3D Printing Application in Wood Furniture Components Assembling

Abstract

Additive manufacturing (AM) is used in many fields and is a method used to replace wood components or wood-jointed furniture components in the furniture industry. Replacing wood joints by 3D printed connectors would be an advantage, considering the fact that during the process of assembling furniture, the execution technology of the joints is difficult, time-consuming, and labor-intensive. Advanced technology of AM applied in furniture manufacturing helps the designers to create new concepts of product design, with no limits of shape, number of joints, color, or size. The diversity of 3D printers and AM technologies provides the selection of materials in relation with the applicability of the 3D printed object. In this respect, the objective of the present research is to design a 3D printed connector to be used for jointing three chair components, namely the leg and two stretchers made from larch (Larix decidua Mill.) wood, and to use reinforced polylactic acid (PLA) fiberglass (20 wt. %) filament for 3D printing this connector using AM with fused filament fabrication (FFF) technology. The design of the connector, the possibility of using this type of material, and the deposition method of filament were investigated in this research. For this purpose, several evaluation methods were applied: microscopic investigation with 50×, 100×, and 200× magnifications, both of the filament and of the 3D printed connector; mechanical testing of corner joint formed with the help of connector between chair leg and the two stretchers; and a microscopic investigation of the connectors' defects that occurred after applying the compression and tensile loads on the diagonal direction of the L-type joint. The microscopic investigation of the composite filament revealed the agglomerations of glass fibers into the core matrix and areas where the distribution of the reinforcements was poor. The heterogeneous structure of the filament and the defects highlighted in the 3D printed connectors by the microscopic investigation contributed to the mechanical behavior of L-type connecting joints. The bending moments resulting from compression and tensile tests of the 3D printed connectors were compared to the results recorded after testing, under the same conditions, the normal mortise-tenon joint used to assemble the abovementioned chair components. The larch wood strength influenced the mechanical results and the conclusions of the microscopic investigations, as well as the analysis of the broken connectors after testing recommended the change of connector design and filament deposition direction.

Keywords: 3D printed connector; additive manufacturing; mortise–tenon joint; polylactic acid (PLA); wood furniture.

Figure 1

Mortise–tenon-jointed chair leg and stretchers.

Figure 2

Designed connector for chair leg and stretchers: (a) 3D modelled part; (b) modelled part in the printer software prepared for 3D printing.

Figure 3

Perimeter and layer deposition of the filament.

Figure 4

Filament and parts samples prepared for microscopic investigation.

Figure 5

Corner-joint test specimens: (a) diagonal tensile testing; (b) diagonal compression.

Figure 6

Microscopy of the cross-cut section of the PLA–glass filament: (a) 50×; (b) 100×; (c) 200×. The circled areas represent defects of the reinforcement material: the matrix did not adhere to the reinforcement (no. 1); gap left by the evulsion of a non-adherent glass fiber to the matrix (no. 2); common evulsion of the glass fiber in the matrix, occurred after cutting the sample (no. 3).

Figure 7

Microscopy of the longitudinal section of the PLA-glass filament: (a) 50×; (b) 100×; (c) 200×. The circled areas represent, as follows: (a) glass fiber disposed longitudinally in the right position; (b) the longest glass fiber measured on the sample; (c) partial exposure of the glass fibers; (d) measured lengths of the glass fibers (the smaller and the longest one).

Figure 8

Connector 1 sample. Crosscut section: (a) 50×; (b) 100×; (c) 200×. The marked areas represent the defects which occurred on the 3D printed connectors: (a) prints of the deposited layers; (b) triangular defect specific to PLA; (c) delamination between layers and fiberglass bundle in detail X.

Figure 9

Connector 2 sample. Crosscut section: (a) 50×; (b) 100×. The marked areas represent, as follows: (a) perimeter marked with 1; overlaid triangular defects marked with 2, fiber–matrix unbound marked with 3, end of the perimeter contour marked with 4; (b) detail marked with 4 more clearly shows the changes of the deposition direction of the layer and the defect which occurred.

Figure 10

Connector 1 sample. Longitudinal section: (a) 50×; (b) 100×; (c) 200×. The marked areas represent, as follows: (a) delamination on the perimeter; (b) crack in the perimeter area; (c) crack between deposited layer and perimeter.

Figure 11

Connector 2 sample. Longitudinal section: (a) 50×; (b) 100×; (c) 200×. The marked areas represent, as follows: (a) areas marked with 1 and 2 show different types of cracks in the matrix, which can be considered macro-defects, and the zone marked 3 highlights the incomplete filling of the matrix.

Figure 12

Larch wood corner joint after testing: (a) tensile; (b) compression.

Figure 13

Tests of 3D printed connecting joint: (a) compression; (b) tensile.

Figure 14

Three-dimensional printed connecting part after compression test: (a) the piece with marked areas of cracks; (b) details of cracks with 10× magnification.

Figure 15

Three-dimensional printed connecting part after tensile test: (a) the piece with marked areas of cracks; (b) details of cracks with 10× magnification (left one for area 1 and right one for area 2).