Design and analysis of spindle head for micro milling machine

Abstract

We are well known of phrase “World is becoming so smaller” i.e. the current era is of micro parts and the sizes of the parts are reducing day by day. On the other hand these small parts required to be manufactured with great accuracy and high surface finish. Usually these complex, three dimensional shapes are manufactured with the special milling machine called micro milling. The problems associated with micro milling are, increase in spindle run out & its vibrations with increase in speed. Also, critical design of high speed bearings & drive system adds to its complex nature. Thus challenge lies with controlling the stated noise factors. It is proposed to have friction disc drive for micro milling machine spindle. In the present work the emphasis is laid on controlling the spindle run out by proper design. Also, analysis of spindle by FEM (Finite element method) is undertaken. The results obtained for designed spindle under stipulated conditions of cutting force (3-7 N) are motivating. The maximum run out for spindle in this case found to be 20μ & minimum is 13μ. The analysis carried out takes in to account the linear as well as non linear aids. The speed adopted in current case is in the range of 1600 to 9600 rad/sec. However it is recommended to use speed in the range of 4000 to 4800 rad/sec. the stiffness of air bearing is kept in the range of 8×10 4 to 8.8×10 5 N/m. it is recommended to keep stiffness of air bearing between 5.2×10 5 to 7.2×10 5 . The diameter of tool shank must be in the range of 2.5 to 3.2mm. Length of tool shank is to be kept in between 38 to 50mm & the tool with young’s 6.8×10 11 N/m 2 must be used so as to have minimum spindle run out.