Ship-Peng Lo

An adaptive-network based fuzzy inference system for prediction of workpiece surface roughness in end milling

Abstract An adaptive-network based fuzzy inference system (ANFIS) was used to predict the workpiece surface roughness after the end milling process. Three milling parameters that have a major impact on the surface roughness, including spindle speed, feed rate and depth of cut, were analyzed. Two different membership functions, triangular and trapezoidal, were adopted during the training process of ANFIS in this study in order to compare the prediction accuracy of surface roughness by the two membership functions. The predicted surface roughness values derived from ANFIS were compared with experimental data. The comparison indicates that the adoption of both triangular and trapezoidal membership functions in ANFIS achieved very satisfactory accuracy. When a triangular membership function was adopted, the prediction accuracy of ANFIS reached is as high as 96%.

An analysis of cutting under different rake angles using the finite element method

Abstract The elastic–plastic finite element method is developed in this study to investigate the effect of the tool rake angle on the chip and the machined workpiece during the precision cutting process. Cutting simulations were conducted under a variety of tool rake angles to explore the effect of tool rake angle on cutting force, the geometric shapes of the chip, the equivalent stress distribution, the residual stress and the surface of the machined workpiece. The findings indicate that an increase in the tool rake angle leads to the following: a decrease in the cutting force required during machining; a smoother chip contour; a smaller difference between the chip thickness and the undeformed chip thickness; a decrease in the equivalent stress distribution; and a less pronounced curvature phenomenon at the initial cutting end of the machined workpiece. Further, the results also show that as the tool rake angle increases from 5 to 15°, the changes in the above-mentioned physical phenomena are more pronounced. In contrast, the increase of tool rake angle from 15 to 20° hardly brought about any changes to these physical phenomena. Therefore, to reach the goal of lowering the above requirements such as the cutting force so as to extend tool life, it is recommended that a tool rake angle of 15° instead of 20° be adopted for cutting.

Finite element modeling for chemical mechanical polishing process under different back pressures

Abstract In this paper, the revolutions of wafer and pad were considered the same and the force forms including the pressure exerted on the top of wafer surface and the carrier back pressure were axisymmetric distributed, a 2D axisymmetric quasi-static model for chemical mechanical polishing process (CMP) was first established. Based on the principle of minimum total potential energy, a 2D axisymmetric quasi-static finite element model with a carrier back pressure compensation for CMP was then established. In this model, the four-layer structures including wafer carrier, carrier film, wafer and pad are involved. The effect of a given carrier back pressure on the stress components and von Mises stress on wafer surface was analyzed and the effect of different carrier back pressures on the von Mises stress and nonuniformity on wafer surface was investigated. The findings indicated that the axial stress was the dominant factor to the von Mises stress distribution on wafer surface. Because that the back pressure had the maximum affect on the axial stress and it made the axial stress increased along the − z direction. Thus, while applying a back pressure, the von Mises stress distribution increased. In addition, the changes of back pressure had the trend to be proportional to the von Mises stress variation and to be inversely proportional to the nonuniformity variation. The result showed obviously that during the CMP process, it could achieve the purpose to improve the planarization of wafer surface by compensating the different carrier back pressures.

A study of modularity operation of systems based on maintenance consideration

A module is a set of some disassembly and/or non-disassembly components or parts. It usually is used not only in supporting or carrying out the same function, but also in decreasing the complexity of a system in maintenance. Traditionally, the module form of a system is created according to either the function requirements or the manufacturing considerations. It is determined mainly depending on the individual condition of systems in designing, and has no concrete and scientific approach to progress system modularity. To overcome the faults in traditional modularity, the present paper presents a method of modularity based on the consideration of system maintenance policy for constructing the system modules. First, the correlations in designing the functions/components within a system are analysed according to four input/output parameters--geometry constraint, mechanical strength, energy flow and signal flow--to build the hierarchy structure of system in combination. Second, the parameters of reliability and cost of these functions/components are then investigated to describe the degradation in usage and to calculate the maintenance cost of each possible module. Third, the aged-maintenance model is used to evaluate the ideal maintenance intervals and the total maintenance costs of these modules so that the optimal module type of the system can be established. Finally, a hydraulic system used in squeezing machinery is adopted to depict the process of system modularity. Ideally, the result in modularity may feedback to designers to modify the design and to ensure the achievement in designing for maintainability.

A study of deformation of the machined workpiece and tool under different low cutting velocities with an elastic cutting tool

Abstract To understand the effects of cutting velocity, tool elastic deformation generated by high normal stresses during metal cutting processing and artificial tool flank wear on the cutting process, an iterative mathematical model for calculating the tool–workpiece contact problem was developed in this paper under the assumption of elastic cutting tools. In this model, the finite element method is used to simulate cutting of mild steel by the P20 cutting tool with constant artifical tool flank wear under the condition of three different cutting velocities. The results obtained in the simulation were found to match the experimental data reported by related studies. The simulation results also indicate that the thrust and the cutting forces are functions of cutting velocity. Besides, both the normal stress on the tool rake face and the residual stress of machined workpiece generally decrease with increase in cutting velocity. According to the findings in this study, though the residual stress of the machined workpiece decreases as the cutting velocity increases, its value is still higher than that in ordinary conditions due both to the influence of tool flank wear and tool elastic deformation. Also, the phenomenon of curvature at the workpiece end easily occurs.

An investigation of sticking behavior on the chip–tool interface using thermo-elastic–plastic finite element method

Abstract This paper presents a high-speed orthogonal cutting model and also establishes a finite element method to analyze the mechanics of steady state in the high-speed orthogonal precision cutting process of oxygen-free high conductivity copper. The paper proposes a variant pseudo-friction coefficient concept to modify the large-deformation finite element formulation and to develop a stress analysis model of the chip–tool interface to solve the problems of the shear stress, normal stress and variant pseudo-friction coefficient on the chip–tool interface. In spite of the high-speed micro-cutting, the effect of high strain rate and high temperature will produce the sticking phenomenon on the rake face of the tool. Not only will the sticking phenomenon shorten tool life, but also will have an effect on the machining accuracy in precision diamond cutting. Therefore, the results in this study can be considered as acceptable consideration during the procedure of high-speed precision cutting.

Ultra-precision orthogonal cutting simulation for oxygen-free high-conductivity copper

Abstract This paper presents an analytical method for predicting the mechanical state of a machined surface with a finite-element model of orthogonal precision cutting. A geometrical separation criterion for the workpiece at the front edge of the tool is also proposed instead of other criteria, and the application of the method is discussed. The flow stress of oxygen-free high-conductivity copper (OFHC copper) was taken as a function of strain, strain rate and temperature in order to reflect realistic behavior in metal cutting. In this paper, a diamond tool was used to conduct the ultra-precision cutting of the OFHC copper. Through the simulation, the residual stress and strain distributions within the machined sub-layer were calculated analytically, the calculated cutting force being found to agree with the experimental results. The simulation results indicate that as far as the impact of temperature, strain and strain rate on OFHC copper is concerned, that of temperature is the most dramatic. The effect of temperature leads to a smaller residual stress in a machined workpiece and limited deformation of the workpiece surface. If the effect of temperature is not considered, the greater is the cutting velocity, the greater is the residual stress of the workpiece and the greater is the deformation of the workpiece surface.

2-D discontinuous chip cutting model by using strain energy density theory and elastic-plastic finite element method

Abstract The formation of discontinuous chip is investigated in this paper. The cutting simulation was conducted on 60–40 brass (60% Cu, 40% Zn) under an extremely low cutting speed. The region of the maximum strain energy density (SED) distribution value relative to the minimum value, i.e. (dw/dv)minmax, was used as the criterion to predict the initial breakage location under the presumption that the curvature direction of the maximum SED was the direction of crack growth. The shape and cutting force of discontinuous chip crack, the stress and strain distribution of the workpiece and chip, and the variation of various nodal force on the chip–tool interface were derived.

A study of the tool-chip interface contact problem under low cutting velocity with an elastic cutting tool

Abstract To understand the effects of elastic deformation of the tool and the crater phenomenon generated by the cutting force and high pressure during metal cutting processing on the cutting process, an iterative mathematical model for calculating the tool-chip contact is developed in this paper under the assumption of elastic cutting tools. In this model, the finite-element method is used to simulate the cutting of mild steel by a cutting tool of three different materials. The results obtained in the simulation are found to match experimental data reported by related studies. The simulation results also indicate that tools with a smaller stiffness produce greater elastic deformation. Further, decrease of the rake angle due to elastic deformation of the tool can result in greater difficulty in internal deformation of the material and an increase in cutting force. The micro-crater phenomenon on the tool face generated by high pressure at the tool-chip interface is the preliminary symptom of crater wear on the tool face. Therefore, under some machining conditions, such as in precision machining or in automation processing where tool compensation is required, the phenomenon of elastic deformation of the tool must be considered carefully to ensure product precision.

Effect of different tool flank wear lengths on the deformations of an elastic cutting tool and the machined workpiece

To understand the effects of tool elastic deformation generated by high normal stresses during metal cutting processing and artificial tool flank wear on the cutting process, an iteration mathematical model for calculating the tool-workpiece contact problem was developed in this paper under the assumption of elastic cutting tools. In this model, the finite element method is used to simulate cutting of mild steel by the P20 cutting tool with three different lengths of artificial tool flank wear. The results obtained in the simulation were found to match the experimental data reported by related studies. The simulation results also indicate that the thrust and the cutting forces are a function of the length of artificial flank wear land. The temperature distribution on the tool flank wear increases with the increase in tool flank wear length. Besides, the normal stress on the wear land generally decreases with the increase in tool flank wear. Factors affecting the tool rake face and tool flank deformation are all derived from the interactions between the normal stress and temperature distribution. The crater deformation on the tool rake face occurs because of the greater effect of normal stress than that of temperature distribution. On the contrary, the convex deformation on the tool flank is formed because the effect of the temperature distribution is greater than that of normal stress.