Improving turning precision of a lens barrel: Application of finite element method and mechanical analysis

Abstract

Lens barrels for optical components require high precision manufacturing for achieving accept able form and precision. The Thorlabs production facility in Mölndal has experienced problems with unwanted deformations in microscope lens barrels. This thesis investigated the source of these deformations and connected the issue to workpiece fixturing during turning operations. Alternative concepts for workpiece holding were researched and evaluated using finite element analysis, mechanical calculation and experimental validation. A finite element model of the current workpiece fixture was developed from solid CAD models in ANSYS 2024 R2. The model was compared to measurements of the current barrel and fixture from a coordinate measuring machine. The simulation was iterated in several steps and the final model achieved good agreement with measured data and reproduced the modes of deformation experienced in production. Design requirements for new solutions were formulated. A number of alternative solutions were then investigated. These included a three-jaw chuck, a fixture with a clamp with relief cuts, commercial elastic collets, a shrink fit assembly and an axially compressing clamp. The concepts were evaluated based on deformation, ability to resist slipping, manufacturability and operational practicability. Of the investigated concepts, the axial clamping fixture was assessed as the best solution due to its low predicted deformation, despite the use of conservative assumptions. The axial clamp was further refined for manufacurability and use with the machine interface. The work demonstrates that finite element simulation, combined with experimental validation and physical measurement, can be used to analyze and improve fixturing systems for manufac turing optical components.