IMPROVE DESIGN QUALITY 

WITH FEA SIMULATION

To make sure all the plastic parts designed and optimized by X-Plast can meet the highest requirements, our team has made strategical investments in FEA simulation solutions and high-end 3D printing technologies over the last couple of years. In an average design project, in order to succeed, several criteria must be fulfilled at the same time. We have introduced structural analysis and topology optimization into our integrated product development processes for injection moulded and 3D printed part development projects. With this integration, we have achieved a dramatically shortened development time combined with the use of 3D printing prototypes, and a significant increase in products performance while saving time and money for our customers.

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Integrated

design process

Excellent teamwork and inhouse technologies were a key factor for success in the HeartBit project. This electronic device has a lightweight housing made of unfilled PC+ABS plastic. All parts are ribbed according to commonly known technical guidelines to reach a maximum stiffness. Our experience shows, that even with a good mouldable shape, sufficient strength can be a problem. Therefore, we used structural FEA simulation to understand the part’s behaviour under different loading conditions.

Identification of loaded areas based on preliminary results. 

As a standard part of our integrated design process injection molding simulation is always used during plastic part design. We can easily determine the best gate location, and based on the filling analysis the fill pattern, weld lines and sink marks can be predicted. As an additional result, the fiber orientation distribution in the part, which is needed for an anisotropic structural analysis, can be exported. Using the fiber orientation and weld line positions, we can increase the quality of the structural analysis. In the current case however the material is unfilled, therefore a simple isotropic material model combined with a nonlinear analysis already led to useful results. 

Based on the results of the preliminary analysis we were able to identify the critically loaded areas next to the screw tubes. The stresses in these conventionally designed ribs exceeded the design limits.

While each development project is different, but we always get inspiration from nature. In the current case we looked at tree roots, as naturally they grow to withstand huge wind loads. On one “side” roots are tensioned ribs, like the ones in our electronic device housing. We used this similarity and redesigned the highly loaded ribs according to bionic principals of the nature.

Stresses became significantly lower and we could improve this weak and potential failure point without manufacturing another prototype and test it under real conditions. With this simple trick combining bionic principles and using simulation results, we saved time and reduced production costs.

We rely on Altair's robust and accurate simulation package

Working with tight deadlines, we always need to push ourselves to find new ways to maximize efficiency. With that in mind, we have noticed that housing is quite big compared to the regions of interest and is symmetrical on two planes. Therefore, we only continued the FEA analysis on one corner of the full housing, resulting additional time savings.

 

This technique allowed us to use a finer mesh with the same computation time. Compared with the full model the computation time was reduced by factor 8. Meanwhile the main results like displacement, stresses and contact pressure were within an acceptable tolerance.

 

TIn this project geometric nonlinearity and the presence of sliding contacts had to be handled. We were able to run quick validations of rib design variants, with a simple two parameter linear elastic material model instead of using a more complex nonlinear one. This way the computational effort was reduced even further. Simulation engineers must make considerations about how the input data affects the results. In this specific case using a simplified linear structural FEA simulation was enough to show, that minor changes are necessary on the product to become more robust. Using Altair simulation solutions we have significantly increased the mechanical properties and minimized the chance for product failure before serial production. Practical knowledge and experience are key factors in the virtual world. The challenge is always to find the best solution to solve the technical issue. Sometimes a linear analysis is more than enough, sometimes much more complex mathematical and mechanical models must be used. Coupling of injection molding (for example Moldflow) and structural FEA simulations – called integrative simulation - is one of these complicated methods. It allows us to include manufacturing influences, fiber orientations, weld lines residual stresses and an anisotropic material model in our investigations.

Keeping all these methods in one hand, together with rapid prototyping and testing capabilities gives us a leading advantage. Our development team at X-Plast keeps pushing the boundaries of design and simulation to meet customer’s future needs.