Analysis of the influence of the initial surface integrity on the result of burnished high torque splined shafts

Abstract. The increasing demand for low surface roughness and long service life in highly loaded components, such as extruder shafts, requires high strength, functional reliability and long-term durability. Extruder shafts are applied in plastics technology and in the food industry for processing plastic melts, mixing and compounding. Screw and kneading elements are required for this purpose. The screw and kneading elements are pushed form-fittingly onto a splined shaft. The torque is transmitted by the splined shaft. [1] Main causes of wear and damage of extruder shafts are corrosion and mechanical load. High surface qualities, increased residual compressive stresses and increased surface hardness are possibilities to increase the durability of the splined shafts. These desired properties can be achieved by applying the ball burnishing technology. [2] By utilizing cold working processes, such as ball burnishing, it is possible to enhance the surface and subsurface properties to increase the lifespan of rotary components intended for transmitting high rotational torques. Due to the importance of considering the roughness of the initial surface, this study aimed to generate various roughness and surface profiles through the turning process to investigate their influence on the burnishing process results. For this purpose, shaft sections made of AISI H11 steel were pre-machined with different cutting inserts in order to set different surface roughnesses. Subsequently, a statistical experimental design was created by using the Taguchi method by varying feed rate, pressure and speed. As a main result, roughness and residual stresses on the surface were measured and compared with the initial conditions.