Methods of measuring residual stresses in components

Residual stresses occur in many manufactured structures and components. Large number of investigations have been carried out to study this phenomenon and its effect on the mechanical characteristics of these components. Over the years, different methods have been developed to measure residual stress for different types of components in order to obtain reliable assessment. The various specific methods have evolved over several decades and their practical applications have greatly benefited from the development of complementary technologies, notably in material cutting, full-field deformation measurement techniques, numerical methods and computing power. These complementary technologies have stimulated advances not only in measurement accuracy and reliability, but also in range of application; much greater detail in residual stresses measurement is now available. This paper aims to classify the different residual stresses measurement methods and to provide an overview of some of the recent advances in this area to help researchers on selecting their techniques among destructive, semi destructive and non destructive techniques depends on their application and the availabilities of those techniques. For each method scope, physical limitation, advantages and disadvantages are summarized. In the end this paper indicates some promising directions for future developments

Experimental and Numerical Analysis of Angular Error in Taper Cutting Using Wire Electrical Discharge Machining

Today, there are far greater demands for higher precision in machining, use fewer tools and ease of operation. Wire electro discharge machining (WEDM) is one, mostly acceptable non-conventional machining processes, using fewer tools; ease machining and producing extreme accurate shapes in hard materials those using in the tooling industry where the extreme precision is required and complexly determines such as extrusion dies in wear-resistant materials, cutting dies, etc. Wire EDM Taper cutting took forward the generation of inclined ruled surfaces, and it is eminently more important in the manufacturing of tooling requiring draft angles. The required angle is reached by applying a relative moment between the lower guide and the upper guide. Deformation arises in the wire, during the machining of taper cutting using Wire EDM. Due to that deformation in the wire, effected to the ruled inclination of machined parts. Such circumstances cause a dimensional error, loss of tolerances and less precision that can prime to the rejection of high added value tooling. To predict the deformation of wire by considering contact mechanics, properties of wire, properties of the guide, boundary conditions, typically used in taper cutting operations, has been taking into the account. FEM is needed to reduce the experimental cost and lack of time consumption and to give a more common approach to the problem. Finite Element Model (FEM) has been used to find out the deformation occurs during wire EDM process by changing the wire parameters like wire tension, wire diameter, taper angle and wire length, which is generally considering in taper cutting. This result intends to give you better understanding shows that taper angle and wire length are the most effective parameters in taper cutting process. Taguchi’s L16 orthogonal array is used to reduce the experimental runs. Traditional Taguchi approach is insufficient to solve a multi-response optimization problem. In order to overcome this limitation, utility theory has been implemented, to convert multi-responses into single equivalent response called overall utility index. Both the results, FEM and experimental have been checked

A Monolithic Internal Strain-Gage Balance Design Based on Design for Manufacturability

This paper proposes an alternative approach to internal strain-gage balance design driven by Design for Manufacturability (DFM) principles. The objective of this research was a reduction in fabrication time and, subsequently, cost of a balance by simplifying its design while maintaining basic stiffness and sensitivity. Traditionally, the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) balance designs have relied on Electro-Discharge Machining (EDM), which is a precise but slow and, therefore, expensive process. EDM is chosen due to several factors, including material hardness, surface finish, and complex geometry, including blind cuts. The new balance design objectives require no blind cuts, and offered a significant reduction in fabrication time, sufficient stiffness, and an acceptable level of sensitivity at the gages for the current design loads. The FF09X is designed to be a direct replacement for the NASA Langley FF09, retaining the same external dimensions, 2-inch x 2-inch x 6-inch, as well as the same load requirements and mounting configuration. Starting with the existing FF09A design, multiple design concepts were considered, including several two-piece designs, before a single-piece design was chosen. The final design is a monolithic balance with the center bored at both the metric and non-metric end and all fillets and rounds not less than 0.0625-inch in radius. Using Design of Experiments (DOE), a Central Composite Design (CC) was used to optimize the cage beam cross-sectional areas and moments of inertia. The FF09X was shown to measure applied forces and moments as effectively as the FF09, while only realizing a small increase in total deflection and decrease in resonant frequency. The overall manufacturing time required to fabricate the FF09X was estimated at 160 hours, which represents a 73% reduction in time when compared to the FF09

Intelligent Control System of Generated Electrical Pulses at Discharge Machining

The book chapter provides a comprehensive set of knowledge in the field of intelligent control of generated electrical impulses for wire electrical discharge machining. With the designed intelligent electrical pulse control system, the stability of the electroerosion process, as well as the increased surface quality after wire electrical discharge machining (WEDM), can be significantly enhanced compared to standard impulse control systems. The aim of the book chapter is also to point out the importance of monitoring in addition to the established power characteristics of generated electrical pulses, such as voltage and current, as well as other performance parameters. The research was mainly focused on those parameters that have a significant impact on the quality of the machined surface. The own’s theoretical and knowledge base was designed to enrich the new approach in increasing the geometric accuracy of the machined surface, as well as the overall efficiency of the electroerosion process for WEDM through intelligent control of generated electrical pulses

Study and analysis of residual stresses in electro-discharge machining(EDM)

Technological advances have led to an increasing use of high strength, high hardness materials in manufacturing industries. In machining of these materials, traditional manufacturing processes are increasingly being replaced by more advanced techniques such as electro-discharge machining (EDM), ultrasonic machining (USM), electric chemical machining (ECM) and laser machining. EDM has found widespread application in MEMS, tool and mould industries and aerospace industries. Therefore, promoting the quality of the EDM process by developing a thorough understanding of the relationship between the EDM parameters and the machined surface integrity has become a major research concern. Electric discharge machining removes materials by melting and vaporizing caused by the high heat within the discharge column. Furthermore, EDM can easily fabricate the precision and complicated parts by choosing the appropriate machining conditions to effectively control the amount of removed materials. Although EDM can obtain fine surface integrity and precise dimensions under finishing condition, the rough machining condition produces larger and deeper discharge craters since the great quantity of the melted material is removed. Furthermore, the melted material is not removed completely because the impulse force is insufficient to flush away the melted material at the end of discharge interval. The remaining melted material is solidified to form a recast layer that distributes micropores and cracks due to the effect of thermal stress during cooling. Thus, the microscopic feature of machined surface is severely coarse that significantly deteriorates the usage life and precision of machinery parts. EDM involves the complex interaction of many physical phenomena. The electric spark between the anode and the cathode generates a large amount of heat over a small area of the work-piece. A portion of this heat is conducted through the cathode, a fraction is conducted through the anode, and the rest is dissipated by the dielectric. The duration of the spark is of the order of microseconds and during this time, a plasma channel is formed between the tool and the work-piece. Electrons and ions travel through this plasma channel. The plasma channel induces a large amount of pressure on the work-piece surface as well. This pressure holds back the molten material in its place. As the plasma starts forming it displaces the dielectric fluid and a shock wave passes through the fluid. As soon as the spark duration time is over and the spark collapses, the dielectric gushes back to fill the void. This sudden removal of pressure results in a violent ejection of the molten and vaporized material from the work-piece surface. Ejected molten particles quickly solidify in contact with the colder fluid and are eventually flushed out by the dielectric. Small craters are formed at locations where material has been removed. Multiple craters overlap each other and the machined surface that is finally produced consists of numerous overlapping craters. Although molten material ejection is not the only means of material removal in EDM, it is, however, the dominant mode of material removal in case of metals. During machining the local temperature in the workpiece gets close to the vaporization temperature of the material. Thus, phase transformation from solid to liquid as well as liquid to vapor occurs during the heating cycle. Part of the transformed material is removed but the rest re-solidifies on the surface of the workpiece. This re-solidified layer is usually called the white layer, as it is not easily etchable. EDM processes carried out in hydrocarbon dielectrics lead to the partial breakdown of dielectrics and this further leads to some diffusion of carbon Below the re-solidified white layer lies a second layer that does not melt but is still affected by heat. For steels, during the cool-down cycle, solid-state transformations occur in this heat-affected zone because the highest temperature reaches beyond the austenite transformation temperature. Finally, all the non-uniform heating and cooling give rise to transient and residual stresses in the workpiece. As a result of these residual stresses surface cracks may be formed in the white layers. Usually, residual stresses are not high enough to cause sub-surface cracks in the parent material but may lead to detrimental effects when the machined work-piece is used in applications. This work is intended on analyzing the cause of residual stress in EDM process. It is also showing how current variation brings about a change in the surface characteristics and how the microstructure variation occurs because of subsequent sparks with constant magnitude. This is studied to draw a relationship between the micro structural change and the generation of residual stresses. Scanning Electron Microscope (SEM) images taken from the samples show the surface variation at different currents. A comparative study shows current variation is a factor for the craters developed at the EDMed surface, and that higher magnitude of current changes the grain structure of the sample drastically and intensifies the magnitude of residual stresses generated in EDMed sample. The solid-solid transformation is brought about at a higher temperature (at higher current) and sample EDMed at higher current is seen to have greater surface roughness

Parameter Optimization On Hybrid Micro Wire Electrical Discharge Turning

Micro-machining is expected to play an important role in today's manufacturing technology. However, the traditional down-scaling process creates challenges relating to process stability and materials behaviour especially for small difficult-to-machine made materials. Therefore, a suitable material removal process to perform micro-machining on cylindrical components is spark erosion process. In this study, the new hybrid micro-machining process is developed. This process is synonym with the name of wire electrical discharged turning (WEDT) which incorporates a turning process of rotating workpiece to continuous travelling electrode wire in electrical discharged conditions produced by wire electrical discharge machine. The objective of this research is to develop and evaluate the advance machinery and equipment for rotary axis mechanism that is being used to rotate the workpieces. The research focuses on optimizing the process parameter of hybrid WEDT for micro-machining straight shaft cylindrical component made of Ti6Al4V as materials. The issues pertaining to hybrid WEDT process on surface roughness (Ra) in the past have been explored comprehensively. The rotary axis mechanism that works well with WEDM machine has been successfully developed and the micro turning operations has been performed. The parameter optimization consideration on Ra begins with two stage screening. Firstly, the suitable combination parameter and its range is properly selected. Then, the selection of appropriate parameters and range is further screened by Taguchi orthogonal array L12. From the 11 process parameters that consist of electrical, non-electrical and rotary axis mechanism characteristics, only four has been selected to perform optimization by response surface methodology (RSM) which are intensity of pulse, voltage open, wire tension and rotational spindle speed. The other parameters are fixed at best level to produce low Ra value which is identified by Alicona Infinite Focus microscope (IFM). The optimal Ra that is produced by experiment through desirability approach is as much as 4.0143 μm with relative error as much as 5.9% compared to the prediction. The parameter and its level are pulse intensity of 8 Notch, wire tension of 14.8 Newton, voltage of 7 Notch and rotational spindle speed of 2390 rev/min. The machined parts surface is being deteriorated accordingly to the violent energy density generated by high pulse intensity and voltage, low wire tension and spindle speed

Investigations on Machining Aspects of Inconel 718 During Wire Electro-Discharge Machining (WEDM): Experimental and Numerical Analysis

Wire electro- discharge machining (WEDM) is known as unique cutting in manufacturing industries, especially in the good tolerance with intricate shape geometry in die industry. In this study the workpiece has been chosen as Inconel 718. Inconel 718 super alloy is widely used in aerospace industries. This nickel based super alloy has excellent resistance to high temperature, mechanical and chemical degradations with toughness and work hardening characteristics materials. Due to these properties, the machinability studies of this material have been carried-out in this study. The machining of Inconel 718 using variation of wire electrode material (brass wire electrode and zinc coated brass wire) with diameter equal to 0.20mm has been carried out. The objective of this study is mainly to investigate the various WEDM process parameters and performance of wire electrodes materials on Inconel 718 with various types of cutting. The optimal process parameter setting for each of wire electrode material has been obtained for multi-objective response. The kerf width, Material Removal Rate (MRR) and surface finish, corner error, corner deviation and angular error are the responses which are function of process variables viz. pulse-on time, discharge current, wire speed, flushing pressure and taper angle. The non-linear regression analysis has been developed for relationship between the process parameter and process characteristics. The optimal parameters setting have been carried out using multi-objective nature-inspired meta-heuristic optimization algorithm such as Whale Optimization Algorithm (WOA) and Gray Wolf Optimizer (GWO). Lastly numerical model analysis has been carried out to determine MRR and residual stress using ANSYS software and MRR model validated with the experimental results. The overlapping approach has been adopted for solving the multi-spark problem and validate with the experimental results

Design and characterization of a low cost dual differential proving ring force sensor utilizing Hall-effect sensors

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (leaf 31).A novel dual differential hall-effect based proving ring force sensor has been designed, manufactured, and tested. Strain gauge based force sensors are among the most common methods of measuring static and dynamic forces, yet they suffer from a wide array of negative attributes including: high cost due to signal amplification instrumentation, high temperature sensitivity, and only moderate dynamic range. The goal of the research herein described was to design and test a low cost, high dynamic range force sensor. Hall-Effect sensors have high bandwidth (>100 kHz), a wide dynamic range, are low in cost (<0.5$), and are ideally suited to dynamic and static force measurements. Proving rings - diametrally loaded hoops of metal, have long been used to measure force yet suffer many setbacks due to their historical designs utilizing mechanical and strain gauge methods of strain detection. A novel nested proving ring flexure has been combined with hall-effect sensors to fulfill the design requirements of a low cost and robust force sensor. Initial data demonstrates that the nested proving ring force sensor herein described is capable of resolving forces of in the range of 0 to 30 Newtons with an accuracy of 0.235 Newtons, all at a potential mass-manufactured cost of U.S.$10.00 per unit.by Christopher W. Rivest.S.B

An investigation and analysis of Process Parameters for EDM Drilling machine using Taguchi method

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