Initial Chip Formation Research Articles

Orthogonal Microcutting of Thin Workpieces

With a broader intention of producing thin sheet embossing molds, orthogonal cutting experiments of thin workpieces are conducted. Challenges in machining thin workpieces are many: machining induced stress and deformation, fixturing challenges, and substrate effects. A setup involving continuous orthogonal cutting with a single crystal diamond toolof an aluminum alloy (Al6061-T6) workpiece fixtured using an adhesive to reduce its thickness is used to study trends in forces, chip thickness, and to understand to what level of thickness we can machine the workpiece down to and in what form the adhesive fails. There are no significant changes observed in the forces and chip thickness between thick and thin workpieces during the experiments, meaning that the cutting energy required is the same in cutting thick or thin workpieces. The limitation to achieve thinner workpiece is attributed mainly due to the detachment of the thin workpiece by peel-off induced by adhesive failure mode, which occurs during initial chip formation as the tool initially engages with the workpiece. We use a finite element model to understand the stresses in the workpiece during this initial tool engagement when it is thick and when it is thin, as well as the effect of the adhesive itself and the effect of adhesive thickness. Simulation results show that the tensile stress induced by the tool at the workpiece-adhesive interface is higher for a thinner workpiece (45 μm) than a thicker workpiece (150 μm) and higher at the entrance. As such, a thinner workpiece is more susceptible to peel-off. The peeling of thin workpiece is induced when the high tensile stress at the interface exceeds the tensile-at-break value of the adhesive.

Study on the Modeling Method for Finite Element Analysis of Chip Formation Process

FEM is a powerful tool for predicting cutting process variables, which are difficult to obtain with experimental methods. In this paper modeling techniques on chip formation by using the commercial FEM code ABAQUS are discussed. Because of the limitations of Lagrangian and Eulerian methods, a modeling method based on ALE (Arbitrary Lagrangian Eulerian) technology is proposed to simulate the chip formation process. It consists of three chip formation analysis steps, i.e. initial chip formation, chip growth and steady-state chip formation. With this modeling method, high speed turning process of stainless steel 2Cr13 is simulated. And the predicted variables are compared with experimental data. It has been found that the results are in good agreement with the experimental ones.

Formation of nanostructured metal particles using negative rake angle cutting tools

The results of initial chip formation demonstrate a very complex interaction between metal chip and rake face of the cutting tool. These complex interactions can impart a sophisticated internal microstructure where grains are strained with nanometer dimensions. Plastic shear strains between two and ten result in the creation of nanostructured grains that are between 45 nm and 150 nm in diameter depending upon the material strained and the magnitude of shear strain. This paper describes how the contact conditions between chip and a negative rake angle cutting tool can control the internal microstructure of the metal chip in order to produce a nanostructured metal. Metal chips produced can act as feedstock for secondary manufacturing processes that produce engineering components that have superior mechanical and physical properties compared to cast and wrought materials.

RETRACTED ARTICLE: Initial shear strain development during formation of nanostructured metal chips

The interaction between a newly formed metal chip and the rake face of a cutting tool reveal the complicated nature of initial chip formation and plastic shear strains during the first few seconds of intimate contact. The loading placed on the metal chip during the first encounter with the cutting tool manifest themselves as an unpredictable curl that forces the chip to move away from the surface of the rake face and produce uneven plastic shear strains throughout the chip. The variation of the load causes instabilities on the shear plane that is directly observed using a high speed camera. As the variation of load progresses, the chip tends to curl away from the tool with varying radii until the apparently curved shear plane becomes linear. The results of initial chip formation demonstrate a very complex interaction between metal chip and rake face of the tool and the resulting development of the shear plane and its effect on plastic shear strains within the metal chip.

Finite element simulation for burr formation near the exit of orthogonal cutting

A coupled thermo-mechanical model of plane-strain orthogonal metal cutting including burr formation is presented using the commercial finite element code. A simulation procedure based on Normalized Cockroft-Latham damage criterion is proposed for the purpose of better understanding the burr formation mechanism and obtaining a quantitative analysis of burrs near the exit of orthogonal cutting. The cutting process is simulated from the transient initial chip formation state to the steady state of cutting, and then to tool exit transient chip flow by incrementally advancing the cutting tool. The predicted burr profile is compared with experimental data and found to be in reasonable agreement. The effect of the tool conditions and cutting conditions on the burr formation process was also investigated.

Finite Element Modeling of Burr Formation in Orthogonal Metal Cutting

A coupled thermo-mechanical model of plane-strain orthogonal metal cutting including burr formation is presented using the commercial finite element code. A simulation procedure based on Normalized Cockroft-Latham damage criterion is proposed for the purpose of better understanding the burr formation mechanism and obtaining a quantitative analysis of burrs at exit. The cutting process is simulated from the transient initial chip formation state to the steady-state of cutting, and then to tool exit transient chip flow, by incrementally advancing the cutting tool. The effects of cutting condition on the non-steady-state chip flow while tool exit can be investigated using the developed finite element model.

Observation of shear plane instability during microgrinding of plastic metals

The abnormal loads placed on the metal chip during the first encounter with the cutting tool manifest themselves as an unpredictable curl that forces the chip to distance itself from the surface of the rake face. Frictional interactions between a metal chip and the rake face of a virgin cutting tool reveal the complex nature of initial chip formation and shear plane instabilities during the first few seconds of intimate contact. The variation of the load causes a shear plane instability that is directly observed using a high-speed camera and a specially designed machining apparatus. As the variation of load progresses, the chip tends to curl away from the tool with varying radii until the apparently curved shear plane becomes linear. The results of initial chip formation demonstrate a very complex interaction between metal chip and rake face of the tool and the resulting development of the shear plane and its effect on chip formation.

Micromachining selected metals using diamond coated cutting tools

Micro and nanotechnology is becoming increasingly important to the needs of society. Therefore, the need to create devices from selected metals becomes more apparent. High-speed milling has been shown to provide a great deal of promise in creating microstructures and in nanotexturing surfaces in engineering materials. Cutting tool rotation is expected to reach 1,000,000 rpm (revolutions per minute) compared with conventional cutting speeds of around 30,000 rpm. Rotating the tool this quickly reduces cutting forces, which produce a high quality of cut so that post-processing is not required. Clearly, strain rates imparted to the workpiece at these speeds are very high and this influences initial chip formation and chip removal mechanisms. High strain rates imparted cause distinct chip formations in certain metals to occur which are similarly observed in other materials. Certain soft metals such as aluminium do not machine very well because the material adheres to the cutting tool. However, high strain rates tend to overcome these limitations. This paper examines high strain rate initial chip formation in metals, compares these results to other materials and shows that an initial chip curl model can be applied to describe high strain rate machining phenomena at the microscale.

High strain rate induced initial chip formation of certain metals during micromachining processes

As microtechnology and nanotechnology become increasingly important to the needs of society, the need to create devices in engineering materials becomes more apparent. High speed milling has been shown to provide a great deal of promise in creating microstructures and in nanotexturing surfaces in engineering materials. Cutting tool rotation is expected to reach 1 000 000 revolutions per minute (rev min−1) compared with conventional cutting speeds of around 30 000 rev min−1. Rotating the tool this quickly reduces cutting forces, which produces a higher quality of cut so that post- processing is not required. Clearly, strain rates imparted to the workpiece at these speeds are very high and this influences initial chip formation and chip removal mechanisms. High strain rates imparted cause distinct chip formations in engineering materials to occur which are similarly observed in other materials, most notably biological materials such as cancellous bone. Certain soft metals such as aluminium do not machine very well because the material adheres to the cutting tool. However, high strain rates tend to overcome these limitations. This paper examines high strain rate initial chip formation in metals, compares these results to other materials, and shows that an initial chip curl model can be applied to describe high strain rate machining phenomena at the microscale.

2D FEM estimate of tool wear in turning operation

Finite element method (FEM) is a powerful tool to predict cutting process variables, which are difficult to obtain with experimental methods. In this paper, modelling techniques on continuous chip formation by using the commercial FEM code ABAQUS are discussed. A combination of three chip formation analysis steps including initial chip formation, chip growth and steady-state chip formation, is used to simulate the continuous chip formation process. Steady chip shape, cutting force, and heat flux at tool/chip and tool/work interface are obtained. Further, after introducing a heat transfer analysis, temperature distribution in the cutting insert at steady state is obtained. In this way, cutting process variables e.g. contact pressure (normal stress) at tool/chip and tool/work interface, relative sliding velocity and cutting temperature distribution at steady state are predicted. Many researches show that tool wear rate is dependent on these cutting process variables and their relationship is described by some wear rate models. Through implementing a Python-based tool wear estimate program, which launches chip formation analysis, reads predicted cutting process variables, calculates tool wear based on wear rate model and then updates tool geometry, tool wear progress in turning operation is estimated. In addition, the predicted crater wear and flank wear are verified with experimental results.

Penetration-rate performance of roller-cone bits

The penetration rate obtained with a roller cone bit is controlled by either the cuttings generation process or cuttings removal process. Most previously reported penetration rate models have not explicitly included the cuttings removal effects. This paper presents a penetration rate model that includes the effect of both the initial chip formation and cuttings removal processes. The model is an extension of a previously published model that neglected the effects of cuttings removal. The cuttings removal effects must be included in a valid penetration rate model because they can often limit the ROP to less than 20% of the expected ROP for perfect cleaning. The model is used to show that the reduction in penetration rate at high borehole pressure is the result of both local cratering effects and global cleaning effects. Increased hydraulics will increase the penetration rate when it is limited by global cleaning effects. The penetration rate reduction due to local cratering effects is largely a function of mud properties and borehole pressure and is not helped much by increases in hydraulics.

Penetration-Rate Performance of Roller-Cone Bits

Summary The rate of penetration (ROP) obtained with a roller-cone bit is limited by either the cuttings-generation or cuttings-removal process. An ROP model that includes the effect of both the initial chip formation and cuttings-removal processes is presented. Laboratory observations show that the reduction in ROP at high borehole pressure is the result of both local cratering effects and global cleaning effects.