CNC Bending

CNC bending is a metal working process that can be used to make U, V or channel shape angles in bendable material, usually sheet metal. A computer controls the machine and the parameters behind each bend. Different types of CNC bending machine presses are used to perform these tasks. A wide range of objects are constructed this way including electrical boxes, air ducts and siding.

Before the integration with computers and manufacturing machines in the 1980’s these presses and benders were operated by hand by a machinist or ‘operator’. A work piece is set above a die block which is in turn pushed against the material resulting in a shape. Most materials have to overcome their tensile strengths and be over bent, seeing that the material will want to sprig back into place. The degree of the over bend solely depends on the type o f material used. Another way to bend involves the U-punch. Pressure is applied and makes a simple U-shape in the material with one punch. Thickness of material and properties of the materials used play important factor. Depending on the thickness the place of the bend will stretch resulting in thinned material.

If the material is harder and less pliable more over bend must be applied. There are many different types of bends. They are: air bending, coining, three-point bending and folding, wiping and rotary bending. The newest of these techniques is the three-point bend. In this process the die height is adjustable with the addition of a tool near the bottom. Heights can be met to within .01 milli meters. A hydraulic cushion controls the tool and ram. Three-point CNC bending can produce accurate angles to within .25 of a degree.

Even though CNC bending involving the three-point technique has high flexibility and is precise, the price of production is extremely high and tooling is much harder to find. CNC bending is very popular with the aero-space industry due to the bend ability of aero-space grade aluminum framing. Nearly every machine shop, big or small, in the States is equipped with either a manual bend press, CNC bending press or both. The size of these machines can range from small hand held devices for smaller jobs. All the way to room sized machines placed on a manufacturing line. Such machines would be found in the auto industry where repeatability and high volume production is a must.