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Impact of Grit Size on Abrasive Waterjet Cutting

Garnet abrasive is used on 95% of all waterjet machines. The size of the garnet abrasive typically used today for waterjet cutting ranges from 50 mesh to 220 mesh, with the most common being 80 mesh. Mesh values do not represent particles of an exact dimension, but represent a distribution of particle sizes. An 80 mesh abrasive will have some particles larger and smaller than exactly 80 mesh. Mesh sizes are usually determined by allowing abrasive to fall through a series of screens – each screen smaller in mesh size from top to bottom. A known quantity of abrasive is placed on the top and vibrated for a fixed period of time, and then the amount of abrasive on each screen is weighed to obtain the distribution.

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Fixture Well, And Often

Everyone who cuts parts out of raw stock or a work-piece knows you can’t cut a good part if it isn’t sufficiently held in place. So, what do we have to consider when we’re talking about waterjet cutting? The good news is a waterjet cuts with low force. Where a milling machine might force a rigid cutting tool into a material at 10, 100, 300 pounds of force (4.5, 45, 136 kg), the waterjet head doesn’t touch the part — just the supersonic stream that exits the head touches the part.The machine can’t tell if the jet is cutting material or just shooting into nothingness. The part, however, does feel low forces during cutting.

Cutting-pizza

Although the picture is of pure waterjet cutting pizza, I’m going to focus on abrasive waterjet cutting applications in this post. Fixturing requirements are different in pure waterjet cutting, partially because the material is often very light and the jet forces are an order of magnitude (10x) lower compared to abrasive waterjet.

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Different Types of Jobs, Different Types of Quotes

It’s true. When our customers quote waterjet work, there are different types of quotes that work better for different jobs. You might think that there is a significant difference in quoting needs between those of our customers who are job shops versus those who conduct in-house cutting, but that is not the case; both have similar job quoting needs for either internal or external customers.

In recent focus groups, Brian Kent (Global Shapecutting Product Manager) and I have had the privilege of talking frankly and in detail with our customers. One of the many things we learned was that our shop owners and programmers have two types of quotes they create each week: the quick quote and the detailed quote. The quick quote is, well, quick – where they hope to be accurate to about 10 percent. With the detailed quote, the stakes are higher. These quotes are done for large dollar projects, recurring projects, or a first-time project for a new, important customer.

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