To minimize the cost per part in abrasive waterjet cutting, the key is balancing cutting speed and abrasive flow rate. Cutting speed determines machine time and labor, while abrasive flow directly affects consumable expenses. The optimum point changes with material type, thickness, and local operating costs.

Fundamental Trade-off

Increasing abrasive flow generally allows faster cutting, but the relationship is not linear. Doubling abrasive flow might increase cutting speed by only 50 to 70 percent. Beyond a certain point, extra abrasive yields very small speed gains. Meanwhile, high abrasive flow wears nozzles faster and increases disposal costs.

Step by Step Optimization Method

First, determine your machine cost per minute. This includes electricity, water, labor, overhead, nozzle wear, and maintenance. A typical value for a 60k psi system is between two and three US dollars per minute.

Second, know your abrasive cost per pound. Garnet abrasive often costs 25 to 40 cents per pound delivered.

Third, run test cuts on the target material at three to five different abrasive flow settings. For each setting, measure the maximum cutting speed that still produces acceptable edge quality.

Fourth, calculate the cost per inch for each test point. Divide machine cost per minute by cutting speed to get machine cost per inch. Multiply abrasive flow by abrasive cost per pound and divide by cutting speed to get abrasive cost per inch. Add both numbers.

Example for One Inch Mild Steel

Assume machine cost at 2.50 dollars per minute and abrasive cost at 0.30 dollars per pound. Test results and calculations appear below.

In this example, the lowest cost per inch occurs at the highest abrasive flow tested, 1.4 lb per minute. Even though abrasive cost rose slightly, the faster cutting speed reduced machine time enough to lower total cost.

When Lower Abrasive Flow Wins

If machine cost is low, say 1.50 dollars per minute, or abrasive cost is high, say 0.60 dollars per pound, the optimum shifts left. At 0.60 dollars per pound abrasive and 1.50 dollars per minute machine cost, the calculation changes completely.

The optimum remains at high flow but the spread is smaller. If abrasive cost reaches 0.80 dollars per pound with the same low machine cost, the 0.6 lb per minute setting may become best.

Practical Guidelines

For thick materials over one inch, high abrasive flow usually minimizes total cost because cutting speed is very slow without it. For thin materials under one quarter inch, lower abrasive flow often wins because speed gains are minimal.

Regular testing is essential because nozzle wear changes the speed versus abrasive relationship. A worn mixing tube reduces cutting speed at all abrasive flows, shifting the optimum toward higher flow rates. Retest every two to three months or after every 200 hours of cutting to maintain lowest possible part cost.