Characterization of Polymerization-induced Workpiece Distortion in Photo-activated Adhesive Workholding

Open Access
Author:
Doll, Kristopher Robert
Graduate Program:
Industrial Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Edward Demeter, Thesis Advisor
Keywords:
  • PAAW
  • Photo-Activated Adhesive Workholding
  • adhesive shrinkage
  • workpiece distortion
Abstract:
Photo-Activated Adhesive Workholding (PAAW) is a new technology that offers fixturing solutions for hard-to-hold manufactured components through the use of temporary UV-cured adhesive joints. One area in need of further development is the handling of compliant workpieces. Adhesive joints experience a decrease in volume as they cure, causing either an accumulation of residual stresses inside the adhesive joint or a distortion of the bonding substrates. Compliant workpieces will elastically distort as these PAAW joints polymerize, making it difficult to achieve tight tolerances as these workpieces are processed. This work characterizes the distortion caused by PAAW adhesive joints in response to factors such as workpiece compliance, joint thickness, and adhesive joint diameter. Empirical models are fit to the experimental data to predict workpiece distortion. The bonding surfaces, known as Grippers, used in PAAW technology transmit a non-uniform distribution of curing light intensity to the adhesive joint by design. The interaction of adjacent adhesive regions with different light intensities and consequently different polymerization rates is explained in terms of a support column model, where the region that develops a significant elastic modulus first will oppose further motion of the substrate. This idea is demonstrated through experiments with varying adhesive joint diameter. To offer insight regarding workpiece distortion reduction for typical industrial use of PAAW fixturing, a scenario involving multiple adhesive joints curing simultaneously and sequentially is explored. A methodology is created to predict the resulting distortion of a workpiece for any PAAW fixturing setup and curing sequence. A case study with experimental results validates the approach. In an attempt to find a low distortion adhesive, a number of different types of filler content and adhesive base resin are evaluated. The adhesive strength, cohesive strength, tensile properties, polymerization shrinkage, and the resulting workpiece distortion are experimentally determined. A model is presented to explain how several of these factors contribute to distortion.