T. Shirakashi

FEM analysis of cutting sequence effect on mechanical characteristics in machined layer

Abstract The cutting process of the affected layer is simulated by FEM and the influence of cutting sequence on residual stress and strain are discussed in this report. The residual stress and strain after machining in the workpiece are affected by the flow stress characteristic of the workpiece and the cutting conditions, like tool geometry and cutting speed. In addition, the affected layer by previous cutting is usually cut again in the following cutting process. Cutting of the affected layer causes the change of cutting forces or shear angle. Thus the residual stress and strain are affected by the cutting sequence, too. In the cutting sequence from roughing to finishing, the residual stress might be changed by each cutting sequence. In case of the rough machining of an annealed workpiece, the tensile residual stress is generated in the cutting direction within the machined surface. The fine machining following the rough machining causes the compressive residual stress on the surface. Repetition of the fine machining, however, does not cause the compressive residual stress any more. According to these results the residual stress level might be controlled by the optimization of machining process.

Chip breaking analysis from the viewpoint of the optimum cutting tool geometry design

Abstract The chip breaking process mechanism of the grooved rake face tools is simulated by thermo-elastic plastic finite element method. The shape, temperature and flow stress of the deformed chip in the initial model of this simulation are obtained from the finite element analysis of the steady state metal cutting mechanism. In this chip breaking simulation, a stress-dependent fracture criterion is used. The chip breakability and the force change at the chip breaker edge are obtained. The simulated results are in good agreement with experimental results for various cutting conditions and various tool geometries. It is verified that this simulation is effective as an analytical approach to the optimum metal cutting tool geometry design.

Feasibility of gentle mode machining of brittle materials and its condition

Abstract In order to discuss the feasibility of the damage-free machining—gentle or ductile mode machining—of brittle materials, a soda-lime glass and an aluminum oxide ceramic are machined under the SEM at very low cutting speed. A smooth ribbon-like chip and damage-free surface can be seen in fine machining of the glass, whilst contrarily in the machining of the ceramic a continuous but not smooth chip is generated but the surface is very smooth. The mechanical state of the machining process of the glass with the flow type chip is analyzed through FEM. The state is almost the same as those in the machining of metal. Finally the transition condition of the machining mechanism from a brittle mode to a gentle one is discussed from the view-point of the size effect of brittle fracture using FEM simulation.

Autonomous turning operation planning with adaptive prediction of tool wear and surface roughness

Abstract Small-sized batch jobs with large product diversification require intelligent machine tools to optimize cutting conditions by adapting to the cutting tools, work materials, and machine tools. Proposed is autonomous operation planning, which optimizes machining operations for each machine tool using adaptive prediction of processes. Machining processes are predicted and optimizes more accurately using the adapting parameters of the governing equations, used for analytical prediction, and/or weight parameters of neural networks through learning of machining results. When considering tool wear and surface roughness simultaneously, machining operations are optimizes to minimize cost by predicting flank wear analytically based on metalcutting theory and by predicting surface roughness with a neural network.

Flow-stress equation including effects of strain-rate and temperature history

Abstract This paper addresses effects of deformation history, temperature history and heat treatment history on the flow-stress variation in terms of the mathematical theory of plasticity. On the basis of this discussion, a new flow-stress equation taking account of effects of such histories is proposed. The equation consists of the strain rate; temperature, and the reference stress which is determined by the plastic deformation energy. The reference stress, the yield stress under the reference condition, is proposed as a measure of the history, and flow-stress is shown to depend on the reference stress but not on total plastic strain. The reference stress is shown to depend only on the generalized deformation energy, which is believed to be related to the stored energy of lattice defects introduced by plastic deformation. Plastic deformation accumulates the generalized deformation energy, and the recovery annihilates the energy. This study proposes a new flow-stress equation consisting of the reference stress, strain rate and temperature. The new flow-stress equation is applied to a forming process With varying conditions, and is consistent with experimental data. Finally, this paper provides mathematical account of the new flow-stress equation. It is shown that the deformation energy is the only parameter that can connect structural change in a lattice and the mathematical theory of plasticity. While any other parameters are possible, the deformation energy is the simplest and a justifiable parameter to evaluate the history.

The Prediction of Effects of Cutting Condition on Mechanical Characteristics in Machined Layer

The analytical method for prediction of mechanical state of machined surface layer was proposed. The residual stress and strain are caused by the mechanical sta.te and the thermal state of cutting process. Within the machined top surface by a sharp edge tool the tensile residual stress in the cutting direction was generated. The effects of cutting conditions such as tool rake angle, frictional characteristics of tool face, flow stress of the work piece and cutting speed on the residual stress were discussed. The distortion of work piece after released from chucking system, caused by rearrangement of residual stress distribution was also obtained. In addition, it may be possible to control the amount of residual stress and its distribution by change of tool edge geometry or using of cutting fluid.

Electrolytic cut-off grinding machine for composite materials

A new cut-off machine for a composite material has been developed. The machine uses a combined system of grinding and electrolysis and it can cut off a fragile composite material consisting of metal and non-metal components. Its fundamental performance is examined on low-carbon steel and cast iron. The machine can reduce the cutting force and roughness of a finished surface due to the effects of electrolysis, which results in less damage to the finished surface, this advantage being remarkable in amorphous-core cutting. The machine leaves no damage on the finished surface of an amorphous core, whereas a conventional cut-off grinder generates many micro-cracks and layer separation due to its large cutting force. This damage reduces the magnetic properties of the core. The new cut-off machine gives a very good performance in the cutting of composite material.

Cutting Performance of Tools with Curved Rake Face

The performance of metal cutting tools having a groove on the rake face is evaluated on the basis of cutting forces, cutting temperature and tool fracture probability. First the orthogonal and steady state cutting is analyzed by an elastic-plastic finite element method and the optimum upwind finite element method for temperature calculation. Then the tool fracture probability is calculated using a probabilistic fracture criterion. The cutting forces and the cutting temperature obtained by the finite element method decrease dramatically when the grooved tools are used. According to the tool fracture probability calculated, the profile of the tool rake face geometry affects on the tool reliability.

Numerical analysis of residual stress in a ground surface layer

A numerical simulating system, where changes of material properties are introduced, was developed to investigate residual stress in a ground surface layer. Several grinding processes are simulated using the system and they were compared with a conventional simulating method. The new system indicates that the changes of material properties make a surface layer yield easily, which layer causes residual stress. A steep raise of tensile residual stress is seen near the ground surface, which loses reliability of the product.

Finite Element Modelling of Machining of Glass Fiber Reinforced Plastics

A finite element modeling of machining of glass fiber reinforced plastics is developed for better understanding of the cutting mechanism. In the modeling, the fracture of both the glass fiber and the polyester matrix during machining is taken into account. A stress criterion is applied to the fracture of the fiber, while a modified strain criterion is applied to the fracture of the matrix. The influences of both the fiber direction angle and rake angle on the cutting mechanism are investigated.