The Effects of Power
A common misconception in waterjet and especially abrasive waterjet cutting is that it is best to use as little power, as little pressure, as little abrasive as possible to get the job done. Nothing could be further from the truth.
The key is to cut as fast as possible. For most applications, the operating cost increase when running your system "flat out" is far outweighed by the money saved by producing more parts in a given time period. The generic curves in the figure below have been generated by countless Universities, waterjet manufacturers, waterjet users, and research companies.
The curves always show the same tendency — as abrasive flow rate is increased from zero, cut speed goes up and cost per inch goes down until a peak point is reached, a point where cut speed and cost per inch are both at their optimum.
Of course with every "rule of thumb" there are exceptions. However for virtually all cutting in the world today, fastest cut speed = lowest cost per inch.
To cut as fast as possible, the system should be operated using the maximum horsepower available. If you have a 60,000 psi pump with 50 HP, then whenever possible use all 50 HP. If you have a 100 HP system but can only effectively run a cutting head that consumes 50 HP, consider running two heads.
Abrasive constitutes 2/3 of the machine operating cost of the equipment. Machine operating cost does not include labor, lease or depreciation, facilities, or other overhead costs. It does include power, water, air, seals, check valves, orifice, mixing tube, abrasive, inlet water filters, long term spares (hydraulic pump, high-pressure cylinders, etc).
Basically, these are all the items that need replacement regularly or over the life of the waterjet system.
In abrasive waterjet cutting it is often thought that to reduce the abrasive flow rate saves money. On the contrary, it wastes money. There is a peak performance point that abrasive waterjets operate.
When you include all overhead the cheapest cutting is always found at the fastest possible speed. This fact is independent of the material you are cutting, or the power of the system.
To select the right pump, first begin by examining how you answer the Application Workup. If you are cutting prototype parts and do not foresee heavy production requirements, then a large pump is likely waste of capital.
On the contrary, if you are to perform in-house production of high volume parts and are in the fortunate position of being able to afford the ideal machine, then a larger pump with multi-head cutting capability is the right choice.
A variety of pump sizes are available. Some manufacturers produce just a few sizes, others make a full range. The full range is listed below in the output and multiple head table.
From there, the order of popularity follows 100 HP, 30 HP, and 150 HP. Over 60% of all pumps produced today are 50 or 100 HP.
Since 1999, there has been a steady increase in the number of multi-head systems using 100 HP and even higher. The upgrade to 100 HP costs a little more ($30,000 to $50,000), but are more productive than 50 HP single head systems.
If you can fairly accurately predict your machine utilization, then you can use a Return On Investment analysis to help decide whether the larger capital investment is justified.