Investigation on the Influence of Nodularity in Machining of Compacted Graphite Iron (CGI)

Licentiate thesis, 2008

Stringency of environmental legislation on emission rates and increasing vehicle performance requirements are pushing the automotive and heavy truck industries to find new solutions for their diesel engines. Two potential opportunities to address these challenges involve increased combustion pressure to obtain more efficient combustion or reducing the weight of the engine. Seeking a solution through the commonly used diesel engine material, gray cast iron, is not possible due to limiting mechanical properties. But Compacted Graphite Iron (CGI) is known to be a suitable material which can meet these new demands. Despite this promise, however, the use of CGI has been limited due to difficulties in its machinability. To overcome this obstacle, better performing and suitable tools is a key factor. A good way to approach this challenge is to gain an understanding of the load picture on the tool and wear mechanisms. In this study, a systematic approach is presented for understanding the cutting process when machining Compacted Graphite Iron (CGI) materials of different nodularity with coated cemented carbide inserts. Cutting forces, tool temperature and tool wear are investigated. The tool temperature was measured with an Infra Red (IR) camera and modelled according to FEM (Finite Element Method) to estimate the temperature in the cutting zone where the IR camera was unable to function. Experimental data from cutting forces, quick-stop tests (e.g. shear plane angle), contact length measurement, tensile test and the results of the IR camera measurements were used, both to calibrate and to validate the temperature model. The results showed that increasing nodularity led to higher cutting forces and temperature. Increasing nodularity had an impact on wear at moderate and high cutting speed, but not at lower cutting speed. By classifying the wear mechanisms, we gained knowledge that may be used in tool design. The results demonstrate the need for complementing the IR camera temperature measurement with modelling to get an estimate of the temperatures in the cutting zone.