Run MIG Beads on Flat Steel

A. Finished-Project Specification

Outcome: a set of flat-position GMAW stringer beads run on identified mild-steel coupons, produced with documented voltage, wire-feed speed, shielding gas, contact-tip-to-work distance, gun angle, and travel speed, and accepted through measured and qualified visual inspection. No joint is fit or welded as part of this chapter's finished work.

B. Bead Practice Schedule (Component Schedule)

Item	Quantity	Material	Preparation	Practice Condition
Flat coupon	As specified by the instructor or procedure, minimum 2	Identified mild steel, thickness per the approved GMAW procedure	Cleaned to bright metal per Chapter 4	Marked with parallel bead lines and start/stop points
Stringer bead	Minimum 4 per coupon, or as specified	Approved solid wire filler	Contact tip trimmed to approved extension before each bead	Consistent spacing, no overlap unless specified

C. Material Takeoff

• Base metal: identified mild-steel flat coupons sufficient for the number of beads specified, at the thickness matched to the approved GMAW procedure.
• Filler wire: approved solid wire classification and diameter consumed during setup verification and bead practice, per Chapter 10's station configuration.
• Shielding gas: approved gas consumed during pre-flow, welding, and post-flow for the full practice session.
• Consumables: contact tips as needed if wear or damage is identified during inspection.
• Fastener and hardware schedule: not applicable. This chapter produces welded coupons, not a fastened assembly.

D. Acceptance Standards

Check	Standard
Bead straightness	Follows the marked line without wandering beyond the approved tolerance for the exercise
Bead width and reinforcement	Consistent along the full bead length, matching the approved acceptance sample
Wetting and toe transition	Smooth blend into base metal at both toes without abrupt edges
Starts and stops	Controlled crater fill at each termination; no abrupt starts or uncontrolled craters
Porosity	No visible surface porosity along the bead length
Undercut and overlap	No undercut or overlap at either bead toe
Spatter	Minimal adherent spatter; excess spatter identified and its cause investigated
Distortion	Coupon remains within flatness tolerance for the exercise after cooling
Documentation	Voltage, wire-feed speed, gas flow, angle, travel, and inspection results recorded for each accepted bead set

E. Preparation — Verification and Coupon Setup

1. Review the approved GMAW practice procedure and coupon layout. Confirm base-metal thickness, wire, gas, and starting parameter range match the station configured in Chapter 10.
2. Verify hot-work controls, ventilation, PPE, cylinder security, machine setup, gas, wire, and polarity. Confirm the Chapter 1 readiness record remains in effect and full GMAW PPE from Chapter 2 is worn.
3. Prepare the coupon to clean bright metal. Remove rust, scale, oil, and contamination from the full coupon surface, not only the bead path.
4. Mark parallel bead lines and start and stop points. Space bead lines to avoid overlap unless the exercise specifies otherwise.
5. Secure the coupon flat and attach the work clamp nearby. Confirm the clamp contacts clean sound metal close to the practice area.

F. Parameter Setting and Recording

1. Verify gas flow immediately before welding. Confirm flow matches the approved starting range recorded in Chapter 10.
2. Set voltage and wire-feed speed to the approved starting values. Use the approved chart for the wire diameter, gas, and coupon thickness.
3. Record contact-tip-to-work distance, gun angle, and travel direction from the procedure. Enter these values on the Session Parameter Record before welding begins.
4. Trim wire to the approved extension. Cut the wire end cleanly immediately before starting each bead.

G. Bead Execution

1. Assume a balanced stance with the gun cable supported. Confirm the stance allows uninterrupted travel along the full marked line.
2. Position the gun at the start point. Align the contact tip over the marked start line at the approved contact-tip-to-work distance.
3. Lower the helmet and trigger the arc. Confirm the helmet has darkened correctly before the arc is struck.
4. Establish a stable puddle before beginning travel. Hold position briefly at the start point until the puddle forms.
5. Maintain the approved work angle. Check gun position against the reference angle throughout the bead.
6. Maintain the approved push or drag travel angle for the exercise. Do not switch travel angle mid-bead.
7. Maintain consistent contact-tip-to-work distance. Adjust stance rather than allowing stickout to drift as you travel.
8. Travel along the marked line at steady speed. Match travel speed to puddle behavior rather than a fixed count.
9. Observe the leading edge and sides of the puddle. Use puddle shape, not arc brightness, to judge travel speed.
10. Keep shielding-gas nozzle clear of excessive spatter. Stop and clean the nozzle if spatter buildup begins to disturb gas coverage.
11. Release the trigger at the endpoint using the approved crater-control method. Fill the crater before breaking the arc.
12. Keep the gun near the end briefly if required for post-flow coverage. Do not withdraw the gun until post-flow gas has protected the cooling puddle.
13. Mark the coupon hot and allow safe cooling. Place the coupon in the designated cooling zone.

H. Between-Bead Inspection and Repeat Beads

1. Inspect the nozzle, tip, and wire extension before the next bead. Correct spatter buildup, tip wear, or incorrect extension before continuing.
2. Remove spatter only after cooling and with appropriate eye and face protection. Do not handle a hot coupon or bead with bare hands.
3. Inspect bead straightness, width, reinforcement, wetting, toe transition, start, stop, porosity, undercut, overlap, and spatter. Compare the completed bead against the Acceptance Standards table.
4. Measure bead width and length. Record measurements using the bead/fillet gauge and steel rule.
5. Identify whether the arc appeared too cold, too hot, unstable, erratic, or inadequately shielded. Note the observation on the parameter log.
6. Check for wire-feed problems, gas disturbance, dirty metal, or excessive stickout. Investigate any bead that does not match the acceptance sample.
7. Change only one parameter or technique variable at a time. Record the specific change before running the next bead.
8. Run additional parallel beads. Continue until the minimum bead count specified in Section B is complete.
9. Keep bead spacing consistent and avoid welding over previous beads unless specified. Verify spacing against the marked lines before each new bead.
10. Monitor machine duty cycle. Allow cooling time between beads as required by the machine manufacturer.
11. Inspect the coupon for distortion and arc strikes. Check flatness against the welding table and note any accidental arc strikes outside the bead path.
12. Compare beads produced with approved small parameter adjustments. Identify which settings produced the most consistent bead.
13. Select the best parameter set under instructor review. Confirm the selected values with the responsible evaluator.

I. Documentation and Shutdown

1. Record final voltage, wire speed, gas flow, angle, travel, defects, and corrections. Complete the Session Parameter Record for the accepted bead set.
2. Obtain qualified visual inspection. Have the instructor or qualified evaluator review the completed coupon against the acceptance sample.
3. Close the cylinder, relieve the system as required, shut down the machine, and complete fire watch. Follow the Chapter 1 shutdown and fire-watch requirements before leaving the area.