Are you looking for a used sheet metal bending machine? Bending machines, also known as press brakes, are machine tools specifically designed to bend or fold metal sheets using processes such as bottom bending and air bending.
What is a sheet metal bending machine?
Press brakes are machine tools used to deform metal sheets by means of bottom bending and air bending. The thickness of the sheet must be taken into account before it can be bent. That is why press brakes, or bending machines, are classified according to the driving force used for bending and the pressing forces the machine applies.
A used sheet metal bending machine is a second-hand press brake that has been overhauled and performs almost like a new one. On these machines the structure plays a key role: it is made up of several elements and can be driven mechanically or hydraulically. Depending on the type of press brake, some can control how far the punch penetrates the metal sheet.
Press brakes shape sheet metal by deformation and work cold.
How a used press brake works
To bend metal sheets, force must be applied to the part so that it undergoes permanent deformation. Sheet metal bending is a metalworking technique that turns flat parts into V shapes, U shapes or channels.
Bending sheet metal is an economical process that helps you save money, as it is easier to deform a flat part than to machine a V-, U- or channel-shaped plate from scratch. Bending the sheet is also better than welding two parts together to obtain the required shape: a bent section is much stronger than a weld.
Bending operations on a used sheet metal bending machine
A sheet metal bending machine can perform three different types of bending: air bending, bottom bending and coining.
Air bending
In this type of forming, the punch forces the sheet into a die, but not far enough for the metal to touch the walls of the die. It is a very flexible method, as it can produce V-shaped, U-shaped and other parts, but it is not as accurate as the other techniques. A used sheet metal bending machine can perform air bending without the geometry of the die matching the required bend exactly. There is no contact between the surfaces.
Bottom bending
In this type of forming, the punch pushes the metal sheet fully into the die. This creates a bend that matches the internal geometry of the die. It is used to make V-shaped parts.
Coining: the most demanding process on a used sheet metal bending machine
Of all the bending methods, this is the most costly and difficult, so it requires an expert machine operator. Coining requires the punch to be driven into the sheet and die with greater force; this creates a permanent deformation with little or no springback. In other words, the sheet does not unbend when the punch is withdrawn from its surface.
What is springback?
When using a used sheet metal bending machine, you may wonder whether the bent sheet can return to its original shape. When sheet metal is bent into a new shape, it springs back slightly towards its original shape once the bending force is removed. This is known as springback.
Springback is caused by the compressive strength of the formed sheet. When a metal plate is bent, one side of the part is stretched while the other is compressed. However, because sheet materials have much greater resistance to compression than to tension, the compressed side remains deformed and then relaxes when the compressive force is removed.
For sheet metal to be bent successfully, a qualified person must carry out the calculations and assess the variables that affect springback. That is why it is important to calculate the bend angle and the exact point where pressure should be applied.
What is bend allowance?
When metal sheets are bent, the outer side of the bend tends to stretch. As a result, the dimensions of the original sheet change. After bending, a sheet may no longer fit the components it is meant to be assembled with. That is why it is important to take the bend allowance into account. The bend allowance is the difference between the length of the flat sheet and the sum of the lengths of each of its sides once bent.
To calculate bend allowances, certain factors must be considered, such as the thickness of the sheet, the bend angles and the bend radii of the part.