Vibration Overlay Welding and Arc Spraying Repair of S195 Diesel Engine Crankshaft Journals

Literature Overview

This technical paper by Hao Jianjun, Shen Yuzeng, and Ma Yuejin from Hebei Agricultural University, published in Agricultural Machinery (2005, Issue 3), presents a practical case study of crankshaft journal repair using two distinct surface engineering technologies: vibration overlay welding and arc spraying. The study addresses a common failure mode in diesel engine maintenance—the undersizing of crankshaft journals beyond the final repair dimension—and demonstrates successful restoration through advanced surface engineering methods. This work is particularly relevant to the agricultural machinery sector where equipment downtime directly impacts production schedules.

Failure Analysis and Repair Challenge

The S195 diesel engine is a widely used agricultural diesel engine. The crankshaft journals (both main journals and connecting rod journals) undergo progressive wear during engine operation due to:

• Bearing friction and sliding contact
• Hydrodynamic lubrication breakdown during start-up and shutdown
• Thermal cycling causing differential expansion
• Contaminant ingress into the lubrication system

When journals wear beyond the final repair oversize dimension, conventional grinding repair is no longer possible, and the crankshaft must be replaced. This presents a significant cost and availability challenge, particularly for older equipment fleets.

Repair Methods Evaluated

Vibration Overlay Welding Process Details

Vibration overlay welding (also known as pulse arc surfacing or micro-arc welding) combines electrical arc energy with mechanical vibration of the electrode to produce fine, uniform weld beads with minimal heat input. The vibration frequency and amplitude are critical process parameters that control:

• Weld bead width and height uniformity
• Heat input per unit length
• Solidification rate and grain structure
• Residual stress level in the deposited metal

For crankshaft journal repair, the process typically involves:

1. Surface preparation: Grinding worn journal to remove all damaged material
2. Preheating: Low-temperature preheat (100-150°C) to reduce thermal stress
3. Multi-pass vibration welding: Building up material to restore oversize dimension
4. Post-weld machining: Precision grinding to final bearing fit dimensions

Arc Spraying Process Details

Arc spraying (also known as wire arc spraying) is a thermal spray process that uses two consumable wire electrodes as both the power supply and the material source. The process involves:

• Melting of wire tips by an electric arc between the two wires
• Propulsion of molten droplets by compressed gas (typically nitrogen or air)
• Impact of droplets on the prepared substrate surface
• Rapid solidification forming a coating with mechanical interlocking and some metallurgical bonding

The coating quality depends on:

• Impact velocity of molten droplets (typically 200-400 m/s)
• Substrate preheating temperature (80-150°C for steel substrates)
• Spray gun stand-off distance (typically 100-200 mm)
• Wire feed speed and arc voltage parameters

Performance Verification and Results

The study employed a rigorous verification protocol:

Off-machine verification:

• Eccentric grinding (偏磨): Grinding with the axis offset to create maximum load on one side of the bearing surface, testing coating adhesion under extreme conditions
• Result: No spalling, peeling, or delamination observed

On-machine verification:

• Bench run-in: Controlled low-load operation to verify coating stability during initial break-in
• Load operation: Full-load testing to verify coating performance under service conditions
• Result: Successful completion of bench run-in and load operation without coating failure

The combination of vibration overlay welding and arc spraying provided complementary advantages:

• Vibration overlay welding provided the bulk material restoration with excellent metallurgical bonding
• Arc spraying could be used for thinner, more precise surface layers where minimal heat input was critical

Engineering Practice Implications

This case study demonstrates the viability of advanced surface engineering techniques for extending the service life of critical engine components. The economic benefit is substantial:

• Crankshaft repair cost is typically 30-50% of new crankshaft replacement cost
• Reduced downtime compared to sourcing and installing a replacement crankshaft
• Preservation of original crankshaft balance characteristics

Quality Control Considerations

For production implementation, the following quality control measures are recommended:

• Pre-repair inspection: Ultrasonic testing of the journal core to ensure no internal cracks exist
• Process parameter documentation: Record all welding/spraying parameters for traceability
• Post-repair inspection: Magnetic particle testing of the repaired surface to detect any cracks introduced during repair
• Dimensional verification: Precision measurement of journal diameter, roundness, and taper after final machining
• Surface finish verification: Measurement of Ra value to ensure bearing compatibility

Study Insights and Reflections

This practical study highlights the importance of having multiple repair technologies available for critical component restoration. The combination of vibration overlay welding and arc spraying provides flexibility in addressing different repair scenarios—thicker material restoration versus thin precision coatings.

A key insight is the importance of the eccentric grinding verification step. This aggressive off-machine test effectively simulates worst-case bearing loading conditions and provides high confidence in coating adhesion before the expensive step of engine assembly and running tests. This approach to verification—escalating from simple to complex testing—minimizes the risk of discovering coating failure only after complete engine assembly.

From a broader perspective, this work contributes to the growing body of evidence supporting surface engineering as a sustainable maintenance strategy. Rather than discarding worn components, advanced repair techniques can restore functionality while maintaining structural integrity, reducing waste and extending asset life.

The study also implicitly addresses an important consideration for welding engineers: the geometric complexity of crankshaft journals presents unique challenges for weld access and heat input control. The vibration welding process, with its low heat input and precise bead control, is particularly well-suited to such constrained geometries where excessive heat could cause distortion of the crankshaft web or journal alignment.