Make MIG Fillet Welds and Butt Welds

A. Finished-Project Specification

Outcome: three completed and documented GMAW practice joints — one lap joint, one T-joint, and one square-butt joint — produced on identified mild-steel coupons in the flat or horizontal position, each with controlled fit-up and tacking, balanced welding, complete spatter removal, measured profile, approved penetration indicators or tests on the butt joint, defect analysis, and final inspection.

B. Component Schedule

Component	Quantity	Material	Finished Size	Preparation
Lap-joint member A	1	Identified mild steel, thickness per chapter coupon specification	Per chapter coupon specification	Weld edge and faying surface cleaned to bright metal
Lap-joint member B	1	Identified mild steel, matching thickness	Per chapter coupon specification	Weld edge and faying surface cleaned to bright metal
T-joint vertical member	1	Identified mild steel, matching thickness	Per chapter coupon specification	Weld edge cleaned to bright metal
T-joint horizontal member	1	Identified mild steel, matching thickness	Per chapter coupon specification	Weld surface cleaned to bright metal
Butt-joint member A	1	Identified mild steel, matching thickness	Per chapter coupon specification	Weld edge cleaned to bright metal, edge condition verified for the specified root gap
Butt-joint member B	1	Identified mild steel, matching thickness	Per chapter coupon specification	Weld edge cleaned to bright metal, edge condition verified for the specified root gap

C. Material Takeoff

• Coupon stock: six identified mild-steel coupons — two per joint type — cut and prepared to the dimensions specified in the chapter coupon specification, plus spare stock for tack repair or remade coupons.
• Filler and shielding: approved GMAW solid wire matching the Chapter 10 station setup, with shielding gas sufficient for tack welds, test beads, and all three final joints.
• Fixture and shim stock: shims, stops, or spacer stock sufficient to set and verify the lap overlap, T-joint angle, and butt-joint root gap and offset.
• Fastener and hardware schedule: not applicable. Joint members are joined by welding, not by mechanical fasteners.

D. Acceptance Standards

Check	Standard
Lap overlap	Matches the chapter coupon specification, held by rule, stop, or fixture through tacking and welding
T-joint angle	Matches the specified angle, verified with a square before, during, and after tacking
Butt root gap and offset	Matches the chapter coupon specification within its stated tolerance
Tack welds	Free of cracking, porosity, poor fusion, and misalignment; defective tacks removed and replaced before final welding
Fillet size (lap and T-joint)	Meets the specified leg size measured with the approved fillet-weld gauge
Weld profile	Continuous, tied in at both members, free of undercut, overlap, porosity, and excessive spatter
Butt-joint penetration indicator	Reverse-side condition inspected against the approved acceptance sample; not claimed as proof of internal fusion from appearance alone
Starts, stops, and craters	Controlled fill with no abrupt termination or arc strikes outside the joint
Distortion	Recorded and compared with the coupon specification's flatness or angular tolerance

E. Joint Review and Surface Preparation

1. Review joint drawings, material thickness, gaps, overlap, alignment, weld size, length, wire, gas, polarity, and parameters. Confirm every value against the chapter coupon specification before cutting or cleaning any coupon.
2. Prepare all joint surfaces to clean metal. Remove rust, mill scale, oil, and contamination from every weld and faying surface identified in the drawing.
3. Measure and label each coupon set. Mark each member with a traceable identifier for the lap, T-, and butt-joint sets before fit-up begins.

F. Fit-Up

1. Fit the lap joint to the approved overlap. Set the overlap distance from the chapter coupon specification using a rule, stop, or fixture.
2. Fit the T-joint to the specified angle and alignment. Hold the vertical member against the horizontal member at the specified angle using a square and fixture.
3. Fit the butt joint to the specified root gap and offset. Set both values using shims, stops, or a fixture and confirm both members lie flat against the table.
4. Use fixtures, stops, shims, clamps, and squares to maintain fit-up. Confirm every joint stays within tolerance before the first tack.
5. Confirm clamps do not block gun access or create unstable restraint. Reposition any clamp that blocks the planned gun path along the full weld length.
6. Attach the work clamp to clean metal. Position the clamp on sound base metal close to the joint being tacked.

G. Machine Verification and Tacking

1. Verify gas, wire, tip, nozzle, polarity, voltage, and wire-feed speed. Confirm the station matches the parameters recorded on the joint traveler before tacking.
2. Place tack welds at the approved locations. Tack each joint at the positions specified in the chapter coupon specification.
3. Inspect tack size, fusion, porosity, cracking, and distortion. Examine every tack before proceeding to the next.
4. Remove and replace defective tacks before final welding. Use the approved method to remove any tack that fails inspection, then replace it and reinspect.
5. Recheck lap overlap, T-joint angle, butt gap, offset, and flatness. Confirm the joint remains within tolerance after the full tack sequence is complete.
6. Plan weld order to balance shrinkage. Identify the sequence for each joint that distributes heat input and limits angular distortion before striking the first final-weld arc.

H. Final Welding

1. Weld the lap-joint fillet using the approved gun angle and travel. Apply the gun angle and travel technique established in Chapter 11 along the full joint length.
2. Maintain fusion at both members. Direct the arc so both the overlapping and underlying members show visible fusion along the weld toe.
3. Inspect and clean the lap joint. Remove spatter and inspect the completed fillet before moving to the next joint.
4. Weld the T-joint fillet with attention to both toes. Maintain the specified work and travel angle so both the vertical and horizontal member toes show fusion.
5. Use the approved sequence if welding multiple sides. Follow the planned order from Section G when the specification requires welds on both sides of the T-joint.
6. Inspect and clean the T-joint. Remove spatter and inspect both completed fillets.
7. Weld the butt joint using the approved travel and puddle control. Maintain a stable puddle along the full joint length using the technique from Chapter 11.
8. Do not weave unless the procedure specifies it. Use a straight stringer pass unless the chapter coupon specification calls for a weave technique.
9. Control starts, stops, and crater fill. Apply the approved crater-control method at the end of each weld pass.
10. Allow joints to cool in the designated area. Mark each joint hot and move it to the hot-metal cooling zone established in Chapter 1.

I. Cleaning, Inspection, Testing, and Records

1. Remove spatter without reducing weld or base-metal dimensions. Use a wire brush, scraper, or chipping tool that does not gouge the weld face or toes.
2. Inspect all joints for profile, size, length, tie-in, undercut, overlap, porosity, crater, start, stop, and distortion. Complete this inspection on all three joints before recording results.
3. Use approved fillet and dimensional gauges. Measure fillet leg size on the lap and T-joints and record the results.
4. Inspect the reverse side of the butt coupon for approved penetration indicators without claiming internal fusion from appearance alone. Compare the reverse-side condition with the approved acceptance sample.
5. Perform an approved break, bend, or section test only when the chapter specification includes it. Do not perform destructive testing unless the coupon specification explicitly calls for it.
6. Do not perform destructive testing without guards, tools, and instructor control. Stop and obtain instructor authorization before any destructive test.
7. Compare results with the approved acceptance sample. Hold each completed joint against the acceptance sample identified in the chapter coupon specification.
8. Identify probable causes of each defect. Connect any observed porosity, undercut, or profile issue to a likely machine, parameter, technique, or fit-up cause.
9. Prepare a corrective-action plan before repair. Define the defect-removal method and corrected setup before any repair welding begins.
10. Repair only approved defects with adequate remaining material. Confirm sufficient base-metal thickness remains before removing and rewelding a defect.
11. Reinspect repaired areas. Apply the same inspection criteria used on the original weld.
12. Record fit-up, tacks, parameters, sequence, dimensions, defects, tests, repairs, and final acceptance. Complete the joint traveler for all three coupons.
13. Complete gas shutdown, machine shutdown, hot-metal control, and fire watch. Close the cylinder, isolate the machine, confirm all coupons are marked or verified cool, and complete the fire-watch period.