The form error prediction in side wall machining considering tool deflection

In this research, an effective method for the form error prediction in side wall machining with a flat end mill is suggested. The form error is predicted directly from the tool deflection without surface generation by cutting edge locus with time simulation. The developed model can predict the surface form error accurately about 300 times faster than the previous method. Cutting forces and tool deflection are calculated considering tool geometry, tool setting error and machine tool stiffness. The characteristics and the difference of generated surface shape in up milling and down milling are discussed. The usefulness of the presented method is verified from a set of experiments under various cutting conditions generally used in die and mold manufacturing. This study contributes to real time surface shape estimation and cutting process planning for the improvement of form accuracy.     

Estimation of cutter deflection and form error in ball-end milling processes

This paper presents a method to analyze the 3-dimensional form error of a ball-end milled surface due to the elastic compliance of the cutting tool. In order to estimate the form error in various cutting modes, the cutting force and the cutter deflection models including the effect of the surface inclination were established. The cutting forces were calculated by using the cutter contact area determined from the Z-map of the surface geometry and the current cutter location. The tool deflection responding to the cutting force was then calculated by considering the cutter and the holder stiffness. The cutter was modeled as a cantilever beam consisting of the shank and the flute. The stiffness of the holder was measured experimentally. Various experimental works have been performed to verify the validity of the proposed model. It is shown that the proposed method is capable of accurate prediction of cutting forces and the surface form error.     

Improved positioning for side milling of ruled surfaces: Analysis of the rotation axis's influence on machining error

This article covers side milling of ruled surfaces using a milling cutter. Flank milling is useful for machining objects such as impellers, turbine blades, fan vanes and all workpieces defined by non-developable, ruled surfaces. In the present article, the influence of parameters defining improved positioning described in a previous study will be appraised. The general idea with improved positioning is to position the milling cutter at a tangent to the 2 directrices of the ruled surface while keeping a point of contact between the milling cutter and the rule considered. This is obtained by a rotation at a point about an imposed axis. Having defined calculation of error between the milled surface and the nominal surface, the influence of the point and the axis of rotation of improved positioning on error will be studied. From this, optimum improved positioning parameters allowing minimisation of error between the ruled surface and the milling cutter will be deduced.     

Analytical models for high performance milling. Part I: Cutting forces, structural deformations and tolerance integrity

Milling is one of the most common manufacturing processes in industry. Despite recent advances in machining technology, productivity in milling is usually reduced due to the process limitations such as high cutting forces and stability. If milling conditions are not selected properly, the process may result in violations of machine limitations and part quality, or reduced productivity. The usual practice in machining operations is to use experience-based selection of cutting parameters which may not yield optimum conditions. In this two-part paper, milling force, part and tool deflection, form error and stability models are presented. These methods can be used to check the process constraints as well as optimal selection of the cutting conditions for high performance milling. The use of the models in optimizing the process variables such as feed, depth of cut and spindle speed are demonstrated by simulations and experiments.     

Estimation and experimental validation of cutting forces in ball-end milling of sculptured surfaces

Chip thickness calculation has a key important effect on the prediction accuracy of accompanied cutting forces in milling process. This paper presents a mechanistic method for estimating cutting force in ball-end milling of sculptured surfaces for any cases of toolpaths and varying feedrate by incorporation into a new chip thickness model. Based on the given cutter location path and feedrate scheduling strategy, the trace modeling of the cutting edge used to determine the undeformed chip area is resulted from the relative part-tool motion in milling. Issues, such as the selection of the tooth tip and the computation of the preceding cutting path for the tooth tip, are also discussed in detail to ensure the accuracy of chip thickness calculation. Under different chip thicknesses cutting coefficients are regressed with good agreements to calibrated values. Validation tests are carried out on a sculptured surface with curved toolpaths under practical cutting conditions. Comparisons of simulated and experimental results show the effectiveness of the proposed method.     

Predictive force model for ball-end milling and experimental validation with a wavelike form machining test

This paper presents a predictive force model for ball-end milling based on thermomechanical modelling of oblique cutting. The tool geometry is decomposed into a series of axial elementary cutting edges. At any active tooth element, the chip formation is obtained from an oblique cutting process characterised by local undeformed chip section and local cutting angles. This method predicts accurately the cutting force distribution on the helical ball-end mill flutes from the tool geometry, the pre-form surface, the tool path, the cutting conditions, the material behaviour and the friction at the tool-chip interface. The model is applied for a complex surface which is a wavelike form used as a validation machining test. The results are compared with experimental data obtained from ball-end milling tests performed on a 3-axis CNC equipped with a Kistler dynamometer.     

The effects of chamfered and honed tool edge geometry in machining of three aluminum alloys

The effects of tool edge geometry in machining have received much attention in recent years due to a variety of emerging machining techniques, such as finish hard turning and micro-machining. In these techniques, the uncut chip thickness is often on the same order of magnitude as tool edge dimension. This paper presents and analyses the results of our recent experimental and theoretical study on the effects of tool edge geometry in machining. Both chamfered and honed tools are investigated covering a wide range of cutting speed and feed rate conditions. The three aluminum alloys 7075-T6, 6061-T6, and 2024-T351 are selected as work materials for particular research purposes. The cutting force, the thrust force, the ratio of the cutting force to the thrust force, and the chip thickness are measured. The similarities and differences in machining with a chamfered tool and with a honed tool are compared. A new slip-line model of chip formation for machining with a chamfered tool is proposed. Good agreement has been reached between the predicted and experimental results. The effects of different aluminum alloys and cutting speeds on the cutting forces, especially on the thrust force, are also studied.     

Experimental analysis of dimensional error vs. cycle time in high-speed milling of aluminium alloy

Manufacturers of machined aluminium parts are among the principal users of high-speed milling. The excellent machinability of aluminium allows this technology to be used with severe cutting conditions, and at the same time permits the machining of complex shapes. There are many factors influencing the quality of manufactured aluminium parts and the economics of the manufacturing process, but little corresponding data is available, making process planning enormously difficult.The aim of the work presented in this article is to experimentally analyse the influence of some of these factors, specifically the feed rate, the type of interpolation and the toolholder, on the dimensional accuracy of the product and the cycle time. Design of experiments (DoE) is used to determine which experiments have to be conducted to obtain a mathematical model that relates the mentioned factors with the responses.The results show that the toolholder has considerable influence over dimensional accuracy and that the type of interpolation appreciably affects the cycle time. Details of the first-order interactions between factors have been included.     

Mechanisms involved in the improvement of Inconel 718 machinability by laser assisted machining (LAM)

The aim of the present research work has been to gain a broader understanding of how or why laser assisted machining (LAM) improves machinability of Inconel 718, a hard-to-machine material of interest in the aeronautic industry. This has been accomplished by, first, running short run tests to determine the laser parameters and configuration for which highest force reductions are obtained and also to determine the effect of cutting parameters (feed, cutting speed and depth of cut) on force reduction. Secondly, long run tests have been performed in order to analyze process variables such as cutting forces, tool wear and surface roughness. Temperatures and hardness have been also measured in order to gain a broader perspective of the process.Experimental results have demonstrated that LAM improves machinability of Inconel 718 since machining forces and final surface roughness are reduced. The novelty reached with the present research work is the identification of three mechanisms associated to the laser heating as the responsible of this machinability improvement: material yield strength reduction, material base hardness reduction (only in precipitation hardened Inconel 718) and elimination of the work hardening generated in previous machining passes. The reduction of the work hardening leads also to a lower notch wear that limits the risk of sudden failure of the cutting tool and thus the wear mode is changed to flank wear, which leads to a controllable tool life and better surface roughness.     

An improved cutting force and surface topography prediction model in end milling

During the milling operation, the cutting forces will induce vibration on the cutting tool, the workpiece, and the fixtures, which will affect the surface integrity of the final part and consequently the product's quality. In this paper, a generic and improved model is introduced to simultaneously predict the conventional cutting forces along with 3D surface topography during side milling operation. The model incorporates the effects of tool runout, tool deflection, system dynamics, flank face wear, and the tool tilting on the surface roughness. An improved technique to calculate the instantaneous chip thickness is also presented. The model predictions on cutting forces and surface roughness and topography agreed well with experimental results.     

Influence of feed, eccentricity and helix angle on topography obtained in side milling processes

Influence of feed, eccentricity and helix angle on surface roughness is presented for side milling operations with cylindrical tools. A model was developed to predict surface topography as well as different roughness parameters. Roughness topography was obtained for one specific tool having grinding errors and eccentricity, for different helix angles.It was found that, as feed increases the number of cutting edge marks on the workpiece’s surface per revolution maintains or increases. As grinding errors and eccentricity increase, the number of cutting edge marks tends to decrease. Regarding helix angle, it was observed that roughness profile does not change along the workpiece’s height if no helix angle is considered. When helix angle is considered and the tool has both high eccentricity and high runout due to grinding errors, roughness heterogeneity bands are observed. The bands’ pattern is repeated along each helix pitch. The higher the helix angle, the narrower the roughness heterogeneity bands become.     

复杂曲面多轴数控加工非线性误差理论分析及控制

针对复杂曲面通常采用的多轴数控加工方式，结合加工用刀具，建立了多轴数控加工的非线性误差的数学模型，分析其影响因素，并给出了有效减少非线性误差的控制方法。     

The analysis of correlative error in principal axis method for five-axis machining of sculptured surfaces

Correlative error is a kind of error between the cutter locations. This text presents a detailed analysis about correlative error in the principal axis method (PAM) that is a strategy of tool positioning for five-axis machining. It points out all the strategies based on linear projection cannot avoid this interference and cannot be disregarded especially in the strategies with large stepover. Accurate calculating is made individually on linear and curve feed and formulae are developed. The author also gave the available application range of PAM and the algorithm for estimating correlative error.     

A neural network approach for force and contour error control in multi-dimensional end milling operations

The problem of controlling the average resultant cutting force together with the contour error in multi-dimensional end milling operations is considered in this study. Two sets of neural networks are used in the control system. The first set is used to specify the feed rate to maintain a desired cutting force. This feed rate is resolved along the feed axes using a parametric interpolation algorithm so that the desired part shape is obtained. The second set is used to make corrections to the feed rate components specified by the parametric interpolation algorithm to minimize the contour error caused by the dynamic lag of the closed-loop servo systems controlling the feed drives. In addition, the control system includes a feedforward input to compensate for static friction effects. Experimental results are presented for machining two-dimensional circular slots and a three-dimensional spherical surface to show the validity of the proposed approach.     

An experimental study of tool wear and cutting force variation in the end milling of Inconel 718 with coated carbide inserts

Inconel 718 is a difficult-to-cut nickel-based superalloy commonly used in aerospace industry. This paper presents an experimental study of the tool wear propagation and cutting force variations in the end milling of Inconel 718 with coated carbide inserts. The experimental results showed that significant flank wear was the predominant failure mode affecting the tool life. The tool flank wear propagation in the up milling operations was more rapid than that in the down milling operations. The cutting force variation along with the tool wear propagation was also analysed. While the thermal effects could be a significant cause for the peak force variation within a single cutting pass, the tool wear propagation was believed to be responsible for the gradual increase of the mean peak force in successive cutting passes.     

Coupled interaction of dynamic responses of tool and workpiece in thin wall milling

Chatter free thin wall machining requires knowledge of the dynamics of a machine-tool system and workpiece either for designing damping solutions or for modelling impact dynamics. Previous studies on thin wall milling mostly focussed on stability studies. However studies on the interaction between the tool and workpiece responses in thin wall machining are scarce in the literature. In this work, the coupled dynamic response of tool and workpiece is presented both for an open (thin wall straight cantilever) and for closed (thin wall ring type casing) geometry structures. Experiments were carried out for different tool overhangs and depths of cut and the machining vibration signal was analysed in time–frequency domain to study the interaction, i.e. coupling, of tool–workpiece dynamic response at various cutting tooth engagement/idle times. The findings from this study highlight the importance of tool's frequency, particularly torsional and first bending modes, in impact dynamics of thin wall milling. Moreover, the differences in dynamic response interaction between a cutting tool and thin wall plate and a cylinder are identified. While the analysis of the open geometry structure showed the presence of tool and workpiece responses for any depth of cut, results on closed geometry structure exhibited a complete dominance of tool mode at higher depths of cut. These findings are of critical importance in understanding the impact dynamics in thin wall milling and also of effectiveness of passive damping solutions.     

Effect of direction of parameterization on cutting forces and surface error in machining curved geometries

The present paper investigates the effect of two variables, namely direction of parameterization and cutter diameter on process geometry, cutting forces, and surface error in peripheral milling of curved geometries. In machining of curved geometries where the curvature varies continuously along tool path, the process geometry variables, namely feed per tooth, engagement angle, and maximum undeformed chip thickness too vary along tool path. These variations will be different when a given geometry is machined from different parametric directions and with different cutter diameters. This difference in process geometry variations result in changed cutting forces and surface error along machined path. This aspect has been studied for variable curvature geometries by machining from both parametric directions and using cutters of different diameter. The computer simulation studies carried out show considerable amount of shift in the location of peak cutting forces with the change in cutting direction and cutter diameter, particularly in concave regions of workpiece geometry. A new parameter γ that relates the instantaneous curvature of workpiece with cutter radius is defined. The larger value of γ is an indicator of greater shift in the location of peak forces from the point of maximum curvature on the workpiece. The simulation results are validated by carrying out machining experiments with curved workpiece geometry and are found to be in good agreement.     

Combination of capacitance and conductive working fluid to speed up the fabrication of a narrow, deep hole in electrical discharge machining using a dielectric-encased wire electrode

An attempt was made to increase the machining speed of a new electrical discharge machining system for fabricating narrow, deep holes in metal. The method employs a wire encased in a dielectric jacket as the tool electrode, in contrast with the conventional pipe electrode. The role of the dielectric jacket is to completely suppress unnecessary secondary discharges occurring between the sidewalls of the wire and the fabricated hole. In the present study, the effectiveness of the combination of conductive working fluid and a capacitor connected to the work piece and the tool electrode was examined. Although electrode wear was severe, machining speed with this combination (saline water at 150–250 μS/cm and capacitance at 8 μF) was twice as fast compared with fabricating a hole ( 0.8–0.9 mm) without a capacitor and saline water in a 20-mm thick carbon steel block. The mechanisms involved are discussed based on electrical circuit theory and electrochemical corrosion.     

Experimental verification of manufacturing error pattern and its utilization in form tolerance sampling

This paper presents an adaptive sampling procedure, which uses manufacturing surface error patterns and optimization search methods for reducing sample size, while maintaining high accuracy. The methodology is demonstrated with straightness and flatness evaluation. Two manufacturing processes, end and face milling are used to fabricate plates used for modeling and subsequent testing. Respective surface errors for each process are quantified and validated using previously published models. The initial points for sampling are identified through such a characterization of the process and its affect on the workpiece. These sampled points are fit using the least-squares method to complete the form evaluation. Points are added to the initial set using optimization search heuristics. The final tolerance value obtained is compared with that obtained from a large population sample to check the accuracy. With such an adaptive approach, it is proposed that the number of points sampled is potentially less than that which would be expected to achieve the same level of accuracy using traditional sampling methods. This paper demonstrates the error modeling and validation aspects of this adaptive sampling procedure.     

Statistical analysis of surface roughness and cutting forces using response surface methodology in hard turning of AISI 52100 bearing steel with CBN tool

The present work concerns an experimental study of hard turning with CBN tool of AISI 52100 bearing steel, hardened at 64 HRC. The main objectives are firstly focused on delimiting the hard turning domain and investigating tool wear and forces behaviour evolution versus variations of workpiece hardness and cutting speed. Secondly, the relationship between cutting parameters (cutting speed, feed rate and depth of cut) and machining output variables (surface roughness, cutting forces) through the response surface methodology (RSM) are analysed and modeled. The combined effects of the cutting parameters on machining output variables are investigated while employing the analysis of variance (ANOVA). The quadratic model of RSM associated with response optimization technique and composite desirability was used to find optimum values of machining parameters with respect to objectives (surface roughness and cutting force values). Results show how much surface roughness is mainly influenced by feed rate and cutting speed. Also, it is underlined that the thrust force is the highest of cutting force components, and it is highly sensitive to workpiece hardness, negative rake angle and tool wear evolution. Finally, the depth of cut exhibits maximum influence on cutting forces as compared to the feed rate and cutting speed.