pressure of nonequilibrium titanium evaporation during additive manufacturing by electron powder bed fusion

Electron beam powder bed fusion (E-PBF) is an attractive technology for the additive manufacturing of metal parts. However, process improvements require precise control of the energy transferred to the powder by the electron beam. Here, we used tunable diode laser absorption spectroscopy (TD-LAS) to measure the velocity distribution functions of titanium atoms evaporated during E-PBF. The narrow spectral ranges emitted by laser diodes allow for high-resolution absorption profiles of the evaporated atoms and thus accurate determinations of their Doppler broadening, density, and temperature during melting. The obtained vapor temperature reveals overheating at the surface of the melt pool relative to the low-pressure (0.1 Pa) boiling point of titanium, indicating that evaporation occurs under nonequilibrium conditions. We characterized the influence of the linear energy density on titanium evaporation and found it to be consistent with the saturation vapor pressure. Our characterization of the vapor properties provides reliable inputs for melt pool simulations. Furthermore, TD-LAS may be further exploited to prevent the evaporation of low-concentration alloy elements, which can induce defects in the printed part.

Areal Analysis Investigation of Selective Laser Melting Parts

Selective laser melting is an additive manufacturing technology used to fabricate metal parts characterized by complex geometries that are difficult or impossible to produce with conventional production methods. One of the major drawbacks of laser melting is the poor surface quality that typically is not satisfactory for functional applications. The aim of this work is to use areal analysis to characterize selective laser melting surfaces. The results highlight a marked variability and anisotropy that cannot be evaluated through traditional measurement. The building orientation and secondary finishing operations are analyzed and discussed. Findings demonstrate how areal analysis can be used to determine how to implement barrel finishing with the aim of reducing anisotropy and increasing surface quality.

Investigation of the influence of process interruption on mechanical properties of metal additive manufacturing parts

Fabrication methods of metals range from traditional subtractive methods to the new and emerging additive manufacturing technologies. As expected, these different metal fabrication and processing methods have a significant impact on the material structure and mechanical properties of final products. While the impact of the manufacturing process on the mechanical properties of metals is well understood for traditional manufacturing methods, the relationship between the additive manufacturing process and product characteristics is quite complex and still an ongoing research topic. Accordingly, many research studies on the material structure and mechanical properties of parts produced using additive manufacturing have been conducted in recent years. However, current literature considers ideal operating conditions while neglecting to consider the impact of printing process interruption on metal additive manufacturing parts. Additive manufacturing processes rely on continuous layer by layer printing of material, with strict melting and solidification requirements. When the printing process is interrupted, thermal dynamics governing binding strength and defect generation within layers are disturbed. It is expected that additive manufacturing process interruptions impact layer binding, which in turn jeopardizes the development of uniform microstructures and mechanical properties of metal parts. Accordingly, in this paper the impact of process interruption on the microstructure and mechanical properties of titanium samples printed using Wire Arc Additive Manufacturing (WAAM) is investigated. Various tests on the sample specimens are conducted including: Acoustic Resonance testing, Nanomechanical testing, X-ray Computed Tomography, and Ultrasonic nondestructive testing (NDT). The results indicate that additive manufacturing process interruption results in serious defects such as porosities and cracking that impact the mechanical properties of additive manufacturing metal parts.

Investigating the Melt-Pool Temperature Evolution in Laser-Powder Bed Fusion by Means of Infra-Red Light: A Review

Recent decades seen the success of Additive Manufacturing (AM) in many industrial applications including aerospace, biomedical, automotive, and tooling. In the manufacturing of metallic parts, AM technology has the ability to produce parts with complex geometries which are difficult or impossible to produce using the conventional fabrication methods, such as machining and casting. Another benefit of AM is the employment of metal and metal alloys which are difficult to machine. Alloys such as titanium, nickel-titanium, and stainless steel have a wide range of applications particularly in the aerospace and biomedical industry. Selective Laser Melting (SLM), also known as Laser Powder Bed Fusion (L-PBF) is a type of AM technology used for the 3D printing of metal and alloy parts. The major drawback in L-PBF technology is the anisotropic properties of the produced parts. From L-PBF, these anisotropies exist due to instant melting and re-solidification of the metal powder, the ultra-high cooling rates and the variant temperature levels across the build layers and within the single layer itself. This article explores the essential role of the melt-pool temperature and temperature gradients that occur during the L-PBF process and their effects on the additively manufactured part’s properties.

A Comprehensive Analysis of AISI 316L Samples Printed via FDM: Structural and Mechanical Characterization

Metal Fused Deposition Modelling is a promising multi-step process able to manufacture metal parts by means of a low-cost additive technique. In this study, a metal-polymer composite filament characterized by homogenous mixture of AISI 316L sinterable metal powders and a multi-component polymeric matrix was used to fabricate samples by means of a FDM printer. A 24 full factorial design of experiments was elaborated to define the possible influence of the relevant printing parameters on dimensional shrinkage, bulk density and overall porosity of printed samples. In addition, the mechanical properties of printed AISI 316L samples were investigated by performing tensile tests, compression tests, Charpy impact tests, Rockwell B and Vickers hardness tests. An X-ray diffraction analysis was conducted to assess the crystallographic structure of the FDM AISI 316L samples.

A new approach for calculating inherent strain and distortion in additive manufacturing of metal parts

Additive manufacturing (AM) of metallic parts is widely utilized for industrial applications. However, quality issues of the printed parts, including part distortion and cracks caused by high temperature and fast cooling, result in high residual stress. This is a challenge that limits the industry acceptance of AM. To overcome this challenge, a numerical modeling method for predicting part distortion at the design stage plays an important role and enables design engineers to remove failures before printing as well as determine the optimal printing process parameters to minimize part deformation. This research proposes an inherent strain-based part deformation prediction method. To determine the inherent strain (IS) value, a micro-scale model for analyzing the temperature distribution is constructed. The IS value is calculated from the temperature gradient. Then, the IS value is used for determining the part deformation. The proposed methodology has been developed and evaluated using a 316L stainless steel cantilever beam in both simulations and experimental results.