Friction stir burnishing (FSB) is a surface-enhancement method used after machining, without the need for an additional device. The FSB process is applied on a machine that uses rotation tools (e.g., machining center or multi-tasking machine). Therefore, the FSB process can be applied immediately after the cutting process using the same machine tool. Here, we apply the FSB to the shaft materials of 0.45% C steel using a multi-tasking machine. In the FSB process, the burnishing tool rotates at a high-revolution speed. The thin surface layer is rubbed and stirred as the temperature is increased and decreased. With the FSB process, high hardness or compressive residual stress can be obtained on the surface layer. However, when we applied the FSB process using a 3 mm diameter sphere tip shape tool, the surface roughness increased substantially (R a = 20 µm). We therefore used four types of tip shape tools to examine the effect of burnishing tool tip radius on surface roughness, hardness, residual stress in the FSB process. Results indicated that the surface roughness was lowest (R a = 10 µm) when the tip radius tool diameter was large (30 mm).

Frictional Stir Burnishing (FSB) is a surface enhancement method after machining without using additional device. The FSB process can be utilized on the machine tool which uses the rotation tools such as a machining center and a multi-tasking machine. Therefore, the FSB process can be applied just after the cutting process on the same machine tool. FSB was applied to the shaft materials of 0.45%C steel by using a multi-tasking machine in this paper. FSB is a process where the burnishing tool rotates at high revolution speed. Then the thin surface layer is rubbed and stirred with a temperature elevation and reduction. However it is difficult to achieve both high hardness and high compressive residual stress by FSB on 0.45%C steel shaft with helical path. In order to overcome this problem, FSB process with double helical path was proposed in this paper. As a result, both high hardness (600 HV) and compressive residual stress (-400 MPa) could be achieved.

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