Holy Ship! Look at that CNC Milling

Computer numerical control (CNC) is programmed code that represents instructions for precise movements. A CNC milling machine uses these instructions to transform raw material into a finished model by removing material with a high degree of precision.

The Ship Propeller

Each component of a large tanker ship is carefully designed and built. A poorly-designed propeller can lead to low fuel efficiency or effect top speeds, and even reduce the lifespan of other ship components.

How is CNC milling used?
Once a propeller design has been selected, molten metal is poured into a mold and left to cool (the propeller is so massive that the metal takes 5 days to cool enough to be broken out of the mold.) It’s then put in an automated milling machine where over the span of 15 days, a computer guided tungsten cutting head grinds the rough surface into a smooth, precise finished product.

Would the product design be possible without CNC milling?
It’s certainly possible to construct a ship propeller without CNC milling, but since rough joints or surfaces would compromise its efficiency, constructing it in one piece is now the preferred method.

What makes the product unique?
Diameter, number of blades & blade outline, angle of attack and camber, and pitch/diameter ratio are just a few factors to be considered when making an efficient ship propeller. With all of these competing design constraints, the design of a ship propeller must be extremely precise.

These propellers are also massive. When I think of CNC milling, I think of precision at a small scale. The design of a ship propeller is a unique example of precise design on a larger scale.

What materials are used in the product?
The propeller is cast in one piece, and is made of a complex alloy involving several different metals: copper, nickel, aluminum, iron and zinc (and more).

If you were to replicate the design, what do you think the workflow looks like from design to prototype?
I think the workflow to replicate this design would involve open water tests on model propellers to determine the design perimeters. From there you’d need to create a mould to pour molten medal into and cast the relative shape before using CNC milling to finish it off.

Is the product parametric in any way? If not, could it be and how?
Different propellers have varied parameters such as number of blades, blade area, pitch ratio etc. Based on the results of open-water tests and the requirement of the vessel, the parameters can be modified and selected to obtain the appropriate design.