The Assessment of the Rheological Characteristics of Various Polyborosiloxane/Grit Mixtures as Utilized in the Abrasive Flow Machining Process

Abstract

Abrasive flow machining (AFM) is a non-traditional machining process used since the mid-1960s, which utilizes a mixture of polyborosiloxane and abrasive grit additions extruded across surfaces and edges and through component cavities. The machining mechanism of this process is still only partially understood due to its complex nature, and the present work undertook to investigate the relationship between the rheological characteristics of several mixtures and their associated machining parameters. This paper addresses those rheological characteristics of the various mixtures used in the present work. Experiments were conducted using low viscosity (LV), medium viscosity (MV) and high viscosity (HV) polyborosiloxane base media, in conjunction with silicon carbide abrasive grit of 60 and 100 mesh size, the ratios of the grit to base polymer used being 0, 1 and 2. The test pieces used were mild steel dies and the equipment used to conduct the experiments was an Extrude Hone mark 7 A machine. The results have shown that progression from low to high viscosity base medium produces a reduction in the temperature rise (for example from 32 to 10°C over 30 cycles) as well as an increase in both the average pressure drop across the die (for example from 1700 to 2674 kPa over 30 cycles) and the processing time (for example from 28 to 406 s over 30 cycles). In addition, the temperature of the medium is seen to be an important variable in the AFM process due to its effects on viscosity. Furthermore, as the usage of a medium increases the viscosity and pressure drop across the die increase.