CJR Propulsion’s production process showcases the benefits of a data-driven approach over traditional design and manufacturing methods
Southampton-based propeller CJR Propulsion is looking to leverage technology through the production process, from design to delivery, to become “the most data-driven propulsion company in Europe”.
When the company initially introduced its computational fluid dynamics (CFD) design software, five-axis CNC machines and robotic machining tools, it found there were aspects of the process, like mould-making, where achieving the desired accuracy levels remained time and resource heavy.
“As new manufacturing hardware and automation software became viable, we saw the immense opportunities they could bring and how they would help ensure every aspect of the design and manufacturing process was as precise and efficient as possible,” said CJR Propulsion managing director Mark Russell.
At the design stage, CJR will typically build a 3D-model of a vessel’s hull in its bespoke CFD software, based on information supplied by the shipbuilder. The flow of water around the propeller is then modelled in various sea conditions and based on this data, an optimal design for the propeller can be generated. The propulsion package can be cleanly aligned with the hull and known appendages, while the long-term performance and fuel efficiency of the propulsion system can be optimised and risks, such as unwanted noise and vibration or cavitation, removed.
"We learnt very quickly that 3D printers have their uses, but also their limitations"
Propeller makers often use ‘off-the-shelf’ patterns for mould-making, with new moulds produced based on blades that must be hand-carved from wood or resin, or in some cases via a 3D printer. “We learnt very quickly that 3D printers have their uses, but also their limitations,” said Mr Russell. CJR uses an automated robotic approach to mould-making, which takes the design generated by the CFD software, performs several geometric tests and then machines a mould from a single block of fine sand and resin. The dense nature of the resin used allows for a highly accurate reproduction of the design, that can operate to minute tolerances.
Thanks to these high levels of accuracy in the robotic mould-making process, CJR can make significant efficiencies at the casting stage. As this technique results in more propellers being cast to tighter tolerances, less material is required for each casting, reducing the cost of the finished product and cutting down on waste.
When propellers are produced using traditional mould-making techniques, a larger volume of metal is required, as inaccuracies are present from the initial stages of the design process and manual grinding is needed to finish the propeller. If a grinder inadvertently takes off too much material on one blade, this must be repeated on all the other blades and can completely alter the propeller’s dynamics.
CJR uses multiple five-axis machine centres for grinding and machining that work autonomously to precise dimensions established at the CAD design stage. The company’s automation software means a propeller can be collected from storage cells, have the required volume of material removed to precisely match the original specification, and then be returned to the rack without any human involvement.
This means that CJR is able to deliver propellers with an ISO accuracy standard of Class S as a minimum, which means the unit is manufactured to tolerances far more stringent than those set out for Class 1 units, which traditional manufacturing techniques can produce.