Machining Damage Research Articles

Vibration Suppression of a Single-Cylinder Engine by Means of Multi-objective Evolutionary Optimisation

This paper presents a new design strategy for the passive vibration suppression of a single-cylindrical engine (SCE) through multi-objective evolutionary optimisation. The vibration causes machine damages and human pain, which are unsustainable problemsthat need to be alleviated. Mathematical forced vibration analyses of a single-cylinder engine, including dynamic pressure force due to ignition combustion, are presented. A multi-objective design problem is set to find the shape and size variables of the crank and connecting rod of the engine. The objective functions consist of the minimisation of the crank and connecting rod mass, and the minimisation of vibration response while the SCE is subject to inertial force and pressure force. Moreover, design constraints include crank and rod safety. The design problem is tackled by using an adaptation of a hybrid of multi-objective population-based incremental learning and differential evolution (RPBIL-DE). The optimum results found that the proposed design strategy is a powerful tool for the vibration suppression of SCE.

Evaluation of the Continuous Wavelet Transform for Detection of Single-Point Rub in Aeroderivative Gas Turbines with Accelerometers.

A common fault in turbomachinery is rotor–casing rub. Shaft vibration, measured with proximity probes, is the most powerful indicator of rotor–stator rub. However, in machines such as aeroderivative turbines, with increasing industrial relevance in power generation, constructive reasons prevent the use of those sensors, being only acceleration signals at selected casing locations available. This implies several shortcomings in the characterization of the machinery condition, associated with a lower information content about the machine dynamics. In this work, we evaluated the performance of Continuous Wavelet Transform to isolate the accelerometer signal features that characterize rotor–casing rub in an aeroderivative turbine. The evaluation is carried out on a novel rotor model of a rotor–flexible casing system. Due to damped transients and other short-lived features that rub induces in the signals, the Continuous Wavelet Transform proves being more effective than both Fourier and Cepstrum Analysis. This creates the chance for enabling early fault diagnosis of rub before it may cause machine shutdown or damage.

High-resolution periodic mode shapes identification for wind turbines

The stability analysis of in-operation wind turbines is a very important topic, that has received considerable attention in the last years. Many identification algorithms have been developed to estimate frequencies and damping ratios, but very few papers have been dedicated to the mode shapes. The knowledge of high-resolution mode shapes could be exploited for several applications including model validation, accurate description of the vibratory content of a machine and spatially-accurate damage detection. In this work, we will present a procedure to compute the high-resolution periodic mode shapes of a wind turbine, and apply it to a high-fidelity wind turbine model. The results show that this methodology is able to identify the first low-damped modes of the system with good accuracy.

Computation of the Distribution of the Fiber-Matrix Interface Cracks in the Edge Trimming of CFRP

Edge trimming is commonly used to bring the CFRP components to right dimension and shape in aerospace industries. However, various forms of undesirable machining damage occur frequently which will significantly decrease the material performance of CFRP. The damage is difficult to predict and control due to the complicated changing laws, causing unsatisfactory machining quality of CFRP components. Since the most of damage has the same essence: the fiber-matrix interface cracks, this study aims to calculate the distribution of them in edge trimming of CFRP, thereby to obtain the effects of the machining parameters, which could be helpful to guide the optimal selection of the machining parameters in engineering. Through the orthogonal cutting experiments, the quantitative relation between the fiber-matrix interface crack depth and the fiber cutting angle, cutting depth as well as cutting speed is established. According to the analysis on material removal process on any location of the workpiece in edge trimming, the instantaneous cutting parameters are calculated, and the formation process of the fiber-matrix interface crack is revealed. Finally, the computational method for the fiber-matrix interface cracks in edge trimming of CFRP is proposed. Upon the computational results, it is found that the fiber orientations of CFRP workpieces is the most significant factor on the fiber-matrix interface cracks, which can not only change the depth of them from micrometers to millimeters, but control the distribution image of them. Other machining parameters, only influence the fiber-matrix interface cracks depth but have little effect on the distribution image.

Cross-sectional TEM study of subsurface damage in SPDT machining of germanium optics.

In addition to surface roughness and shape precision, the subsurface damage (SSD) generated by single point diamond turning (SPDT) of Ge and Si crystal optics is of increasing importance with decreasing wavelength from infrared through visible, UV, and x-ray. There are various components of SSD, e.g.,microcracks, dislocations, strain, and a near-surface amorphous layer, and there are also several techniques to evaluate various components of SSD. Cross-sectional transmission electron microscopy (XTEM) is expensive and not often directly used in the optics laboratory. However, because of its very high sensitivity to SSD and down to atomic resolution, it is often used as an external service for developing SPDT technology and other surface processing techniques. It is shown in the paper that improper sample preparation can generate near-surface amorphization. Measures to avoid this artifact and a test of reliability of XTEM sample preparation are proposed.

Analisis Penerapan Overall Equipment Effectiveness Pada Mesin Power Press Combination Forming 60T

Corrective action on the engine damage is a temporary emergency measure, so further action is required by conducting maintenance activities, prevention of damage (Preventive maintenance), and able to detect abnormal symptoms before the machine breakdown occurs. The sudden impact of machine damage resulted in disruption of planned production performance so that it is necessary to identify and analyze the factors that cause the machine damage. Establish maintenance method using Autonomous Maintenance, Preventive Maintenance and Reliability Centered Maintenance (RCM) concept to prevent machine failure from the beginning, through fault tree analysis (FTA) method, failure mode effect, and analysis (FMEA), mean time between failure (MTBF ) is an analytical activity for implementing RCM systems on machines and critical components, able to identify and detect symptoms of malfunction before the machine is damaged. The results of the research get better application of maintenance system so that identification of important components can be anticipated from the symptoms of damage. Overall, there is an increase in performance seen from the increase of Overall Equipment Effectiveness (OEE) value, still expected to continue to increase according to JIPM 85% standard value. In conclusion FMEA, FTA, MTBF analysis method can be used to build autonomous maintenance, preventive maintenance and reliability centered maintenance so as to facilitate the production and maintenance in determining the proper maintenance of the machine.

Performance Assessment Based on Reliability of Weaving M251 Machine Using Reliability, Availability & Maintainability (RAM) and Cost of Unreliability (COUR) Methods (Case Study at PT Buana Intan Gemilang)

The textile industry is one of industries that has an important role in the national economy. PT Buana Intan Gemilang (BIG) is one of textile industry in Indonesia which uses Weaving machine to produce motif and sajadah fabrics. The purpose of this research is to analyze the reliability of Weaving M251 machine that has the most damage in 2014. To avoid losses due to machine damage, the reliability, availability and maintainability of the machine need to be improved by using Reliability, Availability & Maintainability (RAM) Analysis method. In addition, the total cost caused by RAM problems can be calculated by using Cost of Unreliability (COUR) method. Based on the evaluation using Reliability Block Diagram (RBD) modeling, it is found that the critical subsystem reliability = 44.36% for 144 working hours and the total repair time that the critical subsystem needs to perform in acceptable operational condition , at least in 1 to 70 hours. There are two different forms of availability that have been calculated, therefore inherent availability = 95,546% which is used as leading indicator, and operational availability = 85,572% which used as lagging indicator. as it is compared, lagging indicator does not meet the performance of leading indicator. The total of unreliability cost when the machine is in active repair time = 39,580,689.02 IDR and within downtime = 135,588,452.13 IDR.
 Keywords—Cost of Unreliability (COUR), Lagging Indicator, Leading Indicator, Reliability, Availability & Maintainability (RAM) Analysis.

Identification and Risk Analysis of Mozarella Cheese Production Process

Mozzarella cheese is a food which is very risky to the growth of microorganisms since it has high water content by 54.1%. One way to overcome that problem is to identify and analyze the risks found in the production process of mozzarella cheese. Therefore, the researchers examined the identification and risk analysis of mozzarella cheese production process by conducting a case study in CV XYZ. The methods used were Failure Mode and Effect Analysis (FMEA) and Fault Tree Analysis (FTA). The results revealed that there were 11 risks from 8 steps of the production process. Of the 11 risks, the risks which were included in the critical risks were the risk of contamination during the curd clotting process, low-quality of milk, severe stretcher machine damage, and overly acidic cheese taste. The result of quantitative analysis of FTA indicated that the risk probability during mozzarella cheese production process was 0.110 or the risk was 11%. The probability with the highest value was the probability of contamination risk during the curd clotting process by 0.095. It indicated that contamination during the curd clotting process was the most probable risk in the future. The proposed recommendations for improvement are devising Standard Operating Procedures (SOPs) and Sanitation Standard Operating Procedures (SSOP) based on the company's condition and it should be implemented properly. Then, improving communication with suppliers is also needed so that the company will always get high quality raw materials. Keywords: Qualitative Analysis, Quantitative Analysis, Dairy Product, Failure Mode and Effect Analysis, Fault Tree Analysis

Experimental study on surface quality and machinability of Ti-6Al-4V rotated parts fabricated by low-speed wire electrical discharge turning

This paper firstly focused on analyzing the characteristics of surface damage in low-speed wire electrical discharge machining (LS-WEDM) and introducing the multiple cutting strategy into the LS-WEDT to improve the surface quality and minimize surface defects. Surface and sub-surface damages of Ti-6Al-4V (TC4) workpiece produced in LS-WEDT are discussed, which includes craters, cracks, surface alloying, surface composition, micro-hardness, and white layer. Experimental results indicated that the craters produced in LS-WEDTed surface are extended and very shallow. Although TC4 material has poor thermal conductivity, cracks can completely disappear by decreasing peak current in LS-WEDT, which differs from LS-WEDM. Comparing with LS-WEDMed surfaces, debris adhering on LS-WEDTed surface is very few due to good flushing condition and point contact discharge mechanism. The foreign elements of oxygen and copper are detected on LS-WEDTed surface, but the contents are less than LS-WEDMed surface. The micro-hardness of the heat-affected zone is much lower than substrate and the discontinuous white layer is obtained in LS-WEDT. The LS-WEDTed surface machined after finishing trim cut (FTC) is very smooth with invisible craters, and the white and heat-affected layers’ thickness are greatly reduced. Finally, practical machining is carried out via fabrication of the rotated micro-part and taper pin with diameter of 40 μm.

Analysis of Surface and Subsurface Damage Morphology in Rotary Ultrasonic Machining of BK7 Glass

This paper investigates the formation process of surface/subsurface damage in the rotary ultrasonic machining of BK7 glass. The results show that during the milling using the end face of the tool, the cutting depth and the residual height between the abrasive grains constantly change with the high-frequency vibration, generating lots of cracks on both sides of the scratches. The high-frequency vibration accelerates the chips falling from the surface, so that the chips and thermal damage are reduced, causing the grinding surface quality better. A plastic deformation area is formed during the grinding, due to the non-uniform cutting force on the material surface, and the residual stress is produced in the deformation area, inducing the median/lateral cracks.

Temperature measurement and machining damage in slotting of multidirectional CFRP laminate

ABSTRACTCompared to metallic materials, carbon fiber-reinforced plastics (CFRPs) have lower thermal conductivity and minor thermal expansion coefficient. Despite this, their machining can generate accuracy errors if the cutting temperature is not controlled. In this paper, an experimental study of slotting of multidirectional CFRP laminate (G803/914) with three micrograin carbide burr tools with different geometries is considered in order to investigate tool-workpiece contact point temperature, chip temperature, machined surface damage, subsurface defects and tool degradation. The experiment is made on a computer numerical control (CNC) machine with cutting speed ranging from 80 to 200 m/min and feed per tooth from 0.008 to 0.060 mm/rev/tooth. The data were analyzed in order to establish empirical models showing the dependence of cutting temperature on tool geometry and cutting conditions. Based on the results, it is concluded that cutting speed is the factor influencing cutting temperature the most, the heat generated during slotting is removed mainly by chips and the chip temperature is greater than the tool-workpiece contact temperature of about 18.5°C on average for the three burr tools.

Study on Machining Damage of Helical Milling for C/E Composites

Carbon fiber/epoxy resin composites (C/E composites) are wildly used in manufacture of aircraft fuselages and wings in aerospace industry, due to their excellent properties. However, hole making of C/E composites always results in machining damage, such as burr, tearing, delamination and so on. Milling tools with different shapes were used to conduct helical milling experiments on C/E composites. The influence of tool shape on machining damage was analyzed by measuring the damage area of burr, tearing and delamination. And then the feed speed, axial feed per orbital revolution and spindle speed was changed respectively to study the effect of processing parameters on machining damage. The machining damage can be reduced by choosing appropriate tool shape and processing parameters.

Performance Assessment Based on Reliability of Weaving M251 Machine Using Reliability, Availability & Maintainability (RAM) and Cost of Unreliability (COUR) Methods (Case Study at PT Buana Intan Gemilang)

The textile industry is one of industries that has an important role in the national economy. PT Buana Intan Gemilang (BIG) is one of textile industry in Indonesia which uses Weaving machine to produce motif and sajadah fabrics. The purpose of this research is to analyze the reliability of Weaving M251 machine that has the most damage in 2014. To avoid losses due to machine damage, the reliability, availability and maintainability of the machine need to be improved by using Reliability, Availability & Maintainability (RAM) Analysis method. In addition, the total cost caused by RAM problems can be calculated by using Cost of Unreliability (COUR) method. Based on the evaluation using Reliability Block Diagram (RBD) modeling, it is found that the critical subsystem reliability = 44.36% for 144 working hours and the total repair time that the critical subsystem needs to perform in acceptable operational condition , at least in 1 to 70 hours. There are two different forms of availability that have been calculated, therefore inherent availability = 95,546% which is used as leading indicator, and operational availability = 85,572% which used as lagging indicator. as it is compared, lagging indicator does not meet the performance of leading indicator. The total of unreliability cost when the machine is in active repair time = 39,580,689.02 IDR and within downtime = 135,588,452.13 IDR.

Pneumatic shaping of materials with short-term creep

Equations are derived for assessing the machining forces and damage in workpieces. The mechanical anisotropy of the initial material and the workpiece dimensions affect the stress–strain state, the flow kinematics, and the limits of pneumatic shaping with short-term creep, as here established. The mathematical models obtained and the corresponding theoretical results may be used in developing rotary-drawing technology.

Machining damage of monocrystalline silicon by specific crystallographic plane cutting of wire electrical discharge machining

The machining damage on the certain crystal face of single crystal silicon, the manufacture of which are under diverse parameters of wire electrical discharge machining (WEDM), is tested by means of the micro-observation and X-ray diffraction rocking curve method. In the process of monocrystalline silicon machined by WEDM, when the pulse width is small, the basic methods of material removal are melting and gasification, which are also called normal removal methods. When the pulse width increases to a certain degree beyond the normal removal, thermal spalling removal also occurs, which is considered a compound removal method. The depth of machining damage is difficult to control. The structure of machining damage under two conditions is divided into normal removal and compound removal in this study. To make the depth of machining damage easy to control, compound removal should be avoided when processing the single crystal silicon by certain crystal face cutting of WEDM. Such an approach can provide the premise and guarantee for the subsequent processing of single crystal silicon with certain crystal face in the future.

Effects of cutting edge radius and fiber cutting angle on the cutting-induced surface damage in machining of unidirectional CFRP composite laminates

Carbon fiber reinforced polymer composite laminates are anisotropic, inhomogeneous, and mostly prepared in laminate form before undergoing the finishing operations. The edge trimming process is considered as one of the most common finishing operations in the industrial applications. However, the laminate surface is especially prone to damage in the chip formation process, and the most common damage mode is burrs. Burrs may increase cost and production time because of additional machining; they can also damage the surface integrity. Many studies have been done to address this problem, and techniques for reducing burr size in material removal process has been the focus of the research. Nonetheless, the combined effects of the cutting edge radius and the fiber cutting angle on the burr formation have seldom been conducted, which in turn restricts to find out the mechanism of burr formation. The purpose of the present paper is to study the particular mechanism that leads to burr formation in edge trimming of CFRP laminates and investigate the effects of fiber cutting angle and cutting edge radius on burr formation. The results indicate that the burrs are prone to form in the fiber cutting angle range of 0° < χ < 90° when a large cutting edge radius of the tool is used for both milling and drilling of CFRP composites.

A novel cutting tool design to avoid surface damage in bone machining

With its anisotropic structure, bone machining occurs as shear/serrated cutting mechanisms at low values of uncut chip thickness while at high values it results in fracture cutting mechanisms which lead to significant tissues damages; hence, utilising conventional tools at high material removal rates comes with drawback on surface damages, situation that needs to be avoided. This paper reports on a novel design of a milling cutter which includes on the back of main cutting edge a succession of micro-cutting edges arranged on an Archimedes spiral that allows the limitation of surface damage. That is, by adjusting the feed rate, this tool design allows the change of the cutting mechanism as follows: (i) “shear/serrated” cutting mode: when the feed rate is smaller than a pre-established threshold, only the main cutting edges work which yields a shear/serrated cutting mechanism; (ii) combined “fracture & shear” cutting mode occurring at high feed rate caused by: the main cutting edges working in fracture cutting mechanism while the subsequent micro-cutting edges work under shear cutting mechanism, combination which leads to significant reduction of bone surface damages. This new tool concept was materialised on a solid diamond composite, characterised by excellent heat conduction and low wear rates. Cutting experiments with various values of feed rates showed that the proposed tool designed concept significantly reduced the fracture damage of bone cut surface as well as cutting temperature compared with the dimensionally equivalently conventional tool.

Fast prediction of chatter stability lobe diagram for milling process using frequency response function or modal parameters

Prediction of chatter stability is important for planning and optimization of machining process in order to improve machining efficiency and reduce machining damage. Based on the classical analytical solution of chatter stability for milling process and in-depth analysis of the impact of modal parameters on the stability lobe diagram, a straight forward procedure for fast predicting stability lobe diagram directly using modal parameters of machining system was put forward. In consideration of the fact that the modal parameters of milling system can be estimated directly from the frequency response function using single DOF modal parameter estimation method, stability lobe diagram can be plotted directly using the tool tip’s frequency response function. The machining performances of a machining center with three different cutting tools were evaluated and the corresponding optimized cutting conditions were determined. The correctness of the proposed method was validated by good agreement of the predicted stability lobe diagram with that using the classical analytical method, and simulation results show that its calculation speed had been improved by 2–3 orders of magnitude. As a result, the proposed method of plotting stability lobe diagram using frequency response function can be utilized as an effective tool to select chatter-free cutting conditions in shop floor applications.

Machinability of Continuous-Discontinuous Long Fiber Reinforced Polymer Structures

In the present paper a new material system which combines the properties of continuous and discontinuous fibers (CoDiCoFRP) is investigated. The machinability and the induced damage effects of six material variations are investigated for a milling process at various cutting speeds and feed rates with an uncoated cemented carbide tool. The resulting forces and cutting torque were measured and analyzed for each material. After the milling process, the surface layers of the specimens were analyzed to quantify damage introduced during the milling process. The results show a strong influence of the material structure on the machining forces and damage.

Comparative evaluation on milled surface quality of GFRP composites by different end mill tools

Milling is a machining process that used in the production industry to make components to mate with other component in the assembly. The GFRP materials are not generally subjected to machining unless otherwise the perfect mating is required. The extensive and expensive experimental work is necessary to evaluate the cutting process parameters for achieving the preferred machined quality. In this regard, the present work is focused on minimising the machined surface damage. Moreover, the paper presents the comparative analysis and performance of two different mill tools (one is customised the two fluted brazed carbide tipped tool and other is four fluted solid carbide tool). Subsequently, comparative evaluation of two tools was illustrated by the plotting graphs. Finally experimental results were thoroughly analysed by the scanning electron micrographs to study the cutting characteristics of machined glass fibre reinforced plastic (GFRP) composite surface.