Custom CNC Bent Aluminum Tube for Chairs - Formed Aluminium Pipe Frame Components

Custom CNC Bent Aluminium Tube for Chairs

This product is a bent aluminium tube formed to a chair frame. The tube is cut, CNC bent and, where the design calls for it, drilled or notched so that it can be joined into the leg, back and arm structure of a seating unit. The part is made to the customer drawing rather than to a fixed catalogue shape, so the bend radii, bend angles and overall length follow the chair frame it belongs to.

Aluminium is chosen for a chair frame because a bent aluminium tube gives a high stiffness for its weight, which matters when a frame has to be carried or moved, and because the tube can be finished to match the rest of the product.

Bending and forming

The tube is bent on CNC equipment so that the angle and the position of each bend repeat from part to part. Repeated bends on one tube are held to the drawing so that a pair of side frames comes out as a matched set. Where a frame needs a flat or a notch for a fixing, that operation is carried out after bending while the part is still located in the same setup, which keeps the feature aligned to the bends.

Tooling and repeatability

Each bend needs a die matched to the tube diameter, and the die set is chosen so that the outside wall of the bend does not flatten or wrinkle. On a run of chair frames the same tooling and the same setup are used for every part, which is what makes one frame interchangeable with the next rather than a one-off. Parts are checked after bending against the drawing, so that any drift in the angle is caught before the batch is finished.

Chair frame use

In seating the bent tube forms the front and rear legs, the backrest support and the armrest rail. A chair frame often uses several bends on one tube, and holding those bends to the drawing is what lets the upholstery and the seat pan fit without hand adjustment. The round section also gives a smooth edge where the frame is exposed to the user.

Finish and packing

The part can be supplied in the mill finish or anodized, and the ends can be left square, deburred or capped as required. Finished frames are checked against the drawing and packed so that the bends are not distorted in transit.

Information to supply

Send the tube diameter, wall thickness and alloy, the drawing or a sample showing every bend angle and radius, and the tolerance the assembled frame allows. State whether the tube is to be anodized and whether any holes, slots or threads are to be added after bending.