Zbigniew Zurecki

Cryogenic Machining with Brittle Tools and Effects on Tool Life

With the current popularity of finish hard turning, the need for improved productivity and tool life is of significant importance to manufacturers. The present work explores the effects of cryogenic coolants in machining hardened materials, from an industrial perspective, with emphasis on productivity and tool life improvement, environmental effects, as well as reliable performance characteristics for brittle tools. Both alumina ceramic (Al2O3) and polycrystalline cubic boron nitride (PCBN) tools show significant tool life improvement in cryomachining of hard ferrous materials, such as 52100 bearing steel and A2 tool steel. Significant productivity gains have also been observed in cryogenic machining of WC-Co rolls with polycrystalline diamond (PCD) tools. The enhanced performance of cryomachining is attributed to more efficient heat removal from the cutting insert, as well as reduction in thermal softening of the cutting tools at higher temperatures.

Techniques and Tips to Optimize, Control and Stabilize the Atmosphere inside a Continuous Sintering Furnace

The quality of the atmosphere inside a sintering furnace plays a key role in the final properties of the sintered part. Properties such as the hardness, ductility, dimensions, carbon content, microstructure and magnetic properties among others are influenced not only by time and temperature, but also by the composition, flow rate and stability of the atmosphere within the furnace. The different physical zones within the furnace require different degrees of oxidizing or reducing power to develop the optimum properties in the final sintered part. Presented in this paper are practical techniques and technologies developed over the last 30 years of experiences with production sintering furnaces. The concept of distributed atmosphere introduction, combined with the use of directional atmosphere injectors, flame curtains, and gas curtains are used to stabilize and maintain the atmosphere profile within the furnace. Optimum and proven designs for atmosphere injectors, flame curtains, gas curtains and exhaust systems are presented.