IRWIN RESEARCH AND DEVELOPMENT USES SOLIDWORKS AND ALGOR SOFTWARE TO KEEP PLASTIC PRODUCTS ROLLING OFF THE PRODUCTION LINE

September 4, 1998, Pittsburgh, Pennsylvania - You see them at the deli counter, in your delivery of take-out food, in cafeterias and grocery stores -- plastic food containers created by machines called thermoformers. Irwin Research & Development in Yakima, WA, manufacturer of the best-selling web-fed foam thermoformer in the U.S., is using the software of Pittsburgh-based Algor, Inc. to interface finite element capabilities with their SolidWorks CAD system. By using analysis in conjunction with design software, Irwin Research & Development has been able to produce stronger thermoformer components that keep up with changes in the plastics industry and ensure that consumer products roll off the production lines and into our grocery stores and restaurants.

Thermoforming Creates Plastic Products

Irwin Research & Development manufactures a variety of equipment for the plastics industry, specializing in equipment for thermoforming. Thermoforming is a process by which flat sections of thermoplastic are molded into three-dimensional products. First, the thermoplastic passes through a heat tunnel where it becomes soft and malleable. The thermoplastic may either be unwound from a roll, also called a web, or fed into the heat tunnel as a continuous, flat sheet. The plastic then passes into the former where it is vacuum-stamped between two molds. The molded shape is then trimmed from the excess plastic, which is recycled to make new sections of plastic.

Irwin Research & Development manufactures web-fed thermoformers that use rolls of plastic to create small items such as cups, plates and bowls. More than 700 of Irwin's machines operate in 26 countries worldwide.

Essential Thermoformer Components Reevaluated Due to Changes in the Plastics Industry

Since Irwin's Magnum Thermoformer was first manufactured in 1986, companies producing plastic items have moved from using foam materials to thicker types of plastic. Thicker plastics are sturdier, but these materials also require more pressure to vacuum-stamp shapes into the unformed plastic. Due to the increased pressure and fatigue, essential thermoformer components, called platens, developed cracks in several of the sixty Magnum thermoformers in operation.

A platen is used to transmit pressure from a press mechanism to a mold. Each thermoformer contains two assemblies consisting of a press, platen and mold. A thermoformer with a cracked platen cannot safely be used. In addition, the quality of the product being produced may be compromised. Even with slight deformation, the platen will not be able to tightly seal the two molds together. Without a vacuum-tight seal between molds, the plastic product will not form correctly. For a company producing plastic products, a cracked platen could result in several weeks of down time and several thousand dollars for a new machine component in addition to shipping and labor costs.

"At Irwin Research & Development, we strive to produce components that never fail, even after years of use," said Mechanical Engineer Frederic Pasche. "In 1986, the platen would have been prototype-tested. Now, we use finite element analysis to determine where the highest stresses will occur and discover how to fabricate the platen to prevent future failures."

Finite Element Analysis Used to Uncover High Stress Areas

Based on the platen's geometry, Mr. Pasche created a finite element model with nearly 3000 elements using Algor's Superdraw III. To speed processing without significantly affecting results, Mr. Pasche omitted small features such as mounting holes. An applied pressure of 250,000 lbs. over the surface elements of the finite element model reflected the rating of the press. Boundary conditions fixed the model on all four corners to replicate the platen's attachment to the bushings on which it is lowered and raised. Mr. Pasche used the material property values for steel from the Material Library included with Algor software.

Mr. Pasche then conducted a linear stress analysis and compared the Von Mises stresses to published yield stress for steel. Mr. Pasche discovered that high stresses were occurring where sections of a platen had been welded together. "We set a goal to reduce the Von Mises stresses to below one-third of the yield stress," said Mr. Pasche.

CAD Model Analyzed with Algor to Confirm Design Changes

To reinforce the platen, Mr. Pasche added thickness to the platen's geometry. First, he created a model of the platen in SolidWorks. Since performing the first platen analysis, Irwin Research & Development had invested in Algor's Houdini software. Houdini enabled Mr. Pasche to automatically create a finite element mesh from a SolidWorks IGES file. Houdini offers SolidWorks users three choices for solid FEA meshing of existing designs: tetrahedral; all-brick or hybrid, with bricks on the surface and tetrahedra inside. First, Houdini's Merlin Meshing Technology created a well-shaped surface mesh from the SolidWorks model. Because Algor creates solid meshes from the surface in, a well-shaped mesh on the outside adds the highest possible accuracy to the solid mesh created on the inside.

After the surface mesh was created with Merlin Meshing Technology, Houdini meshed a solid model from the surface in and put the highest quality elements on the surface -- the focus of most engineering. The surface is where loads and boundary conditions are applied and where stress levels tend to be the highest. This principle works with tetrahedral, brick or hybrid models. Houdini can leverage Hypergen technology to apply the highest quality automatic four- and 10-node tetrahedral meshing to a SolidWorks model with its "surface-in" meshing technique. However, Mr. Pasche used Houdini's famous "brick" meshing with Hexagen with the standard option for a hybrid mesh. No special refinement of the automatic, solid finite element mesh was required. Again, Mr. Pasche omitted small features such as mounting holes to speed processing without significantly affecting results.

The model was analyzed using the same loading and initial conditions as used for the original model. Von Mises stress results revealed a much stronger platen. "The new design is approximately four times as strong as the original design," explained Mr. Pasche. "The added strength will help to prevent fatigue failures." As an added measure, Irwin Research & Development is considering fabricating the platen so that the location of the weld does not coincide with the areas of highest stress.

"Performing finite element analysis helps with design," explains Mr. Pasche. "We no longer have to apply the trial-and-error method to prototypes that are expensive and time consuming to produce."

Looking to the Future

Irwin Research & Development relies on finite element analysis because of the demanding time-constraints of the consumer plastics industry. As Irwin Research & Development prepares the Magnum platen for the 21^st century demands of the plastics industry, Mr. Pasche is including 21^st century engineering software technology in his design cycle. Irwin plans to interface SolidWorks with Algor's Accupak/VE Mechanical Event Simulation software for Virtual Prototyping with Linear and Nonlinear Stress Analysis on projects in the future. Accupak/VE replaces physical testing with virtual testing by replicating mechanical events with a computer, helping to determine the behavior of a product in its real-world, worst-case scenario. With Accupak/VE, Irwin Research & Development can predict motion and impact, perform stress analysis for each instant as the event unfolds, determine flexibility, intrinsically determine forces, handle complex shapes and nonlinear behavior and test strength of materials all with one package.

Mr. Frederic Pasche, mechanical engineer at Irwin Research & Development, created a finite element model of the original platen design in Algor (left). Linear stress analysis results (right) revealed high stresses coinciding with welded areas of the thermoformer component.

Mr. Pasche modeled the platen in SolidWorks (left) and made modifications to add strength to the design. Using Algor's Houdini software enabled Mr. Pasche to automatically create a finite element mesh (center) from a SolidWorks IGES file. Von Mises stress results (right) revealed that the new platen design is approximately four times as strong as the original design.