Machining Quality Research Articles

A novel recast layer in situ thinning method for film cooling holes in fast EDM drilling

As the main machining method of film cooling holes, fast EDM (electrical discharge machining) drilling has the defect that the thickness of a recast layer is difficult to control, which can severely affect the service life of a turbine blade on the aero engine parts. In order to reduce the thickness of a recast layer in fast EDM drilling while ensuring machining precision and efficiency, a novel recast layer in situ thinning method, which uses the precision-controlled discharge erosion and tiny energy layer-by-layer thinning strategy, is proposed. Moreover, the recast layer removal mechanism, as well as the influence of this method on fast EDM drilling are systemically investigated, thereby, the optimal combination of machining parameters with different electrode diameters of the in situ thinning method is obtained. Machining results show that with the proposed method, the maximum and average thickness of the recast layer can be well controlled within 2.5 μm and 2 μm, with the highest reduction rate of the recast layer reaching 85.39%, which greatly improves the machining quality of film cooling holes of a turbine blade.

An Exploratory Study of the Surface Integrity of Various FRP Composites in Face Milling Operation

The use of glass, carbon and hybrid /glass/carbon epoxy polymer composites is widely used in the automotive, manufacturing and aerospace sectors. Milling is a secondary production process in which the final shape of the product is produced with the desired shape and high dimensional accuracy. The objective of this study is to enhance our knowledge of the machinability properties of composite materials in the secondary manufacturing industry. In this research study, performing face milling operations with different tools on bidirectional (BD) glass, unidirectional (UD) glass, carbon/epoxy, and glass/carbon/epoxy (hybrid epoxy) polymer composites. This experimental work derives conclusions that contribute to the improvement of the milling process for better surface quality. Taguchi’s L16 Design of Experiments (DOE) and Analysis of Variance (ANOVA) are used to determine the effect of tool type, speed of spindle, rate of feed, cut depth on surface roughness and delamination factor. And it was concluded that glass/carbon hybrid epoxy polymer laminates showed improved surface quality when milled with a Poly Crystalline Diamond (PCD) tool at parametric combinations of rate of feed is 300 mm/min, speed of spindle is 1000 rpm, and cutting depth is 0.5 mm. In addition, the experimental results of the scanning electron microscope examination were also verified. And found excellent machined surface quality and least damage with the above optimal process parameter combinations.

Quality prediction and process optimization in abrasive waterjet cutting of ultra‐thick carbon fiber reinforced polymer

AbstractSurface roughness and delamination extent are key indicators for assessing the surface quality of machined carbon fiber reinforced polymer (CFRP) laminates. This study conducted an in‐depth investigation on the uncontrollable surface quality of abrasive water jet (AWJ) machining of ultra‐thick CFRP. Considering the sensitivity of the laminate structure to the jet impact angle, an optimized response surface methodology was used to analyze the effects of process parameters on surface roughness. Additionally, the differences in surface roughness on both sides of the kerf under non‐orthogonal cutting were examined. Based on these analyses, a surface roughness prediction model was developed. Furthermore, the study comprehensively analyzed the effects of material mechanical properties and process parameters on delamination damage. Using dimensional analysis, a predictive model for the maximum delamination length, considering jet energy dissipation, was established. The novelty of this research is to reveal the difference in surface quality on both sides of the kerf under non‐orthogonal cutting, and to establish prediction models for surface roughness and delamination damage based on the energy dissipation characteristics of ultra‐thick CFRP AWJ machining. This research provides essential modeling foundations for enhancing the controllability of AWJ machining quality for ultra‐thick CFRP complex components.Highlights Surface roughness and delamination damage impact AWJ use for ultra‐thick CFRP. Non‐orthogonal cutting causes surface quality differences on kerf sides. A model for kerf surface roughness at any jet impact angle was established. The delamination mechanism in internal path cutting was analyzed. The delamination length model for ultra‐thick CFRP laminates was established.

The Intelligent Monitoring Technology for Machining Thin-Walled Components: A Review

Thin-walled components are extensively utilized in the aviation, aerospace, shipping, and nuclear energy industries due to their advantages of being lightweight and easily integrated. With an increased design quality and complexity of structures, thin-walled components have rendered traditional offline machining state prediction techniques inadequate for meeting the rising demands for machining quality. In recent years, advancements in intelligent manufacturing have led to the emergence of intelligent monitoring technologies that offer new solutions for enhancing the machining quality. This review categorizes technologies into online signal collection, state recognition, and intelligent decision-making, based on the implementation processes of intelligent monitoring. It summarizes the roles and current development status of various technologies within intelligent monitoring and outlines the existing challenges associated with each technology. Finally, the review discusses the challenges and future development trends of intelligent monitoring technology.

Effect of diamond grain size on mechanical properties and cutting performance of PCD tool in milling of Cf/SiC composites

The polycrystalline diamond (PCD) tools have excellent cutting performance in machining composites. However, the tool wear mechanism of PCD tools in milling Cf/SiC composites remains unclear. There are few researches on the effect of diamond grain size on the cutting performance of PCD tools and material removal mechanism. In this paper, four PCD samples with different grain sizes were prepared under high-temperature and high-pressure condition. The microstructure, flexural strength, and cutting performance of PCD samples was tested. The wear mechanism of the tools was analyzed by observing the wear morphology of the front and rear cutting surfaces of the PCD tools. The influence of diamond grain size on the cutting performance of PCD tools was investigated in terms of tool life, surface roughness and material removal mechanism. The results indicated that the highest bending strength was found in the PCD sample with the grain size of 5 μm, as the diamond grain size increased, the bending strength of the PCD tool decreased. Tool failure was caused by fiber bundles and chip dust scratching the binder and diamond grains. In the same cutting distance, due to the difference in bonding between diamonds of different grain sizes. The 2 μm~30 μm grain size of the PCD tool wear was the slowest, 5 μm grain size of the fastest PCD tool wear. As the grain size decreased, the machined surface quality of Cf/SiC composites improved. The fiber removal mechanisms employed the gradual transition from shear removal to bending removal as the grain size increased.

Surface roughness prediction based on fusion of dynamic-static data

The surface roughness in mechanical milling is a critical indicator of machining quality. Due to the variability in the geometric structure of the workpieces and the complexity of the milling mechanisms, traditional roughness prediction methods often fail to meet the requirements of actual machining scenarios. To enhance the accuracy of surface roughness prediction during the milling process and to ensure its applicability in real-world production, this paper introduces a novel model that integrates Multi-scale Convolutional Neural Network, Stacked Bidirectional Long Short-Term Memory, and Self-Attention mechanisms (MC-SBiL-SA), which integrates dynamic current signals with static process data for roughness prediction. This model involves extracting features from dynamic signal data in various ways, then feeding these features into a BiLSTM network for training. To enable the model to learn more effective data features, an attention mechanism is introduced after the BiLSTM to assign different weights to the data features, thereby amplifying the impact of important features. Finally, the dynamic signal and static process data are combined in a shallow neural network for regression prediction. Comparative results with various baseline models demonstrate that the MC-SBiL-SA model, which fuses dynamic and static data, exhibits superior generalizability and effectiveness in predicting surface roughness.

Noise robust classification of carbide tool wear in machining mild steel using texture extraction based transfer learning approach for predictive maintenance

Acoustics based smart condition monitoring is a viable alternative to mechanical vibrations or image-capture based predictive maintenance methods. In this study, a texture analysis based transfer learning methodology was applied to classify tool wear based on the noise generated during mild steel machining. The machining acoustics were converted to spectrogram images and transfer learning was applied for their classification into high/medium/low tool wear using four pre-trained deep learning models (SqueezeNet, ResNet50, InceptionV3, GoogLeNet). Moreover, three optimizers (RMSPROP, ADAM, SGDM) were applied to each of the deep learning models to enhance classification accuracies. Primary results indicate that the InceptionV3-RMSPROP obtained the highest testing accuracy of 87.50%, followed by the SqueezeNet-RMSPROP and ResNet50-SGDM at 75.00% and 62.50% respectively. However, SqueezeNet-RMSPROP was determined to be more desirable from a practical machining quality and safety perspective, owing to its greater recall value for the highest tool wear class. The proposed acoustics-texture extraction-transfer learning approach is especially suitable for cost effective tool wear condition monitoring involving limited datasets.

Recent Patents of Thermal Error Modeling and Thermal Error Prediction of CNC Machine Tool Spindle

: With the development of machine tools to high precision and high automation, thermal error has become the key reason to hinder the improvement of thermal stability of machine tools. The spindle electrothermal error is an important factor affecting the machining accuracy of highspeed CNC machine tools. The thermal error model of a high-speed motorized spindle is established to compensate the thermal error, which can effectively improve the influence of thermal error on the machining accuracy of machine tools. The thermal displacement during the operation of motorized spindle is the main reason that affects the machining stability and precision of motorized spindle. The thermal error compensation of CNC machine tool spindle can improve the machining efficiency, the machining quality of parts and the service life of CNC machine tools. This paper summarizes the representative patents and papers on thermal error modeling and thermal error prediction in China. By summarizing a large number of patents and papers on modeling, prediction and compensation of thermal error of spindle of CNC machine tools, the modeling method is analyzed and the development trend is discussed. The improvement of thermal error modeling method of CNC machine tool spindle has an important influence on improving machining accuracy, efficiency, and stability. Therefore, in the future, there will be more and more patents for thermal error modeling of CNC machine tools and spindles.

Determination of the Minimum Uncut Chip Thickness of Ti-6Al-4V Titanium Alloy Based on Dead Metal Zone

In Ti-6Al-4V titanium alloy micro-machining, since the uncut chip thickness (UCT) is comparable to the radius of the tool cutting edge, there exists a minimum uncut chip thickness (MUCT), and when the UCT is smaller than the MUCT, the plowing effect dominates the cutting process, which seriously affects the machined surface quality and tool life. Therefore, the reliable prediction of the MUCT is of great significance. This paper used Deform to establish an orthogonal cutting simulation model, studied the effect of the dead metal zone (DMZ) on the micro-cutting material flow, determined the DMZ range, and proposed a new method for determining the MUCT based on the DMZ. Cutting experiments were conducted to verify the accuracy of the simulation model firstly by cutting force, and then confirming the accuracy of the DMZ-based MUCT determination method through chip analysis and surface quality analysis. Finally, the effects of different cutting conditions on DMZ and MUCT were further investigated using the proposed DMZ-based MUCT determination method. The results show that the MUCT of Ti-6Al-4V titanium alloy is 4.833 μm for a tool cutting edge radius of 40μm and a cutting speed of 10 m/min. The DMZ boundary can be used as the boundary of micro-cutting plastic deformation, and the ratio of MUCT to cutting edge radius, hp/rn will gradually decrease with the increase in the tool cutting edge radius and the cutting speed.

Fabrication of micro holes with confined pitting corrosion by laser and electrochemical machining: pitting corrosion formation mechanisms and protection method

Laser and electrochemical hybrid machining (LECM) combines the advantages of high efficiency of laser processing and high surface quality of electrochemical machining and has been employed to process deep micro holes with high surface quality, high precision, and efficiency. However, surface pitting corrosion occurs around the entrance of the micro holes drilled by LECM, which deteriorates their surface quality and mechanical properties. This study revealed the mechanism of surface pitting corrosion formation mechanisms during LECM by characterizing surface micromorphology, chemical composition, microstructures, and surface stress. The difference between surface pitting corrosion area during LECM and the stray current corrosion during electrochemical machining was studied. Micro solid metal particles and inner microcavities were observed in micro pits. The depth of the micro pits was greater than that obtained using electrochemical machining. It has been concluded that in LECM, the surface pitting corrosion occurred owing to the enhanced stray current corrosion and the accumulation of solidified melt particles and cavitation microbubbles in the micro pits. Coaxial gas-assisted LECM was also proposed to restrict the surface pitting corrosion area. Experiments and simulations were conducted to verify the feasibility of minimizing the corrosion area using coaxial gas. The surface pitting corrosion area has been decreased by 85.1% at a coaxial gas pressure of 0.1MPa compared with that without coaxial gas assistance. Finally, the radial cooling holes with a diameter of 1.2mm and an aspect ratio of 125:1 in turbine blades with high surface quality were fabricated. This study provides a promising method to fabricate high-aspect-ratio micro-holes with high surface quality and high efficiency.

Research status of cutting machining NiTi shape memory alloys: a comprehensive review

NiTi shape memory alloys (SMA) have garnered significant interest owing to their shape memory effect, superior corosion resistance, and biocompatibility. This paper reviewed the current research status of cutting machining for NiTi SMA, focusing on turning, milling, and drilling processes, emphasizing the influence of various cutting parameters, tool materials, and cooling methods on machining performance. The optimal turning effect under dry cutting circumstances is achieved when the cutting speed surpasses 100 m/min. The application of Minimum Quantity Lubrication (MQL) in milling, alongside the use of cold air and the optimization of parameters such as feed rate and cutting depth, could diminish cutting force and temperature, thus reducing burr formation. Cemented carbide and high-speed steel covered with TiN are the ideal materials for drilling tools, and the use of substantial cutting fluid yields superior cutting performance compared to MQL. This review concludes that, despite advancements in the study of machining NiTi shape memory alloys, further research is necessary to enhance the efficiency and quality of NiTi SMA machining, particularly with tool material selection and cooling techniques. Finally, based on the current research results, this paper proposes possible future research directions, which provides valuable theoretical guidance for the processing research of NiTi SMA.

Quality Evaluation of Effective Abrasive Grains Micro-Edge Honing Based on Trapezoidal Fuzzy Analytic Hierarchy Process and Set Pair Analysis

Studying the factors affecting machining accuracy, surface quality, and machining efficiency in the powerful honing machining process system, analyzing the basic law between various errors and machining quality, exploring the method of evaluating the quality of honing, and improving the machining quality and transmission performance of hardened gears has important engineering application value. Firstly, this paper establishes an effective abrasive grains micro-edge honing quality evaluation model, proposes a method based on the Trapezoidal Fuzzy Analytic Hierarchy Process (Tra-FAHP) and Set Pair Analysis (SPA) to comprehensively evaluate the quality of the honing process, and obtains the influence weights of each factor on the quality of honing. Secondly, the paper analyzes the influence rules of three types of abrasive grain sizes on helix error, tooth pitch error, tooth profile error, surface roughness, and honing efficiency. Finally, the correctness of the established comprehensive evaluation model of honing quality was verified with the threshold method and weights. The research results show that the model can correctly evaluate the quality of hardened gear honing and can be applied to studying the influence of abrasive grain micro-edge honing on machining characteristics.

Research progress on laser processing of carbon fiber composite materials

AbstractCarbon fiber reinforced polymer (CFRP) is a high‐performance composite material composed of carbon fibers embedded in a polymer matrix. CFRP is extensively used in various sectors such as aerospace, automotive, sports equipment, and construction due to its advantageous properties. Laser processing offers numerous advantages when working with carbon fiber‐reinforced composites, including its non‐contact nature, precision, efficiency, and controllability. However, disparities between carbon fibers and the polymer matrix can lead to challenges during laser processing, such as delamination, heat‐affected zones, and fiber pullout. Consequently, there is a substantial body of literature focusing on improving the quality and efficiency of laser processing for CFRP materials. This paper provides a comprehensive review of various studies investigating the impact of laser parameters (laser mode, pulse frequency, pulse width, and laser wavelength) on carbon fiber‐reinforced plastics. It discusses how different laser parameters affect the processing quality and performance of these materials. Additionally, drawing from recent research findings, the paper explores potential future trends in laser processing for carbon fiber‐reinforced plastics.Highlights The application of laser technology in CFRP, including laser cutting, drilling, welding, and surface treatment, has been extensively researched. A detailed discussion is held regarding the impact of laser mode, wavelength, frequency, and pulse width on the quality of machining. More auxiliary processing has evolved in CFRP manufacturing due to the ongoing advancements in laser technology. The goals of laser processing CFRP technology are increasingly focused on reducing carbon emissions, enhancing energy efficiency, and minimizing waste.

Influence of milling stability on machined surface integrity and fatigue performance of Ti-6Al-4V titanium alloy

Chatter is a deciding factor in milling operations regarding surface integrity and production efficiency. The purpose of this experimental research is to systematically investigate the influence of milling stability on machined surface integrity and fatigue performance of Ti-6Al-4V alloy samples. The surface integrity parameters like roughness, plastic deformation, microhardness, and residual stress were used to evaluate the machined surface quality. The fatigue tests were performed at five tensile stress levels with samples machined under stable, critical stable and unstable (chatter) cutting conditions. The experimental findings show that in comparison with samples produced by stable milling, the machined surface integrity parameters get worse with the increase of chatter amplitude and chatter marks, while fatigue test results show that the average fatigue life of these samples also decreases by about 20 %. The fatigue fracture morphology underscored that multiple fatigue cracks are initiated from the chatter marks on the machined surface. The experimental results provide a quantitative relation between the occurrence of chatter in milling operations and the life expectancy of the corresponding machined parts.

Cutting force reconstruction method based on static bandwidth expansion utilizing acceleration sensors

The cutting force is the most direct indicator reflecting tool wear and machining quality. However, direct cutting force measurement equipment requires high costs and will alter dynamic performance, making it difficult to apply in actual production. A single accelerometer can reconstruct the high-frequency dynamic alternating current (AC) components, but it is limited by bandwidth and cannot accurately reconstruct the low-frequency static direct current (DC) components. To address the existing problems of inaccurate reconstruction for the DC components, this article proposes a static bandwidth expansion technology (BET) using acceleration sensors with regard to its application in the field of broaching. BET reconstructs the low-frequency DC components of the broaching force using the AC components obtained from acceleration signals and the metal cutting area. The AC components of the broaching force are reconstructed from acceleration signals through double integration, combined with a Kalman filter that incorporates dynamic parameters. The complete broaching force signal can be obtained by fusing the AC and DC components. BET overcomes the problem of low-frequency bandwidth distortion in the accelerometer sensor and successfully expands the low-frequency bandwidth of the accelerometer sensor, achieving the function of reconstructing cutting force with a single accelerometer sensor. This technology is applied in the actual machining process, and the reconstructed broaching force based on BET has a high degree of coincidence with the experimentally obtained broaching force in the time-frequency domain.

Analysis and Effect of Cutting Parameters on The Surface Roughness of Type 4140 Steel in The Dry Milling Process

Currently in the world of metal cutting industry, wet machining is still carried out and machining experts continue to strive to reduce the use of coolant so that benefits can be obtained from economic, environmental and operator safety aspects. One of the criteria for determining machining quality is surface roughness. Surface roughness is influenced by machining parameters such as cutting speed, feed depth and feed rate as independent variables. The aim of the research is to obtain surface roughness values ​​for type 4140 steel workpieces due to spindle rotation speed and feed depth, which uses a carbide endmill as a cutting tool. Research activities were carried out with 9 specimens each for dry machining and wet machining using variations in machine spindle rotation of 1200 rpm, 1400 rpm and 1600 rpm with feed depths of 0.5 mm, 0.75 mm, 1 mm. Data processing uses the statics method with a normal distribution curve to obtain surface roughness data. To determine the roughness value of the machined surface, it is tested using a Surface Test measuring instrument. The surface roughness obtained from machining under optimum conditions for dry machining is 1.699 µm, 2.778 µm and 2.868 µm at a machine spindle rotation of 1600 rpm. while those carried out using wet machining obtained respective results of 1.602 µm, 2.654 µm and 2.815 µm at a machine spindle rotation of 1600 rpm. So optimum cutting/slicing is obtained at a spindle rotation speed of 1600 rpm with Ra = 1.699 µm for dry machining while for wet machining the surface roughness value Ra = 1.602 µm is obtained at a spindle rotation speed of 1600 rpm. The comparison of the results of dry machining (Ra= 1.699 µm) and wet machining (Ra= 1.602 µm) to obtain the most optimum Ra surface roughness value is not significant, so it is a good opportunity that dry machining technology can be applied to the metal cutting industry although Until now, many people still use wet machining processes using cutting fluids to cut steel meta

A Five-Axis Toolpath Corner-Smoothing Method Based on the Space of Master–Slave Movement

The smoothing of linear toolpaths plays is critical in improving machining quality and efficiency in five-axis CNC machining. Existing corner-smoothing methods often overlook the impact of spline curvature fluctuations, which may lead to acceleration variations, hindering surface quality improvements. The paper presents a five-axis toolpath corner-smoothing method based on the space of master–slave movement (SMM), aiming to minimize curvature fluctuations in five-axis machining and improve surface quality. The concept of movement space in master–slave cooperative motion is introduced, where the tool tip position and tool orientation are decoupled into a main motion trajectory and two master–slave movement space trajectories. By deriving the curvature monotony conditions of a dual Bézier spline, a G2-continuous tool tip corner-smoothing curve with minimal curvature fluctuations is constructed in real-time. Subsequently, using the SMM and the asymmetric dual Bézier spline, a high-order continuous synchronization relationship between the tool tip position and tool orientation is established. Simulation tests and machining experiments show that with our smoothing algorithm, maximum acceleration values for each axis were reduced by 21.05%, while jerk was lowered by 22.31%. These results indicate that trajectory smoothing significantly reduces mechanical vibrations and improves surface quality.

Development of an elliptic vibration mechanism for wire electrochemical micromachining

A novel flexure-based mechanism driven by two piezoelectric actuators was developed to generate elliptic vibration at the tool cathode in the wire electrochemical micromachining, which presented higher machining quality. The flexure-based mechanism adopted lever type and half bridge-type amplification mechanisms to enlarge the output of the piezoelectric actuator, the cathode wire was installed on the vibration platform through a 3D-printed insulating clamp. In order to predict the output property of the elliptic vibration mechanism, the theoretical analysis including output stiffness, kinematic modelling, and finite element analysis were implemented. A semi-closed loop controller based on the strain measurement of piezoelectric actuators was established to improve the output precision. The experimental setup of the elliptic vibration mechanism was constructed to examine the correctness of the stiffness and kinematic models, the elliptic vibration trajectory was successfully generated on the cathode wire. Furthermore, the elliptic vibration mechanism was used in the wire electrochemical micromachining, the experimental results indicated that the elliptic vibration of the cathode wire effectively improved the machining quality.

Controlling harmful milling vibration for robotic milling system based on the optimization of milling posture and spindle speed

Harmful machining vibration including milling chatter and resonance are easily generated during robotic milling process, and it seriously restrict the machining ability of the robot. To address this problem, a harmful machining vibration-controlled method based on the combined optimization of milling posture and spindle speed is proposed for robotic milling system in this paper. With this context, firstly, the robot stiffness model is established based on the theory of the multi-body with small-deformation, and the stiffness ellipsoid at the tool cutting point is used to optimize the milling posture, so that the structure stiffness of the robot can be enhanced; Then, the robot chatter stability model is constructed considering the modal coupling effect, and the spindle speed is optimized to restrain the milling chatter and resonance. Finally, with the optimized milling posture and spindle speed, the milling process is planned and performed with a Staubli TX-200 robot, and two experiments for workpiece with steel and aluminum are implemented to verify the proposed method. The experiment results demonstrate that the comprehensive optimization of milling posture and spindle speed can efficiently control the harmful machining vibration for the robotic milling system, thus, the machining quality of the workpiece can be improved.

Optimization of a Redundant Freedom Machining Toolpath for Scroll Profile Machining

The scroll disc is a critical functional component of the scroll compression mechanism, and its machining precision and quality directly impact the performance and longevity of the compressor. Current machining methods for scroll profiles face challenges in simultaneously achieving wide applicability, high precision, and high efficiency. This paper addresses issues related to unsmooth toolpaths of machine tool axes and high acceleration in the rotary axis during redundant degrees of freedom scroll profile machining. This paper proposes a toolpath optimization method for redundant axes, with optimization objectives focused on reducing the counts of directional changes in the linear axes and smoothing the trajectories of all axes. Experimental results demonstrate that the proposed method offers higher machining efficiency compared to traditional polar coordinate machining.