Assembly Planbook - July 2008 - (Page 80)

ASSEMBLY Plastics Assembly Plastics: Design for X These tips will help engineers design plastic parts for optimal performance whether they’re welded, bonded or fastened. O When designing plastic parts for adhesive bonding, engineers should maximize the surface area to which the adhesive can bond. Photo courtesy Dymax Corp. By John Sprovieri Editor ne of the great benefits of making parts out of plastic is that they can be assembled in many different ways. Plastics can be joined by ultrasonic welding, vibration welding, spin welding, hot-plate welding, laser welding, induction bonding, staking, snap fits, press fits, adhesives, solvents and threaded fasteners. No matter how the parts will be assembled, engineers are well-advised to consider the joining method as they are designing the parts. Often, a small change—widening a hole, thickening a wall or adding a gusset—can mean the difference between a smooth assembly operation and one hamstrung by constant process faults. Whether the assembly will be welded, bonded or fastened, technology suppliers can provide invaluable guidance on part design. “The fastener is usually the last thing engineers think of when designing an assembly,” bemoans Larry Pickett, marketing director at fastener supplier Acument Global Technologies Inc. (Troy, MI). “Sometimes, we can live with that if the parts are metal, but with plastic, we need to be involved as close to the drafting board as we can get.” “The earlier we are involved in the process, the better,” adds Brian Gourley, manager of the technical services group and Sonics & Materials Inc. (Newtown, CT). “We’ve been joining plastics for years, so we can troubleshoot a process in advance.” Ultrasonic Welding When designing plastic parts for ultrasonic welding, engineers have several options for joint configurations. A butt joint with an energy director is the most common design and the easiest to mold. An energy director is a small triangular-shaped ridge molded into “The fastener is the last thing engineers think of when designing an assembly.” —Larry Pickett, Acument Global Technologies Inc. one of the mating surfaces. The energy director limits initial contact to a very small area and focuses the ultrasonic energy at the apex of the triangle. The concentrated energy melts the ridge and plastic flows throughout the joint area, bonding the parts together. For a stronger bond and a more aesthetic appearance, engineers can use a step joint with an energy director or a tongue-and-groove joint with an energy director. Joints with energy directors are not 80 ASSEMBLY / July 2008 www.assemblymag.com http://www.assemblymag.com

Table of Contents Feed for the Digital Edition of Assembly Planbook - July 2008

Assembly Planbook - July 2008 Contents Editorial Quality in Assembly Station to Station Assembly Lines Assembly in Action Surviving the Roller Coaster The Human Side of Manufacturing Do Your Fasteners Need a Preapplied Thread-Locker? Manufacturing Innovation A Century of Progress Trendsetting Plants Pulse Tools Get Smart Plastics: Design for X Product Reviews Products Advertisers Index Classified Leading Lean

Assembly Planbook - July 2008

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