Injection Blow Molding Design Challenges
Designing parts for injection blow molding (IBM) presents several unique engineering challenges.
First, achieving uniform wall thickness is crucial for both structural integrity and efficient material use. Irregular thickness can lead to defects like warping or uneven cooling. Second, the design must account for the molding process itself, which requires precise control of temperature, pressure, and timing during both injection and blow phases.
Another challenge is creating smooth, consistent surface finishes, especially for complex geometries. The transition between the injection molded parison and the blown shape must be seamless to avoid visible seams or weak spots. The design also needs to consider the mold’s cooling system; efficient heat dissipation is essential for preventing distortion and reducing cycle times.
Additionally, the material’s flow characteristics must be considered when designing the part. Engineers must optimize the parison’s shape and dimensions to ensure even material distribution during blowing. Finally, since IBM often involves thermoplastics, part design must account for shrinkage during cooling to ensure the final product meets dimensional specifications.
In summary, successful injection blow molding design requires a balance of material properties, geometry, and process parameters to ensure high-quality, functional parts.
Engineering Solution
To address the challenges of injection blow molding (IBM), engineers employ several solutions. First, to achieve uniform wall thickness, they design parts with consistent geometry and use simulation software to predict material flow, ensuring balanced distribution during injection and blowing. Features like ribs and gussets are strategically placed to prevent weak spots while maintaining strength. For seamless surface finishes, engineers often use advanced mold design techniques, such as polishing or applying coatings to molds, and incorporate venting to reduce air traps. They also optimize mold temperature control with cooling channels that are precisely placed to prevent uneven cooling and warping. To handle material flow and shrinkage, engineers design the parison with specific geometry that accounts for the material's flow characteristics. Parison thickness is adjusted to allow for even material distribution when blown, and calculations based on the material’s shrinkage rate help ensure dimensional accuracy in the final product. Additionally, advanced mold designs with variable cavity pressure and temperature controls enable tighter tolerances and reduce cycle times. The use of high-quality thermoplastics that are compatible with IBM further minimizes defects. Finally, iterative testing and simulation are used to fine-tune designs before production, ensuring optimal part quality and performance.
ANSYS Fluent Polyflow is a powerful simulation tool for evaluating injection blow molding (IBM) solutions. It enables engineers to model and optimize key aspects of the process, ensuring the design addresses common challenges effectively. To evaluate uniform wall thickness, Fluent-Polyflow simulates material flow through the mold, identifying potential areas of uneven distribution. By adjusting parison geometry and process parameters, engineers can optimize the design to ensure consistent wall thickness across the part. For surface finish and defect reduction, Polyflow helps simulate the cooling process and material behavior, allowing engineers to predict how air traps or material inconsistencies might form during the blow molding phase. Mold design adjustments, such as improved venting or optimized cooling channels, can be tested virtually to achieve smoother surfaces and avoid defects. Fluent Polyflow also evaluates shrinkage and material flow properties. By simulating the behavior of thermoplastics during the injection and blowing process, engineers can adjust the parison design and process parameters to account for material shrinkage, ensuring the final part meets dimensional requirements.
Method
Setting up Injection Blow Molding 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 blow molding 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 blow molding parison and molds 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 fractional factorial DOE is employed which results in 8 unique Polyflow treatments. The images below show the sequence of steps for populating inputs for a Polyflow model.
The translation motion of the ramps as well as the inflation pressure factor are defined by expressions. The chart below shows how the expression values vary with time.
The simulation calculations are executed to generate the results, focusing on minimum thickness, area stretch, and simulation time. Treatments data are analyzed to answer the theory questions and confirm or contradict predictions.
Polyflow Injection Blow Molding Simulation Results
Graphical Analysis: The charts below display the results for the DOE analysis. The charts indicate that the mesh adaption minimum size factor has the most significant impact on the minimum thickness, maximum area stretch, and simulation time in comparison to the other three factors.
The charts below show the smaller minimum adaption size results in smaller minimum parison thickness, larger maximum stretch, and longer simulation time. The other factors have minor impact on the output metrics.
The contour graphics below show the impact of the initial parison thickness on the final thickness distribution. As expected, the larger initial thickness results in a larger final average thickness.
The animation result below shows the process of mold motion followed by inflation.
Video
Setup Details: The following video steps through highlights of the setup.
Ansys Solution Benefits
ANSYS offers advanced capabilities for simulating Injection Blow Molding which offer numerous benefits, including enhanced design optimization, improved reliability, and cost savings. By accurately predicting blow molding 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 IBM processes.
Ansys Fluent-Polyflow enables the evaluation of multiple design/input factors such as mesh adaption sizes, initial parison thickness, and penetration accuracy. 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 Expertise
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 Injection Blow Molding.
We offer support, mentoring, and consulting services to enhance the performance and reliability of your blow molding 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.
Suggested Blogs
- https://blog.ozeninc.com/resources/material-processing-workspace-in-ansys-fluent
- https://blog.ozeninc.com/resources/unlocking-the-versatility-of-ansys-polyflow-a-gateway-to-industrial-innovation
- https://blog.ozeninc.com/resources/stretch-blow-molding-with-ansys-fluent-workspace-polyflow
- https://blog.ozeninc.com/resources/pressing-thermoforming-simulation-with-ansys-fluent-workspace-polyflow
