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Definition
Discontinuities within the weld nugget and/or surrounding area caused by metallurgical changes resulting from welding.
Same as: Fissures (cracks), voids (holes), pores (holes).

Description

Holes may be contained within the nugget at the weld center (Fig. 1), or distributed around the edge at the sheet interface, as is sometimes caused by interfacial expulsion (Fig. 2). Holes may also be surface cavities such as those formed by heavy surface expulsion.

Surface cracks usually radiate from the approximate center of the nugget (Fig. 2), and in extreme cases may pass through the entire thickness of the weld zone. Cracks internal to the nugget may be more random in orientation. Cracks may also exist in the material surrounding the nugget.

Fig. 1. Holes at the center of the weld nugget revealed by sectioning (after teardown).	Fig. 2. Nugget showing a surface crack and holes in the center of the weld. Holes at the edge of the interface were caused by interfacial expulsion.

Detection
Surface cracks and holes may be visually detected before testing. If they have occurred at the sheet interface, they will not be visible until after teardown. Discontinuities within the nugget or at the sheet interface will not be visible until after teardown or joint sectioning.

Significance
Quality, Workplace Issues, Cost, Downtime, Maintenance, Throughput (cycle time; PPH) are all potentially affected by this condition. Special considerations are noted below:

Quality: Depending on their severity and position within the weld, cracks and holes may affect the weld's performance. Holes or cracks at the edge of the weld interface may favor the growth of a crack during destructive testing.

Possible Causes

Strong Possibilities

• Defective air or hydraulic system
• Hold time short
• Incorrect electrode dressing
• Insufficient Cooling
• Squeeze time short
• Weld current high
• Weld force low

Weak Possibilities

• Damaged part
• Dirty material
• Excessive sealer
• Inadequate electrode alignment
• Incorrect cylinder
• Incorrect hoses
• Incorrect material/coating
• Incorrect workpiece selected
• Poor mechanical connection
• Poor or varying part fit-up
• Weld flange too small
• Wrong shank
• Wrong tips
• Wrong transformer

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Information presented by Production Engineering
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