1. Forged medium-carbon steel is the primary material for Kubota crankshafts.
2. Precise alloying with elements like chromium, molybdenum, and nickel for strength.
3. Use of high-quality, clean steel to minimize inclusions and stress points.
4. Micro-alloyed steel variants are employed in certain high-stress models.
5. The material boasts an excellent strength-to-weight ratio.
6. Uniform metallurgical structure is ensured through controlled forging.
7. Steel composition is optimized for both fatigue resistance and machinability.
8. Trace element control guarantees consistent batch-to-batch material properties.
9. The chosen steel grade offers superior toughness under impact loads.
10. Material selection prioritizes long-term dimensional stability under heat and stress.

 

1. Forging & Forming Process

 

1. Crankshafts are precision-forged under immense pressure to align grain flow.
2. Hot forging process shapes the metal while enhancing its inherent strength.
3. Forging eliminates internal porosity, creating a denser, more reliable component.
4. The forging die design is optimized for material distribution and minimal waste.
5. Near-net-shape forging reduces the amount of subsequent machining required.
6. Controlled cooling after forging refines the microstructure.
7. Forging ensures continuous grain lines following the crankshaft's contour, improving fatigue life.
8. This method produces a crankshaft with superior integrity compared to casting.

 

1. Heat Treatment & Surface Hardening

 

1. A through-hardening process (quenching and tempering) provides a balanced core hardness.
2. Tempering relieves internal stresses induced during quenching, improving toughness.
3. Induction hardening is applied specifically to critical areas like journal fillets.
4. Surface hardening on main and pin journals dramatically increases wear resistance.
5. Case hardening creates a hard exterior with a tough, ductile core.
6. Nitriding or nitrocarburizing treatments are used on some models for extreme surface hardness.
7. Heat treatment cycles are computer-controlled for absolute consistency.
8. The resulting hardness profile is meticulously designed to withstand bearing pressures.
9. Treated crankshafts exhibit excellent resistance to micro-welding and scoring.
10. Post-heat-treatment, the component achieves optimal mechanical properties for its service life.

 

1. Machining & Finishing

 

1. CNC machining ensures micron-level precision on all journal diameters and widths.
2. Precision grinding achieves a mirror-like finish on bearing journals.
3. Super-finished journal surfaces minimize friction and reduce oil film breakdown.
4. Fillet rolling is a critical process performed on the radii where journals meet webs.
5. Fillet rolling induces compressive surface stresses, greatly enhancing fatigue strength.
6. All oil passage holes are deburred and polished to prevent stress concentrations.
7. Dynamic balancing is performed to remove any vibrational imbalance.
8. Each crankshaft is polished to remove microscopic peaks that could initiate wear.