Philippe Darnis

Subsurface damage distribution characterization of ground surfaces using Abbott–Firestone curves

Measurement of subsurface damage (SSD) induced by grinding process is of major interest in the development of high laser damage fused silica optical components manufacturing processes. Most SSD measurements methods give only access to the peak to peak value. We herein report on the benefit of using Abbott-Firestone curves to get an insight of the SSD distribution inside the optical material. We evidence on various diamond wheel ground fused silica substrates that such an approach is complementary to a classical SSD peak to peak measurement and bring useful information to optimize a grinding process.

New method to characterize a machining system: application in turning

Many studies simulates the machining process by using a single degree of freedom spring-mass system to model the tool stiffness, or the workpiece stiffness, or the unit tool-workpiece stiffness in modelings 2D. Others impose the tool action, or use more or less complex modelings of the efforts applied by the tool taking account the tool geometry. Thus, all these models remain two-dimensional or sometimes partially three-dimensional. This paper aims at developing an experimental method allowing to determine accurately the real three-dimensional behaviour of a machining system (machine tool, cutting tool, tool-holder and associated system of force metrology six-component dynamometer). In the work-space model of machining, a new experimental procedure is implemented to determine the machining system elastic behaviour. An experimental study of machining system is presented. We propose a machining system static characterization. A decomposition in two distinct blocks of the system “Workpiece-Tool-Machine” is realized. The block Tool and the block Workpiece are studied and characterized separately by matrix stiffness and displacement (three translations and three rotations). The Castigliano’s theory allows us to calculate the total stiffness matrix and the total displacement matrix. A stiffness center point and a plan of tool tip static displacement are presented in agreement with the turning machining dynamic model and especially during the self induced vibration. These results are necessary to have a good three-dimensional machining system dynamic characterization (presented in a next paper).

Relations between subsurface damage depth and surface roughness of grinded fused silica

Relationships between subsurface damage (SSD) depth and peak to valley surface roughness (Rt) have been widely studied and present a major interest for an easy assessment of the SSD depth. We look at the relation between SSD depth and other surface roughness parameters using the Abbott-Firestone curve on a large campaign of grinding tests (with different abrasive grain size, grinding speed and grinding mode). The results reveal that Abbott-Firestone parameters are better for an assessment of SSD depth and that relationships between SSD depth and surface roughness are not universal but depend on the grinding process.

Orthogonal cutting of TA6V alloys with chamfered tools: Analysis of tool–chip contact lengths

In aerospace industry, the materials constituting aircraft evolved considerably in recent decades. The choice of composite materials (carbon fiber–reinforced plastic or multi-material) reduces the weight of structures, but for critical parts that support important forces or temperature, the indicated materials are alloys based on nickel or titanium. Consumption of titanium for the aerospace industry is growing rapidly, and the new generations of aircraft show an increase in the percentage of titanium. The TA6V is mostly used for structural parts, especially for engine pylon. Due to its low thermal properties, it shows a poor machinability, leading tools to undergo severe wears. The aim of this work is to understand the relation between cutting conditions and chamfered tool geometries on chip formation and tool wear. Based on a model dedicated to the understanding of cutting process with chamfered tool and on experimental tests, this work will show the influence of feed, cutting speed, chamfer length and rake angle on tool–chip contact lengths. It will also show the influence of these parameters on the variability of these contacts within a same geometry or cutting condition. This will lead to another interpretation of tool wears and pressures on the rake face.

Comparison of the chip formations during turning of Ti64 β and Ti64 α+β

For a number of years, the rise in the number of titanium alloy grades and therefore of microstructures has hampered the productivity of titanium parts. In order to understand the phenomena involved, this study presents a comparison of the chip formations between two microstructures obtained from the same alloy. The first part presents the two alloys, their microstructures and their methods of production. The chip formation of each material is then presented and shows two completely different processes. The first process is classical, for which shear mechanisms appear to be cyclical. Conversely, the second process depends on the orientation of the microstructure when the shear occurs. For a better understanding of the phenomena, the effect of cutting speed and feed is also discussed. Finally, in the last section, chip formations for the two microstructures are summarized and perspectives are presented.

3D modelling of the mechanical actions of cutting: application to milling

Along the cutting edge, the geometric and kinematic parameters vary greatly and the velocity vector at each point is very sensitive to the current position of the point considered on the cutting edge. The proposed study includes, for each of the three shear zones, the effect of velocity gradients on the strain fields and strain rates. These velocity gradients generate additional displacements of the chip, in three dimensions and, therefore, new force components and cutting moments. This study presents the overall approach for calculating cutting action starting with a detailed description of each feature area. The wrench of action is determined at the tip of the tool based on the elementary forces along the edge.

Experimental study on cutting flexible sheet materials using an oscillating knife

Purpose The purpose of this paper is to understand the impact of the cutting forces on the quality of pieces in industrial cutting of multi-ply textile material. It also tries to establish a cutting model that can simulate the cutting forces in order to understand the behaviour of the blade. Design/methodology/approach Working on an industrial machine, a cutting head with an oscillating knife is instrumented with different sensors. Using this equipment, cutting forces can be analysed experimentally while the fabric is being cut along a straight line. Findings A model of the physical phenomena of the cutting forces is proposed, taking different parameters into account such as the geometry of the blade, the properties of the material being cut and the parameters of the cut. The simulated forces and the monitored forces are compared and parameters for minimising the cutting forces of fabrics are deduced. Research limitations/implications Due to the wide diversity of fabrics, all with different mechanical characteristics, this research only began with the study of denim in a straight cut. Originality/value This paper describes an instrumentation of automatic cutting head for textile. It manages to simulate the action of the fabrics on the blade through effort monitoring and help in the understanding of the multi-ply cutting process.

Determining the Position of Cutting Tool in Drilling for Analysis of Mechanical Actions

The mechanical actions measurement can highlight a series of mechanical phenomena occurring in the cutting process. During the experiments, we use a six-component dynamometer to measured the forces and the moments applied by the tool to the workpiece. In this paper, the authors present a method for determining the cutting tool position in drilling process, with purpose to transport of the moments (calculation of the torsor in each of the holes). Then can be achieved analyze of the forces and moments for every hole.

Correlation between Torsor Measurements on the Chip Orientation

Since some years, the better understanding of the material cutting process has been shown with the benefit of the forces and moments measurement. In this article, simultaneous six mechanical components and chip orientation measurements were realized during turning tests. During these tests, the influence of the depth of cut or feed rate has been observed and correlation between the chip orientation and the moment vector orientation or the central axis characteristics has been shown. Nomenclature

The Preliminary Study of Machinability during Milling of Titanium Alloy (Ti-6Al-4V)

Titanium and its alloys have found wide application in the aerospace, biomedical and automotive industries owing to their good strength-to weight ratio and high corrosion resistance. However, these alloys have very poor machinability, which is attributed to their inherent high strength maintained at elevated temperature and low thermal conductivity leading to high cutting temperatures. This paper presents the findings of an experimental investigation into the effects of cutting speed, feed rate and depth of cut when milling titanium alloy Ti-6Al-4V. The cutting forces were the response variables investigated. This experimental investigation is translated into a mathematical model of cutting forces designed on the basis of the results obtained from this research.