Basic Principles of Vacuum Clamping

First of all we find the normal atmospheric air pressure inside and outside of the vacuum table, which withholds aproximately 1bar. Next some equipment( or workpiece) is placed on the vacuum tables surface and the remaining free space and drilled holes are covered with rubber mats. And thus the air in the interior of the vacuum table can be drawn with a vacuum pump. According to the vacuum pump, a pressure difference between the interior and exterior emerges from aproximately 100mbar to about 950mbar, and the boundary layer is thus represented by the piece of equipment(or workpiece) found on the vacuum table.

As an example, lets say you take a pressure difference of 500mbar. Now depending on the sealing method used with a 200 x 200mm vacuum table the result would be a surface pressure of a maximum 200kp with the equipment or workpiece fully covering the whole table surface.

Since one of the most important things in mechanical preparations is to secure the equipment or workpiece from slipping or moving out of place, it would make sense that you place a mat or some type of material in between the equipment(workpiece) and vacuumplate. Its also good to make sure that this material is airtight and that it also has a high frictional resistance. Depending on the type of vacuum straining, there are various different procedures available here, that can gaurantee a optimal solution depending on your specific needs.

The grid vacuum table (RAL- / RAL-Pro- / R-Series)

The surface of a grid(raster) vacuum table consists solely of armatures, that are connected to a few drilled holes with the vacuum pump. When inserting a moss rubber cord into the armatures one can create a limited boundary around the drilled holes. This limited boundary or field, should correspond the desired workspace. Now the workpiece or equipment can be placed and the vacuum can be started.

Advantages of the grid vacuum table

The workpiece or equipment does not necessarily need a even underside. With considerable unevenness, aproximately one millimeter can be balanced out by the moss rubber cord. For more dificult tasks, rectangular moss rubber cords are also available.
Since the workpiece (equipment) pushes the moss rubber cord into the armature, its underside lies directly on the aluminum surface of the vacuum table, by what it creates utmost accuracy.
Since the system remains sealed during the whole operation, one must not demand so much work to be created from the vacuum pump. Very small outputs of 80-95% of vacuum are sufficient, therefore this procedures becomes very economical.
Uniform oscillations and a delay free layer of the whole underside of the workpiece (equipment).

Disadvantages of the grid vacuum table

This procedure can only be used if no openings have to be milled, this is because if its not sealed then this will cause immediate decrease of retention force.

How can you mill opendings anyway

A further possibility to operate a grid(raster) vacuum table is to produce a adapter mat suitable to the respective workpiece(equipment). This can be produced out of various materials like e.g : hard rubber, rubber and soft-PVC. The thickness depends on the respective armature gaps and widths. This adapter has openings only where the workpiece(equipment) must be held, and is sealed in the places where the milling machine passes through.

Advantages of this method

Openings do not lead to leakage and therefore are no problem.
Maximum retention force with minimal demands required for the vacuum pump.
The workpieces(equipment) do not require postprocessing, because they're whole contour can be worked on using a basic aproach all around.
No paths must remain standing.
The most suitable process in a series(batch) production of smaller parts.
Uniform oscillations and a delay free layer of the whole underside of the workpiece (equipment).

Disadvantages of this method

The manufacturing of a adapter mat is just additional expense and effort, that really only amortizes itself in a series(batch) production. Nevertheless the adapter mat can quickly made with simple means, like for example a scalpel or drilling machine since its not necessary to exactly follow the course of the workpiece(equipment) contour.

Videos show how to work with grid vacuum tables

The hole grid table (GAL-/ GR-/ smart-/ ST-/ SEAL-Series)

The manufacturing of a adapter mat is just additional expense and effort, that really only amortizes itself in a series(batch) production. Nevertheless the adapter mat can quickly be made with simple means, like for example a scalpel or drilling machine since its not necessary to exactly follow the course of the workpiece(equipment) contour.

Disadvantageously this technology merely works with the clamping of thin-walled or frail workpieces(equipment), since above the sack holes they dent themselves in the vacuum. For such uses, only vacuum tables with small suction drilled holes can be used. With a hole grid(raster) vacuum table at first its not even attempted to completely seal the table, but one assumes that after placing the workpiece(equipment) on the vacuum table and one covers the remaining surface that a certain amount of drilled holes will remain open. The vacuum pump works here with a large volume with a slight differential pressure. This operating principle enables openings during the processing of up to about 15% of the surface. Due to the increase of frictional resistance either a hole rubber mat, where great accuracy is required in the Z-Direction, or a sinter rubber mat as a cheap alternative for the cases where simple cutting is sufficient.

To go without saying a adapter mat can also be using during this process. However, to completely be able to work in the same manner with a grid(raster) vacuum table, a vacuum pump with high differential pressure is required. Should this however also be used for other clamping techniques as by means of a adapter mat in connection with a hole grid(raster) vacuum table,it must as mentioned dispose over a large suction volume. Both together, the high pressure and high volume however place very large demands on the performance of the vacuum pump.

Videos show how to work with hole grid vacuum tables

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