High-speed Machining Process Research Articles

Prediction of High Speed Machining Cutting Forces Using a Variable Flow Stress Machining Theory

A variable flow stress machining theory is described where it is used to predict the cutting forces associated with High Speed Machining (HSM) process. The predicted and experimental results for different materials and different cutting conditions are presented and compared and it is shown that the theory developed is capable of predicting the cutting forces and the other parameters associated with the HSM process. The extension of the theory to HSM has been successful within the machining conditions presented here in this paper. Further work is necessary to improve this theory further.

A knowledge base model for complex forging die machining

Recent evolutions on forging process induce more complex shape on forging die. These evolutions, combined with High Speed Machining (HSM) process of forging die lead to important increase in time for machining preparation. In this context, an original approach for generating machining process based on machining knowledge is proposed in this paper. The core of this approach is to decompose a CAD model of complex forging die in geometrical features. Technological data and topological relations are aggregated to a geometrical feature in order to create machining features. Technological data, such as material, surface roughness and form tolerance are defined during forging process and dies design. These data are used to choose cutting tools and machining strategies. Topological relations define relative positions between the surfaces of the die CAD model. After machining features identification cutting tools and machining strategies currently used in HSM of forging die, are associated to them in order to generate machining sequences. A machining process model is proposed to formalize the links between information imbedded in the machining features and the parameters of cutting tools and machining strategies. At last machining sequences are grouped and ordered to generate the complete die machining process. In this paper the identification of geometrical features is detailed. Geometrical features identification is based on machining knowledge formalization which is translated in the generation of maps from STL models. A map based on the contact area between cutting tools and die shape gives basic geometrical features which are connected or not according to the continuity maps. The proposed approach is illustrated by an application on an industrial study case which was accomplished as part of collaboration.

2D high speed machining simulations using a new explicit formulation with linear triangular elements

This paper presents the several advantages of a new explicit formulation using modified linear tetrahedral elements non-sensitive to volumetric locking in the scope of high speed machining simulations. First, the explicit time integration allows obtaining very interesting computational time in very dynamic cases with complex behaviour laws. Then, the use of a tetrahedral mesh permits to use robust non-structured adaptive remeshers too. No chip separation criteria or damage model is used. Our 2D orthogonal cutting model detects automatically the apparition of an adiabatic shear band, and simulates very precisely its evolution and the chip formation. Phenomena relative to adiabatic shearing bands already described in the literature can be observed in detail in the simulation. This model is a powerful tool to improve the understanding of chip formation and adiabatic shear band propagation, and to simplify the optimisation of high speed machining processes in industries.

Identification of Stability Lobes in High-Speed Milling Flexible Parts with Bull-Nose End Mills

Flexible parts such as turbine blade, blisk and monolithic components are widely used in the aeronautical industry, and high Speed Machining (HSM) technology is used to increase productivity and reduce production costs. Chatter is an undesirable phenomenon in high speed machining processes because of deteriorative surface finish, early cutting tool failure and unexpected machine tool damage. It can be avoided in higher speed milling processes if stability lobes is determined. In this paper, a non-linear regenerative force model is applied to a bull-nose tool geometry in order to obtain the machine operation stability lobes. An analytical-experimental method is proposed to obtain the stability lobes during high speed milling flexible parts with bull-nose end mills. The method is calculated and validated.

Experimental study of thermal sliding contact parameters at interface seat of large strains

The study relates to the characterization of thermal sliding contact work piece-tool under great deformations, representative of the secondary shear zone of a High Speed Machining Process (HSMP). The literature shows that the authors consider a perfect thermal contact condition and suppose that the heat flux generated by friction at the sliding interface is divided in the ratio of the thermal effusivities of materials in contact. However the distribution of the normal stress at this interface is large and the thermal contact must become imperfect before the release of the chip. The improvement of HSMP simulation requires the checking of these two assumptions. The proposed experimental approach is founded on temperature field measurement by thermocouples in order to estimate thermal sliding contact parameters at the part/tool interface seat of heat dissipation in same condition as the HSMP: the thermal contact resistances RTC, the generated heat flux φ g and share ratio α of φ g . Experiments were carried out on friction device that reproduces mechanical and thermal contact conditions of a HSMP at the tip tool. The experimental plan allows to study the influence of sliding speed and materials in contact on the thermal parameters. Results show that heat flux is divided into the ratio of the thermal effusivities of materials in contact but the thermal contact is systematically imperfect.

Experimental Study on Wear Mechanism of Cutting Tool and Cutting Temperature in High Speed Machining Superalloy

Two kinds of Cemented carbide tools were used to turn Iron-based superalloy GH2132 at 80m/min-210 m/min under dry cutting condition. Infrared thermometer was used to measure cutting temperature, Tool wear was observed by SEM, and oxygen element distribution of tool surface was analyzed by EDS. Adhesive wear oxidation wear were the main wear mechanisms of the coated cemented carbide tool, Adhesive wear, abrasive were the main wear mechanisms of the carbide tool. Oxidation wear occurs above a certain temperature about 430°C, the higher the temperature the more serious the oxidation wear is. The results might be helpful to guiding the design and selection of tool materials and control of tool wear in high speed machining processes.

High speed end-milling characteristics of pre-sintered Al2O3/Y-TZP ceramic composites for dental applications

Yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics have been utilized as a restorative dental material. Pre-sintered Y-TZP ceramics are machined using the Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) techniques. In this study, pre-sintered 3 mol % yttria-stabilized zirconia (3Y-TZP) bioceramics reinforced with Al2O3 particles were prepared by sintering at relatively low temperature. The machining characteristics of the developed 3Y-TZP composites were investigated using an end-milling process. A series of experiments were performed on a high speed spindle with several sensors: a tool dynamometer, an acceleration sensor, and an acoustic emission sensor. The tool dynamometer was installed below the work-piece, a three-axis acceleration sensor was installed on the spindle head, and the acoustic emission sensor was installed on the fixture. The machining characteristics of the composites material were evaluated in a high speed machining process under various cutting conditions by changing the cutting speed, depth-of-cut, and feedrate. The machined surface was investigated using SEM photographs.

Constant Scallop Tool Path for Triangular Surface Machining

The polyhedral model is widely used in aerospace,automotive,shipbuilding,mould and die industries. However,apart from the iso-planar method,the tool path generation methods for polyhedral machining are very limited. In such a case,the given tool paths are no longer boundary-conformed or efficient. In order to reduce the number of interruptions and rapid traversals during high-speed machining(HSM) process,a constant scallop tool path generation method is proposed. A parametric surface is firstly used to approximate the local neighborhood of a vertex and an algorithm for offset of curve on Triangular surface is developed. On this basis,an accurate tool path is generated by means of the contour offset on triangular surface. Results demonstrate that the proposed method is boundary-confirmed,and can significantly improve the machining efficiency and precision.

Isoparametric and Spiral Toolpath for Free-form Surfaces Machining

By analysis of the validity of tool path, tool path planning is divided into two processes, the choice of curves on surface and the design of effective and rational path arrangement. On this basis, a spiral topology toolpath for continuous cutfing is developed in order to reduce the number of interruptions and rapid traversals during high-speed machining (HSM) process. Based on the isoparametric toolpath, the contour-parallel isoparametric path is firstly created, and then a spiral path is generated as a kind of diagonal curve between the isoparametric offset curves. Experimental results demonstrate that the proposed method is straightforward and avoids the self-intersection of the toolpath, especially suitable for HSM.

Study on the Orthogonal Cutting Process of Al7050T7451 with Uncoated and Coated Tools

Tool wear during high speed machining process plays an important role in machining cost and efficiency. The purpose of this study is to examine the impact of tribological properties of coatings on cutting performance. Finite element methods (FEM) were used to model the effect of coated and uncoated cutting tools (K10) on the machinability of the aluminum alloy 7050T7451. Uncoated, Single coated, such as TiC, TiN and Al2O3 and multi-coated tool were studied. All finite element models were assumed to be plane strain. To achieve constitutive model of Al7050T7451 under conditions of machining that high strain rate, high strain and high temperature occur, high speed impact experiment and material drawing experiment were done. Comparison of FEM results shows that the highest temperatures in tools, the temperature change rates of different tools from surface to its bulk material, and the temperatures in chips are changed greatly. It also shows that the cutting temperature of coated tool is lower than uncoated tools, but cutting forces change very little. All these results show that coatings can be used to reduce adhesion between a tool and a workpiece material. The wear resistance of coated tool can be improved effectively and tool life is increased correspondingly.

Measurement of the thermal contact parameters at a workpiece – tool interface in a HSM process

In high speed machining process, the workpiece-tool thermal contact is not well known. We propose an experimental approach founded on an original measurement principle that allows accurate estimation of the thermal contact parameters. These latter are three: the thermal contact resistance, the generated heat flux density and the partition coefficient of this latter. In this paper we present the principle of measurement of these parameters considering the global theoretical model and its difficult and propose a simpler alternative model. This latter consider separately both sub domains to estimate the thermal superficial conditions. That allows determining the three parameters of contact allowing a precise formulation of the boundary condition at the workpiece-tool interface. The purpose of this simplified model is to uncorrelate the estimates of generated heat flux and the partition coefficient.

The Finite Element Analysis of Serrated Chip Formation in High-Speed Cutting Auto Panel Dies

On the base of analyzing material constitutive model, chip-tool contact friction, and chip separation and fracture, a finite element model (FEM) was built to study the high-speed machining process of alloy cast-iron. The shaping process of serrated chip in high-speed milling alloy cast-iron was simulated and analyzed in detail. It was shown that machining parameters affect the serrated chip forming greatly. The model can be used to optimize machining parameters, prolong tool life and improve machining surface quality.

Design and manufacture of hybrid polymer concrete bed for high-speed CNC milling machine

To maximize the productivity of precision products such as molds and dies, machine tools should be operated at high speeds without vibration. As the operation speeds of machine tools are increased, the vibration problem has become a major constraint of manufacturing of precision products. The two important functional requirements of machine tool bed for precision machine tools are high structural stiffness and high damping, which cannot be satisfied simultaneously if conventional metallic materials are used for bed structure because conventional high stiffness metals have low damping and vice versa. This paper presents the application of hybrid polymer concrete for precision machine tool beds. The hybrid polymer concrete bed composed of welded steel structure faces and polymer concrete core was designed and manufactured for a high-speed gantry type milling machine through static and dynamic analyses using finite element method. The developed hybrid machine tool bed showed good damping characteristics over wide range of frequency (η = 2.93–5.69%) and was stable during high speed machining process when the spindle angular speed and acceleration of slide were 35,000 rpm and 30 m/s2, respectively.

Reliable multi-objective optimization of high-speed WEDM process based on Gaussian process regression

The paper discusses the development of reliable multi-objective optimization based on Gaussian process regression (GPR) to optimize the high-speed wire-cut electrical discharge machining (WEDM-HS) process, considering mean current, on-time and off-time as input features and material remove rate (MRR) and Surface Roughness (SR) as output responses. In order to achieve an accurate estimation for the nonlinear electrical discharging and thermal erosion process, the multiple GPR models due to its simplicity and flexibility identify WEDM-HS process with measurement noise. Objective functions of predictive reliability multi-objectives optimization are built by probabilistic variance of predictive response used as empirical reliability measurement and responses of GPR models. Finally, the cluster class centers of Pareto front are the optional solutions to be chosen. Experiments on WEDM-HS (DK7732C2) are conducted to evaluate the proposed intelligent approach in terms of optimization process accuracy and reliability. The experimental result shows that GPR models have the advantage over other regressive models in terms of model accuracy and feature scaling and probabilistic variance. Given the regulable coefficient parameters, the experimental optimization and optional solutions show the effectiveness of controlling optimization process to acquire more reliable optimum predictive solutions.

Study on clamping method for paper honeycomb based on magnetic field and friction principle

Abstract In order to improve fixture reliability of paper honeycomb during high speed machining process, a new technique and method based on magnetic field and friction force principle is put forward. In this method, the pressures, vertical to honeycomb walls and the clamping plane, are produced because of the gravity of the iron powder injected into the honeycomb and the magnetic force induced by the additional magnetic field. Two kinds of friction force, between iron powder and honeycomb walls, honeycomb and clamping plane, are both controllable by adjusting the parameters, such as electric current intensity, height of iron powder and air gap. The finite element analysis and experiments have validated the feasibility in technique. In addition, a prototype clamping equipment is designed and put into production.

FEM Simulation of the Residual Stress in the Machined Surface Layer for High-Speed Machining

An orthogonal cutting model was presented to simulate high-speed machining (HSM) process based on metal cutting theory and finite element method (FEM). The residual stresses in the machined surface layer were obtained with various cutting speeds using finite element simulation. The variations of residual stresses in the cutting direction and beneath the workpiece surface were studied. It is shown that the thermal load produced at higher cutting speed is the primary factor affecting the residual stress in the machined surface layer.

The building of spindle thermal displacement model of high speed machine center

This article mainly analyzes the issues of spindle thermal displacement upon the acceleration of spindle, and proposes a complex multivariable regression analytical method to build a spindle thermal displacement model, so as to predict the thermal displacement of spindle caused by the heat under every time slot during the practical high speed machining process. Upon using the compensation of spindle displacement model, the largest value of cutting depth of the hole error of 62 μm that is caused by the spindle thermal displacement not being compensated can be reduced to a maximum cutting depth of the hole of 4.62 μm, and its average error value of cutting depth is 1.58 μm. Therefore, upon compensating the spindle thermal displacement model proposed in this study, the machining precision can effectively be improved.

Multi-objective optimisation of high-speed electrical discharge machining process using a Taguchi fuzzy-based approach

The paper describes the application of the fuzzy logic analysis coupled with Taguchi methods to optimise the precision and accuracy of the high-speed electrical discharge machining (EDM) process. A fuzzy logic system is used to investigate relationships between the machining precision and accuracy for determining the efficiency of each parameter design of the Taguchi dynamic experiments. From the fuzzy inference process, the optimal process conditions for the high-speed EDM process can be easily determined as A 1B 1C 3D 1E 3F 3G 1H 3. In addition, the analysis of variance (ANOVA) is also employed to identify factor B (pulse time), C (duty cycle), and D (peak value of discharge current) as the most important parameters, which account for about 81.5% of the variance. The factors E (powder concentration) and H (powder size) are found to have relatively weaker impacts on the process design of the high-speed EDM. Furthermore, a confirmation experiment of the optimal process shows that the targeted multiple performance characteristics are significantly improved to achieve more desirable levels.

B-spline tool offset of a free-form curve in the shoe last high-speed machining CNC system

Aiming at the special requirements of a shoe last high-speed machining process and the large dataset which could be gained by the reverse engineering technique, this paper analyzes the conventional tool-offset methods and presents a B-spline tool-offset model. A simple vector-analyzed algorithm to smooth the tool-offset curve in which there are local strange points is proposed, and then the second tool-offsetting, which obtains the fine data of the machining tool’s center points, is directly processed. To reduce the error from tool offsetting of the C2 continuity curve, this paper gains a smoother curve after processing via the edge points joint algorithm, which effectively solved the overcut or undercut problems in the high-speed machining of the spline curve.

The Use of the Taguchi-Grey Based to Optimize High Speed End Milling with Multiple Performance Characteristics

This paper presents a new approach for the optimization of the high speed machining (HSM) process with multiple performance characteristics based on the orthogonal array with the grey relational analysis has been studied. Optimal machining parameters can then be determined by the grey relational grade as the performance index. In this study, the machining parameters such as cutting speed, feed rate and axial depth of cut are optimized under the multiple performance characteristics including, tool life, surface roughness, and material removal rate(MMR). As shown experimental results, machining performance in the HSM process can be improved effectively through this approach.