Cutting Temperatures Analysis for Machine Work Study

Cutting Temperatures

INTRODUCTION

When metal is cut, energy is expended in deforming the chip and in overcoming friction between the tool and the workpiece. Almost all of this energy is converted to heat  and  high temperatures are produced in the deformation zones and surrounding regions of the chip, tool, and workpiece. Cutting temperatures affect machining performance. Temperatures in the primary deformation zone, where the bulk of the deformation involved in chip formation occurs, influence the mechanical properties of the work material. Complete analyses of the mechanics of cutting use temperature-dependent constitutive models.

MEASUREMENT OF CUTTING TEMPERATURES

Tool–Work Thermocouple Method and Related Techniques

The tool–work thermocouple method was first developed in the 1920s. It uses the tool and workpiece as the elements of a thermocouple. The hot junction is the interface between the tool and the workpiece, and the cold junction is formed by the remote sections of the tool and work piece, which must be connected electrically and held at a constant reference temperature. Required insulation has to be there. 

Infrared Methods

Cutting temperatures can also be estimated by measuring the infrared radiation emitted from the cutting zone.  Since reliable point sensors have been available for some time, they have been applied by a number of researchers to measure rake and relief face temperatures in both cutting and grinding

FACTORS AFFECTING CUTTING TEMPERATURES

The process parameter with the greatest influence on cutting temperatures is the cutting speed. Increasing the cutting speed increases the rate at which energy is dissipated through plastic deformation and friction, and thus the rate of heat generation in the cutting zone. Increasing the feed rate also increases heat generation and cutting temperatures. For moderate ranges of these variables, the cutting speed has a greater influence. The tool–chip interface temperature increases with the square root of the cutting speed but the third root of the feed

THERMAL EXPANSION

Thermal expansion can produce significant dimensional and form errors in precision machining processes. In many cases, errors are caused by the accumulation of hot chips on flat surfaces of the machine tool. A variety of methods for controlling these errors, including modifications of the machine design to eliminate flat surfaces, the use of coolants to ensure chip removal, and the use of constant-temperature fluid baths to control temperatures throughout the system, are used in practice.