Remote Nondestructive Thermal Control of Elastic Abrasive Cutting

*Anna Stoynova, Irina Aleksandrova and Anatoliy Aleksandrov*

### **Abstract**

High temperatures during abrasive cutting lead to increased harmful gas emissions released into the environment, intensified cut-off wheel wear, microstructural changes in the machined material, and occurrence of thermal flaws. Temperature measurement in abrasive cutting is difficult due to the small size of the heated area (only tenths of mm<sup>2</sup> ), high temperatures (above 1000°C), continuous change of the conditions within one cut-off cycle, large temperature gradient (more than 200°C), high cutting speed (above 50 m/s) and high mechanical load. The infrared thermography (IRT) application for thermal control of elastic abrasive cutting have been studied. The performed thermal measurements have been verified with the results obtained from the temperature models of workpiece, cut-off wheel, and cut piece depending on the conditions in elastic abrasive cutting of two structural steels C45 and 42Cr4. The parameters of effective abrasive cutting have been determined by applying multi-objective optimization.

**Keywords:** abrasive technology, elastic abrasive cutting, nondestructive thermal control, multi-objective optimization

## **1. Introduction**

Abrasive cutting is widely used in industry due to its high production rate (machining is performed at a speed of 100–200 mm<sup>2</sup> /s) and low labor costs. It is characterized by high temperatures (above 1000°C) in the cutting zone, intensive wear and deterioration of the abrasive tool cutting ability, spark generation, increased emissions of environmentally harmful gases, high noise level, risk of accidents, changes in the microstructure of surface materials and occurrence of thermal flaws [1–7]. Those disadvantages are related to the high cutting speed (above 50 m/s), constant changes in cutting conditions within a cut-off cycle, and unfavorable geometry of abrasive grains (negative rake angles).

Almost all mechanical work (over 97%) converts into thermal energy and only a small part of it transforms into hidden energy to change the crystal lattice of the material being machined [8, 9].

As a result of the conversion of the mechanical energy used in the cutting process into thermal energy, various heat sources emerge and the process of generating that heat depends on cutting conditions.

As far as every physical phenomenon has two sides—quantitative and qualitative, then, as a rule, the control of the energy transfer in a specific physical phenomenon involves the measurement of two quantities. When controlling heat

exchange processes, the two quantities to be measured are temperature and thermal flux. Measuring the thermal parameters of thermal non-stationary processes, in particular, a rapidly changing thermal flux remains relevant today. Among the techniques for measuring unstable thermal fluxes, those using infrared cameras are preferred [10–12]. Infrared thermography provides remote and wireless real-time measurements of temperature fields of high-speed moving objects. However, to obtain accurate measurements, all emerging noises and interferences need to be compensated or minimized, which is а kind of a "payoff" for the universality of the thermographic thermal control.

By changing the abrasive cutting conditions, which directly define the thickness of the layer of material being cut, and, as a result, the temperatures of the tool, chip, workpiece, and cut piece, the thermal fluxes are controlled and conditions for increasing the tool life, the intensity of the cutting process and the quality of the machined surfaces are provided. Therefore, to improve the effectiveness and applicability of abrasive cutting, it is necessary to study and model the parameters of the process and to optimize the conditions for its implementation. This allows us to apply thermographic monitoring for preventive detection of unexpected changes in the parameters of the elastic abrasive cutting process and for ensuring a high-quality process.

To study the thermal phenomena in elastic abrasive cutting, an innovative approach has been used. It involves a wireless thermal control provided by infrared thermography and the application of the methodology of planned experiments and multi-objective optimization. An original thermographic procedure for increasing the precision of the thermal control during abrasive cutting is offered.
