Ball-end Cutter Research Articles

A continuous oscillating milling strategy based on uniform wear theory for improving the service life of the ball-end cutter

The rapid deterioration of ball-end cutters leads to a shortened lifespan when milling difficult-to-cut materials. This research introduced a continuous oscillating milling approach aimed at enhancing the consistency of cutting-edge wear by dynamically adjusting the tool axis oscillation angle, thus prolonging the tool life. Initially, key processing parameters were determined according to the actual processing conditions. Subsequently, a tool wear model, rooted in continuous oscillating milling, was developed. Using it, an optimization framework for the tool oscillating angle, based on uniform wear theory, was established. Then, the CNC code was compiled according to optimization results. Finally, the proposed milling strategy was demonstrated by cutting tests on Ni-based superalloy GH4169. The results demonstrated that this approach notably extended the tool life.

Analytical method to extract tool workpiece engagement from CAM data for five-axis machining stability prediction

Ball end milling cutters are commonly used for precision machining of complex curved parts in five axis CNC systems. To solve the problem of difficulty in adjusting the spindle speed to achieve stable milling during the five axis milling process of ball end cutters, this paper presents an analytical method for extracting the tool-workpiece engagement (TWE) from computer-aided manufacturing (CAM) data. This method extracts the TWE between the end portion of the ball-end mill and the surface of the workpiece during the processing of free-form surfaces, including slotting, first cutting, and following cutting. Further, the TWE extracted by this method is applied for constructing the cutting force model. The entry and exit angles for each of the micro-element cutting edges under different tool postures are obtained through the conversion matrix, and an efficient full discretization method is used for predicting the stability of the five-axis machining in the slotting mode. Finally, the accuracy and efficiency of the analytical method are verified through simulation and experimentation. The experimental results show that the efficiency of the proposed method increases by about 69% when compared to the arc-surface intersection method and that the predicted value of the five-axis machining stability shows good agreement with the experimental results.

Identification of milling information and cutter-workpiece engagement in five-axis finishing of turbine blades based on NURBS and NC codes

Five-axis milling is frequently used for machining of turbine blades. Cutting force can cause deformation and vibration of blades, which will eventually affect the milling accuracy and surface quality. Modeling of cutter-workpiece engagement (CWE) is a key process to predict cutting force, especially for complex tool geometries and workpiece surfaces. In this paper, a method to modeling ball-end cutter CWE boundaries for blades with free-form surfaces is presented. Firstly, the NURBS theory is employed to get the surfaces before and after finishing. Secondly, milling information such as coordinate systems is extracted from NC codes. Thirdly, the CWE boundaries are extracted based on the NURBS surfaces and extracted information. The proposed model is a combination of discrete and analytical method. Finally, the performance of CWE model is examined from computational accuracy and efficiency, and is verified through milling test. The proposed method provides a visualization of complex engagement between tool and blade in five-axis milling process, and can be further used in simulation of milling force, vibration and deformation.

An oscillating milling strategy based on the uniform wear theory for improving service life of the ball-end cutter

An oscillating milling strategy based on the uniform wear theory for improving service life of the ball-end cutter

Collision avoidance and orientation planning for ball-end cutter

Collision avoidance and orientation planning for ball-end cutter

Predicting cutting forces in 5-axis milling of sculptured surfaces directly from a CAM tool path

The present work is motivated by the fact that for predicting the cutting forces which arise under various cutting conditions, workpiece-tool pairs, machining depths and tool orientation, numerical methods are slower and less efficient than analytical methods. In addition, recent developments in Computer Assisted Machining (CAM) techniques have enabled analytical methods to be applied even with complex workpiece geometry. The method developed in this paper is both practical and inexpensive. It is based on an analytical method using only few approximations and uses the toolpath file as the main information source for the machined surface. This method takes into account both tool position and orientation in a 5-axis finishing milling process with ball-end cutter, independent of the machining parameters and the couple of tool-workpiece materials. However, this calculation must be supplemented by a mechanistic approach in order to obtain results equivalent to those of the experiment. The result is a model which is implemented in a program allowing the visualization of the cutting forces along a given path. The program is easy to apply in practical cases with the possibility of implementing it in a machining software.

Optimal pitch angles determination of ball-end cutter for improving five-axis milling stability

Regenerative chatter is one of the major limitations in five-axis ball-end milling of complex shaped parts, resulting in reduced productivity and poor quality. Although a good solution can be provided for the chatter avoidance and the stability enhancement by using variable pitch cutters, it depends on the optimal selection of pitch angles, and few studies focus on determining the optimal pitch angles combination for the five-axis ball-end milling process in a continuous spindle speed range. In this paper, the pitch angle optimization is based on the fast and accurate stability prediction of five-axis ball-end milling with variable pitch tools. Considering that the search space of the stability border should be reduced as much as possible during the optimization process, an approach combining an improved hybrid multi-step method and an optimization strategy of stable area maximum is presented for efficiently finding the optimal pitch angles. For selected spindle speed ranges and given lead/tilt angles, the optimal pitch angles of variable pitch ball-end cutter are determined with the proposed optimization approach. The experimental results show the average stability of the customized optimal variable pitch ball-end cutter is significantly higher than that of the regular ball-end cutter, validating the proposed optimal pitch angles determination method. Compared with the semi-discretization method, the use of improved hybrid multi-step method for predicting the stability border reduces the simulation time by around 84 %. In contrast to the optimization strategy based on the average characteristic multiplier, the proposed optimization strategy is more efficient because it does not require a large number of characteristic multipliers.

Collision-free and smooth path generation method of five-axis ball-end milling considering effective tool diameter change

Ball-end cutters are widely used in five-axis sculptured surface machining. It is desired to avoid drastic changes of rotary axis movements for improving the kinematics performance of machine tools while ensuring collision-free during five-axis machining. It cannot acquire the optimum solution when cutter orientations are first generated and then adjusted to avoid collisions. The cutter orientations should be generated and optimized in their feasible regions wholly while the computation load is usually large. Different relative postures between a ball-end cutter and workpiece during the machining process will produce different effective tool diameters of the ball-end cutter, resulting in different cutting speeds. Using a variable cutting speed along a tool path can unfavorably affect the process' technological effects (e. g. surface quality, tool life). It is desired to keep the effective tool diameter constant or at a very slightly varying value during five-axis ball-end machining. Moreover, it is also desired to make the cutting point in a high position of the ball-end cutter tool edge, increasing the effective tool diameter. A smooth and collision-free tool path generation method of five-axis ball-end machining while minimizing the effective tool diameter variation and increasing the effective tool diameter of the ball-end cutter along a tool path is proposed. Tool orientations along a tool path are generated and optimized within their feasible regions and the proposed method solves the smoothness tool path generation problem by applying sequentially for the rough and fine search spaces to reduce the computing time. The numerical examples and the machining experiment illustrate the effectiveness of the proposed method.

Tool Orientation Optimization Based on Spatial Tractrix Method for Five-Axis CNC Machining with Ball End Cutters

Tool Orientation Optimization Based on Spatial Tractrix Method for Five-Axis CNC Machining with Ball End Cutters

Effect of Ball End Cutter Tilt Milling on Path Interval of Blade Surface

Different milling posture of ball-end cutter will alter path interval and affect surface scallop-height, which was an important problem to be considered to enhance the quality and efficiency of blade surface. In view of ball end cutter tilt milling of blade surface, the relation equation between path interval and scallop-height was established by constant scallop-height method, based on the determination of collision boundary and milling sensitivity, the optimal tilt angles and path interval of blade surface milling were solved, moreover, by means of cutting simulation method, the differences between tilt milling and traditional non-tilt milling were compared and analyzed from the perspective of scallop height and processing time, and verified through comparative experiments. The results show that the optimal tilt angles of blade surface milling is 36.9°, when the path interval is fixed, the surface roughness of non-tilt milling and tilt milling are 0.719 µm and 0.561 µm respectively, the surface processing quality of tilt milling is 28.2% higher than that of non-tilt milling, when scallop-height is fixed, the total time of non-tilt milling and tilt milling are 31.21 min and 25.46 min respectively, the machining efficiency of tilt milling is 17.1% higher than that of non-tilt milling. The effectiveness of tilt milling method is verified, which can provide reference basis for high-quality and efficient machining of similar blade surfaces.

Research on Modeling of Milling Force of Ball-End Mill Cutter in Multi-hardness Splicing Area of Automobile Panel Die Steel

The structure and the cavity surface hardened steel mold of automobile cover is very complex. In the stamping process, the local structure bears higher extrusion stress than the type surface, which often causes local wear and even cracking. The process of multi hardness splicing joint is applied to ensure the service life of the die according to the features of each part of the mold. The impact load caused by the repeatedly cut-in which always leads to the instability of cutting force in the whole process. The machining quality of the mold surface is reduced. Aiming at the machining process of the ball-end milling cutter in the mold splicing area, the impact at the moment of contact between the cutter and the workpiece is analyzed. The instantaneous chip thickness model that considers impact factors and the state model that calibrates the cutting state by coefficients is established. Finally, the prediction model of the milling force of the splicing area is obtained. The model is verified based on the machining cutting force measurement experiment in the case of die hardened steel Cr12MoV with single hardness and multi-hardness splicing. The average prediction error of experiments and simulation results is within 10%, which proves the accuracy of the model. The results show that the model has certain guiding significance for the actual processing of the splicing area of automobile mold cover parts.

Least variation in tool orientation control for 5-axis CNC machining

We address the problem of minimizing the variation of the tool axis orientation of a 5-axis CNC machine equipped with a ball-end cutter that is designed to maintain a constant cutting speed, which is ensured by a fixed angle ψ between the tool axis a(t) and the workpiece surface normal n(t) at each point of contact as the cutter moves along a specified toolpath. The configuration can be mathematically translated into a pair of curves a(t) and n(t) on the unit sphere with constant parametric distance ψ, and the least variation of the tool axis orientation is achieved when the overall length of the curve a(t) is minimized under certain auxiliary boundary conditions. Using the calculus of variation we show that the solution a(t) consists of arcs of great circles and offset curves of n(t) on the unit sphere. A numerical approximation scheme based on Euler's method of finite differences is also provided.

Ball-end milling cutter design method towards the maximum material removal rate under surface roughness constraints

Cutter design and selection, as one of the indispensable tasks in discrete parts' manufacturing process planning, has seldom been investigated in terms of high machining quality and machining efficiency. In order to fill this gap, this paper studies the influences of main geometric parameters of ball-end cutter (helix angle, flute number, cutter radius) on surface roughness and material removal rate (MRR). Firstly, it is revealed that the fundamental reason why the helix angle affects the cutting force coefficients is the oblique angle, not the axial height or axial position angle. And a novel method of cutting force coefficients prediction for newly designed cutter based on local helix angle is proposed. Then, the influences of cutter parameters on surface roughness and MRR are investigated by theoretical and experimental method. Based on this analysis, cutter evaluation models for machining quality and machining efficiency are established, respectively. Particle swarm optimization (PSO) is used as optimization method to search the optimal cutter. Finally, a novel cutter design method combined with cutter evaluation models is proposed to obtain better surface performance and machining efficiency. According to the experimental results, it can be proved that the cutter designed by this method can maximize MRR under the constraint of meeting the parts' surface roughness requirements. This is of great significance for improve parts' performance and reduce machining cost.

Method for Enhanced Accuracy in Machining Free-Form Surfaces on CNC Milling Machines

Abstract The present article describes a method for enhanced accuracy in machining free-form surfaces produced on CNC milling machines. In this method, surface patch machining programs are generated based on their nominal CAD model. After the pretreatment, coordinate control measurements are carried out. The obtained results of the measurements contain information on the values and distribution of observed machining deviations. These data, after appropriate processing, are used to build a corrected CAD model of the surface produced. This model, made using reverse engineering techniques, compensates for the observed machining deviations. After regeneration of machining programs, the object processing and control measurements are repeated. As a result of the conducted procedure, the accuracy of the manufacture of the surface object is increased. This article also proposes the introduction of a simple procedure for the filtration of measurement data. Its purpose is to minimise the effect of random phenomena on the final machining error correction. The final part of the article presents the effects of the proposed method of increasing the accuracy of manufacturing on ‘raw’ and filtered measurement data. In both cases, a significant improvement in the accuracy of the machining process was achieved, with better final results obtained from the filtered measurement data. The method proposed in the article has been verified for three-axis machining with a ball-end cutter.

Tool wear prediction at different cutting edge locations for ball-end cutter in milling of Ni-based superalloy freeform surface part

Tool wear prediction at different cutting edge locations for ball-end cutter in milling of Ni-based superalloy freeform surface part

Double optimization of the mesoscopic geometric parameters of ball-end milling cutters based on interactive experiment

Double optimization of the mesoscopic geometric parameters of ball-end milling cutters based on interactive experiment

Study on the Formation Mechanism of Surface Adhered Damage in Ball-End Milling Ti6Al4V.

Ball-end cutters are widely used for machining the parts of Ti-6Al-4V, which have the problem of poor machined surface quality due to the low cutting speed near the tool tip. In this paper, through the experiments of inclined surface machining in different feed directions, it is found that the surface adhered damages will form on the machined surface under certain tool postures. It is determined that the formation of surface adhered damage is related to the material adhesion near the cutting edge and the cutting-into/out position within the tool per-rotation cycle. In order to analyze the cutting-into/out process more clearly under different tool postures, the projection models of the cutting edge and the cutter workpiece engagement on the contact plane are established; thus, the complex geometry problem of space is transformed into that of plane. Combined with the case of cutting-into/out, chip morphology, and surface morphology, the formation mechanism of surface adhered damage is analyzed. The analysis results show that the adhered damage can increase the height parameters Sku, Sz, Sp, and Sv of surface topographies. Sz, Sp, and Sv of the normal machined surface without damage (Sku ≈ 3) are about 4–6, 2–3, and 2–3 μm, while Sz, Sp, and Sv with adhered damage (Sku > 3) can reach about 8–20, 4–14, and 3–6 μm in down-milling and 10–25, 7–18, and 3–7 μm in up-milling. The feed direction should be selected along the upper left (Q2: β ∈ [0°, 90°]) or lower left (Q3: β ∈ [90°, 180°]) to avoid surface adhered damage in the down-milling process. For up-milling, the feed direction should be selected along the upper right (Q1: β ∈ (−90°, 0°]) or upper left (Q2: β ∈ [0°, 90°)).

Cutting Force Modeling and Experimental Study for Ball-End Milling of Free-Form Surfaces

In order to improve the machining quality and efficiency and optimize NC machining programming, based on the existing cutting force models for ball-end, a cutting force prediction model of free-form surface for ball-end was established. By analyzing the force of the system during the cutting process, we obtained the expression equation of the instantaneous undeformed chip thickness during the milling process and then determined the rule of the influence of the lead angle and the tilt angle on the instantaneous undeformed chip thickness. It was judged whether the cutter edge microelement is involved in cutting, and the algorithm flow chart is given. After that, the cutting force prediction model of free-form surface for ball-end and pseudocodes for cutting force prediction were given. MATLAB was used to simulate the prediction force model. Finally, through the comparative analysis experiment of the measured cutting force and the simulated cutting force, the experimental results are basically consistent with the theoretical prediction results, which proves that the model established in this paper can accurately predict the change of the cutting force of the ball-end cutter in the process of milling free-form surface, and the error of the cutting force prediction model established in this paper is reduced by 15% compared with the traditional cutting force prediction model.

Velocity effect sensitivity analysis of ball-end milling Ti-6Al-4 V

Ball-end cutters are widely used in industries of dies, molds, and aerospace, which have the problem of poor machined surface quality due to the low cutting speed near the tool-tip. With the increase in the complexity of parts, it will become more and more difficult to avoid the tool-tip participating in the cutting. In this paper, the velocity effect sensitivity of the ball-end cutter is analyzed, and several key positions, including the intersection points of the CWE boundaries, are selected to describe the cutting speed in three dimensions. The relationships between the cutting speed of the critical points and important variables such as the machining inclination angle and the feed direction were investigated. The optimal range of feed direction is obtained when the tool-tip engages in the contact circle. The core aim of the feed direction selection is to make the tool engagement area in a high position by changing the feed direction, to avoid surface damage and improve the quality of the machined surface. Finally, an experimental study was carried out, and the results corroborate the effectiveness of the selection method. In the experiment, it was also found that cutting-out from the cutter contact position can improve the surface quality in the directions of non-optimal range, and the milling force and chips shape will vary with the change of the feed direction.

Research on micro-texture placement position and cutting performance of negative chamfering ball-end milling cutter

In order to optimize the position of the micro-texture on the negative chamfering edge ball-end milling cutter, the experiment of milling titanium alloy with the negative chamfering micro-texture ball-end milling cutter was carried out. The effects of micro-texture at different placement positions (rake and flank faces of cutting tools) on cutting performance were compared when the cutting depth was 0.3 mm, and the effects of negative chamfering and micro-texture parameters on cutting performance of the cutter were studied. Finally, the negative chamfering and micro-texture parameters were optimized based on genetic algorithm. The results show that the micro-texture of the flank face can improve the cutting performance, and the negative chamfering angle and width have the greatest influence on the cutting performance. The parameter optimization results are: the negative chamfering angle is 10.016°, the negative chamfering width is 199.995 μm, the micro-pit diameter is 49.996 μm, the micro-pit spacing is 174.004 μm, and the micro-pit distance from the edge is 109.993 μm. The above research realizes high efficiency and high-quality machining of titanium alloy.