An innovative strategy for open loop control of hot deformation processes

A new strategy for systematically calculating near optimal control parameters for hot deformation processes is presented in this article. This approach is based on modern control theory and involves deriving state-space models directly from available material behavior and hot deformation process models. Two basic stages of analysis and optimization are established in this strategy for nonlinear, open loop control system design for producing required microstructural characteristics, uniformity of deformation and temperature distribution, and other important physical requirements of hot worked products.     

Investigation on the Flexural Creep Stiffness Behavior of PC–ABS Material Processed by Fused Deposition Modeling Using Response Surface Definitive Screening Design

The resistance of polymeric materials to time-dependent plastic deformation is an important requirement of the fused deposition modeling (FDM) design process, its processed products, and their application for long-term loading, durability, and reliability. The creep performance of the material and part processed by FDM is the fundamental criterion for many applications with strict dimensional stability requirements, including medical implants, electrical and electronic products, and various automotive applications. Herein, the effect of FDM fabrication conditions on the flexural creep stiffness behavior of polycarbonate–acrylonitrile-butadiene-styrene processed parts was investigated. A relatively new class of experimental design called “definitive screening design” was adopted for this investigation. The effects of process variables on flexural creep stiffness behavior were monitored, and the best suited quadratic polynomial model with high coefficient of determination (R ²) value was developed. This study highlights the value of response surface definitive screening design in optimizing properties for the products and materials, and it demonstrates its role and potential application in material processing and additive manufacturing.     

Effect of material scatter on the plastic behavior and stretchability in sheet metal forming

Robust design of forming processes is gaining attention throughout the industry. To analyze the robustness of a sheet metal forming process using finite element (FE) simulations, an accurate input in terms of parameter scatter is required. This paper presents a pragmatic, accurate and economic approach for measuring and modeling one of the main inputs, i.e. material properties and its associated scattering.For the purpose of this research, samples of 41 coils of a forming steel DX54D+Z (EN 10327:2004) from multiple casts have been collected. Fully determining the stochastic material behavior to the required accuracy for modeling in FE simulations would require many mechanical experiments. Instead, the present work combines mechanical testing and texture analysis to limit the required effort. Moreover, use is made of the correlations between the material parameters to efficiently model the material property scatter for use in the numerical robustness analysis. The proposed approach is validated by the forming of a series of cup products using the collected material. The observed experimental scatter can be reproduced efficiently using FE simulations, demonstrating the potential of the modeling approach and robustness analysis in general.     

Assessing the affordability of emerging processes for advanced materials

Quality-cost modeling is a method for obtaining approximate yet quantitative information regarding the potential of emerging manufacturing processes to produce highquality, cost-competitive advanced materials. The modeling method is based on the concept of an affordability space—a set of reachable combinations of cost and performance (quality) unique to a particular process and material. The analysis relies on the development of relatively simple (first order) models intended to capture the essential interactions between the material and its processing environment and their use in calculating the final microstructure (on which a quality index is based) and the associated cost. Both cost and quality are functions of the starting state of the material, process conditions used, and the design of the process. The tool allows numerical experiments to be conducted in which the influence of these variables on cost and quality can be explored. Dana M. Elzey earned his Dr.rer.nat. in materials science at the University of Stuttgart in 1989. He is currently a research assistant professor of materials science and engineering at the University of Virginia. Dr. Elzey is a member of TMS.     

IFHTSE global 21: heat treatment and surface engineering in first decades of twenty-first century Part 5 – Modelling based design of surface engineered systems

Abstract

Aspects of surface engineering design, namely, simulation of processing and service behaviour and prediction of properties, are discussed and summarised. Available design techniques are demonstrated by means of examples. Two process simulation modelling approaches, relating to oxidation of Ti alloys and nitriding of steels, are described. A novel optimisation approach to extract Young's modulus, yield strength and work hardening exponent of a power law (load–displacement) material is presented. Design and service behaviour simulation case studies of surface engineered titanium alloy gears for the sports car industry are also presented. It is shown that advances in theoretical principles and computational methodologies and tools, together with the ever increasing abundance and accuracy of thermodynamics and kinetics databases of materials and processing atmospheres, have enhanced the reliability of surface engineering simulations to a level good enough for industrial application. Barriers and development trends in surface engineering design are also addressed.     

Microstructure and oxide particle stability in a novel ODS γ-TiAl alloy processed by spark plasma sintering and laser additive manufacturing

In this work, a novel oxide dispersion strengthened titanium aluminide alloy (Ti-45Al-3Nb-<0.2Y₂O₃ at.%) was developed for powder-based processing technologies with a focus on spark plasma sintering and additive manufacturing. Titanium aluminides are promising structural intermetallics for weight reduction and an increased performance of high temperature components. The alloy design and selection process was supported by computational thermodynamics based on the CALPHAD approach, taking into account requirements for processing as well as long term alloy behavior under service conditions. Processing trials using spark plasma sintering, direct metal deposition and selective laser melting were conducted to study the alloy behavior, microstructure formation and introduction as well as stability of the ODS particles. Additionally, thermal annealing on the sintered and laser consolidated material was performed. Conventional dual phase α₂-Ti₃Al and γ-TiAl duplex and near-lamellar microstructures were obtained from the processed material. The ODS particles were homogeneously distributed in the alloy matrix after processing in the liquid state. For the direct metal deposition process, the novel alloy was compared to the established GE48-2-2 alloy (Ti-48Al-2Cr-2Nb) in terms of phases, microstructure and texture after processing. A significantly reduced texture formation was observed with the novel alloy. The hardness of the consolidated material shows superior properties for ODS-containing TiAl compared to ODS-free material. This work provides a first step towards tailored alloys for AM and the production of ODS TiAl alloys.     

Uncertainty quantification in modelling welding residual stress and distortion

Abstract

Currently available welding simulation methodologies provide deterministic results for the best estimate of the input parameters, such as part geometry, processing conditions and material properties. If there is an uncertainty in any of the input parameters, then a reanalysis needs to be performed with perturbed values of each uncertain variable. However, there can be several hundred input parameters; therefore, the use of reanalysis in uncertainty quantification in welding modelling can be time consuming or computationally prohibitive, especially for three-dimensional modelling. This paper explores the application of design sensitivity analysis in quantifying uncertainty in welding residual stress and distortion computations. Analytic sensitivities are computed by direct differentiation, resulting in a very efficient computational approach. The variation of temperature, welding residual stress and distortion with respect to processing parameters is computed from a first order Taylor expansion of the model output. The approach is demonstrated in a three-dimensional model of a singe pass weld and validated by comparing sensitivity analysis results to reanalyses.     

Tool for optimal design of manufacturing chain based on metal forming

Complex approach to the design of manufacturing processes based on considering the whole Life Cycle (LC) of material, including processing and exploitation stages, is presented in the paper. Modelling of the Life Cycle provides possibility to control the final product properties at the stage of manufacturing. It means that required properties and specific behavior of product under exploitation conditions can be obtained by optimization at the stage of material processing. The concept of the design of the entire manufacturing chain is presented in the paper and the application to manufacturing of the connecting part made of modern bainitic steels is proposed.     

The use of technical cost modeling for titanium alloy process selection

In recent years, both single-melt plasma arc cold hearth melting (PAM) and electron beam cold hearth melting (EBM) followed by a vacuum arc remelting step have emerged as low-cost alternatives for producing single-melt titanium alloy slabs for critical, non-aerospace applications. Technical cost modeling was used to estimate unit cost, identify principal cost drivers, and perform sensitivity analyses for producing 25.4 mm thick Ti-6Al-4V plates for ballistic-shock resistant applications. The results showed that the principal cost drivers are raw material processing, melt processing, and plate rolling. Sensitivity analyses showed that percent revert and process yield could significantly influence or adversely impact the estimated unit cost. A comparison of the estimated unit cost for a worst case of double VAR (2XVAR) with a best case for either PAM- or EBM-processed 25.4 mm thick plate showed a potential cost savings of 57% or 58%, respectively. These results showed the utility of the technical cost modeling approach in enabling process selection and cost control. Author’s Note: This work was performed by the author to showcase the use of technical cost modeling for metallurgical process selection and cost control. For more information, contact K. Sampath, Kreative Koncepts, 615 Demuth Street, Johnstown, PA 15904 USA; e-mail rs127@yahoo.com.     

A novel feedback control system – Controlling the material flow in deep drawing using distributed blank-holder force

The performance of a feedback control system is often limited by the quality of the model on which it is based, and often the controller design is based on trial and error due to insufficient modeling capabilities. A framework is proposed where the controller design is based on classical state space control theory and time series. The system plant has been modeled using non-linear finite element and the gain factors for the control loop were identified by solving the optimal control problem using a non-linear least square optimization algorithm.The proposed design method has been applied on a deep drawing operation where the objective was to control material flow throughout the part using only spatial information regarding flange draw-in. The control system controls both the magnitude and distribution of the blank-holder force.The methodology proved stable and flexible with respect to controlling the dynamic behavior of the system and the numerical tests showed that it is possible to control the material flow.Preliminary experimental results show that the proposed control system can eliminate process instability when the process is subject to a systematic error.     

Characterization of mechanisms of hot deformation of as-cast nickel aluminide alloy

The hot deformation behavior of as-cast Ni₃Al alloy has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing in the temperature range 1100–1250°C and strain rate range 0.001–10 s⁻¹. The mechanisms of hot working have been evaluated using four generations of materials modeling techniques, which included shape of stress–strain curves, kinetic analysis, processing maps and dynamical systems approach. The material exhibited a steady-state flow behavior at slower strain rates but flow softening associated sometimes with broad oscillations, was observed at higher strain rates. The flow stress data did not obey the kinetic rate equation over the entire regime of testing but a good fit has been obtained in the intermediate range of temperatures (1150–1200°C). In this range, a stress exponent value of 6.5 and an apparent activation energy of about 750 kJ/mol have been evaluated. Microstructural investigations have shown that the matrix γ′ phase undergoes dynamic recovery in the presence of harder γ colonies The processing maps revealed four different domains out of which three are interpreted to represent cracking processes. The fourth domain, which has a peak efficiency of about 44%, occurred at 1250°C/0.001 s⁻¹. Microstructural observations revealed that this domain represents dynamic recrystallization (DRX) of γ phase and is desirable for hot working the material. The material exhibits flow instabilities when deformed in the intermediate temperature regime at strain rates higher than 1 s⁻¹ and these are manifested as shear localization.     

A Comparison of Different Nitinol Material Data Sources for Finite Element Analysis

Nitinol (NiTi) is widely used for minimal invasive vascular implants due to its superelastic material behavior. Today computerized finite element analysis (FEA) modeling is a standard tool for the development of medical devices and an essential part of the product design and device approval process (X. Gong and A.R. Pelton, ABAQUS Analysis on Nitinol Medical Applications, Proceedings of ABAQUS User??s Conference, New Port, Rhode Island, 2001, p 1; N. Rebelo and M. Perry, Finite Element Analysis for the Design of Nitinol Medical Devices, Min. Invas. Ther. Allied Technol., 2000, 9(2), p 75). Quality of simulation depends on a multitude of parameters such as the mathematical material model and FE model generation (meshing). As such, a superior material data input is crucial in order to calculate the correct stress and strain conditions. In this study, we used different sources for material data input for our FE simulations. We compared simulated output versus the experimental results using a stent-like structure after various heat treatments. We used NiTi literature data, tensile data from raw as-supplied NiTi tubes as well as tensile and compression data from microtest samples which underwent stent-like processing for our FEA modeling. A FEA model of the diamond shape (DS) was constructed to quantify and visualize the force and motion response after applying different loading conditions similar to physiologic stress and strain. Force-deflection response of the virtual model was compared against the differently processed DS specimen. All results were put into a matrix in order to evaluate the quality of the different inputs for the FEA. The goal of this study was to demonstrate the importance of selecting and applying the correct material parameter inputs and to further show the importance of not just using given parameter, but also calibrating the values to get accurate results of FE simulations.     

Applying numerical Taguchi optimization to metal forming

The central idea behind a numerical approach for parameter tolerance design is the concept that multiple numerical process simulations can be used in accordance with the Taguchi orthogonal experiment arrays to perform parameter sensitivity analysis and for tolerance design using a quality loss function. The quality loss function is analytically defined using a novel material modeling technique based upon the second law of thermodynamics.     

Modeling the Structural Breakdown of Solder Paste Using the Structural Kinetic Model

Solder paste is the most important strategic bonding material used in the assembly of surface mount devices in electronic industries. It is known to exhibit a thixotropic behavior, which is recognized by the decrease in apparent viscosity of paste material with time when subjected to a constant shear rate. The proper characterization of this time-dependent rheological behavior of solder pastes is crucial for establishing the relationships between the pastes’ structure and flow behavior; and for correlating the physical parameters with paste printing performance. In this article, we present a novel method which has been developed for characterizing the time-dependent and non-Newtonian rheological behavior of solder pastes and flux mediums as a function of shear rates. We also present results of the study of the rheology of the solder pastes and flux mediums using the structural kinetic modeling approach, which postulates that the network structure of solder pastes breaks down irreversibly under shear, leading to time and shear-dependent changes in the flow properties. Our results show that for the solder pastes used in the study, the rate and extent of thixotropy was generally found to increase with increasing shear rate. The technique demonstrated in this study has wide utility for R&D personnel involved in new paste formulation, for implementing quality control procedures used in solder-paste manufacture and packaging; and for qualifying new flip-chip assembly lines.     

Optimization of microstructure development: application to hot metal extrusion

A new process design method for controlling microstructure development during hot metal deformation processes is presented. This approach is based on modern control theory and involves state- space models for describing the material behavior and the mechanics of the process. The challenge of effectively controlling the values and distribution of important microstructural features can now be systematically formulated and solved in terms of an optimal control problem. This method has been applied to the optimization of grain size and certain process parameters such as die geometry profile and ram velocity during extrusion of plain carbon steel. Various case studies have been investigated, and experimental results show good agreement with those predicted in the design stage.     

Viblade™: friction stir welding for plastics

Friction stir welding (FSW) is a welding process that may be successfully used with metals. The application of this technology to plastics has had limited success due to their thermal and viscoelastic properties.

Viblade? is a new variant of FSW for plastics: this process heats the material to be welded using a blade and a shoulder which vibrate with a linear alternating motion parallel to the weld line.

This paper has adopted the ‘design of experiments’ technique to assess the influence of the process parameters and blade geometry on the width of the thermally altered zone and the mechanical strength of the joint. In addition, a 2D thermal finite element thermal analysis has been conducted to evaluate the thermal phenomena involved in the process.     

A modular modeling approach for describing the in-plane forming behavior of unidirectional non-crimp-fabrics

Various commercially available unidirectional (UD) non-crimp-fabrics (NCFs) are currently used for manufacturing carbon fiber reinforced plastic (CFRP) parts. These UD NCFs can differ significantly in their forming behavior. For optimizing and ensuring the manufacturability of the forming process of CFRP parts manufactured from UD NCFs these differences have to be taken into account. This motivates developing an efficient and universally applicable modular modeling approach for describing the in-plane forming behavior of various UD NCFs. The first component of this modular approach is a hyperelastic material model that accurately predicts the fiber orientation of UD NCFs during forming. This material model is implemented via a user-defined material subroutine in the commercial finite element package LS-DYNA. The second component is a simple truss structure that allows modeling the various stitch patterns of the different UD NCFs. This modular model can be calibrated via simple tensile tests. To demonstrate the versatility of this approach, the in-plane forming behavior of three different UD NCFs is validated by comparing experimental data and simulation results of the common picture frame test.     

Development and application of alternate timed quenching by water and air

Abstract

Water and air are commonly used quench media with very different quenching powers; further, they are environmentally friendly and of very low cost. Theoretically, alternate quenching by water and air can produce any desired cooling rate between those of each medium alone. While this technology has not been practicable due to the difficulties in process design and control, the recent development of numerical simulation and processing control techniques has established a solid base for its industrial application. A new technology, alternate timed quenching by water and air (AT-quenching), is proposed. The technology has been applied to a medium carbon low alloy steel, the mechanical properties of which do not meet specification after oil quenching, but which suffers cracking after water quenching. The key points are to design the process by computer simulation and to realise it with digitally controlled quenching equipment. The technology has been successfully employed in production of large forged blocks of die steel for plastics moulding, long shaft forgings and forgings for marine crankshaft, effectively solving the difficulties that traditional processes and quenchants encounter.     

Improving the accuracy of calculating the conditions of mechanized surfacing

For some years now, the light engineering sector has been in search of welding and/or joining technologies allowing high-speed processing at low temperatures. This way, damage to galvanized coating, for example in the case of steels, could be avoided or significantly reduced.

Damage to the galvanized coating represents an outwardly visible phenomenon that can have a negative impact on the component's corrosion resistance.

On the other hand, from the metallurgical viewpoint, controlling heat input represents an important way to solve the problems associated with heat joining of metals with incomplete solid-state solubility. The formation of fragile intermetallic phases during cooling, for example, occurs with aluminium/steel or aluminium/titanium. The process and the correct choice of filler materials are key points for the success of the joining method. In the case of the combination of aluminium and steel, zinc represents a suitable filler material, for example for brazing. The melting temperature is around 420°C and the wettability, with regard to galvanized steel, is favoured by the zinc layer, while on the aluminium part, it is possible to avoid the use of flux, thanks to the activating action of the voltaic arc. However, the low melting and vaporization temperatures of zinc make even ‘short arc’ processing rather difficult.

Only new developments in electrical sources for welding, and in particular new processes, offer the possibility of reducing the heat input by modifying the ‘short arc’ process. The difficulties described are also valid for the combination of titanium and aluminium, and are associated with the formation of phases such as Ti _x A1 _y . Again in this case, this paper will present a strategy for joining sheets less than 2 mm thick.

In the past years, an increasing number of strategies to join zinc-coated steels can be observed. Brazing represents a profitable way to join zinc-coated steels at low temperatures, reducing or avoiding zinc evaporation.

In order to completely avoid damaging zinc coating, the set of ZnAl-fìllers was already investigated for laser brazing of zinc-coated steels as well as for joining steel with aluminium.

Furthermore, thanks to new developments in arc wire technology, ZnAl-electrodes can be used for MIG-brazing as well. In this case, the conventional short arc, which normally does not allow brazing with zinc wires as eruption-like evaporation occurs, is modified and controlled. The drop formation on the wire tip, the metal transfer, and the heat input can be controlled and modified very precisely, so that processing of filler material can be performed easily for thin sheets (till 0.8–1.5 mm) and at low-processing speed, below 0.3–0.4 m/min. The control of the heat input occurs due to abruptly reducing the current after short arc.

The disadvantages connected with a lower heat input in the base material are a restricted wetting behaviour of the zinc pool on the base material and the low-brazing speed due to a very high cooling rate. The focus of the presented investigation is the development of strategies, in order to enhance process conditions for brazing sheets of zinc-coated steels and aluminium.     

A new geometric error modeling approach for multi-axis system based on stream of variation theory

This paper introduces a new geometric error modeling approach for multi axes system (MAS) based on stream of variation (SOV) theory, especially for multi-axis precision stage. SOV is used for measuring product quality for some complicated multi operations system, which is widely used in error propagation in engineering field. This paper introduces SOV concept into geometric error modeling for MAS. Instead of different process in manufacture, the new error modeling approach regards each axis as a station in MAS, and calculates the deviations after each station which is considered as upstream factor to next station. It is clear to observe how geometric errors give influence and how deviations accumulate. Different with conventional methods which are only used for error compensation in machine tools, the new error model is beneficial for sensitive error control and optimal configuration selection in design part. In addition, the new error modeling has some merits such as debugging easily due to observe the deviations after every station. A case study of new error modeling procedure for six-axis stage (SAS) in optoelectronic packaging system (OPS) is developed, and applications related to error reduction order and optimal configuration selection are processed based on the new error model.