Design and 3D Printing of Reinforcement Connectors for Mortise and Tenon Joints in Solid Wood Chairs

To address the loosening of mortise and tenon joints in solid wood chairs caused by prolonged use and wood expansion and contraction, this study proposes a reinforcement method using 3D-printed connectors based on polyethylene terephthalate-1,4-cyclohexanedimethanol (PETG) filament. First, the influence of key process parameters (extrusion extent, nozzle travel speed, and nozzle temperature) on the mechanical properties of PETG models was analyzed. Subsequently, based on the optimized process parameters, reinforcement connectors with rib structures were designed and 3D printed. The reinforcement effectiveness was evaluated by comparing the ultimate load of mortise and tenon joints with and without the reinforcement connectors. Results indicated that with the increase of extrusion extent and nozzle temperature, and the decrease of nozzle travel speed, the ultimate strength and Young’s modulus of PETG models increased, improving their mechanical properties. The optimal process parameters were determined as follows: extrusion extent of 105%, nozzle travel speed of 70 mm/s, and nozzle temperature of 250 °C. After installing the reinforcement connectors, the average ultimate load of the mortise and tenon joints reached 445.7 N, which was 34.9% higher than that of joints without reinforcement, demonstrating that the 3D-printed connectors effectively reinforced and protected the mortise and tenon joints.