Frequency–spectrum characteristics of force in end milling with tool wear and eccentricity

The effects of chip load, tool wear, and tool eccentricity on milling force are similar; in order to distinguish them from each other, the spectral characteristics of milling force for four flute end mills was studied. With simplified milling force model, the calculation expression of instantaneous milling force under tool eccentricity was derived based on the 2D geometry of tool cutting into workpiece. Using simulation methods, the amplitude spectra of milling forces under neither wear nor eccentricity, only eccentricity, both wear and eccentricity, and the every phase spectrum of force caused only by wear of one tooth were analyzed. The analysis results showed that the basic and third harmonic amplitudes of spindle frequency were linear only with eccentric distance, the fourth harmonic amplitude was linear only with feed, the second harmonic component was in relationship only with tool wear, and harmonics with same frequency caused by wear of different teeth were in phase or out of phase. Then corresponding milling experiments were done, the relations between experimental harmonic amplitudes of force and milling parameters were analyzed, and were found being in good agreement with above simulation results. These indicate that amplitudes of these harmonics could be taken as indices in recognizing eccentricity, wear, and chip load, respectively, and their variations contain in-process information of tool wear. This study proposes a new idea of identifying tool eccentricity and wear with force itself.     

Prediction of simultaneous dynamic stability limit of time�Cvariable parameters system in thin-walled workpiece high-speed milling processes

A method for predicting simultaneous dynamic stability limit of thin-walled workpiece high-speed milling process is described. The proposed approach takes into account the variations of dynamic characteristics of workpiece with the tool position. A dedicated thin-walled workpiece representative of a typical industrial application is designed and modeled by finite element method. The curvilinear equation of modal characteristics changing with tool position is regressed. A specific dynamic stability lobe diagram is then elaborated by scanning the dynamic properties of workpiece along the machined direction throughout the machining process. The results show that, during thin-walled workpiece milling process, material removing plays an important part on the change of dynamic characteristics of system, and the stability limit curves are dynamic curves with time?Cvariable. In practical machining, some suggestion is interpreted in order to avoid the vibrations and increase the chatter free material removal rate and surface finish. Then investigations are compared and verified by high-speed milling experiments with thin-walled workpiece.     

Failure mechanisms of a PCD tool in high-speed face milling of Ti–6Al–4V alloy

High-speed milling tests were carried out on Ti–6Al–4V titanium alloy with a polycrystalline diamond (PCD) tool. Tool wear morphologies were observed and examined with a digital microscope. The main tool failure mechanisms were discussed and analyzed utilizing scanning electron microscope, and the element distribution of the failed tool surface was detected using energy dispersive spectroscopy. Results showed that tool flank wear rate increased with the increase in cutting speed. The PCD tool is suitable for machining of Ti–6Al–4V titanium alloy with a cutting speed around 250 m/min. The PCD tool exhibited relatively serious chipping and spalling at cutting speed higher than 375 m/min, within further increasing of the cutting speed the flank wear and breakage increased greatly as a result of the enhanced thermal–mechanical impacts. In addition, the PCD tool could hardly work at cutting speed of 1,000 m/min due to the catastrophic fracture of the cutting edge and intense flank wear. There was evidence of workpiece material adhesion on the tool rake face and flank face in very close proximity to the cutting edge rather than on the chipped or flaked surface, which thereby leads to the accelerating flank wear. The failure mechanisms of PCD tool in high-speed wet milling of Ti–6Al–4V titanium alloy were mainly premature breakage and synergistic interaction among adhesive wear and abrasive wear.     

Influence of milling on surface integrity of Ti6Al4V—study of the metallurgical characteristics: microstructure and microhardness

The quality of titanium alloy parts in the aeronautical field demands high reliability, which is largely related to surface integrity. Surface integrity is generally defined by three parameters: a geometric parameter, a mechanical parameter and a metallurgical parameter. The present article addresses the influence of milling on the metallurgical parameter for a surface milled in Ti6Al4V material, focusing in particular on the microstructure and microhardness. Observation of the machined surface from a macroscopic perspective highlight an orange peel phenomenon. This effect is the combined result of redeposition and crushing of the milled material. No plastically deformed layer or lengthening of the grains was observed under the milled surface. As far as microhardness is concerned, a slightly softened region was observed under the milled surface. A diffusion of vanadium from the β phase to the α phase was also noted, but with no change in microstructure.     

减振面铣刀柄Vibration damping milling cutter shank

来自山高刀具的Steadyline被动式动态减振系统能提高生产效率和降低加工成本.减振面铣刀柄可以显著提高铣刀组件的动刚度.这可以应对更高的切削条件,而且加工时更安静,稳定性更佳.主要优点包括更高的生产效率、更佳的表面粗糙度和更长的刀具和主轴使用寿命.     

减振面铣刀柄Vibration damping milling cutter shank

来自山高刀具的Steadyline被动式动态减振系统能提高生产效率和降低加工成本。减振面铣刀柄可以显著提高铣刀组件的动刚度。这可以应对更高的切削条件，而且加工时更安静，稳定性更佳。主要优点包括更高的生产效率、更佳的表面粗糙度和更长的刀具和主轴使用寿命。     

Investigation of the effect of machining parameters on the surface quality of machined brass (60/40) in CNC end milling—ANFIS modeling

Brass and brass alloys are widely employed industrial materials because of their excellent characteristics such as high corrosion resistance, non-magnetism, and good machinability. Surface quality plays a very important role in the performance of milled products, as good surface quality can significantly improve fatigue strength, corrosion resistance, or creep life. Surface roughness (Ra) is one of the most important factors for evaluating surface quality during the finishing process. The quality of surface affects the functional characteristics of the workpiece, including fatigue, corrosion, fracture resistance, and surface friction. Furthermore, surface roughness is among the most critical constraints in cutting parameter selection in manufacturing process planning. In this paper, the adaptive neuro-fuzzy inference system (ANFIS) was used to predict the surface roughness in computer numerical control (CNC) end milling. Spindle speed, feed rate, and depth of cut were the predictor variables. Experimental validation runs were conducted to validate the ANFIS model. The predicted surface roughness was compared with measured data, and the maximum prediction error for surface roughness was 6.25 %, while the average prediction error was 2.75 %.     

Influence of contact parameters on material transfer from steel to TiN coated tool – optimisation of a sliding test for simulation of material transfer in milling

Sliding between crossed cylinders, one large work material cylinder and one smaller coated tool cylinder, can be used to simulate the contact between a chip and the rake face of a cutting tool. However, accurate simulations require the mode of material transfer in the test to match that in real machining. The mode is strongly dependent on normal load and sliding speed, and it is classified into four types; negligible oxide, only iron oxide, iron oxide and alloy oxide, and metallic transfer with coating cracking. A high load proved to be the most important to accurately simulate the mode and area of material transfer occurring in milling. The diameter of the work material cylinder influences the shape of the contact mark, but has no influence on the mode of transfer. This means smaller work material diameters can favourably be used, reducing costs and facilitating handling during both tests and analysis.     

A note on “Selection of cutting parameters in side milling operation using graph theory and matrix approach”

Determination of optimal cutting parameters is one of the vital modules in process planning of parts since economy of machining operations plays an important role in increasing productivity and competitiveness. Recently, Gadakh and Shinde (Int J Adv Manuf Technol 2011) presented a graph theory and matrix approach (GTMA) and few other multiple attribute decision making (MADM) methods for selection of cutting parameters in side milling operation in their paper “Selection of cutting parameters in side milling operation using graph theory and matrix approach” Gadakh and Shinde (Int J Adv Manuf Technol DOI 10.1007/S00170-011-3256-Z, 2011). The authors had presented the experimental results of Chiang-Kao and Lu (Int J Adv Manuf Technol 34:440–447, 2007) to demonstrate the proposed methods. However, the systematic procedures of GTMA and the other MADM methods were already reported exhaustively by Rao (2007), and Gadakh and Shinde (Int J Adv Manuf Technol 2011) had reproduced the related contents. Many computational and fundamental mistakes were also present in their work. Furthermore, the authors had presented the incorrect values of metal removal rate (MRR) and these values were different from the values presented by Chiang-Kao and Lu (Int J Adv Manuf Technol 34:440–447, 2007). This note discusses these mistakes and presents the correct approaches and the results.     

Enhancement and verification of a machined surface quality for glass milling operation using CBN grinding tool—Taguchi approach

Nowadays, the demand for high product quality focuses extensive attention to the quality of machined surface. The (CNC) milling machine facilities provides a wide variety of parameters set-up, making the machining process on the glass excellent in manufacturing complicated special products compared with other machining processes. However, the application of grinding process on the CNC milling machine could be an ideal solution to improve the product quality, but adopting the right machining parameters is required. Taguchi optimization method was used to estimate optimum machining parameters with standard orthogonal array L₁₆ (4⁴) to replace the conventional trial and error method as it is time-consuming. Moreover, analyses on surface roughness and cutting force are applied which are partial determinant of the quality of surface and cutting process. These analyses are conducted using signal to noise (S/N) response analysis and the analysis of variance (Pareto ANOVA) to determine which process parameters are statistically significant. In glass milling operation, several machining parameters are considered to be significant in affecting surface roughness and cutting forces. These parameters include the lubrication pressure, spindle speed, feed rate, and depth of cut as control factors. While, the lubrication direction is considered as a noise factor in the experiments. Finally, verification tests are carried out to investigate the improvement of the optimization. The results showed an improvement of 49.02% and 26.28% in the surface roughness and cutting force performance, respectively.     

Tool fabrication system for micro/nano milling—function analysis and design of a six-axis Wire EDM machine

The dies or molds used for the fabrication of micro products usually are made of ultra-hard materials such as tungsten carbide or silicon carbide and have sophisticated three-dimensional geometries. Such kind of dies or molds can only be fabricated by milling operations instead of grinding processes with ultra-hard milling tools made of PCD or CBN. Electrical discharge machining (EDM) is a good choice for the fabrication of such ultra-hard tools. In this paper, a function analysis and design of a six-axis Wire EDM (WEDM) machine is introduced. Based on the typical micro/nano cutting tool geometry features, a mathematical model between the cutting tool and the electrode wire is built. Then, the mathematical model is analyzed and it turns out that six axes are needed for cutting such complicated tool geometries. According to the WEDM features, first the axes are allocated to the workpiece side and the electrode wire side. The workpiece is assigned three linear motions and one rotary motion around its center line and the wire has two rotary motions. Second, the axis sequences are defined. At last, the best concept of the mechanical structure for the six-axis WEDM machine is selected.     

5-axis double-flank CNC machining of spiral bevel gears via custom-shaped milling tools — Part I: Modeling and simulation

A new category of 5-axis flank computer numerically controlled (CNC) machining, called double-flank, is presented. Instead of using a predefined set of milling tools, we use the shape of the milling tool as a free parameter in our optimization-based approach and, for a given input free-form (NURBS) surface, compute a custom-shaped tool that admits highly-accurate machining. Aimed at curved narrow regions where the tool may have double tangential contact with the reference surface, like spiral bevel gears, the initial trajectory of the milling tool is estimated by fitting a ruled surface to the self-bisector of the reference surface. The shape of the tool and its motion then both undergo global optimization that seeks high approximation quality between the input free-form surface and its envelope approximation, fairness of the motion and the tool, and prevents overcutting. That is, our double-flank machining is meant for the semi-finishing stage and therefore the envelope of the motion is, by construction, penetration-free with the references surface. Our algorithm is validated by a commercial path-finding software and the prototype of the tool for a specific gear model is 3D printed.     

Research on the modeling of burr formation process in micro-ball end milling operation on Ti–6Al–4V

Burrs generated along the finished edges and surfaces in micro-milling operation have significant impact on the surface quality and operational performance of the finished parts and microstructures. In order to obtain a better recognition of burr generation process, 3-dimensional micro-ball end milling operation FEM models on Ti–6Al–4V have been established. As a result, a newfound type of burr lying on the slot base has been detected. According to their generating locations, burrs discovered in the simulation are classified into four types: entrance burr, exit burr, top burr, and slot base burr. Their formation processes, especially the generation procedure of slot base burr, are carefully investigated and analyzed. Furthermore, the correlation between cutting parameters and top burr sizes in micro-ball end milling is investigated. At last, effective validation experiments for the proposed model are conducted and good agreements are achieved in the morphologies of burrs between the experiments and simulations. It can be concluded that the adoption of a small ratio of axial depth of cut to the mill radius has a significant effect in the reduction of top burr generation in micro-ball end milling operation.     

Feed rate modeling in circular–circular interpolation discontinuity for high-speed milling

In this paper, a modeling approach is presented in order to evaluate feed rate during a circular interpolation in high-speed milling. The developed model depends on the type of discontinuity and the kinematic performance of the machine tool. To begin with, a feed rate modeling for circular interpolation with continuity in tangency is developed. After, the discontinuity in tangency between two circular interpolations is replaced by discontinuity in curvature by adding a fillet which is in relation to the functional tolerance ε imposed in the part design. An experimental study has been carried out to validate the models.     

Machinability study of high speed steel for focused ion beam (FIB) milling process – An experimental investigation at micron/nano scale

Nowadays the attention is focused on machining of non-silicon materials for miniaturized devices. High speed steel (HSS) is a non-silicon tool material, which is used in metal cutting applications as well as in micro-medical applications. Focused ion beam (FIB) milling process is highly suited for the fabrication of micro tools and other micro devices manufactured from HSS material. This study investigates the machinability aspects of HSS for FIB milling process. Beam current, extraction voltage, angle of incidence, dwell time and percentage overlap between beam diameters are the FIB process parameters, which have been analyzed experimentally to optimize FIB milling process for maximum material removal rate and minimum surface roughness. Beam current is found as the most significant parameter for controlling the material removal rate and surface roughness.     

A solid trimming method to extract cutter–workpiece engagement maps for multi-axis milling

A solid trimming method is proposed to determine cutter–workpiece engagement (CWE) maps, which are essential to investigate cutting forces, machining errors, and chatter stability in multi-axis milling. In this method, CWE maps, defined as the instantaneous contact area from the cutting flutes’ entrance to exit, are extracted by trimming the removal volume (RV) with the feasible contact surfaces. Compared to the traditional Boolean operation approach, the trimming method extracts CWE maps without the requirement of abundant surface/surface intersection operations. Moreover, instead of using the union solid model associated with all cutter locations, RV is calculated for the first time by introducing the existing concept of analytical tool swept volume, which is previously limited to tool path planning. Verification tests show that the proposed method has the advantages of high accuracy and efficiency.     

Tool trajectory generation based on tool deflection effects in the flat-end milling process (II) —Prediction and compensation of milled surface errors—

In this paper, we present the optimum reference for the compensation of tool trajectory to fulfill the imposed tolerances in flat-end milling process. First, we suggest the milled surface prediction methods considering the tool deflection effects. Based on the predicted error distributions, we propose a cutting process simulation method, which can verify (1) if the tolerance is fulfilled, and (2) if it is possible to compensate the surface errors by the proposed approaches presented in Part I, before the real milling operation begins. As the result of our research, we could make our compensation method very applicable for real industrial cases by considering the imposed manufacturing tolerances. Required experiments for practical examples were performed, and it was found that the results were in good agreement with our predictions.     

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