Identification of a Spatio-Temporal Temperature Model for Laser Metal Deposition

Laser-based additive manufacturing enables the production of complex geometries viaayer-wise cladding. Laser metal deposition (LMD) uses a scanningaser source to fuse in situ deposited metal powderayer byayer. However, due to the excessive number of influential factors in the physical transformation of the metal powder and the highly dynamic temperature fields caused by the melt pool dynamics and phase transitions, the quality and repeatability of parts built by this process is still challenging. In order to analyze and/or predict the spatially varying and time dependent thermal behavior in LMD, extensive work has been done to develop predictive models usually by using finite element method (FEM). From a control-oriented perspective, simulations based on these models are computationally too expensive and are thus not suitable for real-time control applications. In this contribution, a spatio-temporal input–output model based on the heat equation is proposed. In contrast to other works, the parameters of the model are directly estimated from measurements of the LMD process acquired with an infrared (IR) camera during processing specimens using AISI 316 L stainless steel. In order to deal with noisy data, system identification techniques are used taking different disturbing noise into account. By doing so, spatio-temporal models are developed, enabling the prediction of the thermal behavior by means of the radiance measured by the IR camera in the range of the considered processing parameters. Furthermore, in the considered modeling framework, the computational effort for thermal prediction is reduced compared to FEM, thus enabling the use in real-time control applications.

Optimization of the Cutting Regime in the Turning of the AISI 316L Steel for Biomedical Purposes Based on the Initial Progression of Tool Wear

The development of biomedical devices has improved the quality of life for millions of people. The increase in life expectancy generates an increase in the demand for these devices. One of the most used materials for these purposes is 316 L austenitic stainless steel due to its mechanical properties and good biocompatibility. The objective of the present investigation was to identify the dependence between the main cutting force, the initial speed of the tool wear, the surface roughness, and the parameters of the cutting regime. Based on these dependencies, a multi-objective optimization model is proposed to minimize the energy consumed and initial wear rate, as well as to maximize productivity, maintaining the surface roughness values below those established by the ISO 5832-1 standard. The wear of the cutting tool was measured on a scanning electron microscope. For the optimization process, a genetic algorithm based on NSGA-II (Non-nominated Sorting Genetic Algorithm) was implemented. The input variables were the cutting speed and the feed in three levels. The cutting force and surface roughness were set as restrictions. It is concluded that the mathematical model allows for the optimization of the cutting regime during dry turning and with the use of MQL (Minimum Quantity Lubrication) with BIDEMICS JX1 ceramic tools (NTK Cutting Tools, Wixom, MI, USA), of AISI 316 L steel for biomedical purposes. Pareto sets and boundaries allow for choosing the most appropriate solution according to the specific conditions of the workshop where it is applied, minimizing the initial progression of tool wear and energy consumed, and maximizing productivity by guaranteeing the surface roughness values established for these types of parts according to the standard.

Formation and Properties of Nitrocarburizing S-Phase on AISI 316L Stainless Steel-Based WC Composite Layers by Low-Temperature Plasma Nitriding

Stainless steel-based WC composite layers fabricated by a laser cladding technique, have strong mechanical strength. However, the wear resistance of WC composite layers is not sufficient for use in severe friction and wear environments, and the corrosion resistance is significantly reduced by the formation of secondary carbides. Low-temperature plasma nitriding and carburizing of austenitic stainless steels, treated at temperatures of less than 450 °C, can produce a supersaturated solid solution of nitrogen or carbon, known as the S-phase. The combined treatment of nitriding and carburizing can form a nitrocarburizing S-phase, which is characterized by a thick layer and superior cross-sectional hardness distribution. During the laser cladding process, free carbon was produced by the decomposition of WC particles. To achieve excellent wear and corrosion resistance, we attempted to use this free carbon to form a nitrocarburizing S-phase on AISI 316 L stainless steel-based WC composite layers by plasma nitriding alone. As a result, the thick nitrocarburizing S-phase was formed. The Vickers hardness of the S-phase ranged from 1200 to 1400 HV, and the hardness depth distribution became smoother. The corrosion resistance was also improved through increasing the pitting resistance equivalent numbers due to the nitrogen that dissolved in the AISI 316 L steel matrix.

Revisiting the ring hoop test in additively manufactured metal tubes

This paper is focussed on the mechanical and formability characterisation of wire-arc additive manufactured (WAAM) AISI 316-L stainless-steel tubes. The methodology to be presented involved carrying out tension and ring hoop tension tests on specimens extracted from the tube longitudinal, transverse and inclined directions. The force evolutions, acquired from the load cells, and the strain measurements, retrieved from digital image correlation and from thickness measurements along the cracks, allowed obtaining the stress-strain curves, the strain paths and the onset of failure by fracture for the three different tube directions. Special attention was paid to the ring hoop test, which was revisited to determine the appropriateness of using ring specimens with one or two dumbbell geometries. The originality of using the ring hoop tension test in WAAM tubes with strong anisotropic behaviour allowed obtaining strain loading paths that range from plane strain to pure shear deformation conditions. Resort to commercial AISI 316-L stainless-steel tubes during the presentation is included for reference purposes.

Process Variable Optimization of Cold Metal Transfer Technique in Cladding of Stellite-6 on AISI 316 L Alloy Using Grey Relational Analysis (GRA)

In this work, an attempt was made to identify the optimised parameter combination in cold metal transfer (CMT) cladding process of AISI 316 L austenitic stainless steel. cladding process was carried out using stellite 6 filler wire. Experiments were carried out based on L31 central composite design (CCD). Cladding was done with current, Voltage, torch angle and travel speed as input parameters. Quality of the clad was analysed by measuring depth of penetration, weld area, hardness of the clad surface, corrosion rate and clad interface thickness. Grey relation analysis was used to identify the optimised parameter combination. Trial number 18 was identified as the optimised parameter combination. The optimised input parameters are Welding Current 200 Amps, Voltage 19 V, Torch Angle 70⁰ and Welding Speed 150 m/min. ANOVA was used to identify the most influencing parameters on the overall multi-objective function and it was understood that the combined effect of torch angle, travel speed had a significant influence on the clad quality. Further investigation was carried out through an optimised set of parameters. The cladding experiment was conducted and their surface was investigated through clad profile, hardness of the cladded area, interface thickness of cladding region and corrosion rate.

Influences of Shot Peening Parameters on Mechanical Properties and Fatigue Behavior of 316 L Steel: Experimental, Taguchi Method and Response Surface Methodology

Severe plastic deformation methods like shot peening (SP) are known as efficient surface treatments and grain refining processes which afford more effective properties in metallic materials. In the current research, a comprehensive study was carried out on SP of AISI 316 L steel. It included 42 different SP treatments with a wide range of Almen intensities of 12–27 A and various coverage degrees (100%–1500%). Several experimental tests were conducted in order to explore the microstructure, grain size, surface topography, hardness, wettability, and residual stresses of the specimens. Next, two different approaches including Taguchi method (TM), and response surface methodology (RSM) were deployed for modeling, analysis, and optimization. RSM and TM were used to examine the influence of the effective parameters. Based on the optimized results, the fatigue behavior of the selected treatments was investigated experimentally in both smooth and notched specimens. Graphical abstract

Effect of the variation of the electrodeposition time of hydroxyapatite/chitosan coatings on AISI 316L SS

Type AISI 316 L Stainless Steel (316 L SS) plays a crucial role in bone replacement surgery due to its excellent mechanical features, availability at low cost, and ease of fabrication, but its performance is low when in contact with the aggressive conditions of the human body fluids. Chitosan (CTS) is a biopolymer that blended with hydroxyapatite (HAp) could form coatings to improve surface properties of a metallic orthopedic prosthesis, i.e., corrosion-resistance to the base metal and biocompatibility of the ceramic on the metal surface. This work aims to obtain and evaluate HAp/CTS composite coatings deposited on the surface of AISI 316 L SS substrate by electrophoretic deposition (EDP) technique. The influence of the time of deposition on the coating’s characteristics and properties was characterized and discussed. The coatings were structural, elemental, and chemically characterized using X-Ray diffraction and Raman spectroscopy. HV values in a range of 64.7 to 111.5 were observed, showing the lowest HAp/CTS-30.0 coating values for all the loads applied. The lowest HV value was nearby to the reported value for human bone’s hardness, around 47HV; considering that the coating will be in constant contact motion with the bone surface, the contact with a softer surface could decrease the wear on the human bone. The hardness decreases with the coating thickness’s increment because the coating presented a higher plastic deformation than the 316 L SS surfaces. A decrease in the roughness average (Ra) was well noticed as the deposition time increased; meanwhile, the thickness increased as the deposition time increased.

Study on the Effect of Ni Addition on the Microstructure and Properties of NiTi Alloy Coating on AISI 316 L Prepared by Laser Cladding

This paper investigated 55 NiTi commercial alloy powder and 55 NiTi with 5% pure Ni mixed powder (55 NiTi + 5 Ni) coatings fabricated by laser cladding to study the effect of extra Ni addition on the microstructure and properties of the coating. The XRD and EDS results show that the major phases in the coatings were NiTi and Ni3Ti. Besides that, a second phase like Ni4Ti3, Fe2Ti, and NiTi2 was also detected, among which, NiTi2 was only found in 55 NiTi coating. The proportion of the phase composition in the coating was calculated via the software Image-Pro Plus. The hardness of the cladding layer reaches 770–830 HV, which was almost four times harder than the substrate, and the hardness of 55 NiTi + 5 Ni coating was around 8% higher than that of 55 NiTi coating. The wear resistance of the 55 NiTi + 5 Ni coating was also better; the wear mass loss decreased by about 13% and with a smaller friction coefficient compared with the 55 NiTi coating. These results are attributed to the solid solution strengthening effect caused by Ni addition and the second phase strengthening effect caused by the content increase of the Ni3Ti phase in the cladding layer.

Experimental evaluation of electrophoretic deposition-assisted polishing

The quest for precision in manufacturing sector is continuously evolving with the introduction of modern technologies and new techniques. In this research, the characteristics and influential parameters of a recently developed polishing process, known as electrophoretic deposition-assisted polishing (EPDAP), were investigated in external surface polishing of AISI 316 L stainless steel. The results revealed the improvement of surface roughness with increasing axial load up to the certain value of 11 N. The polishing time between 6 min and 12 min was recommended for polishing surfaces having a moderate initial roughness, close to 0.1 µm. Moreover, the increase of tool rotational speed led to the improvement of surface quality, while the variation of applied voltage had insignificant effects on the surface texture. In the second series of experiments, predictive equations of average surface roughness and material removal rate (MRR) were obtained based on analysis of variance. It was concluded that axial load and tool rotational speed are the most influential parameters on surface roughness and MRR, respectively. By performing a multi-response optimization, the optimum levels of control parameters at the same voltage of 15 V were calculated as axial load of 12 N, polishing time of 10 min, and tool rotational speed of 2000 rpm. This combination reduced the average surface roughness by 54.17% relative to the worst condition, which is characterized by the lowest axial loads, rotational speed, and polishing time at the design space. The maximum MRR of 3.975 mg/min was achieved at this optimum point. Assessment of the surface features indicated that the EPDAP process created uniform roughness profiles and resulted in an enhanced surface reflectance.