Poor start and stop welds refer to defects that occur at the beginning and end of a weld bead, where the weld metal does not fuse properly with the base material. These defects can result from factors such as improper welding technique, insufficient preheating, or inadequate preparation of the workpiece. Poor start and stop welds can compromise the structural integrity of the weld joint, leading to issues such as reduced strength, increased susceptibility to cracking, and decreased resistance to corrosion.
Example: Welding of Automotive Frames
Consider the welding of automotive frames in a manufacturing facility. Welded joints are crucial for the structural integrity and safety of automotive frames, ensuring the vehicle’s stability and performance.
Poor Start and Stop Welds Defect:
During the welding of automotive frames, poor start and stop welds can occur if proper welding procedures are not followed or if there are issues with welder technique. These defects manifest as areas at the beginning and end of the weld bead where the weld metal does not properly fuse with the base material, resulting in incomplete penetration or fusion.
Determining Poor Start and Stop Welds:
- Visual Inspection: Poor start and stop welds can often be visually identified by examining the beginning and end of the weld bead. If there are areas where the weld metal does not properly fuse with the base material, it may indicate this defect.
- Radiographic Testing (RT): Radiographic images of the weld joint can provide detailed insight into the internal structure of the weld. Poor start and stop welds appear as areas of incomplete fusion or penetration at the beginning and end of the weld bead in radiographic images.
Radiographic Process:
In the radiographic process for determining poor start and stop welds:
- X-rays or gamma rays are directed through the weld joint onto a film or digital detector.
- The resulting radiographic image shows the internal structure of the weld, including any areas of incomplete fusion or penetration at the beginning and end of the weld bead.
- Poor start and stop welds appear as areas of reduced density or lack of fusion at the beginning and end of the weld bead in the radiographic image, indicating incomplete penetration or fusion.
Prevention Strategies:
- Proper Welding Technique: Train welders on proper welding techniques, including maintaining a consistent arc length, travel speed, and electrode angle, to ensure proper fusion between the weld metal and base material.
- Preheating: Preheat the workpiece to a suitable temperature before welding to reduce the likelihood of poor start and stop welds, particularly in materials with high thermal conductivity or susceptibility to cracking.
- Weld Sequence Planning: Plan the weld sequence to minimize the occurrence of poor start and stop welds, ensuring proper fusion and overlap between adjacent weld beads.
Impact on Weld Quality:
Reduced Strength:
Poor start and stop welds compromise the strength of the weld joint, reducing its load-bearing capacity and increasing the risk of failure under mechanical loads or stress.
Susceptibility to Cracking:
Welds with poor start and stop conditions are more prone to cracking, particularly at the areas of incomplete fusion or penetration, where stress concentrations are highest, further compromising weld quality and structural integrity.
Corrosion Resistance:
Poor start and stop welds create potential pathways for the ingress of moisture, contaminants, or corrosive substances, leading to increased susceptibility to corrosion and reduced service life of the welded component.
Conclusion:
Poor start and stop welds are defects that require careful attention to welding procedures, technique, and preheating to prevent. Through thorough inspection and testing, including radiographic examination, welders and inspectors can ensure the reliability, safety, and quality of welded structures, such as automotive frames, and mitigate the risk of these defects.
