ObjectiveThe insert connection mode between plastic and wood is a common joint form in plastic chair furniture. Optimal design of joint parameters can effectively improve joint strength, thus enhancing the reliability of products.

MethodPP plastic and beech jointed by round tenon was put forward as an example, the wall thickness of plastic part, inserting length and interference fit were selected as the observing factors, and the tensile strength and bending strength were taken as evaluation indexes. A three-factor and three-level Box-Behnken response surface design method was used to establish a mathematical model between joint strength and matching parameters. The significance and interaction of each factor were analyzed by analysis of variance, and the optimal assembling and matching parameters of the joint were obtained by solving the regression equation. On this basis, the comparative analysis of the withdrawal forces of joints was carried out between three different assembly forms interference assembly, gluing assembly and wood screw assembly.

ResultThe results showed that the three design factors had significant effects on the tensile strength of the joints, but only the wall thickness of plastic parts and the depth of insertion had significant effects on the bending strength of the joints, and had nothing to do with the interference fit. The optimum matching parameters of 40 mm round tenon-wood joints were as follows: the wall thickness of plastic parts was 3.2 mm, the depth of joints was 50 mm, and the interference fit was 0.14 mm. Under this condition, the ultimate withdrawal force and the load of bending of joints were 2 139.3 N and 1 306.4 N. In addition, the withdrawal force of the joints with three different assembly methods was as follows: the interference assembly (type I joint) was 966.5 N < the glued assembly (type II joint) was 1 251.4 N < the wood screw connected assembly (type III joint) was 1 607.6 N.

ConclusionThe matching parameters of the plastic-wood insert joint can be optimized by the response surface method to obtain the best mechanical properties. In practical application, it is easy to obtain the maximum joint strength when the design factors are close to the upper limit in the design domain. In addition, the use of wood screws can greatly increase the tensile strength of the joints.