Weld

A customer brought in a shaft that had been welded and needed a through-hole drilled. The weld ran across the center of the shaft at about mid-length. The shaft was 4140 steel, about 80mm in diameter and 1.5 meters long. The weld was a full-penetration butt weld joining two sections of shaft. The customer had welded it using a TIG process with ER70S-6 filler rod. The customer had welded it, stress-relieved it, and then decided they needed a 20mm through-hole for a hydraulic passage. ...

When a bore is out of position or oversized, welding and re-drilling can sometimes save the part. The process involves welding the damaged bore closed, then re-drilling to the correct position and size. I have used this technique on hydraulic cylinders, valve bodies, and large mechanical components. It is not a perfect solution but it beats scrapping a high-value part. The decision to weld-repair a bore comes down to economics and geometry. I evaluate the part against three criteria: the base material must be weldable, the wall thickness after repair must be adequate, and the repair cost must be less than half the replacement cost. If any of these conditions is not met, I recommend scrapping the part and starting fresh. ...