Micro abrasive jet patterning of sloped micro herringbone grooves for journal bearings

Fluid dynamic bearings, which have a feature of high-accuracy rotation, are employed for spindle motors of hard disk drives and cooling funs of central processing unit. There exist micro herringbone grooves on the shaft journal to generate dynamic pressure in the lubricant fluid around the shaft. Although the depth of groove is generally constant, it is expected that dynamic pressure can be increased by decreasing the depth from both ends to central corner of each groove with micron scale. In this study, the purpose is to control machining profiles in abrasive jet machining and to manufacture micro herringbone grooves, whose depth is controlled continuously. At first, the machining speed at each machined region in abrasive jet machining with the nozzle at rest is verified. Then the nozzle feed speed is calculated as functions of spindle axis position based on the target profile. The contours acquired by experiments without the mask agree well with the target one. In addition, nozzle feed speed is calculated by considering the influence of the mask needed in manufacturing of herringbone grooves. As a result, it is found that the controlled sloped herringbone grooves can be manufactured using the proposed abrasive jet patterning.