Highly effective way in five-axis sculptured surfaces machining using flat-end cutter

This paper applied the concept of “contact” in Differential Geometry into the machining of the sculptured surface. I presented the contact principle of the machining of complicated surfaces, using the circumference circle of the cylindrical cutter to sweep the curved surface instead of ball-end mill. This is highly effective method. In this paper an theory for machining complicated surface is presented. By using a flat-end mill instead of ball-end mill, and adjusting the axis relate to the surface, the two surfaces, The swept surface and the required surface, has the same curvature, up to as high as 3th order

Optimisation of machining parameters during ball end milling of hardened steel with various surface inclinations

This paper proposes a method for the reduction of forces and the improvement of efficiency during finish ball end milling of hardened 55NiCrMoV6 steel. The primary objective of this work concentrates on the optimal selection of milling parameters (cutting speed – vc, surface inclination angle α), which enables the simultaneous minimisation of cutting force values and increased process efficiency. The research includes the measurement of cutting forces (Fx, Fy, Fz) during milling tests with variable input parameters and calculation of process efficiency accounting for cutting parameters and surface inclination. The paper then focuses on the multi-criteria optimisation of the ball end milling process in terms of cutting forces and efficiency. This procedure is carried out with the application of the response surface method, based on the minimisation of a total utility function. The work shows that surface inclination angle has a significant influence on the cutting force values. Minimal cutting forces and relative high efficiency can be achieved with cutting speed vc = 375 m/min and surface inclination angle α = 15°

Titanium milling strategies.

This thesis explores the subject of titanium milling and identifies the need for development of titanium milling strategies to address the key process limitations of chatter and tool wear. These subjects are typically studied in isolation and little work has previously been undertaken on titanium milling dynamics. Titanium is often perceived as difficult to machine as the very properties such as high strength at high temperature and low thermal conductivity that make it an attractive engineering material can cause rapid tool wear and limit process parameters. Titanium alloys are increasingly popular within the aerospace industry due to the high strength to weight ratios and titanium and carbon fibre composites have replaced many steel and aluminium components within aerostructures. Titanium is still seen by many as expensive to process and there is not the same degree of understanding and process optimisation within the machining industry as there is for aluminium and steel alloys. The literature review considers both advances in titanium tool wear mechanisms and research into machining dynamics. From the literature review three research hypotheses are developed around the knowledge gaps pertaining to titanium milling stability and process optimisation. The limitations on milling performance and productivity are considered and three areas are identified where the research could be advanced to improve titanium milling productivity through manipulation of parameters and tool geometry, these areas are pocketing strategies, special tooling geometries and process damping. A method for controlling radial immersion for pocketing strategies is developed and it is proven that through control of parameters and toolpaths that tool life and productivity can be optimised and controlled. A study is then undertaken into the performance and modelling of variable helix end mills to explore the hypothesis that the tools will outperform standard and variable pitch cutters and that the performance can be modelled. As part of the validation process an analysis of the linearity of machine tool dynamics is undertaken and it is demonstrated that under speed and load, spindle and machine tool frequency responses can differ from those measured in the static condition. The final part of the research investigates process damping performance and sensitivity to cutting tool geometry and feed rates. A method for evaluating process damping performance is developed and through optimisation of tool geometry and feed per tooth increases in productivity up to 17 fold are demonstrated. A method is then presented for tuning machine tool dynamics to optimise process damping performance and stabilise sub optimum tooling and machine tools. The three core strands of the thesis are brought together and demonstrated in an aerospace case study. Through application of the techniques developed in the thesis a titanium aerostructural component is machined at the same rates as an equivalent steel component and at less than 50% of the planned titanium milling process time

Vibration assisted machining: Modelling, simulation, optimization, control and applications

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University, 30/11/2010.Increasing demand for precision components made of hard and brittle materials such as glasses, steel alloys and advanced ceramics, is such that conventional grinding and polishing techniques can no longer meet the requirements of today's precision manufacturing engineering. Particularly, in order to undertake micro-milling of optical glasses or other hard-machining materials, vibration assisted machining techniques have been adopted. However, it is essential and much needed to undertake such processes based on a scientific approach, i.e. the process to be quantitatively controlled and optimized rather than carried out with a trial-and-error manner. In this research, theoretical modelling and instrumental implementation issues for vibration assisted micro-milling are presented and explored in depth. The modelling is focused on establishing the scientific relationship between the process variables such as vibration frequency, vibration amplitude, feedrate and spindle speed while taking into account machine dynamics effect and the outcomes such as surface roughness generated, tool wear and material removal rate in the process. The machine dynamics has been investigated including a static analysis, machine tool-loop stiffness, modal analysis, frequency response function, etc, carried out for both the machine structure and the piezo-actuator device. The instrumentation implementation mainly includes the design of the desktop vibration assisted machining system and its control system. The machining system consists of a piezo-driven XY stage, air bearing spindle, jig, workpiece holder, PI slideway, manual slideway and solid metal table to improve the system stability. The control system is developed using LabVIEW 7.1 programming. The control algorithms are developed based on theoretical models developed by the author. The process optimisation of vibration assisted micro-milling has been studied by using design and analysis of experiment (DOE) approach. Regression analysis, analysis of variance (ANOVA), Taguchi method and Response Surface Methodology (RSM) have been chosen to perform this study. The effects of cutting parameters are evaluated and the optimal cutting conditions are determined. The interaction of cutting parameters is established to illustrate the intrinsic relationship between cutting parameters and surface roughness, tool wear and material removal rate. The predicted results are confirmed by validation experimental cutting trials. This research project has led to the following contribution to knowledge: (1) Development of a prototype desktop vibration assisted micro-milling machine. (2) Development of theoretical models that can predict the surface finish, tool wear and material removal rate quantitatively. (3) Establishing in depth knowledge on the use of vibration assisted machining principles. (4) Optimisation of cutting process parameters and conditions through simulations and machining trials for through investigation of vibration assisted machining.Financial support was obtained from Brunel University

Protective hood

Protective hood is intended to give limited protection to head and neck. It is an interface device of a properly selected and configured protective ensemble during fire fighting and related emergency response activities

Process planning methodology and evaluation of tool life for micromilling with an application to the fabrication of thin wall structure

Ph. D. Thesis.The scaling down effect on feature geometries and tools used in micromilling results in low feature stiffness and excessive tool wear. To achieve the required costs and tolerances, optimisation of the machining processes and their associated parameters are necessary which requires a thorough understanding of machining characteristics. Furthermore, the compensation must be sought for downscaling issues that arise at the process planning stage. Hence, the effect of the characteristics of the cutting tool, workpiece material and machining parameters are investigated in this research through a critical review of the literature followed by a numerical and experimental study of the impact of process variables. The research findings are used in the development of a process planning methodology for micromilling of components with application to high aspect ratio structures, to assist machine operators and to fill the gap between industrial and academic machining knowledge. From the investigation of machining sequences, the study of machining layer strategy considering the sequence of removal of excess material using numerical simulation, strategic planning of machining layers in relation to feature stiffness is required, in particular to the machining of high aspect ratio features. The results from numerical simulation recommend an improved layer strategy for micromilling of thin wall structures, which were then experimentally validated in relation to machining time and geometrical and surface accuracy. The importance of planning tool entry and exit position in relation to feature rigidity was highlighted. The increase in depth of cut shows to improve the tool engagement reducing the thin wall deflection by 168 μm and appearance of the burr along the wall edge indicated by up to 200% drop in burr width. The investigation of tool paths showed the suitability of strategies for machining of circular and linear geometries. Also, the experimental findings emphasise on considering the feature geometry type in the selection of tool paths to achieve a balance between high-performance machining and improved productivity. This study also investigates tool life, associated with flank wear rate, surface roughness, volumetric tool loss and the degradation of the cutting edge radius for micro endmills where a direct correlation between cutting speed and tool wear rate has been found. The new procedure for tool life prediction in conjunction with clear tool rejection criteria for the micro end mill is recommended. Along with standard procedure for the evaluation of tool change intervals to avoid tool failure and consequential defects in parts produced. In addition to the findings in the literature on machine process planning and findings from the study of machining sequence on the thin wall structure and tool life investigation conducted, a new process planning methodology for micromilling has been proposed. The process planning methodology includes four distinct modules i.e. feature recognition, tool selection, machining parameter selection and machining sequence planning. The feature recognition module proposes a new approach to identify key feature faces and their corresponding machining attributes required for tasks in process planning. In the tool selection module, a new methodology for the evaluation of the machinability index and the tool replacement strategy for micro endmills are proposed to guide the operator in the task of tool selection and estimating tool replacement intervals. The machining parameter module provides a systematic approach for the selection spindle speed, feedrate and depth of cut. The machine sequence planning module assists the operator in selecting a suitable tool path and tool layer strategy along with a compensate technique for tool path errors. An artefact with thin wall features has been fabricated using the methodology proposed and the conventional process planning method. The results show the part processed using the proposed methodology achieved better geometrical tolerance, and improved repeatability. It also show a 17% improvement in mean surface roughness, which demonstrates the effectiveness of the proposed methodology

A cost effective approach to enhance surface integrity and fatigue life of precision milled forming and forging dies

Previously held under moratorium from 8 August 2019 until 19 January 2022The machining process determines the overall quality of produced forming and forging dies, including surface integrity. Previous research found that surface integrity has a significant influence on the fatigue life of the dies. This thesis aims to establish a cost-effective approach for precision milling to obtain forming and forging dies with good surface integrity and long fatigue life. It combined experimental study accompanied by Finite Element Modelling and Artificial Intelligence soft modelling to predict and enhance forming and forging die life. Four machining parameters, namely Surface Speed, Depth of cut, Feed Rate and Tool Lead Angle, each with five levels, were investigated experimentally using Design of Experiment. An ANOVA analysis was carried out to identify the key factor for every Surface Integrity (SI) parameter and the interaction of every factor. It was found that the cutting force was mostly influenced by the tool lead angle. The residual stress and microhardness were both significantly influenced by the surface speed. However, on the surface roughness it was found that the feed rate had the most influence. After the machining experiments, four-point bending fatigue tests were carried out to evaluate the fatigue life of precision milled parts at an elevated temperature in a low cycle fatigue set-up imitated for the forming and forging production. It was found that surface roughness and hardness were the most influential factors for fatigue life. A 3D-FE-Modelling framework including a new material model subroutine was developed; this led to a more comprehensive material model. A fractional factorial simulation with over 180 simulations was carried out and validated with the machining experiment. Based on the experimental and simulation results, a soft prediction model for surface integrity was established by using Artificial Neural Networks (ANN) approach. These predictions for SI were then used in a Genetic Algorithm model to optimise the SI. The confirmation tests showed that the machining strategy was successfully optimised and the average fatigue duration was increased by at least a factor of two. It was found that a surface speed of 270 m/min, a feed rate of 0.0589 mm/tooth, a depth of cut of 0.39 mm and a tool lead angle of 16.045° provided the good surface integrity and increased fatigue performance. Overall, these findings conclude that the fundamentals and methodology utilised have developed a further understanding between machining and forming/forging process, resulting in a good foundation for a framework to generate FE and soft prediction models which can be used to in optimisation of precision milling strategy for different materials.The machining process determines the overall quality of produced forming and forging dies, including surface integrity. Previous research found that surface integrity has a significant influence on the fatigue life of the dies. This thesis aims to establish a cost-effective approach for precision milling to obtain forming and forging dies with good surface integrity and long fatigue life. It combined experimental study accompanied by Finite Element Modelling and Artificial Intelligence soft modelling to predict and enhance forming and forging die life. Four machining parameters, namely Surface Speed, Depth of cut, Feed Rate and Tool Lead Angle, each with five levels, were investigated experimentally using Design of Experiment. An ANOVA analysis was carried out to identify the key factor for every Surface Integrity (SI) parameter and the interaction of every factor. It was found that the cutting force was mostly influenced by the tool lead angle. The residual stress and microhardness were both significantly influenced by the surface speed. However, on the surface roughness it was found that the feed rate had the most influence. After the machining experiments, four-point bending fatigue tests were carried out to evaluate the fatigue life of precision milled parts at an elevated temperature in a low cycle fatigue set-up imitated for the forming and forging production. It was found that surface roughness and hardness were the most influential factors for fatigue life. A 3D-FE-Modelling framework including a new material model subroutine was developed; this led to a more comprehensive material model. A fractional factorial simulation with over 180 simulations was carried out and validated with the machining experiment. Based on the experimental and simulation results, a soft prediction model for surface integrity was established by using Artificial Neural Networks (ANN) approach. These predictions for SI were then used in a Genetic Algorithm model to optimise the SI. The confirmation tests showed that the machining strategy was successfully optimised and the average fatigue duration was increased by at least a factor of two. It was found that a surface speed of 270 m/min, a feed rate of 0.0589 mm/tooth, a depth of cut of 0.39 mm and a tool lead angle of 16.045° provided the good surface integrity and increased fatigue performance. Overall, these findings conclude that the fundamentals and methodology utilised have developed a further understanding between machining and forming/forging process, resulting in a good foundation for a framework to generate FE and soft prediction models which can be used to in optimisation of precision milling strategy for different materials

FINISH-MACHINING STRATEGIES FOR BLADED DISKS

Integrally Bladed Rotors (IBRs) or Bladed Disks (Blisks) are strategic components of compressor or turbine stages of aircraft engines. Development of manufacturing techniques and materials have aided the integration of two components, blades and the disk, which were originally manufactured separately and then assembled. A single component brings great benefits such as weight reduction, which is key the in aerospace sector. IBR components bring new challenges to the manufacturing industry due to the difficult to cut materials used, paired with complex geometries which limit the access of tooling and limits various efficient cutting strategies for the finish milling operations. Instead, a point milling strategy is commonly used to achieve drawing specifications but at a cost of machining time. Therefore, finish milling is by far the most time-consuming machining operation of IBR blades. However, many efforts from industry are directed to optimize machining times through roughing operations, which are faster to implement internally within the manufacturing engineering department, and often are not affected by fixed process approvals that are in place for the last few millimetres of material removal. This includes approval from the materials department on surface integrity modifications of the final surface, and complex approval processes with the final clients. An EngD project is an ideal scenario for the development of finish machining strategies for the reasons explained above. This thesis takes a real IBR case study as a starting point and navigates through a logical path for the development of its blade finish milling operation to provide a novel industrial optimization strategy. The research question evolves as each chapter explores different aspects of this challenging industrial problem. Initially, in chapter 2, surface integrity is explored within the typical working window (range or map of parameters selected for a given experiment), due to the relevancy of the surface integrity in the finished component. This is explored through an experimental approach which concludes surface integrity is not affected in the analysed range. Instead, chatter is identified and research efforts are then directed to improve finish machining of IBR blades through the understanding and mitigation of chatter. Chapter 3 seeks to analyse tool and component dynamics and includes a brief search into literature about process damping to understand how it might play a role in chatter mitigation. A new research line is then investigated to improve finish milling of IBR blades. A very simple concept of modifying finish milling stock is developed, using a scientific method based on Finite Element Analysis (FEA) and parametrizing the blade in order to maximize natural frequencies of interest. Once an optimized blade stock geometry has been obtained, a further literature review is carried out on chatter mitigation techniques. A knowledge gap is found in the current literature regarding time domain model for Sinusoidal Variable Spindle Speed (SVSS) model for ball end mill tools. This is observed as an opportunity to do a theoretical contribution to the predominantly experimental EngD thesis. A current time domain model has been further developed to incorporate SVSS and ball end mill geometry. Finally, implementation of variable speed in industrial environment has been researched. A further knowledge gap is identified in the implementation of variable speed in commercial milling machines, as most research up to date has been realized either theoretically or in laboratory conditions. In response to this need, a new method has been developed to be able to implement variable spindle speed and variable feed straight forwardly in a wide range of commercial milling machines. To end up with, a machine characterisation has been completed in order to identify the working window to apply the Variable Spindle Speed (VSS) method, and experimental trials have been carried out to demonstrate the capability of this approach. This thesis starts presenting a case study of IBRs with the need to improve current finish machining strategies and delivers new solutions from various perspectives, complementing each other and readily available to implement in the industry environment