DESIGNING PLASTIC PARTS FOR ASSEMBLY Machinery's Handbook, 31st Edition
600
Before Welding
During Welding
After Welding
Induction Coil
Before Welding
After Welding
Before Welding
After Welding
Flat to Flat
Flat to Groove
Before Welding After Welding
Tongue and Groove
Before Welding After Welding
Before Welding After Welding
Shear Stepped Fig. 24. Typical Joint Designs Used in Induction-Welding Plastics Assembly
Assembly with Fasteners.— Metal fasteners of high strength can overstress plastics parts, so torque-controlled tightening or special design provisions are needed. Examples of poor and preferred designs are shown in Fig. 25. The shoulder of the metal screw shown in the lower right portion of Fig. 25 meets the metal component when it is tightened, sparing the plastic part from over-compression. Where force cannot be satisfactorily con - trolled, even with a shoulder screw, various types of washers can be used to spread the compression force over wider areas. Metal inserts are available in a wide range of shapes and sizes for permanent installation of metal threads or bushings in plastics parts. Inserts are typically installed in molded bosses, designed with holes to suit the insert to be used. Some inserts are pressed into place and others are installed by methods designed to limit stress and increase strength. Gener ally, the outside of the insert is knurled or otherwise provided with projections of various configurations that penetrate the plastics and prevent movement under normal torques ex - erted during assembly. “Helicoil” inserts have large standard threads on the outside and receive a smaller standard screw inside, thus lowering the assembly torque on the plas - tic by distributing it to the larger outside contact area. Inserts can also be installed with equipment similar to that used for ultrasonic welding, the plastics being melted to enhance contact with the metal and reduce insertion stresses.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online