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•surface roughness model for cylindrical milling depending on cutter’s displacements.•model of cutter’s displacements depending on run out and deflections.•surface formation mechanism ...affected by feed per tooth and tool displacement.•contribution of tool’s displacement envelope in machined surface formation.
In this work a new approach to surface roughness parameters estimation during finish cylindrical end milling is presented. The proposed model includes the influence of cutting parameters, the tool’s static run out and dynamic phenomena related to instantaneous tool deflections. The modeling procedure consists of two parts. In the first stage, tool working part instantaneous displacements are estimated using an analytical model which considers tool dynamic deflections and static errors of the machine – tool-holder – tool system. The obtained height of the tool’s displacement envelope is then applied in the second stage to the calculation of surface roughness parameters. These calculations assume that in the cylindrical milling process, two different mechanisms of surface profile formation exist. Which mechanism is present is dependent on the feed per tooth and the maximum height of the tool’s displacement envelope. The developed model is validated during cylindrical milling of hardened hot-work tool steel 55NiCrMoV6 using a stylus profiler and scanning laser vibrometer over a range of cutting parameters. The surface roughness values predicted by the developed model are in good agreement with measured values. It is found that the employment of a model which includes only the effect of static displacements gives an inferior estimation of surface roughness compared to the model incorporating dynamic tool deflections.
Fixtures are a critical element in machining operations as they are the interface between the part and the machine. These components are responsible for the precise part location on the machine table ...and for the proper dynamic stability maintenance during the manufacturing operations. Although these two features are deeply related, they are usually studied separately. On the one hand, diverse adaptable solutions have been developed for the clamping of different variable geometries. Parallelly, the stability of the part has been long studied to reduce the forced vibration and the chatter effects, especially on thin parts machining operations typically performed in the aeronautic field, such as the skin panels milling. The present work proposes a commitment between both features by the presentation of an innovative vacuum fixture based on the use of a vulcanized rubber layer. This solution presents high flexibility as it can be adapted to different geometries while providing a proper damping capacity due to the viscoelastic and elastoplastic behaviour of these compounds. Moreover, the sealing properties of these elastomers provide the perfect combination to transform a rubber layer into a flexible vacuum table. Therefore, in order to validate the suitability of this fixture, a test bench is manufactured and tested under uniaxial compression loads and under real finish milling conditions over AA2024 part samples. Finally, a roughness model is proposed and analysed in order to characterize the part vibration sources.
The paper presents the results of a study investigating the roughness parameters Rq, Rt, Rv, and Rp of finished-milled magnesium alloys AZ91D and AZ31B. Carbide end mills with varying edge helix ...angles were used in the study. Statistical analysis was additionally performed for selected machining conditions. In addition, modelling of selected roughness parameters on the end face for the AZ91D alloy was carried out using artificial neural networks. Results have shown that the tool with λs = 20° is more suitable for the finish milling of magnesium alloys because its use leads to a significant reduction in surface roughness parameters with increased cutting speed. Increased feed per tooth leads to increased surface roughness parameters. Both radial and axial depth of cut has an insignificant effect on surface roughness parameters. It has been proven that finish milling is an effective finishing treatment for magnesium alloys. In addition, it was shown that artificial neural networks are a good tool for the prediction of selected surface roughness parameters after finishing milling of the magnesium alloy AZ91D.
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•A Lanchester damper was realised as a free weight within a thin-walled shell.•Air was used as the internal viscous media to simplify damper fabrication.•A tuning strategy is proposed ...to achieve a wide operating range.•A set of dampers with various masses and fixed tuning are proposed for end user.•Chatter is avoided at first trial without calculations, measurements, or tuning.
This paper proposes a simple damper consisting of a cylindrical weight moving freely within a thin-walled shell to eliminate flexible workpiece vibrations during finish milling. Owing to the air viscosity, the appropriate gap between the weight and shell provides intensive energy dissipation. A theoretical model and a rational damper tuning strategy are presented to provide sufficient efficiency for a wide operating range. Impact and cutting tests confirmed the predicted efficiency, which was higher than that of a particle damper. Increase of workpiece chatter stability by 45 times was obtained. A set of dampers with various masses is designed as an end user product. Examples of industrial applications are presented.
Ti6A14V is a well-known 'Difficult to Cut' material in the aerospace industry. Ti6Al4V shows strain hardening, poor thermal conductivity and chemical reactivity at elevated temperatures, which ...implies low machinability. This work presents an experimental investigation of 3D finish milling of Ti6Al4V material by Taguchi design of experiments, having L25 array. The considered process parameters are cutting speed, feed, depth of cut, tool type, coolant type and computer aided manufacturing strategy. The experimentation is conducted on the 3D finish milling process, and the performance in terms of tool life, tool wear and surface integrity were recorded. The fuzzy technique for order of preference by similarity to ideal solution, a multiple-criteria decision-making tool, was applied on experimental responses. The yielded optimum results are derived at minimum cutting speed, moderate depth of cut, feed rate per tooth and collaboration under high concentrated wet lubrication using a PVD-TiAlN cutting tool driven by streamline computer aided manufacturing strategy. In addition, analysis of variance confirms the influential process parameter contribution on the respective performance. Finally, optimised process parameters were applied for the gear bracket finish milling through streamline CAM strategy, which results in minimum flank and crater wear with an average surface roughness of 0.17 microns.
In five-axis milling, determining the continuously changing Cutter Workpiece Engagement (CWE) remains a challenge. Solid models and discrete models are the most common methods used to predict the ...engagement region. However, both methods suffer from long computation times. This paper presents an analytical method to define the CWE for toroidal and flat-end cutters during semi-finish milling of sculptured parts. The staircase workpiece model that resulted from rough milling was used to verify the method. The length of each cut at every engagement angle can be determined by finding two points: the lower engagement (LE) point and the upper engagement (UE) point. An extension of the method used to calculate the grazing point in swept envelope development was utilized to define the LE-point. The test showed that the existence of an inclination angle significantly affected the location of the LE-point.
For the UE-point, it was first assumed that the workpiece surface was flat. A recalculation of the CWE was then performed to obtain a more accurate engagement profile with the actual surface. A technique called the Toroidal-boundary method was employed to obtain the UE-point when it was located on the toroidal side of the cutting tool. Alternatively, a method called the Cylindrical-boundary method was used to calculate the UE-point for a flat-end cutter on the cylindrical side of the toroidal cutter. The proposed model was successfully used to generate CWE data for two model parts with different surface profiles. The accuracy was verified twice: first, by comparing the coordinates of the UE-points with respect to the workpiece surface and second, by using Siemens-NX. The results proved that the proposed method was accurate. Moreover, because this method is analytical, it is more efficient in terms of computation time compared with discrete models.
•An analytical method for Cutter-Workpiece Engagement (CWE) calculation in five-axis milling is proposed.•Two types of cutters: flat-end and toroidal cutters are covered in this research.•The method is applicable for semi-finish milling.•Straight (Flat)—staircase sculptured surfaces as a result of three-axis rough milling are used as a reference surface for CWE.•Various tool inclination angles and scheduled feedrate are tested to see the influence on the CWE (cut area).
To achieve higher accuracy in the prediction of cutting forces in finish milling process of sculptured parts, the curvatures of in-process workpiece surface are necessary to be taken into ...consideration in the calculation of cutter-workpiece engagement boundaries. These curvatures, however, are not readily available in tool path data, as the main existing source of geometrical information of the process. In this paper, first, a new straightforward algorithm is proposed to extract the principal curvatures and principal directions of the in-process workpiece surface from ball-end finish milling tool path data. These quantities, then, are employed to calculate the boundaries of engagement between the tool and workpiece geometries. In the next step, the cutting forces acting on a helical ball-end tool are formulated utilizing mechanistic approach and with the inclusion of radial run-out effect. By minimizing the square error between the predicted and experimentally measured cutting forces, the cutting force coefficients and radial run-out parameters are identified. Finally, the validity of the proposed force model is demonstrated by comparing the simulated forces with experimental measurements. The performed simulations show that the model can well capture the variation of milling forces along curved tool paths resulting from the variation of surface curvatures. Furthermore, it is shown that depending on the machining tolerance used in the tool path generation step, saw-tooth-like fluctuations may appear in the time history of milling forces originating from the approximation of curved paths by single steps (straight lines). All of the geometrical input parameters of the proposed force model are extracted from tool path data and hence it is quite flexible to be integrated into process modeling/optimization systems.
Thin floor machining is a challenging and demanding issue, due to vibrations that create poor surface quality. Several technologies have been developed to overcome this problem. Ad hoc fixtures for a ...given part geometry lead to meeting quality tolerances, but since they lack flexibility, they are expensive and not suitable for low manufacturing batches. On the contrary, flexible fixtures consisting of vacuum cups adaptable to a diversity of part geometries may not totally avoid vibrations, which greatly limits its use. The present study analyses the feasibility of thin floor milling in terms of vibration and roughness, in the cases where milling is conducted without back support, a usual situation when flexible fixtures are employed, so as to define the conditions for a stable milling in them and thus avoid the use of ad hoc fixtures. For that purpose, the change of modal parameters due to material removal and its influence on chatter appearance have been studied, by means of stability lobe diagrams and Fourier Transform analysis. Additionally, the relationship between surface roughness and chatter frequency, tooth passing frequency, and spindle frequency have been studied. Ploughing effect has also been observed during milling, and the factors that lead to the appearance of this undesirable effect have been analyzed, in order to avoid it. It has been proven that finish milling of thin floors without support in the axial direction of the mill can meet aeronautic tolerances and requirements, providing that proper cutting conditions and machining zones are selected.
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