Designing it right the first time

It was the early 1980s when signs first appeared in all types of manufacturing facilities that read “Make it right the first time.” At that point, the phrase had nothing to do with computer-aided design simulation technology—it was merely a reminder to focus on quality when making products.

   Fast forward to 2001 and you find the same phrase applied today with a not-so-subtle shift. The difference? It has also become a design motto, and refers pointedly to the use of simulation tools such as finite-element and moldfilling analyses.

   Adopting the technology at toy-making giant Lego, where 1.4 million parts are molded every hour, has proven to be a major cost saving device. “With volumes at this level, every small change in material usage and cycle time has a substantial impact on costs,” says Jesper Kjærsgaard Christensen, a Lego CAE consultant. “Some of Lego’s part runs are 30 million or more, so a 3 percent reduction in materials can save 1 million Kronas (about $125,000). Last year, we saved $625,000 in materials on just five parts. It’s not unusual for us to see that kind of savings over four to five parts per year.”

Adding Tools
The product development team at Lego (at the company’s headquarters in Billund, Denmark) includes more than 300 engineers and managers developing new designs for the approximately 200 to 300 new parts created each year. Two years ago, when the company realized that product safety, time-to-market, and cost reduction were the three most critical issues it faced, Lego added simulation software tools—MSC.Marc, MSC.Patran and MSC.Nastran—to the Unigraphics and Moldflow packages already being used by its designers.

   While simulation with finite-element modeling (FEM) may seem a little heavy-handed for the plastic bricks that make up the bulk of Lego’s production, it makes sense from several perspectives. “When you’re the leading manufacturer of products to stimulate creativity, imagination, fun, and learning, you have everybody’s attention, both customers and competitors,” says Christensen. “So maintaining state-of the-art product development tools is imperative.”

   The types of analysis performed at Lego include fatigue, strength/stiffness, and strength/thickness analysis. These help ensure safety, especially for products targeted to the zero- to five-year-old market, as well as reduce material usage where possible. In the future, Lego will couple flow and structural analysis to get the ansiotropic material data and residual stresses for moldfilling analysis input.

At the end of its two-year simulation implementation program, Lego has achieved its aims. For one, safety and quality are the focus of new product development. At the same time, these tools have reduced dependency on physical prototyping, eliminating costly changes to tooling, as well as substantially reducing manufacturing costs, especially those related to materials and tooling.

Brick by Brick
Today, an FEM team at Lego is responsible for virtual development of parts and tooling, beginning in the concept development phase. The team’s objectives are to focus on product safety, reduce overall cycle time, increase functionality of toys, and make material/structural knowledge available to more people within the organization. Christensen explains, “FEM delivers the ability to see mechanical behavior at an earlier stage in the product development process. We are trying to keep our designs virtual as long as possible, because when the product is virtual, the costs involved in making changes are minimal.”

   By determining earlier how a part will behave, designers create better mold designs. As a result, fewer tooling changes are made, and costs associated with making physical prototypes and molds are substantially reduced. “With a virtual prototype it’s possible to make almost all the changes before the tooling is made,” says Christensen.

   With new software come new processes, and in an organization the size of Lego, change isn’t always easy. Implementation required a well-thought-out plan that proved the concept as new software and processes were added.

   FEM was implemented as a three-phase process, including proof of concept, training, and production implementation. Christensen explains, “During the first phase, we benchmarked different FEM products, deciding on MSC.Marc, MSC.Patran, and MSC.Nastran because of their features, ease of use, and technical support. The second phase included training and comparing simulation tests with known results to better understand how the software should be used. The third phase included implementing structural calculations in the development phase and establishing an FEM team that is capable of avoiding structural problems in Lego tools and parts.”

   Currently, the Lego simulation team includes five people—four dedicated to product development and one dedicated to mold design. “The most interesting part is being able to work simultaneously,” he adds. “For example, the designer may not be sure if there is a problem when he brings us a design. We can then use the software for development, even before the design has been finalized. We also use simulation to find problem areas and sometimes to define a concept.”

Basic Benefits
Simulation and actual tests are run on Lego parts as well as the tools used to mold them. Designers may run a linear stress analysis on a tool part for a 2-by-4 Lego brick using MSC.Nastran, and then switch to MSC.Marc to perform contact analysis. MSC. Marc nonlinear analysis can also simulate a compression test on a 1-by-16 Lego Technic element. On this same part, the software can simulate a torque test or generate a force-displacement diagram for contact analysis.

   One of the many benefits FEM brings to the table is improved design, according to Christensen. He says, “We’re not afraid to try a new solution. With simulation, our designs have been more stable. It provides an opportunity to try more solutions and have the confidence that when you have a very strict schedule, the virtual solution will work in reality.”

   Another plus is the reduction in overall cycle time, from concept to finished part. In some instances, design time is either the same or possibly longer, but total production time is reduced because late changes are dramatically reduced. “If we are able to reduce the molding cycle time, the cost savings can be significant. We are more confident that the injection mold won’t break down, which can be a significant cost. At the moment, a mold has to run for 24 hours with only two maintenance sessions. By reducing the number of breakdowns we increase productivity, too.”

   Simulation also helps Lego designers understand where stresses are, and where they are not. With this knowledge, an engineer can make what might seem like an insignificant change of mass. Yet, the resulting material savings can be great.