Different types of metal have different properties that make some metals more difficult to bend than others. As an example, a steel wire is typically easier to bend than sheet metal, which is easier to bend than steel pipes. But a gold pipe could be bent in the same manner as a steel wire or thin steel strip. Knowing the type of metal you are bending is the first step to determining how to bend it properly and safely.
Metals are typically considered ductile in that they can be bent and worked to a certain point without the risk of breaking. Some types of metal are more flexible and malleable while others are more brittle. Gold, aluminum, copper and sterling silver are all workable with little risk of breaking or cracking. Steel and iron are more brittle, especially when subjected to cool temperatures. These metals are more easily bent using heat.
There are metal bending tools commercially available including small jigs for bending wire and metallic strips and press brakes for bending sheet metal. No matter if you use these tools or build your own, there are two primary ways to bend metal: cold bending or hot bending. Cold bending uses leverage to bend the metal into the proper shape. This is particularly useful with softer metals, as well as wire of all ductility. Hot bending uses a torch or other high heat source to heat the metal until it softens and can be bent to the proper angle. Pipes and tubes are often bent using this method.
The purpose of the metal should always be considered when the metal is being bent. For example, bending pipes that will later be pressurized must be done carefully because most pipe fitters and plumbers recommend that pressurized pipes be no more than three to five percent out of round. Bending metal can also weaken the metal due to the process, such as applying high heat with an oxy-fuel torch, used to bend it. The dangers posed to the metal by the method should be weighed carefully against the future use of the metal before bending.