Pitch End Mills Research Articles

Key structure design and vibration reduction performance analysis of four-tooth unequal pitch end mill based on spectral characteristics

The unequal pitch end mill can effectively suppress the vibration in the cutting process, and it is widely used in the processing of key parts. In this article, the four-tooth unequal pitch end mill is taken as the research object. Combined with the actual working conditions, the key structural parameters and process parameters are optimized from the perspective of spectrum energy distribution and processing efficiency, and the vibration reduction performance of the tool is analyzed and verified. First, the influence of process parameters, inter-tooth angle and helix angle of unequal pitch milling cutter on spectrum amplitude is analyzed. Second, for the milling aluminum alloy AL7075-T6, the most significant parameters affecting the vibration reduction performance of the milling cutter-tooth angle and helix angle and the matching process parameters were optimized. Finally, in order to explore the milling performance of unequal pitch end mills, experiments were carried out on equal pitch and unequal pitch end mills under the same process parameters. The gap between the two tools in milling force and milling vibration was analyzed, and the superiority of unequal pitch end mills in improving milling stability was verified.

Research on design and milling performance of unequal gradient helix and variable pitch end mill

It is difficult to obtain excellent surface quality and dimensional accuracy of the low-rigidity frame and beam parts made by titanium alloy, due to the obvious vibration and large elastic deformation during side milling. The variable helix and pitch cutting tool is usually used to reduce vibration, which does not consider the unequable stiffness in the milling area. Therefore, the concept of Unequal Gradient Helix and Variable Pitch (UGHVP) is proposed in this research. The helix angles of the UGHVP vary with the stiffness of the milling area position, which will lead to milling forces and vibration decreasing as the stiffness weakens. As a result, the surface quality and dimensional accuracy will be increased, of which the advantages are analyzed. The mathematical models of the UGHVP circumferential cutting edges and groove sections are derived, which provide theoretical support for tool grinding. The models are visualized by numerical simulation. Finally, the comparison experiment with the conventional variable helix and pitch end mill was completed by side-milling the designed feature samples. The results showed that the milling forces perpendicular to the milling surface by the UGHVP were smaller and less fluctuating, which could obtain less elastic deformation theoretically. The milling vibration was smoother, especially when cutting in and out. Besides, the larger the axial depth of cut, the more obvious the superior performance of the UGHVP tool. Better surface quality and dimensional accuracy were obtained, which proved the excellent performance of the UGHVP.

Analytical prediction of chatter stability with the effect of multiple delays for variable pitch end mills and optimization of pitch parameters

Analytical prediction of chatter stability with the effect of multiple delays for variable pitch end mills and optimization of pitch parameters

Rapid stability analysis of variable pitch and helix end mills using a non-iterative multi-frequency solution

Variable pitch and helix end mills disturb the regeneration mechanism that causes chatter vibrations, and as such, they enable stable, high-performance, and high material removal rate milling processes. The regeneration mechanism is altered by the non-uniform tool geometry that results in multiple or distributed delays between vibrations imprinted on the machined surface. The design procedure for these cutters needs characterization of the stability diagrams to decide the non-uniform geometry that improves the absolute minimum stable depth of cut as well as the changes in the size and location of stability pockets. This paper presents a unified method to rapidly analyze the stability of variable helix and pitch cutters with multiple or distributed delays using a non-iterative multi-frequency domain approach that uses the Nyquist criterion to check stability at every spindle speed and depth of cut tuple. Predictions are benchmarked with the established and widely used semi-discretization method and verified with previously published experimental data, which are further validated by our own experiments. The proposed method is as accurate as of the established one while offering computational savings of up to 94%. Since explorations of alternate and better designs were potentially precluded by the computational inefficiency of previous methods, and since the method proposed herein is fast and accurate, it can help to accelerate the design of improved variable helix and pitch end mills for their use in industrial settings.

Analysis of vibration reduction mechanism for variable pitch end mills

Analysis of vibration reduction mechanism for variable pitch end mills

Influence of Wear and Tool Geometry on the Chatter, Cutting Force, and Surface Integrity of TB6 Titanium Alloy with Solid Carbide Cutters of Different Geometry

In this paper, vibration-free milling cutters (variable helix (VH) and variable pitch (VP) end mills) and standard (SD) end mills are used to machine TB6 (Ti-10V-2Fe-3Al) titanium alloy in order to study the influence of wear and geometric structure parameters of milling cutters on chatter, cutting force and surface integrity of machined surfaces. The results of the tests show that the wear of milling cutters has a significant influence on the chatter, cutting force, roughness, residual stress, and microhardness. Geometric structure parameters of milling cutters also have a clear impact on both chatter and cutting force. Also, chatter and cutting force have significant effects on roughness and residual stress, which are in turn affected by tool geometric structure parameters, separately.

Chatter Behavior in the Milling Process of Inconel 718: Effects of Tool Edge Radius

Inconel 718 is widely used in various high end industries such as aerospace, nuclear plant, petrochemical plants etc. Inconel 718 is used for these applications due to unique mechanical properties such as high mechanical strength at elevated temperatures, high resistance to corrosion, and high strength to weight ratio. The unique properties of Inconel 718 made it difficult to be machined due to rapid work hardening and high cutting temperature. In addition, chatter vibration further increases the difficulty in machining of Inconel 718. In this paper, an experimental study on the effects of tool edge radius to the chatter behaviour was investigated. The dynamic responses of the milling process were recorded and analysed in both time domain and frequency domain. The results showed the variable helix and pitch end mill tool with larger tool edge radius able to mitigate chatter vibration at lower cutting speeds. Variable helix and pitch end mill with specific tool edge radius able to mitigate chatter vibration under the same cutting parameters. Experiments shows proper selection of tool edge radius improves the stability of end milling machining process.

Design of irregular pitch end mills to attain robust suppression of regenerative chatter

Abstract This paper presents a design method of irregular pitch end mills, which ensures robust suppression of total regeneration in milling. Firstly, general formulation of irregular pitch angles is explained for simultaneous suppression of multi-mode regenerations. An index named “Regeneration Factor ( RF )” is introduced to quantify regenerative effect. Minimizing the mean value of the | RF | within a certain frequency range, suppression frequencies are distributed in the proposed method, resulting in robust suppression of regeneration regardless of chatter frequency and/or spindle speed variations. Experimental investigations verified significant robustness of the end mill with the proposed design against the spindle speed variation.

Surface plastic deformation and surface topography prediction in peripheral milling with variable pitch end mill

Peripheral milling with variable pitch end mills is available to improve the surface integrity during final machining. Among the indicators of surface integrity, surface plastic deformation and surface topography are the foremost characteristics. In this paper, two main aspects are included. On the one hand, a unique generic technique in terms of depth of plastic deformation, plastic strains distribution for analyzing the plastic deformations on the work piece is presented. The presented technique applies the problem of the Flamant–Boussinesq in the plastic deformation problem. Through experimental verification, the analytical results have a higher accuracy. On the other hand, the surface generation mechanism in peripheral milling with variable pitch end mills is studied. Corresponding surface generation model, which is used to predict the generated surface topography with incorporating the cutting process parameters and several sources of machining error such as tilting, run-out, deflection of the tool and work piece displacement, is proposed. Through a set of cutting tests, it is confirmed that the presented model predicts the surface texture and roughness parameters precisely. By the sensitivity analysis, Helix angle and feed rate have significant influences on surface topography, while the effects of cutting speed on surface topography can be neglected when the effects of the machining error sources on the behavior and performance of the model are not considered. Among the sources of machining errors, the deflection of the tool has the most significant impact on the surface profile. The sequence is the displacement of the work piece and the run-out of the tool.

Study on vibration reduction mechanism of variable pitch end mill and cutting performance in milling titanium alloy

The vibration reduction mechanism of variable pitch end mills was analyzed by the theory of energy balance of the frequency spectrum line. The variable pitch mill can reduce the forced vibration in the cutting process due to the uniform distribution of frequency spectrum line energy and lower peak energy of the cutting force. Aimed at the vibration phenomenon which restricted the efficiency in cutting aero material titanium alloy, high-speed cutting experiments of titanium alloy Ti6Al4V were set with variable and equal pitch mills under dry and down-milling environment. The influences of cutting speeds on cutting forces and tool vibration were analyzed at time domain and frequency domain, respectively, by which the vibration reduction mechanism of variable pitch mill was verified. Due to the misalignment of end mill no. 3, high-level cutting forces and tool vibration were caused by the unequal cutting load on each edge. It is found that severe tool vibration was produced under the cutting speed of 150 m/min because of low-frequency resonance in the cutting process.

Design and Application of High-Speed Variable Pitch End Mill Based on Milling Stability

The strong demand for increasing productivity and workpiece quality in milling process makes the machine-tool system operate close to the limit of its dynamic stability. Milling cutters with variable pitch angles can be very effective in improving stability against chatter for certain speed ranges, which will be predicted by the model presented here. The present paper deals with the design of structural geometry of variable pitch end mills in detail. Based on the analysis of tooth engagement factor, which is expressed and extended in the paper, an approach is proposed to design variable pitch end mill with high milling stability. The certain speed ranges with high milling stability are given.

Milling force vibration analysis in high-speed-milling titanium alloy using variable pitch angle mill

Chatter may cause fast wear of tools and poor surface quality of the workpieces at high cutting speed and it will happen on different process parameters; how do we select the suitable cutting speed to suppress the chatter? In this paper, a signal analysis method for milling force and acceleration is adopted to identify chatter, which can obtain the results not only in frequency of chatter but also in the contribution for milling force at different frequencies. Through the milling experiment, the machining vibration behaviors of milling Ti–6Al–4V with variable pitch end mill were investigated. Milling force and acceleration signals obtained from experiment were analyzed and compared at stable and unstable milling processes. The experimental results show that when the chatter occurs, milling forces were found to increase dramatically by 61.9–66.8% compared with that of at stable cutting; machining surface quality became poor and machined surface roughness increases by 34.2–40.5% compared with that of at stable cutting.

Design for variable pitch end mills with high milling stability

The strong demand for increasing productivity and workpiece quality in milling process makes the machine–tool system operate close to the limit of its dynamic stability. Besides predicting accurately chatter stability, it is required that some optimizations should be conducted, e.g., cutter structure, for improving the dynamic stability limits. Milling cutters with variable pitch angles can be very effective in improving stability against chatter for certain speed ranges, which will be predicted by the model presented here. The present paper deals with the design of structural geometry of variable pitch end mills in detail. Based on the analysis of tooth engagement factor, which is expressed and extended in the paper, an approach is proposed to design variable pitch end mill with high milling stability. The certain speed ranges with high milling stability are given. An example of the design of variable pitch end mills is illustrated to demonstrate the validity of this method.

Modelling of the stability of variable helix end mills

Chatter in milling is still the main obstacle in achieving high-performance machining operations in industry. In this paper, an analytical model is presented to predict the chatter stability of the variable helix end mills. Owing to the lack of accurate and rapid modelling, variable helix tools are used simply on a trial and error basis, in the hope that they will improve the stability of the process. This work provides a comparative study of the performance of variable helix and variable pitch end mills. Time domain chatter recognition techniques and analytical models are explored and tested against experimental results. For the experimental validation, aluminium test pieces were used to enable a broad range of spindle speeds to be covered. The linearity of the machine tool dynamics is explored through validation of standard stability lobes. A comparison of the predicted and observed performance of variable helix against constant helix, variable pitch end mills are presented. The stability lobes are validated for each of the variable helix, variable pitch and standard tools. The analytical model assumes the variable helix tools to behave as variable pitch tools, calculating the average pitch angle for each flute. This approximation is proven to be accurate for some of the cases. For certain combinations of pitch and helix angle greatly enhanced stability is demonstrated empirically with up to a 20-fold increase in depth of cut for the variable helix over the equivalent variable pitch tool. This enhanced stability is neither predicted by the analytical nor time domain solutions. The time domain chatter recognition criterion is investigated and found to have little influence on the predicted stability plots. It is concluded that the enhanced stability is a result of some mechanism not represented in the well-established time domain model. It is possible that this is a result of the disturbance of regeneration in the manner of an alternating spindle speed or due to a non-linear process damping effect.

工具変形を考慮した不等ピッチ切れ刃エンドミルの切削加工モデル

Instantaneous force with static deflection feedback model is applied to predict cutting force and dimensional surface error generation in peripheral milling with irregular tooth pitch end mills. It is demonstrated that the irregular tooth pitch end mill reduces the dimensional surface errors according to the chip regeneration mechanism. Unlike in case of uniform tooth pitch cutters, chip loads on each flute are different in milling with irregular tooth pitch cutters. The excess surface error generated by the flutes which have larger chip loads is removed by the following flutes which have smaller chip load due to the irregular tooth pitch. In order to predict precise cutting force and dimensional surface error for the irregular tooth pitch end mill, the chip regeneration mechanism or the static tool deflection has to be considered to derive the accurate chip loads. Predicted cutting force and dimensional sur face error show good agreement with experimental results. Up to 20% reduction in surface errors is achieved by using the irregular tooth pitch end mills tested.

Cutting force and dimensional surface error generation in peripheral milling with variable pitch helical end mills

Mechanics of cutting force and dimensional surface error generation are presented for variable pitch helical end mills. It has been known that the variable pitch cutters reduce the chatter vibrations by disturbing the regeneration mechanism in dynamic milling. In this paper, it is also demonstrated that the variable pitch cutters reduce the dimensional surface errors caused by the static deflection of slender end mills. Since the pitch angles between the adjacent flutes are different, each flute experiences different chip loads, hence leading; to the varying surface errors imprinted at each tooth period. The excess surface errors left by the flutes, which have larger chip loads, are removed by the following flutes with smaller effective chip loads due to variable pitch. Unlike in the case of uniform pitch cutters, the regeneration of chip thickness mechanism is always present in milling with a statically flexible, variable pitch end mills. A mathematical model. of force and surface prediction, which considers the chip regeneration mechanism under static end mill deflections, is presented with experimental verifications. Up to 20% reduction in surface errors are achieved by using variable pitch over uniform pitch cutters.

Standards for Noise Emission of Machine Tools

This paper presents a design method of irregular pitch end mills, which ensures robust suppression of total regeneration in milling. Firstly, general formulation of irregular pitch angles is explained for simultaneous suppression of multi-mode regenerations. An index named “Regeneration Factor ( RF )” is introduced to quantify regenerative effect. Minimizing the mean value of the | RF | within a certain frequency range, suppression frequencies are distributed in the proposed method, resulting in robust suppression of regeneration regardless of chatter frequency and/or spindle speed variations. Experimental investigations verified significant robustness of the end mill with the proposed design against the spindle speed variation.