Session: 03-04-02: Advanced Machining and Finishing Processes

Paper Number: 112899

112899 - A Futuristic Approach to Micro-Milling With Linear Motion Compliant Mechanism Based Platforms 

Miniaturization of components in various industries is increasing tremendously, leading to the high demand for different microfabrication techniques. Micro-milling is one of the prominent material removal-based techniques. Most of the current micro-milling motion platforms are linear guideways with ballscrews as they offer low friction or air bearings with magnetic actuation. With ball screw drives, friction cannot be entirely eliminated, and positioning within 5 microns or less is quite challenging. Air bearing magnetic actuation platforms, although they can give positioning accuracies in the sub-micron range, often turn out to be a highly expensive alternative.

We explore in this paper an alternative approach of compliant mechanism-based motion control platform for micro-milling. Compliant mechanisms obtain their entire motion through the elastic deformation of flexible beams and do not have any hinge or prismatic joints normally found in conventional rigid link mechanisms and thus there is no relative motion between two parts touching each other. No separate guideways are required to move along predetermined path. Thus, there is no friction, backlash, and wear in such compliant mechanism based motion platforms which leads to highly reliable and repeatable ultraprecise motion. 

The proposed XY motion platform is a serial configuration of two double parallelogram compliant mechanisms. The optimized flexural beams have been used to reduce the parasitic error produced in an orthogonal direction while moving in either of the X or Y directions. Optimization strategies have been borrowed from the previous literature. The compliant motion stages are assembled using assembly guidelines developed previously to avoid any warpage during assembly. The platform is integrated with a commercial Galil motion control board and operated using G codes. The Z axis of the machine is a lead screw based motion stage with a stepper motor, and a DC motor with a speed controller has been used as a machine spindle. Positioning within +/-1.71 microns in X and Y directions during machining is demonstrated along with a cross-axis error of around +/- 2.5 microns in X and Y axes while machining in Y and X axes, respectively, over a range of 20 mm each. This positioning accuracy can be further reduced at the nanometres level with a more robust control strategy, since the compliant based motion platforms have no friction or backlash.

Further, a few basic geometries, micro channels and complex shape have been micro-milled on brass workpieces using the proposed compliant mechanism based micro milling machine. The dimensions of the machined components are characterised and compared with the CAD models. The Mach 3 software generates NC codes of the components to be fabricated from CAD models and communicates with the developed machine. To our surprise, no vibrations of the compliant mechanism due to cyclic machining forces of excitation were observed. In fact control compliance was found to assist prevention of tool damage usually observed with rigid body motion control platforms.

Overall, the basic capabilities of the compliant motion platforms for micro-milling have been established. More research in this direction is required to unfold the new doorways for complaint based motion stages in machining platforms.

Presenting Author: Abhijit Anandrao Tanksale Indian Institute of Technology Bombay

Presenting Author Biography: ABHIJIT TANKSALE is a Ph.D. student in the Mechanical Engineering Department, Indian Institute of Technology Bombay, Mumbai, India. His research interests are theoretical and experimental analysis of compliant mechanisms with large deformation.

Authors:

Abhijit Anandrao Tanksale Indian Institute of Technology Bombay
Ratnesh Bafna Indian Institute of Technology Bombay
Prasanna Gandhi Indian Institute of Technology Bombay