Fig. 4.2.2 a Workpiece topography after turning. b Workpiece topography after turning and burnishing
Deep rolling is based on the combination of three simultaneously working physical effects:
●A deep layer of residual compressive stress on a component surface.
●A strength increase through cold working.
●The elimination of micro notches and the improvement of surface roughness quality.
Compressive stress, generated 本文来自优,文,论#文,网，www.youerw.com 加7位QQ324.9114找源文 in the axial direction are most important for the improved fatigue strength.
In the past, deep rolling was only applied to special machines; however, nowadays, due to the evolution in the design and configuration of deep rolling devices, it can be incorporated in machines such as lathes and turning centers.
The deep rolling device can be incorporated in the lathe turret as with any other tool.
Several successful applications of combined turning and deep rolling processes have been addressed by researchers and industrial manufacturers, from automotive engine parts, such as shafts of valves, through railway applications, such as wheel axes, to aeronautic parts such as turbine discs, blades (Fig. 4.2.3) and shafts or landing gears.
Fig. 4.2.3 Deep rolling of turbine blades
4.3 Ultrasonic Assisted Turning
In difficult-to-cut and brittle materials several research approaches have been carried out for the purpose of modifying the mechanics of chip formation to improve process capabilities, in terms of chip breakage, decrease in forces and friction, and thus an increased tool life.
Fig. 4.3.1 Principle of ultrasonic vibration, where x(t) is the ultrasonic movement (20–40 kHz)
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