Zhuojin Pipe Fitting Co., LtdPLC-Based MIG/MAG Automatic Welding Equipment for Stainless Steel Disinfection Tank Circumferential Welds
Literature Overview
Song Jinhui, from Shandong Jiaotong Vocational College, published this study in Welding Machine (2012, Vol. 42, No. 7, pp. 44-47). The paper describes the development of a complete automatic welding system for circumferential welds on stainless steel disinfection tanks. The system integrates mechanical design, PLC-based control, and MIG/MAG welding technology to achieve high-quality, repeatable welds with improved productivity.
Core Technical Points
System Architecture and Component Design
The automatic welding equipment comprises four major subsystems:
| Subsystem | Components | Function |
|---|---|---|
| Frame and support | Steel frame structure | Support all components; provide rigidity |
| Workpiece clamping and rotation | Chuck, hydraulic/pneumatic clamps, servo motor | Hold and rotate tank shell sections |
| Welding carriage | Linear guide, motorized drive | Control travel speed and torch position |
| Wire feeding | Servo motor-driven wire feed unit | Precise wire feed rate control |
| Control system | PLC, touch screen HMI, inverter, relays | Coordinate all operations; manage welding parameters |
Dual-Torch Configuration
A distinctive feature of this system is the dual-welding-torch arrangement, which enables simultaneous welding of two circumferential seams. This configuration is particularly advantageous for disinfection tanks, which typically consist of cylindrical shell sections joined by butt welds, with additional internal or external reinforcement welds. The dual-torch setup:
- Reduces welding time by approximately 40-50% compared to single-torch sequential welding.
- Requires careful synchronization to prevent interference between adjacent weld zones.
- Demands precise torch-to-torch spacing (typically 150-250 mm) to avoid heat interaction effects.
PLC Control Program Structure
The control system operates through a hierarchical program structure:
- System initialization: Parameter loading, safety checks, component homing.
- Workpiece loading and clamping: Automatic clamp actuation with position verification.
- Welding parameter selection: Multiple welding programs stored in PLC memory for different joint configurations, wall thicknesses, and material grades.
- Welding execution: Coordinated control of wire feed speed, travel speed, rotation speed, and arc parameters.
- Post-weld operations: Cooling, unclamping, and data logging.
Welding Parameters for Stainless Steel Disinfection Tanks
| Parameter | Value | Notes |
|---|---|---|
| Base material | SUS304 or SUS316L | Food-grade stainless steel |
| Wire electrode | ER308L or ER316L | Low-carbon matching filler |
| Shielding gas | 98% Ar / 2% CO₂ or 95% Ar / 5% CO₂ | Dual-shield or single-shield |
| Welding current | 180-260 A | Depends on wall thickness |
| Arc voltage | 20-26 V | Constant voltage (CV) mode |
| Wire feed speed | 4-7 m/min | Matched to current |
| Travel speed | 0.3-0.8 m/min | Matched to rotation speed |
| Wire diameter | 1.0 or 1.2 mm | Solid wire |
| Polarities | DCEN | Standard for MIG stainless |
Quality Control and Defect Prevention
The automatic welding system addresses several common defects in manual stainless steel circumferential welding:
| Defect | Manual Welding Risk | Automatic Welding Mitigation |
|---|---|---|
| Inconsistent penetration | Operator fatigue, technique variation | Precise parameter control; consistent travel speed |
| Oxidation discoloration | Inadequate shielding | Consistent gas flow; proper torch angle |
| Sensitization cracking | Excessive interpass temperature | Controlled heat input; back-step welding |
| Sizing inconsistency | Manual torch control | Fixed torch-to-work distance |
| Undercut | Travel speed variation | Synchronized rotation and travel |
For stainless steel disinfection tanks, which are subject to sanitary requirements, the weld interior surface must be smooth and free of crevices to prevent bacterial colonization. The automatic welding process produces a more uniform bead profile than manual welding, which is advantageous for subsequent electropolishing or mechanical polishing operations.
Engineering Practice Integration
The described system is well-suited for medium-volume production of standardized tank designs. The PLC-based control allows quick program switching between different tank diameters and wall thicknesses, reducing setup time between production runs. The touch-screen HMI interface simplifies operator training and reduces the skill dependency of the welding operation.
For pipe manufacturing applications, similar PLC-controlled automatic welding systems are widely used for:
- Circumferential welds on pipe spools (per ASME B31.3 or B31.4 requirements).
- Longitudinal welds on LSAW pipe (per API 5L or ISO 15590).
- Automatic TIG welding of thin-wall stainless steel pipes (per ASTM A269).
The key advantage of PLC-based systems over purely hardwired controls is flexibility: welding parameters, travel sequences, and error-handling routines can be modified through software without physical rewiring.
Study Insights
This paper provides a practical engineering case study in the integration of mechanical design, control systems engineering, and welding technology. The dual-torch approach is particularly noteworthy for production environments where throughput is a critical constraint. However, the study does not address several important aspects that would be relevant in a complete engineering specification: weld procedure qualification per applicable codes (e.g., ASME Section IX, AWS D1.6), non-destructive testing protocols, and long-term reliability considerations for the control system components. For engineers designing similar systems, these aspects must be incorporated into the overall quality plan to ensure code compliance and product integrity.