Waterjet-Cut-specific Inputs

The following user inputs apply specifically to the Waterjet Cut process:

• Number of Parts in Stack – Waterjet cutting supports stacking multiple parts if part thickness permits (maximum effective stack thickness is 12.7 mm). If stacking is not feasible, the default value is 1.0.

o Default value

o Computed value

o User override

Note: As with other geometry-dependent PSO (Process Setup Option) settings, a value that is valid when you first enter it may be rendered invalid if you change the geometry at a later time. For example, you might have a component with a thickness of "5 mm" can have a valid stack value of "2". But if the height of the part is later changed to "10 mm", the stack value of "2" may no longer be valid, and costing operations may no longer succeed. aPriori checks the validity of these PSO settings only when they are first entered, and cannot re-evaluate them when geometry changes.

• Orifice Type (1)

o Sapphire – (Default) Most common. Provides balance of cost (typically ` $15 - $30 each) and operating life (typically 50 to 100 cutting hours with good water quality; half that in abrasive applications).

o Ruby – Similar to sapphire, but stream characteristics are suitable for abrasive cut, not for pure water.

o Diamond -- Considerably longer run life (~16 – 20X) but is 10 to 20 times more expensive.. Suitable for 24-hour operation. Can sometimes be ultrasonically cleaned and reused

• Orifice Diameter (1) -- Default value determined from machine properties. Can be overridden with customer-specific value.

• Abrasive Flow Rate (2) -- Default value determined from machine properties. Can be overridden with customer-specific value. Abrasive flow rates represent a large portion of the total hourly cost (average cost of garnet is $0.7275/kg), but the initial cost savings of reducing flow rate is outweighed by much greater costs of increased cutting time and increased replacement cost of expendable parts.

• Mixing Tube Diameter (3) -- Default value determined from machine properties. Can be overridden with customer-specific value.

• Nozzle Type (4)

o Low-Cost Composite Carbide – Operating life 35 to 60 hours. Recommended for rough cutting or training.

o Mid-Life Composite Carbide – (Default) Operating life 80 to 90 hours. Recommended for general purpose.

o PremiumComposite Carbide -- Operating life 100 to 150 hours. Recommended for both precision and general purpose applications.

• Feed Rate Small/Large Features -- Default values determined from machine properties can be overridden with customer-specific values. A “feature” is part of the model. If a feature is “small” (see below) relative to the whole part, then cutting speed in this area is decreased. If a feature is “large” relative to the whole part, then the cutting speed in this area is increased.

A feature is determined to be “small” if:

o the ratio of a feature edge length to the part edge length is less than 0.01.

o the “minimum concave radius” is less than the “small Feature Feed Radius” (one of the machine parameters).

o the “minimum convex radius” is less than the “small Feature Feed Radius” (one of the machine parameters).

o the (diameter of hole)/2 is less than the “small Feature Feed Radius”.

Any feature which is not determined to be “small” is treated as “large”.

A note about kerfs

Waterjet Cut can control the kerf -- or the width of the cut -- by swapping parts in the nozzle, as well as by changing the type and size of abrasive. Typical abrasive cuts have a kerf in the range of 0.04 in to 0.05 in, but can be as narrow as 0.02 in. Non-abrasive cuts are normally 0.007 in to 0.013 in, but can be as small as 0.003 in, which is approximately that of a human hair. These small jets can permit small details in a wide range of applications. Due to its relatively narrow kerf, water jet cutting can reduce the amount of scrap material produced, by allowing uncut parts to be nested more closely together than traditional cutting methods.

Why do two similar holes return different cycle times?

Consider the holes in the following illustration:

Both holes have a diameter of 7.32 mm and a length of 10.00 mm, yet Waterjet Cut cycle time for the hole on the left is 85 seconds, while the hole on the right takes only 19 seconds. This is actually correct, and here is why:

The simple hole on the left is contained within a pocket. The two are not concentric and are not considered a multistep hole, but the same logic applies if this was a multistep hole with a counterbore. The circular pocket cannot be made using waterjet because the feature does not extend the entire thickness of the part. (Only through-features can be made with waterjet.) So for this part, the blank perimeter and the simple hole are made using Waterjet Cut, but the pocket is machined. The length of that simple hole when made with Waterjet Cut depends on the order of operations. In most cases (especially when nesting), the blank and simple hole will be cut on the waterjet first and then transferred to a mill for the circular pocket. Since the pilot hole is created first, it is cut using the full thickness of the part and must run at a slower rate. The more rare case would be to machine the pocket first and then transfer to the waterjet. In that case, the material above the simple hole would already be removed and the waterjet could run at a faster rate, but again, this is a rare case.