How To: Sheet metal separation with LaserFLEX
In most cases, laser processing of sheet metal begins with picking up individual sheets from a stack of sheet metal. What may seem simple at first glance proves to be quite challenging in practice: the sheets literally stick together. This can lead to delays in the process and damage to material and machinery due to falling sheets. Remmert LaserFLEX Automation uses various techniques to prevent this.
The 'bonding' of stacked sheets does not occur in a chemical sense; rather, it is a combination of several physical effects that create the impression of adhesion. The thinner and lighter the sheets are, the stronger these effects can be.
Air pressure/vacuum: if two smooth sheets stack together, there is hardly any air between them. In order to separate them, air must flow into the gap. When you lift one sheet off the other, a vacuum is created between them. The air pressure from outside (approximately 1 bar) pushes the sheets together. This is similar to the action of a suction cup, only weaker.
Surface forces (adhesion): So-called van der Waals forces act between very smooth metal surfaces. This effect can be observed on polished or freshly rolled sheet metal.
Moisture and capillary forces: Thin layers of moisture from the air or lubricating oil form a liquid film. Liquids in a thin gap generate capillary forces. These capillary forces pull the plates together. Oil films from production (rolling oil) can also increase this effect.
Possible residual magnetism: Steel sheets that have been machined in the vicinity of magnets, or that are magnetic due to cold forming, can easily attract each other.
Reliable separation of metal sheets
The challenge is a) to pick up only one sheet from the stack and b) not to move the sheets underneath if possible. What can happen? If a second sheet is lifted due to the effects described above, there is a risk that it will fall off. This can cause damage to the machine. If the next sheet on the stack is only twisted, at best it cannot be picked up automatically. Even worse: it lies so crookedly on the stack that it becomes jammed when it is put back into the rack. In either case, material damage occurs and the process comes to a standstill.
To prevent this, we use a coordinated combination of different technologies in the removal unit of our LaserFLEX automation system. This is to reliably ensure that only one sheet is removed from the stack.
1. First, the stack height is detected by a light barrier. As soon as this is detected, the removal unit lowers to the correct distance.
2. an optional expansion magnet is used, for example for thin sheets. This moves to the side of the stack of sheets; when activated, the stack is fanned out.
3 An air nozzle blows air under the lifted sheet. This compensates for the negative pressure created during lifting.
4. the rows of suction cups perform an undulating movement to separate the trays. For this purpose, the front rows of suction cups are movable and the rows of suction cups are activated one after the other.
5. The final double sheet control checks whether only one sheet has been picked up. The target sheet thickness is taken from the respective production job and compared.