Digital simulation of machining

Over the last ten years, the evolution of machining techniques has led to the development of a new production concept that boosts productivity: High-Speed Machining (HSM).

Thermomechanical characteristics are even more important in UHV operations than in conventional machining. This is why the main lines of scientific research are very UGV-oriented.

The machining operation consists of removing material using a cutting tool. The workpiece (turning) or the tool (milling) is driven in rotation. With a combined tool and feed movement, material is removed at the interface between the tool tip and the workpiece (chip removal).

High Speed Machining is characterized by high cutting speeds (relative speed of the tool in relation to the workpiece). These high speeds generate a specific cutting phenomenon.

By increasing the cutting speed beyond the speed limits of conventional machining, we begin by crossing a zone of unusable speeds in which cutting conditions are degraded (rapid tool wear, poor surface finish...), then we arrive in the UHS domain where cutting conditions are excellent. The boundary between these zones is arbitrary and depends on the materials being machined.

The modeling of these phenomena, with a view to predicting machining operations, remains a very delicate task, depending on the objectives we set ourselves, especially if we are concerned with details on a microscopic scale.

Thermal stresses are generated during cutting by self-heating within the workpiece material and by friction at the tool/workpiece interface.

In conventional machining, heat energy is dissipated not only in the swarf, but also in the workpiece and tool, in significant proportions. As a result, the material undergoes a local heat treatment (surface hardening) which modifies the characteristics of the finished part.

In HSM, the nature of chip formation is different, and more than 80% of the cutting energy is evacuated in the chips. Although higher energies are involved, there is no time for heat exchange between the chip and the workpiece: the latter remains virtually at room temperature.

The aim of this article is to present machining simulation techniques at different scales:

• human scale: simulation of the machining environment: tool, machine, kinematics... ;

• macroscopic scale: tool/part for visualizing trajectory defects, predicting surface states, etc. ;

• microscopic scale: the cutting edge/material interface: numerical simulation of cutting – finite element modeling.

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