The sheet metal bending process, which is also referred to as forming, folding, edging, flanging and die bending, is a process of deforming sheets (by putting a bend or fold into it). Essentially turning a flat piece of metal into a bent piece of metal, or a piece of metal which holds a different shape.
Planning Part Shapes
When planning part shapes, this begins with a “purpose”, the shape is then entirely driven by this purpose. For example, a bracket may need to hold something, so a specific shape is required for it to be able to achieve this. It could instead be required to cover something; therefore, the bends and measurements would have to allow for this.
Designs/drawings can be sent in done already, but often at ADS we will receive enquiries where we are asked to design something from scratch. A customer may come in and say, “can you design a cover which will fit over this unit” and our job is then to design something which will be as efficient as possible.
Michael Marigliani, a previous Estimator at ADS Laser Cutting who had been in the industry for 17 years, says “once you have been doing the job a while you learn to visualise it and predict what the bends will look like; experience definitely has a part to play in predicting what the bends will look like”.
Predicting what the part will look like after each bend is something that can be done through the use of software.
At ADS we have software which can be used both from the programming side of things in the office for designs/drawings and also software which is used by the press brake operators in the factory. This shows the operator step-by-step the bends in action and what they will look like once performed.
Michael Marigliani, an Estimator at ADS Laser Cutting who has been in the industry for 17 years, says “once you have been doing the job a while you learn to visualise it and predict what the bends will look like; experience definitely has a part to play in predicting what the bends will look like”.
Variables which are taken into account to achieve the desired bend include flange length (when a workpiece is folded, the part of the workpiece which is left/overhangs would be the flange), thickness of the part, radius required and also any features on the flat blank which may be affected by the bend – quite often there will be holes or slots close to the bend line which when formed can split open or crack.
Main Difficulties with Sheet Metal Bending
Difficulties which can be presented with sheet metal bending vary project to project, but a common problem is when shapes are awkward to form. Examples include, where the part is going to collide with the tool on the press, where the design has been sent in which are too small to form or where the tonnage required exceeds capabilities.
There are steps which can be taken to overcome these, though. If the required tooling is unable to avoid collisions, “part-bending” can be used where the metal would be bent part of the required way and then re-hit. “Overbending” is another method which can be used, as the name suggests the part is over-bent before being flattened to form the correct shape.
If tonnage is the issue either a design concession is proposed in order for the tooling to be changed and tonnage required lowered, or work arounds incorporated such as splitting a long flange into halves and then welding this back together. This is again where experience comes into play to devise and achieve these work arounds.
Punch and Die Selection
The most important consideration when selecting punch and die tooling is conformance with the drawing/design. A customer may ask for a very specific radius to be formed, so tooling will be picked which generates this radius.
In some cases, there may be some leeway, if this is the case then tooling is chosen which allows for the least amount of tonnage to be used or which will create the least deformation. An example of this is where there may be requirements to go down a V size if there are holes or other features which may be affected by the bend, so in cases like this decisions to go down a V size will allow for the least deformation to be caused to the other features of the workpiece.
The most common type of die which is used is the V die (V size), these will all have a V shape to a certain angle (88 degrees or 60 degrees, for example). There are various widths which accommodate different material thickness and radii.
Another common type of die is used for “dutch folding” which overfolds and crushes. These are designed to fold a part back on itself and crush it flat. This method is commonly used to put a safe edge on parts where hands will go for example.
These common types of die are used almost all of the time, although there is a long list of tools such as square cut dies for example, which are used for more specialist applications.
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