Theory And Technology Of Precision Honing Process On Stainless Steel Valve Core

The servo valve is a pair of precision matching parts consists of valve housing and valve core, which are widely applied in the automated controlling systems of aerospace, aviation, precise machinery and apparatus. Stainless steel is one of the mostly used materials to make servo valve, and the precision of dimension, quality of surface and the crossing hatches of the surface of the precision valve core has important influence on the reliability and lifetime for the servo valve. In order to satisfy the needs of quality and performance of the precision parts used in different area, grinding or honing is often used as a final process to obtain an outside surface having a certain quality and crossing hatches for the valve core which has been processed by grinding wheel before. At present, in the practical manufacturing process in a domestic company, the process on a precise valve core made of 9Cr18 stainless steel stays on the skill that applying manual grinding and polishing after the valve core is ground by grinding wheel, aiming at improving the surface quality and forming crossing hatches by hands. However, the quality of the valve core after manually polished is over relied on the experience and skills of the operators, thus, the quality can hardly be stable and unified, and the efficiency and yield rate are also difficult to keep high, which result in the bottle neck of the company requiring solved immediately.According to the problems in the manual grinding and polishing on precision valve core, the paper proposes a processing method that applying automated external honing as the final step to replace manual grinding after the valve core processed by grinding wheel; aiming at the requirement of surface quality and crossing hatches, the paper conducts kinematic analysis and simulation on honing process, researches and develops automated external honing machine for special use on valve core, and carries out many process experiments, from which the proper parameters are obtained for process.The main researching work of the paper and its conclusions are as following:The paper conducts kinematic analysis and simulation for external honing process, establishes the honing motion equations, and the paper also gets the condition that affects the completeness and repetitiveness of honing crossing hatches, analyzes the factors and regular pattern that affects the density and the uniformity of the crossing hatches which are verified through experiments. During the honing process, for forming better and denser hatches, shuttling times (honing time), rotating velocity should be increased properly, and choosing less crossing angle, as a result of which good hatches and surface quality will be attained.The paper develops an automated external honing machine used for finishing the precision valve core through controlling the rotation of the work-piece and adjusting the shuttling movement of the honing stone to realize the machining. The machine replaces the manual polish completely, realizes the automated honing for work-piece with less than 20mm in diameter and less 200mm in length. By setting different parameters, the machine can finish the surface in required honing pressure, honing velocity as well as the crossing angles.Based on the external honing machine developed by the paper, many experiments are conducted on valve core made of stainless steel. And the experiments focus on the influence that the parameters and conditions have, such as the abrasive of honing stone, grain size, honing pressure, time, rotating velocity, shuttling velocity, on the Ra, MMR, crossing angles and density of hatches etc. Thus, a set of optimal parameters and conditions is obtained for honing machining. The paper applies the optimal parameters from the experiment on a 9Cr18 stainless steel inΦ15mm×100mm and can get a surface with crossing hatches and less than Ra 18nm.