Previous studies only reported that the material piling up effect will occur in the cutting processes with relatively small feed rates, and even in this case, there is no further theoretical report ...to touch its generation mechanism. In this work, it is the first time to experimentally report that obvious material spreading phenomenon together with the material piling up effect appears in the cutting process, whose uncut chip thickness is less than the minimum uncut chip thickness (MUCT). It is found that one part of the material to be cut will be piled up in front of the cutter’s rake face. Meanwhile, the remained part flows into the cutter’s clearance face, followed by further compression. As a result, the cutting tooth actually does not remove the material, but rolls the material by its rounded edge. Just because of this rolling effect, the flowed material is deformed and spread along the width direction of the workpiece surface, and this spreading behaviour leads to that the width of the machined workpiece is larger than its initial value. The spread width of the workpiece is quantitatively characterized by using Tselikov’s theory, which is widely used to capture the rolling behaviour. The volume of the material piled up in front of the cutter’s rake surface is calculated by subtracting the volume of the spread material, which is calculated based on the spread width, from the volume of the initial material to be cut according to the volume invariance principle. Subsequently, the height of the piled up material is calculated by geometrically modelling the piling up area as a triangle region. Based on the above analyses, the material spreading and piling up mechanisms in cutting are theoretically explored. The validity of the theoretically calculated spread width and piling up height is verified by the numerical results obtained from finite element simulations. Finally, a cutting force model that can characterize the influences of spreading and piling up effects is established. Several cutting experiments, including both the micro and conventional milling tests, confirm that the proposed methods can give better prediction accuracy of the cutting forces, especially when the ratio of feed rate to the radius of the rounded cutting edge is small.
•The cutting width spreading and piling up effects are observed and theoretically modelled.•The influence of the piling up effect on cutting force is studied in detail.•The simulated and predicted spread width and piling up height have good agreements.•The proposed method can achieve better force prediction accuracy for small feed.
•Reduction of forces and improvement of efficiency during finish ball end milling.•Multi-criteria optimisation in terms of cutting forces and efficiency.•Relations between ball end milling process ...efficiency and surface inclination angle.•Optimised forces and process efficiency achieved for vc=375m/min and α=15°.
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=375m/min and surface inclination angle α=15°.
Despite the growth of composites and other lightweight materials, aluminium alloys remain an attractive choice of the aerospace industry due to their mature manufacturing processes, good resistance ...to fatigue crack growth and superior damage tolerance. In the aerospace industry, the drilling process is the most challenging among all the other machining process as millions of holes are required for producing riveted and bolted joints in the assembly operation of the aircraft's structures. The major challenges which arise from the drilling of these alloys are characterized by the poor hole quality which might initiate cracks within the airframe structure and reduces their reliability. This results in the rejection of parts at the assembly stage which directly impacts the manufacturing cost. Hence, appropriate selection of tool geometry, tool material and coatings, optimal cutting speed and feed rate, as well as drilling machines, is required to meet the requirement of machined parts. This motivates both academia and industries to further research on the application of drilling operations in the aircraft industry. This review aims to document details on drilling forces, drilling parameters, drill tool geometry, drill materials and coatings, chips formation, analysis of tool wear and hole metrics such as the hole size and circularity error, surface roughness, and burrs formation during the drilling of different aluminium alloys used in the aerospace industry. The focus will be mainly on Al2024 and Al7075 alloys since they are most commonly used and reported in the open literature.
Vibration-assisted machining (VAM) is implemented in titanium alloy processing to solve some challenges, such as difficulty in chip breaking, large cutting forces, and high cutting temperatures. ...Based on the multi-region dynamic angles and the double-side wedge angle deformation mechanism, this study improves the vibration-assisted drilling (VAD) cutting forces and chip breaking model. The dynamic kinematics angles, the behavior of parameter influence, and the cutting strain effect of intermittent VAM are analyzed. VAD and conventional drilling (CD) experiments are carried out for model validation and mechanism analysis. The experiments show that the maximum deviation of the drilling forces simulation value and the experimental value is 9.13 %. Compared with the CD, the cutting force of the VAD is decreased by 10.1 %–46.2 %. The dynamic feed angle causes multiple cutting angles fluctuations, which affects cutting performance. The adjustment of the VAD cutting parameter value could reduce the chip length by 26.6 %–43.9 %. Material cutting strain presents multi-region characteristic, which influences the chip morphology. This study provides a reference for VAM parameter optimization.
•An improved integrated PF-LSTM identification methodology is proposed to predict stochastic tool wear values of micro milling.•The proposed identification method bridges the gap between the ...in-process stochastic tool wear progression and historical measured data.•On account of the acquired in-process tool wear, the cutting force model is modified in ploughing- and shearing-dominant regimes.•The process nonlinearities are combined with the in-process stochastic tool wear values to estimate the instantaneous uncut chip thickness.
Micro milling aims to manufacture miniature structures with high quality and complex features, and the stochastic time-varying tool wear is a crucial factor which has great influence on machining quality and efficiency of micro milling process. To improve the precision of machining and sustainability of micro cutting tools, the in-process tool wear conditions should be identified and updated ahead of time. In this work, an improved integrated estimation method is proposed based on the long short-term memory (LSTM) network and particle filter (PF) algorithm to predict the stochastic tool wear values. The integrated PF-LSTM identification methodology is developed to predict the in-process stochastic tool wear progression on the basis of the historical measurement data. With the estimation of in-process stochastic tool wear, the cutting force model is modified, in which the influence of tool run-out and the trochoidal trajectory of cutting edge are also considered. The proposed integrated estimation method of in-process stochastic tool wear and the modified cutting force model were validated by the micro milling experiments with workpiece material Al6061. It can be seen from the comparison results that the availability and sustainability of micro cutting tool have been improved, and the prediction accuracy also could be increased by 3.4% compared with that without considering the influence of tool wear.
Turn-milling operations are machining processes that couple the rotational movement of the workpiece while conventional milling is carried out. This technology is an interesting alternative for ...machining large work diameters or massive eccentric parts as in the large format or aeronautic industries. Adding a rotational movement to the workpiece presents several advantages, but it is difficult to set the cutting parameters in the optimum operation window. The literature describes some approaches to predict the cutting forces based on the uncut chip geometry however, the effect of the cutting parameters is not well understood. This research presents a new approach to predict the instantaneous uncut chip geometry in orthogonal centric turn-milling operations based on the boundary lines of the uncut geometry. The accurate prediction of this geometry is fundamental to understanding the process mechanics, the cutting force and the machining temperature predictions. The presented models are able to predict the uncut chip geometry in large and small depth of cut regimens and were used to predict the cutting forces in several scenarios. The force predictions were validated with experimental data, demonstrating a good correlation with experimental data and overall error of around 15%. The findings presented in this research therefore could provide theoretical foundation for efficient machining strategies in the orthogonal centric turn-milling operations.
•Approach to calculate the uncut chip in orthogonal turn-milling operations.•Two operative regimens were detected “large and small”.•Models to predict the uncut chip were developed for both regimens.•Cutting force predictions from uncut chip models and mechanistic methodology.
Acetabular cartilage reaming is one of the significant procedures for guaranteeing artificial hip joint reconstruction quality in total hip arthroplasty. However, reaming issues like reamer slippage, ...deformation, cartilage damage and thermal necrosis are still persistent for lacking understanding of cartilage cutting mechanics. In this work, two-dimensional orthogonal cutting experiments of acetabular cartilage were conducted to investigate the effect of cartilage material, tool geometry and process parameters on cutting forces. The results show that cutting forces are closely related to the structural characteristic of cartilage, and cutting forces increase with cutting depth and cutting position in the thickness direction. Cutting speed has little effect on cutting forces when cutting depth is small and cutting forces increase with cutting speed when cutting depth is large. Cutting forces decrease with rake angle and increase with corner radius and have no significant change with clearance angle. ANOVA shows that forces are more sensitive to cutting depth and rake angle than to cutting speed. These results can deepen the understanding of the mechanics of the cartilage cutting process and assist the development of innovative cutting devices.
Titanium alloys (Ti) are widely used in a number of industry sectors due to their outstanding physical and mechanical properties. However, these properties result in high cutting forces and ...temperatures during the machining process, which deteriorates the machinability of titanium alloys. Recently, additive manufacturing (AM) technologies have been used to fabricate Ti parts with complex contours. These AMed parts, although being near-net shape, require finish machining operation due to poor surface integrity. This paper presents a comprehensive state-of-the-art review on the machinability of titanium alloys fabricated by various AM techniques, in the light of investigations carried out to understand the cutting forces, surface finish and tool wear when machining/micro-machining AMed Ti. Moreover, the influence of cooling/lubrication methods and material properties of the AMed parts was also analyzed. From this review, it was found that the improvement in the mechanical properties of the AMed Ti led to larger cutting forces and higher temperatures, which significantly affected the tool wear and surface quality after the finish machining post-processing operations. Nonetheless, there is very limited literature that reports on significantly improving the machinability of AMed Ti components, which requires significant research attention in future studies.
•A milling cutter system with embedded thin film sensors in each inserts is proposed.•A dedicated milling force decoupling model is proposed and calibrated.•Cutting forces on each insert can be ...monitored without reducing system stiffness.•For the first time online estimation of separate inserts’ working condition is achieved.
Among all the monitoring data which could be captured in a machining process, the cutting forces could convey key knowledge on the conditions of the process. When the machining involves a single cutting edge the relationship between the output forces (measured with off-the-shelf dynamometers) and condition of the process, is somehow straight forward. However, when multiple cutting edges are in contact with the workpiece, the conventional dynamometers, that cannot separate the reaction forces on each cutting edge, lose significant information that could be used to in-detail monitor the machining process. To this end, this paper presents a novel concept of instrumented wireless milling cutter system with embedded thin film sensors in each cutting inserts, thus the cutting forces acting on each cutting edge could be monitored without reducing the stiffness and dynamic characteristics of the machining system. For this to happen, a dedicated milling force decoupling model for the developed instrumented milling cutter system is proposed and calibrated, and for the first time the accurate on-line estimation of the separate inserts’ working conditions is achieved. The validation demonstrates a satisfactory agreement between the forces measured from the dynamometer and the proposed monitoring system prototype with the error less than 10%. Furthermore, the experimental results also indicate that the monitoring system prototype could also identify the tool insert conditions such as worn and chipped, which could be of high relevance to the analysis of the insert failure mechanism and its progress. Not only the proposed method and easy implementable but above all, it allows the monitoring of the condition (e.g. worn, chipped) of each insert, ability that has not been previously reported.
Cutting force detection can contribute to predicting the productivity and quality of end milling operations. Instantaneous cutting force prediction of digital twins in end milling operations should ...be near real-time and accurate. This paper proposes an image-based approach that can contain more useful information due to a higher dimension and simplify the complexity of computing geometric data. The cutter frame image (CFI) is utilized as one of the inputs of a convolutional neural network (CNN) to predict instantaneous cutting forces. Considering the convenience of capturing massive data, the approach uses cutting forces generated from a mechanistic force model instead of experimental cutting forces to train the CNN. The correlation coefficient
R
2
value between predicted results and simulated results is 0.9999 and the average time cost per image is 0.057 s in a cutting condition, which validates the possibility to use the image-based method to predict instantaneous cutting forces accurately and efficiently in the digital twin.
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