Standard Process Flow for Laser Cladding Repair of Rotating Shaft Blades

Laser cladding repair for shaft-type rotating blades is a systematic engineering process that must strictly follow the full-process control of "pre-assessment - pretreatment - cladding processing - post-treatment - quality inspection" to ensure stable and reliable repair quality. The specific process flow is as follows:

1. Pre-repair Assessment and Plan Formulation

Before initiating the repair, a comprehensive assessment of the failed shaft-type rotating blades must be conducted to clarify repair objectives and technical parameters. This is the prerequisite for ensuring a successful repair:

(1) Failure Analysis

Through visual inspection (using the naked eye or a magnifying glass to observe surface wear, cracks, spalling, or corrosion marks) and non-destructive testing (such as penetrant testing PT to detect surface micro-cracks, magnetic particle testing MT to detect near-surface defects in ferromagnetic materials, ultrasonic testing UT to identify internal pores or inclusions), the failure mode is accurately determined.

(2) Feasibility Judgment

Based on the extent of failure and the condition of the base material, assess whether the blade has repair value and the post-repair usage requirements. Strictly evaluate whether the fatigue performance of the repaired layer meets standards to avoid re-failure shortly after repair.

(3) Plan Formulation

Clarify repair objectives and determine core technical parameters; select cladding materials based on the base material and operating conditions; set laser parameters such as laser power, spot diameter, and powder feed rate; plan auxiliary processes, determine whether preheating or post-heating is needed, and specify the type and flow rate of shielding gas.

2. Pretreatment: Clearing Repair Obstacles and Ensuring Base Material Cleanliness

The core goal of pretreatment is to remove surface impurities and defects from the base material, creating conditions for a strong bond between the cladding layer and the base material. It mainly includes the following steps:

(1) Surface Cleaning

Oil removal: For cutting oil, lubricating oil, or grease on the surface of shaft-type blades, use ultrasonic cleaning to ensure no oil residue remains—oil vaporizes during cladding, causing pores in the cladding layer;

Scale and corrosion product removal: For thick scale formed during long-term use, first use sandblasting, then an angle grinder; acid pickling can be applied, followed by drying;

Drying treatment: Cleaned components must be thoroughly dried to avoid bubbles from water evaporation during cladding—in addition to drying, compressed air can be used to blow the surface, paying special attention to areas prone to water accumulation such as blade roots and journal grooves.

(2) Defect Treatment

Crack treatment: Based on crack locations marked by non-destructive testing, use an angle grinder to create "V-shaped" or "U-shaped" grooves along the crack path; after grooving, use penetrant testing PT again to confirm complete crack removal; for fine cracks (width <0.1mm), use electrical discharge machining to enlarge the crack, then clean the groove;

Surface leveling treatment: For unevenly worn journal or blade surfaces, use a lathe (for shaft-type components) or a milling machine (for blade surfaces) for rough machining, turning the worn surface to a flat state while reserving a 0.5-1mm cladding allowance; ensure surface roughness after machining to allow laser energy to act uniformly on the base material surface, avoiding insufficient local cladding due to surface unevenness.

(3) Fixture Fixation

Shaft-type rotating blades require cladding in a rotating state (to ensure uniform cladding layer thickness in the circumferential direction), so precise fixation and coaxial positioning must be achieved through specialized fixtures.

3. Cladding Processing: Precise Parameter Control for High-Quality Cladding

Cladding processing is the core execution stage, relying on CNC laser cladding equipment, parameter optimization, and process monitoring to ensure cladding layer quality:

(1) Equipment Debugging and Parameter Optimization

Equipment preheating: Start the laser generator and preheat for 30-60 minutes until the laser output power stabilizes; check the powder feed system, add a small amount of cladding powder, test the stability of the powder feed rate, and ensure no clogging in the powder feed tube; check the shielding gas system and test argon flow rate;

Parameter trial cladding: Select a non-working area of the component for trial cladding; after trial cladding, observe the cladding layer appearance (whether it is smooth, free of pores, cracks, or lack of fusion), use a hardness tester to measure cladding layer hardness, and use a metallographic microscope to examine the bonding interface (whether it is metallurgical bonding with no obvious gaps); optimize parameters based on trial cladding results—for example, if pores appear in the cladding layer, appropriately reduce scanning speed or increase shielding gas flow rate; if bonding strength is insufficient, increase laser power or preheating temperature.

(2) Formal Cladding

Cladding sequence planning: Follow the principle of "dispersing heat input and reducing stress." For shaft-type components, use a cladding sequence "from both ends to the middle" or "spiral progression along the circumferential direction"; for blade components, repair the blade root first, then the working surface, and finally the blade tip;

Layered cladding control: If the cladding thickness exceeds 3mm, use layered cladding (each layer 0.5-1mm thick). After each layer, allow natural cooling to room temperature (or preheating temperature) before proceeding to the next layer to avoid stress accumulation from excessive interlayer temperature; stagger the scanning direction of adjacent layers by 90° to reduce internal stress concentration in the cladding layer; during cladding, use an infrared thermometer to monitor molten pool temperature in real time;

Process monitoring: Use the equipment's built-in vision system to observe the molten pool state. If the molten pool is unstable, pause immediately, check shielding gas flow rate or powder feed status, adjust parameters, and then continue; for large components, segmental cladding can be used to reduce overall deformation.

(3) Protective Measures

Inert gas shielding: Use a dual system of "coaxial shielding + side-blown shielding";

Environmental control: If working in an open workshop, set up a simple protective enclosure; for highly demanding aerospace engine blades, perform cladding in a sealed inert gas protective box.

4. Post-treatment: Stress Relief, Precision Restoration, and Performance Assurance

After cladding processing, the component surface may have stress concentration, dimensional deviations, and surface roughness issues. Post-treatment is needed to optimize performance and precision, ensuring it meets assembly and usage requirements. It mainly includes the following steps:

(1) Stress Relief Treatment

The "rapid heating - rapid cooling" characteristic of laser cladding generates thermal stress between the cladding layer and the base material. If not relieved in time, it can easily lead to cladding layer cracking (especially for high-hardness, high-brittleness cladding materials) or performance degradation during use.

(2) Dimensional Repair and Precision Adjustment

The cladding layer surface may have unevenness, and the thickness may have slight deviations. Mechanical processing is needed to restore design dimensions and precision:

(3) Surface Cleaning and Appearance Finishing

Impurity removal: Use compressed air to blow away iron chips and dust generated during processing, then wipe the surface with alcohol to remove oil stains and residual debris; for dead corners such as blade roots and journal grooves, use a high-pressure water gun or a soft brush to clean, avoiding residual impurities that could affect assembly;

Edge finishing: Use a handheld grinder or file to chamfer component edges and groove transitions, avoiding sharp edges that could cause stress concentration or injure operators; after finishing, manually check to confirm no burrs or unevenness, ensuring a smooth and flat appearance.