Thermoforming presents several design challenges, primarily due to the material's behavior when heated and molded.
First, there's the material stretch—when plastic is heated, it becomes soft and malleable, but this can lead to uneven stretching during forming, causing variations in thickness and strength. Designers must account for uniformity in material flow to avoid weak spots or excess material that can lead to warping or excess scrap. Additionally, tooling complexity is a major factor. The molds must be precise and well-designed, as imperfections can result in surface defects or poor part fit. The design must also accommodate draft angles—slight tilts on mold surfaces that allow parts to release easily—but this can limit design freedom, especially for parts with intricate geometries. Another challenge is thermal control: parts must be uniformly heated, and maintaining consistent temperatures across the material can be difficult, especially with thicker parts. Finally, post-processing requirements, such as trimming, can add to production time and cost, as edges often need to be cleaned up after forming. Overall, thermoforming requires careful planning, material selection, and mold design to ensure quality and efficiency.
To address thermoforming challenges, engineers employ several strategies. Material selection is crucial; choosing the right thermoplastic with consistent flow properties and the ability to maintain uniform thickness during forming helps prevent stretch issues. To improve tooling precision, molds are designed with tolerances that account for material shrinkage and expansion during heating. Using multi-zone heating systems ensures consistent temperature distribution, reducing the risk of uneven forming. Additionally, molds with adjustable cooling channels help maintain uniform cooling rates, preventing distortion after forming. In terms of draft angles, engineers carefully balance ease of part removal with design aesthetics by integrating slight angles into the mold, which minimizes impact on intricate shapes. For parts with complex geometries, engineers may use multi-part molds or vacuum-assist technologies to improve material flow and avoid stretching in critical areas. These solutions combine to optimize both design and manufacturing efficiency.
Ansys Fluent Workspace Polyflow provides a powerful simulation environment for evaluating thermoforming solutions. It combines computational fluid dynamics (CFD) with material flow analysis, allowing engineers to model how thermoplastics behave under heat and pressure during the forming process. Using Polyflow, engineers can simulate material flow patterns, temperature distribution, and stretching effects, helping identify potential issues like thinning or uneven heating before physical prototyping. The software enables precise thermal management simulations, allowing engineers to adjust and optimize the multi-zone heating systems for consistent temperature control across the material. It also aids in fine-tuning mold design by predicting the material’s behavior at different stages, helping prevent defects like warping or incomplete forming. By integrating material properties such as viscosity and elasticity, Polyflow predicts material flow through complex geometries and helps optimize draft angles to ensure ease of part release without compromising design integrity. Engineers can also assess the performance of vacuum-assist systems and fine-tune cooling channels for optimal post-forming shape retention. This comprehensive approach allows engineers to evaluate and improve thermoforming processes digitally, enhancing efficiency and quality.
Setting up thermoforming simulation with Ansys Fluent Workspace Polyflow in this discussion involves several steps. These steps include thought map, product map, and Polyflow case setup.
Thought Map: A thought map of thermoforming characteristics is generated to organize and represent ideas, concepts, or information in a structured way. The thought map below shows the objective of the simulation study and questions asked to address the objective. Each question is followed by a theory, action, and prediction to address each question. Results would also be added to the bottom of each branch as they are generated.
Product Maps: A product map of the thermoforming preform and mold is generated to list and categorize product features. A product map indicates factors that correspond to theories/actions in the thought map.
Polyflow Simulation: Polyflow models are generated per the studies produced by the thought map. In this case a one-factor, two-level study is employed which results in two unique Polyflow treatments. The images below show the sequence of steps for populating inputs for a Polyflow model.
The chart below shows the transient mold motion and the inflation pressure factor.
The simulation calculations are executed to generate the results. Treatments are analyzed to answer the theory questions and confirm or contradict predictions.
Graphical Analysis: Below is an animation of preform thickness result using shell mesh elements.
Below is an animation of preform thickness result with volume mesh elements.
These animations show a similar thickness result between shell and volume element meshes.
The chart below illustrates the difference between the simulations in terms of memory usage and CPU time. Use of volume elements consumes twice as much memory and consumes 4 times as much CPU time.
A benefit of using volume elements that may outweigh the memory and time is that one may output the geometry of the final deformed shape in .stl format. This geometry can be used for further analysis such as structural analysis. The image below shows a section view of the final shape.
Setup Details: The following video steps through highlights of the setup.
ANSYS offers advanced capabilities for simulating thermoforming which offer numerous benefits, including enhanced design optimization, improved reliability, and cost savings. By accurately predicting thermoforming performance, manufacturers can design products that meet specific requirements more efficiently.
Ultimately, ANSYS Fluent Polyflow provides a comprehensive, virtual environment to fine-tune material behavior, mold design, and process parameters, leading to more efficient production, reduced trial-and-error, and improved part quality in thermoforming processes.
Ansys Fluent Polyflow enables the evaluation of simulation factors such as shell or volume element. A manufacturing engineer can evaluate multiple design options to understand the molding behavior. Beyond Polyflow, ANSYS provides tools such as LS-Dyna, DesignXplorer, OptiSLang, and Mechanical for further design parametrization and evaluation.
Ozen Engineering Inc. leverages its extensive consulting expertise in CFD, FEA, optics, photonics, and electromagnetic simulations to achieve exceptional results across various engineering projects, addressing complex challenges like thermoforming.
We offer support, mentoring, and consulting services to enhance the performance and reliability of your thermoforming system. Trust our proven track record to accelerate projects, optimize performance, and deliver high-quality, cost-effective results for both new and existing systems. For more information, please visit https://ozeninc.com.
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