Transient Analysis of a Ceramic High Temperature Heat Exchanger and Chemical Decomposer

Ceramics are suitable for use in high temperature applications as well as corrosive environment. These characteristics were the reason behind selection silicone carbide for a high temperature heat exchanger and chemical decomposer, which is a part of the Sulphur-Iodine (SI) thermo-chemical cycle. The heat exchanger is expected to operate in the range of 950°C. The proposed design is manufactured using fused ceramic layers that allow creation of micro-channels with dimensions below one millimeter. A proper design of the heat exchanges requires considering possibilities of failure due to stresses under both steady state and transient conditions. Temperature gradients within the heat exchanger ceramic components induce thermal stresses that dominate other stresses. A three-dimensional computational model is developed to investigate the fluid flow, heat transfer and stresses in the decomposer. Temperature distribution in the solid is imported to finite element software and used with pressure loads for stress analysis. The stress results are used to calculate probability of failure based on Weibull failure criteria. Earlier analysis showed that stress results at steady state operating conditions are satisfactory. The focus of this paper is to consider stresses that are induced during transient scenarios. In particular, the cases of startup and shutdown of the heat exchanger are considered. The paper presents an evaluation of the stresses in these two cases.

Flank Correction for Spiral Bevel and Hypoid Gears on a Six-Axis CNC Hypoid Generator

Because the contact bearings of spiral bevel and hypoid gears are highly sensitive to tooth flank geometry, it is desirable to reduce the flank deviations caused by machine errors and heat treatment deformation. Several methods already proposed for flank correction are based on the cutter parameters, machine settings, and kinematical flank motion parameters of a cradle-type universal generator, which are modulated according to the measured flank topographic deviations. However, because of the recently developed six-axis Cartesian-type computer numerical control (CNC) hypoid generator, both face-milling and face-hobbing cutting methods can be implemented on the same machine using a corresponding cutter head and NC code. Nevertheless, the machine settings and flank corrections of most commercial Cartesian-type machines are still translated from the virtual cradle-type universal hypoid generator. In contrast, this paper proposes a flank-correction methodology derived directly from the six-axis Cartesian-type CNC hypoid generator in which high-order correction is easily achieved through direct control of the CNC axis motion. The validity of this flank correction method is demonstrated using a numerical example of Oerlikon Spirac face-hobbing hypoid gears made by the proposed Cartesian-type CNC machine.

Geometric Modeling of Cutter/Workpiece Engagements in 3-Axis Milling Using Polyhedral Models

Modeling the milling process requires cutter/workpiece engagement (CWE) geometry in order to predict cutting forces. The calculation of these engagements is challenging due to the complicated and changing intersection geometry that occurs between the cutter and the in-process workpiece. This geometry defines the instantaneous intersection boundary between the cutting tool and the in-process workpiece at each location along a tool path. This paper presents components of a robust and efficient geometric modeling methodology for finding CWEs generated during 3-axis machining of surfaces using a range of different types of cutting tool geometries. A mapping technique has been developed that transforms a polyhedral model of the removal volume from Euclidean space to a parametric space defined by location along the tool path, engagement angle and the depth-of-cut. As a result, intersection operations are reduced to first order plane-plane intersections. This approach reduces the complexity of the cutter/workpiece intersections and also eliminates robustness problems found in standard polyhedral modeling and improves accuracy over the Z-buffer technique. The CWEs extracted from this method are used as input to a force prediction model that determines the cutting forces experienced during the milling operation. The reported method has been implemented and tested using a combination of commercial applications. This paper highlights ongoing collaborative research into developing a Virtual Machining System.

On the Optimisation Into Wire Electro-Discharge Machining of Al/Al2O3P Composites

Non-traditional process like wire electro-discharge machining (WEDM) is found to show a promise for machining metal matrix composites (MMCs). However, the machining information for the difficult-to-machine particle-reinforced material is inadequate. This paper is focused on experimental investigation to examine the effect of electrical as well as nonelectrical machining parameters on performance in wire electro-discharge machining of metal matrix composites (Al/Al2O3p). Taguchi orthogonal array was used to study the effect of combination of reinforcement, current, pulse on-time, off-time, servo reference voltage, maximum feed speed, wire speed, flushing pressure and wire tension on kerf width and cutting speed. Reinforcement percentage, current, on-time was found to have significant effect on cutting rate and kerf width. The optimum machining parameter combinations were obtained for cutting speed and kerf width separately.

Virtual Five-Axis Flank Milling of Jet Engine Impellers: Part 1 — Mechanics of Five-Axis Flank Milling

Jet engine impeller blades are flank-milled with tapered, helical, ball-end mills on five-axis machining centers. The impellers are made from difficult-to-cut titanium or nickel alloys, and the blades must be machined within tight tolerances. As a consequence, deflections of the tool and flexible workpiece can jeopardize the precision of the impellers during milling. This work is the first of a two part paper on cutting force prediction and feed optimization for the five-axis flank milling of an impeller. In Part I, a mathematical model for predicting cutting forces is presented for five-axis machining with tapered, helical, ball-end mills with variable pitch and serrated flutes. The cutter is divided axially into a number of differential elements, each with its own feed coordinate system due to five-axis motion. At each element, the total velocity due to translation and rotation is split into horizontal and vertical feed components, which are used to calculate total chip thickness along the cutting edge. The cutting forces for each element are calculated by transforming friction angle, shear stress and shear angle from an orthogonal cutting database to the oblique cutting plane. The distributed cutting load is digitally summed to obtain the total forces acting on the cutter and blade. The model can be used for general five-axis flank milling processes, and supports a variety of cutting tools. Predicted cutting force measurements are shown to be in reasonable agreement with those collected during a roughing operation on a prototype integrally bladed rotor (IBR).

Nanoscale Molding of a Zirconium Based Bulk Metallic Glass

Geometrically complex, high aspect ratio microstructures and limited aspect ratio nanostructures have been successfully fabricated in supercooled Bulk Metallic Glass (BMG) substrates by molding against patterned Silicon and Silicon dioxide substrates. However, demand exists for similar metallic substrates with high aspect ratio, nanoscale features. Van Der Waals based interfacial energies between the supercooled liquid BMG and the Silicon cavity represent a substantial obstacle to the direct scaling of the molding process to the nanoscale. In an effort to investigate these effects, experiments were conducted using molds of various compositions: Silicon, SiO2 and SiO2 coated with Gold. The Gold coating failed to impact molding performance due to the thin layer deposited. However, drastically superior results were obtained by using a Silicon mold because of the variation in interfacial interaction between the BMG and the mold material. In addition, a theoretical model to predict achievable aspect ratio is presented and was found to be in qualitative agreement with experimental results. Finally, a value for the surface tension of Viterloy-1b within it’s supercooled liquid state was deduced from experimental data.

MCAD-ECAD Integration: Overview and Future Research Perspectives

The domain of Electrical Computer-Aided Design and Engineering (ECAD/ECAE) has been subject to major and rapid change over the past couple of years. Electrical Engineering Computer-Aided Design (CAD) tools developed in the early to mid-1990s no longer meet future requirements. Consequently, a new generation of Electrical Engineering CAD systems has been under development for about a decade now. An overview of advances in this field is presented in the introductory part of this paper. This overview also sets the context and provides background information for the main topic, MCAD-ECAD-integration, to be addressed in the remainder of this paper. Many complex engineered systems encompass mechanical as well as electrical engineering components. Unfortunately, contemporary CAE environments do not provide a sufficient degree of integration in order to allow for multi-disciplinary product modeling and bi-directional information flow (i.e. automated design modifications on either side) between mechanical and electrical CAD domains. Overcoming this barrier of systems integration would release a tremendous efficiency potential with regard to the efficient development of multidisciplinary product platforms and configurations. An overview of the state-of-the-art in MCAD-ECAD integration is presented. In addition, associated research questions are postulated and potential future research perspectives discussed.

Dynamic Analysis of Handling Compliant Sheet-Metal Blanks

Automating material handling of flexible sheet-metal blanks in stamping process requires attention due to its significant impact on product quality and productivity. This paper investigated the capability of a fully dynamic and nonlinear finite element technique in developing virtual material handling process of compliant sheet-metal blanks subject to time varying movability conditions. The technique used explicit time integration to avoid the formulation of stiffness matrix by a direct integration of the equations of motion. The influence of holding end-effector layout scheme and movability conditions on the final part quality was investigated.

An Ablation Parameter Study and Micromachining of NiTi Based Shape Memory Alloy Using Femtosecond Laser

The use of femtosecond lasers for the micromachining of engineering materials with micro and submicron size features is slowly but steadily increasing. This increase though presents challenges in understanding the interaction mechanism of femtosecond laser pulses with a material and defining process parameters for quality machining. This manuscript will present the setup for a 3DOF femtosecond laser microfabrication (FLM) system and its use in studying the ablation (single and multi shot) characteristics and incubation coefficient of nickel-titanium (NiTi) shape memory alloy. Understanding of these characteristics could allow for the identification of new applications of smart materials in the macro, micro, nano and MEMS domains.

The Effect of Materials Testing Mode on Mechanical Behavior Under Temperature Influence in Complex Deformation Processes

Complex deformation processes such as forming and machining involve large strain, high strain rate, high temperatures, strain rate/temperature coupling, and potential loading history effects. The conventional empirical and semi-empirical plasticity models are not adequate for characterizing dynamic mechanical behavior of work materials at the complex loading scenarios. The accuracy of characterizing the dynamic mechanical behavior in deformation processes using any constitutive models is strongly affected by materials testing data in which a constitutive model is fitted. Tension or compression tests have been widely used to approximate material properties in various manufacturing processes. However, it has been a critical question whether tension or compression test should be utilized for capturing the true nature of complex material deformations. In this study, the influences of two material testing modes on mechanical behavior of AISI52100 steel (62 HRc) were investigated using the internal state variable (ISV) plasticity model. Twenty material constants have been found by nonlinear fitting the ISV plasticity model to the base line test data obtained from each deformation mode. It has shown that the material testing modes have profound effects on some materials constants of the ISV model. The stress sensitivity study to ISV model parameters has identified the critical material constants for reflecting the nature of material deformation. The different testing modes have significant influence on the material constants associated with isotropic hardening rather than kinematic hardening.