Sheboygan Falls, WI-based Bemis Contract Group, a division of Bemis Manufacturing, prides itself in bringing the latest injection and extrusion technologies to a select group of industry segments. The Bemis Contract Group(BCG) brings value through expertise in product and tool design, as well as product development and project management. All of its machines are computer controlled and robotically attended. Some are state of the art multi-material molding capable. Sizes range from 165 to 6,600 ton. The facility operates 24/7 and is part of a two million square foot corporate headquarters. BCG's other facility in Lenoir, NC is similarly equipped.
Bemis Contract Group project engineer Jeff Lallensack recently worked with CAE Services Corporation, a plastic engineering service provider serving various markets including medical, electronic, packaging, and automotive. Mercury Marine contacted Lallensack to design and manufacture a complex engine cover and associated mold for its Verado family of new four-stroke marine outboard engines. The customer approached Bemis engineers with industrial design sketches - no CAD models were yet generated.
"We asked CAE Services to become involved in this project because of the complexity of the part, the material involved, and concerns about part warpage," says Lallensack. The material proposed for this application, Zytel 70G 33, a 33 percent glass-filled nylon, had never been used before. The marine top is Class-A painted and is a show-surface part. "Aesthetics were critical in this application," Lallensack notes. "Due to the complexity of the part, assembly requirements, and other issues, we decided to employ CAE Services Moldflow analysis expertise."
The 13-pound part required a single cavity mold. Other specifications included part strength and durability. "A boater had to be able to stand on the engine cover at a temperature of approximately 200 degrees. In addition, when the part is assembled, it mates with other parts so the shape of the lid was critical," Lallensack says. The part also contains the latching mechanism for it to attach to the rest of the cowling.
Lallensack and his team relied on the CAE Services analyses to provide information about what areas of the part were critical in terms of its mold. They wanted results that predicted any hot spots in order to achieve even cooling throughout the tool. "We also relied on the analyses to determine if there were any warpage problems so that we could address them prior to building the tool," Lallensack notes.
Tim Lankisch, part of the CAE Services engineering team, adds, "Using Moldflow Plastics Insight (MPI) software, we introduced flow leaders to promote more flow to a certain area of the mold. We found that the last area of fill was causing a knit line on this cosmetic part. By introducing flow leaders we could see what the effects of thickening certain wall sections. This process worked very well by adding just a half millimeter of wall section."
In terms of warpage, Lankisch and his team analyzed the warpage and found that there were a couple of issues causing inward warpage of the part. "In addition, there were some cooling and shrinkage issues," Lankisch adds. "In total, we and our customer were able to understand what the warpage was going to look like prior to molding the part."
Lallensack says the analysis results correlated very closely with reality. "You can't predict exactly how the part will mold, however, the Moldflow results do provide a trend or direction of the warp we would experience."
Within two to three weeks of initially contacting CAE Services, Lallensack had the results they originally anticipated. Due to the complexity of the mold and the part, Bemis deemed the analysis as an insurance policy. "By working with CAE Services, we wanted to avoid expensive tool changes in the future, adhere to project deadlines, and maintain customer satisfaction," adds Lallensack. In doing so, Bemis incurred little to no rework. "The analyses assured that our part and mold were accurate".
"The cost of the analyses was definitely less expensive than trial and error methods. We were able to save two to three weeks in manufacturing time," Lallensack adds. For this project, he said the Moldflow analyses were very good tools for predicting filling patterns and venting issues.
As for CAE Services, Lallensack says that he will continue to work with the firm. "I have recommended them to internal and external colleagues. I have worked with the firm for nearly four years, and to this date, I've agreed with every analysis they have provided us."