• The Korean Journal of Rheology
• /
• v.8 no.3_4
• /
• pp.215-225
• /
• 1996

평판형의 열가소성 수지를 유리전이온도 이상으로 가열한 다음 압력을 가함으로써 원하는 형상의 제품을 성형하는 열성형공정은 대상 수지가 큰 변형을 일으킬 뿐만 아니라 비선형적 거동을 보이게 된다. 따라서 수지의 변형거동 예측과 최적성형조건의 설정에 많은 어려움과 시행착오를 거치게 되는 바, 열성형 공정의 최적화를 위한 연구의 일환으로 원형 평판위 수지를 대상으로 수지의 부풀림 거동과 이에 따른 두께 분포를 예측할수 있는유한요 소법의 수치모사 알고리듬을 개발하고자 하였다. Piola-Kirchhoff 응력 텐서와 Green 변형 텐서 및 lagrangian 변형 텐서를 사용하여 평판상의 응력-변형에 대한 비선형의 에너지 수 지식을 수립하고 Newton-Raphson 반복수렴법을 이용하여 근사적으로 해석하였으며 수지의 유변학적 구성방정식으로는 neo-Hookean 모델, Mooney-Rivlin 모델 및 Ogden 모델등의 초탄성 모델을 사용하여 그결과를 비교하였다. 수치모사에는 두께가 매우 얇기 때문에 두께 방향의 응력변화를 무시할수 있는 membrane 가정을 도입한 2차원적 해석과 두께 방향의 응력 변화를 고려하는 3차원적 해석을 모두 수행하고 그 차이를 비교하였으며 3차원적 해석 의 경우에는 penalty법을 이용하여 비 압축성을 만족하였다. 일차적으로 내압을 받는 두꺼 운 원통계에 대한 수치모사 해석을 수행하고 완전해와 비교함으로써 개발된 수치모사 알고 리듬의 열성형 공정에의 적용 타당성을 검증하였으며 이를 이용하여 원형 평판의 자유부풀 림거동을 예측한 결과 Treloar 등의 실험결과와 잘 부합함을 확인하였다. 또 간단한 형상의 금형이 있는 경우와 반지름 방향으로의 온도변화에 따른 수지의 변형거동을 해석함으로써 실제 열성형 공정에서 요구되고 있는 성형품의 두께 분포를 균일하게 하기 위한 방안을 제 시하였다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.5
• /
• pp.505-511
• /
• 2016

The aim of this study is to investigate the thermoforming characteristics of an inner case with three refrigerator cavities using three-dimensional(3D) thermoforming analyses. We perform fundamental formability analyses using a 3D model of the mould for the inner case. We carry out tensile tests at the elevated temperature to examine the properties and characteristics of the thermoformed material. Then, we design sub-processes of the thermoforming process for the inner case. In addition, we develop suitable finite-element models for different sub-processes. We investigate the deformed shapes and thickness distributions of the inner case for different sub-processes using the results of the thermoforming analysis. Finally, we discuss the formability and thermoforming characteristics of the inner case with three cavities.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2013.05a
• /
• pp.957-958
• /
• 2013

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2012.10a
• /
• pp.801-802
• /
• 2012

• Journal of the Korean Society for Precision Engineering
• /
• v.32 no.11
• /
• pp.953-960
• /
• 2015

The thermoforming process has been widely used to manufacture medium- and large-sized plastic parts because of the relatively low cost and high productivity, as compared with other plastic forming processes. One of current salient issues of thermoforming industries is the reduction of trial and error during the production of the thermoformed product. Hence, there is a significant increasing interest in the thermoforming analysis by the thermoforming industries. The goal of this paper is to investigate a methodology of the three-dimensional thermoforming analysis for medium- and large-sized plastic parts. There is a discussion about methodologies of thermoforming analysis, as well as material modeling, and three-dimensional finite element analysis. Furthermore, there is an examination, through case studies, about the applicability of the proposed methodology concerning the thermoforming analysis.

• Membrane Journal
• /
• v.33 no.5
• /
• pp.248-256
• /
• 2023

Indium tin oxide (ITO) transparent electrode film has been widely adopted for the various applications such as display and electric vehicle. In this paper, we studied how to enhance the thermoforming stability of ITO film by applying the highly conductive Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin layer. Based on the change of sheet resistance value, the influence of the additional solvent with different boiling point was investigated for the PEDOT:PSS coating solution. In addition, by analyzing optical transmittance and Raman spectrum, we confirmed the key mechanism which determine the final electrical conductivity of the PEDOT:PSS on ITO film using an ethylene glycol solvent. The final ITO transparent electrode coated with PEDOT:PSS performed the outstanding endurance of electrical conduction even in 126% stretching condition.

• The Korean Journal of Rheology
• /
• v.11 no.1
• /
• pp.18-27
• /
• 1999

Predicting the deformation behaviors of sheets in thermoforming processes has been a daunting challenge due to the strong nonlinearities arising from very large deformations, mold-polymer contact condition and hyperelasticity constitutive equations. Nonlinear numerical analysis is always required to face this challenge especially for realistic processing conditions. In this study a 3-D algorithm and the membrane approximation are developed for thermoforming processes. The constitutive equation is expressed in terms of the 2nd Piola-Kirchhoff stress tensor and the Cauchy-Green deformation tensor. The 2-term Mooney-Rivlin model is used for the material model equation. The algorithm is established by the finite element formulation employing the total Lagrangian coordinate. The deformation behavior and the stress distribution results of 3-D algorithm with various point boundary conditions are compared to those of the membrane approximation algorithm. Also, the slip boundary condition and the no-slip boundary condition are applied for the systems that have molds. Finally, the effect of sheet temperatures on the final thickness distribution is investigated for the ABS material.

• Journal of computational fluids engineering
• /
• v.18 no.3
• /
• pp.20-25
• /
• 2013

In various manufacturing industries, an in-mold decoration (IMD) process for plastic objects is widely utilized because a film forming and an injection molding processes run simultaneously. In the present study, the deformation of polymer film and filling of resin in the IMD process were numerically investigated to evaluate the quality of the plastic object formed by the IMD process, which consists of thermoforming and injection molding processes. To obtain the initial shape of the polymer film during the injection molding process, the deformation of the polymer film in the thermoforming process was pre-formed using the vacuum conditions to attach the film to a cavity. Since the properties and deformation of polymer film are greatly affected by the behavior of polymer resin being injected into a mold cavity, numerical simulations for the injection molding and film forming were performed with one-way coupling method. The results showed that the injected resin could lead to the tearing of the polymer film in local regions near the corners. In order to verify the proposed numerical methodology, the numerical results of the deformation patterns printed on the initial polymer film were compared with the experimental data. The proposed methodology to couple film forming analysis with injection molding analysis can be used to predict the deformation of film in IMD process.

• 한국금형공학회:학술대회논문집
• /
• 2008.06a
• /
• pp.69-73
• /
• 2008

본 연구에서는 고분자 플라스틱 부품의 친환경 외장성형공법인 Insert Film 사출성형공법중 첫 번째 공정인 진공성형공정에서 진공금형의 표면온도 균일화 기술에 대해 연구를 수행하였다. 진공금형의 온도분포 균일화를 위한 금형설계 및 설계된 금형에 대한 온도분포 평가를 위한 ANSYS를 이용한 유한요소열해석을 수행하였으며, 이때 정상상태 및 과도상태를 함께 평가하였다. 설계 결과를 바탕으로 금형을 제작하였으며, 생산성을 고려하여 4캐비티로 제작된 금형에 대해 금형표면의 온도분포 평가실험을 수행하였다. 또한 금형내 캐비티 온도센서 및 제어시스템을 설치하여 진공금형표면 온도분포가 항상 일정하게 유지될 수 있도록 금형시스템을 개발하였다. 결과적으로 일정한 온도범위의 금형표면온도제어가 가능하였다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.5
• /
• pp.816-822
• /
• 2001

The thermoforming process is widely used in the plastics industry to produce articles for the packaging, automotive, domestic construction and leisure industries. The microcellular foaming process appeared at M.I.T. in 1980s to save a quantity of polymer materials and increase their mechanical properties. The glass transition temperature of polymer materials is one of many important process variables in appling the microcellular foaming process to the conventional thermoforming process. The goal of this research is to evaluate the relation between gas absorption and glass transition temperature in batch process using microcellular foaming process. The weight gain ratio of polymer materials has a conception of gas absorption. Polymers such as acrylonitrile-butadiene-styrene(ABS), polystyrene(PS) have been used in this experiment. According to conventional Chows model and Cha-Yoon model, it was estimated with real experimental result to predict a change of glass transition temperature as a function of the weight gain ratio of polymer materials in batch process to gain microcellular foamed plastic products.