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Activity 002: Weld Repair Practice β€” Grind, Re-Weld & Re-Inspect

Activity ID: U6M4-ACT-002 Duration: 45 minutes Objective: Students will practice the complete weld repair cycle: identify a defect, grind it out, re-weld, and re-inspect against acceptance criteria. Group Size: 2 students

Overview

Using their own previous weld samples (from U6M2 or U6M3 activities), students will identify their worst weld, perform a proper repair, and verify the repair meets quality standards. This teaches the critical skill that every welder uses regularly β€” nobody produces perfect welds 100% of the time.

Materials & Equipment Needed

  • Previous weld samples from each student (T-joint fillets or butt joints)
  • MIG or TIG welder (matching the process used for the original weld)
  • Angle grinder with grinding disc (ΒΌ" thick) and flap disc (80 grit)
  • Wire brush and chipping hammer
  • Fillet weld gauge
  • Soapstone or marker
  • Magnifying loupe
  • Welding clamps and magnets
  • Full welding and grinding PPE
  • Fire extinguisher within 15 feet

Instructions & Procedure

Phase 1: Defect Identification (5 minutes) 1. Each student selects one of their previous weld samples that has a visible defect 2. Inspect the weld using the 7-step procedure from Activity 001 3. Identify and document the defect: - Type: ____ - Location: ___ - Size/extent: __ - Probable cause: __ 4. Mark the defective area with soapstone β€” indicate start and end of the repair zone (add ΒΌ" beyond the visible defect on each side)

Phase 2: Grinding Out the Defect (10 minutes) 1. Secure the workpiece in a vise or with clamps 2. Put on grinding PPE: face shield, safety glasses, hearing protection, leather gloves 3. Using the angle grinder with grinding disc: - Begin grinding at the center of the defective area - Remove weld metal until you reach sound base metal - Create a U-shaped groove that allows the welding torch access to the root - Extend the grinding ΒΌ" beyond the marked defect boundaries - Smooth the groove walls with the flap disc 4. Inspect the ground area: - Is all defective material removed? (Use loupe to verify) - Is the groove shape appropriate for re-welding? - Are the groove walls smooth and clean? 5. Wire brush and clean the ground area

Phase 3: Re-Welding (15 minutes) 1. Set up the welder with appropriate parameters for the material and thickness 2. Clean the repair area with acetone 3. Position the workpiece for welding access 4. Weld the repair: - Start the bead ΒΌ" before the ground area (on sound original weld) for proper tie-in - Fill the ground groove with steady, consistent weld passes - End ΒΌ" past the ground area on the other side (tie-in to sound weld) - Apply crater fill technique at the end 5. If the repair requires multiple passes, clean between passes 6. Allow cooling for 2 minutes

Phase 4: Re-Inspection (8 minutes) 1. Wire brush the repair weld thoroughly 2. Perform the full 7-step visual inspection on the repair: - Profile and dimensions - Toe inspection (undercut, cold lap) - Surface porosity check - Crack inspection - Blend into original weld (smooth transition?) 3. Measure and compare to acceptance criteria 4. Record the pass/fail result 5. Compare the repair to the original defect β€” document: - Did the repair correct the original defect? - Did the repair introduce any NEW defects? - Is the repair area equal or better quality than the rest of the weld?

Phase 5: Discussion & Debrief (7 minutes) 1. Each student presents their repair: original defect β†’ repair process β†’ result 2. Discuss: Was the repair harder than the original weld? Why? 3. Instructor evaluates repairs and provides feedback 4. Key question: "What would you do differently to prevent this defect from occurring in the first place?"

Discussion Points

  • Why must you grind beyond the visible defect boundaries?
  • What would happen if you just welded over the defect without grinding?
  • How does the repair weld tie into the original weld at the start/end?
  • In a professional setting, how many repair attempts are typically allowed before the part is scrapped?

Expected Outcomes

  • Students demonstrate the complete repair cycle independently
  • Repair welds pass visual inspection (or show significant improvement over the original defect)
  • Students can articulate the root cause and prevention for their specific defect

Assessment Rubric

Criteria Excellent (4) Proficient (3) Developing (2) Beginning (1)
Defect Identification Accurate type, location, cause Correct identification with minor gaps Partial identification Cannot identify defect
Grinding Quality Complete removal, smooth groove, proper extent Good removal with minor rough areas Incomplete removal Defective material remains
Repair Weld Quality Passes visual inspection, smooth blend Minor issues but significant improvement Partial improvement New defects introduced
Root Cause Understanding Clear explanation of cause and prevention Good understanding of cause Partial understanding Cannot explain the defect

Safety Considerations

  • Grinding PPE is DIFFERENT from welding PPE: face shield (not welding helmet), plus safety glasses, plus hearing protection
  • Never switch directly from grinding to welding without changing PPE β€” face shields are not welding-grade
  • Grinding discs can shatter β€” inspect for cracks before use, never exceed rated RPM
  • Grinding produces hot sparks and particulates β€” clear combustibles, ensure ventilation
  • Small workpieces can be grabbed by the grinding disc β€” secure firmly before grinding
  • Fire watch required: 30 minutes after the last welding operation

Last Updated: 2026-03-19