Proceedings of ICOMAST2006 International Conference on Manufacturing Science and Technology August 28-30,2006, Malaka ,Malaysia 173 PRECISION MICRO-FINISHING BY ELECTRO-CHEMICAL HONING A. K. Dubey, H. S. Shan 1 and N. K. Jain Mechanical and Industrial Engineering Department, Indian Institute of Technology, Roorkee- 247 667. India 1 Corresponding Author: Prof. H.S. Shan, Mechanical and Industrial Engineering Department, IIT Roorkee (India). <hsshan@gmail.com>. ABSTRACT Surface conditions and shape deviations produced by manufacturing methods have pronounced influence on the resulting functional properties of engineering components during service. Electro-Chemical (EC) based processes are finding ever increasing applications in a great variety of industries, especially in the aerospace and auto industries. Electro-Chemical Honing (ECH) is an effective EC based nontraditional micro-finishing process that combines the electrolytic dissolution with controlled functional surface generating capabilities of honing, thus becoming an idle choice for improving the surface quality (and consequently the service life) of critical components. This paper reports the results of a comprehensive study on the influence of key ECH process parameters such as current intensity, electrolyte concentration, speed ratio, electrolyte flow, electrolyte temperature, stick-out pressure and abrasive grit-size on the dominant machining criteria, i.e., surface roughness improvement. Percent improvement in the Ra as well as Rmax values has been analyzed for a pre-bored hole. Results indicate that the current intensity, electrolyte concentration, stick-out pressure and abrasive grit-size are the major players affecting the response significantly. If a distinct co-ordination of electrolytic dissolution and mechanical abrasion is achieved, ECH can be developed as a precision machining process for micro-finishing the critical components of tribological relevance. More than ninety percent improvement in surface quality can be achieved alongwith a precise control over the shape deviations. Some important features of the ECH setup, which was designed and fabricated, are also highlighted. Keywords: Electro-Chemical Honing; Rotary to Reciprocating Speed Ratio; Percent Improvement in Ra; ANOVA; Sodium Nitrate Electrolyte. 1. INTRODUCTION Stringent requirements on surface quality, tolerances and production rates, coupled with the production of complex shapes and contours, led to the ever-increasing applications of advanced machining hybrid processes. By combining electrochemical dissolution and conventional honing in a simultaneous action, electro-chemical honing (ECH) can provide a unique range of benefits to the machined surfaces [1]. The ability of ECH to offer the fast metal removal capabilities of ECM and the controlled functional surface generating capabilities of honing in a single operation alongwith an unmatched flexibility with regard to control of machined surface characteristics in generating a distinct cross-hatch lay patterned as well as a completely stress free surface, has led to its widespread use in many industries [2]. ECH is still in its infancy in many respects. The parametric relationships, mechanism of material removal and the surface quality issues have not been effectively evaluated. The present study highlights some key facts concerning these aspects. 2. EXPERIMENTATION 2.1. Experimental set-up The ECH set-up (Fig. 1) consists of a power supply; ECH tool and drive; electrolyte supply and cleaning; and work holding and positioning systems. A potential of 3-30 VDC (adjustable) and current 200 A (adjustable), is applied across the cathode stainless steel tool body - anode workpiece gap. The ECH tool is stroked through the bore with a controlled generating motion of simultaneous rotation and reciprocation using a variable speed DC servomotor and programmable stepper-motors. The expandable non-conducting honing sticks, protruding from four locations around the circumference and controlled by a light spring- mechanism, maintain uniform tool-work gap. These sticks act to remove the passivating metal oxide films preferentially from high spots. The spring stiffness and their initial compression can be adjusted to obtain a desired stick-out pressure. Fig. 1. Schematic of developed ECH setup 1. Electrolyte settling tank 2. Flow control valve 3. 1 st stage filter cum magnetic separator 4. Electrolyte tank 5. Temperature control system 6. Stainless steel pump 7. Pressure gauge 8. Flow meter 9. 2 nd stage filter cum magnetic separator 10. Mist collector 11. DC power source 12. Carbon brush and slip ring assembly 13. Copper connector 14. Seal hub 15. Hydraulic cum mechanical seal 16. Tool body 17. Honing sticks 18. Workpiece 19. Electrolyte exit holes 20. Work chamber 21. Fixture cum electrolyte inlet sleeve.