As the saying goes, “the high-rise building is flat”, the preparation of sheet metal parts is a very important basic stage in the furniture manufacturing process. “Luban Classroom” divides the materials into three types: straight-line parts preparation, rubber-prepared materials, and curved preparations. This issue will bring you the latter two.




Glue preparation
In layman's terms, glue preparation is to glue narrow and short parts together. The glue preparation material is mainly used for large-area, large-section or curved-shaped solid wood parts, and the dimensional stability of the parts after the glue is increased. The rubber-bonding operation requires that the joint surface be smooth and smooth, so the rubber-covering operation includes the lead processing such as batch processing and wool processing, and then lengthening or widening.






Glue preparation materials are generally divided into three types: short material length (finger joint), narrow material width (panel), and sawing and bending.


Short material length (finger joint)
Short length is the length of the glue. It is mainly used for the long-term use of surplus materials to improve material utilization. Common extension forms include docking, mitering, and finger jointing.






In the process, the long-term operation generally includes the steps of material selection, milling, gluing, lengthening, and drying.


Step 1: Select materials. It should be noted that the spliced wood should be of the same kind or materiality; the defects such as dead knots and cracks should be removed before splicing. In addition, for the same batch of materials, the moisture content difference should be controlled within 2%.






Step 2: Milling machining. Refers to the installation of the corresponding finger-joint knife on the milling machine. The figure below shows the general milling machine and its working principle.






In enterprises with high degree of automation, automatic double-head milling machines are often used, which can realize automatic feeding, automatic turning, pier head, double-head milling, automatic glue coating and so on. It can be combined with other devices to form a fully automatic finger-joint or jigsaw line.


Step 3: Glue. The commonly used glue is PVAc, and it is better to fill the glue with a glue and a small amount of glue when it is pressurized. Generally, single-head glue is applied, but for hardwood and greasy wood, it is necessary to apply double-head glue and increase the amount of glue applied. The glued sheet should be pressurized as soon as possible (not more than 3 minutes), and since the PVAc glue is not easy to form a film at low temperatures, the room temperature is required to be greater than 15 °C.






Due to the small contact area and unevenness of the finger joint, manual brushing is often used. With the update of modern mechanical technology, there has also been an automatic machine for finger-jointing, which works as shown below.






Step 4: Take the lead. The glued processing is applied to the glued square material by a special finger joint device, generally including a fixed length stage of the sheet material - pressurization of the upper pressure beam - pressurization of the side pressure beam - longitudinal pressure bonding and the like. Pressurization is suitable for tightness and tightness. The longer the gums and the lower the pressure, the greater the density of the wood, and the greater the pressure.






Is there a problem with the fingering process? Collection of the map to solve!


Master Lu


Master Lu corrects (fingerprint)


Narrow material width (plain)
Narrow material width, that is, the width of the glue, is mainly used to make large panel parts, large section parts and so on. The following picture shows the common imposition form.






In essence, the narrow material width (panel) is similar to the short material length (finger joint). Therefore, the two processes have similar processes and have the same requirements for wool. Such as eliminating defects such as thrift, selecting materials with similar properties, and controlling the moisture content to within 2%.
It is worth mentioning that the adjacent plates should be at right angles to prevent voids. It is not allowed to have a gap in the adjacent plate surface for the flatness of the entire line.






If the adjacent squares are not right angles or the split surfaces are not parallel, the board will slip, as shown below.






Same as finger jointing, after the board is assembled, the room temperature is also required to be above 15 °C, and the sun is not allowed to be exposed. Generally, the drying time should not be less than 24 hours, and the bonding strength reaches a maximum after one week of drying.


Saw bending
Compared to the circular sawing machine, the band saw blade has a narrow saw blade and a wide sawing path. It is the most commonly used preparation machine for curved parts and shaped parts. For parts with uniform thickness and small difference in curvature, it is also possible to prepare materials by bending. However, there are different methods and precautions for components of different shapes.


1. Round or nearly round parts. Usually the excess scrap on the blank is first sawn off to facilitate the direction of rotation. As shown below.






2. Shaped parts. For parts with sharp turns or low curvature on the sawing surface, several kerfs can be sawed in the corresponding positions to facilitate the rotation of the saw blade and the falling of the residual material, as shown below.




Figure: Parts sawed with sharp bends


3. Beveled parts. For the beveled parts, the corresponding beveled form can be made, and the bevel can be sawed directly by a band saw or a circular saw, as shown below.
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