چکیده
This paper introduces the basic principles, process characteristics, and specific applications of laser cladding technology in diesel engine crankshaft repair. Taking the repair of the active gear shaft neck wear in the G6190ZLLCZZ-3R marine diesel engine crankshaft as an example, the entire process is detailed, including data collection, flaw detection, preheating treatment, laser cladding, thermal insulation and cooling, subsequent machining, polishing, cleaning, and quality inspection. Laser cladding technology offers advantages such as low dilution rate, high bonding strength, and minimal thermal deformation, making it suitable for the repair of high-precision, high-load components like crankshafts, with excellent economic and promotion potential.

۱. مقدمه
Diesel engines, as efficient power units, are widely used in ship propulsion and power generation systems. The crankshaft is the core component of a diesel engine, responsible for converting the reciprocating motion of the piston into rotational motion, transmitting torque to accessories such as the fuel pump and oil pump through the active gear. During prolonged operation, crankshafts are prone to wear, particularly at the active gear shaft neck, which requires a high level of repair precision and incurs high costs. Laser cladding is a surface modification method that uses a laser beam to melt the cladding material and the substrate surface, followed by rapid solidification to form a metallurgical bond. This method, with its dense coating, strong bonding force, and broad material applicability, provides a new avenue for crankshaft repair.

2. Laser Cladding Technology Process and Features
There are two types of laser cladding processes: pre-deposited and synchronous. The pre-deposited method places the cladding material on the substrate surface before melting with the laser, while the synchronous method feeds the material during laser irradiation, typically in powder or wire form. The technology has the following characteristics:

Fast cooling speed (up to 10⁶ K/s), which promotes fine crystal structure formation.

Low dilution rate (<5%) and metallurgical bonding with the substrate.

Minimal heat input, making it possible to control workpiece deformation.

A wide selection of cladding materials, enabling the cladding of high-melting-point alloys on low-melting-point substrates.

A wide range of cladding thickness (0.2-2.0 mm), ideal for localized repairs.

The process is easily automated.

3. Crankshaft Original Data Collection and Preprocessing
The crankshaft to be repaired is made of QT800-2A material, with wear observed on the active gear shaft neck (BC section in Figure 2). The outer diameter of the shaft neck was measured and found to deviate from the standard size (Ø1100.180.200.180.20 mm), with uneven wear. Dye penetrant and ultrasonic inspections confirmed that the surface had no cracks or other defects. The original hardness of the shaft neck was measured at HRC43. The shaft neck was then turned to Ø109.50 mm to eliminate roundness and cylindricity deviations, preparing it for cladding.

4. Laser Cladding Process

Preheating: The crankshaft is placed on a lathe and rotated slowly, with a furnace used to evenly heat the repair area to 250°C.

Cladding Repair: A semiconductor laser is used with iron-based alloy wire to perform synchronous feeding cladding. During the process, strict control of the temperature gradient ensures that the cladding layer bonds metallurgically with the substrate, without cracks or porosity.

Thermal Insulation: After cladding, the repair area is covered with thermal insulation cotton and held for 30 minutes before cooling to room temperature.

Measurement: The shaft neck size after cladding is approximately Ø112.10 mm, with a cladding layer thickness of about 1.3 mm and 0.95 mm of material reserved for machining. The hardness of the repair area was increased to HRC47.

5. Post-Laser Cladding Machining

Machining: The cladding surface is smoothed by turning to Ø110.50 mm.

Grinding: The final size is ground to Ø110.20 mm to meet the interference fit requirements with the gear.

Keyway Adjustment: The keyway width is milled from 22.7 mm to 24 mm, and the depth is milled from 4.6 mm to 5 mm.

Strength Calculation: Based on the diesel engine’s rated power of 440 kW and a speed of 1300 rpm, the torsional shear stress at the repair area was calculated to be 7.39 MPa, which is lower than the material’s allowable stress of 256 MPa, satisfying the service requirements.

Polishing and Cleaning: The repair area is polished using green polishing paste and cleaned with a detergent.

Inspection: The repair area was checked using dye penetrant and ultrasonic testing, confirming no defects.

6. Conclusion
Laser cladding technology, as an efficient and reliable surface repair method, demonstrates significant advantages in the repair of key components such as crankshafts. This paper presents a specific repair case that verifies the technology’s effectiveness in restoring dimensions and enhancing surface properties, while also being economically viable. With the development of laser technology, its application in ship repair and manufacturing is expected to expand significantly.