In the last few years, Edison Welding Institute (EWI) engineers have developed Magnetic Pulse Welding (MPW) applications for a variety of similar and dissimilar material combinations, in the process helping to reduce overall manufacturing costs while improving welds. Now, EWI, and Professor Glenn Daehn at The Ohio State University extended the process to structural crimp joints.
These joints use grooves, nuts, knurls, and threads to provide strength values that are comparable to those of the parent materials. EWI says it’s an efficient, elegant, and low-cost solution for joining dissimilar materials and for applications where metallurgical bonding is not required. Compared to welding, equipment for crimping is more robust, lower cost and smaller in size.
Crimping is a joining technique in which the plastic deformation of the components produces mechanical interlocking. The electromagnetic-pulse (EM) process uses high frequency currents to produce high intensity (~ 200 Mpa) and short duration (10-20?s) magnetic pressure to cause plastic deformation of the workpiece.
Most applications of EM crimping are tube joining to mandrels with surface features. Tube is accelerated to high velocities prior to contact with the mandrel. There are three major benefits for high velocity crimping, EWI claims. First, the organization says, in high-velocity crimping two pieces can be easily conformed to each other to cause macroscopic interlock. Second, high-velocity crimping almost always produces a natural interference fit, or a state of residual stress that holds the two components together. Lastly, there is an opportunity to use surface indentation to hold components together, in a manner similar to the operation of threaded fasteners.
EM crimping could replace riveted assemblies, welding applications, and traditional mechanical joining processes, EWI says. This process can help reduce manufacturing cost, increase joint reliability and simplify joining equipment. But, EWI admits that the flexible and simple-to-use process may pose design challenges due to the complex electromagnetic reactions behind it. Moreover, there is very little engineering science information in the literature on how to design an EM crimp joints and predict joint characteristics.