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Unformatted text preview: 6 The simulation of polymer processing You have seen in SPAP (and are studying further in this course) that: • Polymers have complex, history-dependent stress-strain properties; • These properties depend strongly on their history during processing; and • The rheological and thermal properties of the material during processing are themselves very complex. Achieving good mouldings has, therefore, always been difficult. Traditionally it was achieved through jealously guarded craftmanship and experience. 1 Designer specified component shape and material based on end use; 2 Mouldmaker designed parting plane, ejection, feed system and cooling system; 3 Moulder set up machine parameters: pressures, cycle times, temperatures. Because there was not feedback between these stages, many mouldings performed poorly in service. During the 1970s–80s, the status of thermoplastics evolved from that of cheap substitutes for ‘real’ materials to that of advanced technological materials in their own right. This resulted mainly from deeper understanding of their constitutive properties. With this understanding, and with progress in computing, came the processing simulation software which is the subject of this course. At first only melt flow was simulated. Every stage in processing, as well as loading in service, can now be simulated. Simulation allows concurrent engineering: stages 1-3 are carried out simultaneously by simulation, before metal is cut. These notes provide background — in an industrial context — for your self-taught tutorials in Autodesk® Moldflow® Insight, the industry standard software system for simulating injection moulding. The capabilities of Moldflow Insight are outlined in the brochure at http://images.autodesk.com/adsk/files/moldflowinsight10_overview_bro_us_lr.pdf Learning outcomes After completing this section you should be able to… 1 Demonstrate an awareness of the strategies available for injection moulding simulation, the basic methods used by simulation software, and their potential benefits and limitations. 2 Demonstrate understanding and make appropriate use of the following terminology: concurrent engineering, domain, discretisation, elements, cells, laminates, mesh, 2.5D/3D analysis, ‘what-if’ study. ME4 Polymer Processing Technology PSL 2 December 2009 6.1 Mathematical models The basis for all moulding flow simulation is the solution of the Navier-Stokes equations using numerical techniques. In principle this can be done without making simplifying assumptions. The equations can be solved analytically only by making many assumptions, and only for a few very simple cases — which include the cases in Notes §2-3. However, these special cases are useful for making estimates, for developing insight, and for testing software....
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- Fall '10
- Finite Element Method, Partial differential equation, Polymer Processing Technology