Fixturing refers to holding work material in place while the waterjet cuts parts from it. For most jobs, it’s critical that the material doesn’t move during cutting, as any movement will affect the precision of the part and can mar the surface. Compared to other cutting methods, the sideways forces of abrasive waterjet cutting are low and the downward force is concentrated to a small area. What many new waterjet operators are unaware of is that the jet drives a significant amount of air into the catcher tank that causes the water to bubble under the workpiece. That bubbling can easily lift the material and move it sideways.
One great advantage of machining with an abrasive waterjet is that fixturing flat plate or sheet material is quick and easy. Users should always fixture in the X, Y, and Z directions with enough force that the part cannot wiggle. This can be tested by trying to move the workpiece by hand. If it can move at all, then it needs more fixturing.
Fixturing made specifically for OMAX Waterjets
A Material Holding Kit will keep the material secure for high precision cutting. The kit includes track assemblies and vertical load clamping arms. It mounts into the waterjet slat bed and is customized to fit the exact OMAX or MAXIEM machine dimensions. The Material Holding Kits can be purchased at the OMAX Marketplace. Note that even when solidly clamped along the edges, a lightweight material can be lifted by the jet action. Placing steel weights on lightweight material helps prevent lifting.
Fixturing with a corner square
If somebody prefers to build their own system to secure sheet or plate material, they can cut and mount a corner square or “L”. The corner square should be mounted with screws to the edge of the waterjet table. Use spreader clamps to hold the material flush against the corner square. Avoid clamping directly to the slats because this will not provide reliable support against sideways motion. In cases where it’s harmful to push on the material with a spreader clamp, for example, the material may become weak from the cuts and can deform or break, or the material must be cut completely in half, clamps can be added directly to the corner square.
Making a really long square is unnecessary. A second piece bolted far from the corner of the square can be cut at the same time as the square and used to locate a long plate. The square material should be no thicker than the material being cut to prevent the nozzle from breaking against the square. A small relief at the corner of the square prevents interference with sharp corners of the workpiece. The corner location can be set as a home position for easy reference to locations on the workpiece.
Tips for cutting small parts and preventing frosting
The table slats support the material from the bottom. But very small parts can fall between the slats and become lost. To prevent this when cutting long, slender parts, cut them with the long direction perpendicular rather than parallel to the slats, so that they are supported by at least two slats. If the part is so small that it spans less than two slats in its longest direction, tab the part and cut or break the tab manually after cutting is completed. A small part that isn’t tabbed might move as the last part of the cut is finished and becomes loose. The part can be scarred if it moves into the jet.
Some materials are damaged by the jet reflecting off the slats and frosting or scarring the support surface. A sacrificial material can be placed between the material and the slats to shield the work material from the reflected jet. Thin sheet metal, pressed board, and plywood are common sacrificial materials.