Firm Cuts Seat Design Costs by 60% Using Topology-Optimization Software25 Apr, 2013 By: Beth Stetenfeld
Design Concepts calls on PareTOWorks, a new SolidWorks add-in, to confidently eliminate the metal hinge in a stadium seat.
Imagine you're a team member at a product design firm, and your team has an idea for an innovative new stadium seat. The project poses a number of challenges, including the following:
- Tight competition requires that you minimize materials and manufacturing costs for the seat.
- Limited time and engineering resources mean that the design process must be fast and efficient.
- The design must maintain high standards for quality and appearance, and must meet specific safety requirements.
That was the scenario for Design Concepts, an award-winning product design consultancy in Madison, Wisconsin. Fortunately, new topology-optimization software — in the form of an add-in to SolidWorks — helped the firm cut design time by about 60% and design costs by more than 50%. In addition, the team eliminated the need for a metal hinge in the seat, which previously constituted 60% of the total manufacturing cost.
A rendering illustrates the new folding stadium seat, redesigned by Design Concepts.
The lead mechanical engineer on the project, Chris Strahm, believes topology optimization will become a powerful tool for designers. "It's exciting," he said. "Now we have a new approach to starting an engineering-heavy project. There's greater potential for a unique design for our clients."
The add-in, named PareTOWorks, uses generic geometry and specific user-defined constraints to arrive at a first proof of principle (POP) model within minutes — or even seconds. From there, it's a matter of a few adjustments to create a presentation-ready design option.
PareTOWorks is being developed by Krishnan Suresh, an associate professor in the College of Engineering at the University of Wisconsin–Madison. The name stems from pareto-optimal solutions to topology optimization, he explained, with pareto-optimal meaning many solutions to engineering problems that have conflicting objectives.
Topology, as described in a recent Science News article by Julie Rehmeyer, is essentially the study of connections. "For a topologist," she noted, "two objects are the same if one can be shrunk or stretched into the same shape as the other, but without punching holes or gluing anything together, since that would change the way the parts of the object connect to one another."
Topology optimization means using engineering and mathematical principles to optimize the shape and geometry of an object to meet specific performance targets, explained Suresh. He developed PareTOWorks specifically to help mechanical engineers apply topology optimization to product design.
PareTOWorks is used at the onset of a project. A simple one- or two-feature solid body is created in SolidWorks, representing the general shape of the product, and then optimized using the PareTOWorks add-in. The output of this optimization is a stereolithography (STL) file, such as the example shown below.
Front and back isometric views show the optimized output of the stadium seat design.
This STL file then serves as an underlay for the construction of the final product geometry, modeled in Solidworks. "We essentially build over the STL file that defines the key structural areas for us," explained Strahm. In addition to saving designs in STL format, users can impose draw directions for casting and injection-molded parts.
PareTOWorks gives even small organizations a powerful tool that works on PCs and small networks, Suresh said. Because it relies on assembly-free, finite-element analysis, the software requires very little RAM. Users can, optionally, accelerate PareTOWorks using inexpensive graphics processing units (GPUs).
Optimized Seat Design
The stadium seat project required a compromise, said Strahm, between cutting costs — by reducing the volume of plastic and fiberglass and eliminating the metal hinge — and ensuring sufficient structure to meet functional requirements defined by the ANSI/BIFMA X5.1 standards for chair performance.
These trade-offs were a perfect challenge for PareTOWorks, he said, because designers could set up the simulation so material was only reduced in predefined areas of the seat. Topology optimization allowed the engineers and design team to input predetermined measurements, industry standards, and materials parameters, as well as set predefined values for acceptable seat stress levels.
Front and back isometric views show the molded components of the redesigned seat.
In this type of design project, said Strahm, topology optimization software "allows the designer to quickly define and quantify structural areas important in the product-development process, when timing and budget considerations sometimes weigh heavily in the decision-making process."
For Strahm, being able to easily incorporate the software into his normal workflow was an added bonus. "It was nice to require only a brief overview of the new software, and then be able to use it right away. I didn't have to spend two to three weeks learning new software. It was fully integrated into our existing CAD package, and we could just start working with it."
Design Concepts began the project without PareTOWorks, then turned to the add-in software to test and complete the design. Strahm estimated that for a project like this, developing a working model the traditional way takes about a week. With PareTOWorks, in contrast, the first iteration was completed within minutes, requiring only minor adjustment to establish the first POP, he said.
Eliminating the Metal Hinge
The aluminum hinge in the original design satisfied a series of static loading and dynamic impact-testing requirements. Using PareTOWorks, engineers were able to integrate the functionality of the hinge into the plastic seat back and seat pan, eliminating 60% of the cost associated with the original design.
To satisfy the design constraints, engineers found a compromise between cutting costs through materials reduction and maintaining sufficient structure to satisfy the ANSI/BIFMA standards. PareTOWorks made this type of compromise achievable, said Strahm, "by allowing the user to set up the simulation such that material will only be taken away in predefined areas, and stress levels observed will remain below predefined values."
"We set the simulation to try to optimize geometry by reducing the materials volume," Strahm said. In effect, the engineers worked to make the plastic seat as light as possible, while still meeting manufacturing standards, performance expectations, aesthetic goals, and safety requirements.
PareTOWorks helps design engineers surpass the status quo, Strahm observed. They can move away from the old strategy of benchmarking known designs, so there's more potential to develop truly unique products.
Using traditional benchmarking and hand-calculation methods, Strahm said, "you're afraid to be creative; you're afraid to go off the beaten path because of very serious consequences." Having the parameters entered at the start, and then designing free of those concerns might inspire a more original design, he said.
"We work closely with industrial designers. There's a lot of communication back and forth — engineering vs. aesthetics. This tool defines for me the important engineering structural elements, and I can provide more definition to the industrial engineers about the ultimate end product."
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