Optimize by Land and Sea

In the last decade, automakers and their suppliers began losing weight at a dramatic pace, through a diet of carefully selected optimization software. The strategy is driven in part by the direct correlation between fuel economy and the consumers’ personal economy. A lighter car that yields better mileage per gallon is generally more appealing to a buyer. Another motivation to shed every ounce of excess materials from the design comes from stricter environmental standards and regulatory requirements.

For Voith Turbo, which manufactures hydrodynamic drives, coupling and braking systems, lightweight products are part of its vision to balance economic, ecological and social factors. On its homepage, the company states, “Sustainability is a cross-functional responsibility shared by our Corporate Board of Management, Group Divisions and Corporate Departments.”

The quest for lighter design has long been a proponent of the division that produces planetary gear systems, or gears that revolve around a central gear (the system’s metaphorical Sun). But when engineers adopted SIMULIA Tosca Structure, an optimization software package that bears the same name as a Puccini opera, the weight reduction turned dramatic—more than 30%.

The Limits of Manual Optimization

The planet carrier is a component in Voith Turbo’s automatic transmission system. Its rounded, disc-like shape was consistent with how such a part traditionally looks. To optimize it, Voith Turbo previously employed “a manual process,” says Bernd Wöhrle from the Technical Calculations Bus Drive Systems division.

“The planet carrier was designed in a traditional way based on its function and in accordance with the other existing planet carriers,” Wöhrle says. “The component has been constantly optimized in different details for better and more efficient manufacturability. With the manual optimization process, we could only study minimal design changes/improvements based on existing design, because it was time consuming, and involved extensive prototype testing. It took huge efforts to get minimal improvements.”

To conduct design analysis, Voith Turbo uses Abaqus, part of Dassault Systemes’ SIMULIA product family. In April 2013, when Dassault Systemes acquired FE-DESIGN GmbH, the latter’s Tosca product line (comprising Tosca Structure and Tosca Fluid) became part of Dassault Systemes’ simulation software portfolio.

The Tosca software titles are developed for structural and flow optimization. According to FE-DESIGN, Tosca Structure is suitable for designing “lightweight, rigid and durable components and systems.”

Does That Look Right?

The software-driven optimization started with the CAD model of the planet carrier. The engineers created the finite element analysis (FEA) and imported it into Tosca Structure to define the optimization task—including the design space, the region in which they’d like the optimization algorithm to find the perfect topology. They excluded critical joints and connecting features from the design space. This ensured the new design would not alter how the component fit into the larger assembly. They also placed further restrictions to satisfy the manufacturing requirements. Perhaps most critical of all, the functional stiffness of the planet carrier must guarantee bearing durability and equal load on the tooth flanks.

In most cases, a design proposed by the optimization software contains jagged surfaces and organic features not feasible for manufacturing. Due to Tosca Structure’s available set of manufacturing constraints, the optimization results came close to the final manufacturing design. Thus the engineers only needed to perform minor refinements in their CAD system to fit their existing manufacturing processes.

When the project began, Voith Turbo’s aim was to “improve the performance of the planet carrier component with the aim to reduce its weight using topology optimization,” says Wöhrle. He and his engineers might not have anticipated the optimal shape proposed by Tosca Structure’s built-in algorithm. After running iterative simulations and design assessments, Tosca Structure proposed a component that weighed one-third less than the original design.

The evolution of Voith Turbo’s planet carrier component, from the original design, to mesh model, to optimized shape. Image courtesy of Dassault Systemes and Voith Turbo.

But can the new design withstand the stresses and loads the planet carrier is expected to bear in day-to-day operations? “We became convinced because all doubts were eventually eliminated on the test bench,” Wöhrle says. “The analytic procedure guided us to a complete redesign with a performance which exceeded our expectations by far.”

The experience with the planet carrier prompted Wöhrle and his colleagues to start looking for weight-reduction opportunities in other components, and to start using Tosca at the beginning of the design cycle whenever possible.

Wöhrle says SIMULIA Tosca Structure gave the planet carrier “vast improvements in terms of weight and manufacturability. Within a shorter development time, one gets an efficient redesign.”

Sailing Faster with Composites

The weight advantage that comes with composite design is a more recent discovery for automakers, but the secret has been with watercraft engineers for a long time, according to Thomas Hahn, managing director of the engineering firm iXent.

“The boat building industry has mastered composite design for 30 years,” he says. “They were among the first using this material in a successful manner. The challenge in automotive is to mass-produce parts (hundreds or thousands a day), compared to yachting industry, where most high-tech yachts are one-off designs.”

The role of composites is not restricted to the boat’s hull and outer shell. Every part, from rigging to gearbox, is fair game for weight-reduction, thus a candidate for composite infusion.

iXent used Tosca Structure to optimize the Alegre 3 racing boat gearbox. Its design space was transformed into a topology result with crude meshes that were then refined, then turned into a form suitable for verification in FEA.

Winch specialist Jon Williams enlisted the engineering firm iXent to design the stiffest and lightest possible support for Alegre 3, a 72-ft. IRC Mini-Maxi racing boat designed by Mark Mills and built by Longitud Cero Composites.

“These supports are used to secure a gear box which typically powers a winch on deck or a hydraulic pump and gets driven by one or several driveshaft under deck,” iXent’s Hahn says. “The required power for this task is generated by the human force of up to eight crew members operating the so-called ‘coffee grinders’ at several positions on the boat.”

iXent turned to Dassault Systemes’ Tosca Structure to identify the initial topology in the concept phase. The software, Hahn says, “supports us in an early phase of projects by calculating a proposal of a 3D structure, which is optimized with respect to weight and stiffness or other physical targets. This approach is quite useful on the path to creative and innovative ideas and solutions—sufficient flexibility and openness in the design envelope and the customer’s vision provided. One of the very strong aspects of this approach is that multiple load cases can be incorporated simultaneously into such a study—an important fact since it is very difficult also for experienced engineers to visualize and determine load paths when several load cases come in play.”

Batman Onboard

The FEA model gave iXent engineers guidance on the design space—the cylindrical region that serves as the basis for topology variation. In Tosca Structure’s open environment, iXent was able to use simulation data not only from Dassault Systemes’ Abaqus, but also from competing software like MSC Nastran. “Topology optimization is a first step in the design of a product. The results will give the experienced engineer additional input and clarity about the feasibility of the concept chosen and will help in the choice of the manufacturing method and the detailing work later on,” says Hahn. The software-proposed optimal shape reminded engineers of the Bat signal used by the Caped Crusader, so it became known internally as “Batman.”

After smoothing the topology results with the built-in smoothing module, iXent engineers imported the geometry into CATIA software for further detailing. The next steps, Hahn says, were “Adding manufactural (draft angles, etc.) and also functional aspects (layer orientation, thickness and stacking sequences) to the CAD model … Some iterative analysis has to be done to ensure to use the minimum laminate scantling for the loads defined.”

The resulting gearbox is 17% lighter than the usual design of such a component in a racing yacht, iXent revealed.

“Our original component for the race yacht is already lighter than similar parts in a car, which are usually made out of isotropic material,” says Hahn. “In that respect, the 17% weight saving is much more significant than a 30% saving in an automotive part.”

More Info

• Dassault Systemes SIMULIA
• iXent
• Voith Turbo