Research On Interference Fit Technology Of Armature Modules

In the electro hydraulic servo value, an armature module is responsible for the connection of electricity and liquid, and its assembly quality determines the control performance of electro hydraulic servo value. The assembly method of an armature module is pressing assembly, and the assembly process is of low automation degree. The process of assembly performed basically by operators. Throughout the manual assembly process, the assembly quality of armature modules is affected by some subjective and objective factors, such as the mood and operational experience of operators, so modules’assembly quality has bad consistency and assembly percent of pass is low, leading to vast waste of manpower and resources. At present, how to improve the assembly quality of modules has become a problem that needs to be addressed urgently.Based on the current tooling of armature modules, matched tooling of automatic press fitting device, improving positioning accuracy of parts, has been designed. Analyzing the connection method, assembly requirements and assembly process, judgment indexes and main influencing factors of assembly quality of armature modules were determined. Analyzing relationship between each main influencing factor and assembly quality of armature modules, the article provides references and methods for the improvement of assembly quality of armature modules.Applying stress calculation formulas of multilayer thick cylinder interference fits obtained from thick-walled cylinder theory, relationships among contact surface stress, equivalent stress, and magnitude of interference were analyzed. The minimum and maximum allowed contact stresses were obtained by the required minimum connection force between parts and materials’yield strength, then inequalities which can determine the scopes of interference values were obtained. Based on inequalities, using the graph algorithm and referring to the standard tolerance value table and basic deviation value table of GB/T1800.3-1998, the reasonable scopes of interference values were identified by using theory.The equivalent stress distribution of armature modules when a bourdon rod has form error was analyzed with finite element software ANSYS WORKBENCH, then the reasonable scopes of interference values were identified. Influences of interference values, friction coefficient, form error on press mounting curve of parts and connection force between parts were analyzed. Influence of interference values on equivalent stress was analyzed. Influences of tilt pressing of parts and pressing when part’s hole is sloped on the parallelism error of armatures were analyzed, then influence degree of interference values, friction coefficient, form error work on assembly quality were identified. The allowed scopes of tilt angle of parts and parts’inner hole were obtained. All these allowed scopes provide references for research and manufacture of equipment and determination of process precision of parts.Based on the analyses of manual pressing process and tooling of manual press machine, matched tooling of automatic press machine was designed, then clamping and press fitting process of automatic press machine were introduced. The tooling includes upper part and lower part, and the upper part is responsible for the clamping of suppressed parts, and the lower part is responsible for the clamping of a bourdon tube. The positioning between suppressed parts and a bourdon tube is through the vision alignment system to cooperate to complete.