Orthogonal Turn-milling Research Articles

Chatter Stability of Orthogonal Turn-Milling Process in Frequency and Discrete-Time Domains

Abstract As the industry seeks better quality and efficiency, multitasking machine tools are becoming increasingly popular owing to their ability to create complex parts in one setup. Turn-milling, a type of multi-axis machining, combines milling and turning processes to remove material through simultaneous rotations of the cutter and workpiece with the translational feed of the tool. While turn-milling can be advantageous for large parts made of hard-to-cut materials, it also offers challenges in terms of surface form errors and process stability. Because tool eccentricity and workpiece rotation lead to more complexity in process mechanics and dynamics, traditional milling stability models cannot predict the stability of turn-milling processes. This study presents a mathematical model based on process mechanics and dynamics by incorporating the unique characteristics of the orthogonal turn-milling process to avoid self-excited chatter vibrations. A novel approach was employed to model time-varying delays considering the simultaneous rotation of the tool and workpiece. Stability analysis of the system was performed in both the discrete-time and frequency domains. The effects of eccentricity and workpiece speed on stability diagrams were demonstrated and validated through experiments. The results show that the tool eccentricity and workpiece speed alter the engagement geometry and delay in the regeneration mechanism, respectively, leading to significant stability diagram alterations. The proposed approach offers a comprehensive framework for the stability of orthogonal turn-milling and guidance for the selection of process conditions to achieve stable cuts with enhanced productivity.

Effect of tool posture on chatter vibration in turn-milling

Turn-milling is a machining method for milling a rotating work material. It has attracted attention as a method for milling difficult-to-cut materials with high efficiency. The milling process enables lower cutting temperature and high chip disposability compared to conventional turning resulting from the interrupted cutting. In addition, turn-milling allows for a larger reduction of workpiece diameter in one tool path due to the higher degree of freedom in the cutting tool posture motion. In order to achieve high-efficiency cutting, it is important to avoid chatter vibration, which has several negative effects, including poor surface quality, machine tool damage, etc. However, few studies have focused on the chatter vibration of turn-milling, and most of those have focused on orthogonal turn-milling. The object of this study is to investigate the effect of tool posture on chatter vibration in 5-axis turn-milling. Instantaneous cutting forces were obtained based on a point cloud simulation model, in which the tool and workpiece are expressed as points, and the chatter stability of turn-milling was predicted by time domain simulation. Cutting experiments were then performed under several conditions with different tool postures, and we confirmed that the predicted chatter stability limits agreed well with the experimental results. In addition, the simulations showed that tool posture has a significant effect on the change in the contact area between the tool and workpiece, which in turn affects the occurrence of chatter vibration.

The Impact of Cutting Modes on the Output Turn-Milling Parameters for High-Speed Steel

The article describes the orthogonal turn-milling technology applied for powder high speed steels. The cutter with carbide inserts was used in the experiments. The orthogonal turn-milling model was developed to improve the surface quality by choosing optimal cutting modes based on the simulation results. The mathematical model makes it possible to predict geometric surface deviations. The impact of cutting speed, tool feed and radial depth of cut on the geometric surface parameters was identified. The results make it possible to achieve the satisfactory level of surface quality without deteriorating the machining productivity. The avenues for further research are outlined.

Cutting Forces during Inconel 718 Orthogonal Turn-Milling.

Inconel 718 is a material often used in the aerospace and marine industries due to its properties and ability to work in harsh environments. However, its machining is difficult, and therefore methods are sought to facilitate this process. One of such methods is turn-milling. This paper presents the forces during orthogonal turn-milling of the Inconel 718 alloy. In this machining, both the side and the end edge are involved in the material removal, which causes the tool to be more loaded. The forces during turn-milling can be up to 50% higher than in the case of milling, which causes damage to the tool. Tool wear during machining has a significant impact on the values of the cutting force proportional coefficients. In the case of the tested material, it is important to take it into account when creating cutting force models.

Study on the relationship between material removal rate and tool flank temperature in orthogonal turn-milling

Study on the relationship between material removal rate and tool flank temperature in orthogonal turn-milling

Mathematical modeling of cutting layer geometry and cutting force in orthogonal turn-milling

Abstract Orthogonal turn-milling is a highly efficient and precise cutting technology by combining low-speed rotation of the workpiece, high-speed rotation of the cutter, and moving the cutter along the workpiece. The technology is widely used in aeronautics and astronautics industries to cut various hard-to-machine materials. Orthogonal turn-milling involves more motions than conventional machining operations, for instance turning and milling, and therefore, it is difficult to set the optimum cutting parameters. Cutting force prediction based on cutting layer geometry can be used to optimize cutting parameters in orthogonal turn-milling. However, the cutting layer geometry in orthogonal turn-milling is not well understood. In this work, a method is proposed for assessing different types of cutting layer geometries in orthogonal turn-milling. Each geometry of cutting layer is modelled analytically, which leads to a mathematical model of the corresponding cutting force. The models are validated by cutting experiments. Finally, the cutter wear experiments validate the trends of cutting forces corresponding to the different cutting layer geometries. The present models offer a theoretical guidance for efficient machining strategies in orthogonal turn-milling.

Prediction of chatter stability for enhanced productivity in parallel orthogonal turn-milling

To increase productivity and the material removal rate, an increasing number of factories have been employing multiple tools for simultaneous cutting. Among these tools is parallel orthogonal turn-milling, which is an important parallel-processing method. However, a dynamic interaction occurs during the cutting processes due to the waviness induced on the shared cutting surface and the dynamic coupling through the machine structure, creating machining vibrations, or chatter, which affect the quality of the machined surface. Therefore, to reduce or avoid the vibration problem during the cutting process, chatter stability of parallel orthogonal turn-milling was examined in this study. Initially, a chatter mechanism model of parallel orthogonal turn-milling was designed, and the limit-critical axial depth of the cut formula was obtained. Next, the model parameters of the machine tool were obtained based on the hammer test method. A parallel orthogonal turn-milling stability lobe diagram (SLD) with tool tip runout was constructed. Finally, the experimental results were verified on a high-efficiency turn-milling machine tool. The results showed that chatter can be predicted for parallel orthogonal turn-milling and an SLD can provide a reference for the selection of machining parameters. In addition, the SLD can also guide the formulation of processing technology specifications. Our results are extremely significant for ongoing research in the field of machining methods.

Machinability of damage-tolerant titanium alloy in orthogonal turn-milling

The damage-tolerant titanium alloy TC21 is used extensively in important parts of advanced aircraft because of its high strength and durability. However, cutting TC21 entails problems, such as high cutting temperature, high tool tip stress, rapid tool wear, and difficulty guaranteeing processing quality. Orthogonal turn-milling can be used to solve these problems. In this study, the machinability of TC21 in orthogonal turn-milling is investigated experimentally to optimize the cutting parameters of orthogonal turn-milling and improve the machining efficiency, tool life, and machining quality of TC21. The mechanism of the effect of turn-milling parameters on tool life is discussed, the relationship between each parameter and tool life is analyzed, and the failure process of a TiAlN-coated tool in turn-milling is explored. Experiments are conducted on the integrity of the machined surface (surface roughness, metallographic structure, and work hardening) by turn-milling, and how the parameters influence such integrity is analyzed. Then, reasonable cutting parameters for TC21 in orthogonal turn-milling are recommended. This study provides strong guidance for exploring the machinability of difficult-to-cut-materials in orthogonal turn-milling and improves the applicability of orthogonal turn-milling for such materials.

Cutting parameter study of CFRP machining by turning and turn-milling

The use of carbon fibre reinforced plastic (CFRP) structures in rotationally symmetrical components opens up a new field of lightweight construction with great potential for reducing the mass of moving components. Due to the material anisotropy, the machining of these structures can cause component damages. In this paper, the machining results of CFRP shafts conducted by turning and orthogonal turn-milling are presented. The characteristics of the applied processes are evaluated concerning the achievable shape and surface quality of the workpiece. Furthermore, the possibilities for the machining of fits on CFRP shafts are discussed.

Chatter stability of orthogonal turn-milling analyzed by complete discretization method

Orthogonal turn-milling is a primary method of turn-milling, which is used for cutting. It is widely used for machining difficult-to-cut materials, slender rods, thin-wall rotary parts, and large rotary parts. As with turning and milling, chatter is generated by orthogonal turn-milling and affects machining productivity, machining accuracy, and tool life. Various methods are available to predict the chatter-stability lobes of orthogonal turn-milling, such as the zero-order analytical, multi-frequency solution, temporal finite-element-analysis, semi-discretization, and full-discretization methods. However, the zero-order analytical method may not be suitable for the actual conditions of orthogonal turn-milling. The multi-frequency solution, temporal finite-element analysis, and semi-discretization methods suffer from poor efficiency, and the full-discretization method involves complex iterative equations and halfway discretization. To overcome these obstacles, we propose herein a different stability model for orthogonal turn-milling. We use this model to investigate a cutting process for orthogonal turn-milling and obtain stability-lobe diagrams using the complete discretization method based on the Eulerian method. The diagrams are verified by comparing them against the experimental results for chatter. Furthermore, we simulate and analyze how feed per revolution of tools affects the cutting stability for orthogonal turn-milling. These models and results can provide theoretical guidance for maximizing the processing efficiency and surface quality of workpiece manufactured by orthogonal turn-milling.

A Novel Approach for Minimization of Tool Vibration and Surface Roughness in Orthogonal Turn Milling of Silicon Bronze Alloy

The advanced manufacturing system is aimed to produce components at right quantity, quality and cost. Turnmilling is one of the advanced machining techniques that combines turning and milling processes for high metal removal rate. In orthogonal turn milling, bottom surface of the end mill cutter removes material from the surface of a rotating workpiece. Optimization of process parameters plays an important role in machining to improve quality and productivity and reduce production cost. In the present work, an advanced teaching learning based optimization (TLBO) technique was introduced to optimize process parameters in orthogonal turn milling of Silicon Bronze. Experiments were conducted at five levels of cutting speed, feed and depth of cuts. Experimental results of surface roughness and amplitude of cutter vibration were analysed using analysis of variance. The experimental results were also used to optimize process parameters through TLBO. Experiments were also conducted using TLBO optimized process parameters and the results were compared with TLBO results. The TLBO results were found to be in good agreement with target values of the responses. Artificial neural networks were developed for the surface roughness and amplitude of cutter vibration to verify optimization.

Analytic model of process forces for orthogonal turn-milling

The manufacturing process of turn-milling offers high productivity, high geometrical flexibility, safe chip breaking and machining of twist-free surfaces. However, the achievable accuracies and surface qualities do not allow the substitution of finish grinding processes. Thereby the dynamic profile of process forces is one of the main disturbance values. This paper presents a new process model of orthogonal eccentric turn-milling without axial feed. Thus the focus lies on the analysis of the process forces and their dynamic behavior caused by the changing chip cross section area on the face cutting edge. The developed model considers single and multiple cutting edge tools and has a geometrical-empirical character. This model describes the process kinematics and the error inducing process forces in orthogonal turn-milling. Their dynamic profile can be analyzed and minimized using multiple cutting edge tools and customized pre-machining of the workpiece surface topography with the goal of creating a robust process to substitute the finish grinding process in high precision applications. Such applications include, for example, the main and pin bearing seats of crank shafts used in the automotive and truck industry or even for large ship engines. The key feature is to minimize the form deviation of the cylindricity, which results from straightness and roundness of the workpiece surface to below 10 µm for crank shafts used in the truck industry. The model is adjusted and verified by experimental tests.

Surface Quality Evaluation in Orthogonal Turn-Milling Based on Box-Counting Method for Image Fractal Dimension Estimation

Turn-milling is a relatively new cutting process combining the both advantages of turning and milling, during which the tool and the workpiece rotate simultaneously. Due to the small axial cutting force, turn-milling is especially suitable for the machining of miniature parts. Usually, the surface quality is characterized by roughness, but the size of miniature parts is difficult to meet the requirements of the sampling length, which will have a huge influence on the characterization results. This paper introduces the box-counting method for image fractal dimension estimation to evaluate the surface quality of miniature parts during orthogonal turn-milling. The fractal dimension is an independent parameter for scale, which is not influenced by the sampling length. The effect of cutting parameters on surface quality of miniature parts during turn-milling is also studied.

The Surface Roughness Modeling of End Milling on Orthogonal Turn-milling Process

The surface roughness of workpiece in turn-milling has become the research emphasis in recent years as an important evaluating factor. Based on the theoretical analysis of the residual height in orthogonal turn-milling, a roughness prediction model is established. The influences of turning speed, milling speed, radius of workpiece and axial cutting depth are discussed. It can be concluded that the ratio of turning speed and milling speed, the difference between radius of workpiece and axial cutting depth are the direct factors which affect the surface roughness.

Taguchi based optimization of process parameters in orthogonal turn milling of ASTM B139

In advanced Manufacturing system, tool condition Monitoring is one of the important activities to control process parameters for better machining. Machining parameters such as cutting speed, feed rate and depth of cut are process parameters cause changes in condition of tool in machining. The main objective of this work is to evaluate the effect of various input cutting parameters on a tool life. Orthogonal turn milling operations are carried out on vertical milling machine on ASTM B139 material and determined surface roughness of the workpiece while machining and amplitude of cutter vibrations. According to design of experiments, 16 experiments are conducted by changing the input process parameters. In this work, a new apparatus Laser Doppler Vibrometer is used to collect the amplitude of cutter vibrations dynamically in the form of signals these are analyzed by using the fast Fourier Transform analyzer and these collected data are analysed by using the Taguchi and Analysis of Variance to determine the significant parameters. The effect of individual cutting parameter on surface roughness and amplitude of cutter vibrations are calculated with the Analysis of Variance.

Modeling and Emulation of 3d Dither Stability in Orthogonal Turn-Milling

Aiming at 4-axial orthogonal turn-milling by end mill, its theoretical 3d model for stable range of dither was put forward on the basis of its cutting principle by using analytical method. Based on modal trial, the stable range leaf figure of end mill’s dither in 4-axial turn-milling with eccentricity was simulated and analyzed. The results show that besides geometrical shape of mill, material of workpiece and frequency response function of machine-tool’s structure etc that can produce dither in 4-axial turn-milling, the rotating speed of mill and cutting depth are also related to dither. In trial of 4-axial turn-milling by end mill, the results of cutting force spectrum analysis show that: cutting is stable and un-dither when frequency of cutter tooth cutting-in plays leading role in force spectrum. Dither is produced when modal frequency of system plays leading role in force spectrum, the measured value of cutting force and surface roughness are also higher than those in the condition of un-dither. Thus the theoretical model and results of emulation can predict stability of end mill’s dither in 4-axial orthogonal turn-milling with eccentricity correctly and can provide theoretical guidance for surface quality and processing efficiency of workpiece.

Analytical modeling on 3D chip formation of rotary surface in orthogonal turn-milling

Orthogonal turn-milling is a relatively new process technology, the coupling turning and milling processes together and enjoying the advantages of both. However, to the best knowledge of the authors, few studies on the chips of the orthogonal turn-milling have been reported, although the understanding of the chips is important when studying turn-milling mechanism, machining heat and tool wear. In this paper, the analytical models of 3D chips (under both centric and eccentric situations) are proposed based on the orthogonal turn-milling principle and the mathematical expressions of chip thickness and height are obtained considering both side and end cutting edges. Based on the models, numerical analysis is performed to understand the relationships between chip dimensions and cutting parameters. To verify the proposed models and numerical results, the validation experiments are conducted. The comparison shows the consistency between theoretical and experimental results in terms of chip geometries and volumes under different cutting speeds and feed rates. Some findings are presented based on this study, which might provide a theoretical foundation and reference for the orthogonal turn-milling mechanism research.

Multi-response optimization in orthogonal turn milling by analyzing tool vibration and surface roughness using response surface methodology

Turn milling is one of the machining processes used to mill circular work pieces while the work piece rotates about its own axis. Orthogonal milling is one of the turn milling processes where the bottom part of cutter removes material from the rotating work piece with high metal removal rate. In this article, tool condition was studied by analyzing surface roughness and vibration of cutter with the use of response surface methodology. According to design of experiments, 16 experiments were conducted on ASTM B139 phosphor bronze with high-speed steel end mill cutter on four-axis milling machine. The response surface methodology was used to find out significant parameters that are affecting surface roughness and amplitude of cutter vibration. A multi-response optimization technique was used to identify optimum cutting parameters for less surface roughness and amplitude of cutter vibration.

Cutting force prediction in orthogonal turn-milling by directly using engagement boundaries

Despite of the studies in the last decades, there are still some gaps in understanding of the distinctive behaviors of orthogonal turn-milling. In order to improve the performance of this new technology, deeper investigations are required. This work deals with the mechanics in non-eccentric orthogonal turn-milling. The engaged areas of both side edge and end edge are analyzed. Then, the boundary conditions used to extract them are derived. The two sets of cutting force coefficients for the side edge and end edge are calibrated based on slot milling and plunge milling, respectively. The total cutting forces are calculated as a sum of the cutting forces on both side edge and end edge. The proposed cutting force model is validated experimentally on a five-axis machine tool. In addition, comparative experiments have been conducted to investigate the effects of cutting depth and longitudinal feed rate on the cutting force in tool axis direction.

Effects of tool axis offset in turn-milling process

The orthogonal turn-milling process draws increasing attention parallel to the developments in multi-tasking machine tools. However, the effects of process parameters used in orthogonal turn-milling are not fully understood. The basic objective of this study is to describe one of the most important and unique cutting parameters which is the tool axis offset, and determine its effects on process outputs such as cutting force, surface quality and tool wear. In order to achieve this objective, the effect of the tool axis offset is defined based upon geometrical relationships which are used to develop a mechanistic force model. Surface quality including the tool axis offset effect is examined by both analytical and experimental methods. Additionally, tool wear experiments were conducted to obtain the tool life under different settings for the tool axis offset. It is found that the process outcomes such as cutting forces, surface quality and tool life can be improved by taking into account the tool axis offset in orthogonal turn-milling operation. As a valuable conclusion, the proposed models and experimental results can be used to select a proper tool axis offset value while performing orthogonal turn-milling process in order to improve the process outcome.