A study on the residual stress and spring back of thermoformed films

열성형 공정에서 발생하는 필름의 잔류응력 및 스프링 백에 관한 연구

  • Park, Du-Yong (Dep. of Aeronautical & Mechanical Design Eng., Korea Nat'l Univ. of Transportation) ;
  • Park, Dong-Hyun (Dep. of Aeronautical & Mechanical Design Eng., Korea Nat'l Univ. of Transportation) ;
  • Lee, Ho-Sang (Dep. of Aeronautical & Mechanical Design Eng., Korea Nat'l Univ. of Transportation)
  • 박두용 (한국교통대학교 항공.기계설계학과) ;
  • 박동현 (한국교통대학교 항공.기계설계학과) ;
  • 이호상 (한국교통대학교 항공.기계설계학과)
  • Received : 2022.02.23
  • Accepted : 2022.03.31
  • Published : 2022.03.31

Abstract

Thermoforming is a plastic manufacturing process that applies a force to stretch a film of heated thermoplastic material over an engineered mold to create a 3-dimensional shape. After forming, the shaped part can then be trimmed and finished to specification to meet an end-user's requirements. The process and thermoplastic materials are extremely versatile and can be utilized to manufacture parts for a very wide range of applications. In this study, based on K-BKZ nonlinear viscoelastic model, thermoforming process analysis was performed for an interior room-lamp. The predicted thickness was minimum at the corner of a molded film, and maximum at the center of the bottom. By using the Taguchi method of design of experiments, the effects of process conditions on residual stresses were investigated. The dominant factors were the liner thickness and the film heating time. As the thickness of the liner increased, the residual stress decreased. And it was found that the residual stress decreased significantly when the film heating temperature was higher than the glass transition temperature. A thermoforming mold and a trimming mold were manufactured, and the spring back was investigated through experiments. The dominant factors were film heating time, liner thickness, and lower mold temperature. As the film heating time and liner thickness increased, the spring back decreased. In addition, it was found that the spring back decreased as the lower mold temperature increased.

Keywords

Acknowledgement

본 연구는 정부(교육부)의 재원으로 한국연구재단(No.2018 R1D1A3B07045339)과 중소벤처기업부의 기술개발사업(S3157893)의 지원에 의한 연구임.

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