Defect-free Component Research Articles

Improved mechanical properties and thermal conductivity of laser powder bed fused tungsten by using hot isostatic pressing

In this study, the microstructure evolution, mechanical properties and thermal conductivity of laser powder bed fused tungsten subjected to the subsequent hot isostatic pressing (HIP) processes with natural cooling (NC) and ultra-rapid quenching (URQ) were investigated. The results showed that the relative density was significantly improved after HIPping regardless of the cooling rates. The HIP-URQ treatment led to a near defect-free component with increased recrystallization and reduced dislocation density. The enhanced comprehensive mechanical properties, including the ultimate compressive strength of 1180 MPa without sacrificing microhardness was achieved for the HIP-URQ sample. Furthermore, the highest thermal conductivity of 168.6 W/(m·K) related to the densification behaviour and microstructure evolution during the HIP treatments was reported.

Identification of the Optimal Blank Holder Force through In-Line Measurement of Blank Draw-In in a Deep Drawing Process

During the forming process, variations in noise parameters can negatively impact product quality. To prevent waste from these fluctuations, this study suggests a method for the in-line optimisation of the deep drawing process. The noise parameter considered is the friction coefficient, assuming the variability in lubrication conditions at the blank–tool interface. The proposed approach estimates the noise factor variability during the process by tracking the draw-in of the blank at critical points. Using this estimation, the optimal blank holder force (BHF) is calculated and then adjusted in-line to modify blank sliding and prevent critical issues on the component. For this purpose, a Finite Element (FE) model of a deep drawing case study was developed, and numerical simulation results were used to construct surrogate models while estimating both the friction coefficient and optimal BHF. The FE model’s predictive capability was verified through preliminary experimental tests, and the control logic was numerically validated. Results show the effectiveness of this control type. By adjusting the BHF just once, a defect-free component is achieved. This method overcomes the limitations of feedback controls, which often need multiple adjustment steps. The time required to estimate the friction coefficient and the maximum time available for adjusting the BHF without causing defects was identified.

Laser Powder Bed Fusion Process Optimization of AlSi10Mg Alloy Using Selective Laser Melting: Dynamic Performance of Fatigue Behaviour, Microstructure, Hardness and Density

The quality of a selective laser melting (SLM) component depends on build orientation and layer thickness, which are directly influenced by processing parameters. The present research of layer-by-layer additive simulation before starting the SLM process has several advantages, such as saving time, cost, and material. In this main investigation, the dynamic performance of fatigue strength, density, and hardness of AlSi10Mg alloy was produced by the SLM-AM according to the design of experiments. The L9 orthogonal array of the Taguchi method was created to perform the experimental development process. Finally, the obtained optimal process parameter with the highest values of fatigue strength, density, and hardness was found at a laser power of 225 Watts, a scan speed of 500 mm/s, and a hatching distance of 100 μm. The experimental density result was achieved with a high density value of 99.6% (2.66 g/cm3) and a defect-free component and hardness of 126±5 HV. The future scope of this study will use optimal process parameters to find out mechanical properties for as built and preheated conditions for aerospace applications.

Simulation of Micro-Powder Injection Molding Using a Dynamic Mesh Approach

Abstract Powder injection molding (PIM) is capable of manufacturing complex small components out of metals and ceramics. With increasing market demand micropowder injection molding (micro-PIM) is improving rapidly which calls for improved numerical models of different stages of PIM. The injection stage is quite important as different defects may occur during injection that cannot be eliminated in the subsequent processes. Injection pressure and velocity are critical controlling parameters to manufacture a defect-free component. However, in most of the simulations, either injection pressure or injection velocity is taken as a constant value, while in reality, the injection molding of the piston moves at different speeds, and injection pressure and velocity change accordingly. In the experimental part of the present work, the piston movement is tracked using a high-speed camera which was mimicked in mold filling simulation of an alumina feedstock, considering the Dynamic Mesh approach. The solution of the full Navier–Stokes equation in an Eulerian-multiphase framework is used to simulate the mold filling where the secondary phase is air that is displaced by moving melt front. Additionally, a scalar equation was used to account for the liquid fraction of the feedstock. It is further demonstrated that the proposed model provides insight into the fluid-dynamic aspect of the mold-filling process.

A Review of Metal Injection Moulding on WC-Co Cemented Carbide Comprised of Grain Growth Inhibitors (GGI)

This paper aims to provide a summary of metal injection moulding technologies utilising cemented WC-Co carbides comprised of grain growth inhibitors (GGI). The advanced manufacturing of metal injection moulding (MIM) has the ability to produce cement nanostructured carbides. In addition, the nature of the feedstock plays a crucial role when manufacturing a defect-free component at each point of the MIM phase, thus the interactions between the metal powder and the binder combining, moulding, and debinding are important to be recognised. The primary objective of this analysis is to investigate the characterization of feedstock to form a homogenous mixture. There are five criteria to classify features of the feedstock which include powder characteristics, binder composition, powder content ratio, mixing cycle, and approaches to palletization. Not only that, the feedstock must meet specific criteria; higher powder loading with excellent flowability by the rheological approaches. The second goal of the research is to re-evaluate feedstock’s flow properties in relation to rheological activity in terms of index flow behaviour (n), activation energy (E), and mouldability (α). MIM practitioners have continued to underestimate erratic product quality, including inadequate regulation, distortion, and internal and external defects. These defects can arise in the early processing phases, but often occur only after sintering or debinding. The approaches are also challenging to provide. This chapter includes a description of MIM defects. Explanations are listed and recommendations are provided for these defects.

Metallurgical assessments on 316L stainless steel thin walled plate fabricated through GMAW based typical Wire Arc Additive Manufacturing

Wire Arc Additive Manufacturing (WAAM) is developing trendy process for the fabrication of metal components nowadays. In the present study, the concept of WAAM is employed but typical concept is used for fabricating a thin walled plate sample using AISI 316L grade of stainless steel. The plate size is limited for ease up to laying only three weld beads in traverse direction rather than vertically as in the case of additive manufacturing. The chemical composition of fabricated sample is analysed for checking the use of WAAM for metal component fabrication. The ferrite number is also found and reported for supporting the fabricated component to withstand the corrosion. The low carbon steel was used as a parent metal to deposit the fabricating stainless steel thin plate. Microstructure of interface between base metal and fabricating metal is also revealed for confirming defect free component fabrication. These results are found to be satisfactory enough and thus the WAAM shall be used for the fabrication of desired components also especially in stainless steels.

A critical review on the additive manufacturing of aluminium alloys

Today's demand for additive manufacturing has increased. In particular, in materials processing. The main reason for this is that in material processing, the defect free component is made by additive manufacturing. Aluminium based component is being used very much today, but when aluminium based alloy is processed with any other method, several types of defects occur. While fewer defects have been observed in aluminium based components made from additive manufacturing. Further, t is quite a task to fabricate aluminium structures using selective layer melting (SLM) as many parts suffer defects. This paper highlights the recent advancements that have been made to improve the same in recent years and some key topics that require further studying, which is necessary for industrial demands.

Numerical simulation aided design of heat sink using Z-cast

In this paper study the flow of the molten metal into the cavities during filling and to find out the defects of the air entrapment in the complex geometry of the component, which challenges the optimized gating design. To establish an easy and free-flowing gating design for the component and to drive out the air present in the cavities effectively to obtain a defect free component. To completely design the runner and gating system to the component to get the best cycle time to produce large volumes easily. The model was meshed to the given quality factor (FDM Mesh). The defects can be predicted prior to the die designing to optimize the casting process to minimize the rejection and improve productivity and quality of the component. Intricate components can be easily designed by using the simulation tool to detect the defects of the proposed gating and the runner design. Percentage of components clearing the quality test during iteration-1 was 56% and after iteration −2 it got improved to 95%. The complete phenomenon of the liquid metal flow in the die can be observed and analyzed to predict the behaviour of the liquid metal accommodating the cavity. The ‘Heat Sink” was successfully designed to eliminate the defects and proposed design was altered. Several defects of the proposed gates, where the gates were not filling the cavities due to the obstructions in the configuration of the component. The ribs on the component were obstructing the free flow of the metal in the component in the initial design where the air got entrapped between the ribs and were creating voids. This could be easily observed during the simulation. Hence all the necessary parameters were collected after the modification and the gating system redesigned in a way where there could be no defects, during the filling or in the solidification of the component.

Experimental and simulation analysis on multi-gate variants in sand casting process

The present work proposes an improved multi-gate designs (MGDs) in sand casting process, using both experimental and simulation (FLOW 3D) approaches, aiming to produce defect-free component. In this regard, the variant MGDs were developed and compared with the existing designs reported in the previous studies. Accordingly, the following new MGDs: side sprue serial connection (SSSC), centre sprue serial connection (CSSC), side sprue parallel connection (SSPC), centre sprue parallel connection (CSPC) and centre sprue runner extension parallel connection (CS-RE-PC) were modelled for both techniques. The experimental set-ups were developed for the aforementioned designs to study the flow behaviour of aluminium alloy and water. The validity of aluminium alloy flow characteristics in closed mould condition was checked with the water mould experimentation. The quality of the casting was examined by visual inspection, optical microscopy, ultrasonic and X-ray tests. From the results obtained, it was evident that CS-RE-PC mould set-up or design was most suitable with a runner system for four-cavity application. This design exhibited best flow rate, as a nearly defect-free casting component was produced. Comparison of the FLOW 3D simulation results with similar experimental findings provided potential opportunity to reduce both cast product rejection rate and rework, and consequently it aids enhancement of the productivity and profitability in a manufacturing/casting industry.

Thermal simulation and phase modeling of bulk metallic glass in the powder bed fusion process

One of the major challenges with the powder bed fusion process (PBF) and formation of bulk metallic glass (BMG) is the development of process parameters for a stable process and a defect-free component. The focus of this study is to predict formation of a crystalline phase in the glass forming alloy AMZ4 during PBF. The approach combines a thermal finite element model for prediction of the temperature field and a phase model for prediction of crystallization and devitrification. The challenge to simulate the complexity of the heat source has been addressed by utilizing temporal reduction in a layer-by-layer fashion by a simplified heat source model. The heat source model considers the laser power, penetration depth and hatch spacing and is represented by a volumetric heat density equation in one dimension. The phase model is developed and calibrated to DSC measurements at varying heating rates. It can predict the formation of crystalline phase during the non-isothermal process. Results indicate that a critical location for devitrification is located a few layers beneath the top surface. The peak is four layers down where the crystalline volume fraction reaches 4.8% when 50 layers are built.

An approach toward multiscale modeling of direct metal laser sintering process

Direct Metal Laser Sintering (DMLS) is a relatively new technology which produces three dimensional fully dense complex shaped components directly from the powder material in a layer by layer fashion. This is a rapid manufacturing technique, in which the qualities of build parts are dependent completely on the microstructure along with process parameters. Thus, for fabricating of a sound defect-free component in DMLS process, it is required to understand the processing mechanism as well as the process parameter effect. Also to predict the part microstructures during the process may be an important factor for process optimization. The present article gives an idea about the DMLS process with its process feature and provides a comprehensive knowledge for further application of numerical modeling approaches on multiple lengths and time scales to describe different aspects of DMSL process.

Stress intensity factors of corner cracks at set-in nozzle–cylinder intersection of a PWR reactor pressure vessel

Reactor pressure vessel (RPV) is the central and the most important component of a pressurized water reactor (PWR). The fracture mechanics analysis of different parts of the RPV under various loading conditions is compulsory as it is not always possible to manufacture a crack- or defect-free component. The strength of a crack, in an engineering component, is normally evaluated by computing the stress intensity factors (SIFs) along the crack front. In this paper, for the fracture mechanics analysis of the set-in nozzle of a 300-MW RPV, the SIFs of a wide range of corner surface cracks at the nozzle–cylinder intersection are being presented. The considered RPV is made of a nuclear-grade steel designated as ‘SA-508 Gr.3 Cl.1’. The analyzed corner cracks are in the range of ‘0.01 < a/t < 0.25’ and ‘0.33 < a/c < 1.0’, where ‘a’ and ‘c’ represent minor and major axes of the crack, respectively; and ‘t’ is the thickness of the vessel wall at the nozzle–cylinder intersection. In this study, both the linear elastic fracture mechanics (LEFM) and elasto-plastic fracture mechanics (EPFM) based SIFs are provided under normal operating conditions of the plant. The shape and size of the plastic zone at the crack tip, using von Mises failure criterion, is also presented.

Quantitative Feeder Design for Metal Castings

Casting simulation packages are used to check a design for its castability. A better starting design should need fewer simulation cycles to arrive at a defect-free component thus cutting computation and manpower costs. Quantitative design of the feeding system is done by an analysis of the solidification pattern of the 3D model of the cast component. A clustering algorithm uses the solidification time/temperature data from the simulation to divide the casting into 3D feeding sections. The sections are created by following hotspots surrounded by areas of decreasing solidification time. Feeders are built by the feeder design module of AutoCAST casting design software. The initial simulation as well as the efficacy of the rigging is tested through the advanced simulation module FLOW+ of AutoCAST X. An industrial case study illustrates the software pipeline in a virtual foundry trial.

Diffusion Welding of Thick Components Fabricated by Inserted Powder Injection Molding*

AbstractPowder injection molding consisting of four stages – feedstock preparation, injection, debinding and sintering – is a unique technique to produce small and complex metal or ceramic components in high quantity. One of the limitations of this method is the production of thick components, which arises from difficulties in de-binding stage. In this study, a novel method is presented to produce thick components with large sections by powder injection molding using preformed inserts in the injection stage. By using a wrought insert on which the feedstock is injected, the thickness of an injected section that needs to be debound, is decreased, while the whole thickness of the component is still large. The key point in this method is the amount of diffusion welding of the wrought insert and the injected feedstock to form an integrated component. 316L stainless steel has been used as material for both insert and feedstock. The effects of insert/component diameter ratio and the sintering atmosphere on diffusion welding have been studied. Finally, a defect-free thick component with a diameter of 20 mm is fabricated with a bonded area at the interface of the insert and injected section having shear strength up to 427 MPa.

Rheological Properties Analysis of WC-Co Injection Feedstock

In order to produce a defect-free component, the feedstock composition plays as a critical factor. The feedstock needs to meet the following criteria; high solid loading with excellent flowability. The flowability of the feedstock is greatly determined by the rheological response. Therefore, the aim of this paper is to investigate the rheological behaviour of MIM feedstock comprising of WC-Co powder, with a binder system of Palm Stearin (PS) and Polyethylene (PE), by means of a capillary rheometry. The viscosity and shear rate of various feedstocks at powder loading ranging from 59, 61 and 63% were measured at L/D = 10 die. The rheological properties such as flow behaviour index, activation energy and moldability parameter of each feedstock were calculated and from the analysis, it was concluded that they show a good pseudo-plastic behaviour within acceptable ranges in MIM.

Rheoforging of thin case for IT devices with optimal process parameters and new type die design

The latest trend in the cell phone component industry to use aluminium and magnesium alloys has resulted in the advanced processing technologies. Semi-solid forming process that is advantageous for the mass production of thin parts with complex shapes have been of interest as a promising tool for near net-shape manufacturing. This study describes a semi-solid forming process for the development of a 1 mm-thick cell phone case by using the rheological material prepared by electromagnetic stirring equipment. Thus, a new type of die design for indirect rheoforging was proposed to efficiently control the primary α-Al phase particles in the thin part under rheological conditions. Their microstructure and mechanical properties were investigated and compared to parts produced without electromagnetic stirring. Those products fabricated by electromagnetic stirring had better mechanical properties and globular microstructures than those fabricated without electromagnetic stirring. Several processing parameters such as punch velocity (30 mm/s), punch pressure (75–250 MPa), stirring time (10 s), and solid fraction (0–20%) were used. The optimal condition that resulted in a defect-free component with the improved mechanical properties was explained and discussed.

Component Assessment Data Requirements from Creep-Fatigue Tests

Abstract Typically, the lifetime assessment of high temperature components, for which both creep and fatigue are principal damage mechanisms, involves (1) the determination of the stress/strain state at critical locations and (2) a numerical evaluation of the consequential damage condition. Until recently, there has not been a standard procedure specifically covering creep-fatigue testing practices. Creep-fatigue tests had been performed for many years, but the reliability and the form of the information generated was dependent on the expertise and specific interests of individual test laboratories. This situation is now resolved by the publication of a new ASTM standard based on an Electrical Power Research Institute (EPRI) led initiative. The way in which the guidance contained in this new standard specifically aims to provide creep-fatigue data requirements for defect-free component assessment is examined. Cyclic/hold tests, usually involving a simple cycle shape representative of the service transients experienced by the target component, are particularly informative in the provision of data to indicate the concurrent influences of cyclic loading on creep deformation characteristics and creep deformation on cyclic plastic response. The crack initiation endurances of such tests also provide the basis of creep-fatigue damage summation representations for a given material. Sequential creep-fatigue testing can be used to quantify the effects of prior cyclic deformation on creep rupture or prior creep deformation on fatigue endurance. The use of such test methods is also considered.

Feasibility Study on Producing Components with Embedded Channel by Powder Injection Moulding

Feasibility study on producing components with embedded channel by powder injection moulding (PIM) is conducted in this paper. The base plate with open channel was produced by co-injection moulding of polymeric material and ceramic feedstock. The polymeric material acted as the sacrificial material to fill the channel feature. A cover plate was then over-moulded onto the base plate to form green assembly, which was then debinded and sintered. The embedded channel was created when the sacrificial material was removed during the debinding and sintering stage. This process eliminates the need for additional joining process required by conventional manufacturing process which could cause misalignment and leakage under harsh working environment such as high pressure and high temperature. Joining was found between the cover plate and the base plate in over-moulding stage. Temperature and time during solvent debinding played important roles in order to obtain defect free component. Low temperature and short time in solvent debinding resulted in insufficient wax loss which led to various types of defects. A fair good sintered component was obtained under optimal debinding condition at 50 °C for 48 hours. The embedded channel was observed clearly by x-ray inspection without blockage by foreign particles. The shape of the channel was well retained and perfect bonding was formed in the central area of the two plates.

In-situ monitoring of actively cooled plasma facing components using acoustic and thermal methods

Plasma facing components (PFC) for modern steady state fusion devices have to withstand heat fluxes up to 20 MW m−2. In case of internal defects in the components, a critical heat flux event can occur at an incident heat flux lower than expected in a defect-free component. It is therefore essential to develop in-vessel means for on line safety monitoring to prevent PFC destruction, and health monitoring during shutdown to control PFC damage. Two methods are developed in this paper, covering these topics.

Piping elbows with cracks Part 2: Global finite element and experimental plastic loads under opening bending

Experimental and finite element (FE) plastic load results of cracked piping elbows under opening in-plane bending are presented and compared with data from similar defect-free components. The elbows used were short-radius components with an outside diameter of 88.9 mm and thickness 5.49 mm. Axial (at the crown) and circumferential (at the intrados) blunt crack-like defects were produced using electric discharge machining (EDM) procedures. Both short (0 = 21° axial or 2β = 46° circumferential) and long (0 = 75° axial or 2β = 120° circumferential) defects were investigated with three depth-thickness ratios a/t = 0.5, 0.75 and 1.0. The FE simulations employed the measured true stress-strain properties for the elbow material and included geometric non-linear behaviour. The results obtained show that piping elbows under opening bending can tolerate substantial defects, with reductions in plastic loads compared with the defect-free component of the order of 15 per cent or less in most cases, except when the defect is through-wall and circumferential and covers an angle 2β = 120° or more, in which case the reduction in plastic load can be as high as 40 per cent.