Welding of wood
Have you ever wondered how to join two pieces instead of using glue? Say for example, can you join two pieces of wood to make it appear as a single piece? The answer lies in the fine craftsmanship of a mechanical engineer who knows the emerging science of “mechanically-induced wood flow welding” pretty well. Now to “weld” wood, which is quite a promising technology, you need to force pieces of lumber together by pressing (at 60 – 330 psi) and rubbing the parts to-and-fro at a very high speed for 4 to 5 seconds. The friction created in between the pieces heats and melts the primary components of wood, lignin and fibers present on the exposed surface. In the next few seconds, the molten lignin of both the surfaces intertwines in a matrix and finally solidifies when the friction movement is stopped and the interface cools down. It results in the formation of a full piece of wood of desired shape and size.
Laboratory for Timber Construction IBOIS of Ecole Polytechnique (EPFL), Switzerland applied the principle of friction welding to weld wood for the first time. The University of Tennessee has also been exploring the same area. Their research is mainly focused on the fabrication and application of welded timber panels. The research work has produced small-scale welded wooden samples successfully. Those samples have gone through tests of bending and shear-giving and have yielded positive results. Here it should be noted that the structural design of welded timber construction requires a calculation tool for strength prediction to make those lumber pieces work practically. Initially probabilistic methods were used to determine the load bearing capacity. There the welded joints had both parallel and perpendicular natural fiber patterns. The mathematically calculated and experimentally determined strength were found to stay in good agreement with each other. Further research in this sphere will encourage investigations into more complex systems.
Now let us come back to the basics and take a tour of the history of welding science. As a preconceived belief, welding is possible using only a good conductor of thermal energy and electricity. The parent materials should be joined in such a manner that the physical and the chemical properties of the welded portion remain same as the matter itself. Not only the finished product should look like a single piece but must also retain the ditto chemical qualities. Therefore welding of wood, if judged in this light, does not seem to have any real life acquaintance. However, standing in 2016, this chapter in mechanical engineering has passed the test of time in the very ritualistic way of how welding is done. It is an almost unthinkable phenomenon! After all, Science never fails to surprise. At every instance, and that too in a very pleasant way.
- · Reference:
The websites of EPFL & the University of Tennessee