Considerations When Stacking Materials for Waterjet Cutting

Increasing Part Production

There are a variety of waterjet cutting methods that can be employed in an effort to increase the overall throughput of your machine. Some of the more popular methods include part nesting, common line cutting, and material stacking. Stacking is a simple yet effective way of increasing part production, and can be done with both abrasive and water-only waterjet applications.

Water-Only

There are certain waterjet applications that do not require the use of an abrasive medium to cut through the material. Plastic, foam, and rubber are all examples of materials that can be cut with a water-only system. Depending on thickness, these types of materials can be stacked and multiple parts cut at once. The full benefits of stacking are realized when output is limited by either the machine’s top speed or the geometry of the part itself.

Take for example a material that could effectively be cut at 2,000 ipm, such as .1” foam. If the material is cut in single layers on a waterjet that has a maximum speed of 500 ipm, part production will be limited and full production efficiency will not be achieved. If the material is stacked in multiple layers, however, the machine's 500 ipm max speed is not so much of a limiting factor, as it can now potentially cut the same amount of material as if it was running at 2,000 ipm and cutting single layers. By utilizing material stacking, the machine is able to overcome its max speed limitations and increase production.

Another scenario where output may be limited is when the geometry of the part contains many corners. While a particular waterjet may have a maximum cut speed of 2,000 ipm, acceleration will limit the maximum speed that may be achieved. This is because the waterjet must slow down when approaching corners to ensure they remain sharp. For example, if a machine has an acceleration of 20 in/s2 and is cutting a square with 12" sides, the maximum speed it will be able to achieve is 929 ipm. For the first six inches of the cut, it will accelerate from zero to 929 ipm and then start slowing down to an instantaneous velocity of zero to go around the next corner. In this instance, stacking material can potentially increase output by taking advantage of the actual maximum speed, as more parts will be produced even though the waterjet is moving slower than it is capable.

Abrasive

Stacking materials when cutting with abrasive can also increase productivity. The benefits of stacking are maximized when cutting very thin materials. These thin materials require proportionately less energy to be cut, so a significant portion of the stream’s energy goes directly into the waterjet tank. By stacking thin materials, a larger percentage of the cutting stream will be put to work, increasing the efficiency of the cut and reducing abrasive waste.

Materials being cut with abrasive must be clamped very tightly. Any gaps in between the layers will increase the amount of water and abrasive that is able to get in, pushing the materials apart and causing cutting issues. Stacking should also be avoided if the part requires many pierce points, as piercing also tends to push stacked material apart.

Cost-Benefits Analysis

While stacking may increase machine throughput, it is important to determine if the cost is worth the benefit. Doubling the amount of parts per cut may come at a cost of a speed reduction that can negate the benefits. The increase in abrasive usage and a potential reduction of edge quality should also be considered. We recommend experimenting with the waterjet’s settings and number of parts in the stack in order to achieve the desired combination of part quality and output.

Click here to see the benefits of stacking foam on a water-only cutting system.

For more information on increasing the efficiency and throughput of your waterjet cutting system, contact WARDJet at 1-844-927-3538, or drop us a line at www.wardjet.com/get-in-touch.