machinery feature | Modelling software German researchers
have calculated the ideal
conditions for extruding tubing from liquid silicone rubber
geometry is parameterised. That is, various dimensions of the die are defined as adjustable parameters which can be changed to modify the die geometry. This is done in SolidWorks, because for complex profile dies the geometry cannot easily be broken in simple elements such as bricks and prisms. The parameterised die geometry created within
SolidWorks is then passed through the extrusion die simulation software – Plastic Flow’s PolyXtrue – for flow simulation. PolyXtrue is available as an add-on to SolidWorks. The square die analysed by the software has a die channel that gradually changes into a thin-walled square cross-section. It was used to extrude a profile in ABS. The thin gap portion of the die consists of two different plates: the channel gap in the final plate near the exit is 2mm for the two horizontal walls, and 1.5mm for the vertical walls. The length of the final die plate is 1cm. The outer cross-section of the intermediate die plate is the same as that of the final plate near the exit. However, the channel gap in the horizontal and vertical portions of the intermediate plate is varied to balance the flow at the die exit. The length of the intermediate plate (2cm) is kept
constant during the optimisation process. As expected, with the larger channel gap (2mm) in the
horizontal walls in both the exit plate and the intermedi- ate plate, the exit velocity is higher in the horizontal walls and lower in the vertical walls. The flow at the exit of the square die was balanced by the die optimisation software by changing the thickness of the horizontal and vertical walls in the intermediate die plate. In order to accelerate the flow in the vertical walls, the software increased the thickness of the vertical walls in the intermediate plane from 1.5mm to 2.02 mm, while the thickness of the horizontal walls in the intermediate plate was decreased from 2mm to 1.69mm. “This software is expected to reduce the development time for extrusion dies by more than 50%,” said Gupta.
Virtual improvement Compuplast has added two new modules to its Virtual Extrusion Laboratory (VEL) software, which allows simulation of extruded parts. The ‘3D Shell Simulation’ and ‘3D Profile Die’
modules have been introduced to version 6.9 of the software. According to the company, the new modules combine the advantage of interactivity – by entering geometry and process parameters – with 2D and 3D FEM calculation methods. The modules can produce results in a few minutes, says Compuplast – and includes tools that can analyse melt conditions and evaluate and display them in the
14 PIPE & PROFILE EXTRUSION | March 2017
‘3D Visual Studio’ environment. The ‘3D Profile Die’ is particularly suitable for profile
tools that have large channel dimensions compared to the adapter, or complex product geometries. The module can describe the plate or inlet and outlet cross sections by means of two-dimensional sections, as well as the areas between them – which can be fully imaged in 3D. The software ensures a fast, accurate calculation of
the correct geometry according to Agfiss, which repre- sents Compuplast in Germany, Austria and Switzerland.
Silicone modelling Researchers at the Technical University of Munich (TUM) in Germany have calculated the ideal conditions for extruding tubing from liquid silicone rubber (LSR). In the study, the researchers developed a formula for
the flow rate, for an in-die-curing silicone extrusion – in order to describe this process mathematically, and be able to predict the capabilities of this technology. The calculations were compared with experimental results, in order to determine their validity. Silicone extrusion is routinely used to process
challenging applications such as medical tubing – as they have the material has the necessary radiation, chemical and temperature stability combined with physiological inertness and elasticity. The viscosity of the uncured silicones must be high
enough to create a dimensionally stable extrudate – and even with high viscosities, achievable precision and tolerances are limited. The proposed extrusion process vulcanizes the extrudate inside a heated die – while in a standard process, this is done downstream.
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