Bendability of advanced high strength steels—A new evaluation procedure

The significant lightweight engineering potential of advanced high strength steels (AHSS) is limited by its moderate formability and altered failure behavior compared to mild steel grades. Especially bendability is crucial in automotive applications. The failure phenomena and underlying damage mechanisms in small curvature bending of AHSS are revealed in this work. A new characterization approach based on optical strain measurement is presented to comprehensively identify the failure stages, critical strains and bending angles in a user-independent manner. The novel approach is generalized and broadly applicable. Thus it gives a prerequisite for improved and material specific industrial process design in future.     

A generic coordinate transformation uncertainty assessment approach and its application in machine vision metrology

A measurement result is complete only when accompanied by a quantitative statement of its uncertainty [1]. However, there is no unified approach to the expression and computation of uncertainty, especially when coordinate transformations are involved. A generic approach to the uncertainty analysis of coordinate transformations based on constrained optimization uncertainty analysis is presented in this paper. The nonlinear constrained optimization algorithm used in this paper is a more generic algorithm for coordinate referencing than conventional 3-2-1 nesting method. We performed analysis on two types of uncertainty computation that relate to the final measurement: uncertainty of a single point in a world frame and uncertainty of distance measurement. The proposed method provides a mechanism for on-line assessment of measurement uncertainties on any coordinate measuring machines, mechanical or optical. Results of Monte Carlo simulation from a structured-light optical coordinate measurement machine (CMM) show that under normal machine operation conditions the approximations are valid.     

A new experimental approach for obtaining diffuse-strain flow stress curves

A new experimental approach for determining the sheet metal flow stress curve for diffuse necking deformation through the hydraulic bulge expansion (HBE) test is introduced. For this approach, a flat sheet of metal is bulged under the load of hydraulic pressure within the confines of a rigid binder/die tool set of circular die opening. The hydraulic pressure and volume flow rate of the pressurized water entering the die cavity are recorded in real time. Operating under the assumption of thin-walled pressure vessel behavior, the real time data are used to compute the flow stress curve for the material type considered. The novel aspect of the proposed technique is the use of water volume measurement for determining the radius of curvature of the expanding dome. An example flow stress curve for 1.0 mm thick DDQ cold rolled sheet steel is shown to be in good agreement with the flow stress curve obtained through the standard uniaxial tension test. One key advantage of this proposed method is that the analyst may determine the diffuse necking portion of the flow stress curve without employing cumbersome techniques associated with uniaxial tensile test methods. Two disadvantages of the proposed method are the uncertainty associated with having to assume a yield surface, and the error associated with having to assume membrane behavior in the work piece. The introduction of this new method will increase researchers’ access to practical methods for obtaining sheet metal flow stress curves.     

Analysis and optimization of the HVOF process by combined experimental and numerical approaches

Thermal spraying with the HVOF technology is a well known approach to dense metallic, ceramic and cermets coatings with good mechanical properties. Any attempt for improving HVOF coating properties requires a fundamental understanding of the mechanisms that occur during HVOF spraying. Thermal spray processes are not only optimized by empirical testing and by correlation analysis between process parameters and coating properties but also with numerical approaches. Recent attempts to understand the momentum and heat transfer mechanisms between flame and particles, and thus improve the control of the thermokinetic deposition process by analysis of fundamental thermophysical and fluid mechanical processes, have led to computational modeling of the spraying process and verification of simulation results by in-flight particle analysis.This paper focuses on modeling (tracking) of the particle properties during HVOF spraying using alumina powder. The particle properties are sensitive to a large number of process parameters (e.g., gas temperature, gas expansion velocity, pressure, spraying distance, spray powder particle diameter, nozzle geometry, etc.). Variation of the operating parameters of the HVOF process (gas flow rates, stoichiometric oxy/fuel ratio, nozzle design, etc.) is performed during modeling and simulation. The SprayWatch® system for particle in-flight measurement is used for verification of the numerical analysis result.     

Development of an Optical Sensor for the Measurement of the Material Flow in Deep Drawing Processes

In this paper a new optical sensor and its applications are presented. The prediction of faults that occur during the layout of deep drawing processes (e.g. cracks) remains a significant problem. Therefore, at the IFUM a new optical sensor principle has been developed for the contact-free recording of the material flow. The sensor recognizes special patterns on the sheet surface. The measured material (low can be used for the determination of local strain. The optical Sensor could be utilized instead of using expensive optical systems or manual methods (e.g. with a measurement grid) for the deformation measurement, which still require a special preparation of the specimen.Furthermore, the material flow can be used as the controlled variable for the closed loop control of deep drawing processes with varying blank holder forces along the flange. On the one hand the data recorded with the new optical Sensor is used to increase the quality of the FE-simulation. On the other hand a press with a multipoint drawing tool will be regulated by the control loop. A fuzzy controller is under development for the automatic connection between the material flow and the blank holding force.     

Implications from the Poliak–Jonas criterion for the construction of flow stress models incorporating dynamic recrystallization

Dynamic recrystallization (DRX) processes are widely used in industrial hot working operations, not only to keep the forming forces low, but also to control the microstructure and final properties of the workpiece. According to Poliak and Jonas, the onset of DRX can be detected from an inflection point in the strain hardening rate as a function of flow stress. Various models are available that predict the evolution of flow stress from incipient plastic flow to steady-state deformation in the presence of DRX, but their consistency with the criterion of Poliak and Jonas has not been investigated. This work analyzes the conditions that a flow stress model incorporating DRX has to fulfill to be consistent with the criterion of Poliak and Jonas. As the most important inconsistency, it is found that a model might suffer from insufficient differentiability at the critical point. For all models that use a classical JMAK equation for the DRX kinetics, it is shown that the Avrami exponent must exceed a value of 3. If the Avrami exponent is at most 3, a kink may develop in the strain hardening rate, and the second derivative criterion is violated. For DRX kinetics based on nucleation and growth rates that are functions of time, criteria are derived that ensure consistency with the criterion of Poliak and Jonas. DRX kinetics that are consistent with the second derivative criterion are put forward, drawing upon kinetics proposed by Cahn for transformations that originate at grain boundaries. Finally, a minimal model that is consistent with the second derivative criterion is formulated.     

Development and evaluation of an on-machine optical measurement device

Demand for fabricating micro-features such as fine holes, micro-cavity for injection moulding, and micro-pin using both conventional (turning, milling, etc.) and non-conventional edge detection method (EDM), wire cut EDM, etc.) processes is increasing significantly. To successfully achieve micro-machining, development of a miniature machine tool, process technology, and on-machine measurement is essential. However, in such tool-based micro-machining processes, proper tool shape monitoring, precision processing, and dimensional control require significant attention. Since these are tool-based machining processes, tool shape monitoring and control are also important technologies to be established.In this study, an on-machine measuring device was developed based on non-contact optical method to inspect dimensions of the fabricated tools (e.g. electrodes for EDM) as well as the wear of tools used for the respective processes. The developed inspection system uses a laser light source and a photo-electronic device. To minimize errors due to the change of tool measurement position and the Fresnel diffraction of laser light, an edge detection algorithm using a linear discrimination function is proposed in this study. Furthermore, an intensity measuring method was added for specimen with a smaller diameter. The experimental results show that the developed on-machine optical inspection system has the accuracy and stability to effectively monitor the fine dimensions of tools and their wear.     

Modeling of material removal in mechanical type advanced machining processes: a state-of-art review

Performance of any machining process is evaluated in terms of machining rate and surface finish produced. Higher machining rate and better surface finish are desirable for better performance of any machining process. Comprehensive qualitative and quantitative analysis of the material removal mechanism and subsequently the development of analytical model(s) of material removal (MR) are necessary for a better understanding and to achieve the optimum process performance. Analytical MR models are also necessary for simulation, optimization and planning (i.e. operation and process planning) of the process, prediction of process performance indicators, verification and improvements of experimental results, selection of appropriate models for specific type of work material and machining conditions, etc. Since the inception of different unconventional machining processes, various investigators have proposed different analytical models of material removal as functions of controllable process variables. A continual need for a comprehensive and exhaustive review of various analytical material removal models for different advanced machining processes is being felt. This paper is intended to fulfil this need in the area of advanced machining. Various analytical and some semi-empirical/empirical material removal models (approximately 40) for different mechanical type advanced machining processes have been comprehensively and exhaustively reviewed, and have been presented in a format suitable for quick reference.     

Fluid structure interaction (FSI) modelling of deep hole twist drilling with internal cutting fluid supply

This paper presents a novel approach for coupling of thermal FE and CFD simulations to predict the temperature distribution in the cutting process. The developed FSI model considers experimentally validated workpiece temperature to simulate the heat convection interactions in drilling operations. This innovative method allows not only for the common analysis of the flow behaviour, but additionally for the detailed investigation of the temperature distribution within the cutting fluid. The simulation provides indications for an insufficient fluid supply of the cutting edge and the results can contribute significantly to the further optimisation of thermally high stressed cutting tools and processes.     

Modelling the abrasive flow machining process on advanced ceramic materials

Abrasive flow machining (AFM) is a unique machining method used to achieve high surface quality on inner, difficult-to-access and on outside contours. Using AFM, it is possible to realise predefined edge rounding on any brittle or hard material. AFM is easy to integrate in an automated manufacturing environment. The abrasive medium applied during AFM is a fluid consisting of a polymer which carries silicon carbide or super-abrasive grains. With a specified pressure and temperature, this fluid flows in alternating directions along the contours of the workpiece resulting in an abrasive effect. AFM is also well suited to process advanced ceramic materials. Especially advanced ceramics are playing increasingly a significant role as a substitute for metals. However the high costs for the inevitable finishing process on ceramics prevent a more frequent use. This paper represents the technological results of a research-project discovering the fundamental principles of AFM on advanced ceramic materials such as a correlation between flow processes, surface formation and edge rounding. Furthermore an insight into a process model is given, which was developed using modern simulation techniques. The overall objective of this approach is to anticipate work results like surface quality and edge rounding on any user-defined geometry.     

A novel contact/non-contact hybrid measurement system for surface topography characterization

A novel surface profile measurement instrument, developed for the characterization of engineering surfaces, is presented. The instrument is of a hybrid type and is capable of contact and non-contact measurement, making it suitable for a wider range of applications. It has an optical displacement sensor and a stylus displacement sensor. For contact measurement, the vertical measurement range and resolution of the instrument are 1 mm and 10 nm, respectively. For non-contact measurement, they are 500 μm and 3 nm, respectively. The instrument has been successfully used for several forensic applications, demonstrating its unique flexibility and high reliability as a novel surface topography instrument.     

Determination of appropriate sampling conditions for three-dimensional microtopography measurement

Currently, there are no national or international standards available for the measurement of surface roughness in three-dimensions. The selection of measuring parameters (for example, the sampling interval and area) therefore relies largely on the experiences of users and is fraught with subjectivity. This is inconvenient, particularly for inexperienced users; moreover, this practice makes it difficult for inter-comparisons of measurement results to be conducted.

This paper aims to develop an objective criterion for selecting appropriate sampling conditions. A philosophy of surface roughness measurement in terms of the Nyquist wavelength limit is discussed. A sampling interval selection approach, based on spectral analysis, is then proposed. The proposed approach is not only applicable for the three-dimensional measurement scenario, but is also useful for the traditional two-dimensional measurement approach. The proposed technique has the added advantage that it can also be used to check the suitability of the measurement probe tip for any particular application. Experimental results based on measurements carried out on a large range of engineering surfaces (using a stylus instrument) are presented to demonstrate the effectiveness of the proposed approach.     

Eco-efficiency of manufacturing processes: A grinding case

Despite increased attention on energy-efficiency in manufacturing, other resources used as well as the quality performance of manufacturing processes have to be taken into account. This paper presents an eco-efficiency approach to evaluating energy as well as resource efficiency of manufacturing processes. The case of a grinding process is used to demonstrate the potential of the approach since e.g. coolant and dressing have an impact on quality performance and the environment. Based on the analysis, strategies for improving eco-efficiency of manufacturing processes are proposed.     

Constitutive Relationship of IN718 Alloy for Thermoviscoplastic and Microstructure Evolution Coupled Analysis

The interaction between thermomechanical parameters and microstructure evolution is so intense that it must be considered during the finite element method (FEM) simulation of the hot plastic working process, for materials that are difficult to deform. Taking the microstructure evolution into account, a novel type of constitutive relationship has been put forward for the IN718 alloy. The microstructure evolution model was first established for the dominant microstructure evolution processes. Then the microstructure evolution models and the method to determine the local flow stress of the corresponding microstructure for current thermomechanical parameters and deformation history were presented. Once the local flow stresses of different structures and their volume contributions were defined, the apparent flow stress of the material could be determined as the weighted sum of the local flow stresses and volume contributions. To validate the proposed method, a thermoviscoplastics and microstructure evolution coupled analysis for a forging process of a critical IN718 disk forging was performed. The predicting results were in close agreement with the experimental data.     

连铸过程中电磁流体力学的数值模拟现状及发展趋势

对连铸过程中电磁流体力学的数值模拟的研究现状进行了综合评述。介绍了一种应用于连铸过程中的低频电磁流体力学数值模拟的新方法,并给出了其在圆坯旋转搅拌、CSP薄板坯电磁制动和板坯二冷辊式行波搅拌中的应用实例。该方法特点是分别建立电磁场模型和流场模型,并采用磁感应方程实现电磁场和流场模型之间的耦合。结果表明,目前的方法可较为准确地描述连铸过程中的电磁场分布和电磁流体力学特点,并能够对电磁搅拌参数和连铸工艺过程进行优化。最后,提出了连铸过程中电磁流体力学数值模拟技术的未来发展趋势。     

Detection of shape deviations and measurement errors by a point cloud analysis

For the enhancement of technical workpiece surfaces with even larger dimensions, the application of microstructures on the surface is an appropriate way to improve the fitness for use without changing the properties of the basic material. Considering the extremely small dimensions of approximately 5–20 μm of the applied microstructure, the quality assurance faces new challenges related to the obtainment and evaluation of measurement data. This article presents an approach for the automated detection of shape deviations of a microstructure, as well as the detection of measurement errors during an optical or tactile measurement. The explained algorithm is based on the analysis of the measurement points within a point cloud by observing the distances between the single points. To illustrate the disturbance in the measurement point cloud every point is evaluated by an adaptive weighting function. The weighting of each measurement point can then be visualized by plotting the whole point cloud according to a corresponding color scale. The suitability of the point cloud analysis is demonstrated by the examples of a shape deviation (artificial groove) and a measurement error, occurred by measurement via confocal microscopy.     

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.     

Fabrication of free-form surfaces using a long-stroke fast tool servo and corrective figuring with on-machine measurement

Fabrication of free-form surfaces that are frequently demanded for the construction of optical imaging systems is described. To obtain a tool motion with large amplitude and high bandwidth, a novel long-stroke fast tool servo is proposed and installed on the Z-axis of a diamond turning machine as an additional synchronized axis. In addition, a special on-machine measurement device is used to measure the optical parameters of the machined surface and to compensate for the residual form of errors that are commonly produced in the diamond turning process. Actual machining test results show that the proposed procedures are capable of generating the copper free-form mirrors of 50 mm diameter to a form accuracy of 0.15 μm in peak-to-valley value error.     

An intelligent approach to welding robot selection

In a shipyard where multiple stationary and mobile workcells are employed in the fabrication of components of complex sub-assemblies,efficient operation requires an intelligent method of scheduling jobs and selecting workcells based on optimum throughput and cost. The achievement of this global solution requires the successful organization of resource availability,process requirements,and process constraints. The Off-line Planner (OLP) of the Programmable Automated Weld Systemd (PAWS) is capable of advanced modeling of weld processes and environments as well as the generation of complete weld procedures. These capabilities involve the integration of advanced Computer Aided Design (CAD), path planning, and obstacle detection and avoidance techniques as well as the synthesis of complex design and process information. These existing capabilities provide the basis of the functionality required for the successful implementation of an intelligent weld robot selector and material flow planner. Current efforts are focused on robot selection via the dynamic routing of components to the appropriate work cells. It is proposed that this problem is a variant of the “Traveling Salesman Problem” (TSP) that has been proven to belong to a larger set of optimization problems termed nondeterministic polynomial complete (NP complete). In this paper, a heuristic approach utilizing recurrent neural networks is explored as a rapid means of producing a near optimal, if not optimal, bdweld robot selection.