مدل سازي فرآيند شكل دهي حرارتي پليمر HIPS

چكيده انگليسي :

Modeling of Thermoforming Process of HIPS Polymer Mojtaba Khaleghi m khaleghi@me iut ac ir July 13 2015 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Mohammad Mashayekhi mashayekhi@cc iut ac irAbstract Thermoforming is widely employed in industry for the manufacture of light weight thin walledprouducts from thermoplastic polymeric sheets This process is used for industrial products includingsignage housings and hot tubs It also produces much of the packaging in use today including blister packs egg cartons and food storage containers This process has many advantages over other methods of producingthese products but also it has some limitations The most important limitation or weakness of this process isnonuniform thickness distribution of the final product To overcome this limitation various methods havebeen developed such as using plug molds or prestretching the sheet before forming Controlling the processparameters is another way to achive a uniform thickness distribution In thermoforming a heated thermoplastic sheet is stretched into the desired shape by applyingvaccum pressure or mechanical load In this process producing a part with a good quality and minimal timeand cost is the objective of producers For this perpose manufacturers have used trial and error methods toreduce costs and improve products but these methods were costly and time consuming Over many yearsattempts have been made to simulate thermoforming process and thereby exploit modern computational toolsfor process optimisation However progress in this area has been greatly hampered by insufficientknowledge of the response of polymer materials under thermoforming conditions and an inability to measurethis and other processing phenomena accurately In this research modelling of thermoforming process of a rectangular polymeric specimen has beencarried out with the aim of obtaining a suitable thickness distribution Also effects of process parameters onthe thickness distribution of the final product have been investigated For this purpose ABAQUS simulationsoftware was used and constitutive equation of Maxwell viscoelastic model was adopted for describing thebehavior of high impact polystyrene HIPS thermoplastic polymer during the forming process and theconstitutive equation was implemented in user subroutine VUMAT Shell elements were used for thediscretization of the sheet because sheet thickness is much less than other dimensions A quarter of the sheetand mold was modeled in the software for the sake of symmetry The verification of the subroutine has been carried out in two ways First pure shear test at constantstrain rate on a shell element with Maxwell viscoelastic model for material behavior was simulated andsimulation results were compared with experimental data Secondly simulation of one the ABAQUSbenchmark problems was carried out with the user subroutine and results were compared with exsistedresults Finally simulation of the thermoforming process of the rectangular specimen in air slip formingprocess was considered and Thickness distribution of the final product along the symmetric planes wasinvestigated Simulation results were in good agreement with experimental results Effects of frictioncoefficient plug velocity sheet temperature and sheet dimension on the final part thickness was investigated By increasing friction coefficient plug speed sheet dimension and decreasing sheet temperature partthickness increases Friction coefficient has an important effect on the thickness distribution of the finalproduct Keywords Thermoforming Polymer ABAQUS Viscoelastic materials User subroutines

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مدل سازي فرآيند شكل دهي حرارتي پليمر HIPS