The Role and Machining Process of Marine Crankshafts

Marine crankshafts are core components of marine engines. Their primary function is to convert the reciprocating motion of pistons into rotary motion and output power to drive the ships propeller. During operation, the crankshaft is subjected to enormous alternating stresses (including gas pressure, inertial forces, and centrifugal forces), so it must have extremely high strength, wear resistance, and fatigue resistance.

In terms of the machining process, the manufacturing of large marine crankshafts (especially crankshafts for large-bore medium-speed diesel engines) is complex and precise. A typical process includes:

Rough Machining: Milling the end faces and drilling center holes, rough turning the main journals and transition fillets.

Finish Machining: Using a turning-milling center to finish mill the main journals and connecting rod journals, finish machining the flange face and oil holes.

Hole Machining: Machining oblique oil holes and straight oil holes to ensure the accuracy of the lubrication channels.

Grinding and Polishing: Precision grinding the journals and flange with a cam grinding machine, and finally polishing the journals and transition fillets to reduce stress concentration.

Strengthening Treatment: Improving surface hardness and fatigue strength through induction hardening, nitriding, or fillet rolling processes.

Key technical challenges include controlling deformation, ensuring journal coaxiality, and oil hole accuracy. Modern processes use CNC technology and simulation optimization (such as finite element analysis) to improve efficiency and quality, significantly shortening the processing cycle.