Surface Integrity of AISI H13 in End Milling and Electrical Discharge Machining Process

Abstract

Industries are forced to seriously evaluate their design and manufacturing of their products due to the competition in the marketplace. Product characteristics such as tolerance specification, appearance, and service life now become a major concern for machined components. One of the most important aspects in machined components is surface integrity. It involves mainly the surface roughness and micro hardness changes during machining operation, which should be controlled and monitored to fulfill the product functions and customer needs. This paper presents the comparison effect of the end milling and EDM parameters on the surface integrity of AISI H13 tool steel (HRC50 3). The parameters studied were the cutting speed (224 m/min – 280 m/min), feed rate (0.25 mm/tooth) and depth of cut (0.3 mm-0.8 mm for end milling process. Whereas for EDM, the parameters studied were the peak current (1 and 4 A), pulse ON-time (6 and 12 μs), and pulse OFF-time (2 μs). The electrodes used were graphite and copper. In this study, the workpiece surface and recast layer were examined using an optical microscope. The observation revealed that both processes of end milling and EDM had cause the formation of three layers structure, i.e. white, martensite quenched and bulk material layers. The subsurface alteration for EDM process is considered rigorous as compared with the end milling process. Damages beneath the machined surface such as micro cracks and void were observed for EDM process, and microscopic pitting and surface roughning for end milling process. The measurement of the microhardness beneath the machined surface of AISI H13 was carried out using Vickers microhardness tester to characterize its mechanical properties. It was found that the highest hardness of 1010 Hv was in the white layer, and hardness of martensite quench layer was 423 Hv, which was lower than the bulk material layer of 430 Hv in EDM process. Whereas, a maximum of 550 Hv was measured directly underneath the generated surface, i.e. 30% more as compared to the hardness of the basic material in the end milling process.