Engineering Review: Multi-pass Welding MIG/MAG Welding Robot – Sao Paulo, Brazil

Field Report: Robotic Multi-pass Integration for Tool Steel Applications

Location: São Bernardo do Campo, São Paulo, Brazil

Date: October 24, 2023

This report details the implementation and optimization of a high-deposition MIG/MAG Welding Robot system within a heavy-duty tooling workshop in the industrial corridor of São Paulo. The primary objective was to transition from manual GTAW (TIG) to an automated multi-pass strategy for Tool Steel welding, specifically targeting the refurbishment of large-scale injection molding dies and forging inserts. The transition necessitated a comprehensive suite of Arc Welding Solutions to manage the high thermal sensitivity and metallurgical constraints inherent in high-alloy tool steels.

1. Site Conditions and Infrastructure Challenges

The facility in São Paulo presents specific environmental challenges that impact robotic arc stability. High ambient humidity and seasonal temperature fluctuations necessitate rigorous shielding gas management. We observed that standard industrial CO2/Argon mixes often suffered from dew point inconsistencies in the local supply chain. To counteract this, we integrated a high-precision gas mixing station directly into the Arc Welding Solutions package to ensure a consistent 82/18 Argon-CO2 ratio, which is critical for stabilizing the spray transfer mode during the filler passes of the MIG/MAG Welding Robot.

Furthermore, the local power grid in the ABC region of São Paulo experienced voltage drops during peak industrial hours. This required the installation of a dedicated power conditioning unit for the robotic controller and the inverter power source. Without stable primary power, the synergic curves of the robot would drift, leading to porosity—a fatal flaw in Tool Steel welding.

2. Technical Synergy: MIG/MAG Welding Robot and Arc Solutions

The core of this deployment lies in the synergy between the 6-axis MIG/MAG Welding Robot and the advanced Arc Welding Solutions software layer. Unlike mild steel applications, welding tool steel requires precise control over the heat input to avoid excessive grain growth in the Heat Affected Zone (HAZ).

Adaptive Arc Control

We implemented a “Pulse-on-Pulse” regime provided by the arc solution software. This allowed the robot to maintain a stable arc length even as the tool steel workpiece underwent thermal expansion. The robot’s motion controller was synced with the power source via a high-speed Fieldbus interface, enabling real-time adjustments to wire feed speed based on the torch’s distance-to-workpiece, as measured by through-arc sensing. In the context of the São Paulo workshop, where workpiece positioning is often subject to minor jigging tolerances, this adaptive capability reduced rework by 35%.

Multi-pass Strategy and Path Programming

For a 20mm deep groove in H13 tool steel, we programmed a 12-pass sequence. The MIG/MAG Welding Robot utilized a stringer bead technique rather than a weave. Weaving in Tool Steel welding often results in localized overheating. By using the robot’s high repeatability (±0.05mm), we were able to stack beads with a precise 50% overlap. This consistency is impossible for a manual operator over an 8-hour shift, especially given the pre-heating requirements of the substrate.

3. Metallurgical Considerations in Tool Steel Welding

Welding tool steels (AISI H13, P20, or D2) involves managing the transition from the base metal to the weld deposit without inducing martensitic cracking. In our São Paulo field test, the base material was pre-heated to 350°C using induction coils. The MIG/MAG Welding Robot had to operate within a strict interpass temperature window of 350°C to 450°C.

Interpass Temperature Management

One of the “lessons learned” during this deployment was the integration of an infrared pyrometer into the Arc Welding Solutions loop. The pyrometer provided a signal to the robot controller; if the interpass temperature exceeded 450°C, the robot would automatically enter a dwell cycle or move to a different quadrant of the die to distribute the heat. This automated thermal management is vital for maintaining the hardness profile of the tool steel after post-weld heat treatment (PWHT).

Wire Selection and Chemistry

We utilized a specialized metal-cored wire designed for tool steel refurbishment. The MIG/MAG Welding Robot was calibrated for a 1.2mm wire diameter. Metal-cored wires are preferred here because they offer higher deposition rates than solid wires while providing a wider, more forgiving fusion profile. This is particularly useful in São Paulo’s heavy industry, where the “time-is-money” pressure on die repair often leads to rushed prep work.

4. Lessons Learned: Field Observations

Practical application in the field revealed several nuances that are often overlooked in a laboratory setting. Below are the primary takeaways from the São Paulo site:

A. Torch Geometry and Access

Tool steel dies often have deep cavities. The standard 22-degree robotic torch was insufficient. We switched to a 45-degree neck with a high-flow gas nozzle. However, the increased length of the neck introduced slight wire-feed oscillations. We corrected this by upgrading the Arc Welding Solutions to include a push-pull drive system. For MIG/MAG Welding Robot setups, the further the wire travels from the feeder, the more critical the drive roll tension becomes.

B. Spatter Management

Even with pulsed arc regimes, Tool Steel welding produces fine spatter that can clog the nozzle, disrupting shielding gas flow. We implemented an automated nozzle cleaning station (reamer) that the robot visits every 3 passes. In the dusty environment of the São Paulo industrial zone, we also added an air-curtain to the robotic cell to prevent airborne particulates from contaminating the weld pool.

C. Operator Training and Local Integration

A significant hurdle was the “black box” syndrome—local operators were intimidated by the complexity of the Arc Welding Solutions. We simplified the HMI (Human Machine Interface) to show only critical variables: Interpass Temperature, Wire Feed Speed, and Arc On-Time. By empowering the local technicians to adjust the travel speed within a ±5% margin, we saw a marked increase in “ownership” of the robotic cell, leading to better daily maintenance.

5. Quantifiable Results

The implementation of the MIG/MAG Welding Robot for Tool Steel welding yielded the following data points over a 3-month observation period:

• Deposition Rate: Increased from 1.2 kg/h (Manual GTAW) to 3.8 kg/h (Robotic MIG/MAG).
• Defect Rate: Ultrasonic testing (UT) showed a reduction in slag inclusions and cold-lap from 8% to 0.5%.
• Consumable Efficiency: 15% reduction in shielding gas waste due to optimized pre-flow and post-flow settings within the arc solution software.

6. Conclusion

The deployment in São Paulo confirms that while Tool Steel welding is inherently difficult due to its carbon equivalent and hardenability, the use of a MIG/MAG Welding Robot—supported by robust Arc Welding Solutions—provides a repeatable path to high-quality repairs. The key to success is not just the robot itself, but the integration of peripheral thermal sensing and adaptive arc logic. For future sites in Brazil, we recommend a “Cooling-First” approach to the robotic cell design, ensuring that the high-duty cycles of the robot do not overheat the workpiece beyond its critical transformation temperatures. This field report stands as a benchmark for transitioning South American tooling shops toward high-efficiency automated welding.

End of Report.