Objective  Dowel rotation welding is a new type of green connection technology in wood structures and furniture. There are few studies on rotary welding of bamboo tenon at home and abroad, the optimal welding process parameters of bamboo dowel are unknown. The difference between bamboo dowel and wood dowel in rotation welding also needs to be studied.

  Method  Welded joints were manufactured by rotation welding with bamboo dowels and spruce substrate. The withdraw resistance of joints was tested to get better process parameters for bamboo dowel rotation welding. The ratio of substrate predrilled to bamboo dowel diameter, bamboo dowel rotation rate, bamboo dowel moisture content and bamboo dowel insertion rate were selected as parameters for orthogonal tests. Single-factor tests were designed based on the results of orthogonal tests for three factors: the hole/dowel diameter, rotation rate and insertion rate. Compared with beech dowels, temperature monitoring, scanning electron microscopy and infrared spectroscopy were taken to the weld layer.

  Result  According to the orthogonal and single-factor tests , the optimal process parameters were followings: the moisture content of bamboo dowel of 12%, rotation rate of 1 270 r/min, the hole/dowel diameter of 7/10 and insertion rate of 600 mm/min, the average withdraw resistance of this solution was 4 588 N. The order of influence of the factors in single-factor tests was hole/dowel diameter > insertion rate > rotation rate. Beech dowel was selected as control, the withdraw resistance of bamboo dowel rotation welding joints increased by 49.3% compared with beech dowel. The temperature monitoring results showed that the peak temperature of bamboo dowel welded layer was greater than that of wood dowel welded layer. Scanning electron microscope observation of the welded layer on the surface of the dowel revealed that bamboo fibers were intertwined on the surface of dowel, and bamboo fiber was less likely to break than wood fiber when rotating and welding. The bamboo fibers in welded layer became entangled with each other, which was not observed in the welded layer of wood dowels. Infrared spectroscopic analysis of the weld layer found that the bamboo dowel rotation welding mechanism was similar to that of wood dowel, significant thermal degradation of hemicellulose during the welding process, the relative content of lignin increased and cellulose content was almost unchanged.

  Conclusion  Compared with orthogonal tests, the welding process parameters are further optimized by single factor tests, and the optimum welding process parameters of bamboo dowel are obtained. The rotation welding mechanism of bamboo dowel is similar to wood dowel, but bamboo dowel can generate higher temperatures during rotary welding and the welded layers have unique intertwining of fibers, and the hemicellulose of bamboo dowel is less degraded during the welding process. Using bamboo dowels to replace wood dowels for rotation welding can greatly improve the withdraw resistance of the connected nodes.