Comparative potential of alternative wood welding systems, ultrasonic and microfriction stir welding

Abstract

Two alternative welding systems were evaluated for wood welding. Ultrasonic welding produces joints of good strength but it appears to be applicable only to thin wood pieces. It does not appear that further possible process improvement could bring the joint strength to a structural level. Microfriction stir welding does show potential for welding continuously wooden plates without any limitation on length of wood pieces. The strength of the weld obtained was low due to the limited depth of the weldline. Optimisation of parameters is necessary. A drawback at present appears to be the limited thickness of the wooden pieces that can be welded. X-ray micro densitometry, scanning electron microscopy and optical microscopy showed that the main difference compared to the other techniques is that in the microfriction stir weld, there is a veritable welded line of molten material. This molten material comes from the wood in contact with the rotating steel cylinder, which has flowed down in the micro gap between the two pieces of timber where it has bonded by solidifying.