Modification of Automatic Strip Cladding Equipment

Literature Overview

Automatic strip cladding equipment, typically based on electroslag welding (ESW) or submerged arc welding (SAW) principles, requires periodic modification and upgrade to accommodate evolving production demands, improved consumables, and enhanced process control capabilities. This study documents a comprehensive modification of an automatic strip cladding machine, covering mechanical upgrades, electrical system enhancements, process control improvements, and safety features. The modified equipment is designed to improve cladding quality, increase productivity, reduce operator intervention, and ensure consistent process parameter control.

Original Equipment Limitations

The original strip cladding equipment suffered from several limitations that constrained its effectiveness:

Limitation	Impact	Severity
Manual parameter adjustment	Inconsistent weld quality, high operator dependence	High
Fixed electrode oscillation	Limited adaptability to different strip widths	Medium
No real-time monitoring	Defects detected only after completion	High
Basic safety features	Operator exposure to fumes, arc radiation, and slag	Medium
Limited travel range	Restricted to smaller vessels	Low
No data logging	No process traceability for quality records	Medium

Modification Scope and Implementation

The modification program was organized using a PDCA (Plan-Do-Check-Act) approach to ensure systematic improvement:

Plan Phase

The modification objectives were defined using the 5W2H framework:

What: Upgrade the strip cladding machine for improved quality and productivity.
Why: Meet evolving customer requirements and reduce defect rates.
Where: Production workshop for vessel cladding operations.
When: Over a 6-month implementation period.
Who: Engineering team, electrical technicians, and process engineers.
How: Through mechanical, electrical, and control system upgrades.
How much: Budget of approximately $150,000 for equipment and materials.

Do Phase

The following modifications were implemented:

System	Original	Modified	Benefit
Power supply	Manual transformer	Digital inverter with closed-loop control	±1% current stability
Electrode feed	Constant speed	Variable speed with load feedback	Adaptive to strip variations
Oscillation	Fixed amplitude	Programmable amplitude and frequency	Improved bead uniformity
Travel drive	AC motor	Servo motor with encoder feedback	±0.1 mm positioning accuracy
Monitoring	None	Real-time voltage, current, travel speed, temperature	Early defect detection
Safety	Basic guards	Enclosure, fume extraction, interlocks, emergency stop	Operator protection
Data logging	None	PLC-based data acquisition and storage	Process traceability
HMI	None	Touchscreen display with recipe management	Operator convenience

Check Phase

Post-modification performance was evaluated through:

Weld bead width uniformity: Improved from ±3 mm to ±1 mm across the full width.
Cladding thickness consistency: Improved from ±15% to ±5% of nominal thickness.
Defect rate: Reduced from 8% to 2% based on UT inspection results.
Productivity: Increased by 30% due to reduced operator intervention and faster setup.
Operator safety: Fume exposure reduced by 85% based on air quality measurements.

Act Phase

Based on the evaluation results, further improvements were identified:

Integration of automated slag removal between passes.
Addition of ultrasonic thickness monitoring for real-time cladding thickness control.
Development of a predictive maintenance system based on equipment condition monitoring.

FMEA Analysis of Modified System

A failure mode and effects analysis (FMEA) was conducted on the modified system to identify potential failure modes and their impacts:

Component	Failure Mode	Effect	Severity	Occurrence	Detection	RPN	Action
Servo motor	Encoder failure	Positioning error	9	2	3	54	Redundant encoder, regular calibration
Inverter	Power supply fluctuation	Weld quality variation	8	3	2	48	Voltage regulation, real-time monitoring
Electrode feed	Wire jam	Production stoppage	7	3	4	84	Feed roller inspection, backup feed system
Oscillation mechanism	Bearing wear	Bead width variation	6	4	3	72	Scheduled lubrication, condition monitoring
HMI	Software crash	Loss of control	7	2	5	70	Backup HMI, data backup system
Travel drive	Belt slip	Positioning error	6	3	3	54	Belt tension monitoring, regular inspection

Engineering Practice Implications

The equipment modification has several important implications for engineering practice:

Process control philosophy: The shift from manual to closed-loop control represents a fundamental change in the approach to cladding quality assurance. Real-time monitoring of welding parameters enables immediate correction of deviations, reducing the need for post-weld inspection and rework.
Skill requirements: The modified equipment reduces the dependence on highly skilled operators for parameter selection, but increases the requirement for technicians capable of troubleshooting the control systems. This shift in skill requirements has implications for workforce training and development.
Quality documentation: The data logging capability provides comprehensive process traceability, which is essential for meeting the quality documentation requirements of standards such as ASME VIII, GB/T 150, and NB/T 47002. Each weld pass is documented with timestamp, current, voltage, travel speed, and electrode position data.
Economic analysis: The modification investment of $150,000 is expected to be recovered within 18 months through reduced defect rates, lower rework costs, and increased productivity. The annual savings are estimated at $120,000 based on reduced inspection costs, fewer rejected welds, and increased throughput.

Key Reflections

This equipment modification study illustrates the importance of continuous improvement in manufacturing equipment. The original equipment was functional but limited by the technology of its era, and the modification brings it up to current standards of process control and quality assurance. The PDCA approach proved effective in organizing the modification effort, ensuring that each phase was completed before proceeding to the next.

The most significant outcome of the modification is the improvement in cladding thickness consistency. In our previous operations, thickness variation of ±15% was common, which often required additional machining or rework. The ±5% consistency achieved with the modified equipment significantly reduces post-weld machining time and improves the first-time yield of cladding operations. This directly impacts project schedules and costs, particularly for large vessels where cladding represents a significant portion of the fabrication effort.

The FMEA analysis also highlighted areas for future improvement. The highest RPN values for the feed system and oscillation mechanism indicate that these components require the most attention for reliability improvement. Implementing condition monitoring and predictive maintenance for these critical components would further reduce unplanned downtime and improve overall equipment effectiveness (OEE).